An investigation into the impact of the shelter on the algal biomass and treated water quality : the case of Ggaba III water treatment plant

Abstract

Algal biomass has led to difficulties during water treatment like filter clogging, odors and algal toxins. The shelter was placed over the clarifiers and the filters of the three Ggaba National water and sewerage Corporation (NWSC) water treatment plants: to solve the algal problem due to fact that algae depend on light to grow; and other issues such as contamination by bird droppings and dust. The study investigated the impact of the shelter on the algal problem and treated water quality at Ggaba III water treatment plant, located in Kampala, Uganda. Samples collected were tested within a day or refrigerated at 40C. The tests that were conducted were for pH, colour, turbidity, chlorophyll-a and microcystin-LR. Standard methods were used for each of these tests according to APHA, AWWA & WEF (2010) for pH, colour, turbidity and chlorophyll-a; and ELISA methods according to Allan, et al. (2016). for microcystin-LR. The results showed that the species of algae in the raw water included microcystis spp, merismopedia spp, planktolyngbya spp, anabaena spp to mention but a few. These reduced in numbers down the treatment train; with a percentage decrease of 96.59%. From the experimental set ups, it was determined that the shelter significantly impacted on the supernatant pH (p = 0.003 < 0.05 and 6.25% reduction), the supernatant apparent colour (p = 0.01 and 51.71% reduction), filtered sample colour (p = 0.000 and 8.19% reduction), filtered sample turbidity (p = 0.000 and 87.88% reduction) and microcystin-LR (p = 0.776 and 7.32% reduction). There was no significant impact of pre-chlorination on the microcystin-LR (P>0.05) regardless of time of day. The microcystin-LR concentrations for all the samples during the study; did not exceed the daily recommended standard of 1µg/m making the water safe to consume. It is recommended that Uganda National Water and Sewerage Corporation (NWSC) and/ or NEMA should invest resources to constantly monitor: the different species of algae in the water bodies, chlorine used for pre-chlorination and its by- products and microcystin-LR and other toxins produced by algae. It is also recommended that NWSC should allow adequate budgeting for the construction, improvement, and maintenance of shelters at the treatment plants.