FeCl3 was found to be generally superior to the other two coagulants in removing all the parameters like color TSS COD

source : http://civil.eng.usm.my/awam07/sample%20paper.doc

Three types of coagulants were examined using standard jar test apparatus, i.e., aluminum sulphate (alum), ferric chloride (FeCl₃) and ferrous sulphate (FeSO₄). The effects of agitation speed, settling time, pH, coagulant dosages and temperature were exermined. At 300 rpm of rapid mixing and 50 rpm of slow mixing and 60 minutes settling time, higher removals of suspended solids (over 95%), colour (90%) and COD (43%) were achieved at pH 4 and 12. FeCl₃ was found to be superior compared with other coagulants. At pH 4 and 12, fair removal of suspended solids was observed at reasonably lower amount of coagulant, i.e., 600 mg/L. However, about 2500 mg/L of coagulant was required to achieve good removals at pH 6. Better removals were achieved at higher temperature.

The coagulation-flocculation process was employed for the treatment of reactive dye wastewaters, with ferric chloride hexahydrate employed as the coagulant. The process was found to be very effective with a more than 99.5% colour removal. Typical representatives of monochlorotriazine reactive dyes, with azo and anthraquinone chromophores, were CI Reactive Red 45 and CI Reactive Green 8, which were chosen as the model dyes. In order to determine the optimum pH range and coagulant concentration, a series of jar tests was done. Further experiments were conducted using a square flocculation tank with turbine impeller applying rapid and slow mix operations. The optimisation of initial rapid mixing, which has an important role in the overall coagulation process efficiency, was carried out. The optimum combination of velocity gradient and time of rapid mix was suggested for reactive dye wastewater treatment. Sedimentation curves for both model dyes were also obtained.

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FeCl₃ was found to be generally superior to the other two coagulants in removing all the parameters.

FeCl₃ at pH 4 (at a coagulant dosage of 600 mg/L) and pH 6 (at a coagulant dosage of 2500 mg/L).

exhibited better performance with 90% and 97% removals, respectively.

 

Table 2:Removal of suspended solids, colour and COD at different pH values and dosages of coagulants.

pH	Results	Suspended Solids			Colour			COD
		Alum	FeCl3	FeSO4	Alum	FeCl3	FeSO4	Alum	FeCl3	FeSO4
4	Optimum/ economical dosage (mg/L)	600	600	600	600	600	600	600	600	600
	Initial* concentration	1106	1106	1068	6450	6460	7275	2660	2565	3320
	Final** concentration	282	59	582	2554	626	5485	1862	1472	1291
	% Removal	74.5	94.7	45.5	60.4	90.3	24.6	30	42.6	61.1
6	Optimum/ economical dosage (mg/L)	2500	2500	2500	2500	2500	2500	2500	2500	2500
	Initial* concentration	983	786	878	7005	7100	7003	3015	2980	3066
	Final** concentration	291	8	506	3159	249	5953	2204	1648	2422
	% Removal	70.4	99	42.4	54.9	96.5	15	26.9	44.7	21
12	Optimum/ economical dosage (mg/L)	600	600	600	600	600	600	600	600	600
	Initial* concentration	1106	932	1068	6460	6658	7270	3210	3565	3320
	Final** concentration	90	52	197	2558	1738	2690	2793	2777	2825
	% Removal	91.9	94.4	81.6	60.4	73.9	63	13	22.1	14.9

 

 

 

COD removal efficiency of poly-silicate-aluminium-ferric chloride (PSAFC) and polyferric chloride (PFC) coagulant increased with increasing dose of coagulants, and that the performance of PSAFC and PFC coagulants was superior to PAC coagulant. This difference in efficiency may also be attributed to the copolymers of Si(IV), Al(III) and Fe(III). However, compared with PFC, PSAFC can easily reach high COD removal efficiency below coagulant dose 0.3 g/L. Thus, from the economic point of view, PSAFC is more suitable for treatment of wastewater effluent from dye manufacturing

 

 

Source :http://civil.eng.usm.my/awam07/sample%20paper.doc