Fungal community diversity and their contribution to nitrogen cycling in in-situ aerated landfills: Insights from field and laboratory studies.

The application of in-situ aeration technology in landfills has been reported to promote fungal growth, but the community diversity and function of fungi in the aerated landfill system remain unknown. This study firstly investigated an in-situ aerated remediation landfill site to characterize the fungal community diversity in refuse. And to further reveal the fungal involvement in the nitrogen cycling system, laboratory-scale simulated aerated landfill reactors were then constructed. The results in the aerated landfill site showed a significant correlation between fungal community structure and ammonia nitrogen content in the refuse. Dominant fungi in the fungal community included commonly found environmental fungi such as Fusarium, Aspergillus, Gibberella, as well as unique fungi in the aerated system like Chaetomium. In the laboratory-scale aerated landfill simulation experiments, the fungal system was constructed using bacterial inhibitor, and nitrogen balance analysis confirmed the significant role of fungal nitrification in the nitrogen cycling process. When ammonia nitrogen was not readily available, fungi converted organic nitrogen to nitrate, serving as the main nitrification mechanism in the system, with a contribution rate ranging from 62.71 % to 100 % of total nitrification. However, when ammonia nitrogen was present in the system, autotrophic nitrification became the main mechanism, and the contribution of fungal nitrification to total nitrification was only 15.96 %. Additionally, fungi were capable of directly utilizing nitrite for nitrate production with a rate of 4.65 mg L-1 d-1. This research article contributes to the understanding of the importance of fungi in the aerated landfill systems, filling a gap in knowledge.

Deep-dewatering of sewage sludge using double dielectric barrier discharge (DDBD) plasma technology.

Deep dewatering of sewage sludge is essential for optimizing disposal and resource recovery. This study explores the potential of Double Dielectric Barrier Discharge (DDBD) plasma for enhancing waste activated sludge (WAS) dewatering. Key operational parameters (applied voltage, treatment duration, and air feeding rate) were systematically investigated using a two-step approach: Single Factor-at-a-Time (SFAT) and central composite design (CCD) within the response surface methodology (RSM) framework. The aim was to identify influential factors and their optimal settings for maximizing dewatering efficiency while minimizing energy usage. Higher applied voltages (30 kV) and longer treatment durations (40 min) notably improved % moisture reduction (%MR) (92.92 % and 94.35 %, respectively). ANOVA analysis emphasized the equal and substantial impact of applied voltage and treatment duration on %MR and energy efficiency (EE), whereas the air feeding rate exhibited no significant effect. However, it's worth noting that %MR and EE did not display a strictly linear relationship, suggesting complex interactions. Furthermore, two soft sensing models were developed: a quadratic model for %MR and a linear model for energy efficiency (EE). Results showed minimal reductions in TOC content, maintaining values between 13.68 % and 14.28 % compared to untreated sludge 14.37 %. The study also revealed that ROS generated by DDBD plasma played a key role in sludge disintegration, as observed through SEM and FTIR, enhancing dewatering efficiency by the destruction of sludge flocs and the transformation of organic substances. In conclusion, DDBD plasma technology offers a sustainable solution for effective sludge dewatering in WWTPs, preserving organic content.

CO2 uptake in ethanol-driven chain elongation system: Microbial metabolic mechanisms.

CO2 as a byproduct of organic waste/wastewater fermentation has an important impact on the carboxylate chain elongation. In this study, a semi-continuous flow reactor was used to investigate the effects of CO2 loading rates (Low = 0.5 LCO2·L-1·d-1, Medium = 1.0 LCO2·L-1·d-1, High = 2.0 LCO2·L-1·d-1) on chain elongation system Ethanol and acetate were utilized as the electron donor and electron acceptor, respectively. The results demonstrate that low loading rate of CO2 has a positive effect on chain elongation. The maximum production of caproate and CH4 were observed at a low CO2 loading rate. Caproate production reached 1.88 g COD·L-1·d-1 with a selectivity of 62.55 %, while CH4 production reached 129.7 ml/d, representing 47.4 % of the total. Metagenomic analysis showed that low loading rate of CO2 favored the enrichment of Clostridium kluyveri, with its abundance being 3.8 times higher than at of high CO2 loading rate. Metatranscriptomic analysis revealed that high CO2 loading rate induced oxidative stress in microorganisms, as evidenced by increased expression of heat shock proteins and superoxide dismutase genes. Further investigation suggested that genes associated with the reverse ß-oxidation pathway, CO2 uptake pathway and hydrogenotrophic methanogenesis pathway were reduced at high CO2 loading rate. These findings provide insight into the underlying mechanisms of how CO2 affects chain elongation, and it could be a crucial reason for the poor performance of chain elongation systems with high endogenous CO2 production.

Effect of temperature on fungal nitrification in simulated in-situ aeration of aged MSW landfill.

Fungal nitrification is one kind of heterotrophic nitrification that involves certain species of fungi promoting the transformation of organic nitrogen and ammonia nitrogen to nitrite/nitrate. In this study, simulated aerated landfill reactors (SALRs) were constructed to investigate fungal nitrification in aged municipal solid refuse, with a focus on understanding the effect of temperature on the performance of fungal nitrification as well as fungal contribution to ammonia nitrogen transformation. Different nitrogen metabolism patterns have been observed in the system with fungi only (SALRF) and complete microbial consortium, i.e., bacteria + fungi (SALRC). At a temperature of 35 °C, autotrophic nitrification dominated the ammonia nitrogen transformation, while fungal nitrification did not significantly contribute to ammonia removal. However, at elevated temperatures (i.e., 45 °C and 55 °C), fungi played a crucial role in ammonia transformation through fungal assimilation and fungal nitrification, with bacterial function suppressed. Furthermore, 45 °C was found to be the optimal temperature for fungal nitrification, exhibiting the highest nitrification rate (13.98 mg L-1 d-1) which accounted for 49.80% of total nitrification rate in the aerated landfill. High throughput sequencing revealed reshaping of fungal community in response to temperature variation. The abundance of Aspergillus fumigatus, with a relative abundance ranging from 67.13% to 92.71% at elevated temperatures, suggested its significant potential for fungal nitrification. These findings have implications for the promotion of nitrogen cycle through strengthening fungal nitrification in aerated landfill sites which often operate at high temperatures.

Enhanced ethanol-driven carboxylate chain elongation by Pt@C in simulated sequencing batch reactors: Process and mechanism.

Carboxylate chain elongation can create value-added bioproducts from the organic waste. The effects of Pt@C on chain elongation and associated mechanisms were investigated in simulated sequencing batch reactors. 5.0 g/L of Pt@C greatly increased the synthesis of caproate, with an average yield of 21.5 g COD/L, which was 207.4% higher than the trial without Pt@C. Integrated metagenomic and metaproteomic analyses were used to reveal the mechanism of Pt@C-enhanced chain elongation. Pt@C enriched chain elongators by increasing the relative abundance of dominant species by 115.5%. The expression of functional genes related to chain elongation was promoted in the Pt@C trial. This study also demonstrates that Pt@C may promote overall chain elongation metabolism by enhancing CO2 uptake of Clostridium kluyveri. The study provides insights into the fundamental mechanisms of how chain elongation can perform CO2 metabolism and how it can be enhanced by Pt@C to upgrade bioproducts from organic waste streams.

Strategy of electron acceptors for ethanol-driven chain elongation from kitchen waste.

A two-phase kitchen waste (KW) fermentation was proposed in the current study to enhance medium-chain fatty acids (MCFAs) production from kitchen waste. In particular, effect of acetate to butyrate ratio (ABR) on MCFAs production was investigated which can be regulated by different pH and organic loading during the acidification phase. Medium ABR (1.00) was obtained when pH is 5.5 and organic loading is 20 g VS/L in FW acidification fermentation. Subsequent chain elongation fermentation demonstrated that the highest yield of caproate 9.67 g/L with selectivity of 79 %, and highest ethanol conversion efficiency of 1.11 was achieved in medium ABR system. Microbial community study showed that medium ABR significantly enrich the functional bacteria especially Clostridium kluyveri. The study provides a new method for chain elongation enhancement without addition of other additives in kitchen waste fermentation system and gives a guide for the regulation of the short-chain fatty acids distribution in its acidification phase.

Humic Substances Derived From Biomass Waste During Aerobic Composting and Hydrothermal Treatment: A Review.

Humic substances (HSs) occupy 80% of organic matter in soil and have been widely applied for soil remediation agents, potential battery materials, and adsorbents. Since the HS extraction rate is very low by microbial degradation in nature, artificial humification processes such as aerobic composting (AC) and hydrothermal treatment (HT) have attracted a great deal of attention as the most important strategies in HS production. This article aims to provide a state-of-the-art review on the development of conversion of biomass waste into HSs based on AC and HT for the first time in terms of mechanisms, characteristics of HSs' molecular structure, and influencing factors. In addition, some differences based on the aforementioned information between AC and HT are reviewed and discussed in the conversion of biomass waste into HSs in a pioneering way. For biomass waste conversion, a feasible strategy on effective humification processes by combining AC with HT is proposed.