Application fields of kitchen waste biochar and its prospects as catalytic material: A review

Negative impacts of perishable waste biochar to Escherichia coli and exploring potential damage factors

Agricultural application of pyrolysis‑carbonized perishable wastes can target reduction treatment and resource utilization of the wastes. However, potential undesirable impact has rarely been assessed. In this study, the adverse effect of perishable waste biochars (PWB) from different pyrolysis temperatures on Escherichia coli (E. coli) was explored and the potential risk factors were further analyzed. The results showed that PWBs pyrolyzed at 350, 500, and 650 °C inhibited the growth of E. coli, and PWB pyrolyzed at 500 °C showed the most inhibition. The exposure to PWB damaged the antioxidative system, as revealed by the concentration-dependent increasing of intracellular ROS. In addition, the toxicity at the gene level in terms of cell division and growth inhibition, the damage of cell membrane, antioxidant system disturbance, and DNA damage occurred, resulting in loss of the cell rules of morphology and eventual death. According to our results, the inhibitory effect on the growth of E. coli was mainly caused by PWB solids, accounting for >70 %. The membrane disruption and oxidative damage of E. coli by PWB were possibly induced by the direct physical interaction between cell and char particles. The growth of E. coli can be partly influenced by PWB extraction solutions that varied between PWB types, due to the differences in pH, released DOC and the production of extracellular ∙OH. The exploration of these potential hazards could provide new insights into the fate and toxicity of PWB in the environment and help guide the safe and sustainable applications for PWB.

Biochar-Derived Persistent Free Radicals: A Plethora of Environmental Applications in a Light and Shadows Scenario

Biochar (BC) is a carbonaceous material obtained by pyrolysis at 200-1000 °C in the limited presence of O2 from different vegetable and animal biomass feedstocks. BC has demonstrated great potential, mainly in environmental applications, due to its high sorption ability and persistent free radicals (PFRs) content. These characteristics enable BC to carry out the direct and PFRs-mediated removal/degradation of environmental organic and inorganic contaminants. The types of PFRs that are possibly present in BC depend mainly on the pyrolysis temperature and the kind of pristine biomass. Since they can also cause ecological and human damage, a systematic evaluation of the environmental behavior, risks, or management techniques of BC-derived PFRs is urgent. PFRs generally consist of a mixture of carbon- and oxygen-centered radicals and of oxygenated carbon-centered radicals, depending on the pyrolytic conditions. Here, to promote the more productive and beneficial use of BC and the related PFRs and to stimulate further studies to make them environmentally safer and less hazardous to humans, we have first reviewed the most common methods used to produce BC, its main environmental applications, and the primary mechanisms by which BC remove xenobiotics, as well as the reported mechanisms for PFR formation in BC. Secondly, we have discussed the environmental migration and transformation of PFRs; we have reported the main PFR-mediated application of BC to degrade inorganic and organic pollutants, the potential correlated environmental risks, and the possible strategies to limit them.

Mutualistic microbial community of Bacillus amyloliquefaciens and recombinant Yarrowia lipolytica co-produced lipopeptides and fatty acids from food waste

Bioconversion is an important method for transforming food waste (FW) into high value-added products, rendering it harmless, and recycling resources. An artificial microbial consortium (AMC) was constructed to produce FW-based lipopeptides in order to investigate the strategy of FW bioconversion into value-added products. Exogenous fatty acids as a precursor significantly improved the lipopeptide production of Bacillus amyloliquefaciens HM618. To enhance fatty acid synthesis and efflux in AMC, the recombinant Yarrowia lipolytica YL21 (strain YL21) was constructed by screening 12 target genes related to fatty acids to replace exogenous fatty acids in order to improve lipopeptide production. The levels of fengycin, surfactin, and iturin A in the AMC of strains HM618 and YL21 reached 76.19, 192.80, and 31.32 mg L^-1, increasing 7.24-, 12.13-, and 3.23-fold compared to the results from the pure culture of strain HM618 in flask with Landy medium, respectively. Furthermore, free fatty acids were almost undetectable in the co-culture of strains HM618 and YL21, although its level was around 1.25 g L^-1 in the pure culture of strain YL21 with Landy medium. Interestingly, 470.24 mg L^-1 of lipopeptides and 18.11 g L^-1 of fatty acids were co-produced in this AMC in a bioreactor with FW medium. To our knowledge, it is the first report of FW biotransformation into co-produce of lipopeptides and fatty acids in the AMC of B. amyloliquefaciens and Y. lipolytica. These results provide new insights into the biotransformation potential of FW for value-added co-products by AMC.

Effects of Municipal Solid Waste on Planting Properties and Scouring Resistance of Vegetation Concrete (Wuhan, China)

Vegetation concrete (VC) laid as a reinforcement base and covered by a soil layer with vegetation has been increasingly used to beautify the landscape, reduce environmental pollution and control stormwater runoff. In this study, the effects of municipal solid waste (MSW) on vegetation characteristics of modified VC were tested under different mix compositions. We first explored the effects of the mixed concrete environment on Festuca elata and perennial Ryegrass for 60 days. Then, the influence of various MSW contents added to different percentages of cement on scouring resistance of VC was examined. The experimental results revealed that the germination rates and plant heights of both species decreased with the increase in concrete content. Considering the scouring resistances, the optimal mix proportion of MSW-modified VC was recommended as No. 25, with 5% KW fertilizer, 8% cement and 0.5% wheat straw in this study. Furthermore, adding a small amount of fallen leaves or silica fume to VC can promote the growth of both species to some extent, although these additions had an inverse effect on the scouring resistances. The results contribute to beneficial knowledge for future research on the feasibility of the use these species with VC technology for slope ecological restoration.

Effects of biochar-based materials on the bioavailability of soil organic pollutants and their biological impacts

Motivated by the unique structure and superior properties, biochar-based materials, including pristine biochar and composites of biochar with other functional materials, are considered as new generation materials for diverse multi-functional applications, which may be intentionally or unintentionally released to soil. The influencing mechanism of biochar-based material on soil organisms is a key aspect for quantifying and predicting its benefits and trade-offs. This work focuses on the effects of biochar-based materials on soil organisms within the past ten years. 206 sources are reviewed and available knowledge on biochar-based materials' impacts on soil organisms is summarized from a diverse perspective, including the pollutant bioavailability changes in soil, and potential effects of biochar-based materials on soil organisms. Herein, effects of biochar-based materials on the bioavailability of soil organic pollutants are detailed, from the perspective of plant, microorganism, and soil fauna. Potential biological effects of pristine biochar (PBC), metal/metal compounds-biochar composites (MBC), clay minerals-biochar composites (CMBC), and carbonaceous materials-biochar composites (CBC) on soil organisms are highlighted for the first time. And possible mechanisms are presented based on the different characters of biochar-based materials as well as various environmental interactions. Finally, the bottleneck and challenges of risk assessment of biochar-based materials as well as future prospects are proposed. This work not only promotes the development of risk assessment system of biochar-based materials, but broadens the strategy for the design and optimization of environmental-friendly biochar materials.