Green waste and sewage sludge feeding ratio alters co-composting performance: Emphasis on the role of bacterial community during humification

Unveiling the effect of PFOA presence on the composting process: Roles of oxidation stress, carbon metabolism, and humification process

Perfluorooctanoic acid (PFOA), an emerging pollutant, has been frequently detected in organic solid waste. It becomes a major concern for compost application, but studies on its toxic effects during composting are rare. This study evaluated the impact of PFOA presence at the environmentally relevant level on the humification process and microbiology during composting. The results showed that the PFOA presence (15.5 μg/kg dry) caused 45.5 % and 40.5 % decreases in the total organic carbon and humic acid-like substances, respectively. PFOA negatively affected microbial activity during the thermophilic period, as evidenced by the increases in reactive oxygen species and lactate dehydrogenase concentration. It altered the microbial community with an enrichment of Bacteroidota, conducive to resisting press. Unexpectedly, the PFOA presence induced hormesis at the maturity period, consistent with stimulated carbon metabolism (i.e., glycolysis and oxidative phosphorylation). The modulated microbial metabolism stimulated the catabolic metabolism of small-molecule humus precursors and reduced intracellular quinone availability. Furthermore, the secretion of auxiliary activities for crude fiber degradation was suppressed, which decreased the generation of extracellular quinone, and thereby impeded the humification process. These findings deciphered the metabolic response of composting to PFOA presence and highlighted the potential carbon loss of PFOA-containing composting.

A review on green waste composting, role of additives and composting methods for process acceleration

Effective disposal of green waste has been a challenging task faced by urban bodies for a long time. Composting can be an effective method to manage green waste by recovering nutrients that can be used as organic manure. However, there are some limitations to green waste composting, such as a low degradation rate and the requirement for high manpower and space. Many researchers have studied ways to minimize the limitations of green waste composting through different approaches. These include the use of co-composting materials, inoculating agents, and process modifications such as multi-stage composting. In this review, we systematically summarized the physicochemical characteristics of green waste and green waste compost, optimum ratios of additives, and process modifications during the composting of green waste reported in various articles. This review is helpful for early-career researchers and individuals new to the field of green waste composting by providing them with key concepts and recent developments in the field. The study suggests that the sustainable selection of additives or methods for composting green waste should depend on resource availability, climatic conditions, and the characterization of the feedstock.

The bioaugmentation effect of microbial inoculants on humic acid formation during co-composting of bagasse and cow manure

The effective degradation of recalcitrant lignocellulose has emerged as a bottleneck for the humification of compost, and strategies are required to improve the efficiency of bagasse composting. Bioaugmentation is a promising method for promoting compost maturation and improving the quality of final compost. In this study, the bioaugmentation effects of microbial inoculants on humic acid (HA) formation during lignocellulosic composting were explored. In the inoculated group, the maximum temperature was increased to 72.5 °C, and the phenol-protein condensation and Maillard humification pathways were enhanced, thus increasing the HA content by 43.85%. After inoculation, the intensity of the microbial community interactions increased, particularly for fungi (1.4-fold). Macrogenomic analysis revealed that inoculation enriched thermophilic bacteria and lignocellulose-degrading fungi and increased the activity of carbohydrate-active enzymes and related metabolic functions, which effectively disrupted the recalcitrant structure of lignocellulose to achieve a high humification degree. Spearman correlation analysis indicated that Stappia of the Proteobacteria phylum, Ilumatobacter of the Actinomycetes phylum, and eleven genera of Ascomycota were the main HA producers. This study provides new ideas for bagasse treatment and recycling and realizing the comprehensive use of resources.

Effect of different bulking agents on fed-batch composting and microbial community profile

The current study focused on analyzing the effect of different types of bulking agents and other factors on fed-batch composting and the structure of microbial communities. The results indicated that the introduction of bulking agents to fed-batch composting significantly improved composting efficiency as well as compost product quality. In particular, using green waste as a bulking agent, the compost products would achieve good performance in the following indicators: moisture (3.16%), weight loss rate (85.26%), and C/N ratio (13.98). The significant difference in moisture of compost products (p < 0.05) was observed in different sizes of bulking agent (green waste), which was because the voids in green waste significantly affected the capacity of the water to permeate. Meanwhile, controlling the size of green waste at 3-6 mm, the following indicators would show great performance from the compost products: moisture (3.12%), organic matter content (63.93%), and electrical conductivity (EC) (5.37 mS/cm). According to 16S rRNA sequencing, the relative abundance (RA) of thermophilic microbes increased as reactor temperature rose in fed-batch composting, among which Firmicutes, Proteobacteria, Basidiomycota, and Rasamsonia were involved in cellulose and lignocellulose degradation.

Biochemical changes, metal content, and spectroscopic analysis in sewage sludge composted with lignocellulosic residue using FTIR-MIR and FTIR-NIR

The use of lignocellulosic residues, originating from sawdust, in composting sewage sludge for organic fertilizer production, is a practice of growing interest. However, few studies have explored the effect of the proportion of sawdust and sewage sludge raw materials on composting performance in the humification process. This study assessed the addition of sawdust in the sewage sludge composting process, regarding carbon content, presence of heavy metals, and humification of the organic compost. The experimental design employed was a randomized complete block design with five treatments featuring different proportions of organic residues to achieve C/N ratios between 30-1 (T1: 100% sewage sludge and 0% sawdust, T2: 86% sewage sludge and 14.0% sawdust, T3: 67% sewage sludge and 33% sawdust, T4: 55% sewage sludge and 45% sawdust, and T5: 46.5% sewage sludge and 53.5% sawdust) and five replications, totaling 25 experimental units. The addition of lignocellulosic residue in sewage sludge composting increased the levels of TOC and the C/N ratio, reduced the levels of pH, P, N, Na, Ba, and Cr, and did not interfere with the levels of K, Ca, Mg, S, CEC, labile carbon, and metals Fe, Zn, Cu, Mn, Ni, and Pb. The increase in the proportion of sawdust residue favored the degradation of aliphatic groups, increasing the presence of aromatic structures and reducing humification at the end of composting. The use of sawdust as a lignocellulosic residue in sewage sludge composting is a viable and efficient alternative to produce high-quality organomineral fertilizers.

Elucidating carbon conversion and bacterial succession by amending Fenon-like systems during co-composting of pig manure and branch

The essential point of current study was to investigate the effect of a Fenton-like system established by oxalic acid and Fe(II) on gas emission, organic matter decomposition and humification during composting. Branches were pretreated with Fenton reagents (0.02 M FeCl2·4H2O + 1.5 M H2O2) and then adding 10 % oxalic acid (OA). The treatments were marked as B1 (control), B2 (Fenton reagent), B3 (10% OA) and B4 (Fenton-like reagent). The results collected from 80 d of composting showed that adding Fenton-like reagent benefited the degradation of organic substances, as reflected by the total organic carbon and dissolved organic carbon, and the maximum decomposition rate was observed in B4. In addition, the Fenton-like reagent could improve the synthesis of humus characterized by complex and stable compounds, which was consistent with the spectral parameters (SUVA254, SUVA280, E253/E203 and Fourier transform-infrared indicators) of DOC. Furthermore, the functional microbial succession performance and linear discriminant effect size analyses provided microbial evidence of humification improvement. Notably, compared with the control, the minimum value of CH4 cumulation was reported in B4, which decreased by 30.44 %. Concluded together, the addition of a Fenton-like reagent composed by OA and Fe(II) is a practical way to improve the humification. Furthermore, the mechanisms related to the promotion of humification should be investigated from free radicals, functional genes, and metabolic pathways.

Forest waste composting-operational management, environmental impacts, and application

In Portugal, the number of fires and the size of burnt areas are rising dramatically every year, increasing with improper management of agroforestry wastes (AFRs). This work aims to study the composting of these wastes with minimal operational costs and understand the environmental impact and the compost application on burnt soil. Thus, a study of life cycle assessment (LCA) was carried out based on windrow composting processes, considering the avoided environmental impacts associated with the end-product quality and its application as an organic amendment. Three composting piles were made with AFRs from the Residual Biomass Collection Centre (RBCC) in Bodiosa (Portugal). Sewage sludges (SS) from an urban wastewater treatment plant were used as conditioning agent. One pile with AFRs (MC) and another with AFRs and SS (MCS) were managed according to good composting practices. Another pile with the AFRs was developed without management (NMC), thus with a minimal operational cost. Periodically, it was measured several physical and chemical parameters according to standard methodologies. Eleven environmental impacts of compost production, MC and MCS, were analyzed by a LCA tool, and their effect on the growth of Pinus pinea was evaluated, using peat as reference. Composting evolution was expected for both piles. Final composts, MC and MCS, were similar, complying with organic amendment quality parameters. Compost NMC, with no operational management, showed the highest germination index. Piles MC and MCS showed similar environmental impacts, contributing to a negative impact on global warming, acidification, and eutrophication. Greater growth was obtained with application of MCS, followed by MC, and finally, peat. Composting is a sustainable way to valorize AFRs wastes, producing compost that could restore burnt soils and promote plant growth and circular economy.

Effective Carbon Dioxide Mitigation and Improvement of Compost Nutrients with the Use of Composts' Biochar

Composting is a process that emits environmentally harmful gases: CO2, CO, H2S, and NH3, negatively affecting the quality of mature compost. The addition of biochar to the compost can significantly reduce emissions. For effective CO2 removal, high doses of biochar (up to 20%) are often recommended. Nevertheless, as the production efficiency of biochar is low-up to 90% mass loss-there is a need for research into the effectiveness of lower doses. In this study, laboratory experiments were conducted to observe the gaseous emissions during the first 10 days of composting with biochars obtained from mature composts. Biochars were produced at 550, 600, and 650 °C, and tested with different doses of 0, 3, 6, 9, 12, and 15% per dry matter (d.m.) in composting mixtures, at three incubation temperatures (50, 60, and 70 °C). CO2, CO, H2S, and NH3 emissions were measured daily. The results showed that the biochars effectively mitigate CO2 emissions during the intensive phase of composting. Even 3-6% d.m. of compost biochars can reduce up to 50% of the total measured gas emissions (the best treatment was B650 at 60 °C) and significantly increase the content of macronutrients. This study confirmed that even low doses of compost biochars have the potential for enhancing the composting process and improving the quality of the material quality.