Modeling effects of manganese, zinc and lead from industrial wastewaters on microbial activities in facultative waste stabilization ponds

The work embodied in this thesis is based on an experimental set-up that involved the study of the effects of manganese (Mn2+), zinc (Zn2+) and lead (Pb 2+) metal ions on microbial growth kinetics by following the rate of change of bio-mass concentration during batch experiments of artificial laboratory scale Waste Stabilisation Ponds (WSPs). Different concentrations of Mn2+ reactors keeping all environmental parameters constant(pH, light intensity, basic nutrients).The combined effects of Mn2+ , Zn2+ and Pb2+ ions were determined by mixing these metallic ions in equal ratios of 1/1/1, 5/5/5, 10/10/10 and 20/20/20 mg/l of Mn2+ , Zn2+ and Pb2+ ions, respectively. Inocula seeded to the system were obtained from Vingunguti primary facultative pond system used to treat industrial wastewater. A synthetic feed solution containing 210 mg/I glucose (corresponding to 180 mg/I and 300mg/I respectively) served as sources of carbon The analyses were done at the Environmental Engineering Laboratory at the prospective College of Engineering and Technology (pCET) and in the Microanalysis Laboratory, in the Chemistry Department, Faculty of Science, University of Dar es Salaam. The laboratory experiments showed that a rise in the concentration of the heavy metals increases the mortality rate of heterotrophic bacteria, and vice versa. Experimental data showed that Zn2+ ions were less toxic than Mn2+, Zn2+ ions. Moreover, bio-kinetic parameters were not adversely affected by the presence of Zn2+ ions up to a concentration of 10 mg/I in the sediment. However, for Mn2+, this was true for a concentration of less than 10mg/I. For Pb2+ ions, the bio-kinetic parameters were slightly unaffected until a threshold Pb2+ ion concentration of 5 mg/I in the sediment was reached. However, a concentration of 10 mg/I and