Impacts of alum residues from Morton Jaffray water works on water quality and fish, Harare, Zimbabwe.

Muisa, Norah (2010) Impacts of alum residues from Morton Jaffray water works on water quality and fish, Harare, Zimbabwe. UNSPECIFIED thesis, UNSPECIFIED.

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Metal pollution of freshwater resources due to human activities is a major problem confronting most urban centres in developing countries. A study was carried out on the impacts of aluminium (Al) sulphate (alum) residues from Morton Jaffray Waterworks on Al concentrations in fish, sediment and water in the Manyame River and Lake Manyame. Morton Jaffray Waterworks and Lake Manyame are located southwest of Harare, the capital city of Zimbabwe in the Upper Manyame Catchment. Lake Manyame is the third largest commercial fishery in Zimbabwe and the second-largest raw water supplier to Morton Jaffray. Morton Jaffray supplies drinking water to Harare and its satellite towns. Alum is the sole coagulant used at Morton Jaffray such that aluminium hydroxide dominates the resulting residues. Alum doses and frequency of discharge of residues have been increasing since mid-90s than is optimal. These residues are discharged directly into Manyame River immediately upstream of Lake Manyame at a total rate of approximately, 108 800 m3/day which is about 80 and 90 % of the 60 to 70 tonnes of alum used each day. However, most studies in literature on metal water pollution and toxicity to aquatic life have mainly focused on all other sources of pollution other than water treatment plants. Residues from Morton Jaffray Waterworks have been linked to fish kills in Lake Manyame. Bioaccumulation of aluminium in fish and the subsequent toxic effects have been reported in literature. Therefore, the study investigated the extent to which the waterworks’ residues affected the water and sediment quality of the river and lake and fish in the lake, particularly, Nile tilapia (Oreochromis niloticus), in respect of Al concentrations. Total aluminium concentrations in the water, sediments, residues and fish were determined. In addition, other parameters were measured namely; total solids, total dissolved solids, conductivity, pH, dissolved oxygen, temperature, and sediment texture. Eight depth integrated water samples, and sediment grab samples and six adult fish were collected between January and March, 2010, from Manyame River and Lake Manyame at six selected sites. Three grab residue samples were collected before discharge. Variations in all the parameters among the sites, and fish tissues were significantly different (ANOVA; p<0.05). Aluminium levels surpassed permissible maximum levels and other levels in documented studies for all the sites during both sampling campaigns. This indicated the presence of other sources of aluminium though their magnitude was less compared to Morton Jaffray. Total aluminium levels were generally in the order of; sediments > fish > water while in fish, the general order was; liver > kidney > gill > muscle. The residues are greatly increasing aluminium concentrations in the affected water bodies and fish. There is need for interventions in water treatment practices for the protection of aquatic life as well as human life which is highly dependent on the aquatic life and water. These interventions include: treatment of the residues before discharge; strict monitoring of the quality of the residues before discharge; local standards for quality of residues discharged into waterways from waterworks; re-use of the residues as well as reduction of alum used for water processing or use of other effective but harmless coagulants.,WATERnet

Item Type: Thesis (UNSPECIFIED)
Uncontrolled Keywords: Waste generation,water treatment plants,aquatic systems,Bioaccumulation of heavy metals,waste disposal,sediments
Divisions: Universities > State Universities > University of Zimbabwe
Depositing User: Mr. Edmore Sibanda
Date Deposited: 06 Dec 2015 22:00
Last Modified: 06 Dec 2015 22:00

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