Assessment of the performance of Lubigi sewage and faecal sludge treatment plant,

Abstract

80% of wastewater released into the environment is without adequate treatment. As such, nearly 2 billion people in the world are exposed to diseases such as dysentery and cholera. One method for treating faecal sludge is by co-treating the faecal sludge with wastewater with a recommended faecal sludge flow rate of 3.6%. The design of the Lubigi treatment plant does not meet this requirement with a FS flow rate of 8% and this could lead to operational problems of the treatment plant and failure to meet effluent requirements.

Samples were picked over a period of five weeks from the influent wastewater and the effluent from the faecal sludge thickening tanks and analyzed for total suspended solids, biochemical oxygen demand, total nitrogen, total phosphorous and faecal coliforms and flow measurements also made to characterize the two wastewater streams. The pond removal efficiencies were also determined by analyzing samples picked from the influent to and effluent from the anaerobic and facultative ponds. The final effluent was also compared to the NEMA discharge standards. The pond geometry and sludge depths were measured.

The influent wastewater quality parameters ranged as follows: TSS; 270-391mg/l, BOD5; 209.1-622.2mg/l, TN; 70.2 -281.4mg/l, TP; 15.4-84.5mg/l and FC; 4.64×105- 4.9×106cfu/100ml. The effluent from the faecal sludge thickening tanks quality parameters ranged as follows; TSS; 201.5- 321.6mg/l, BOD5; 1002.9 - 1621.5mg/l, TN; 130.2–311.4mg/l, TP; 77.8–121.5mg/l, FC; 5.1×105-1.372×106cfu/100ml. The removal efficiencies of the anaerobic ponds ranged from 70-80% whereas the removal efficiencies of the facultative ponds ranged from 82-93% for the different parameters. TSS concentrations met the effluent discharge standards unlike the other parameters. The facultative ponds L:W ratios were slightly above recommendation and the HRTs for the ponds were lower than the design values.

There is accumulated sludge in the anaerobic ponds and the facultative ponds likely have accumulated sludge near the inlet. Effluent from the treatment system is discharged into the environment with high nutrient, BOD5 and FC contents. Ways of improving the treatment system include increasing the breadth of the facultative pond by about 7 metres, providing multiple inlets to the facultative pond, increasing the desludging frequencies and reducing the faecal sludge flow at the plant.