WATER TREATMENT FOR INDUSTRIAL USE Prof. Palak Trivedi

Why water treatment needed for industrial use  Industrial water treatment are needed because lack of proper water treatment can lead to the reaction of solids and bacteria within pipe work and boiler housing. Steam boilers can suffer from scale or corrosion when left untreated leading to weak and dangerous machinery, scale deposits can mean additional fuel is required to heat the same level of water because of the drop in efficiency.corrosion  Corrosion in low pressure boilers can be caused by dissolved oxygen, acidity and excessive alkalinity. Water treatment therefore should remove the dissolved oxygen and maintain the boiler water with the appropriate pH and alkalinity levels. Without effective water treatment, a cooling water system can suffer from scale formation, corrosion and fouling and may become a breeding ground for harmful bacteria such as those that cause Legionnaires' Disease. This reduces efficiency, shortens plant life and makes operations unreliable and unsafe.

3 stages of waste water treatment  Primary  solids are separated  Secondary  dissolved biological matter is converted into a solid mass by using water-borne bacteria  95% of the suspended molecules should be removed  Tertiary  biological solids are neutralized then disposed, and treated water may be disinfected chemically or physically

Types of treatment  Mechanical treatment(Primary)  Influx (Influent)  Removal of large objects  Removal of sand and grit  Primary Sedimentation  Biological treatment(Secondary)  Trickling bed filter  Activated sludge  Chemical treatment(Tertiary)  Disinfection

Secondary treatment(Biological treatment)  Degrade biological content (dissolved organic matter) of the sewage  Ex: human waste, food waste, soaps, detergent  Added bacteria and protozoa into sewage  3 different approaches  Fixed film system  Suspended film system  Lagoon system

Activated Sludge Process  Suspended Film Systems is most commonly use for Secondary(Biological) treatment.  stir and suspend microorganisms in wastewater  settled out as a sludge  pumped back into the incoming wastewater  Ex: Activated sludge, extended aeration  Activated Sludge Process  mixed community of microorganisms  Both aerobic and anaerobic bacteria may exist  Biological floc is formed

Activated Sludge Process Diagram

Activated Sludge Process General Description of Activated Sludge Process  Used for secondary level of wastewater treatment to remove the soluble organic and provide further removal of suspended solids.  Consists of aeration tank and clarifier. BASIC REQUIREMENT  Mixed populations of active microorganisms (suspended growth in aeration tank and returned sludge from secondary clarifier)  Availability of oxygen --- aeration system.  Good contact between the microorganisms and food (organic) - agitation of air and sufficient contact time.  Availability of nutrient --- P., N. and others  Favorable environmental conditions --- T( o C), pH.

 Activated sludge is a process in sewage treatment in which air or oxygen is forced into sewage liquor to develop a biological floc which reduces the organic content of the sewage. In all activated sludge plants, once the sewage has received sufficient treatment, excess mixed liquor is discharged into settling tanks and the effluent is run off to undergo further treatment before discharge. Part of the settled material, the sludge, is returned to the head of the aeration system to re-seed the new sewage entering the tank. The remaining sludge is further treated prior to disposal.

 Activated sludge: Biomass produced in raw or settled wastewater (primary effluent) by the growth of organisms in aeration tanks in the presence of dissolved oxygen. The term "activated" comes from the fact that the particles are teeming with bacteria, and protozoa. Activated sludge is different from primary sludge in that the sludge contains many living organisms which can feed on the incoming wastewater. What is Activated Sludge?

Activated Sludge Process:  A biological treatment process in which a mixture of sewage and activated sludge is agitated and aerated. The activated sludge is subsequently separated from the treated sewage by settlement and may be re-used. A common method of disposing of pollutants in wastewaters.

 In the process, large quantities of air are bubbled through wastewaters that contain dissolved organic substances in open aeration tanks. Oxygen is required by bacteria and other types of microorganisms present in the system to live, grow, and multiply in order to consume the dissolved organic "food", or pollutants in the waste. After several hours in a large holding tank, the water is separated from the sludge of bacteria and discharged from the system. Most of the activated sludge is returned to the treatment process, while-the remainder is disposed of by one of several accepted methods.

 Sewage is domestic, municipal, or industrial liquid waste products. How it is disposed varies by the area, and the local commitment to the environment. In some countries, notably the United States, national law mandates sanitary treatment of sewage, and outfalls are regulated. Surprisingly, many quite wealthy countries have untreated outfalls directly to surface water, often causing disease, pollution and undrinkable tapwater.

 Sewage may be carried directly through pipelines to outfalls, or from upstream sources via river systems. Sewage is often from storm water runoff of streets, parking lots, lawns and commercial and industrial areas. In some urban areas, sewage is carried separately in sanitary sewers while runoff from streets is carried in storm drains. Access to either of these is typically through a manhole.

Treatment which can apply after activated sludge process  After Activated Sludge Process remove disease-causing organisms from wastewater(effluent), we apply Tertiary treatment.  3 different disinfection process  Chlorination  UV light radiation  Ozonation  Advanced Treatment which can apply after activated sludge process  Nitrogen removal  Ammonia (NH 3 ) → nitrite (NO 2 - ) → nitrate (NO 3 - )  Phosphorous removal  Precipitation with iron or aluminums salt  Lead to eutrophication  May cause algae bloom

What can effluent use for?  discharged into a stream, river, bay, lagoon or wetland  used for the irrigation of a golf course, green way or park  If it’s sufficiently clean, it can be used for groundwater recharge

Sludge treatment  Primary sludge usually have strong odors  Secondary sludge have high concentration of microorganism  Goals of treatments are:  Reduce odors  Remove water reduce volume  Decompose organic matter Sludge disposal  Superheat sludge and convert into small granules that are rich in nitrogen  Sell it to local farmer as fertilizer  Spread sludge cake on the field  Save landfill space

Deairation of water(Removal of Dissolved O2)  Boiler Corrosion: It is the decay of boiler material due to chemical or electrochemical attack of its environment. The corrosion in boilers is due to dissolved oxygen, dissolved CO2 and acids produced by the hydrolysis of dissolved salts. Therefore, removal of these prevents the corrosion of boilers.  Removal of Dissolved O2: Dissolved oxygen in water is mainly responsible for the corrosion of a boiler. The dissolved oxygen in water attacks the boiler material at high temperatures.

2Fe + 2H2O + O2 2Fe(OH)2 4Fe(OH)2 + O2 + 2H2O 2[Fe2O3·3H2O] (rust)  Dissolved oxygen can be removed from water by chemical and mechanical means. Sodium sulphite, hydrazine, etc. are some of the chemicals used for removing oxygen. 2Na2SO3 + O2 2Na2SO4 N2H4 + O2 N2 + 2H2O  Hydrazine is found to be an ideal compound for removing dissolved

 Hydrazine is found to be an ideal compound for removing dissolved oxygen since the products are water and inert N2 gas. It removes oxygen without increasing the concentration of dissolved salts.  Dissolved O2 can also be removed from water by mechanical deaeration. In this process, water is allowed to spray slowly by the perforated plates fitted inside the tower. Vacuum is applied to this tower and the sides of the tower are also heated. High temperature and low pressure reduce the quantity of dissolved O2 in water.

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