Anaerobic digestion of toluene-laden wastewater under oxygen-deficient mesophilic condition and concurrent retrieval of methane-enriched biogas

Increasing population in the world resulted in the crisis of both water and energy and therefore demanding the treatment of wastewater to make it fit for human use. The present study aims at the degradation of wastewater containing hazardous toluene along with the simultaneous recovery of energy, i.e., biogas which can overcome the crisis of both resources to some extent. For this, anaerobic digestion of toluene with varying concentration was achieved under the mesophilic condition when fed with different amount of substrate level. Examination of the feasible concentration of toluene and glucose (co-substrate) dosage to the reactor was performed in order to evaluate the performance of the anaerobic reactor. During the experiment, toluene degradation and chemical oxygen demand (COD) removal were examined periodically, and the efficiency of degradation was compared with the varying amount of glucose (0.5, 1, and 2 g/L). The high COD removal efficiency (77%) and methane (CH₄) production (298 μL) was achieved after degrading 200 mg/L toluene sample when the reactor is fed with 1 g/L of glucose. Thus, 1 g/L was found to be the optimal amount of substrate level suitable for degradation and the efficiency is decreased if the amount of glucose is increased or decreased from this optimal amount. Furthermore, the scanning electron microscopy studies revealed the highly porous nature of sludge fed with 1 g/L glucose than others. Moreover, energy-dispersive x-ray analysis of sludges indicates the presence of different elemental components (carbon, oxygen, silicon, calcium) that confirmed the presence of microbial secretions involved in degradation.