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Research on Fe3+ reduction coupled to anaerobic ammonium oxidation (Feammox) and its associated processes in the moderately low-dissolved oxygen (DO) urban natural environment is lacking. To clarify seasonal and spatial variations in Feammox, iron-reducing, and anaerobic ammonium oxidation (anammox) in urban green spaces, we examined the physicochemical indices and functional genes acd, acm, Geo, and hszA in topsoils and wetland soils across four seasons. Further, we performed 16S rRNA high-throughput sequencing. The Feammox-related gene acm was detected in all topsoil samples. Season and habitat affected soil physicochemical indices influencing gene distributions. Moisture content (45.3%) and Fe3+ (13.3%) mediated genetic changes. Competition between Feammox and iron-reducing bacteria (IRB) lowered the distributions of acd and acm in summer and increased these in winter. The acd and acm distributions were higher in wetland soil than in forestland soil. The dominant phyla, Nitrospirota, Actinobacteriota, and Desulfobacterota, correlated positively. Network analysis revealed that the relative abundances of acd, Geo, and hszA correlated positively with Flavobacterium and Thermomonas, Subgroup_2, and Candidatus_Solibacter, respectively. Feammox, iron-reducing, and anammox microorganisms correlated positively but competition existed between certain taxa. Candidatus, Sphingomonas, and Geobacter are linked to Feammox, iron reduction, and anammox. Here, we demonstrated the theoretical feasibility of developing Feammox-based nitrogen removal technology under moderately low-DO conditions, providing a reference for elucidating the ecological contribution of Feammox in an urban green heart.

BACKGROUND: Animal manure is one of the significant sources of antibiotic resistance genes (ARGs) and an emerging pollutant that poses a threat to human beings. Composting is a common method of treating manure. The effect of composting on the ARGs in manure has become an active research area in recent years. In this study, three common aeration strategies were used to study the removal of ARGs and to clarify their microbial mechanism during composting, i.e. forced aeration (with three ventilation rates), turn windrow and static pile. RESULTS: Results showed that the variation pattern of ARGs was highly dependent on the succession of the microbial community, and environmental factors accounted for 44% of the variation. Most ARGs (tetW/tetO/tetH, qnrS, ermB and blaTEM) could be significantly reduced after composting for 77 days, but sulfonamide resistance genes (sulI/sulII) and the integrase gene (intI) were highly enriched, particularly in forced aeration treatment. These enrichments were closely correlated with an increase in the genera belonging to Actinobacteria, Proteobacteria and Bacteroidetes and a decrease in the genera affiliated with Firmicutes. CONCLUSIONS: The temporal variations in ARGs were consistent under different aeration treatments. Further study should focus on optimizing the composting conditions to reduce recalcitrant ARGs. © 2019 Society of Chemical Industry

BACKGROUND: Composting is a significant source of nitrous oxide (N₂O) emissions. Although numerous studies have correlated quantities of functional genes with N₂O production during composting, information is lacking about the variations of related microbial community structures. This study investigates the responses of ammonia oxidizing and nirK‐type denitrifying bacteria in terms of both community structures and quantities relating with N₂O emissions during pig manure composting with different techniques. RESULTS: The techniques (forced aeration, turn windrow and static pile) significantly affected the N₂O emissions during composting. The forced aeration treatment had the highest cumulative N₂O emission rate which accounted for 2.4% of the initial nitrogen. Terminal‐restriction fragment length polymorphism (T‐RFLP) and clone sequencing analyses of bacterial amoA and nirK genes showed the variations in community structures of ammonia oxidizing and nirK‐type denitrifying bacteria under different composting techniques. Co‐existence of Nitrosomonas spp. with 45‐bp terminal restriction fragment (T‐RF) of the amoA gene and denitrifier with 189‐bp T‐RF of the nirK gene could contribute to the substantial emissions of N₂O in the forced aeration technique. CONCLUSIONS: Results from this study highlight the role of microbial community structure influencing N₂O emissions and provide unique insights for further understanding of the mechanisms of N₂O emissions among different composting techniques. © 2019 Society of Chemical Industry

Sugarcane bagasse as a biomass solid waste has good prospects as a carbon source for biological wastewater treatment. However, it has rarely been investigated for aerobic denitrification (AD). Herein, we investigated its carbon release performance and constructed a bagasse-loaded sequencing batch biofilm reactor (SBBR) to investigate the feasibility of sugarcane bagasse as a carbon source and filler for AD bacteria to treat wastewater with low carbon–nitrogen ratios (C/N). Results showed that chemical oxygen demand (COD) leaching from sugarcane bagasse was 418.07 ± 17.05 mg/g; high-temperature and high-pressure operation had no significant effect on the carbon release performance of the bagasse. A shake-flask experiment revealed that adding sugarcane bagasse significantly enhanced the AD flora denitrification effect in low C/N wastewater; the removal process of NO3−–N by AD flora followed first-order kinetics. In the SBBR inoculated with AD flora, biofilm formation on the bagasse surface was evident; the NO3−–N removal rate reached 20.20 ± 4.27% after 28 operation cycles, which was significantly higher than that of the control sequencing batch reactor during the same period, and the effluent COD stabilized below 50 mg/L. The results provide a reference for AD application in the practical wastewater treatment and biomass resource utilization of sugarcane bagasse.

The substrate to inoculum (S/I) ratio is crucial for the rapid start-up of solid-state anaerobic digestion (SS-AD) systems. In this study, the performance of methane production and microbial community structure were evaluated during co-digestion of rape straw (RS) and dairy manure (DM) at different S/I ratios (2:3, 1:1, 2:1, 3:1, and 4:1) in batch hemi-solid-state anaerobic digestion (HSS-AD) tests. The highest methane yield of 209.1 mL/g VSadded and highest volumetric methane production of 0.4 L/(L·d) were achieved at S/I ratios of 2:3 and 2:1, respectively. Lower S/I ratios (1:2, 1:1, and 2:1) steadily produced biogas throughout the AD period, while higher S/I ratios (3:1 and 4:1) failed to produce biogas during the initial stage of AD because of excess accumulation of volatile fatty acids and low pH. The predominant bacteria and archaea in stable digesters were Firmicutes and acetoclastic Methanosaeta, respectively, while Bacteroidetes predominated and the relative abundance of hydrogenotrophic Methanobacterium increased significantly in acidic digesters. Amounts of bacteria and archaea were inhibited in acidic digesters. Our results provide useful information for enhancing efficient methane production and advancing the understanding of the microbiome in HSS-AD of RS and DM at different S/I ratios.

This study compared 4 different struvite crystallization process (SCP) during the composting of pig feces. Four combinations of magnesium and phosphate salts (H3PO4+MgO (PMO), KH2PO4+MgSO4 (KPM), Ca(H2PO4)2+MgSO4 (CaPM), H3PO4+MgSO4 (PMS)) were assessed and were also compared to a control group (CK) without additives. The magnesium and phosphate salts were all supplemented at a level equivalent to 15% of the initial nitrogen content on a molar basis. The SCP significantly reduced NH3 emission by 50.7-81.8%, but not the N2O. Although PMS group had the lowest NH3 emission rate, the PMO treatment had the highest struvite content in the end product. The addition of sulphate decreased CH4 emission by 60.8-74.6%. The CaPM treatment significantly decreased NH3 (59.2%) and CH4 (64.9%) emission and yielded compost that was completely matured. Due to its effective performance and low cost, the CaPM was suggested to be used in practice.

In this study, complicated model sulfur compounds in crude oil were biodesulfurized in a batch process by microbial consortium enriched from oil contaminated soil. Dibenzothiophene (DBT) was selected as model sulfur compounds. Ultrasonic radiation was used to pre-oxidize the model sulfur compounds before the biodesulfurization (BDS) process. The enhancement mechanism of ultrasound pre-oxidation (UPO) on the biodesulfurization of DBT was investigated. The effects of initial conditions on the biodesulfurization of DBT in UPO/BDS system such as solution initial pH, DBT initial concentration, sulfur source, biocatalyst initial concentration, and incubation temperature were discussed. The results show that the application of UPO before BDS procedure significantly improved the efficiency of the biodesulfurization and allowed sulfur removal in shorter time through oxidizing DBT to DBT sulfone, resulting in shortening the "4S" pathway for biodesulfurization from 4 steps to 2 steps, enhancement in reaction velocity and enzyme-substrate affinity as well as reduction in substrate inhibition. The concentration of 2-HBP increased fast with the use of ultrasound pre-oxidation, which was dependent on solution initial pH, DBT initial concentration, sulfur source, biocatalyst initial concentration, and incubation temperature.

The aim of this study was to uncover ways to mitigate greenhouse gas (GHG) emissions and reduce energy consumption during the composting process. We assessed the effects of different aeration rates (0, 0.18, 0.36, and 0.54 L/(kg dry matter (dm)·min)) and methods (continuous and intermittent) on GHG emissions. Pig feces and corn stalks were mixed at a ratio of 7:1. The composting process lasted for 10 weeks, and the compost was turned approximately every 2 weeks. Results showed that both aeration rate and method significantly affected GHG emissions. Higher aeration rates increased NH3 and N2O losses, but reduced CH4 emissions. The exception is that the CH4 emission of the passive aeration treatment was lower than that of the low aeration rate treatment. Without forced aeration, the CH4 diffusion rates in the center of the piles were very low and part of the CH4 was oxidized in the surface layer. Intermittent aeration reduced NH3 and CH4 losses, but significantly increased N2O production during the maturing periods. Intermittent aeration increased the nitrification/denitrification alternation and thus enhanced the N2O production. Forced aeration treatments had higher GHG emission rates than the passive aeration treatment. Forced aeration accelerated the maturing process, but could not improve the quality of the end product. Compared with continuous aeration, intermittent aeration could increase the O2 supply efficiency and reduced the total GHG emission by 17.8%, and this reduction increased to 47.4% when composting was ended after 36 days.

Six ARGs (tetX, sul1, qnrS, blaTEM, ermB and intl1) were quantified by qPCR, along with concentrations of inorganic nitrogen (ammonia, nitrite, nitrate), total phosphorous (TP) and chemical oxygen demand (COD). The sewage treatment facilities had elimination effects on the six target genes; absolute abundance decreased from 104–107 copies/mL in the influent to 103–105 copies/mL in effluent, and the removal efficiencies were 74.27–96.51%; the highest removal performance was for tetX. The main treatment units for eliminating ARGs were the aeration tank and the secondary sedimentation tank. Absolute abundances of ARGs in the effluent and downstream water were 3.24–18.83 and 1.86–8.55 times higher than that in the upstream river, respectively. The absolute abundances of different target ARGs were positively correlated (R = 0.6762 ± 0.1777), indicating similar elimination mechanisms, and a positive correlation between ARGs and ammonia nitrogen (R = 0.5025 ± 0.2711). Raw wastewater contained numerous ARGs, which were partially removed by the WWTP. However, there remained a high absolute abundance of ARGs in effluent, causing an increase in water-phase ARGs in the receiving river. Hence, effluent was an important pollution point source for the receiving river.

The use of biological pretreatment in anaerobic digestion systems has some potential; however, to date, these methods have not been able to effectively increase methane production of lignocellulose of municipal solid waste (LMSW). In this study a thermophilic microbial consortium (MC1) was used as a pretreatment method in order to enhance biogas and methane production yields. The results indicated that sCOD concentration increased significantly in the early stages of pretreatment. Ethanol, acetic acid, propionic acid, and butyric acid were the predominant volatile organic products in the MC1 hydrolysate. Biogas and methane production yields of LMSW significantly increased following MC1 pretreatment. In addition, the methane production rate of the treated LMSW was greater than that observed from the untreated sample.

Struvite crystallization (SCP) is combined with a nitrification inhibitor (dicyandiamide, DCD) to mitigate the NH3 and N2O emission during composting. The MgO and H3PO4 were added at a rate of 15% (mole/mole) of initial nitrogen, and the DCD was added at rates of 0%, 2.5%, 5.0%, 7.5% and 10% (w/w) of initial nitrogen respectively. Results showed that the combination use of SCP and DCD was phytotoxin free. The SCP could significantly reduce NH3 losses by 45-53%, but not the DCD. The DCD significantly inhibits nitrification when the content was higher than 50mgkg(-1), and that could reduce the N2O emission by 76.1-77.6%. The DCD degraded fast during the thermophilic phase, as the nitrification will be inhibited by the high temperature and high free ammonia content in this stage, the DCD was suggested to be applied in the maturing periods by 2.5% of initial nitrogen.

The two-phase anaerobic co-digestion of cassava dregs (CD) with pig manure (PM) was evaluated using four sequencing batch reactors (SBRs) and a continuously stirred tank reactor (CSTR). The effect of seven different PM to CD volatile solid ratios (10:0, 8:2, 6:4, 5:5, 4:6, 2:8 and 0:10) on the acidification phase was investigated. Results indicated the concentrations of soluble chemical oxygen demand, NH 4 –N and volatile fatty acids increased substantially at seven ratios. Co-acidification of PM and CD performed well. Methanogenic fermentation of the acidification products at seven ratios was steady in CSTR. The highest methane yield and VS removal of 0.352 m 3 /kg VS added and 68.5% were achieved at PM:CD (4:6). The microbial population in CSTR was analyzed using molecular methods. Findings revealed that bacteria such as Firmicutes and Bacteroidetes , archaea such as Methanobacteriales and Methanomicrobiales were advantageous populations. Co-digestion of PM and CD supported higher quantity and diversity of methanogens.