02 - Stream & Effluent standards, Oxygen sag curve, Self Purification.pptx

Industrial wastewater treatment describes the processes used for treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater (or effluent) may be reused or released to a sanitary sewer or to a surface water in the environment. Some industrial facilities generate wastewater that can be treated in sewage treatment plants. Most industrial processes, such as petroleum refineries, chemical and petrochemical plants have their own specialized facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the regulations regarding disposal of wastewaters into sewers or into rivers, lakes or oceans.

1. Industrial and Municipal Waste Management C.E 8.3.1 Unit I Asst. Prof. Prachi Desai, Don Bosco College of Engineering 1

2. Stream standards and Effluent standards Effluent standards : effluent standards refer to the quality of water coming from a pipe or outfall. They are based on economics than on absolute protection of the stream. Easy to control. Detailed stream analyses are not required. They do not establish an overall level of pollutant loading for a given water body. Ratio of wastewater to stream flow is not considered. Treatment is obligatory irrespective of the size of industry. Asst. Prof. Prachi Desai, Don Bosco College of Engineering 2

3. Stream standards and Effluent standards Stream Standard : Standard of the water in a particular water course to which a sewage treatment plant is discharging into. If a stream standard exists the Effluent standard for a particular WWTP is set by working back from the Stream standard. They are based on establishing classification of quality for a stream. The quality of the receiving water is regulated to maintain established stream classification. Prevention of excessive pollution/ Loading is limited to what the stream can assimilate No consideration of type and location of industry. Allows public to establish goals for present and future water quality. Confusion of zone of different classification. Controversy over proportion of stream to be reserved for future usage (municipal, industrial, agriculture etc.) Opposition from industry/ public to change the established classification A detailed stream analysis is required to determine the level of wastewater treatment required to maintain the health of the ecosystem Cost of treatment may affect the survival of industry Asst. Prof. Prachi Desai, Don Bosco College of Engineering 3

4. Oxygen sag curve SELF PURIFICATION OF RIVER WATER It is a natural process of rivers, lakes or canals to recover the rate of dissolved oxygen values of the highest concentration of oxygen which is one of the best indicators of water quality. FACTORS AFFECTING SELF PURIFICATION DILUTION: When sufficient dilution water is available in the receiving water body where the waste water is discharged, the DO level in the receiving stream may not reach to zero. CURRENT: When strong water current is available , the discharge waste water will be thoroughly mixed with stream water preventing deposition of solids. In small current the solid matter from the waste water will get deposited at the bed following decomposition and reducing DO. Asst. Prof. Prachi Desai, Don Bosco College of Engineering 4

5. Oxygen sag curve FACTORS AFFECTING SELF PURIFICATION TEMPERATURE: The quantity of DO available in stream water is more in cold temperature than in hot temperature. Also, as the activity of micro organisms is more at the higher temperature, hence , the self purification will take less time hot temperature than in winter. SUNLIGHT: Algae produces oxygen in presence of sunlight due to photosynthesis. Therefore, sunlight helps in purification of stream by adding oxygen through photosynthesis. RATE OF OXIDATION: Due to oxidation of organic matter discharged in the river DO depletion occurs. This rate is faster at higher temperature and low at lower temperature. The rate of oxidation of organic matter depends upon chemical composition of organic matter. Asst. Prof. Prachi Desai, Don Bosco College of Engineering 5

6. Oxygen sag curve Deoxygenation curve: In a polluted stream, the DO content goes on reducing due to decomposition of volatile organic matter. The rate of deoxygenation depends upon the amount of organic matter remaining to be oxidized at a given time as well as on the temperature of reaction, hence at given temperature, the curve showing depletion of DO with time i.e. deoxygenation curve is similar to the first stage BOD-curve. Asst. Prof. Prachi Desai, Don Bosco College of Engineering 6

7. Oxygen sag curve Reoxygenation curve: In order to counter the balance of the consumption of DO due to deoxygenation, atmosphere supplies O2 to water and the process is called reoxygenation. The rate at which the oxygen is supplied by atmosphere to the polluted water depends upon:- The depth of receiving water Condition of flow Oxygen deficit Temperature Asst. Prof. Prachi Desai, Don Bosco College of Engineering 7

8. Oxygen sag curve Oxygen deficit:- The oxygen deficit D at any time in a polluted river stream is the difference between the actual DO content of water at that time and the saturation DO content at the water temperature. Oxygen Deficit = DO sat –DO actual In order to maintain clean conditions in a river stream, the oxygen deficit must be nil and this can be found out by knowing the rates of deoxygenation and reoxygenation. Asst. Prof. Prachi Desai, Don Bosco College of Engineering 8

9. Factors Affecting Self Purification If Cs = Concentration of Sewage and Cr = Concentration of River, organic content, BOD, suspended solids, dissolved oxygen in the sewage and river having discharge Qs = Discharge of Sewage and Qr = Discharge of River respectively, the resulting concentration C of the mixture is given by   9

10. Zones of pollution in a river or Stream 10

11. Zones of pollution in a river or Stream A polluted stream undergoing self- purification can be divided into following four zones Zone of degradation Zone of active decomposition Zone of recovery Zone of clearer water Zone of Degradation: This zone is found for a certain length just ahead of the point where sewage is discharged into the river. Water becomes dark and turbid with formation of sludge deposits at the bottom. Bacteria will start oxidation of the organic matter the DO is reduced to about 40 % of the saturation valve Oxygenation occurs but is slower than deoxygenating. These conditions are unfavorable to the development of aquatic life; and as such, algae dies out, but certain type of fish may be present feeding on fresh organic matter. Moreover, certain typical bottom worms such as limondrilus and Tubifex appear with sewage fungi. 11

12. Zones of pollution in a river or Stream Zone of Active Decomposition Heavy pollution. Water becomes grayish and darker than in the previous zone. DO concentration falls down to zero Anaerobic conditions may set in with the evolution of gases like methane, carbon dioxide, hydrogen sulphide, etc.. bubbling to the surface, with masses of sludge forming ugly scum layer at the surface. Rate of deoxygenating becomes lesser than the re-aeration rate and DO again rises to the original level (i.e. above 40 %) In this region, the bacteria flora will flourish. At the upper end, anaerobic bacteria will replace aerobic bacteria, while at the lower end, the position will replace aerobic bacteria, while at the lower end the position will be reversed. Protozoa and fungi first disappear then reappear. Fish life will be absent. Algae and tubifex will also be absent. Maggots and Psychoda (Sewage fly) larvae will, however, be present in all but the most septic sewage. 12

13. Zones of pollution in a river or Stream Zone of Recovery the river stream tries to recover from its degraded condition to its former appearance. The water becomes clearer, and so the algae reappears while fungi decreases. BOD decreases and DO content rises above 40 % of the saturation value; Protozoa, Rotifers, Crustaceans and large plants like sponges, Bryozoans, etc. The organic material will be mineralized to form nitrate, phosphate, carbonates, etc.. Zone of Clearer Water the river attains its original condition with DO rising up to the saturation value. Water becomes attractive in appearance, fish ( which requires at least 4 to 5 mg /l of DO) and usual aquatic life prevails. Some pathogenic organisms may still, however survive and remain present, which confirms the fact that “ once the river water has been polluted, it will not be safe for drinking, unless it is properly treated. 13