The generation of organic wastes, such as sludge from wastewater treatment plants and food waste, is an inevitable byproduct of human activity. In line with the Federal Pollution Prevention Act of 1990 and the principles of Green Chemistry, waste that cannot be prevented or recycled must be managed in an environmentally sustainable manner. Conventional waste management methods, including incineration and landfilling, pose significant environmental risks, such as greenhouse gas emissions and soil and groundwater contamination.
Anaerobic digestion (AD) offers a sustainable and eco-friendly alternative for managing organic waste. This biochemical process converts waste into biogas and nutrient-rich fertilizers. To enhance the performance of AD, this study incorporates three key strategies: 1. applying thermal hydrolysis as a pretreatment technique to non-easily biodegradable feedstock (sludge); 2. mixing feedstocks (thermally pretreated sludge with food waste); and 3. introducing biochar as a conductive material.
Sludge was thermally pretreated to improve its biodegradability and facilitate methane production. An additional benefit of this pretreatment is the reduction of pathogens in the resulting digestate, which aligns closely with green chemistry principles. The co-digestion of thermally pretreated sludge and food waste at varying ratios revealed that increasing the proportion of food waste enhanced methane production. Thermally pretreated sludge alone produced 169 mL/gTCOD (total chemical oxygen demand) of methane, whereas a mixture containing 20% thermally pretreated sludge and 80% food waste yielded 309 mL/gTCOD, representing an 82% increase in methane production.
Furthermore, biochar derived from wood residues, a green and non-toxic alternative to conventional nanoparticles, was incorporated into the process. Preliminary results suggest that higher methane yields may be obtained in reactors containing biochar compared to those without. With this approach, more biogas is produced and a nutrient-rich and less hazardous digestate is generated.
Integrating thermal pretreatment and biochar into the AD process results in a sustainable pathway toward enhanced waste valorization, renewable energy generation, and environmentally responsible waste management. These innovations underscore the alignment of anaerobic digestion with the principles of green chemistry and its potential to address global sustainability challenges.