1. 2.Waste Water Characteristics  Studying the characteristics of sewage will help us in determining the type of treatment required to remove the impurity to the required level that does not harm the environment  Sewage characteristics include: 1. Physical Characteristics 2. Chemical Characteristics 3. Biological Characteristics

2. Cont. ……. 1. Physical Characteristics Of Sewage  include those items that can be detected using physical senses.it includes: a. Color c. Temperature e. Turbidity b. Odor d. Solids a. Color  Color of sewage can be detected by naked eye, and it indicates the type of the sewage  If the color is gray, yellowish or light brown, it indicates fresh sewage

3. Cont. …….  If the color is black or dark brown, it indicates stale and septic sewage  Color of sewage sometimes indicates the source of sewage Sewage ColorProbable source GrayDomestic BlackSeptic condition or industrial sewage flow Red or other soil colorSurface run-off entering to sanitary sewage or industrial flow Green, yellow, othersIndustrial wastes not pretreated (paints,…) RedBlood from abattoir or sewage from other industries

4. b. Odor  Fresh sewage is practically odorless.  Sewage starts to become stale when its dissolved oxygen is exhausted which starts after three to four hours of production.  When the dissolved oxygen is exhausted, it starts emitting offensive odor, especially due to hydrogen sulfide gas produced due to decomposition of the sewage

5. c. Temperature  The normal temperature of sewage is slightly higher than the temperature of water supply  Effects of temperature variations on the behavior of the sewage: i. Affects the solubility of gases in the sewage ii. Affect biological activity of bacteria found in the sewage ii. Affect viscosity of the sewage thereby influencing the settling rate of solids found in the sewage

6. d. Solids  Sewage is normally 99.9% water and 0.1% solids  There are different types of solids in sewage 1. Suspended solids- solids that are not dissolved in wastewater. 2. Floatable solids -solids that float in waste water 3. Settle able solids - solids that settle in waste water 4. Colloidal particles -Very small suspended solids that neither float nor settle 

7. e. turbidity  is a measure of water clarity how much the material suspended in water decreases the passage of light through the water 2. Chemical Characteristics of Wastewater  The chemical characteristics of wastewater of special concern are: a. pH d. Chloride content b. DO (Dissolved Oxygen) e. Nitrogen Content c. Oxygen Demand (COD and BOD)

8. Cont. …….  Knowing the chemical characteristics of wastewater helps us in indicating: i. Sewage strength ii. Extent and type of treatment required iii. The stage of sewage decomposition a) pH  describe the acid or base properties of waste water  If the pH < 7 = acidic or septic sewage

9. Cont. …….  If the pH > 7 = alkaline sewage  Fresh sewage is generally alkaline. But as time passes and the sewage gets septic, its pH tends to fall due to production of acids by bacterial action  Since the efficiency of certain treatment plants depends upon the availability of suitable pH, we have to know the pH of the sewage to apply appropriate treatment system

10. Cont. …….  pH values less than 5 and more than 10 indicate presence of industrial wastes and are not compatible with biological wastewater operations  For proper treatment, wastewater pH should normally be in the range of 6.5 to 9.0  Pre-treatment system should be applied at the source to bring the pH to the required range before discharging it to sanitary sewages  extreme pH values damage biological treatment units

11. Cont. …….  If the pH value of a sewage coming to a wastewater treatment plant is from 5 to 10, no pretreatment is required at the sources  For sewages with pH values less than 5 and more than 10, pretreatment is required at sources b) Dissolved Oxygen (DO)  DO should be sufficient for the normal operation of microorganisms and living matters found in the sewage and treated sewage (effluent) receiving water body

12. Cont. …….  While discharging treated sewage into river or any other water body, it is necessary to insure at least some amount of DO in the sewage to be disposed c) Oxygen Demand  Amount of oxygen required to oxidize organic matter completely to CO2, H2O and other products.

13. Cont. …….  There are two methods of determining the oxygen demand of sewage 1. Chemical Oxygen Demand (COD) and 2. Biochemical Oxygen Demand (BOD) 1. Biological Oxygen demand (BOD)  BOD is the amount of oxygen consumed to aerobically oxidize the biodegradable organic compounds of sewage  determined in laboratory by mixing or diluting a known volume of sample of sewage with a known volume of aerated pure water and then calculating the DO of the diluted sample

14. Cont. …….  The diluted sample is then incubated for 5 days at 20C0 and its DO is again measured  The difference between the initial DO and the final DO indicates the oxygen consumed for biological oxidation of organic compounds found in the sewage and it is called BOD5  The BOD value is most commonly expressed in milligrams of oxygen consumed per liter of sample during 5 days of incubation at 20 °C

15. Cont. …….

16.  Determination of BOD has the following important applications in the field of sanitary engineering: a. To measure the strength of sewage b. To measure amount of pollution in a stream c. To determine efficiency of treatment plant d. For design of waste water treatment units e. To establish stream and effluent standards for pollution regulatory agencies f. To establish sewage charge rate (Polluter pays principle)

17. Cont. …….  From the figure the following correlations are derived:  If progressive exertion of BOD is plotted against time we get the following curv e

18. Cont. …….  Let,  L 0  or (BOD ultimate) or UBOD  Y t = BOD t (BOD exerted or absorbed )  L t = L 0 e -kt (BOD remain)  BOD t = L 0 - L t = L 0 – L 0 e -kt = L 0 (1-e -k ⅹ t )  BOD 5 = L 0 (1-e –k ⅹ 5 ) ………………oxygen demand during 5 days  K = 0.23d -1 usually, K, reaction constant

19. Cont. …….  The constant K varies with temperature as follows  K T = k 20 (  ) T-20,  = 1.047 or as given  The initial BOD (Biological oxygen demand), L, varies with temperature as follows  BOD T or L T = L 20 *(0.02T + 0.6)  Where L T = oxygen demand (BOD) at T°C and L 20 = oxygen demand (BOD) at 20 °C

20. 2. Chemical Oxygen Demand (COD)  COD is the amount of chemical oxidation required to convert organic matter in water and wastewater to carbon dioxide  The laboratory determination of COD, lies in using a strong oxidant like potassium dichromate (K 2 Cr 2 O 7 ) or potassium permanganate (KMnO4) solution to stabilize the organic matter to determine the molecular oxygen used from the oxidant solution in oxidizing the organic matter present in the given wastewater

21. Cont. …….  In order to perform this test, a known quantity of wastewater is mixed with a known quantity of standard solution of potassium dichromate, and the mixture is heated  The advantage of COD measurements is that they are obtained very quickly (within 3 hours), but they have the disadvantages that they do not give any information on the proportion of the wastewater that can be oxidized by bacteria, nor on the rate at which bio-oxidation occurs

22. d. Chloride Content  Chlorides are driven from kitchen wastes, human excreta and urinary discharges.  The normal chloride content of domestic sewage is 120 mg/lit  When the chloride content of sewage is found to be higher, it indicates the presence of industrial wastes or infiltration of sea water, there by indicating sewage strength

23. e. Nitrogen Contents  The presence of nitrogen in sewage indicates the presence of organic matter and may occur in one or more of the following forms:  Free ammonia indicates recently staled sewage  Presence of nitrites indicate the presence of partly decomposed (not fully oxidized) organic matter and shows incomplete treatment of organic wastes  The presence of nitrates indicate the presence of fully oxidized organic matter and show well oxidized and treated sewage

24. 3. Biological Characteristics of Waste water  The biological characteristics of sewage are due to the presence of bacteria and other living microorganisms, such as algae, fungi, protozoa, etc. The former are more active  Wastes are usually treated by supplying them with oxygen so that bacteria can utilize the waste as food  The routine bacteriological tests, as performed for water supply samples, are generally not performed because of the high concentration of bacteria present in it, The general equation is

25. Strength of Sewage Contaminants Unit Concentration WeakMediumStrong Total solids (TS)mg/l3507201200 Total dissolved solids (TDS)mg/l250500850 Fixedmg/l145300525 Volatilemg/l105200325 Suspended solidsmg/l100220350 Fixedmg/l205575 Volatilemg/l80165275 Settle able solidsmg/l51020 BOD 5, 20 o cmg/l110220400 TOCmg/l80160290 CODmg/l2505001000 Nitrogen (total as N)mg/l2044085 Organicmg/l8115335 Free ammoniamg/l122550 Nitritesmg/l000 Nitratesmg/l000 Phosphorus (total as P)mg/l4815 Organicmg/l1335 Inorganicmg/l3510 Chloridesmg/l3050100 Sulfatemg/l203050 Alkalinity (as CaCO 3 )mg/l50100200 Greasemg/l50100150 Total coliformsNo/100 ml10 6 - 10 7 10 7 - 10 8 10 7 - 10 9 Volatile organic compoundsµg/l< 100100 - 400> 400

26. THE END!!