Sustainable management of petrochemical wastewater using algal-bacterial granules followed by biogas and biochar production: A techno-economic perspective

Despite several studies on algae-bacterial systems for treating industrial wastewater, there remains a gap in research focused on the recyclability of the resulting sludge to ensure economically sustainable waste man agement. Hence, this study focuses on utilizing the ABGS technique to treat petrochemical wastewater laden with mono-ethylene glycol (MEG), then managing the produced sludge using the anaerobic digestion and pyrolysis processes. The bioreactor containing ABGS (RA-B) was operated by increasing the MEG loading rates (GLR) from 2 to 8 kg/m3 /d for 90 days, and its performance was compared with the bioreactor including bacterial granular sludge (RB). The chemical oxygen demand (COD), ammonia nitrogen, total inorganic nitrogen, and phosphorus removal efficiencies for RA-B were better than the RB unit by 6.23 %, 8.13 %, 37.67 %, and 19.24 %, respectively, at GLR = 4 kg/m3 /d. The anaerobic digestion of the exhausted RA-B granules for 40 days obtained a biogas recovery of 220 ± 11.25 mL/g VS, higher than the RB digestion scenario by 13.4 %. The sludge digestate was thermally treated to yield 0.68 g biochar/g, with an O:C molar ratio < 0.2 and P content of 23 %. The economic feasibility of the combined ABGS/digestion/pyrolysis scheme could earn profits from pollutants’ shadow price, biogas sales, biochar marketing, and carbon credits, achieving 8.93-year payback period. Because the RA-B granules could fulfill sustainable development goals related to climate change mitigation, and human health and aquatic life protection, future studies should focus on understanding the microbial consortia responsible for MEG degradation and determining the different biochar applications