Sulfate reduction behavior in the leachate saturated zone of landfill sites

Effect of microplastics on sulfate reduction in landfill leachate-saturated zone

The sulfate reduction behavior in the leachate-saturated zone of landfills is significantly influenced by the type of microplastics (MPs) and temperature. This study established different temperature conditions based on the leachate-saturated zone of landfills to investigate the sulfate reduction behavior influenced by different types of MPs at different temperatures. The results showed that H2S release was more intense under the influence of polylactic acid (PLA). Additionally, the cumulative H2S release increased with rising temperature. In the PLA group, the cumulative H2S release at 55 °C was 33.2, 2.3, and 1.4 times higher than at 25 °C, 35 °C, and 45 °C, respectively. The sulfate reduction behavior in the PS, PE, and PVC groups is relatively weak, with the cumulative H2S release at 55 °C being only 0.004-0.01 times that of the PLA group. Compared to the influence of temperature, the type of MPs was the main factor contributing to significant differences in the dissimilatory sulfate reduction (DSR) process. The DSR functional genes were more easily enriched in PLA, leading to the release of large amounts of H2S. However, for the assimilatory sulfate reduction (ASR) process, the overall consumption of SO42- for microbial synthesis of cell components was not significantly influenced by the type of MPs. Furthermore, temperature was the main factor contributing to significant differences in the ASR process, with the enrichment ability of MPs for ASR functional genes decreasing as the temperature increased. Additionally, compared to the PS, PE, and PVC, PLA was more conducive to the growth and enrichment of dissimilatory sulfate-reducing bacteria , but the dominant genus responsible for H2S release was determined by temperature. The dominant genus changed from Desulfonatronum and Thermodesulfomicrobium at mid-to-low temperatures (25 °C and 35 °C) to Candidatus_Desulforudis at high temperatures (45 °C and 55 °C) in the PLA group. This study reveals the sulfate reduction behavior under the influence of MPs in the leachate-saturated zone of landfills, providing new insights for landfill management and pollution control, such as controlling the entry of microplastics at the source to reduce the risk of significant H2S release.

Sulfur cycle process accelerates microbial fuel cells driven denitrification system: Low sulfate yield and enrichment of functional microorganisms

The denitrification of dual-chamber microbial fuel cells cathodic chamber driven by sulfur powder has the advantages of economy, efficient and pollution-free. However, the low electron utilization of anodic chamber (ACE) and high sulfate (SO42-) production limit its application. Therefore, the cooperation of calcined pyrite (CP) and γ-FeOOH was proposed to solve the above bottleneck problems (S-CP-γ-FeOOH). The results showed that after adding CP and γ-FeOOH to S system, the nitrate removal rate (NRR) changed from 20.39 ± 0.37 % to 94.11 ± 1.40 %; ACE increased from 11.10 ± 0.76 % to 61.05 ± 7.82 %; and SO42- content decreased by 61.26 %. CP and γ-FeOOH promoted the intra/extracellular electron transfer process. SO42- was reduced to sulfur compounds after γ-FeOOH was added, which improved the electron generation efficiency of the anodic chamber. The addition of CP and γ-FeOOH not only enriched sulfur-oxidizing bacteria and enhanced their metabolic activity, but γ-FeOOH also promoted sulfate-reducing bacteria, all of which improved NRR.

Sustainable removal of gaseous Hg0 using sulfur functionalized biochar: Adsorption experiment and life cycle assessment

Maximizing the sorption capacity of gaseous Hg0 by sulfur-functionalized biochar can lead to increased energy consumption and the production of secondary environmental pollutants such as greenhouse gases. This study evaluates the environmental impact of producing sulfurized biochar through a life cycle assessment (LCA), weighing these impacts against the benefits of enhanced Hg removal efficiencies. The biochar's Hg0 adsorption capacity, which ranges between 3 and 22 μg-Hg0/g-biochar, is influenced by several factors: it increases with higher sulfur loading (0-15 %), higher O2 levels (0-21 %), and longer pyrolysis times (1-5 h). However, it also decreases with increased pyrolysis temperature (100-500 °C). XPS and FT-IR analysis confirm that the sulfur in the biochar primarily exists as elemental sulfur, but each sulfurization condition also resulted in the formation of sulfate, organic sulfur, and sulfone. LCA results indicate that using biochar as a sorbent for Hg0 is carbon-negative when the biochar is disposed of in landfills. Sensitivity analysis showed that increasing mercury adsorption capacity through excessive investment in energy and resources does not necessarily reduce the overall environmental impact. Consequently, when selecting an adsorbent for mercury removal, it is crucial to consider both sorption capacity and environmental impact.

Reduced sulfur compound formation from a leachate-saturated zone under changing temperature conditions

In the leachate-saturation zone of landfills, sulfate reduction is influenced by temperature and electron donors. This study assessed sulfate reduction behaviors under varied electron donor conditions by establishing multiple temperature variation scenarios based on stable temperature fields within the leachate-saturation zone. The results showed that temperature variations altered the microbial community structure and significantly influenced the sulfate reduction process. A more pronounced effect was observed with a temperature difference of 30 °C compared to one of 10 °C. In addition, sulfate reduction was influenced by the presence of electron donors and acceptors. In the middle and low-temperature regions (35 °C and 25 °C), sulfate reduction reaction of acidic organic matter was more significant, while alcohol and saccharide organic substances were more effective in promoting sulfate reduction at high-temperature regions (55 °C). Notably, a 30 °C temperature difference within the leachate-saturation zone significantly altered the microbial community structure, which influenced the sulfate reduction behavior. In particular, Firmicutes and Synergistota played essential roles in mediating the variance in sulfate reduction efficiency with a 30 °C decrease and 30 °C increase, respectively. The results also revealed that temperature changes within landfills were influenced by leachate migration, therefore, controlling leachate recharge can help prevent secondary risks associated with sulfate reduction processes.

Anaerobic microbial metabolism in soil columns affected by highly alkaline pH: Implication for biogeochemistry near construction and demolition waste disposal sites

Construction and demolition wastes (CDWs) have become a significant environmental concern due to urbanization. CDWs in landfill sites can generate high-pH leachate and various constituents (e.g., acetate and sulfate) following the dissolution of cement material, which may affect subsurface biogeochemical properties. However, the impact of CDW leachate on microbial reactions and community compositions in subsurface environments remains unclear. Therefore, we created columns composed of layers of concrete debris containing-soil (CDS) and underlying CDW-free soil, and fed them artificial groundwater with or without acetate and/or sulfate. In all columns, the initial pH 5.6 of the underlying soil layer rapidly increased to 10.8 (without acetate and sulfate), 10.1 (with sulfate), 10.1 (with acetate), and 8.3 (with acetate and sulfate) within 35 days. Alkaliphilic or alkaline-resistant microbes including Hydrogenophaga, Silanimonas, Algoriphagus, and/or Dethiobacter were dominant throughout the incubation in all columns, and their relative abundance was highest in the column without acetate and sulfate (50.7-86.6%). Fe(III) and sulfate reduction did not occur in the underlying soil layer without acetate. However, in the column with acetate alone, pH was decreased to 9.9 after day 85 and Fe(II) was produced with an increase in the relative abundance of Fe(III)-reducing bacteria up to 9.1%, followed by an increase in the methanogenic archaea Methanosarcina, suggestive of methanogenesis. In the column with both acetate and sulfate, Fe(III) and sulfate reduction occurred along with an increase in both Fe(III)- and sulfate-reducing bacteria (19.1 and 17.7%, respectively), while Methanosarcina appeared later. The results demonstrate that microbial Fe(III)- and sulfate-reduction and acetoclastic methanogenesis can occur even in soils with highly alkaline pH resulting from the dissolution of concrete debris.

Sulfate reduction behavior in response to landfill dynamic pressure changes

During the long-term stabilization process of landfills, the pressure field undergoes constant changes. This study constructed dynamic pressure changes scenarios of high-pressure differentials (0.6 MPa) and low-pressure differentials (0.2 MPa) in the landfill pressure field at 25 °C and 50 °C, and investigated the sulfate reduction behavior in response to landfill dynamic pressure changes. The results showed that the pressurization or depressurization of high-pressure differentials caused more significant differences in sulfate reduction behavior than that of low-pressure differentials. The lowest hydrogen sulfide (H2S) release peak concentration under pressurization was only 29.67% of that under initial pressure condition; under depressurization, the highest peak concentration of H2S was up to 21,828 mg m-3, posing a serious risk of H2S pollution. Microbial community and correlation analysis showed that pressure had a negative impact on the sulfate-reducing bacteria (SRB) community, and the SRB community adjusted its structure to adapt to pressure changes. Specific SRBs were further enriched with pressure changes. Differential H2S release behavior under pressure changes in the 25 °C pressure environments were mediated by Desulfofarcimen (ASV343) and Desulfosporosinus (ASV1336), while Candidatus Desulforudis (ASV24) and Desulfohalotomaculum (ASV94) played a key role at 50 °C. This study is helpful in the formulation of control strategies for the source of odor pollution in landfills.

Potential risks of organic contaminated soil after persulfate remediation: Harmful gaseous sulfur release

Persulfate is considered a convenient and efficient remediation agent for organic contaminated soil. However, the potential risk of sulfur into the soil remediation by persulfate remains ignored. In this study, glass bottles with different persulfate dosages and groundwater tables were set up to simulate persulfate remediation of organic pollutants (aniline). The results found sulfate to be the main end-product (83.0%‒99.5%) of persulfate remediation after 10 days. Moreover, H2S accounted for 93.4%‒99.4% of sulfur reduction end-products, suggesting that H2S was the final fate of sulfur. H2S was released rapidly after one to three days at a maximum concentration of 33.0 ppm, which is sufficient to make a person uncomfortable. According to the fitted curve results, H2S concentration decreased to a safe concentration (0.15 ppm) after 20‒85 days. Meanwhile, the maximum concentration of methanethiol reached 0.6 ppm. These results indicated that secondary pollution from persulfate remediation could release harmful gases over a long time. Therefore, persulfate should be used more carefully as a remediation agent for soil contamination.

Microplastic, a possible trigger of landfill sulfate reduction process

The environmental impact of microplastics (MPs) formed from landfill has not been gained enough attention. This research investigated the characteristics of the MPs occurrence in landfills through field sampling. It shows that the MPs abundance in the landfill surface soil and non-landfill areas can reach 3573 items·g-1 and 3041 items·g-1, respectively. The vertical abundance of MPs increases significantly with depth, ranging from 387 to 11,599 items·g-1 with small size (≤10 μm, 65.61 %) and flake or wedge shape (38.48 %). The leachate movement in a longitudinal direction enables MPs to accumulate more easily in the landfill bottom layer with high moisture abundance. The abundance of MPs are significantly correlated with SO42- and S2- content, the two typical metabolic substrate and product of sulfate reduction process. In such heterogeneous environment, this significant correlation is not a random phenomenon in terms of the MPs have known substantial impact on biogeochemical processes. Microplastic is a possible trigger of landfill odor emission related with sulfate reduction. This research could serve as a reference for MPs and odor pollution management in landfills.

Effects of anode materials on nitrate reduction and microbial community in a three-dimensional electrode biofilm reactor with sulfate

Graphite rod corrosion and peeling are serious problems in three-dimensional electrode biofilm reactors (3D-BERs). In this study, titanium rods, titanium suboxide-coated titanium rods and graphite rods were used as anodes to investigate the effect of anodic materials on the electrochemical and bioelectrochemical reduction of nitrate and sulfate. The results showed that the reactor with the titanium suboxide-coated titanium rod anode (3D-ER-T) exhibited a stable NO3--N removal efficiency (46%-95%) with a current range of 160-320 mA in the electrochemical reduction process. In the bioelectrochemical reduction, the removal efficiencies of NO3--N and SO42- and nitrogen selectivity in the 3D-BER with titanium suboxide-coated titanium rod anode (3D-BER-T) were higher than those in the 3D-BER with titanium suboxide-coated graphite rod anode (3D-BER-G). The removal efficiencies of NO3--N and SO42- and nitrogen selectivity were 92%, 43% and 86%, respectively, in 3D-BER-T under 320 mA and HRT 12 h. Anode materials affected the microbial community. Hydrogenophaga and Dethiobacter were the dominant bacteria in 3D-BER-T, while OPB41 and Sulfurospirillum were dominant in 3D-BER-G. Nitrate and sulfate were effectively removed in 3D-BER-T by the synergistic work of electrochemical reduction, bioelectrochemical reduction and indirect electrochemical reduction. The resupply/reserve mode of the electron donor promoted the load of shock resistance of 3D-BER-T via the sulfur cycle. Titanium suboxide coating could significantly enhance the anti-corrosion ability of matrix anodes.

Sulfate reduction behavior in response to changing of pressure coupling with temperature inside landfill

The behavior of sulfate reduction, which was the source of hydrogen sulfide (H2S) odor, was investigated under changing pressure and temperature conditions inside landfills. The results showed that the release of H2S and methyl mercaptan (MM) was significantly inhibited at 25 °C and 50 °C under pressure, and the highest H2S and MM concentrations released were only 0.82 %-1.30 % and 1.87 %-4.32 % of atmospheric pressure, respectively. Analysis of the microbial community structure and identification of sulfate-reducing bacteria (SRB) revealed that temperature significantly altered the microbial community in the landfill environment, while pressure inhibited some bacteria and induced the growth and reproduction of specific bacteria. Key SRB (Desulfosporosinus-ASV212, Desulfitibacter-ASV1744) mediated differentiated sulfate reduction behavior in the pressure-bearing environment at 25 °C, while key SRB (Dethiobacter-ASV177, Desulfitibacter-ASV2355 and ASV316) were involved at 50 °C. This study provides a theoretical basis for the formulation of landfill gas management and control strategies.

Quantification of indicator and pathogenic bacteria in manures and digestates from three agricultural biogas plants over a one-year period

Interest in the conversion of manure in biogas via anaerobic digestion (AD) is growing, but questions remain about the biosafety of digestates. For a period of one year, we monitored the impact of three mesophilic agricultural biogas plants (BPs) mainly fed with pig manure (BP1, BP3) or bovine manure (BP2) on the physicochemical parameters, the composition of the microbial community and the concentration of bacteria (E. coli, enterococci, Salmonella, Campylobacter, Listeria monocytogenes, Clostridium perfringens, Clostridium botulinum and Clostridioides difficile). The BP2 digestate differed from those of the two other BPs with a higher nitrogen content, more total solids and greater abundance of Clostridia MBA03 and Disgonomonadacea. Persistence during digestion ranked from least to most, was: Campylobacter (1.6 to >2.9 log10 reduction, according to the BP) < E. coli (1.8 to 2.2 log10) < Salmonella (1.1 to 1.4 log10) < enterococci (0.2 to 1.2 log10) and C. perfringens (0.2 to 1 log10) < L. monocytogenes (-1.2 to 1.6 log10) < C. difficile and C. botulinum (≤0.5 log10). No statistical link was found between the reduction in the concentration of the targeted bacteria and the physicochemical and operational parameters likely to have an effect (NH3, volatile fatty acids and total solids contents, hydraulic retention time, presence of co-substrates), underlining the fact that the fate of the bacteria during mesophilic digestion depends on many interacting factors. The reduction in concentrations varied significantly over the sampling period, underlining the need for longitudinal studies to estimate the impact of AD on pathogenic microorganisms.

Investigation on the microbial community of an accelerating stabilization landfill by aeration engineering

The microbial community of the landfill undergoing aerobic stabilization process by aeration engineering was investigated. The municipal solid wastes (MSWs) were sampled from two aeration well sites with different landfill temperatures (65.5°C and 41.7°C) under higher and lower stabilization level. The physical component, chemical property, and microbial population of MSWs were analyzed and compared. The result showed that the phylum Firmicutes was dominant in the aerobic landfill; and the genus Weissella and Syntrophaceticus were more abundant in high, and low temperature site, respectively. The bacterial distribution showed difference on two temperature sites and four landfill depths, mainly affected by the ammonia-nitrogen and moisture content of MSWs. The ecological profiles of the microorganisms responded the aeration engineering were predicted. The anaerobic hydrolytic and acetogenic microorganisms were decreased in abundance, while the facultative Lactobacillus increased when the landfill under a higher stabilization level. The function abundances of methane oxidation, sulfide oxidation, and aerobic chemoheterotrophy were enriched by aeration engineering, which was the microbial mechanism for accelerating the stabilization process of landfill.

Containment of sulfate in leachate as gypsum (CaSO4·2H2O) mineral formation in bio-cemented sand via enzyme-induced carbonate precipitation

Enzymatically induced carbonate precipitation (EICP) using urea hydrolysis is a well-known bio-cementation process that not only promotes the precipitation of calcium carbonate (CaCO₃) but can provide excess calcium cations for further reaction depending on the substrate constituents and reaction stage. This study presents the EICP recipe to contain sulfate ions in landfill leachate sufficiently using remaining calcium cations and a series of tests were conducted to validate its ability to retain sulfates. The reaction rate for 1 M CaCl₂ and 1.5 M urea was identified by controlling the purified urease content and the curing time of the EICP process. The results showed that 0.3 g/L of purified urease produced 46% CaCO₃ and reduced sulfate ions by 77% after 3 days of curing. The shear stiffness in EICP-treated sand was enhanced 13 times by CaCO₃ precipitation followed by 1.12 times increment due to subsequent precipitation of gypsum (CaSO₄·2H₂O) crystals implying sulfate containment. A cost-efficient EICP treatment using soybean crude urease instead of lab-grade purified urease exhibited lower sulfate removal efficiency (i.e., 18%) with only nominal formation of gypsum in the EICP-treated sand. The addition of gypsum powder was effective in increasing sulfate removal by 40% when soybean crude urease was used for EICP.

Addition of exogenous microbial agents increases hydrogen sulfide emissions during aerobic composting of kitchen waste by improving bio-synergistic effects

The effect of microbial agents (MA) on hydrogen sulfide (H₂S) emissions in the compost is still a controversial issue. This study examined the effects and microbial mechanisms of MA on H₂S emissions during the composting of kitchen waste. The results showed that MA addition can promote sulfur conversion to elevate H₂S emissions by approximately 1.6 ∼ 2.8 times. Structural equations demonstrated that microbial community structure was the dominant driver on H₂S emissions. Agents reshaped the compost microbiome, showing more microorganisms participated in sulfur conversion, and enhanced the connection between microorganisms and functional genes. The relative abundance of keystone species associated with H₂S emissions increased after adding MA. Particularly, the sulfite and sulfate reduction processes were intensified, as evidenced by an increasing in the abundance and pathways cooperation of sat and asrA after MA addition. The outcome provides deeper insights into MA on regulating the mitigation of H₂S emissions in compost.

Sulfate reduction behavior in pressure-bearing leachate saturated zone

Attention should be paid to the sulfate reduction behavior in a pressure-bearing leachate saturated zone. In this study, within the relative pressure range of 0-0.6 MPa, the ambient temperature with the highest sulfate reduction rate of 50°C was selected to explore the difference in sulfate reduction behavior in a pressure-bearing leachate saturated zone. The results showed that the sulfate reduction rate might further increase with an increase in pressure; however, owing to the effect of pressure increase, the generated hydrogen sulfide (H₂S) could not be released on time, thereby decreasing its highest concentration by approximately 85%, and the duration extended to about two times that of the atmospheric pressure. Microbial community structure and functional gene abundance analyses showed that the community distribution of sulfate-reducing bacteria was significantly affected by pressure conditions, and there was a negative correlation between disulfide reductase B (dsrB) gene abundance and H₂S release rate. Other sulfate reduction processes that do not require disulfide reductase A (dsrA) and dsrB genes may be the key pathways affecting the sulfate reduction rate in the pressure-bearing leachate saturated zone. This study improves the understanding of sulfate reduction in landfills as well as provides a theoretical basis for the operation and management of landfills.

Arsenic methylation behavior and microbial regulation mechanisms in landfill leachate saturated zones

Arsenic (As) is a potential contaminant in landfill. As methylation has been considered as a detoxification mechanism to address this problem. In this study, microcosm incubation was used to simulate leachate saturation zone (LSZ) and other landfill zones scenarios to explore the As methylation behavior. The As methylation rate of LSZ is 11.75%, which is slightly higher than that of other zone of landfill (10.87%). However, the difference was greatly increased by the addition of moderate content of As(III), with values of 29.25% in LSZ and 4.61% in other zones. The microbial community structure varied greatly between zones and a higher abundance of arsM was observed in the LSZ, which enhanced As methylation. Based on the annotated As functional genes from the KEGG database, the microbial As methylated pathway was summarized. Higher relative abundances of gst and arsC promoted the formation of more trivalent As substrates, stimulating the methylation behavior for As detoxification in the LSZ. According to microbial arsM contribution analysis, unclassified_p__Gemmatimonadetes, unclassified_p__Actinobacteria, unclassified_o_Hydrogenophilales, and Intrasporangium were the primary As methylation bacteria in the LSZ, while unclassified_f__Chitinophagaceae and unclassified_c_Gammaproteobacteria were the primary contributors in other landfill zones. These results highlight the specific As methylation process in the LSZ, and these insights could improve the control of As contamination in landfill sites.

Unravelling microbial drivers of the sulfate-reduction process inside landfill using metagenomics

Hydrogen sulfide (H₂S) is one of the common landfill odor. This research demonstrates that the sulfate transformation behavior is significantly enhanced during the landfill process, accompanied by a shift in microbial structure. The relative abundance of dissimilatory sulfate reduction (DSR) and thiosulfate oxidation by SOX (sulfur-oxidation) complex gradually decreases through the landfill processes while the assimilatory sulfate reduction (ASR) demonstrates the opposite behavior. The major module for landfill sulfate reduction is ASR, accounting for 31.72% ± 2.84% of sulfate metabolism. Based on the functional genes for the sulfate pathway, the drivers for sulfate biotransformation in landfills were determined and further identified their contribution in the sulfate metabolism during landfill processes. Pseudomonas, Methylocaldum, Bacillus, Methylocystis and Hyphomicrobium were the top 5 contributors for ASR pathway, and only one genus Pseudomonas was found for DSR pathway. Among the 26 high-quality metagenome-assembled genomes of sulfate functional species, 24 were considered novel species for sulfuric metabolism. Overall, this study provides unique insight into the sulfate transformation process related to the H₂S odor control in landfill management.

Localized intensification of arsenic methylation within landfill leachate-saturated zone

Leachate-saturated zone (LSZ) of landfills is a complicated biogeochemical hotspot due to the continuous input of electron donors and acceptors from the top refuse layer with leachate migration. In this study, the methylation behavior of the arsenic (As) was investigated. The results indicate that As-methylation processes are influenced by temperature fields in LSZ. The dimethylarsinic acid biotransformation capability can be enhanced with an increase in temperature. Microbial diversity, quantification of functional gene (arsM), and co-occurrence network analysis further characterized the drivers of As methylation in LSZ. As-biogeochemical cycle pathways, as well as As-functional gene distribution among different temperature fields, were modeled on the basis of KEGG annotation. Binning analysis was further employed to assemble As-methylated metagenomes, enabling the identification of novel species for As methylation in landfills. Then, 87 high-quality draft metagenome-assembled genomes (MAGs) were reconstructed from LSZ refuse samples; nearly 15 % (13 of 87) belonged to putative As-methylates functional MAGs. Combined with the model of the As-biogeochemical cycle, nine putative functional species could complete methylation processes alone. The findings of this study highlighted the temperature influence on the As-methylation behavior in LSZ and could facilitate the management of As contamination in landfills.

Dissimilatory sulfate reduction in the cake layer of a full-scale anaerobic dynamic membrane bioreactor for hotel laundry wastewater treatment: Bacterial community and functional genes

Dissimilatory sulfate reduction (DSR) in cake layer of full-scale anaerobic dynamic membrane bioreactor for treating hotel laundry wastewater was studied. Change (Δ) of sulfate concentration (ΔSO₄^2-) was positively correlated to dynamic cake layer (DCL) development, while ΔS^2- was negatively correlated. ΔSO₃^2- and ΔS_{organic sulfur} remained around 1.5-2.5 and 1.2-2.3 mg-S/L, respectively. Thus, DSR was the predominant sulfate reduction process in DCL. 33 binned genomes from DCL microbiome samples possessed one or more DSR functional genes. But only four binned genomes possess all functional genes, and thus can achieve complete DSR. However, no significant variations of these DSR bacteria was obseared during DCL development. Metagenomic analysis predicted that sulfate reduction in DCL was mainly carried out by collaborations between bacteria with incomplete DSR pathways. Among which, sulfite → sulfide by dissimilatory-sulfite-reductase expression bacteria was the key process. Overall results suggested that controlling dissimilatory-sulfite-reductase activities could prevent sulfide buildup in the effluent.

Sulfate-reduction behavior in waste-leachate transition zones of landfill sites

The sulfate reduction behavior of the waste-leachate transition zone of landfill was investigated at different temperatures and moisture contents. Marked differences in the sulfate reduction behavior were observed in the waste-leachate transition zone. The highest H₂S concentration was observed when the solid-to-liquid ratio was 1:3 at both temperatures. Although more leachate led to higher H₂S concentrations, the solid-to-liquid ratio was likely of subordinate significance compared with temperature. The microbial community was more unstable at 50 °C and more extensive mutualistic interactions among bacteria were observed, resulting in SRB showing a more violent response to changes in the solid-to-liquid ratio. At 25 °C, it's the opposite. A temperature of 25 °C was suitable for most SRB (such as Desulfomicrobium and Desulfobulbus), while some specific SRB that did not contain the functional genes (such as Dethiobacter and Anaerolinea) played a pivotal role in the significant differences in sulfate reduction behavior observed at 50 °C. This study provides a theoretical basis for controlling the release of H₂S from landfill.

Evolution of sulfate reduction behavior in leachate saturated zones in landfills

The sulfate reduction behavior of the landfill leachate saturated zone under different temperatures was investigated. The results showed that temperature had significant effects on sulfate reduction behavior. The sulfate reduction efficiency was the highest at high temperatures (55 °C and 45 °C), followed by mesophilic temperature (35 °C). Normal temperature 25 °C was far less effective than 55 °C, 45 °C and 35 °C. High abundances of aprA and dsrA genes were distributed under high temperatures. Through indicator species analysis and functional comparison, some key taxa were identified as putative key genera for sulfate reduction. Under high temperature, Paenibacillus could effectively degrade dimethyl sulfide. DsrAB is present in the genome of Tissierella. Gordonia, Syntrophomonas, and Lysinibacillus under mesophilic temperature indicates the potential of these organisms to degrade heterogenous biomass, environmental pollutants or other natural polymers with slow biodegradation. This microbial function is similar to that of the putative key genera under normal (25 °C) temperature. Most of the putative key genera belong to Firmicutes, Proteobacteria and Myxococcota. This study provides theoretical support for the control of hydrogen sulfide release from landfills.

Microbial characteristics of the leachate contaminated soil of an informal landfill site

Because informal landfills are not constructed in a regulated manner, they will inevitably become a source of leachate pollution to the surrounding environment over time. Microbes are an important part of the soil system, playing a vital role in maintaining the normal functionality of soil. This study investigated the microbial composition and co-occurrence pattern in the leachate contaminated soil of an informal landfill site. The landfill leachate underwent horizontal and vertical migration through the contaminated soil, resulting in significant differences in the microbial compositions of horizontal surface soil (CS) and vertical subsurface soil (DS and ES) compared to uncontaminated soil (S). The microbial diversity of CS, DS, and ES was lower than that of S. Due to the migration of landfill leachate, the microbial composition of the surface soil was substantially changed. The dominant phyla in S included Proteobacteria (26.88%), Chloroflexi (23.68%), Actinobacteroita (17.36%), and Acidobacteroita (16.86%), but in contaminated soils, Firmicutes (35.27-86.68%) were the dominant bacteria. A network analysis indicated that Bacilli, Clostridia, and Thermacetogeniazai of the Firmicutes were the keystone taxa and played a vital role in maintaining the stability of the soil ecosystem. A functional annotation of prokaryotic taxa (FAPROTAX) analysis showed that the microbes involved in the C-, N-, and S-cycles in contaminated soil were significantly different to those in uncontaminated soil. The proportion of (aerobic)-chemoheterotrophy and cellulolysis functional communities in contaminated soils was significantly reduced, while there was an increase in functional communities, such as anammox and denitrification, which are not conducive to soil nitrogen fixation. This negatively affected the maintenance of normal soil ecological functions. This study identified the microbial characteristics in leachate contaminated soil and the results will be beneficial for the remediation of contaminated soil in informal landfill sites.

Emerging onsite electron donors for advanced nitrogen removal from anammox effluent of leachate treatment: A review and future applications

Partial nitrification-anammox process is promising in leachate treatment, but the 11% residue nitrate limits the total nitrogen removal efficiency. Denitrification or partial denitrification and anammox are both practical polishing processes of anammox effluent, requiring extra electron donors. Fortunately, there are organic matter, sulfide and methane in leachate or produced by leachate treatment, which can serve as onsite electron donors. In this review, the mechanisms and processes using these three kinds of electron donors for residue nitrate reduction in anammox effluent of leachate are systematically summarized and discussed. It can be concluded that, biodegradable organic matter is an effective electron donor, sulfide is a promising electron donor, methane is a potential electron donor. Two possible applications in future based on anammox treatment of fresh and mature leachate using sulfide and methane as onsite electron donors are proposed. Through sulfide reutilization, energy-saving with about 14% of aeration reduction can be achieved.

The nutrient-improvement bacteria selected by Agave lechuguilla T. and their role in the rhizosphere community

Agave lechuguilla has one of the widest distributions among other agave species in the Chihuahuan Desert. Their capacity to grow in poorly developed soils and harsh conditions has been related to their association with plant growth-promoting rhizobacteria. In this work, we explored how soil properties and plant growth stage influence the composition of the rhizobacterial communities, their interactions, and the enzymatic activity and abundance of nitrogen-fixing bacteria and organic phosphorus-mineralizing bacteria in two subregions of the Chihuahuan Desert. We found that mature plants of lechuguilla stimulated the activity and abundance of nutrient-improvement rhizobacteria, and these soil samples had a higher content of total organic carbon, ammonium (NH4) and nitrite + nitrate (NO2+NO3). Nutrient availability seems to be an essential driver of the bacterial community's structure since the genera with more connections (hubs) were those with known mechanisms related to the availability of nutrients, such as env. OPS17 (Bacteroidetes), Gemmatimonadaceae uncultured, S0134terrestrial group, BD211terrestrial group (Gemmatimonadetes), Chthoniobacteracea and Candidatus Udaeobacter (Verrucomicrobia). This work shows that the late growth stages of lechuguilla recruit beneficial bacteria that favor its establishment and tolerance to harsh conditions of the arid lands.

The synergistic effect of rumen cellulolytic bacteria and activated carbon on thermophilic digestion of cornstalk

To explore the bioaugmentation of rumen cellulolytic bacteria (RCB) and activated carbon (AC) on thermophilic digestion of cornstalk, biochemical methane potential tests were carried out. Adding RCB or AC can improve methane production, while simultaneous existence of AC (10 g/L) and RCB (5%) obtained the best performance. The maximum cellulose degradation rate, methane production rate and methane yield were 66.92%, 32.2 L/(kgVS·d), and 144.9 L/kgVS, which increased by 30.23%, 51.17%, and 20.35% compared with control group. The cellulolytic and fermentative bacteria (Hydrogenispora), syntrophic acetate-oxidizing bacteria (norank_o_MBA03), and hydrogenotrophic Methanothermobacter were crucial for thermophilic digestion of cornstalk. The enhancement of AC was due to the enrichment of Hydrogenispora and Methanothermobacter, while RCB can increase the abundance of cellulolytic bacteria (Halocella and norank_o_M55-D21) and mixotrophic Methanosarcina. The synergetic effect of AC and RCB owing to the enriched cellulolytic bacteria, the enhanced syntrophic acetate oxidation and the concentrated carbon metabolic flow to methane.

Application of ultrasound irradiation in landfill leachate treatment

Landfilling is known to be the most widely used method in municipal solid waste management in many countries. Landfill leachate containing different recalcitrant compounds are recognized to contaminate the soil and water and accordingly threat both the human health and environment. A variety of chemical and biological methods have recently been employed for landfill leachate treatment, one of which is the ultrasonic process. In this review, the efficiency of the ultrasound-assisted method for leachate treatment, factors influencing the treatment process are studied by defining a search protocol. The results showed that ultrasound can reduce pollutants by creating cavitation, microstreaming, and microturbulence. Increasing turbidity in initial of irradiation time and increasing the cost of treatment are the disadvantages of using ultrasonic in leachate treatment. Moreover, ultrasound-assisted method leads to improve the leachate quality, especially the COD/BOD. Therefore, ultrasound can be considered a good pretreatment for biological processes. Although, the application of this process in combination with other treatment processes such as biological processes and advanced oxidation increases the efficiency of leachate treatment, its efficiency depends on several factors such as exploitation features and leachate quality.

An integrated strategy to enhance performance of anaerobic digestion of waste activated sludge

Anaerobic digestion (AD) is an essential process in wastewater treatment plants as it can reduce the amount of waste activated sludge (WAS) for disposal, and also enables the recovery of bioenergy (i.e. methane). Here, a new pretreatment method to enhance anaerobic digestion was achieved by treating thickened WAS (TWAS) with ferric (as FeCl₃) and nitrite simultaneously for 24-hour at room temperature. Biochemical methane potential tests showed markedly improved degradability in the pretreated TWAS, with a relative increase in hydrolysis rate by 30%. A comparative experiment with the operation of two continuous-flow anaerobic digesters further demonstrated the improvement in biogas quantity and quality, digestate disposal, and phosphorus recovery in the experimental digester. The dosed FeCl₃ (i.e. ~6 mM) decreased the pH of TWAS to ~5, which led to the formation of free nitrous acid (FNA, HNO₂) at parts per million levels (i.e. ~6 mg N/L), after dosing nitrite at 250 mg NO₂^--N/L. This FNA treatment caused a 26% increase in methane yield and volatile solids destruction, 55% reduction in the viscosity of sludge in digester, and 24% less polymer required in further digestate dewatering. In addition, the dosed Fe(III) was reduced to Fe(II) which precipitated sulfide and phosphorus, leading to decreased hydrogen sulfide concentration in biogas, and increased percentage of vivianite in the total crystalline iron species in digested sludge. Our study experimentally demonstrated that combined dosing of FeCl₃ and nitrite is a useful pretreatment strategy for improving anaerobic digestion of WAS.