Assessment of Bentonite Clay Pretreatment of Pharmaceutical Industry Wastewater in Kenya

Abstract

Serious negative effects on aquatic ecosystems and human health can result when raw or partially treated pharmaceutical effluent is disposed into the environment. Pharmaceutically Active Compounds (PhACs) can go through biological wastewater treatment plants unaltered and find their way into water bodies. Pharmaceutical effluent also contains a substantial amount of suspended solids and COD which need to be reduced to acceptable levels before disposal. This study characterized pharmaceutical effluent in Kenya and investigated the applicability of bentonite as a coagulant aid in its pretreatment. Wastewater samples had a COD range of 418.70- 195.63 mg/l, TOC 117.50- 99.47 mg/l, BOD 263.23- 85.23 mg/l, TSS 210.37- 74.33 mg/l and pH of 7.08- 6.18. PhACs found in the samples included ciprofloxacin, sulfamethoxazole, ibuprofen, metronidazole and trimethoprim. Optimized coagulation using ferric sulfate at a dosage of 20 mg/l achieved maximum removal for TSS, turbidity, COD and TOC of 81.78%, 91.67%, 20.20% and 33.39% respectively and 83.88%, 91.70%, 25.25% and 41.63% with PAC at a dosage of 15 mg/l. Both coagulants achieved very little removal of PhACs. To investigate the effectiveness of bentonite, optimization of its dosage was carried out. Its optimum dosage was found to be 10 g/l, and this amount was mixed in the sample wastewater for 1 hour before coagulation was done. The maximum TSS, turbidity, COD and TOC removal by ferric sulfate together with bentonite was 96.82%, 98.81%, 30.30% and 54.20% respectively, and 96.96%, 98.21%, 48.48%, and 63.03% for PAC with bentonite. The use of bentonite reduced the optimal dosage of both ferric sulfate and PAC to 10 mg/l. This treatment resulted in complete removal of ciprofloxacin and ibuprofen. Maximum reduction of sulphamethoxazole, metronidazole and trimethoprim was 27.85%, 37.30% and 52 42% respectively. This study showed that pharmaceutical factories in Kenya fall under the formulation, drug mixing and preparation category, which produce effluent of low strength. Each factory had different treatment procedures but all included coagulation/ flocculation, using either aluminium or iron salts. Other methods of treatment employed in these factories included activated carbon filtration, ozonation, dissolved air floatation and activated sludge. The existing treatment systems needed improvement due to challenges of high chemical usage, poor floc formation and settling and high operational and maintenance costs. Bentonite pretreatment proved to be effective as it produced better quality effluent with improved removal of PhACs and reduced amount of coagulants used in comparison to optimized coagulation without bentonite. It is recommended that, with the addition of bentonite dosing equipment, pharmaceutical factories in Kenya should incorporate bentonite pretreatment into coagulation process to improve its efficiency. About 240 kilograms of bentonite would be required to treat 24,000 liters of pharmaceutical wastewater. During application, optimization of bentonite dosage should be carefully done to avoid excesses that could cause problems with coagulant dosing and formation of large volumes of sludge.