Browsing by Author "Wekwe, Wema Wilson"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Modeling effects of manganese, zinc and lead from industrial wastewaters on microbial activities in facultative waste stabilization ponds
    (University of Dar es Salaam, 2003) Wekwe, Wema Wilson
    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
  • No Thumbnail Available
    Item
    A study of East African marine and freshwater algae as indicators of heavy metal pollution.
    (University of Dar es Salaam, 1990) Wekwe, Wema Wilson
    This dissertation describes the determination of the heavy metals chromium, manganese, iron, cobalt, nickel, copper, zinc, cadmium and lead in species of marine and freshwater algae and in seawater from the coast of Dar es Salaam using atomic absorption spectrophotometric (AAS) methods. An assessment of these algae as possible indicators of marine heavy metal pollution was carried out. Seventeen species of green, brown and red seaweeds were collected from Oyster Bay (near the Police Officers Mess) and Mbudya Island, whereas Spirogyra spp were collected from freshwater ponds at Buguruni Malapa Relini and at the Matsushita Electric Company (EA) Limited in Dar es Salaam. The algae samples, after collection, were washed with distilled water and dried at 1050c for 4 hours. Wet digestion was carried out using HNO3, H2SO4 and H202. The heavy metals were determined with a flame atomic absorption spectrophotometer (FAAS). Seawater samples were subjected to an ammonium-lpyrrolidinedithiocarbamate (APDC) - methyl isobutyl ketone (MIBK) extraction. The heavy metals in the seawater samples were determined on the atomic absorption spectrophotometer (Perkin Elmer model 2380) with a graphite furnace and employing the deuterium background correction facility. Most of the algae species studied were found to contain detectable amounts of heavy metals. The heavy metals found in the eight species of algae within the division of Chlorophyta (green algae) ranged as follows (results presented in µg / g dry weight of alga). Cr: 0.5 to 3.15, Mn: 3.5 to 30.5, Fe: 230 to 3085, Co: 0.78 to 1.2, Ni: 0.55 to 2.3, Cu: 0.5 to 11.51, Zn: 23.5 to 74.6, Cd: 0.06 to 0.27 and Pb: 0.17 to 1.7. The six species of algae within the division of Phaeophyta (brown algae) contained heavy metals in the ranges given below (µg per g dry weight of alga). Cr: 1.1 to 2.0, Mn: 6.5 to 58.6, Fe: 180 to 1190, cobalt was below the detection limit, Ni: 0.35 to 1.72, Cu: 1.0 to 5.54, Zn: 21 to 71.0, Cd: 0.05 to 0.5 and Pb: 0.9 to 2.85. The three species of algae within the division of Rhodophyta (red algae) contained heavy metals in the following ranges (µg per g dry weight of alga). Cr: 0.73 to 2.38, Mn: 1.7 to 26.5, Fe: 119 to 1110, cobalt content was below the detection limit, Ni: 0.62 to 0.64, Cu: 1.5 to 3.0, Zn: 23.5 to 47, Cd: 0.09 to 0.12 and Pb: 1.9 to 1.96. Heavy metal contents in freshwater algae were low compared to marine algae. Concentration factors were calculated for each element and for each algae species. Large concentration factors (K-values) were obtained for all elements and species. The maximum K-values found were: Cr - 3.2 x 105, Mn - 7.3 x 105, Fe - 6.2 x 105, Co - 9.5 x 104, Ni - 9.6 x 103, Cu - 3.2 x 104, Zn - 9.3 x 104, Cd - 8.5 x 104 and for Pb - 9.5 x 104. Thus the marine algae species studied are capable of concentrating several of these heavy metals with each species having its own selection of the heavy metals concentrated. A comparison of these K-values with those from polluted seawaters, shows that the algae species studied have a potential for use as pollution indicators. The following species can be used as pollution indicators for the metals given in brackets: Halimeda discoidea (Cu, Ni, Fe and Mn); Cladophora fascicularis (Fe, Cr and Co); Chaetomorpha crassa (Cr and Zn); sargassum polycystum (Zn and Cd); Padina tetrastromatica (Mn and Pb).