Feasibility studies on the use of activated clays as coagulants / coagulant aids for water treatment
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Date
2002-12-12
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Abstract
Three clay samples (from Asokwa, Kasi and Mfensi in the Ashanti Region) have been studied for their possible use as coagulants / coagulant aids in the treatment of water. Before use, each clay sample had a portion of it heat activated and another portion acid activated. Each activated clay was used for treatment of raw water samples from Barikese. The water samples were similarly treated with alum to serve as a control test. The changes in colour, turbidity, pH, iron, chromium, manganese, faecal and total coliform content were then monitored.
All the acid activated clays performed well as coagulants. However, the heat activated clays did not give any encouraging results. 10% acid activated Asokwa clay sample (AAA 10) was the best coagulant among the treated clay samples. It gave comparable results in colour, turbidity, and iron reductions as alum. AAA10 reduced colour and turbidity by 95% and 88.9% respectively. The effective pH range for optimum performance of AAA10 was 4.5 — 7.0 as compared to 5.5 — 7.5 for alum. AAA1 0 significantly reduced the pH of the water, thus the final pH at the optimal dosage of 8g/1 was 4.9. Furthermore a reduction of 93 and 100% in faecal and total coliform were recorded. Iron and chromium removals were 62.5 and 50% respectively and a settling time of 25mm was recorded. A major demerit of AAA10 was that the sludge produced was about 100 times that of alum.
All the treated clays performed as coagulants aids. The heat activated clay samples performed better as coagulant aids, however, their capacity to remove heavy metals were lower. Therefore, 10% acid activated Asokwa clay sample (AAA10) was again the best coagulant aid among the treated clay samples. Using AAA10 as coagulant aid, high reductions in colour, turbidity, iron and chromium were obtained (colour- 95%, turbidity- 88.9%, iron-100%, chromium- 100%). Also a reduction of 85.8 and 100% in faecal and total coliform were obtained respectively. The effective pH range for optimum performance of AAA 10 as coagulant aid was 5.5 — 9.5. An optimal dosage of 0.065g/l of alum with 0.lg/l AAA10 as coagulant aid was obtained at a pH of 6.68. A settling time of 40mm was recorded, however the sludge produced was about twice that of alum.
This study has therefore revealed that activated clays are technically feasible for the treatment of surface water.
Description
A thesis submitted to the Board of Postgraduate Studies,
Kwame Nkrumah University of Science and Technology in partial
fulfilment of the requirements for the award of Master of Science, 2002