Valorizing kitchen waste to produce value-added fertilizer by thermophilic semi-continuous composting followed by static stacking: Performance and bacterial community succession analysis

Characteristics concerning the evolution of dissolved organic matter and dynamics of bacterial community during continuous thermophilic composting of oxytetracycline fermentation residue

Continuous thermophilic composting (CTC) is a potential technique to recycle oxytetracycline fermentation residue (OFR) with the extremely high level of antibiotics but is still not explored. To investigate the efficiency of CTC on treating OFR, the differences between this technique and conventional composting in the evolution of dissolved organic matter and dynamics of bacterial community were compared. The higher degradation efficiency of oxytetracycline (OTC) was obtained in CTC than conventional composting. The transformation of organic matter occurred faster and the maturity degree of compost product was higher in CTC than conventional composting. Compared with conventional composting, CTC increased the bacterial diversity and screened some functional microorganisms related to OTC degradation and organic matter transformation. The results indicate that CTC is a precise strategy for efficiently recycling OFR as soil amendment.

Sustainable valorisation of kitchen waste through greenhouse solar drying and microwave pyrolysis- technology readiness level for the production of biochar

This study proposes an integrated and sustainable approach for the effective conversion of kitchen waste into valuable products through a two-step process. The primary step involves the implementation of greenhouse solar drying to reduce the moisture content of kitchen waste. The secondary step implies microwave pyrolysis for effective degradation of kitchen waste to biooil, biogas and biochar. Biooil and biogas can be used as renewable fuel source. Biochar can be used as soil amendment. Selection of atmospheric conditions for biochar preparation is discussed, highlighting its crucial role in biochar characteristics. This article highlights, technology readiness level of biochar production from kitchen waste to assess the economic viability for the scalability of the process. In this entirety, the conversion of kitchen waste to valuable products through microwave pyrolysis has significant potential to address the challenges posed by high moisture content and heterogenous nature. With continued research and innovation, it is possible to develop a wide array of value-added products from kitchen waste, ultimately leading to a more eco-friendly and economic approach to waste management.

Graphical Abstract

Insights into effects of thermotolerant nitrifying and sulfur-oxidizing inoculants on nitrogen-sulfur co-metabolism in sewage sludge composting

In this study, high temperature thermotolerant nitrifying bacteria (TNB) and high temperature thermotolerant sulfide oxidizing bacteria (TSOB) were obtained from compost samples and inoculated into sewage sludge (SS) compost. The effects of inoculation on physical and chemical parameters, ammonia and hydrogen sulfide release, nitrogen form and sulfur compound content change and physical-chemical properties during nitrogen and sulfur conversion were studied. The results showed that inoculation of TNB and TSOB increased the temperature, pH, OM degradation, C/N ratio and germination index (GI) of compost. Compared with the control treatment (CK), the addition of inoculants reduced the release of NH3 and H2S, and transformed them into nitrogen and sulfur compounds, the hydrolysis of polymeric ferrous sulfate was promoted, resulting in relatively high content of sulfite and sulfate. At the same time, the physical and chemical properties of SS have a strong correlation with nitrogen and sulfur compounds.

Converting kitchen waste into value-added fertilizer using thermophilic semi-continuous composting-biofiltration two-stage process with minimized NH3 emission

Thermophilic semi-continuous composting (TSC) is effective for kitchen waste (KW) treatment, but large amounts of NH3-rich odorous gas are generated. This study proposes a TSC-biofiltration (BF) two-stage process. Compost from the front-end TSC was used as the packing material in the BF to remove NH3 from the exhaust gas. The BF process was effective in removing up to 83.7 % of NH3, and the NH3 content was reduced to < 8 ppm. Seven days of BF improved the quality of the product from TSC by enhancing the germination index to 134.6 %, 36.5 % higher than that in the aerated-only group. Microbial community analysis revealed rapid proliferation and eventual dominance in the BF of members related to compost maturation and the nitrogen cycle from Actinobacteria, Proteobacteria, Chloroflexi, and Bacteroidetes. The results suggest that the TSC-BF two-stage process is effective in reducing NH3 emissions from TSC and improving compost quality.

Continuous thermophilic composting of distilled grain waste improved organic matter stability and succession of bacterial community

Continuous thermophilic composting (CTC) is potentially helpful in shortening the composting cycle. However, its universal effectiveness and the microbiological mechanisms involved are unclear. Here, the physicochemical properties and bacterial community dynamics during composting of distilled grain waste in conventional and CTC models were compared. CTC accelerated the organic matter degradation rate (0.2 vs. 0.1 d-1) and shortened the composting cycle (24 vs. 65 d), mainly driven by the synergism of bacterial genera. Microbial analysis revealed that the abundance of Firmicutes was remarkably improved compared to that in conventional composting, and Firmicutes became the primary bacterial phylum (relative abundance >70 %) during the entire CTC process. Moreover, correlation analysis demonstrated that bacterial composition had a remarkable effect on the seed germination index. Therefore, controlling the composting process under continuous thermophilic conditions is beneficial for enhancing composting efficiency and strengthening the cooperation between bacterial genera.

Effect of biodrying of lignocellulosic biomass on humification and microbial diversity

By optimizing the carbon to nitrogen (C/N) ratio, this study accomplished an improved level of humification and microbial diversity in the biodrying process of lignocellulosic biomass. The results demonstrated that C/N ratio of 20 accelerated the decomposition of refractory lignocellulose, resulting in lower greenhouse gas emissions and the production of highly mature fertilizer with a germination index of 119.0% and a humic index of 3.2. Moreover, C/N ratio of 20 was found to diversify microbial communities, including Pseudogracilibacillus, Sinibacillus, and Georgenia, which contributed to the decomposition of lignocellulosic biomass and the production of humic acid. Hence, it is recommended to regulate the C/N ratio to 20:1 during the biodrying of biogas residue and wood chips to promote the economic feasibility and bioresource recycling.