Tannery Waste Water Treatment through Aggregation of Bio-sorption and Chemical Coagulation Aided by Indigenous Coagulant

Abstract

Tannery in Bangladesh seems a source of pollution load and waste water to all because there are 270 registered tanneries where approximately 220 MT raw hides and skins are taking for the production of leather in Bangladesh. The leather industry has crossed the record $1-billion mark in exports in 2013-2014. According to the Department of Environment, the tanneries discharge 22,000 cubic meters of untreated liquid toxic waste daily. These pollution load and waste water should need treatment to make environmentally sustainable and living. From this point of view, we worked on tannery waste water processing. The paper highlights the initiation of Algal treatment with chemical coagulation process aided by natural coagulant for waste water processing in Bangladesh. The methodology of this process starts with mixing of waste water from different section of beam house operations at a definite ratio. The mixer takes nearly six hours to settle down. After sedimentation, the turbidity decreases at a reasonable amount i.e. 1428 NTU whereas before sedimentation it was 9050 NTU (2100P Turbid Meter of HACH). Later the supernatant was collected for algal treatment. After algal treatment the turbidity reduced to 530 NTU from 1428 NTU and the DO level increased up to 4.48 mg/L at 33.6 °C (HQ 40d of HACH) where DO level was 0.24 mg/L at 33.6°C in raw mixer. In addition, the amount of alum as chemical coagulant was reduced in tannery waste water treatment by using indigenous snail shell powder as coagulant aid in conjunction with alum. In case of untreated sample after sedimentation required alum dozing was 6 mL/ 40 mL sample. After algal treatment, required alum dozing reduced to 4 mL/ 40 mL sample. By adding 3 mL/ 40mL liquid natural coagulant as coagulant aid, alum dozing was further minimized to 1 mL/ 40mL sample. The odour was more tolerable than raw mixer after algal treatment but after adding alum aided by natural coagulant, the odour was more acceptable than before. The diversified technique can hopefully reduce a reliable chemical cost in treatment process, considerable amount of pollution load and increase DO level and thus make effluent environment friendly to discharge. Finally, the DO level increases up to 6.56 mg/L at 33.7 0C and turbidity reduces to 183 NTU, pH reduces to 7.6, odour turns to be tolerable limit.