Life cycle and efficiency assessment of fixed-bed bioreactor using recycled shredded plastics compared with conventional activated sludge bioreactor for dairy wastewater treatment

Adopting a highly efficient and low-cost bed bioreactor for the treatment of high-strength dairy wastewater has received unprecedented significance. Therefore, the concept of "waste as a resource" was brought up in this study and recycled shredded plastics (RSPs) were used to structure a fixed bed for activated sludge expansion. The performance of the RSP-attached growth system (AGS) and conventional suspended growth system (SGS) with intermittent anaerobic/aerobic conditions were scrutinized for dairy wastewater treatment. In addition, their environmental repercussions, greenhouse gas (GHG) emissions, and ecological footprint were explored to provide innovative insights into the field of research. The AGS system outperformed with substantial COD, nitrate, and phosphorus removal efficiencies (>89 %) in hydraulic retention time of 4 h, aeration time of 27 min, and COD/P ratio of 120. Notably, the SGS system outcompeted in the environmental impacts and energy usage, which accounted for 1.03-4.38 times higher than that for the AGS system. The electricity consumption and wastewater treatment process had striking roles in human carcinogenic toxicity, freshwater/marine ecotoxicity, and human health. The most required energy for AGS and SGS operations was supplied by fossil fuels, which increment GHG emissions from 4.31 to 8.77 kg CO2 eq for the AGS and SGS, respectively. Moreover, the reduction of electricity usage dramatically decreased human carcinogenic toxicity and marine ecotoxicity. Summing up, this study sheds light on the RSPs' capability to support activated sludge and ensure alignment with environmental criteria for dairy wastewater treatment.