CHE 262 CHEMICAL PROCESSES AND SUSTAINABILITY
CHAPTER 2 WATER TREATMENT PROCESSPrepared by: Mohd Shahrul Nizam Bin Salleh
Characteristic from surface sources - unsuitable for human consumption, industrial use, commercial use etc.
1) 2) 3) 4)
Characteristics : Turbid Colour Acids, salts and gases corrosive action impart hardness of water Bacteria Water borne diseases.
Objectives : To remove harmful microorganisms or chemicals, thereby preventing the spread of disease in order to supply clean and safe water for public demand
Good water source : Raw water with a coliform count of up to 5000/100mL and turbidity up to 10 units Poor water source : Raw water with coliform counts that frequently exceed 20,000/100 mL and turbidities that exceed 250 units.
WATER TREATMENT - POLLUTANT
Content must be removed from the water source Waste Solid material / Colloidal particles Pathogen Heavy Metal Exceed dissolved salt
WATER TREATMENT SELECTION
FACTORS CONTRIBUTE TO THE SELECTION OF TREATMENT METHOD :
Sources of water intake Characteristic of water
1 WATER INTAKE
SELECTION CRITERIA FOR WATER INTAKE LOCATION : Must have the best available water quality Far from strong current adverse affect water intake potential
Quantity of water demand can be achieved even at a very low water flow rate Near to water treatment plant Easily accessible & possess adequate space and facilities for maintenance works
SURFACE WATER TREATMENT 1) 2) 3) 4) 5) 6) 7) 8)
Typical treatment plant for surface water : Screening and grit removal Primary sedimentation (settling/clarification) Coagulation (Rapid mixing) Flocculation Secondary sedimentation Filtration Sludge processing Disinfection
GROUNDWATER TREATMENT 1) 2) 3) 4) 5) 6) 7)
Typical treatment plant for groundwater : Aeration Flocculation/precipitation Sedimentation Recarbonation Filtration Disinfection Solids processing
WATER TREATMENT PROCESSWater Intake Pump House Screening
The selection criteria for water intake location:
must have the best available quality far from strong current that can adverse affect water intake potential quantity of water demand can be achieved even at a very low water flow rate near to water treatment plant easily accessible and possess adequate space and facilities for maintains works.
SCREENING AND GRIT REMOVAL
Surface water often has large debris, such as sticks, leaves, fish, and trash, floating in it. These objects can damage the water treatment system and others mechanical devices. It must be removed before the water enters the treatment plants.
After screening, the finer but denser, mainly inorganic suspended matter is removed by allowing the water to pass slowly through a chamber where it settles down to the bottom. The aim being to remove grit sa as to prevent wear of machinery and unwanted accumulation of heavy inert matter in pumps sumps or in flocculation/ sedimentation tanks It is usual to design these grit chambers to settle out only those suspended particles that are larger than 0.2 mm in diameter and have a specific gravity greater than 2.65.
Used to control the growth in water of micro-organisms which release taste and odor, producing substances or of those organisma which when killed, may decompose and produce taste and odor
Required if the raw water is too dirty. Store the raw water temporarily before proceed to the main process. Removes the particles that will settle out by gravity alone within few hours.
Sedimentation basin/clarifier suspended solids settlement.
circular/rectangular tank holds water for
Equipped with bottom scraper and hopper that removes collected sludge.
Provide oxygen from the atmosphere for the oxidation of dissolved iron and manganese to their insoluble form and to liberate carbon dioxide and hydrogen sulphide thereby reducing corrosiveness and removing odour it can increase the dissolved oxygen content in water thereby causing it to have a sparkling appearance and water freshness. The efficiency depends on the amount of surface contact between air and water, their time contact and the type of aerator and is generally measured by the decrease in the concentration of carbon dioxide in the water
COAGULATION AND FLOCCULATION
principally preparation of water for sedimentation and filtration at economically high rates of flow The purpose of this process is to destabilize colloidal particles and enable them to become attached to other particle, so that they may be removed in subsequent process Form particles large enough to be removed by the subsequent settling or filtration process. Coagulant chemicals are added to water, rapid mixing ; causing a reduction of the forces tend to keep particles apart.
MOST COMMONLY USED COAGULANTS :Chemicals Alum (Aluminium Sulphate) Ferric Chloride Ferric Sulphate Cationic Polymers Description Often used in conjuction with cationic polymers May be more effective than alum in some application Effective in some waters and more economical in some location Can be used alone as the primary coagulant or in conjunction with aluminium or iron coagulant
The floc that is formed is made up of small particles (micro floc) which still have a positive charge from the coagulant added. They continue to neutralize negatively charged particles like those of colour and turbidity. Finally, the micro floc particles begin to collide and stick together to form larger settleable floc particles. There are many physical and chemical factors that affect the success of a particular coagulant, including mixing condition, pH, alkalinity, turbidity and temperature of the water. the optimum pH range for coagulation of turbidity waters is usually 5.7 to 6.5. Both alum and ferric sulphate are affected by the alkalinity of the raw water. An effective floc will not form if the alkalinity in the water is not high enough. Increase in turbidity, temperatures and mixing energy can also improve coagulation.
Sedimentation is the process of deposited the floc and thus reduces the amount of suspended particles that must be removed by the filters create conditions in which the flow is as possible for a long enough period to permit the maximum practicable amount of floc to be settled before the water reaches the outlet end of the tanks
process of separating suspended impurities from water by passage through a bed of granular materials the filter media The purpose of filtration process is to remove the particulate impurities and fine floc that still not settle during the sedimentation process from the water being treated These impurities consist of suspended particles (fine silts and clays), colloids and biological forms (bacteria and plankton). The type of media filter used here are rapid sand and dual media
Final step of treating the water. The purpose of disinfection process is making water safe for consumption by destroying harmful organisms. The disinfectant chemical that is used here is chlorine gas. Chlorine gas is easily obtained, relatively cheap and most importantly, it leaves residual chlorine that can be measured. Chlorine must be dosed within the range of 1.8 to 2.0 to ensure that water at the last place still contains at least 0.2 ppm of chlorine.