John Mmari Onyari

Distribution of Cr, Pb, Cd, Zn, Fe and Mn in Lake Victoria sediments, east Africa.

The presence of many metals at trace or ultra-trace levels in the human environment has received increased global attention. Sediments as a sink for pollutants are widely recognized pollution sources and diagenesis and biochemical transformations within the sediment may mobilize pollutants posing a threat to a wider biological community. The natural (background) concentrations of heavy metals in lake sediments can be estimated either by analysis of surface sediments in non-polluted regions or by analysis of core samples antedating modern pollution. The distribution pattern of heavy metals in tropical freshwater systems has been little studied. The authors found increased concentrations of lead and other trace metals in Lake Victoria. Thus this study was initiated in order to further investigate the distribution patterns of lead and other metals in Lake Victoria.

Multicomponent Polymers of Poly(Lactic Acid) Macromonomers with Methacrylate Terminal and Copolymers of Poly(2-Hydroxyethyl Methacrylate)

Abstract Poly(lactic acid) macromonomers with methacrylate terminal functionality have been synthesized from the cyclic dimer of lactic acid (referred to as lactide) with 2-hydroxyethyl methacrylate (HEMA) as initiator and stannous 2-ethyl hexanoate as catalyst. The macromonomers were characterized with FT-IR, NMR, GPC, DSC, WAXS, and CD. The molecular weights of the macromonomers ranging from M n 1425 to 19,169 are predictable from the lactide/HEMA ratio in the polymerization feeds. The properties of the macromonomers vary with the stereochemistry of the lactide and the composition. Circular dichroism measurements demonstrate that there is little racemization during polymerization.

Heavy metals in sediments from Makupa and Port-Reitz Creek systems: Kenyan Coast.

Copper, zinc, lead and cadmium heavy metals were determined in sediments from the Kenyan Coast. Sediment samples were obtained from Makupa and Port Reitz Creek systems. The samples were digested using concentrated hydrochloric acid and the metal content determined using Atomic Absorption Spectrophotometer (AAS). The method of analysis was evaluated using Soil-7 certified reference material (International Atomic Energy Agency, IAEA). For comparison, sediment samples were also analysed using Energy Dispersive X-ray fluorescence technique and results obtained show good agreement. Higher metal concentrations were obtained in Makupa Creek sediments (Cu, 102+/-46.0; Zn, 1017+/-840; Pb, 103+/-35.8; Cd, 51.0+/-14.3) as compared to Port Reitz Creek system (Cu, 21.6+/-7.1; Zn, 57.1+/-17.9; Pb, 26.2+/-11.6; Cd, 1.38+/-0.7). There was significant (p=0.05) variation in the elemental concentrations between and within sites. Industrial activities and a nearby municipal dumpsite were associated with the higher elemental concentrations particularly in Makupa Creek.

Lead contamination in street soils of Nairobi City and Mombasa Island, Kenya.

The advent of modern industrialization and, in particular, the motor vehicle has witnessed dramatic increases in lead usage both as a component of lead-acid storage battery and from 1923 as organic lead alkyl anti-knock additive in petroleum. Several workers have established a correlation between increasing lead concentration in roadside soils and vehicular traffic density. Although researchers studied the heavy metal content in Lake Victoria sediments, no urban roadside soils were investigated. Since lead is used as a petrol additive in Kenya, it is necessary to document the extent and magnitude of lead contamination of roadside soils in inland and coastal urban environments and evaluate its environmental implications.

Study on the microstructure of African wild silk cocoon shells and fibers

Silk fibers and cocoon shells from four African wild silkmoths Gonometa postica, Anaphe panda, Argema mimosae and Epiphora bauhiniae-were studied to gain insight into the structure-property-function relations and potential commercial application. The surface and cross-section of cocoon shells and fibers revealed the presence of prominent structural variations. Cocoon shells were multilayered and porous structures constructed from highly cross-linked fibers that are densely packed within the sericin/gum. Fibers had fibrillar sub-structures running along the fiber axis and with greater number and size of voids. The ecological significance and implication of these structures for further application are discussed.

Equilibrium and Kinetics studies for the biosorption of aqueous Cd (II) ions onto Eichhornia crasippes biomass

Batch experiments were carried out to determine the capacity of E. crasippes biomass to adsorb Cd (II) ions from aqueous solutions with respect to contact time and initial concentration of Cd (II) ions, adsorbent dosage, pH and temperature. The experimental data were modeled by Langmuir and Freundlich isotherm models. The data fitted well with the Freundlich model which implies that the adsorption was multilayer. The data was also subjected to Kinetic models and the pseudo-second-order model found to fit the data. The macrophyte biomass used in this study did not undergo any chemical modification or pretreatment, which when added to its abundance and its low cost make it a green alternative for the removal of Cd (II) ions from water and waste water.

Enzymatic Decolorization of Malachite Green Dye by a Newly Isolated Bacillus Cereus Strain wwcp1

Enzymatic decolorization of Malachite Green (MG) dye was studied using crude enzyme from a newly isolated Bacillus cereus strain wwcp1. 98% decolorization efficiency was achieved within 24 hours using an initial dye concentration of 1.0 x 10 -5 M. Batch experimental results revealed that the decolorization process was highly dependent on contact time, initial MG concentration, aqueous solution temperature and pH. Biodegradation of MG dye was monitored spectrophotometrically and metabolites confirmed by thin layer chromatography (TLC). The comparison of TLC chromatograms before and after decolorization confirmed that crude protease enzyme had the ability to degrade MG dye. The results provide evidence that the crude enzyme from Bacillus cereus strain wwcp1 is an effective and potential candidate for industrial wastewater treatment.

Process optimization for production of biodiesel from croton oil using two-stage process

Croton oil was extracted from dry seeds by a mechanical pressing machine then filtered to remove solid impurities. Biodiesel was prepared from the oil through a two-stage process in a biodiesel reactor. The optimum reaction conditions were determined by varying parameters such as temperature, oil:methanol ratio and amount of catalysts used. The optimum conditions established in this study were temperatures of 50 o C and 60 o C for esterification and transesterification respectively, methanol:oil ratio of 3:1 and 6:1 for esterification and transesterification respectively and a base catalyst mass of 1% (w/w) of the oil for transesterification. Esterification was done for two hours while transesterification was done for one hour. A maximum yield of 88% biodiesel which had an acid value of 0.336 mg KOH/g, a density of 0.8858 g/cm 3 and viscosity of 4.51 cs at 40 o C was obtained. The flash point of the biodiesel was greater than 200 o C which made it safer to store and transport as compared to diesel which had a flash point of 65 o C. Both the cloud and pour points of the biodiesel were lower than that of petro-diesel, implying that its blends were more suitable for lower temperature operations. All properties of the biodiesel that were tested satisfied the recommended American Society for Testing and Materials (ASTM) values.

Removal of Cu(II) from Aqueous Solution Using a Micaceous Mineral of Kenyan Origin

A micaceous mineral (MicaM) available locally in Kenya was utilized as an inexpensive and effective adsorbent for the removal of Cu2+ ions from aqueous solution. The effects of contact time, pH, temperature, adsorbate and adsorbent concentrations, and the concentration of electrolyte on the removal of Cu2+ ions were studied. Maximum removal of Cu2+ ions occurred over the pH range 4.0–7.0. The adsorption of Cu2+ ions increased with an increase in the dose ratio of mineral to Cu2+ ion concentration and decreased with adsorbent particle size. Isotherm analysis of the adsorption data obtained at 25°C showed that the adsorption of Cu2+ ions on MicaM followed both the Langmuir and Freundlich isotherms. The uptake of Cu2+ ions increased on increasing the pH of the solution from 1.5 to 7.0 as well as on increasing the temperature from 25°C to 60°C. An adsorption capacity of 0.850 g/g was achieved for MicaM towards the Cu2+ ion. This study has demonstrated that locally abundant micaceous mineral can be used as an effective adsorbent for the treatment of waters containing Cu2+ ions without any prior chemical pretreatment.

Efficacy of Mangrove (Rhizophora Mucronata) Roots Powder in Adsorption of Lead (II) Ions from Aqueous Solutions: Equilibrium and Kinetics Studies

The removal of Pb (II) ions by adsorption onto mangrove roots adsorbent was investigated in this present paper. The removal of lead ions from aqueous solutions was investigated in batch mode which involved the study of the effects of initial pH, temperature, initial concentration of the lead ion, adsorbent dosage and contact time on lead ions removal. Adsorption was found to increase with increase in temperature, contact time adsorbent dose and pH. The adsorption data was well described by both the Freundlich and Langmuir isotherm models. The adsorption capacity (Qmax) from the Langmuir isotherm for Pb (II) was found to be 13.698 mg/g. Pseudo-second order kinetic model was found suitable for describing the kinetics of the adsorption process. These results indicated that mangrove roots can be used as low cost adsorbent for the removal of lead ions from aqueous solutions.