This paper assesses the technical and economic sustainability of a combined system of an up-flow anaerobic sludge blanket (UASB)-down-flow hanging sponge (DHS) for sewage treatment. Additionally, this study compares UASB-DHS with current technologies in India like trickling filters (TF), sequencing batch reactor (SBR), moving bed biofilm reactor (MBBR), and other combinations of UASB with post-treatment systems such as final polishing ponds (FPU) and extended aeration sludge process (EASP). The sustainability of the sewage treatment plants (STPs) was evaluated using a composite indicator, which incorporated environmental, societal, and economic dimensions. In case of the individual sustainability indicator study, the results showed that UASB-FPU was the most economically sustainable system with a score of 0.512 and aeration systems such as MBBR, EASP, and SBR were environmentally sustainable, whereas UASB-DHS system was socially sustainable. However, the overall comparative analysis indicated that the UASB-DHS system scored the highest value of 2.619 on the global sustainability indicator followed by EASP and MBBR with scores of 2.322 and 2.279, respectively. The highlight of this study was that the most environmentally sustainable treatment plants were not economically and socially sustainable. Moreover, sensitivity analysis showed that five out of the seven scenarios tested, the UASB-DHS system showed good results amongst the treatment system.
Keywords: Composite indicator; India; UASB–DHS; sewage treatment plants; sustainability.