A techno-economic feasibility study on removal of persistent colour and COD from anaerobically digested distillery effluent: a case study from India

The present study aims at evaluating the potential options for further reduction of persistent dark brown colour and COD from anaerobically digested distillery effluent from a distillery in West Bengal, India. Two alternatives viz. physico-chemical method and attached growth biological method were evaluated for their potential and cost effectiveness in removing the COD and colour from the effluent. Under the physico-chemical option, detailed coagulation study was carried out with a number of coagulants such as alum, potash alum, ferric chloride, ferrous sulphate and lime. Then, additional removal of COD as well as colour was tried by applying an oxidant such as hydrogen peroxide or bleaching powder. Finally, adsorption study was performed with adsorbents viz. powdered activated alumina, wood charcoal and activated bone char. Under the biological treatment option, the efficacy of two fungi namely Aspergillus fumigatus and Coriolus versicolor was studied in batch mode under sterile condition for different dilutions. Finally, the performance of A. fumigatus was evaluated in continuous mode under ambient condition with the aid of fabricated lab scale bio-filters for different flow rates. All experimental results clearly showed that the removal of colour and COD were inter-related. Physico-chemical treatment was efficient in overall 96% COD removal and 93% colour removal with a treatment cost of Rs. 3.21 per litre (1$ = Rs. 46), if double coagulation-flocculation followed by peroxide treatment followed by adsorption onto acid-treated bone char was adopted. Only double-flocculation followed by adsorption was also an alternative yielding an overall 84% COD removal and 74% colour removal at a very nominal cost of Rs. 0.41 per litre. A maximum of 70% colour could be removed by 10% A. fumigatus inoculum in raw wastewater sample in batch mode under sterile conditions. However, under ambient winter conditions, the maximum colour removal of 48% and COD removal of 32% could be achieved in continuous flow bio-filters. Treatments of the distillery wastewater by proposed physico-chemical method as well as by bio-filters employing attached growth of A. fumigatus have emerged out to be a promising and cost-effective option for the concerned industry as compared to conventional dilution approach.