Characterisation and Adsorption of Heavy Metals in Industrial Effluent From Paint and Coating Industries in Nairobi, Kenya

Abstract

In the recent past, the environment in both developing and developed countries have witnessed environmental degradation due to persistent metal ion pollutants among other pollutants. In this respect, a study was conducted to estimate status of physico-chemical characteristics of effluents emanating from three paint factories in the main industrial area of Nairobi County. The effluents were analysed for temperature, conductivity, pH, oil and grease, total suspended solids (TSS), chemical oxygen demand (COD), biological oxygen demand (BOD), total phosphorus, total nitrogen, total sulphur and heavy metal ions of Cadmium, Lead and Chromium. The results were as follows: pH 6.48±0.14 - 6.89±0.04, temperature 28.07±0.12-28.30±0.12 oC, electrical conductivity 837.33±6.66-881.33±8.62 μS/cm, COD 916.77±28.15 -1881.20±24.82 mg/L, BOD 149.00±1.41 - 183.00±1.41 mg/L, total phosphorus 145.00±3.61-149.32±1.22 mg/L, TSS 6382.3±658.013-7395.33±364.23 mg/L, oil and grease 3525.00±17.52-6374.33±23.03 mg/L, total sulphur 72.62±3.11-73.41±1.71 mg/L, total nitrogen 1586.67±29.14-4442.67±70.47 mg/L. Heavy metal concentrations were 3.03±0.83-4.18±0.09 mg/L, 2.07±0.66-3.04±0.83 mg/L and 5.38±1.41-17.21±1.67 mg/L respectively for cadmium, chromium and lead. Adsorbent was made from waste rubber tyres by soaking chopped tyres in 1M potassium hydroxide solution for 3 hours and consequently pyrrolizing at 700 °C for two hours. The prepared activated carbon was washed with dilute hydrochloric acid and distilled water. The adsorbent was then tested for its suitability in removing three heavy metal ions namely cadmium, lead and chromium from the effluent samples. The optimum adsorption conditions for the uptake of these ions were investigated by varying adsorbent dosage, pH and contact time. The results indicated that metal adsorption was dependent on these factors. The optimum conditions were: pH of 4-6, adsorbent dosage 0.5-0.6 % (w/v) and adsorption time of 90-105 minutes. The adsorption isotherms studies indicated that Langmuir model fitted well with analytical values obtained for cadmium, lead and chromium metal ions adsorption better than Friedrich isotherm.