The implications of using organic-rich industrial wastewater as biomethanation feedstocks

Acetic acid and methanol are found in wastewater of many industries and they can be excellent substrates for anaerobic digestion (AD). However, the research determining the efficient use of these wastewater as AD substrates and evaluating their impact on the AD process is scarce. The current study aims to assess the use of acetic acid-rich (WW-HAc) and methanol-rich (WW–MeOH) wastewater for methane production by evaluating (1) their effect on the AD process pH, (2) their toxicity on a typical non-acclimated methanogenic inoculum, (3) their effect on the methanogenic activity and (4) their effect on the acetate metabolic pathway when co-digested in continuous, manure-based anaerobic reactors. The pH experimental results showed that an organic loading (OL) of 5.97 g VS L⁻¹ of WW-HAc lowered the pH below the optimum range for AD (6.5–8.5). The toxicity test on AD process showed that IC50 (half-maximal inhibitory concentration) was 6.9 and 14.31 g VS L⁻¹ for WW-HAc and WW-MeOH, respectively. In the continuous reactors experiment, high organic loading rates of up to 5.7 and 9.7 g VS L⁻¹ d⁻¹ for WW-HAc and WW-MeOH, respectively, where achieved under steady state (i.e., less than 10% variation in production), with 79% and 87%, respectively of the maximum theoretical methane production. Radioisotopic analysis showed that aceticlastic methanogenesis was dominant in both reactors. Overall, the assessment of using acetic acid-rich and methanol-rich wastewater as substrates, revealed significant production benefits for the AD process together with operational restrictions that must be followed to prevent toxicities or overloading effects.