CHEMICAL TREATMENT METHODS DONE BY: MAHASWARI JOGIA WASTE MANAGEMENT TECHNIQUES (HCE 24) SEMINAR ON:

CONTENTS  INTRODUCTION  CHEMICAL TREATMENT  COAGULATION  NEUTRALIZATION  PRECIPITATION  OXIDATION  REFERENCES 4/15/ DSCE,CHEMKCAL ENGG DEPT

INTRODUCTION ● Industries use water that obtained from the water treatment system for a variety of purposes, such as: - For manufacturing goods. - For heating. - For cooling. - As carrier of raw material. - As carrier of waste matter. - As a solvent. ● The resulting water is then classified as a wastewater. 4/15/ DSCE,CHEMKCAL ENGG DEPT

● The indiscriminate discharge of these wastewater streams into the environment can - Render soils "sick ". - Pollute the receiving bodies of water. - Cause air pollution by generating obnoxious gases. ● Discharge untreated wastewater into the domestic sewer system makes the task of treating domestic sewage, a very difficult and costly exercise. ● To prevent any health hazards caused by discharging wastewater into the environment and protect domestic sewage, the wastewater must be treated before discharge. 4/15/ DSCE,CHEMKCAL ENGG DEPT

CHEMICAL TREATMENT Treatment methods in which the removal or conversion of contaminants is brought about by the addition of chemicals or by other chemical reactions. Precipitation, adsorption, and disinfection are the most common examples used in wastewater treatment. Basically the treatment includes: -Coagulation -Precipitation -Disinfection -Oxidation -Neutralization, scale control 4/15/ DSCE,CHEMKCAL ENGG DEPT

Very fine suspended particles present in wastewaters cannot be removed in sedimentation due to settling velocity is very low. Fine colloidal or dispersed particles contain electric charges and continuously in motion known as Brownian motion and they are not settled down by gravity force. Very fine suspended particles can be removed by increasing their size(flocculated particles). Certain chemical compounds called coagulants are added to the wastewater which on thorough mixing form a gelatinuous precipitate called floc. COAGULATION 4/15/ DSCE,CHEMKCAL ENGG DEPT

After which they pass through sedimentation tank and settle down. It takes place in rapid mix, or flash mix basins which are very rapid. The primary function of rapid mix basin is to disperse the coagulant so that it contacts all of the wastewater. Over the years a number of different substances have been used as coagulants. The most common ones -Alum(Al 2 (SO 4 ) 3.18H 2 O). -Ferrous Sulfate(FeSO 4.7H 2 O). -Lime Ca(OH) 2. -Ferric Chloride (FeCl 3 ). -Ferric Sulfate (Fe 2 (SO 4 ) 3 ). 4/15/ DSCE,CHEMKCAL ENGG DEPT

Principle of Coagulation In coagulation, individual particles combine together. When a coagulant is used in water, it forms a spongy gelatinous precipitate which absorbs fine size particles in water and binds them together. The whole process results into bigger particles which are heavier and easily settle able. Properties of common coagulants React quickly Cheap Easy to handle and store React in longer range of pH Electrolyte ( positively charged) High valance ions for high efficiency Not detoriate 4/15/ DSCE,CHEMKCAL ENGG DEPT

Coagulation & Flocculation Process 4/15/ DSCE,CHEMKCAL ENGG DEPT

ALUM [Al2(S04)3 18H2O]: Alum is the most widely used coagulant in water treatment. It reacts quickly giving excellent stable flocs. It is cheap and can be easily stored and handled. The alum when added to raw water, reacts with natural alkalinity in water (if that is insufficient, lime may be added) so as to form a gelatinuous precipitate of aluminium hydroxide. It increases the sulphate hardness and corrosiveness of water to a small extent. 4/15/ DSCE,CHEMKCAL ENGG DEPT

NEUTRALIZATION If a waste stream is found to be hazardous due to corrosivity, neutralization is the primary treatment used. It is used as a pretreatment system before a variety of biological, chemical, and physical treatment processes. It is the process of adjusting the pH of water through the addition of an acid or a base, depending on the target pH and process requirements. Some processes such as boiler operations and drinking water standards need neutral water at a pH of 7. 4/15/ DSCE,CHEMKCAL ENGG DEPT

Water or wastewater is generally considered adequately neutralized if: (1) its damage to metals, concrete, or other materials is minimal; (2) it has little effect on fish and aquatic life; (3) it has no effect on biological matter (i.e., biological treatment systems). PARAMETERS WHICH AFFECT NEUTRALIZATION: -pH -alkalinity/acidity -Hardness -Buffers 4/15/ DSCE,CHEMKCAL ENGG DEPT

Fig: continuous neutralization tank 4/15/ DSCE,CHEMKCAL ENGG DEPT

PRECIPITATION It is used for removing dissolved metals from waste water solution containing toxic materials. To convert this dissolved metal into solid particles, a precipitation reagent is added. A chemical reaction occurs where dissolved metals form solid particles. Filtration can be used to remove the particles from the mixtures. How well the process takes place depends on the types of metal present, its concentration, and reagent used. 4/15/ DSCE,CHEMKCAL ENGG DEPT

Example : in hydroxide precipitation, calcium or sodium hydroxide is used as a reagent to create solid metal hydroxides. But the main difficulty being the mixture of metals in waste water making it difficult to precipitate. 4/15/ DSCE,CHEMKCAL ENGG DEPT

OXIDATION It is a waste water treatment which involves the use of oxidizing agents such as ozone, hydrogen peroxide, permanganate, chloride, chlorine, oxygen etc. The electrons move from the oxidant to the pollutants in waste water. They undergo structural modification becoming less destructive compounds. Alkaline chlorination uses chlorine as oxidizing agent against cyanide. But it can lead to production of toxic chlorinated compounds hence require further steps. 4/15/ DSCE,CHEMKCAL ENGG DEPT

APPLICATIONS: Reduce concentration of the residual organics Controls odors Remove ammonia Reduce microbial content Common oxidation agents used in wastewater treatment: -Oxygen(O 2 ). -Chlorine (Cl 2 ). -Sodium hypochlorite (NaClO). -Calcium hypochlorite (Ca(ClO) 2 ). -Potassium permanganate(KMnO 4 ). -Hydrogen peroxide(H 2 O 2 ). 4/15/ DSCE,CHEMKCAL ENGG DEPT

Centralized water treatment prepared by Innocent L Swai, Bsc EHS Flow equalization and neutralization by Ramesh K. Goel, Joseph R.V. Flora, and J. Paul Chen wastewater engineering– objectives of wastewater treatment, primary treatment of wastewater by Dr. Asha Gupta Waste water engineering treatment and reuse by metcalf and eddy REFERENCE 4/15/ DSCE,CHEMKCAL ENGG DEPT

THANK YOU !! 4/15/ DSCE,CHEMKCAL ENGG DEPT