UNIT I PLANNING FOR SEWERAGE SYSTEMS

UNIT I PLANNING FOR SEWERAGE SYSTEMS

Sources of wastewater generation Effects of wastewater generation Estimation of sanitary sewage flow Estimation of storm runoff Factors affecting Characteristics and composition of sewage and their significance Effluent standards Legislation requirements

If all of the Earth’s available freshwater from the ground, lakes, swamps, and rivers were condensed to a single sphere, that sphere would be 270 km in diameter, which, if placed tangent to the Earth’s surface, would stand 270 km high and project a shadow that is the size of Croatia

Distribution of Earth’s water

A survey of 3.2 lakh slum dwellers in undeclared slums of Chennai revealed that only
Currently, there are only 714 public toilets in Chennai for a population of lakhs and an official slum population of over a million (Census 2011). 0.01% for Total population 0.07% for slum population

Introduction The liquid waste- wastewater is essentially the water supply of the community after it has been used in a variety of applications Wastewater may be defined from the standpoint of sources of generation as a combination of the liquid or water-carried wastes removed from institution, commercial and industrial establishments When this wastewater accumulates and is allowed to go septic, the decomposition of the organic matter it contains will lead to nuisance conditions The immediate and nuisance free removal of wastewater from its sources of generation followed by treatment, reuse or disposal into the environment is necessary to protect public health and the environment.

Introduction Wastewater engineering is that branch of environmental engineering in which the basic principles of science and engineering are applied to solve the issues associated with the treatment and reuse of wastewater. The ultimate goal of wastewater engineering is the protection of public health in a manner commensurate with environmental, economic, social and political concerns.

Pollution from informal housing

Looking north on Palm Springs Drive near the intersection of Firestone Court during and after construction.

SAFE DISPOSAL OF THE SEWAGE
For safe disposal of the sewage generated from a locality efficient collection, conveyance, adequate treatment and proper disposal of treated sewage is necessary. To achieve this following conditions should be satisfied: 1. Sewage should not pollute the drinking water source, either surface or groundwater, or water bodies that are used for bathing or recreational purposes. 2. The untreated sewage during conveyance should not be exposed so as to have access to human being or animals and should not give unsightly appearances or odour nuisance, and should not become a place for breeding flies. 3. It should not cause harm to public health and adversely affect the receiving environment. The collection system is meant for collection of the sewage generated from individual houses and transporting it to a common point where it can be treated as per the needs before disposal.

SAFE DISPOSAL OF THE SEWAGE
In olden days, waste generated from water closets was collected by conservancy methods and other liquid waste was transported through open drain to finally join natural drains. Since, the excreta was carried through carts, it was not hygienic method for transportation to the disposal point. Now, collection and conveyance of sewage is done in water carriage system, where it is transported in closed conduit using water as a medium.

In the past disposal of waste from water closets was carried out manually and waste water generated from kitchen and bathrooms was allowed to flow along the open drains. This method is known as old conservancy system of sanitation This primitive method was modified and replaced by a water carriage system, in which these wastes are mixed with sufficient quantity of water. This waste is carried through closed conduits under the conditions of gravity flow. This method is known as modern water carriage system.

ADVANTAGES OF THE WATER CARRIAGE SYSTEM
The carriage of wastes on head or carts is not required. Bad smell, which was unavoidable during open transport of sewage, is not occurring due to transport of this polluted water in closed conduits. The old system was posing the health hazards to sweepers and to the nearby residents, because of the possibilities of flies and insects transmitting disease germs from the accessible carts to the residents food eatables. This is avoided in water carriage system because of transport of night soil in close conduits. The human excreta is washed away as soon as it is produced in water carriage system, thus storing is not required as required in the old system of manual disposal. Thus, no bad smells are produced in closed conduit transport.

ADVANTAGES OF THE WATER CARRIAGE SYSTEM
In the old system, the wastewater generated from the kitchen and bathrooms was required to be carried through open roadside drains for disposal. This is avoided in sewerage system as the open drains could generate bad odours when used for disposal of organic wastes. The water carriage system does not occupy floor area, as the sewers are laid underground. In addition, the construction of toilets one above the other is possible in water carriage system and combining latrine and bathrooms together as water closets is possible. This is one of the important advantages of water carriage system.

DRAWBACKS OF WATER CARRIAGE SYSTEM
A large network of pipes is required for collection of the sewage; hence, the capital cos for water carriage system is very high. In addition, the operation and maintenance of sewerage system is very expensive. Large wastewater volume is required to be treated before disposal. Assured water supply is essential for efficient operation of the water carriage system.

DEFINITIONS Industrial wastewater: It is the wastewater generated from the industrial and commercial areas. This wastewater contains objectionable organic and inorganic compounds that may not be amenable to conventional treatment processes. Night Soil: It is a term used to indicate the human and animal excreta. Sanitary sewage: Sewage originated from the residential buildings comes under this category. This is very foul in nature. It is the wastewater generated from the lavatory basins, urinals and water closets of residential buildings, office building, theatre and other institutions. It is also referred as domestic wastewater.

DEFINITIONS Sewage: It indicates the liquid waste originating from the domestic uses of water. It includes sullage, discharge from toilets, urinals, wastewater generated from commercial establishments, institutions, industrial establishments and also the groundwater and stormwater that may enter into the sewers. Sewage Treatment Plant is a facility designed to receive the waste from domestic, commercial and industrial sources and to remove materials that damage water quality and compromise public health and safety when discharged into water receiving systems or land. Sewer: It is an underground conduit or drain through which sewage is carried to a point of discharge or disposal.

DEFINITIONS Sewerage: The term sewerage refers the infrastructure which includes device, equipment and appurtenances for the collection, transportation and pumping of sewage, but excluding works for the treatment of sewage. Stormwater: It indicates the rain water of the locality. Subsoil water: Groundwater that enters into the sewers through leakages is called subsoil water.

DEFINITIONS Sullage: This refers to the wastewater generated from bathrooms, kitchens, washing place and wash basins, etc. Composition of this waste does not involve higher concentration of organic matter and it is less polluted water as compared to sewage. Wastewater: The term wastewater includes both organic and inorganic constituents, in soluble or suspended form, and mineral content of liquid waste carried through liquid media. Generally the organic portion of the wastewater undergoes biological decompositions and the mineral matter may combine with water to form dissolved solids.

Domestic or sanitary wastewater refers to liquid wastes discharged from urinals, latrines, bathrooms, kitchen sinks, washbasins etc., of the residential, business buildings and institutions. Industrial wastewater consist of liquid wastes originating from the industrial processes of various industries such as dyeing, papermaking, brewing etc., The runoff resulting from the rain storms was used to be called storm drainage SEWAGE = DOMESTIC SEWAGE + INDUSTRIAL SEWAGE

Municipal wastewater is the general term applied to the liquid collected in sanitary sewers and treated in municipal plants Domestic sewage is composed of human body waste and sullage which is the wastewater resulting from personal washing, laundry, and cleaning of kitchen utensils

Composition of sewage Sewage consist of about 99.9% water and 0.1 % solids, the solids are either organic or inorganic. The organic solids consist of about 65% protein, 25% carbohydrate and 10% fats. Faeces and to a less extent urine contain millions of intestinal bacteria and small numbers of other organisms The organic mater contributed per person per day in domestic wastewater is approximately 110g of suspended solids and 90g of BOD in communities where substantial portion of the household kitchen waste is discharged to the sewer system

Effects of wastewater generation
If the untreated wastewater is allowed to accumulate, it will lead to highly unhygienic conditions. The organic matter present in the wastewater will undergo decomposition with production of large quantities of malodorous gases. If the wastewater is discharged without treatment in the water body, this will result in the depletion of Dissolved Oxygen (DO) from the water bodies.

Due to depletion of DO, the survival of aquatic life will become difficult, finally leading to anaerobic conditions in the receiving waters. The nutrients present in the wastewater can stimulate the growth of aquatic plants, leading to problems like eutrophication. In addition, the untreated domestic wastewater usually contains numerous pathogenic or disease causing microorganisms, that dwell in the human intestinal tract or it may be present in certain industrial wastewaters. The wastewater contains inorganic gritty materials. The continuous deposition of this inorganic material may reduce the capacity of water body considerably over a period.

Generally domestic sewage does not contain any inorganic matter or organic compounds in highly toxic concentration.

Deaths Due To Pollution

Deaths Due To Pollution Another dangerous pollution - lead pollution is caused mainly due to operating lead smelters, metal processing plants, incinerators and using chemical paints. Besides fatal effects on human beings and animals, when high amounts are absorbed, lead can cause birth defects in unborn children. In 2010, exposure to lead pollution have caused 0.2 million deaths each in East Asia and South Asia.

Pollution Deaths, Asian Scenario
INDIA – 2.6 Million death 1st Place

Death Toll Due To Unsafe Water
INDIA – 4.5 Lakh death 1st Place

ROLE OF DESIGN ENGINEER
The role of design engineer is to develop a treatment scheme that will guarantee the technical feasibility of the scheme, taking into consideration other factors such as construction and maintenance costs, The availability of construction materials and equipment, as well as specialized skilled personals for operation and maintenance of the treatment plant.

WASTEWATER TREATMENT SCHEME
Primary treatment consists of Screens - for removal of floating matter grit chamber - for removal of inorganic suspended solids primary sedimentation tank - for removal residual settleable solids which are mostly organic Skimming tanks may be used for removal of oils;

In conventional treatment plant no separate skimming tank is used and oil removal is achieved by collecting the scum in primary sedimentation tank. This primary treatment alone will not produce an effluent with an acceptable residual organic material concentration. Biological methods are used in the treatment systems to effect secondary treatment for removal of organic material. In biological treatment systems, the organic material is metabolized by bacteria. Depending upon the requirement for the final effluent quality, tertiary treatment methods and/or pathogen removal may be included.

Majority of wastewater treatment plants uses aerobic metabolism for the removal of organic matter. The popularly used aerobic processes are 1) Activated sludge process, 2) oxidation ditch, 3) trickling filter, and 4) aerated lagoons.

Stabilization ponds use both the aerobic and anaerobic mechanisms. In the recent years, due to increase in power cost and subsequent increase in operation cost of aerobic processes, more attention is being paid for the use of anaerobic treatment systems for the treatment of wastewater including sewage. Recently the high anaerobic process such as Upflow Anaerobic Sludge Blanket (UASB) reactor is used for sewage treatment at many places.

Depending on the mode of disposal the tertiary treatment may be given for killing pathogens, nutrient removal, suspended solids removal, etc. Generally secondary treatment followed by disinfection will meet the effluent standards for disposal into water bodies. When the treated sewage is disposed off on land for irrigation, the level of disinfection needs will depend on the type of secondary treatment and type of crops with restricted or unrestricted public access.

The various types of water pollutants can be classified in to following major categories: (1) Organic pollutants (2) Pathogens (3) Nutrients and agriculture runoff (4) Suspended solids and sediments (organic and inorganic) (5) Inorganic pollutants (salts and metals) (6) Thermal Pollution (7) Radioactive pollutants.

Quantity Estimation of Sewage
The sewage collected from the municipal area consists of wastewater generated from the residences, commercial centers, recreational activities, institutions and industrial wastewaters discharge into sewer network from the permissible industries located within the city limits. Before designing the sewer, it is necessary to know the discharge i.e., quantity of sewage, which will flow in it after completion of the project. Accurate estimation of sewage discharge is necessary for hydraulic design of the sewers. Far lower estimation than reality will soon lead to inadequate sewer size after commissioning of the scheme or the sewers may not remain adequate for the entire design period.

Quantity Estimation of Sewage
Very high discharge estimated will lead to larger sewer size affecting economy of the sewerage scheme Lower discharge actually flowing in the sewer may not meet the criteria of the self cleansing velocity and hence leading to deposition in the sewers. Since sewers are design to serve for some more future years, engineering skills have to be used to accurately estimate the sewage discharge.

Sources of Sanitary Sewage
1. Water supplied by water authority for domestic usage 2. Water supplied to the various industries for various industrial processes by local authority. 3. The water supplied to the various public places such as, schools, cinema theaters, hotels, hospitals, and commercial complexes. 4. Water drawn from wells by individuals to fulfill domestic demand.

Sources of Sanitary Sewage
5. The water drawn for various purposes by industries, from individual water sources such as, wells, tube wells, lake, river, etc. 6. Infiltration of groundwater into sewers through leaky joints. 7. Entrance of rainwater in sewers during rainy season through faulty joints or cracks in sewers.

Dry Weather Flow Dry weather flow is the flow that occurs in sewers in separate sewerage system or the flow that occurs during dry seasons in combined system. This flow indicates the flow of sanitary sewage. This depends upon the rate of water supply, type of area served, economic conditions of the people, weather conditions and infiltration of groundwater in the sewers, if sewers are laid below groundwater table.

Evaluation of Sewage Discharge
Correct estimation of sewage discharge is necessary. Otherwise sewers may prove inadequate resulting in overflow or may prove too large in diameter, which may make the system uneconomical and hydraulically inefficient. Apart from accounted water supplied by water authority that will be converted to wastewater, following quantities are considered while estimating the sewage quantity a. Addition due to unaccounted private water supplies b. Addition due to infiltration Storm water drainage may also infiltrate into sewers. This inflow is difficult to calculate. Generally, no extra provision is made for this quantity. This extra quantity can be taken care of by extra empty space left at the top in the sewers, which are designed for running ¾ full at maximum design discharge.

Evaluation of Sewage Discharge
c. Subtraction due to water losses d. Subtraction due to water not entering the sewerage system Net quantity of sewage: Generally, 75 to 80% of accounted water supplied is considered as quantity of sewage produced

Design period The future period for which the provision is made in designing the capacities of the various components of the sewerage scheme is known as the design period. The design period depends upon the following: Ease and difficulty in expansion, Amount and availability of investment, Anticipated rate of population growth, including shifts in communities, industries and commercial investments, Hydraulic constraints of the systems designed, and Life of the material and equipment.

Design period Following design period can be considered for different components of sewerage scheme. Sno Type and name of the component structure Reason for the selected period Design Period in years 1 Laterals less than 15 cm diameter Requirement s may change faster in limited area Full development 2 Trunk or main sewers Difficult & costly to enlarge 40 to 50 years 3 Treatment Units Growth and interest rates being high to moderate 15 to 20 years 4 Pumping plant Additional unit can be easily installed in short notice of time 5 to 10 years

Design Discharge of Sanitary Sewage
The total quantity of sewage generated per day is estimated as product of forecasted population at the end of design period considering per capita sewage generation and appropriate peakfactor. The per capita sewage generation can be considered as 75 to 80% of the per capita water supplied per day. The increase in population also result in increase in per capita water demand and hence, per capita production of sewage. This increase in water demand occurs due to increase in living standards, betterment in economical condition, changes in habit of people, and enhanced demand for public utilities.

Population Forecasting
Design of water supply and sanitation scheme is based on the projected population of a particular city, estimated for the design period. Any underestimated value will make system inadequate for the purpose intended Similarly overestimated value will make it costly. Change in the population of the city over the years occurs, and the system should be designed taking into account of the population at the end of the design period. Factors affecting changes in population are: • increase due to births • decrease due to deaths • increase/ decrease due to migration • increase due to annexation.

Population Forecasting
The present and past population record for the city can be obtained from the census population records. The population at the end of design period is predicted using various methods as suitable for that city considering the growth pattern followed by the city. 1) Arithmetical Increase method 2) Geometrical Increase method 3) Incremental Increase method 4) Decreasing Rate method 5) Simple Graphical method 6) Comparative graphical method 7) Master plan method 8) The apportionment method 9) The Logistic curve method

Variation in Sewage Flow
Variation occurs in the flow of sewage over annual average daily flow. Fluctuation in flow occurs from hour to hour and from season to season. The typical hourly variation in the sewage flow is shown

The peak will defer if the sewage has to travel long distance. This is because of the time required in collecting sufficient quantity of sewage required to fill the sewers and time required in travelling. As sewage flow in sewer lines, more and more sewage is mixed in it due to continuous increase in the area being served by the sewer line. This leads to reduction in the fluctuations in the sewage flow and the lag period goes on increasing. The magnitude of variation in the sewage quantity varies from place to place and it is very difficult to predict. For smaller township this variation will be more pronounced due to lower length and travel time before sewage reach to the main sewer and for large cities this variation will be less.

For estimating design discharge following relation can be considered: Maximum daily flow = Two times the annual average daily flow (representing seasonal variations) Maximum hourly flow = 1.5 times the maximum daily flow (accounting hourly variations) = Three times the annual average daily flow As the tributary area increases, peak hourly flow will decrease. For smaller population served (less than 50000) the peak factor can be 2.5, and as the population served increases its value reduces. For large cities it can be considered about 1.5 to 2.0. Therefore, for outfall sewer the peak flow can be considered as 1.5 times the annual average daily flow. Even for design of the treatment facility, the peak factor is considered as 1.5 times the annual average daily flow.

The minimum flow passing through sewers is also important to develop self cleansing velocity to avoid silting in sewers. This flow will generate in the sewers during late night hours. The effect of this flow is more pronounced on lateral sewers than the main sewers. Sewers must be checked for minimum velocity as follows: Minimum daily flow = 2/3 Annual average daily flow Minimum hourly flow = ½ minimum daily flow = 1/3 Annual average daily flow The overall variation between the maximum and minimum flow is more in the laterals and less in the main or trunk sewers. This ratio may be more than 6 for laterals and about 2 to 3 in case of main sewers.

Factors Affecting the Quantity of Stormwater
The surface run-off resulting after precipitation contributes to the stormwater. The quantity of stormwater reaching to the sewers or drains is very large as compared with sanitary sewage. The factors affecting the quantity of stormwater flow are as below: i. Area of the catchment ii. Slope and shape of the catchment area iii. Porosity of the soil iv. Obstruction in the flow of water as trees, fields, gardens, etc.

Factors Affecting the Quantity of Stormwater
The factors affecting the quantity of stormwater flow are as below: v. Initial state of catchment area with respect to wetness. vi. Intensity and duration of rainfall vii. Atmospheric temperature and humidity viii. Number and size of ditches present in the area

Measurement of Rainfall
The rainfall intensity could be measured by using rain gauges and recording the amount of rain falling in unit time. The rainfall intensity is usually expressed as mm/hour or cm/hour. The rain gauges used can be manual recording type or automatic recording rain gauges.

Rain gauge Station

Automatic recording rain gauges.

Methods for Estimation of Quantity of Storm Water
1. Rational Method 2. Empirical formulae method In both the above methods, the quantity of storm water is considered as function of intensity of rainfall, coefficient of runoff and area of catchment. Time of Concentration: The period after which the entire catchment area will start contributing to the runoff is called as the time of concentration. The rainfall with duration lesser than the time of concentration will not produce maximum discharge.

The runoff may not be maximum even when the duration of the rain is more than the time of concentration. This is because in such cases the intensity of rain reduces with the increase in its duration. The runoff will be maximum when the duration of rainfall is equal to the time of concentration and is called as critical rainfall duration. The time of concentration is equal to sum of inlet time and time of travel. Time of concentration = Inlet time + time of travel

Inlet Time: The time required for the rain in falling on the most remote point of the tributary area to flow across the ground surface along the natural drains or gutters up to inlet of sewer is called inlet time. The inlet time ‘Ti’ can be estimated using relationships similar to following. These coefficients will have different values for different catchments. Ti = [0.885 L3/H]0.385

Where,Ti = Time of inlet, minute L = Length of overland flow in Km from critical point to mouth of drain H = Total fall of level from the critical point to mouth of drain, m Time of Travel: The time required by the water to flow in the drain channel from the mouth to the point under consideration or the point of concentration is called as time of travel. Time of Travel (Tt) = Length of drain/ velocity in drain Time of concentration Tc = Ti + Tf

Runoff Coefficient: The total precipitation falling on any area is dispersed as percolation, evaporation, storage in ponds or reservoir and surface runoff. The runoff coefficient can be defined as a fraction, which is multiplied with the quantity of total rainfall to determine the quantity of rain water, which will reach the sewers. The runoff coefficient depends upon the porosity of soil cover, wetness and ground cover.

Empirical formulae for rainfall intensities
The relationships between rainfall intensity and duration are developed based on long experience in field. Under Indian conditions, intensity of rainfall in design is usually in the range 12 mm/h to 20 mm/h. For T varying between 5 to 20 minutes For T varying between 20 to 100 minutes T a b 5 to 20 mins. 75 10 20 to 100 mins. 100 20

The overall runoff coefficient for the catchment area can be worked out as follows: Overall runoff coefficient Where, A1, A2, ….An are types of area with C1, C2, …Cn as their coefficient of runoff, respectively.

The typical runoff coefficient for the different ground cover is provided in the below table Runoff coefficient for various sources Sno Type of Surface Value of K 1 Water Tight Roof surface 2 Asphalt Pavement 0.85 – 0.90 3 Stone, brick, wood-block pavement with cemented joints 4 Stone, brick, wood-block pavement with uncemented joints 5 Water bond Macadam roads 6 Gravel road and walks 0.15 – 0.30 7 Unpaved streets and vacant lands 0.10 – 0.30 8 Parks, Lawns, gardens, meadows etc., 0.05 – 0.25 9 Wooden lands 0.01 – 0.20

(1) Rational method Storm water quantity, Q = K.PC.A / 36 Q = Quantity of storm water, m3/sec K = Coefficient of runoff PC = intensity of rainfall (cm/hour) for the duration equal to time of concentration A = Drainage area in hectares

(2) Burkli Ziegler formula
Storm water quantity Q = Quantity of storm water, m3/sec = Coefficient of runoff p = intensity of rainfall (cm/hour) for the duration equal to time of concentration A = Drainage area in hectares S0= The slope of the ground surface in metres per thousand metres

(3) Dicken’s formula Peak Discharge in cumecs QP = Peak Discharge in cumecs M = Catchment area in Km2 C = a constant depending upon all those fifteen to twenty factors which affect the runoff (C=11.5)

(3) Dicken’s formula QP = Peak Discharge in cumecs M = Catchment area in Km2 C = a constant depending upon all those fifteen to twenty factors which affect the runoff (C=6.8) Location of Catchment Value of C1 Areas within 24Km from the coast 6.8 Areas within 24Km – 16Km from the coast 8.8 Limited areas near hills 10.1

(5) Nawab Jung Bahadur formula
(4) Inglis formula QP = Peak Discharge in cumecs M = Catchment area in Km2 (5) Nawab Jung Bahadur formula QP = Peak Discharge in cumecs M = Catchment area in Km2 C2 = 48 to 60

(6) Dredge or Burge’s formula
Storm water quantity Qp = Quantity of storm water, m3/sec L = Length of the drainage basin in Kilometres M = Catchment area in Km2

4 Mark Question Determine designed discharge for a combined system serving population of with rate of water supply of 135 LPCD. The catchment area is 100 hectares and the average coefficient of runoff is Given Population = 50,000 Rate of water supply = 135 lpcd Catchment Area = 100 Hectares Average coefficient of runoff =0.60 To Find Designed Discharge for combined system

Solution Estimation of sewage quantity STEP 1 Assumption 1: Considering 80% of the water supplied will result in wastewater generation Quantity of sanitary sewage Q Q = Population x Quantity of water supply x 0.8 =50000 x 135 x 0.80 = 5400 m3/day = m3/sec STEP 2 Assumption 2: Considering peak factor of 2.5 Design discharge for sanitary sewage = x 2.5 = m3/sec

Estimation of storm water discharge STEP 3 Intensity of rainfall, PC Therefore, PC = 100/( ) = 2 cm/h Storm water runoff, Q = K.PC.A /36 Q = 0.6 x 2 x 100/(36) = 3.33 m3/sec Design discharge for combined sewer = = 3.49 m3/sec

8 Mark Question The catchment area is of 300 hectares. The surface cover in the catchment can be classified as given below: Sno Type of Cover Coefficinet of runoff K Percentage of area 1 Roof s 0.90 15 2 Pavements and yards 0.80 3 Lawns and gardens 0.15 25 4 Roads 0.40 20 5 Open Ground 0.10 6 Single Family dwelling 0.50 10

Calculate the runoff coefficient and quantity of storm water runoff, if intensity of rainfall is 30 mm/h for rain with duration equal to time of concentration. If population density in the area is 350 persons per hectare and rate of water supply is 200 LPCD, calculate design discharge for separate system, partially separate system, and combined system. Given Population density in the area = 350 persons per hectare Catchment Area = 300 hectares Rate of water supply = 200 lpcd Intensity of rainfall = 30mm/h = 3cm/h To Find 1) Average coefficient of runoff 2) Quantity of stormwater runoff

Solution Estimation of storm water discharge for storm water drain of separate system STEP 1 Overall runoff coefficient Where, A1, A2, ….An are types of area with C1, C2, …Cn as their coefficient of runoff, respectively.

C = 0.44 Estimation of storm water discharge STEP 2 Storm water runoff, Q = K.PC.A /36 Q = 0.44 x 3 x 300/(36) = 11 m3/sec Estimation of sewage discharge for separate system sanitary sewer STEP 3 Assumption 1: Considering 80% of the water supplied will result in wastewater generation Quantity of sanitary sewage Q Q = Population density x Area x Quantity of water supply x 0.8 = 350 x 300 x 200 x 0.80 = m3/day = m3/sec

= m3/day = m3/sec Assumption 2: Considering peak factor of 2 Design discharge for sanitary sewage = x 2 = m3/sec Estimation of discharge for partially separate system STEP 4 Storm water discharge falling on roofs and paved courtyards will be added to the sanitary sewer. Average coefficient of runoff = (0.90 x x 45) / 90 = 0.85 Discharge = 0.85 x 30 x 90 / 360 = m3/sec Total discharge in the sanitary sewer of partially separate system = = m3/sec Discharge in storm water drains = 11 – = m3/sec

Factors affecting Characteristics and composition of sewage and their significance

Sewage Characteristics
PHYSICAL CHEMICAL BACTERIOLOGICAL (BIOLOGICAL)

PHYSICAL TURBIDITY COLOUR ODOUR TEMPERATURE CHEMICAL Total Solids pH value Chloride Nitrogen Fats, Grease & Oil Sulphides, Sulphates and H2S gas Dissolved oxygen BOD (Biochemcial Oxygen Demand) COD (Chemcial Oxygen Demand) BACTERIOLOGICAL CHARACTERISTICS & TESTING

Characterization of wastes is essential for an effective and economical waste management programme. It helps in the choice of treatment methods deciding the extent of treatment, assessing the beneficial uses of wastes and utilizing the waste purification capacity of natural bodies of water in a planned and controlled manner. While analysis of wastewater in each particular case is advisable, data from the other cities may be utilized during initial stage of planning.

Domestic sewage comprises spent water from kitchen, bathroom, lavatory, etc. The factors which contribute to variations in characteristics of the domestic sewage are daily per capita use of water, quality of water supply and the type, condition and extent of sewerage system, and habits of the people. Municipal sewage, which contains both domestic and industrial wastewater, may differ from place to place depending upon the type of industries and industrial establishment. The important characteristics of sewage are discussed here.

Temperature The observations of temperature of sewage are useful in indicating solubility of oxygen, which affects transfer capacity of aeration equipment in aerobic systems, and rate of biological activity. Extremely low temperature affects adversely on the efficiency of biological treatment systems and on efficiency of sedimentation. In general, under Indian conditions the temperature of the raw sewage is observed to be between 15 and 350C at various places in different seasons.

The pH The hydrogen ion concentration expressed as pH, is a valuable parameter in the operation of biological units. The pH of the fresh sewage is slightly more than the water supplied to the community. However, decomposition of organic matter may lower the pH, while the presence of industrial wastewater may produce extreme fluctuations. Generally the pH of raw sewage is in the range 5.5 to 8.0.

Colour and Odour Fresh domestic sewage has a slightly soapy and cloudy appearance depending upon its concentration. As time passes the sewage becomes stale, darkening in colour with a pronounced smell due to microbial activity.

Solids Though sewage generally contains less than 0.5 percent solids, the rest being water, still the nuisance caused by the solids cannot be overlooked, as these solids are highly degradable and therefore need proper disposal. The sewage solids may be classified into dissolved solids, suspended solids and volatile suspended solids. Knowledge of the volatile or organic fraction of solid, which decomposes, becomes necessary, as this constitutes the load on biological treatment units or oxygen resources of a stream when sewage is disposed off by dilution.

Solids The estimation of suspended solids, both organic and inorganic, gives a general picture of the load on sedimentation and grit removal system during sewage treatment. Dissolved inorganic fraction is to be considered when sewage is used for land irrigation or any other reuse is planned.

NITROGEN CYCLE UNDER AEROBIC OXIDATION

SULPHUR CYCLE UNDER AEROBIC OXIDATION

CARBON CYCLE UNDER AEROBIC OXIDATION

AEROBIC OXIDATION

NITROGEN, CARBON AND SULPHUR CYCLE UNDER ANAEROBIC OXIDATION

Nitrogen and Phosphorus
The principal nitrogen compounds in domestic sewage are proteins, amines, amino acids, and urea. Ammonia nitrogen in sewage results from the bacterial decomposition of these organic constituents. Nitrogen being an essential component of biological protoplasm, its concentration is important for proper functioning of biological treatment systems and disposal on land. Generally, the domestic sewage contains sufficient nitrogen, to take care of the needs of the biological treatment.

For industrial wastewater if sufficient nitrogen is not present it is required to be added externally. Generally nitrogen content in the untreated sewage is observed to be in the range of 20 to 50 mg/L measured as TKN. Phosphorus is contributing to domestic sewage from food residues containing phosphorus and their breakdown products. The use of increased quantities of synthetic detergents adds substantially to the phosphorus content of sewage. Phosphorus is also an essential nutrient for the biological processes.

The concentration of phosphorus in domestic sewage is generally adequate to support aerobic biological wastewater treatment. However, it will be matter of concerned when the treated effluent is to be reused. The concentration of PO4 in raw sewage is generally observed in the range of 5 to 10 mg/L.

Chlorides Concentration of chlorides in sewage is greater than the normal chloride content of water supply. The chloride concentration in excess than the water supplied can be used as an indexof the strength of the sewage. The daily contribution of chloride averages to about 8 gm per person. Based on an average sewage flow of 150 LPCD, this would result in the chloride content of sewage being 50 mg/L higher than that of the water supplied.

Chlorides Any abnormal increase should indicate discharge of chloride bearing wastes or saline groundwater infiltration, the latter adding to the sulphates as well, which may lead to excessive generation of hydrogen sulphide

Organic Material Organic compounds present in sewage are of particular interest for environmental engineering. A large variety of microorganisms (that may be present in the sewage or in the receiving water body) interact with the organic material by using it as an energy or material source. The utilization of the organic material by microorganisms is called metabolism. The conversion of organic material by microorganism to obtain energy is called catabolism and the incorporation of organic material in the cellular material is called anabolism.

Organic Material In practice two properties of almost all organic compounds can be used: (1) organic compound can be oxidized; and (2) organic compounds contain organic carbon. In environmental engineering there are two standard tests based on the oxidation of organic material: 1) the Biochemical Oxygen Demand (BOD) and 2) the Chemical Oxygen Demand (COD) tests. In both tests, the organic material concentration is measured during the test. .

Organic Material The essential differences between the COD and the BOD tests are in the oxidant utilized and the operational conditions imposed during the test such as biochemical oxidation and chemical oxidation. The other method for measuring organic material is the development of the Total Organic Carbon (TOC) test as an alternative to quantify the concentration of the organic material.

Biochemical Oxygen Demand (BOD)
The BOD of the sewage is the amount of oxygen required for the biochemical decomposition of biodegradable organic matter under aerobic conditions. The oxygen consumed in the process is related to the amount of decomposable organic matter. The general range of BOD observed for raw sewage is 100 to 400 mg/L. Values in the lower range are being common under average Indian cities.

Chemical Oxygen Demand (COD)
The COD gives the measure of the oxygen required for chemical oxidation. It does not differentiate between biological oxidisable and nonoxidisable material. However, the ratio of the COD to BOD does not change significantly for particular waste and hence this test could be used conveniently for interpreting performance efficiencies of the treatment units. In general, the COD of raw sewage at various places is reported to be in the range 200 to 700 mg/L.

In COD test, the oxidation of organic matter is essentially complete within two hours, whereas, biochemical oxidation of organic matter takes several weeks. In case of wastewaters with a large range of organic compounds, an extra difficulty in using BOD as a quantitative parameter is that the rate of oxidation of organic compounds depends on the nature and size of its molecules. Smaller molecules are readily available for use by bacteria, but large molecules and colloidal and suspended matters can only be metabolized after preparatory steps of hydrolysis.

It is therefore not possible to establish a general relationship between the experimental five-day BOD and the ultimate BOD of a sample, i.e., the oxygen consumption after several weeks. For sewage (with k=0.23 d-1 at 20oC) the BOD5 is times of ultimateBOD, and ultimate BOD is 87% of the COD. Hence, the COD /BOD ratio for the sewage is around 1.7.

Toxic Metals and Compounds
Some heavy metals and compounds such as chromium, copper, cyanide, which are toxic may find their way into municipal sewage through industrial discharges. The concentration of these compounds is important if the sewage is to treat by biological treatment methods or disposed off in stream or on land. In general these compounds are within toxic limits in sanitary sewage; however, with receipt of industrial discharges they may cross the limits in municipal wastewaters

Dissolved oxygen Importance Why is oxygen in water important?
Dissolved oxygen (DO) analysis measures the amount of gaseous oxygen (O2) dissolved in an aqueous solution. Oxygen gets into water by diffusion from the surrounding air, by aeration (rapid movement), and as a product of photosynthesis. DO is measured in standard solution units such as milligrams O2 per liter (mg/L), millilitres O2 per liter (ml/L), millimoles O2 per liter (mmol/L), and moles O2 per cubic meter (mol/m3). DO is measured by way of its oxidation potential with a probe that allows diffusion of oxygen into it.

Dissolved oxygen The saturation solubility of oxygen in wastewater can be expressed as Cs =  (0.99)h/88 x /(T )

BOD Biochemical oxygen demand or BOD is a procedure for determining the rate of uptake of dissolved oxygen by the organisms in a body of water BOD measures the oxygen uptake by bacteria in a water sample at a temperature of 20°C over a period of 5d in the dark. The sample is diluted with oxygen saturated de-ionized water, inoculating it with a fixed aliquot of microbial seed, measuring the (DO) and then sealing the sample to prevent further oxygen addition. The sample is kept at 20 °C for five days, in the dark to prevent addition of oxygen by photo-synthesis, and the dissolved oxygen is measured again. The difference between the final DO and initial DO is the BOD or, BOD5. .

BOD Once we have a BOD5 value, it is treated as just a concentration in mg/L BOD can be calculated by: Diluted: ((Initial DO - Final DO + BOD of Seed) x Dilution Factor BOD of seed (diluted activated sludge) is measured in a control: just deionized water without wastewater sample. Significance: BOD is a measure of organic content and gives an indication on how much oxygen would be required for microbial degradation.

BOD BOD of water @ 5 days at 20°C = 68% of Total Demand
The first demand during the first 20 days occurs due to the oxidation of the oxygen matter which is called as first stage demand or carbonaceous demand. The latter demand occurs due to oxidation of ammonia and is called nitrogenous demand or second stage demand.

1% Diluted sample means 1mL of sewage is diluted to make 100mL of test sample

Composition of Sewage (Sewage Sampling)
Quality of sewage varies Surface is different from bottom Morning is different from noon and evening No ideal time and ideal condition for taking sewage samples since quality is continuosly changing A composite sample is preferred to avoid such problems A composite sample is a one which is composed of a mixture of grab samples proportional to the rate of flow of sewage at the time of sampling

Grab sample

Composite sample

Composition of Sewage (Sewage Sampling)
The characteristics of sewage may change due to biological activity To avoid this problem preservative is added Commonly used preservatives Chloroform Formaldehyde Sulphuric acid

Chemical analysis of Sewage
Constituents Strong Medium Weak Solids Total 1000 500 200 Volatile 700 350 100 Fixed 150 80 Suspended 300 400 250 70 50 30 Dissolved Settleable (ml/l) 12 8 4 BOD C DO -

Chemical analysis of Sewage
Constituents Strong Medium Weak Nitrogen Total 85 50 25 Organic 35 20 10 Free Ammonia 30 15 Nitrates 0.1 0.05 Nitrites 0.4 0.2 0.10 Chlorides 175 100 Alkalinity 200 Fats 40

Effluent Discharge Standards
As per schedule VI of the environmental protection rules 1986, The effluent discharge standards is framed

Legislation Requirements
Water (Prevention and control of pollution) Act 1974 Environmental protection Act 1986 Protecting and improving the quality of the environment Preventing, controlling the environmental pollution Pollution Control Boards – CPCB & SPCB under Water Act

Water (Prevention and control of pollution) Act 1974 amended in 1988
Air (Prevention and control of pollution) Act 1987 amended in 1987 Environmental protection Act 1986 Hazardous Waste (Management and Handling Rules) amended in 2004

Oxygen depletion in streams

DO sag definitions

Cumulative oxygen supply + demand
Plotting the two kinetic equations separately on a cumulative basis and adding these graphically produce the DO sag curve

Streeter-Phelps Model*
Mass Balance for the Model Not a Steady-state situation rate O2 accum. = rate O2 in – rate O2 out + produced – consumed rate O2 accum. = rate O2 in – – rate O2 consumed Kinetics Both reoxygenation and deoxygenation are 1st order * Streeter, H.W. and Phelps, E.B. Bulletin #146, USPHS (1925)

Kinetics* for Streeter-Phelps Model
Deoxygenation L = BOD remaining at any time dL/dt = Rate of deoxygenation equivalent to rate of BOD removal dL/dt = -k1L for a first order reaction k1 = deoxygenation constant, f’n of waste type and temp. *See Kinetics presentation if unfamiliar with the mathematical processing

Developing the Streeter-Phelps
Rate of reoxygenation = k2D D = deficit in D.O. k2 = reoxygenation constant* Where T = temperature of water, ºC H = average depth of flow, m ν = mean stream velocity, m/s D.O. deficit = saturation D.O. – D.O. in the water There are many correlations for this. The simplest one, used here, is from O’Connor and Dobbins, 1958 Typical values for k2 at 20 °C, 1/d (base e) are as follows: small ponds and back water sluggish streams and large lakes large streams with low velocity large streams at normal velocity swift streams rapids and waterfalls > 1.15

Combining the kinetics
Net rate of change of oxygen deficiency, dD/dt dD/dt = k1L - k2D where L = L0e-k1t OR dD/dt = k1L0e-k1t - k2D

Integration and substitution
The last differential equation can be integrated to: It can be observed that the minimum value, Dc is achieved when dD/dt = 0: , since D is then Dc Substituting this last equation in the first, when D = Dc and solving for t = tc:

Example: Streeter-Phelps
Wastewater mixes with a river resulting in a BOD = 10.9 mg/L, DO = 7.6 mg/L The mixture has a temp. = 20 C Deoxygenation const.= 0.2 day-1 Average flow = 0.3 m/s, Average depth = 3.0 m DO saturated = 9.1 mg/L Find the time and distance downstream at which the oxygen deficit is a maximum Find the minimum value of DO

Solution…some values needed
Initial Deficit Do = 9.1 – 7.6 = 1.5 mg/L (Now given, but could be calculated from proportional mix of river DO, presumably saturated, and DO of wastewater, presumably zero) Estimate the reaeration constant: k2 = 3.9 v½ (1.025T-20)½ H3/2 k2 = 3.9 x (0.3m/s)½ ( )½ (3.0m)3/2 = d-1

Solution…time and distance
Note that the effects will be maximized almost 70 km downstream

Solution…maximum DO deficiency
Note that this BOD could have been calculated from mixing high-BOD wastewater with zero or near-zero BOD The minimum DO value is = 6 mg/L Implication: DO probably not low enough for a fishkill, but if continued could lead to species differentiation and discourage sensitives species like trout.

UNIT I PLANNING FOR SEWERAGE SYSTEMS

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UNIT I PLANNING FOR SEWERAGE SYSTEMS

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