Reduced greenhouse gas emission by reactive oxygen species during composting.

Reactive oxygen species (ROS) is produced in the composting, which effectively promote organic matter transformation and humification process, but the effect of ROS on greenhouse gas emissions in this process has not been understood. This study proposed and validated that ROS can effectively reduce greenhouse gas emissions intheprocessofcomposting. Compared with ordinary thermophilic composting (oTC), thermophilic composting (imTC) that was supplemented by iron mineral increased ROS production by 1.38 times, and significantly reduced greenhouse gas emissions by 45.12%. Microbial community analysis showed no significant difference in the abundance of microbes involved in greenhouse gas production between oTC and imTC. Further correlation analysis proved that ROS played a crucial role in influencing greenhouse gas emissions throughout the composting process, especially in the initial phase. These findings provide new strategies for managing livestock and poultry manure to mitigate climate change.

Reactive Oxygen Species Triggered Oxidative Degradation of Polystyrene in the Gut of Superworms (Zophobas atratus Larvae).

Oxidative decomposition of polystyrene (PS) by insects has been previously demonstrated, yet little is known about the oxidation mechanism and its effect on the metabolism of plastics within the insect gut. Here, we demonstrate the generation of reactive oxygen species (ROS) in the gut of superworms (Zophobas atratus larvae) under different feeding trails, which in turn induced the oxidative decomposition of ingested PS. The ROS were commonly generated in the larva gut, and PS consumption resulted in a significant increase of ROS with a maximum ·OH of 51.2 µmol/kg, which was five times higher than in the bran feeding group. Importantly, scavenging of ROS significantly decreased the oxidative depolymerization of PS, indicating a vital role of ROS in effective PS degradation in the gut of superworms. Further investigation suggested that the oxidative depolymerization of PS was caused by the combinatorial effect of ROS and extracellular oxidases of gut microbes. These results demonstrate that ROS were extensively produced within the intestinal microenvironment of insect larvae, which greatly favored the digestion of ingested bio-refractory polymers. This work provides new insights into the underlying biochemical mechanisms of plastic degradation in the gut.

Enhanced degradation of microplastics during sludge composting via microbially-driven Fenton reaction.

It has been increasingly documented that the hydroxyl radical (•OH) can promote the transformation of organic contaminants such as microplastics (MPs) in various environments. However, few studies have sought to identify an ideal strategy for accelerating in situ MPs degradation through boosting the process of •OH production in practical applications. In this work, iron-mineral-supplemented thermophilic composting (imTC) is proposed and demonstrated for enhancing in situ degradation of sludge-based MPs through strengthening •OH generation. The results show that the reduction efficiency of sludge-based MPs abundance was about 35.93% in imTC after treatment for 36 days, which was 38.99% higher than that of ordinary thermophilic composting (oTC). Further investigation on polyethylene-microplastics (PE-MPs) suggested that higher abundance of •OH (the maximum value was 408.1 µmol·kg-1) could be detected on the MPs isolated from imTC through microbially-mediated redox transformation of iron oxides, as compared to oTC. Analyses of the physicochemical properties of the composted PE-MPs indicated that increased •OH generation could largely accelerate the oxidative degradation of MPs. This work, for the first time, proposes a feasible strategy to enhance the reduction efficiency of MPs abundance during composting through the regulation of •OH production.

Reactive oxygen species accelerate humification process during iron mineral-amended sludge composting.

The production of hydroxyl radicals (OH) has been documented during composting. However, the effect of OH on composting efficiency remains unclear. Here, iron mineral supplemented thermophilic composting (imTC) is proposed and demonstrated for enhancing OH production and accelerating the maturation of composting. The results indicated that the maximum OH production of imTC was 1922.74 µmol·kg-1, which increased by 1.39 times than that of ordinary thermophilic composting (oTC). Importantly, the increase of OH could greatly enhance organic matter degradation and humic substances formation during imTC, resulting in shorting the maturity time by 25 %. Enrichment of laccase-producing bacteria resulted in higher laccase activity (31.85 U·g-1) in imTC compared with oTC (23.82 U·g-1), which may have contributed to the higher level of humification in imTC treatment. This work, for the first time, proposes a feasible strategy for improving composting efficiency through the regulation of OH production during aerobic composting.

Degradation of microplastics by hydroxyl radicals generated during microbially driven humus redox transformation.

The production of ·OH during transformation of redox active substances has been increasingly documented, and it causes the ageing or degradation of microplastics (MPs) in natural systems. However, the contribution of the humus redox cycle to ·OH generation and MPs transformation has previously been overlooked, even though it is ubiquitous in alternating anoxic-oxic environments. In this work, the integrated pathways of ·OH generation during the redox transformation of humic acids (HAs) and the contribution of this ·OH to the transformation of MPs were investigated for the first time. It was found that ·OH could be produced continuously during successive cycles of redox transformation of HAs mediated by Bacillus thermotolerans SgZ-8 through exogeneous HAs dependent and independent pathways. O2·- and H2O2 were identified as the key intermediate species, which were produced by both microbial aerobic respiration and HA oxidation. The ·OH generated by HA redox cycles could lead to a weight loss of PS-MPs of 18.1% through oxidative degradation during a period of 8 weeks of anoxic-oxic incubation. The EDC of HAs is closely related to ·OH production, which could have a large influence on the effectiveness of oxidative degradation of PS-MPs during various HAs redox cycles in temporarily anoxic environmental systems. These findings provide new insights into ·OH formation and MPs transformation through microbially driven humus redox cycles in alternating anoxic-oxic environments.

Extensive production and evolution of free radicals during composting.

The production of free radicals has been widely documented in natural systems, where they play an important role in most organic matter and contaminants transformation. Here, the production and evolution of free radicals were systematically investigated during composting. Results indicated that multiple reactive oxygen species and environmentally persistent free radicals (G-factor 2.003-2.004) were generated with dynamic changes during composting. The ·OH yield fluctuated significantly with a maximum content of 365.7-1,262.3 µmol/kg at the thermophilic phase of composting, which was closely correlated with the changes of Fe (II) (Pearson's r = 0.928-0.932) and the electron-donating capacity of humus (Pearson's r = 0.958-0.896) during composting. Further investigation suggested that microorganisms driven iron/humus redox conversion could contribute to the production and dynamic changes of free radical during composting. These findings highlight the abiotic processes involving free radicals, and provide a new perspective for humification and contaminants removal during composting.

Free radicals accelerate in situ ageing of microplastics during sludge composting.

Composting is the last "barrier" for microplastics (MPs) in the entry of organic solid wastes into the environment. The transformation of MPs is thought to be mainly driven by microorganisms during composting, whereas the contribution of abiotic processes that involve free radicals is often overlooked. Herein, we provide initial evidence for the generation of free radicals during sludge composting, including environmental persistent free radicals and reactive oxygen species, which accelerate the oxidative degradation of MPs. The ·OH yield of composting fluctuated greatly from 23.03 to 277.18 µmol/kg during composting, which was closely related to the dynamic changes in Fe(II) (R2 = 0.926). Analyses of the composted MPs physicochemical properties indicated that MPs were aged gradually with molecular weights decrease from 18% to 27% and carbonyl index value increase from 0.23 to 0.52. Further investigation suggested that the microbially-mediated redox transformation of iron oxides could occur on the MPs surface accompanied by the production of abundant free radicals, thereby leading to the damage of MPs during composting. These results reveal the critical role of free radicals in MPs ageing under oxic/anoxic alternation conditions of composting and provide new insights into the bio-chemical mechanism of contaminant removal or transformation during sludge composting.

[Biodegradation of Polystyrene by Geobacillus stearothermophilus].

Biodegradation is the most sustainable treatment method for waste polystyrene (PS). Thermophiles possess highly efficient biotransformation capabilities that could enhance the biodegradation efficiency of organic solid wastes. However, detailed research on the degradation of PS plastics by thermophile is scarce. Here, the degradation performance of a strain of Geobacillus stearothermophilus FAFU011 (FAFUA011) isolated from compost was examined. The results showed that strain FAFUA011 could utilize PS as the sole carbon source for growth and formed a stable biofilm on the surface of PS fragments. During 56 days of degradation, FAFU0011 caused a total mass loss of PS of 4.2% and decrease in molecular weight of 17.4%-18.2%. Based on SEM observations, FAFUA011 causes erosion hollows on the surface of PS, thus increasing the type and number of oxygen-containing structures that alter its hydrophilic properties. These changes facilitate the colonization of other microorganisms and further promote biodegradation. Based on 2D-COS analysis, the chronological order of the change in functional groups during the degradation process were identified as follows:1491 cm-1(C-H) > 1450 cm-1(C-H) > 1601 cm-1(C=C) > 1027 cm-1(C-O) > 1068 cm-1(C=O) > 1366 cm-1(C-OH). Overall, these results reveal that FAFU011 could promote the thermophilic bio-oxidative degradation of PS plastic.

Enhanced in situ Pb(II) passivation by biotransformation into chloropyromorphite during sludge composting.

Composting is an effective technology for the disposal and utilization of solid biowastes. However, conventional composting is inefficient for the passivation of heavy metals in solid biowastes, thus limiting the applications of compost derived from solid biowaste. Here, a thermophilic biomineralization strategy was proposed and demonstrated during sludge composting for in situ heavy metals passivation via thermophiles inoculation. It was found that Thermus thermophilus could promote the transformation of Pb(II) into the most stable chloropyromorphite [Pb5(PO4)3Cl, Ksp = 10-84.4] during composting. After 40 days of composting with T. thermophilus FAFU013, the most insoluble residual fractions of Pb increased by 16.0% (from 76.5% to 92.5%), which was approximately 3 times higher than that of the uninoculated control. The DTPA-extractable Pb decreased to 11.5%, which was 14.4% less compared with the uninoculated control, indicating a significant Pb passivation by inoculation of T. thermophilus FAFU013. A series of batch experiments revealed that Pb(II) could be rapidly accumulated by selective biosorption and gradually transformed into chloropyromorphite through the biomineralization of T. thermophilus FAFU013. This study provides new insight into the mechanism of heavy metal passivation during composting and the problem associated with the disposal of Pb-contaminated solid biowastes through the biomineralization of thermophiles.

Preparation of High-Performance CdS@C Catalyst Using Cd-Enriched Biochar Recycled From Plating Wastewater.

Biochar is widely used for the adsorptive removal of Cd from water and soil, but the Cd-enriched biochar produced carries a risk of secondary pollution. In this work, biochar derived from rice straw was used to adsorb Cd from plating wastewater. The Cd-enriched biochar showed a saturated adsorption capacity of about 63.5 mg/g and could be recycled and used in a mesoporous carbon-supported CdS (CdS@C) photocatalyst after pyrolysis carbonization and a hydrothermal reaction. The results demonstrated that the as-prepared CdS@C photocatalyst contained mixed cubic and hexagonal CdS phases, with a considerably lower band gap (2.1 eV) than pure CdS (2.6 eV). CdS@C exhibited an enhanced photocatalytic performance for the degradation of organic dyes under visible light irradiation compared with pure CdS due to its excellent light-harvesting capacity and efficient electron-hole separation. Moreover, the continuous formation of active species (h+, •OH, and O2•-) was responsible for the photodegradation of organic dyes using CdS@C. This work provides new insights for the safe disposal of Cd-enriched wastewater and for improving the economic viability of Cd-contaminated resources by recovering a value-added photocatalyst.

Enhanced in situ biodegradation of microplastics in sewage sludge using hyperthermophilic composting technology.

Land spreading of sewage sludge is a major source of environmental microplastics (MPs) contamination. However, conventional sludge treatments are inefficient at removing sludge-based MPs. Herein, hyperthermophilic composting (hTC) technology is proposed and demonstrated in full-scale (200 t) for in situ biodegradation of sludge-based MPs. After 45 days of hTC treatment, 43.7% of the MPs was removed from the sewage sludge, which is the highest value ever reported for MPs biodegradation. The underlying mechanisms of MPs removal were investigated in lab-scale polystyrene-microplastics (PS-MPs) biodegradation experiments. The hTC inoculum degraded 7.3% of the PS-MPs at 70 °C in 56 days, which was about 6.6 times higher than that of the conventional thermophilic composting (cTC) inoculum at 40 °C. Analyses of the molecular weight and physicochemical properties of the PS-MPs residuals indicated that hyperthermophilic bacteria in hTC accelerated PS-MPs biodegradation through excellent bio-oxidation performance. High-throughput sequencing suggested that Thermus, Bacillus, and Geobacillus were the dominant bacteria responsible for the highly efficient biodegradation during hTC. These results reveal the critical role of hyperthermophilic bacteria in MPs biodegradation during hTC, highlighting a promising strategy for sludge-based MPs removal from the real environment.