Effect of Protozoa on Faecal Bacteria Removal in Macrophyte and Algal Waste Stabilization Ponds

Protozoa populations and the types of microbiota were determined at various depths (0.1m, 0.35m and 0.63m) in macrophyte and algal ponds receiving medium strength sewage. The set up consisted of 3 pond systems comprising water lettuce, duckweed and algal ponds operating in parallel. Each system consisted of four ponds operating in series with a hydraulic retention time of 7 days per pond. The effect of protozoa on the removal of faecal bacteria was determined through the elimination of protozoa by filtering wastewater from the second pond of each treatment system. In the water lettuce and duckweed ponds, protozoa were concentrated in the sediments. In the algal ponds protozoa were mostly found in the sediments and on the surface. The following protozoa were common in all the ponds: Bodo, Vahlkampfia . Other biota like copepods, mites and nematodes were also found in the 3 pond systems. The protozoan Petalomonas and Chironomus insect larvae were found only in the water lettuce and duckweed ponds. Vorticella and other unidentified ciliates were unique to the algal ponds. The algal ponds had the highest number of species diversity and the highest number of protozoa, followed by water lettuce and duckweed. The algal ponds were dominated by Euglena . Other algae such as Chlorella, Chlorococcum, Phacus, Ulothrix, and some diatoms were also found but in small quantities. When floating algae covered the ponds, Spirogyra and some coenocytic algae in strands dominated the algal community. The presence of protozoa on the removal of faecal bacteria was found to have a significant effect in the removal of E. coli and Salmonella (p