The European Union (EU) Urban Water Reuse Legislation outlines the important challenges to obtaining a green environment. Biochar-assisted treatment processes combined with green substances could be a beneficial option in order to deal with the challenges in EU water reuse legislation. Biochar alone might not be sufficient for achieving higher quality reclaimed water. Even so, a modification of biochar should be carried out by adding an efficient green material such as nanoclay to ensure quaternary treatment is achieved. Nanoclay substances have attracted attention recently owing to their many environmentally friendly advantages for wastewater treatment. The combination of biochar and nanoclay could be an efficient adsorber by the intercalation of the properties of both biochar and nanoclay. From this point of view, this study mainly aimed to investigate the effects of nanoclay addition on malt-dust-derived biochar for wastewater reclamation. Then, a new green improvement index (GII) was developed to determine the effect of nanoclay addition on the biochar adsorption process for wastewater reclamation. This study presented two new biochar-based mechanistic models: a data-driven sensitivity analysis and an uncertainty analysis by Monte Carlo simulation. According to the multivariate statistical analysis, the mixing ratio of malt-dust-derived biochar and nanoclay (bentonite) was 1:2 for the maximum pollutant removal efficiency from brewery industry wastewater. The green improvement index (GII) was in the range of 0.255-0.317, so the nanoclay addition improved the overall wastewater quality by 25.5-31.7%. At the end of the biochar-assisted nanoclay adsorption, Class-A-quality reclaimed water from brewery wastewater was achieved. Also, a virtual benefit–cost analysis was performed, where the economic amendment was ensured by reclaimed water use achieved by the biochar-assisted nanoclay process instead of freshwater reuse.