Tang, Zhang, & Li (2024) A novel strategy combining hydrogenotrophic methanogens’ bioaugmentation and biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More biostimulation for simultaneous polycyclic aromatic hydrocarbon biodegradation and bioenergy recovery. Royal Society of Chemistry. https://doi.org/10.1039/D4RA03732D

A recent study introduces an innovative strategy combining bioaugmentation with hydrogenotrophic methanogens and biochar biostimulation to enhance the biodegradation of polycyclic aromatic hydrocarbons (PAHs) and simultaneously recover bioenergy. PAHs, generated from activities like burning fossil fuels and industrial operations, are carcinogenic and can accumulate in sediments, posing severe environmental and health risks. Traditional methods for removing PAHs, such as volatilization and chemical oxidation, are often costly and can cause secondary pollution. Microbial degradation offers a more eco-friendly and sustainable solution.

The study focuses on both low molecular weight (LMW) PAHs, which have 2-3 benzene rings, and high molecular weight (HMW) PAHs, which have 4-7 rings. HMW PAHs are more resistant and toxic to organisms. The researchers explored anaerobic biodegradation, a less-documented approach for mixed PAHs, and introduced a novel method combining bioaugmentation using methanogenic archaea and biostimulation using biochar.

The preparation involved creating a PAH solution with 16 types of PAHs dissolved in n-hexane. Biochar was produced from cattle manure through slow pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More, and hydrogenotrophic methanogens (HM) were enriched using a continuous stirred tank reactor. Five treatment reactors were set up, with various combinations of glucose, PAHs, FeCl3, biochar, and HM added at different stages.

Results showed that adding PAHs inhibited methane production and caused an accumulation of volatile fatty acids (VFA), indicating PAH toxicity to methanogens. However, the combination of biochar and HM significantly alleviated these inhibitory effects, allowing methane production to recover. The biochar and HM group exhibited a 7.5% higher cumulative methane production compared to the Fe3+ and bioaugmentation group. This strategy achieved over 90% removal of most PAHs.

The study also observed significant changes in the microbial community structure. Biochar and HM enriched direct interspecies electron transfer (DIET) guilds, such as Streptococcus and Methanosarcina, which were crucial for PAH removal and methane recovery. The findings suggest that biochar can act as a shelter for PAH-degrading bacteria and facilitate electron transfer, enhancing PAH degradation.

The implications of this research are significant for sewage treatment plants, surface and groundwater remediation, and industrial wastewater pre-treatment. This novel strategy offers an efficient and sustainable solution for managing PAH contamination while generating valuable bioenergy. The study demonstrates the potential of combining bioaugmentation and biostimulation to tackle environmental pollutants effectively, paving the way for future applications in waste management and renewable energy production.