Module 3: WATER POLLUTION CONTROL BY PHYSICO-CHEMICAL AND ELECTROCHEMICAL METHODS

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1 Module 3: WATER POLLUTION CONTROL BY PHYSICO-CHEMICAL AND ELECTROCHEMICAL METHODS Lecture Topic No. of Hours (13) 1 Introduction to Water Pollution and Control 1 2 Pre-treatment & Physical treatment: Flow equalization 1 3 Pre-treatment & Physical treatment: Aeration - Part Pre-treatment & Physical treatment: Aeration Part Pre-treatment & Physical treatment: Coagulation and Flocculation - Part 1 6 Pre-treatment & Physical treatment: Coagulation and Flocculation - Part 2 7 Setting and Sedimentation: Part Setting and Sedimentation: Part Settling Chamber Design 1 10 Filtration 1 11 Water Pollution Control By Membrane Based Technologies 1 12 Water Pollution Control by Adsorption: Part Water Pollution Control by Adsorption: Part Electrochemical Treatment 1 1 1

2 Lecture 1 Introduction to Water Pollution and Control

3 WATER TREATMENT Each wastewater treatment and disposal system consists of the following: collecting the wastewater, transporting it to treatment plant, treating the wastewater, and disposing of the resulting effluent. The objective of wastewater treatment is to remove undesirable compounds and residues as possible and bring the wastewater to the quality of the designated use. Although potable water is never produced at the treatment plant, wastewater treatment is done to at least of that minimum quality that no nuisance condition or health hazard results because of the final disposal of the effluent and that the quality of the water in receiving streams is not altered. It is also necessary that the effluent from the treatment plant meets the discharge standards as decided by Central Pollution Control Board. WASTEWATER COLLECTION SYSTEMS The water collection system transports wastewater from its origin to a designated destination. The purpose of a wastewater collection system is to safeguard the public and other persons involved from health hazards associated with the wastewater. Sanitary collection systems which use conveying structures and pumps are designed to remove these domestic and industrial wastes. Interceptors and traps are used as preventive maintenance measures prior to the wastewater entering the collection system [1]. WASTEWATER TREATMENT There are basically three types of stages or processes that take place to render wastewater for disposal. These processes are called primary, secondary, and tertiary treatment. Likewise, there are three types of treatment plants -- primary, secondary, and tertiary -- that reduce the pollutant load in wastewater and chlorinate it before discharging the effluent into outfall sewer. UNITS FOR TREATMENT OF WATER A. Pre- and primary treatment. This includes one or many of the following: Screening: Removes bigger size debris like bricks, glass, etc. that may damage later equipmets Grinding (includes shredding): Reduces the size of bigger size of solids to smaller size that can be handled by the later equipments Grit removal: Blocks gravel, sand, silt, etc. from going further

Flow equalization: Helps in equalizing the hydraulic and organic loadings to optimum values for

improves solids separation and settling, etc.

solids settled during primary sedimentation Overall primary treatment removes 90-95% settleable

convert dissolved, suspended and colloidal organic wastes to more stable solids and thus remove

Secondary sedimentation: Removes the accumulated biomasss after the secondary treatment C.

4 Flow equalization: Helps in equalizing the hydraulic and organic loadings to optimum values for maximum efficiency Aeration/air floatation: Removes soluble odorous gases such as H 2 S, improves solids separation and settling, etc. Primary sedimentation: Separates settleable organic and floatable solids Sludge removal: Removes solids settled during primary sedimentation Overall primary treatment removes 90-95% settleable solids, 40-60% total suspended solidss and 25-35% BOD 5 [2]. B. Secondary treatment: This mainly involves biological treatment, settling, clarification and sludge removal. Biological treatment can be done by y a number of methods as given below: Biological processes convert dissolved, suspended and colloidal organic wastes to more stable solids and thus remove majority of BOD. Secondary sedimentation: Removes the accumulated biomasss after the secondary treatment C. Tertiary Treatment: This may include, but is not limited to, one or more of the following: Carbon absorption: Removes recalcitrant pollutants Nutrient Removal: Removes limiting nutrients such as nitrogen and phosphorus that could affect the receiving water body and cause eutrophication [2]. Chemical oxidation including wet-air oxidation: Oxidizes recalcitrant pollutants Membrane processes: Removes inorganic and other pollutants based upon its size

5 Electrodialysis: Electricity is used for the separation process and removing charged particles Reverse osmosis: Pressure is for forcing water molecules to the cleaner side Ion exchange: Removes ionic pollutants by exchange process Chlorination including ozone treatment, UV treatment: Destroys pathogens present in the effluent Disposal: Treated effluent is either used for some beneficial use such as irrigation, etc. or is directly discharged to water bodies Land application: Reduces TSS, BOD, nutrients, etc. D. Solid Treatment: Converts sludge generated in primary and secondary sedimentation to biosolids for use as soil conditioners, fuel, etc. [3]. Differences in the treatment methodologies for ground water and surface water like from a river can be envisaged from the figures as given below: Hard ground water Turbid surface water Figure 3.1.1: Treatment steps for ground and surface water [3].

6 REFERENCES [1] Metcalf & Eddy, Tchobanoglous, G., Burton, F. L., Stensel, H. D. Wastewater engineering: treatment and reuse/metcalf & Eddy, Inc., Tata McGraw-Hill, [2] Drinan, J. E. Water and Wastewater Treatment a Guide for the Nonengineering Professionals, CRC Press, US, [3] Peavy, H. S.; Rowe, D. R.; Tchobanoglous, G. Environmental Engineering, International Edition, McGraw-Hill Book Company, 1985.

WASTEWATER TREATMENT OBJECTIVES

WASTEWATER TREATMENT OBJECTIVES The student will do the following: 1. Define wastewater and list components of wastewater. 2. Describe the function of a wastewater treatment plant. 3. Create a wastewater