While several studies have implemented the anaerobic digestion of cheese whey wastewater (CWW) to generate biogas, there is still a research gap in finding appropriate techniques to prevent medium acidification and avoid secondary pollution from digestate sludge disposal. Hence, this study represented (i) the synergetic effect of greywater (GW) with CWW to alleviate the medium inhibition causes and (ii) the recycling of anaerobic digestate to prepare biochar. The CWW/GW fraction of 25/75 (v/v) showed the best co-digestion performance, where about 43.10 ± 2.27% of initial chemical oxygen demand (CODinitial) was converted to bio-CH4. The co-digestion of CWW with GW could mitigate the inhibition impacts caused by volatile fatty acids (VFAs) accumulation and provide a balanced C/N ratio, supporting the methanogenic growth patterns. The pyrolysis of digestate sludge showed a promising route to generate biochar, having high carbon content, multiple surface functional groups, and a large specific surface area. The obtained bio-CH4 recovery (150.86 ± 7.64 mL/g COD) and biochar yield (0.65 ± 0.05?g/g dry sludge) were used to determine the economic feasibility of an integrated anaerobic co-digestion/pyrolysis project at a CWW/GW discharge of 50 m3/d (792.5?kg COD/d). The profits related to biogas, biochar, carbon credit, and pollution reduction could reach up to 49,976 USD/year, with a net profit of 26,111 USD/year. The cash-flow depicted that the proposed CWW/GW management system could recover the initial investment in an 8.97-year payback period. The study demonstrated that the CWW/GW co-digestion/pyrolysis pathway could fulfill several SDGs related to pollution reduction, climate change mitigation, and economic growth development. Graphical Abstract: (Figure presented.)
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