Biomethanation followed by land application and algae production for disposal of spentwash

Distillery spentwash generating from molasses-based alcohol distilleries poses a significant challenge to the Indian sugar industry and environment. Therefore, primary attention was focussed on biomethanation of raw distillery spentwash through high rate reactors and recycling of Biomethanated Distillery Spentwash (BDS) in agriculture as a source of plant nutrients. The biomethanation was carried out at different hydraulic retention times (HRTs) using upflow anaerobic sludge blanket (UASB) and upflow anaerobic hybrid reactor (UAHR) and HRT of 6 days was found to be optimum. Based on the findings of the laboratory study, full scale UASB reactors were operated at 6 days HRT. During study period, operation of the reactors revealed the stable condition which was indicated by 62.19 to 66.59%, 72.42 to 77.11% and 58.47 to 60.46% of COD, BOD and TS reductions respectively at an Organic Loading Rate (OLR) of 2.15 to 4.60 kg COD m-3 d-1. The results showed that the biomethanation significantly reduced the pollution load and also generated renewable energy. The produced biogas use in power boiler resulted in significant reduction of dependency on fossil fuels and also cut down of carbon dioxide emission to atmosphere from the fossil fuels. The field experiments conducted with groundnut and sugarcane crops showed that BDS could be very well used as a source of plant nutrients for sustaining the crop yields, soil productivity and its health without polluting the soil and ground water. Further, K fertilizer could be completely skipped off during BDS utilization, which not only saved the K fertilizer input but also could considerably cut short the fertilizer import bills. The use of a growth medium consisting of biomethanated distillery spentwash represents a good low cost alternative for large scale production of Spirulina sp. as well as for simultaneous treatment of the spentwash. Hence, it is concluded that the combination of biomethanation through high rate anaerobic reactors followed by land application for agricultural production and utilization for large scale production of Spirulina sp. is best suited technology for the effective disposal of distillery spentwash in an eco-friendly manner.