Sources of raw water supply :
- Surface waterEg : river, lakes, ponds, ect
- Ground water (tube well)
* suspended solids (clay, silt)
* soluble solids (dissolved colour, hardness, silica)
Impurities must be removed prior the use for domestic & industrial use (boiler, cooling tower, process)
In water clarification, the followings can take place :* removal of colloidal suspended solids & colour
* removal of iron & manganese (thru' efficient method)
* reduction of organic materials (taste/odor)
* TDS (Total disolved solid) will not reduce, but increase if alum/iron salt is used
* Chlorine will increase if chlorination is used
The jar test is a common laboratory procedure used to determine the optimum operating conditions for water or wastewater treatment. This method allows adjustments in pH, variations in coagulant or polymer dose, alternating mixing speeds, or testing of different coagulant or polymer types, on a small scale in order to predict the functioning of a large scale treatment operation. A jar test simulates the coagulation and flocculation processes that encourage the removal of suspended colloids and organic matter which can lead to turbidity, odor and taste problems.
We must do jar test before treatment, this is for know type of chemical is suitable, howmany types of chemical to be used, how much to add, sequence of adding chemicals, and what will be the treated water quality.
The main purpose of raw material treatment is to produce water with desired quality and with lowest cost. Cost need to be considered by an operation (not only chemical usage alone) but total water management savings.
In raw water treatment, it involves coagulation and flocculation to remove the suspended solid and turbidity from the raw water. Turbid water contains settleable and dispersed solids. Each particle is stabilized by negative (-) charges on its surface, causing it to repel neighbouring particles.
THREE basic steps involve in water clarification :
1. pH adjustment (if pH>7 or <7)
Raw water mixed with chemical will go through a clarifier for impurities removal.
Step 1 : pH adjustmentWe must adjust pH before, depend on pH raw water.:
- if pH raw water below 7, we can use : soda ash (Na2CO3), caustic soda (NaOH) or lime (Ca(OH)2)
- if pH raw water more than 9, w can use : HCl , H2SO4
It is very imfortant to get correct pH before addition of coagulant (especially alum).
Step 2 : CoagulationThis is for charge neutralization process, destabilize colloids in water by neutralizing the forces that keep them apart. For that we must add chemical coagulant & applying mixing energy. Chemical coagulants commontly used are : Alum, PAC (poly aluminium Cloride), ferric cloride, polyelectrolytes or organic coagulant.
Step 3 : FlocculationThis is for floc building process, It need polymers are added to agglomerate small flocs to form big ones so that it can settle fast.