Presentation on theme: "WATER QUALITY ASSESSMENT AND POLLUTION CONTROL"— Presentation transcript:
1WATER QUALITY ASSESSMENT AND POLLUTION CONTROL WMA 318Prof. O. Martins and Dr O.Z. OjekunleDept of Water Res. Magt. & AgrometUNAAB. Abeokuta. Ogun StateNigeria
2PROPERTIES OF WATERWater is a chemical compound of oxygen and hydrogen and in the gaseous state can be represented by the molecular formula H2O. The isotopes of hydrogen and three isotopes of oxygen exist in nature, and if these are taken into account, 33 varieties of water are possible.The physical properties of liquid water are unique in a number of respects, and these departure from what might be considered as normal for such a compound are of the greatest importance with respect to both the existence of life on earth and the operation of many geochemical processes.The boiling point and freezing point of water are both far higher than would be the theoretically expected, considering the low molecular weight of the compound, and the range of temperature over which water as a liquid is wider than might be expected. The reason for these and other departures from “normal” behaviour can be gained by more detailed consideration of the molecular structure of the compound.
3MOLECULAR STRUCTURE OF WATER The spheres representing the ions coalesce to some extent, and the molecule might be thought of as a sphere having two rather prominent bubbles of “blisters” attached to it. Te bonds connecting the hydrogen’s to oxygen describe an angle of 105o, so that the two hydrogen are relatively close together on one side of the molecule.Although this representation of the molecule is somewhat empirical it helps to explain some of the abnormal features of the behaviour of water. The molecule has dipolar properties because the positive charge associated with the hydrogen are connected on one side of the molecule, leaving a degree of negativity on the opposite side. Forces of attraction thus exist between hydrogens of one molecule and the oxygen bonds. They hold molecule together in a fixed pattern in the solid state. In contrast to the orderly arrangement of molecules in crystal of ice, the molecules of liquid water are in a chaotic condition of disorder. Hydrogen bonds still remain an important force but their arrangement is continually shiftingThe cohesive forces represented by the hydrogen bonds impact to liquid water is high heat of vaporization. The forces also tend to prevent the passage to electric currents and impart to the fluid its high dielectric constant. The attraction between molecules of a liquid is shown at a liquid surface by the phenomenon called Surface tension. The surface of water is 75.6 dynes per centimeter at 0oC and 71.8 dynes per centimeter at 25oC, which are very high values compared with the many other liquids
4PROPERTIES OF WATER Chemical Constitution of Water 1 Ionic and Non IonicIonicAnionCations2 Major AnionsBicarbonate, Chloride, SulphateMajor CationsSodium, Potassium, Calcium, MagnesiumNon-IonicSiO2, Dissolved gases, oily Substance, Synthetic detergent, etc
5CHARACTERISTICS OF WATER HardnessCarbonate (Temporary) Hardness CaCO3Non Carbonate (Permanent) Hardness CaSO4Concentration of Hydrogen-ion, which are expressed in pH units. It is the—Log10H+Specific Electrical Conductance- Increases with temperature: values must therefore be related to the same temperature (2%)ColourAlkanity: Ability to neutralize acid; due to the presence of OH-, HCO3-, CO32-,Acidity: Water with pH 4.5 is said to have acidity; caused by the presence of free mineral acids and carbonic acidsTurbidity: Measure of transparency of water column; indirect method of measuring ability of suspended and colloidal materials to minimize penetration of light through water.Dissolved gasses: O2, N2, CO2, H2S, CH4, NH3, etc.
6PHYSICAL CHEMICAL PARAMETER Since water is not found in its pure in nature, it is important to determine its combined physical, chemical and biological characteristics. This is done through monitoring of water for its quality.Physical chemical parameter analyzed in natural environments; Atmosphere (rainfall), hydrosphere (river, lakes, and oceans) and Lithosphere (Groundwater) are similar-
7PHYSICAL CHEMICAL PARAMETER (Cont) Temperature: Measurement is relevantFor Aquatic lifeControl of waste treatment plantsCooling purposes for industriesCalculation of solubility of dissolved gasesIdentification of water sourceAgriculture IrrigationDomestic uses (Drinking, bathing)Instrument of measurement is thermometerpH: Controlled by CO2/HCO3-/CO32- Equilibria in natural water. Its values lie between 4.5 and 8.5. It is importantChemical and biological properties of liquidAnalytical workMeasurement is done in the field. Most common method of determination is the electrometric method, involving a pH-meter. It is important to calibrate the meter with standard pH buffer solutions
8PHYSICAL CHEMICAL PARAMETER (Cont) Dissolved Oxygen: Water in contact with the atmosphere has measurable dissolved oxygen concentration. It values depends onPartial pressure of O2 in the gaseous phaseTemperature of the waterConcentration of salt in the water (the higher the salt content in water, the lower the concentration of dissolved oxygen and the other gases).Measurement is important inEvaluation of surface water qualityWaste-treatment processes controlCorrosivity of waterSepticityPhotosynthetic activity of natural water
9MEASUREMENT & RELATIONSHIP OF PHYSICAL CHEMICAL PARAMETERS Temperature: Temperature affects the density of water, the solubility of constituents (Such as oxygen in water), pH, Specific conductance, the rate of chemical reactions, and biological activity of water. Continuous water quality sensor measure temperature with thermistor, which is a semiconductor having resistance that changes with temperature. Thermistor are reliable, accurate, and durable temperature sensors that require little maintenance and are relative inexpensive. The preferred water-temperature scale for most scientific work ids the Celcius scale. measure temperature to plus or minus 0.1 degree celcius (oC)
10MEASUREMENT & RELATIONSHIP OF PHYSICAL CHEMICAL PARAMETERS (Cont) Specific Conductance: Electrical conductivity is a measure of the capacity of water to conduct an electrical current and is a function of the types and quantities of dissolved substance in water. As concentration of dissolved ions increase, conductivity of the water increases. Specific conductance is the conductivity expressed in units of Microsiemen per centimeter at 25oC. Specific conductance are a good surrogate for total dissolved solids and total ions concentrations, but there is no universal linear relation between total dissolved solids and specific conductance.Specific conductance sensors are of 2 types: contact sensors with electrodes and sensor without electrodes.
11MEASUREMENT & RELATIONSHIP OF PHYSICAL CHEMICAL PARAMETERS (Cont) Salinity: Although Salinity is not measured directly, some sondes include the capability of calculating and recording salinity based on conductivity measurement. Conductivity has long been a tool of estimating the amount of chloride, a principle component of salinity in water. Salinity is commonly reported using the Practical Salinity Scale (PSS), a scale developed to a standard potassium-chloride solution and based on conductivity, temperature and barometric pressure measurement.Before developing the PSS, salinity was reported in part per thousand/million. Salinity expressed in the PSS is a dimensionless value, although by convection, it is reported as practical salinity unit.
12MEASUREMENT & RELATIONSHIP OF PHYSICAL CHEMICAL PARAMETERS (Cont) Dissolved Oxygen: Sources of DO in surface waters are primarily atmospheric reaeration and photosynthetic activity of aquatic plants. DO is an important factor in chemical reactions in water and in the survival of aquatic organisms. In surface water, DO concentration typically range from 2-10mg/l. DO saturation decreases as water temperature increases, and DO saturation increases with increased atmospheric pressure. Occasion of super saturation (greater than 100 percent DO saturation) often are related to excess photosynthetic production of oxygen by aquatic plants as a result of nutrient (nitrogen and Phosphorus) enrichment, sunlight and warm water temperature.DO may be depleted in inorganic oxidation reaction or by biological and chemical processes that consume dissolved, suspended or precipitated organic matter.The DO Solubility in saline environments is dependent on salinity as well as temperature and barometric pressure. DO in water that have specific conductance values of greater than 2000 microsiemens/centimeter should be corrected for salinity.The newest technology for measuring DO is the Luminescent sensor that is based on dynamic fluorescence quenching.
13MEASUREMENT & RELATIONSHIP OF PHYSICAL CHEMICAL PARAMETERS (Cont) pH: The pH of aqueous solution is controlled by the interrelated chemical reactions that produce or consume hydrogen ions. The pH of a solution is a measure of the effective hydrogen-ion concentration. More specifically, pH is a measure that represents the negative base-10 logarithm of hydrogen-ion activity of a solution, in moles per liter. Solutions having a pH below 7 are described as acidic, and solutions with pH greater than 7 are described as basic or alkaline. Dissolved gases such as carbon dioxide, hydrogen sulphide and ammonia, apparently affect pH. Dagasification (for example, loss of carbon dioxide) or precipitation of a solid phase (for example, calcium carbonate) and other chemical, physical, and biological reactions may cause the pH of a water sample to change appreciably soon after sample collection.The electrometric pH-measurement method, using a hydrogen-ion electrode, commonly is used in continuous water-quality pH sensors.A correctly calibrated pH sensor can accurately measure pH to pH units; however, the sensor can be stretched, broken or fouled easily. If the streamflow rates are high, the accuracy of the pH measurement can be affected by streaming-potential effects.
14MEASUREMENT & RELATIONSHIP OF PHYSICAL CHEMICAL PARAMETERS (Cont) Turbidity: Turbidity is defined as an expression of the optical properties of a sample that cause light rays to be scattered and absorbed, rather than transmitted in straight lines through a sample. ASTM further describe turbidity as the presence of suspended and dissolved matter, such as clay, silt, finely divided organic matter, plankton, other microscopic organisms, organic acids, and dyes. Implicit in this definition is the fact that colour, either of dissolved materials or of particles suspended in the water also can affect turbidity.Turbidity sensors operate differently from those for temperature, specific conductance, DO, and pH, which convert electrical potentials into the measurement of constituent of interest. Submersible turbidity sensors typically direct a light beam from light-emitting diode into water sample and measure the light that scatters or is absorbed by suspended particles in water.Most commercially available sensors report data in Nephelometric Turbidity Units (NTU)/ with a sensor range of and an accuracy of -+5 percent or 2NTU, whichever is greater.
15WATER QUALITY ASSESSMENT AND POLLUTION CONTROL WMA 318 PART 2
16NoteFor any water body to function adequately in satisfying the desired use, it must have corresponding degree of purity.Drinking water should be of highest purity. As the magnitude of demand for water is fast approaching the available supply,the concept of management of the quality of water is becoming as important as its quantity.
17ContaminantAre physical, chemical, biological or radiological substances found as unwanted residue in or on a substance.Pathogens: Are micro organisms that can cause diseases e.g bacteriaMetals (Metals that are harmful in relatively small amounts are labeled toxic)
18Disease caused by contaminants Salmonella Typhi Typhoid feverVibro Cholera CholeraEntameoba histolytica Amoeba DysenteryEscherichia Coli (E. Coli) GastroenteritsEnterovirus PolioHepatitis Infestious HepatitisHeavy Metal Cancer
19Water Purification Process Abstraction: Abstraction involves pumping and transportation of raw water, a process with high rate of electrical energy consumption. It occurs at the intake.Screening: Is defined as the process whereby relatively large and suspended debris is removed from the water before it enters the plant.Aeration: Aeration (Air Stripping) is a physical treatment process whereby air is thoroughly mixed with water to removed dissolved gasses and odour.Coagulation: Addition of chemical to remove suspended solids.Flocculation: A chemical flocculent, such as aluminium sulphate, is mixed rapidly with the water to remove mud.Sedimentation: Also known as clarification- is the gravity-induced removal of particles.Filtration: Involves the removal of suspended particles from water by passing it through a layer or bed of a porous granular material e.g sand. The filter water the passed through nozzles, the nozzles and sand in the filter beds must be cleaned periodically (This is known as back washing).Chlorination: After filtration, the water looks much more cleaner than it was in the dam or river but it may not yet be healthy to drink because it may contain unseen micro-organism (bacteria) that are dangerous to the human body and can serious illness (such as diahorrea)4.5 liters – 1 Gallon. 1 Liter – 100cl. 1 m3 – 5 drums or 200 liter volume.
20WATER QUALITY OBJECTIVES AND REQUIREMENT A major advantage of the water quality objectives approach to water resources management is that it focuses on solving problems caused by conflicts between the various demands placed on water resources, particularly in relation to their ability to assimilate pollution. The water quality objectives approach is sensitive not just to the effects of an individual discharge, but to the combined effects of the whole range of different discharges into a water body. It enables an overall limit on levels of contaminants within a water body to be set according to the required uses of the water.
21WQ CriteriaFor some other water quality variables, such as dissolved oxygen, water quality criteria are set at the minimum acceptable concentration to ensure the maintenance of biological functions.
22Examples of the development of national water quality criteria and guidelines in Nigeria In Nigeria, the Federal Environmental Protection Agency (FEPA) issued, in 1988, a specific decree to protect, to restore and to preserve the ecosystem of the Nigerian environment. The decree also empowered the agency to set water quality standards to protect public health and to enhance the quality of waters
23Background Information FEPA approached this task by reviewing water quality guidelines and standards from developed and developing countries as well as from international organisations and, subsequently, by comparing them with data available on Nigeria's own water quality.The standards considered included those of Australia, Brazil, Canada, India, Tanzania, the United States and the World Health Organization (WHO). These sets of data were harmonised and used to generate the Interim National Water Quality Guidelines and Standards for Nigeria
24Background Information (Cont) These sets of data were harmonised and used to generate the Interim National Water Quality Guidelines and Standards for Nigeria. These address drinking water, recreational use of water, freshwater aquatic life, agricultural (irrigation and livestock watering) and industrial water uses. The guidelines are expected to become the maximum allowable limits for inland surface waters and groundwaters, as well as for non-tidal coastal waters. They also apply to Nigeria's transboundary watercourses, the rivers Niger, Benue and Cross River, which are major sources of water supply in the country.
25THE NATIONAL ENVIRONMENTAL STANDARDS AND REGULATIONS ENFORCEMENT AGENCY (NESREA) Prior to the dumping of toxic waste in Koko village, in Delta State, in 1987, Nigeria was ill equipped to manage serious environmental crisis, as there were no institutional arrangement or mechanisms for environmental protection and enforcement of environmental laws and regulations in the country.Arising from the Koko toxic episode, the Federal Government promulgated the Harmful Waste Decree 42 of 1988, which facilitated the establishment of the Federal Environmental Protection Agency (FEPA) through Decree 58 of 1988 and 59 (amended) of FEPA was then charged with the overall responsibility of environmental management and protection. It is on record that by the establishment of FEPA, Nigeria became the first in African country to establish a national institutional mechanism fir environmental protection.
26NESREA (Cont)In the wisdom of Government, FEPA and other relevant Departments in other Ministries were merged to form the Federal ministry of Environment in 1999, but without an appropriate enabling law on enforcement issues. This situation created a vacuum in the effective enforcement of environmental law standards and regulations in the country.To address this lapse, the Federal Government in line with Section 20 of the 1999 constitution of the Federal Republic of Nigeria, established the National Environmental Standard and Regulations Enforcement Agency (NESREA), as a parastatal of the federal Ministry of Environment. By the NESREA Act 2007, the Federal Environmental Protection Agency Act Cap F10 LFN 2004 has been repealed (NESREA 2007).
27Table 1 Definition Related to Water Quality and Pollution Control
28Water quality criteria for individual use categories Water quality criteria have been widely established for a number of traditional water quality variables such as pH, dissolved oxygen, biochemical oxygen demand for periods of five or seven days (BOD5 and BOD7), chemical oxygen demand (COD) and nutrients. Such criteria guide decision makers, especially in countries with rivers affected by severe organic pollution, in the establishment of control strategies to decrease the potential for oxygen depletion and the resultant low BOD and COD levels.
29Development of criteria for Aquatic DO Numerous studies have confirmed that a pH range of 6.5 to 9 is most appropriate for the maintenance of fish communities.Low concentrations of dissolved oxygen, when combined with the presence of toxic substances may lead to stress responses in aquatic ecosystems because the toxicity of certain elements, such as zinc, lead and copper, is increased by low concentrations of dissolved oxygen.High water temperature also increases the adverse effects on biota associated with low concentrations of dissolved oxygen.
30Criteria for Aquatic Life DO The water quality criterion for dissolved oxygen, therefore, takes these factors into account. Depending on the water temperature requirements for particular aquatic species at various life stages, the criteria values range from 5 to 9.5 mg/l, i.e. a minimum dissolved oxygen concentration of 5-6 mg/l for warm-water biota and mg/l for cold-water biota. Higher oxygen concentrations are also relevant for early life stages. More details are given in Alabaster and Lloyd (1982) and the EPA (1976, 1986).
31BOD RequirementIn Nigeria, the interim water quality criterion for BOD for the protection of aquatic life is 4 mg O2 l-1 (water temperature °C), for irrigation water it is 2 mg O2 l-1 (water temperature °C), and for recreational waters it is 2 mg O2 l-1 (water temperature °C) (FEPA, 1991).
32Drinking Water Criteria Quality criteria for raw water generally follow drinking-water criteria and even strive to attain them, particularly when raw water is abstracted directly to drinking-water treatment works without prior storage. Drinking-water criteria define a quality of water that can be safely consumed by humans throughout their lifetime. Such criteria have been developed by international organisations and include the WHO Guidelines for Drinking water Quality (WHO, 1984, 1993) and the EU Council Directive of 15 July 1980 Relating to the Quality of Water Intended for Human Consumption (80/778/EEC), which covers some 60 quality variables. These guidelines and directives are used by countries, as appropriate, in establishing enforceable national drinking-water quality standards.
33IrrigationPoor quality water may affect irrigated crops by causing accumulation of salts in the root one, by causing loss of permeability of the soil due to excess sodium or calcium leaching, or by containing pathogens or contaminants which are directly toxic to plants or to those consuming them.
34IrrigationEven when the presence of pesticides or pathogenic organisms in irrigation water does not directly affect plant growth, it may potentially affect the acceptability of the agricultural product for sale or consumption. Criteria have been published by a number of countries as well as by the Food and Agriculture Organization of the United Nations (FAO)
35Irrigation Criteria Takes into Account Water quality criteria for irrigation water generally take into account, amongst other factors, such characteristics as crop tolerance to salinity, sodium concentration and phytotoxic trace elements.The effect of salinity on the osmotic pressure in the unsaturated soil zone is one of the most important water quality considerations because this has an influence on the availability of water for plant consumption.Sodium in irrigation waters can adversely affect soil structure and reduce the rate at which water moves into and through soils. Sodium is also a specific source of damage to fruits.Phytotoxic trace elements such as boron, heavy metals and pesticides may stunt the growth of plants or render the crop unfit for human consumption or other intended uses.
36Livestock wateringLivestock may be affected by poor quality water causing death, sickness or impaired growth. Variables of concern include nitrates, sulphates, total dissolved solids (salinity), a number of metals and organic micropollutants such as pesticides. In addition, bluegreen algae and pathogens in water can present problems.Some substances, or their degradation products, present in water used for livestock may occasionally be transmitted to humans.The purpose of quality criteria for water used for livestock watering is, therefore, to protect both the livestock and the consumer.
37Livestock Water Standard Criteria for livestock watering usually take into account the type of livestock, the daily water requirements of each species, the chemicals added to the feed of the livestock to enhance the growth and to reduce the risk of disease, as well as information on the toxicity of specific substances to the different species
38Recreational useRecreational water quality criteria are used to assess the safety of water to be used for swimming and other water-sport activities. The primary concern is to protect human health by preventing water pollution from faecal material or from contamination by microorganisms that could cause gastro-intestinal illness, ear, eye or skin infections.Criteria are therefore usually set for indicators of faecal pollution, such as faecal coliforms and pathogens. There has been a considerable amount of research in recent years into the development of other indicators of microbiological pollution including viruses that could affect swimmers. As a rule, recreational water quality criteria are established by government health agencies.
39Amenity useCriteria have been established in some countries aimed at the protection of the aesthetic properties of water. These criteria are primarily orientated towards visual aspects. They are usually narrative in nature and may specify, for example, that waters must be free of floating oil or other immiscible liquids, floating debris, excessive turbidity, and objectionable odours. The criteria are mostly non-quantifiable because of the different sensory perception of individuals and because of the variability of local conditions.
40Commercial and sports fishing Water quality criteria for commercial and sports fishing take into account, in particular, the bioaccumulation of contaminants through successive levels of the food chain and their possible biomagnification in higher trophic levels, which can make fish unsuitable for human consumption.
41In India, the Central Pollution Control Board (CPCB) has developed a concept of designated best use. ClassCriteriaDrinking Water Source without conventional treatment but after disinfectionA1.Total Coliforms Organism MPN/100ml shall be 50 or less2. pH between 6.5 and 8.53. Dissolved Oxygen 6mg/l or more4. Biochemical Oxygen Demand 5 days 20 C, 2mg/l or lessOutdoor bathing (Organised)B1.Total Coliforms Organism MPN/100ml shall be 500 or less3. Dissolved Oxygen 5mg/l or more4. Biochemical Oxygen Demand 5 days 20 C, 3mg/l or lessDrinking water source after conventional treatment and disinfectionC1. Total Coliforms Organism MPN/100ml shall be 5000 or less2. pH between 6 and 93. Dissolved Oxygen 4mg/l or morePropagation of Wild life and FisheriesD1. pH between 6.5 and 8.52. Dissolved Oxygen 4mg/l or more3. Free Ammonia (as N)Irrigation, Industrial Cooling, Controlled Waste disposalE1. pH between 6.0 and 8.52. Electrical Conductivity at 25 C micro mhos/cm, maximum 22503. Sodium absorption Ratio Max. 264. Boron Max. 2mg/lBelow-ENot meeting any of the A, B, C, D & E criteria
42A colour coding frequently used to depict the quality of water on maps Blue waterThis water can be directly used for drinking, industrial use, etc.Green waterWater contained in soil and plants is termed as green waterWhite waterAtmospheric moisture is white waterBrown or grey waterVarious grades of wastewater are shown by brown or grey colour
44Suspended particulate matter and sediment The attempts in some countries to develop quality criteria for suspended particulate matter and sediment aim at achieving a water quality, such that any sediment dredged from the water body could be used for soil improvement and for application to farmland.Another goal of these quality criteria is to protect organisms living on, or in, sediment, and the related food chain. Persistent pollutants in sediments have been shown to be accumulated and biomagnified through aquatic food chains leading to unacceptable concentrations in fish and fish-eating birds.NOTE: SEE VARIOUS TABLE FOR DATA
45WATER QUALITY ASSESSMENT AND POLLUTION CONTROL WMA 318 PART 3
46TYPES OF WATERWater is commonly described either in terms of its nature, usage, or origin. The implications in these descriptions range from being highly specific to so general as to be non-definitive. Ground waters originate in subterranean locations such as wells, while surface waters comprise the lakes, rivers, and seas.
47TYPES OF WATER (Cont) Fresh Water (precisely less than 0.5%) Fresh water may come from either a surface or ground source, and typically contains less than 1% sodium chloride. It may be either "hard" or "soft," i.e., either rich in calcium and magnesium salts and thus possibly forming insoluble curds with ordinary soap. Actually, there are gradations of hardness, which can be estimated from the Langelier or Ryznar indexes or accurately determined by titration with standardized chelating agent solutions such as versenates.
48TYPES OF WATER (Cont) Brackish Water Brackish water contains between 0.5 or 1 and 2.5% sodium chloride, either from natural sources around otherwise fresh water or by dilution of seawater. Brackish water differs from open seawater in certain other respects. The biological activity, for example, can be significantly modified by higher concentrations of nutrients. Fouling is also likely to be more severe as a consequence of the greater availability of nutrients.The main environmental factors responsible, singly or in combination, for these differences are the salinity, the degree of pollution, and the prevalence of silt.
49TYPES OF WATER (Cont) Seawater Seawater typically contains about 3.5% sodium chloride, although the salinity may be weakened in some areas by dilution with fresh water or concentrated by solar evaporation in others. Seawater is normally more corrosive than fresh water because of the higher conductivity and the penetrating power of the chloride ion through surface films on a metal. The rate of corrosion is controlled by the chloride content, oxygen availability, and the temperature.
50SalineWater is classified as "saline" when it becomes a risk for growth and yield of crops. Saline water has a relatively high concentration of dissolved salts (cations and anions). Salt is not just "salt" as we know it - sodium chloride (NaCl) - but can be dissolved calcium (Ca2+), magnesium (Mg2+), sulfate (SO42-), bicarbonate (HCO3-), Boron (B), and other compounds.Water can be both saline and sodic, or saline-sodic. If water has an EC greater than 4 (2 for horticulture) and a Sodium Adsorption Ration (SAR) greater than 12, it is considered saline-sodicThe concentration is usually expressed in parts per million (ppm) of salt.If water has a concentration of 10,000 ppm of dissolved salts, then one percent (10,000 divided by 1,000,000) of the weight of the water comes from dissolved salts.
51Classification of Salinity Slightly saline water contains around 1,000 to 3,000 ppm %Moderately saline water contains roughly 3,000 to 10,000 ppm %Highly saline water has around 10,000 to 35,000 ppm of salt %Seawater has a salinity of roughly 35,000 ppm, equivalent to 35 g/L %Brine Greater 50,000 ppm. 5.0% above
52Salinity in Different Water Bodies Water salinity based on dissolved salts in parts per thousand (ppt)Fresh waterBrackish waterSaline waterBrine< 0.50.5 – 3030 – 50> 50
53Relationship between Tidal and Salinity Salinity variations of the tidal water irrigating the rice fields at Warri mangrove swamp were studied for one calendar year. It was found that the mean pH is 7.24 for low tides and 7.14 for high tides, and pH is highest in July for both high and low tides. Sodium, calcium and magnesium, the major cationic constituents of the soluble salts in the saline tidal irrigation water, as well as potassium a minor ionic constituent were all found to be highest in June at both low and high tides. Also, both the Electrical Conductivity (EC) and the derived Sodium Adsorption Ration (SAR) were highest in June. Salinity at both high and low tides is highest in June but lowest in September for high tides and in October for low tides. The indications are that the adverse effects of salinity are largely responsible for the poor initial growth and survival of the rice variety during early seedling stage. From salinity point of view, it would appear that October is the most favourable month to transplant rice at the Warri mangrove swamp.
54Effects of SalinitySaline water reduces plant growth to varying degrees, with grass and grain crops generally showing less sensitivity and field crops being most sensitive. Aside from biomass reduction, salinity can have additional effects on plants. For example, in a study by Bauder et al., both inoculated and non-inoculated alfalfa were grown with irrigation waters of progressively higher salinity levelsCorrection of SalinityThere are no amendments, chemicals, or additives available commercially that can be added to saline water to make the salt go away. Dilution with a non-saline water or salt precipitation with an evaporation process which leaves the salt behind and traps the evaporated water can be used. Dilution of saline irrigation water is only possible if there is a source of non-saline water with which to dilute the saline water
55TYPES OF WATER (Cont)Effect of velocity on the corrosion of metals in seawaterThe combination of high conductivity and oxygen solubility is at a maximum at this point (oxygen solubility is reduced in more concentrated salt solutions). The corrosion of numerous metals in a wide range of saline waters is reported in the following Table.
56TYPES OF WATER (Cont) Distilled or Demineralized Water The total mineral content of water can be removed by either distillation or mixed-bed ion exchange. In the first case, purity is described qualitatively in some cases (e.g., triple-distilled water), but is best expressed, for both distilled and demineralized water, in terms of specific conductivity. Water also can be demineralized by reverse osmosis or electrodialysis.
57TYPES OF WATER (Cont) Steam Condensate Water condensed from industrial steam is called steam condensate. It approaches distilled water in purity, except for contamination (as by DO or carbon dioxide) and the effect of deliberate additives (e.g., neutralizing or filming amines).
58TYPES OF WATER (Cont) Boiler Feedwater Make-up The feedwater make-up for boilers is always softened and subsequently deaerated. It may vary in quality from fairly high dissolved solids (e.g., Zeolite-Treated), to very pure demineralized feed for high-pressure boilers. It tends to be highly corrosive, because of its softness, until thoroughly deaerated. This term is more precise than “boiler feedwater”, which may include recirculated steam condensate in various ratios to fresh make-up water.
59TYPES OF WATER (Cont) Potable Water Potable water is fresh water that is sanitized with oxidizing biocides such as chlorine or ozone to kill bacteria and make it safe for drinking purposes. By definition, certain mineral constituents are also restricted. For example, the chlorinity will be not more than 250 ppm chloride ion in the United States or 400 ppm on an international basis.
60TYPES OF WATER (Cont) Process or Hydrotest Water/Firewater These terms are essentially non-definitive, since the water employed may be of almost any chemistry, ranging from demineralized water to quite saline fresh water or even seawater in some cases. “Produced water” is that which originates in oil and gas production, emanating from geological sources with the hydrocarbons.
61TYPES OF WATER (Cont) Cooling Water Cooling water is another undefined term, although it implies that any necessary treatment against excessive scaling or corrosion has been applied, or corrosion-resistant material selected. This may include anything from fresh water to seawater, and may comprise either an open- or closed-loop system, or a once-through system.
62TYPES OF WATER (Cont) Waste Water By definition, waste water is any water that is discarded after use. Sanitary waste from private or industrial applications is contaminated with fecal matter, soaps, detergents, etc., but is quite readily handled from a corrosion standpoint. Industrial wastes from chemical or petrochemical sources can contain strange and specific contaminants which greatly complicate materials selection, especially in the uses of plastics and elastomers.
63WATER QUALITY ASSESSMENT AND POLLUTION CONTROL WMA 318 PART 4
64SOURCES OF WATER POLLUTION The surface water and groundwater systemsSurface water is the water we see in streams, rivers, wetlands, and lakes across the country. Every square mile of ground drains into one of these bodies of water. The area drained is known as a watershed. As smaller creeks and rivers feed into larger ones, the size of the watershed increases.
65SOURCES OF WATER POLLUTION (Cont) While surface water is found in the form of rivers and lakes, groundwater is stored in aquifers. Aquifers are formations of cracked rock, sand, or gravel that hold water and yield enough water to supply wells or springs. More than 95 percent of the world’s usable water resources are stored in its groundwater.Approximately third-quarter of all Nigerians depends on groundwater for their drinking water. In most times, 80 percent of all Nigerians depend on groundwater for their drinking water, and more than 97 percent of all rural Nigerians, depend on groundwater for their drinking water supplies.
66SOURCES OF WATER POLLUTION (Cont) As people pump and use water from these underground aquifers, the water must be replaced. Aquifers are replenished or recharged by water seeping down through the soil from surface water supplies. In some parts of the country, groundwater supplies are very deep, and pollutants may be filtered out by layers of soil, sand, and gravel.In parts of Nigeria, there are more direct links to the groundwater. In some parts of north-central and south of Nigeria, the groundwater supply may come within a few meters of the soil surface. That’s why this area of south is covered with wetlands and prairie potholes. In these areas, there is much less filtration by the soil and a greater risk of contamination by animal wastes, pesticides, and other pollutants. In other parts of the country, like the east and some part of the south west corner, limestone sits just below the soil surface. This limestone layer, or karst, can crack, erode, and form caverns that allow water and any pollutants to travel with little filtering from the soil.
67SOURCES OF WATER POLLUTION (Cont) Non-point source pollution refers to pollutants that come from a widespread area and cannot be tracked to a single point or source. Soil erosion, chemical runoff, and animal waste pollution are all examples of non-point source pollution. Non-point source pollution is major water quality problem by sheer volume and in terms of current and future economic costs to the nation.
68SOURCES OF WATER POLLUTION (Cont) Point source pollution – also known as “the end of the pipe pollution”– can be traced to a specific source, such as a leaking chemical tank, effluents coming from a waste treatment or industrial plant, or a manure spill from a hog confinement lagoon. Although this may seem easy to control, there are economic, political, and other factors involved. For known point source pollution threats, households, communities, industry, and agribusiness must deal with the problem of disposing of wastes and by-products.
69TREATMENT OF POLLUTANTS TREATMENT METHODSThere are various levels of treatment that prevent dumping raw waste products from being dumped into surface waters. Industrial wastes may require special treatment to remove harmful chemicals before reentering the water system.For the more common problem of organic wastes, the three main treatment methods for treating waste water areseptic systems, lagoons, and sewage treatment plants.Each method must be properly sized so that the treatment system is able to handle the volume of waste entering it.Septic systems are designed for individual households,lagoons may meet the needs of small towns, andsewage treatment facilities are necessary for controlling pollution.
70TREATMENT OF POLLUTANTS (Cont) Septic systemsSeptic systems are generally used in rural areas to handle household wastes. They usually use a large tank buried in the ground to contain and break down household sewage. Attached to the tank is a series of perforated pipes that are buried in a drain field and are usually surrounded by crushed rock or gravel to facilitate drainage. Fats, oils, and grease, as well as large waste particles, are stored and later pumped out of the holding tank, while the water and suspended solids in the water flow into the soil through the perforated pipes. The soil around the septic system filters many harmful compounds, and bacteria break down organic matter.
71TREATMENT OF POLLUTANTS (Cont) STANDARD: Septic systems are most popular in rural and suburban areas and must be located in soils that meet standards for percolation or the ability to drain away water. standards require a maximum percolation rate of one inch of water in 60 minutes. A slow percolation rate allows soil bacteria to break down wastes as they move into soil layers.CONCERN: Septic systems are generally a greater source of concern for groundwater pollution than for surface water pollution. However, septic systems are a real concern for surface water pollution when they are located near lakes, rivers, and streams. Of particular concern are lakes with high concentrations of tourist homes.Note: 1 Cube Inch is equal cm3, Multiple inch by 2.54 to get Centimetre
72TREATMENT OF POLLUTANTS (Cont) LagoonsMany communities, feedlot operators, and industries use lagoons to control wastes. A lagoon is simply one or a series of shallow holding pits into which wastes are pumped and treated. In a well-designed lagoon system, the material is aerated so bacteria can break down the organic matter.STANDARD: In municipal lagoons, the water generally stays in the lagoon for at least 30 days for this process to be completed. Then the water is removed and treated with chlorine as needed to destroy remaining bacteria. The remaining solids must be disposed of by spreading on farm fields or burying.CONCERN: Lagoons are inexpensive to construct and operate compared to other systems. However, poorly constructed lagoons and lagoons built where the water table is very high have been found to leak. The most often found contaminant tends to be nitrates.
73TREATMENT OF POLLUTANTS (Cont) Treatment plantsWe require two levels of sewage treatment.Primary sewage treatment simply filters out unwanted items such as sticks, stones, garbage, and other debris that arrive at the treatment plant and allows time for the solid materials to settle out.Secondary treatment uses aeration and aerobic, or oxygen-using, bacteria to break down organic wastes. The water is then treated with chlorine to kill bacteria and discharged into adjacent rivers and streams.Treatment plants remove approximately90 percent of the organic waste and suspended solids,less than 70 percent of the toxic metals and synthetic organic chemicals,50 percent of the nitrogen in the form of nitrates, and30 percent of the phosphorus in the form of phosphates.CONCERN: This remaining discharge is still high in nutrients and is not pure water entering the surface water. More advanced treatment systems are available, but they are rarely used due to their high cost. The remaining sludge is sent to a landfill as waste or applied to the land as a soil additive.
75TREATMENT OF POLLUTANTS SUMMARY Runoff pollution is difficult to control. The best method of control is limited use of chemical pesticides.The speed and amount of movement depends on whetherthe pesticide is water-soluble,the soil type,the amount of rain, andthe proximity of the water table to the surface.Over time, nearly all pesticides break down to other chemicals as they are exposed to sunlight and air. Generally, it is these base chemicals that are detected in groundwater.Some agricultural drainage wells provide direct pathways for pollutants to enter groundwater.The forms of nitrogen that cause problems as pollutants are the nitrate and ammonium forms. The nitrate form is water-soluble and moves with the water into surface water or groundwater. The ammonium form attaches to soil particles.
76MAINTAINING AND IMPROVING WATER QUALITY Cultural,Mechanical,Biological andChemical Control
77The best solution is prevention Just as there is no single source of water pollution, there is no single answer to solve the problem. Once water has become contaminated, it is very difficult, if not impossible, to clean. Surface water flows quickly, and a pollutant will generally be diluted as it enters larger bodies of water. However, even large bodies of water, such as the Gulf of Mexico near the mouth of the Mississippi River, cannot tolerate many years of eroded soils, increased nutrients, and chemical pollution.Groundwater, however, moves very slowly. In heavy clay layers or in bedrock, water might only move several inches per year. Even in gravel and sand aquifers, groundwater may move only several hundred to a thousand feet per year. Once the water is polluted, it will spread out slowly over a period of many years.Some problems, such as hazardous waste sites, require massive, expensive clean-up procedures. With other problems, such as large manure spills, little can be done but let the wastes become diluted as they reach larger bodies of water.However, there are steps to take to reduce some of the most serious problems such as siltation from erosion is passed legislative law to warn deterrent
78Other Methods AreNo-till and minimum-till farming: Most of the crop residues - the stalks and leaves of the harvested crop - are left on the surface of the field with no-till and minimum-till farming. Crops are planted into the crop residue the next year. This may reduce soil loss by up to 90 percent. The residue helps keep raindrops from directly hitting the soil and breaking it into small erodible particles.With no-till or minimum-till farming, crop residue remains to protect the soil from rain or wind.Contour farming: Contour farming involves planting crops in rows that circle around a hill in contours rather than in straight rows that go up and down the hill. These contours help break the water flow. With conventional farming methods, straight rows encourage the water to run down the row and wash along soil.
79Other Methods Are (Cont) Terraces: For very steep hillsides, terraces may be required. Terraces are constructed by planting a short slope with grass or other cover crops and then planting the level area with crops. This pattern of short slopes and planting areas follows the hillsides. This practice breaks up the steep hill into a series of shorter slopes and level areas and slows down the water flow. Since the terraces are planted in grass, they hold the slope in place and reduce erosion. Terracing provides good protection for steeper slopes, especially if combined with low-till or no-till farming.Grassed waterways: Where concentrated water runoff occurs due to the sloping of several hills or along bottom slopes, planting grass or hay is recommended. As water collects and runs along these erosion-prone areas, the denser root systems of the grasses help hold the soil in place to prevent these areas from washing out and forming gullies.
80Other Methods Are (Cont) Grasses and filterstrips: Stream banks and road ditches also need to be protected. Plants growing on banks and slopes help hold the soil. Along stream and river banks, filter-strips of grasses and trees help slow down water run-off and help prevent soil from washing into waterways.Filter strips help reduce erosion along stream and river banks.
81Good pest management depends Since polluted groundwater is nearly impossible to clean, prevention is the only solution. For pesticides, this means reducing the use of chemicals and focusing on an integrated pest management program that controls weeds and insects by more natural means whenever possible and resorting to pesticides only as a last resort.Good pest management depends on four methods of s control: cultural, mechanical, biological, and chemical.
82CULTURAL CONTROLCultural control relies on planting factors such as crop rotation and planting after weeds have been killed following germination. Good management starts with scouting fields on a regular basis. Keeping records of past problem areas helps control pests, as well as the need for chemical means of controlling pests.The first step is to determine the seriousness of the infestation of weeds or insects. This is where trade-offs take place.Will the potential loss of crop yield be greater than the cost of chemical treatment?Are there other options that might be cheaper and less environmentally dangerous?There are no set answers since each farm is different and each year brings new challenges.
83MECHANICAL CONTROLMechanical weed control or cultivation is one of the oldest forms of control. Tools like the rotary hoe are used when plants are small, while a cultivator is used on larger plants. Although mechanical control requires the use of fuel to pull the implement across the fields,it results in reduced chemical control.Most farmers substituting mechanical control for herbicides estimate that it costs them about half of what their neighbors spend on chemical control.
84BIOLOGICAL CONTROLBiological control introduces insects and plant diseases that target specific weed or other pest populations. One example in the Midwest is the introduction of the musk thistle weevil which feeds on musk thistles. Thistles are tough weeds to control, and the weevil appears promising in controlling pest populations.Insect control is best suited for pasture land rather than crop land Cultivation tends to disrupt the life cycle of the insects.Researchers are also developing microbial controls. These microbes are essentially plant diseases that occur naturally. The microbes are cultured in labs and sprayed on fields where they select the weeds but not the crops.One major advantage of biological control is that the diseases can adapt to changing weeds so they can’t build up resistance or tolerances, which has occurred with herbicides and insects.Musk thistle weevils are used as a biological control on thistles.
85CHEMICAL CONTROLFarmers using other controls methods must occasionally resort to chemical control for tough cases. However, even when chemical control is required, it’s possible to reduce the amounts of chemicals used.Careful calibration or setting of the sprayer is essential to not over-apply chemicals.In addition, many farmers use banding techniques that spray chemicals in a narrow band over the crop row and rely on cultivation for the weeds between rows. An Iowa State University research study shows that this method reduces the amount of chemicals used by 50 to 67 percent, while maintaining the corn yield on 99 percent of the fields tested.
86Controlling nitrate pollution General management practices may help ease the problem of nitrate pollution, but they also rely on trade-offs that protect both the economic interests of the farmer and the natural environment.The bottom line is not to apply more nitrogen based fertilizers, either artificial or natural animal byproducts, than the crops need for that growing season.Since ammonia may be lost to the air and nitrates may be moved with the water, it is economical for the farmer to apply only the amount of nitrogen needed and only at the time it is needed by the plants.
87SUMMARYStorm water, drainage systems in town and city are also considered to be dispersed sources of many pollutant, because, even though the pollutant are often convene into streams or lakes in drainages pipes or storm sewer, they are usually many of these discharges scattered over a large area.
88SUMMARY (Cont)Pollutants from dispersed sources are much more difficult to control. Many people think that sewage is the primary culprit in water pollution problems, but dispersed sources cause a significant fraction of the water pollution in Nigeria. The most effective way to control the dispersed sources is to set appropriate restriction on land use.
89SUMMARY (Cont)In addition to being classified by there origin, water pollutant can be classified into group of substances base primarily on there environmental or health effect. E.g., the following lists identify 9 specific types of pollutants.Pathogenic organismOxygen-demanding substancesPlant nutrientsToxic organicsInorganic chemicalsSedimentsRadioactive substancesHeatOil
90SUMMARY (Cont)Domestic Sewage is a primary source of the first three types of pollutant.Pathogen or diseases causing micro-organism are excreted in the feaces of infected person and may be carried into water receiving sewage discharges. Sewage from communities with large population is very likely to contained pathogen of some type.Sewage also carries oxygen demanding substance—the organism waste that exert a biochemical oxygen demand as they are decomposed by microbes. BOD changes the ecological balance in a body of water by depleting the Dissolved Oxygen DO content.Nitrogen and phosphorus, the major plant nutrients are in sewage, too, as well as in runoff from farm and from suburban lawns.
91SUMMARY (Cont) SOLUTION Conventional Sewage treatment processes significantly reduce the amount of pathogens and BOD in sewage, but do not eliminate them completely. Certain virus, in particular, may be somewhat resistant to the sewage disinfection processes. (A virus is an extremely small pathogenic organism that can only be seen with electron microscopes). To decrease the amount of Nitrogen and Phosphorus in sewage, usually some form of advanced sewage treatment must be applied.
92Toxic ChemicalToxic organic chemical, primary pesticide may be carry into the water in the surface runoff from agricultural areas. Perhaps the most dangerous type is the family of chemical called Chlorinated hydrocarbons. Common examples are known by there common chemical names as chlordane, Dieldrin, Heptachlor, and the famous DDT., which has been banned all over the world. They are very effective poison against insect that demand agriculture crops. Unfortunately, they can kill fish, birds, and animals, including humans. And they are not very biodegradable, taking more than 30 years in some cases to dissipate from the environment.
93Inorganic and OilPoisonous inorganic chemical, specifically those of the heavy metal group, such as lead, mercury, and chromium, also usually originate from industrial activities and are considered hazardous waste.Oil is washed into surface water in ruoff from road and parking lot, and groundwater can be polluted from leaking underground tanks, accidental oil spills from large transport tankers at a sea occasional occur, causing significant environmental damage. Blow out accident at offshore oil wells can release many thousand of tonnes of oil in a short period of time. Oil spills at sea may eventually move towards shore, affecting aquatic life and damaging recreational areas.
95EXPRESSING CONCENTRATION The properties of solutions, suspensions and colloids depend to large extent on their concentrations. A dilute or weak solution has a relatively small amount of solute dissolved in the solvent. It has a characteristic different from those concentrated or strong solution of the same substances, in which a relatively large amount of solute is present. Since concentrations need to be expressed quantitatively, instead of qualitatively terms like dilute or strong, concentration are usually expressed in terms of mass per unit volume, part per million or billion, or percent.MASS PER UNIT VOLUME: One of the common types of concentration is milligram per liter (mg/L). For example, if a mass of 10 mg of oxygen is dissolved in a volume of 1 L of water, the concentration of that solution is expressed simply as 10mg/L. If 0.3g of salt is dissolved in 1500mL of water, then the concentration is expressed as 300mg/1.5L=200mg/L, where 0.3g = 300mg and 1500mL = 1.5L (1g=1000mg/L; 1L=1000mL).Very dilute solutions are more conveniently expressed in term of micrograms per liter (g/L). For example, a concentration of 0.004mg/L is preferably written as its equivalent 4g/L. Since 1000g=1mg, e.g., a concentration of 1250g/L is equivalent to 1.25mg/L.In air, concentrations of particulate matter of gases are commonly expressed in terms of micrograms per cubic meter (g/m3).
96PART PER MILLION: One liter of water has a mass of 1kg PART PER MILLION: One liter of water has a mass of 1kg. But 1kg is equivalent to 1000g or 1 million mg. therefore, if 1 mg of a substance is dissolved in 1 L of water, we can say that there is 1 mg of solute per million mg of water. In other words, there is one part per million (1 ppm)Neglecting the small changes in the density of water as substances are dissolved in it, we can say that, in general, a concentration of 1 mg per liter is equivalent to one part per million: 1mg/L=1ppm. Conversion is very simple; for example, a concentration of 17.5 mg/L is identical to 17.5ppmThe expression mg/L is preferred over ppm just as the expression g/L is preferred over its equivalent of ppb. But both types of units are still used and the student should be familiar with each.
97PERCENTAGE CONCENTRATION: Concentrations in excess of 10000mg/L are generally expressed in terms of percent, for conveniences. For practical purposes, the conversion of 1 percent = mg/L be used even though the density of the solutions are slightly more than that of pure water (10000mg/L = 10000mg/ mg = 1 mg/100 mg = 1 percent).The concentration of salts in seawater is about 35000mg/L. To convert to percent salts, divide by 10,000 obtaining 3.5 percent. The concentration of wastewater sludge may be about 3 percent solids. To convert this to mg/L, multiply by 10,000 getting 30000mg/L solids.A concentration expressed in terms of percent may be also computed using the following expression. Percent = (Mass of Solute (mg)/ Mass of Solvent (mg)) X 100
98U.S CUSTOMARY UNITS: The expression grains per gallon (gpg) are sometimes used for concentrations of certain substances in water. One grain per gallon is equivalent to a concentration of 17.1 milligrams per liter: 1gpg=17.1mg/LThe expression pounds per million gallon is also used in US customary unit of concentration for water treatment applications. Since 1 gallon of water weighs 8.34lb, 1 gal/mil gal is the same as 8.34 lb/mil gal. Or we can say that 1mg/L = 8.34 mil gal to convert from mg/L to lb/mil gal, multiply by 8.34; to go from lb/mil gal to mg/L. divide by 8.34
99EXAMPLE: A 500-mL aqueous solution has 125mg of salt dissolved in it EXAMPLE: A 500-mL aqueous solution has 125mg of salt dissolved in it. Express the concentration of this solution in terms of (a) mg/L, (b)ppm, (c)gpg (d) Percent and (e) lb/mil galSolution(125mg/500mL)X1000mL/L = 250mg/L250mg/L = 250 ppm(250 mg/L X 1gpg)/17.1 mg/L = 14.6 gpgApplying this equation Percent = (Mass of Solute (mg)/ Mass of Solvent (mg))X 100Percent = 0.125g/500g X 100 = percent Or divide 250mg/L by 10,000 to get percent250 mg/L X 8.34 = 2090 lb/mil galEXAMPLE: How many pounds of chlorine gas should be dissolved in 8 mil gal of water to result in a concentration of 0.2 mg/L0.2 mg/L X 8.34 = 1.67 lb/mil galAnd 1.67 lb/mil gal X 8 mil gal = 13 lb
100BIOCHEMICAL OXYGEN DEMAND: Bacteria and other microorganisms use organic substance for food. As they metabolize organics are broken down into simpler compounds, such as CO2 and H2O, and the microbes use the energy released fro growth and reproduction.When this process occurs in water, the oxygen consumed is the DO. If oxygen is not continually replaced in the water by artificial or natural means, then the DO level will decrease as the organic are decomposed by the microbes. This need for oxygen is called Biological Oxygen Demand. In effect, the microbes “demand” the oxygen for use in the biochemical reactions that sustain them. Organic waste in sewage is one of the major types of water pollutants. It is impractical to isolate and identify each specific organic chemical in these wastes and to determine its concentration. Instead, the BOD is used as an indirect measure of the total amount of biodegradable organics in the water. The more organic material there is in the water; the higher the BOD exerted by the microbes will be.
101In addition to being used as a measure of the amount of organic pollutant in streams or lakes, the BOD is used as a measure of the strength of sewage. This is the most important parameters for design and operation of water pollution control plant. A strong sewage has a high concentration of organic material and a correspondingly high BOD. The complete decomposition of organic material by microorganisms takes time, usually 20d or more under ordinary circumstances. The amount of oxygen used to completely decompose or stabilize all the biodegradable organics in a given volume of water is called Ultimate BOD, or BODL for example, if a 1-L volume of municipal waste requires 300 mg of oxygen for complete decomposition of the organics, the BODL would be expressed as 300mg/L. One liter of waste from an industrial or food processing plant may require as much as 1500 mg of oxygen for complete stabilization of the waste. In this case, the BODL would be 1500mg/L, indicating a much stronger waste than ordinary municipal or domestic sewage. In general, then, the BOD is expressed in terms of mg/L of oxygen.The BOD is a function of time. At the very beginning of a BOD test, or time = 0, no oxygen will have been consumed and the BOD = 0. As each day goes by oxygen is used by the microbes and the BOD increase. Ultimately, the BODL is reached and the organics are completely decomposed. A graph of the BOD versus time has the characteristic shape called the BOD Curve.
102The BOD curve can be expressed mathematically by the following equation: BODt = BODL X (1 – 10-kt)Where BODt = BOD at any time t. mg/LBODL = Ultimate BOD, mg/Lk = constant representing the rate of BOD reactiont = time, dThe rate at which oxygen is consumed is expressed by the constant k. the value of this rate constant depend on the temperature, the type of organic material, and the types of microbes exerting the BOD. For the ordinary domestic sewage at a temperature of 20oC, the value of k is usually about 0.15/d
103Example: A sample of sewage from a town is found to have a BOD after 5 d (BOD5) of 180mg/L. Estimate the Ultimate BOD (the BODL) of the sewage assuming that k = 0.1/d for this waste water.SolutionBODt = BODL X (1 – 10-kt)180 = BODt = BODL X (1 – 10-kt) , It implies that 180 = BODL X ( X5)Therefore 180 = BODL X ( ) ; 180 = BODL X 0.684Rearranging terms to solve for BODL givesBODL = 180/0.684 = 260 mg/L Rounded off.This is particularly true when the BOD data are used to monitor the efficiency of a water pollution control plant. It has been found that more than two-third of the BODL is usually exerted within the first 5d of decomposition. For instance, in the preceding example, the 5d BOD is 180/260 = 0.69, or 69% of the ultimate BOD. For practical purposes, the 5d BOD, or BOD5, has been chosen as a representation of the organic content of water or waste water. For standardization of results, the test must be conducted at a temperature of 20oC.In summary, the parameter of BOD5 is the amount of dissolved oxygen used by microbes in the 5 d to decompose organic substances in water at 20oC.
104Measurement of BOD5The traditional BOD test is conducted in the standard 300-mL glass BOD bottles. The test for 5-d BOD of water sample involves taking two DO measurements: an initial measurement when the test begins, at time t = 0, and a second measurement, at t = 5, after the sample has been incubated in the dark for 5 d at 20oC. The BOD5 is simply the difference between the two measurements.For example consider that a sample of water from a stream is found to have an initial DO of 8.0 mg/L. It is placed directly into a BOD bottle and incubated for 5 d at 20oC. After the 5 d, the DO is determined to be 4.5mg/L.The BOD is the amount of oxygen consumed, or the difference between the two DO readings. That is, BOD5 = 8.0 – 4.5 = 3.5mg/L.Very clean bodies of surface water usually have a BOD5 of about 1 mg/L due to the presence of naturally occurring from decaying leaves and animal wastes. BOD5 values in excess of 10 mg/L, however usually indicate the presence of sewage pollution.
105EXPERIMENTATION: When measuring the BOD5 of sewage, it is necessary to first dilute the sample in the BOD bottle. Domestic sewage usually has a general BOD value of 200 mg/L. If the sample were not diluted, the entire DO will be completely depleted and it would not be possible to get a DO reading on the fifth day. Computation of the BOD5, using this dilution method in a 300-ml BOD bottle, is done by using the following equation:Where DO0 = Initial DO at t = 0D05 = DO at t = 5dV = Sample volume, mL
106EXAMPLE: A 6.0-ml sample of wastewater is diluted to 300 mL with distilled water in a standard BOD bottle. The initial DO in the bottle is determined to be 8.5 mg/L, and the DO after 5d at 20oC is found to be 5.0 mg/L.Determine the BOD5 of the wastewater and compute its BODL. Assume that k = 0.1/dSOLUTION:BOD5 = (( ) X 300)/ 6.0 = 3.5 X 300/6.0 = 180 mg/LNow applying BODt = BODL X (1 – 10-kt)180 = BODL X (1 – X5) andBODL = 180/0.684 = 260mg/L
107CHEMICAL OXYGEN DEMAND The BOD test provides a measure of the biodegradable organic material in water, i.e., of the substance that microbe can readily use for food. There might also be non biodegradable or slowly biodegradable substance that will not detected by the convectional BOD test.The Chemical Oxygen Demand, COD is another parameter of water quality which measures all organics, including the non biodegradable substances. It is a chemical test using a strong oxidizing agent (Potassium Dichromate), sulphuric acid and heat. The result of the COD test can be available in just 2hours, a definite advantage over the 5d required for the standard BOD test.COD values are always higher than BOD values for the same sample, but there is generally no consistent correlation between the two tests for different wastewater. In other word, it is not feasible to simply measure the COD and then predict the BOD. Because most waste water treatment plant are biological in their mode of operation, the BOD is more representative of the treatment process and remains a more commonly used parameter than the COD.
108SOLIDS: Solids occurs in water either in solution or in suspension SOLIDS: Solids occurs in water either in solution or in suspension. These 2 types of solid are distinguish by passing the water sample through a glass-fibre filter. By definition, the Suspended Solid are retain on top of the filter and the Dissolved Solid pass through the filter with the water.If the filtered portion of the water sample is placed in a small dish and then evaporated, the solid in the water remain as a residue in the evaporating dish. This material is usually called Total Dissolved Solid TDS. The concentration of TDS is expressed in term of mg/L. it can be calculated as follows.Where A = equal to weigh of dish plus residue. MgB = Weight of empty dishC = Volume of sample filtered mL.
109Example: The weight of an empty evaporating dish is determined to be g. After a water sample is filtered, 100mL of the sample is evaporated from the dish. The weight of the dish plus dried residue is found to be g. Compute the TDS concentration= 200mg/LIn drinking water, dissolved liquid may caused taste problems. Hardness, corrosion, or aesthetic problem may also accompany excessive TDS concentration. In wastewater analysis and water pollution control, the suspended retained on the filtered are of primary importance and are referred to as TOTAL SUSPENDED SOLID TSS.The TSS concentration can be computed using the TDS equation,where A represent the weight of the filtered plus retained solidB represent the weight of the clean filterC represent the volume of the sample filtered
110Hardness is usually expressed in term of milligram per liter of calcium carbonate, CaC03; grains per gallon are also used to express hardness concentration. Water with more than 300mg/L of hardness is generally considered to be hard, and water with less than 75mg/L is considered to be soft. Very soft water is undesirable in public supply because it tends to increase corrosion problem in metal pipes; also, some health official believe it to be associated with the incident of the heart disease.
111DilutionIn water pollution control, it is often necessary to predict the BOD concentrations and the DO levels downstream from a sewage discharge point. One of the first computations needed for this involves the effect of dilution. Assuming that pollutant is completely mixed in the streamflow (at a point just below the end of the mixing zone), one can calculate the diluted concentration of any water quality parameter using the following mass balance equation:cd = (csQs + cwQw)/(Qs + Qw)where cd = diluted concentration or temperaturecs = original stream concentration or temperaturecw = waste concentration or temperatureQs = stream dischargeQw = waste discharge
112A fundamental concept in science is the law of conservation of matter A fundamental concept in science is the law of conservation of matter. This means that when there is no appreciable conversion of mass into energy, the sum of the masses of substances entering into a reaction must always equal the sum of the masses of products of reaction. Even if there in no chemical reaction occurring, the law of conservation underlies the concept of mass balance (also called material balance), and is useful in environmental technologyMass balance calculations play an important role in the design and operation of water, sewage, air and solid waste treatment processes. In treatment systems, the physical, chemical, and biological processes usually occurs in vessel or tanks called reactors, and the particular reactions or processes are referred to as unit processes. In the simplest case, it can be said that the input must equal the output, or, in other words, “what goes in must go out.” If this does not occur, there must be an accumulation (depletion) of the material in the reactor equal to the difference between the input and output, or accumulation = input-output. Since, in this kind of situation, the composition of material in the reactor changes with time, it is referred to as an unsteady-state operation. In the steady state operation, it can be assumed that the rates of input and output are constant, as is the composition of the completely mixed reactor.Suppose, for example, two pipes containing salt solutions discharge into a tank in which the two solutions are completely mixed, and the third pipe carries the mixture out of the tank
113The solution in the first pipe has a concentration of c1 mg/L and that in the second pipe has a concentration of c2 mg/L. the flow rate of the pipes are Q1 and Q2 respectively. The concept of mass or material balance can be applied to determine the concentration of the mixed solution discharged from the tank because under steady-state conditions, the total amount of salt entering the tank must be equal to the total amount leaving the tank. In other words, since the salt neither decays nor reacts with other substance (in this example), the concentration of salt in the mixture in the tank stay constant over time.The product of concentration of volume flow rate equals the mass flow rate because mg/L X L/d = mg/d where the volume flow rate in this example is expresses in terms of liter per day, or L/d. for convenience here, consider that the time interval is 1 day. Then the product of c1 X Q must equal the mass of salt entering the vessel in 1 d from the first pipe. Similarly, c2 X Q equals the mass of salt entering the tank from the second pipe. The total mass of salt entering the tank in 1 d, that is, the input, must be equal to the sum from the two pipes, or input = c1 X Q1 + c2 X Q2.
114The total mass of salt leaving the tank equals the product of the concentration in the mixture c3 and the volume flow rate leaving the tank. Because water is actually incompressible, however, that flow rate must be Q1 + Q2. Therefore, the output of salt is c3 X (Q1 + Q2). Because the concept of mass or material balance applies here and output = input, the following relationship is obtained:c3 X (Q1 + Q2) = c1 X Q1 + c2 X Q2Solving the above equation for c3 by dividing both sides by (Q1 + Q2), we obtained the following mass balance equationc3 = (c1 X Q1 + c2 X Q2)/Q1 + Q2Mass balance calculation can be applied to the natural environmental systems, such as streams, rivers, lakes and even the atmosphere e.g Stream pollution.
115EXAMPLE: The BOD5 of an effluent from a municipal sewage treatment plants is 25mg/L and the effluent discharge is 4 ML/d. the receiving stream has a BOD5 of 2 mg/L and the stream flow is 40 ML/d. compute the combined 5-day BOD in the stream just below the mixing zone.SOLUTION: Applying cd = (csQs + cwQw)/(Qs +Qw)cd = (2 X X 4)/ 40 X 4 = 180/44 = 4.1mg/LWhere cd represent the diluted BOD5 in the combined flowEXAMPLE: A river has a dry-weather discharge of 100 cfs and a temperature of 25oC. Compute the maximum discharge of cooling water at 65oC that can be discharged from a power plant into the stream. Assume the legal limit on the temperature increase in stream is 2oCSOLUTION: The maximum allowable stream temperature is = 27oCApplying mass balance equation cd = (csQs + cwQw)/(Qs +Qw)27 = (25 X X Qw)/100 + Qw200 = 38Qw : Qw = 5.3 cfsThe discharge of warm water cannot be exceed 5.3 ft3/s if the stream temperature is not to increase more than 2oC
116COMPUTATION OF MINIMUM DO It is important to be able to predict the minimum dissolved oxygen level in a polluted stream or river. For Example, if a new sewage treatment plant is to be discharge its effluent into a trout stream, it is possible that conventional (secondary) treatment levels will not remove enough BOD to prevent excessively low DO downstream. To determine if some form of advanced treatment is required to preserve the stream for trout spawning and survival, it is necessary to compute the minimum DO caused by the sewage effluent and to compare it to the allowable value for trout streams.One technique used to describe and predict the behaviour of a polluted stream uses the so-called Streeter-Phelps equation. This equation is based on the assumption that the only two processes taking place are deoxygenation of BOD and the reaeration by oxygen transfer at the surface, as previously discussed. Two key formulas from the Streete-Phelps model of stream pollution and oxygen sag follow. Figure 5.11 illustrate some of the variables in these equations. The minimum DO in the stream is the difference between the saturation DO level and the critical oxygen deficit. The formulas are
117COMPUTATION OF MINIMUM DO (Cont) Tc=Dc=Where tc = Time it takes for the critical oxygen deficit or minimum DO to develop, dDc = Critical oxygen deficit, mg/LDi = Initial oxygen deficit at time t = 0 just below the point of waste discharge into the stream, mg/LBODL = Ultimate BOD in the stream just below the point of waste discharge, mg/Lk1 = Deoxygenated rate constant, d-1k2 = The reaeration rate constant, d-1
118COMPUTATION OF MINIMUM DO (Cont) The value of k1 if generally taken to be the same as the rate constant for the BOD reaction in this equation BODt = BODL X (1-10-kt); it can be determined in the laboratory. The value of k2 depends on the velocity and the depth of the flow and can be determined from field studies or by an appropriate formula. The reaeration rate constant k2 can be vary from about 0.1 for the sluggish to about 4.0 for a swallow turbulent stream. Both rate constants, k1 and k2 depend on temperature.The equation tc and Dc look complicated, and they are. They are presented here to illustrate the power of mathematics as a tool for modeling the environment and helping solve water pollution problems. But as complicated as they may appear, the Streeter-Phelps equations are not completely accurate representations of the oxygen profile in a polluted stream or river. Other factors that affect the oxygen balance include photosynthesis and respiration of rooted plants and algae and the oxygen demand of benthic (bottom) deposits. Equations that have been developed to include these factors are even more complicated than the equation tc and Dc
119COMPUTATION OF MINIMUM DO (Cont) EXAMPLE: The BODL in a stream is 3 mg/L and the DO is 9.0 mg/L. The streamflow is 15mgd. A treated sewage effluent with BODL =50mg/L is discharged into the stream at a rate of 5 mgd. The DO of the sewage effluent is 2 mg/L. Assuming that k1 = 0.2, k2 = 0.5, and the saturation DO level is 11 mg/L, determine the minimum DO level in the stream. For a stream velocity of 0.5 ft/s, how far downstream does the minimum DO occur?SOLUTION: First, it is necessary to compute the diluted BODL and DO using the Mass Balance EquationBODL = (15 X X 50)/ = 295/20 = 14.8mg/LDO = (15 X X 2)/ = 145/20 = 7.3 mg/LNow compute the initial oxygen deficit asDi = saturation DO – Initial DO = 11.0 – 7.3 = 3.7mg/LApplying the Streeter-Phelps Model Equations for tc
120COMPUTATION OF MINIMUM DO (Cont) Tc= = =(0.33)log 1.56 = 0.64 dIt will take about 0.64 d (roughly 15hours) for the minimum DO to occur.Now applying next Streeter-Phelps Model Equation for Dc givesDc= = 9.87 X (0.745 – 0.479) X = = 4.4 mg/LThe minimum DO in the stream is the difference between saturation DO and the critical oxygen deficit, or 11.0 – 4.4 = 5.6 mg/L. At a velocity of 0.5 ft/s, in 0.64 d the distance downstream for the minimum DO is 0.64 d X 24 h/d X 3600 s/h X 0.5 ft/s = ft approximately 5 million.