Pollutant removal from water using plant materials

Abstract

Removal of pollutants from contaminated water is a necessary measure in protection of the environment and human health. The use of biomaterials for removal of heavy metal from polluted water is eco-friendly and economical technique for developing countries. This study evaluated locally available biomaterials namely; banana pith, Opuntia Spp. and Maerua Decumbent as bio-coagulants and bio-sorbents of heavy metals. Banana pith, Opuntia Spp. and Maerua Decumbent biomass were characterized using proximate, elemental and functional groups analyses. Proximate analysis followed the Standard Methods (AOAC, 1999) whereas elemental analysis was conducted using Perkin-Elmer Series II CHNS/O 2400 Elemental Analyzer and functional group analysis using Fourier Transform Infrared (FT-IR) Spectroscopy, Model 8400. Bio-coagulants and bio-sorbents were used to remove turbidity, COD and selected heavy metals; lead, chromium, copper and zinc from contaminated surface water and paint industry wastewater. Turbidity was measured using a turbidity meter SGZB while heavy metal analysis was done with the help of an atomic absorption spectrometer AAS- 6200 Shimadzu. The study applied response surface methodology (RMS) for optimization of coagulation and flocculation processes in treatment of paint wastewater. Characterization of the study biomaterials revealed that they comprised of polysaccharides, proteins and lipids with functional groups that included amino, carboxyl, sulfate and hydroxyl. An 80% removal rate of heavy metals through bio-sorption was achieved. Langmuir and Freundlich isotherm models described the sorption data for the studied biomass, (R2 ≈0.9) indicating single layer sorption on homogeneous material. Sorption kinetic data was best described by the second order kinetic models. The calculated qe approached the experimental values xxiv indicating that chemical sorption process may have been dominant. The highest chromium uptake of 2.36 mg/g by banana pith was achieved at an initial influent concentration of 20 mg/l, flow rate 3 ml/min and bed depth 6 cm in continuous flow studies. Coagulation –flocculation process kinetics revealed that banana pith, Maerua Decumbent and Opuntia Spp. followed second order kinetics with a peri-kinetic flocculation half-life of 1.16, 0.78 and 0.84 minutes respectively; and rate constants k of 0.0027, 0.004 and 0.00037 l/mg.min respectively. Optimization of paint wastewater treatment using Response Surface Methodology resulted in maximum turbidity removal from paint wastewater of 99.24 %, at optimum conditions of pH 5.56, Maerua Decumbent dosage of 1.0 g/l and settling time 52.3 minutes. The 100% lead removal was realized at pH 6.81 and Maerua Decumbent dosage of 1.16 g/l. Some 99.97 % removal of chromium was achieved at pH 5.78 and Maerua Decumbent dosage of 1.03 g/l. At pH 5.00 and Maerua dosage of 1.3 g/l, an optimum zinc removal rate of 81.2% and optimum iron removal rate of 85.6 % were achieved. Confirmatory experiments validated the model to within 4% error. This research demonstrates the potential use of bio-coagulants in water and wastewater treatment.