Isolation and application of a mixotrophic sulfide-oxidizing Cohnella thermotolerans LYH-2 strain to sewage sludge composting for hydrogen sulfide odor control

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.

Cellulosimicrobium sp. Strain L1: A Study on the Optimization of the Conditions and Performance of a Combined Biological Trickling Filter for Hydrogen Sulfide Degradation

Sulfide is a toxic and hazardous substance in the agricultural environment, which can cause damage to humans and livestock when exposed to large amounts of air. In this study, we performed one-factor optimization of the culture conditions and culture fractions of the Cellulosimicrobium sp. strain L1 and combined it with a biological trickling filter cell for the degradation of hydrogen sulfide for 24 consecutive days. The degradation effect of strain L1 and the biological trickling filter (BTF) on hydrogen sulfide was investigated, and the changes in intermediate products in the degradation process were briefly analyzed. The results showed that strain L1 had the highest conversion efficiency when incubated with 3 g/L sucrose as the carbon source and 1 g/L NH4Cl as the nitrogen source at a temperature of 35 °C, an initial pH of 5, and a NaCl concentration of 1%. The concentration of thiosulfate increased and then decreased during the degradation process, and the concentration of sulfate increased continuously. When strain L1 was applied to the biological trickling filter, it could degrade 359.53 mg/m3 of H2S. This study provides a deeper understanding of sulfide degradation in biological trickling filters and helps promote the development of desulfurization technology and the treatment of malodorous gasses produced by the accumulation of large quantities of livestock manure.

A critical review on characterization, human health risk assessment and mitigation of malodorous gaseous emission during the composting process

Composting has emerged as a suitable method to convert or transform organic waste including manure, green waste, and food waste into valuable products with several advantages, such as high efficiency, cost feasibility, and being environmentally friendly. However, volatile organic compounds (VOCs), mainly malodorous gases, are the major concern and challenges to overcome in facilitating composting. Ammonia (NH3) and volatile sulfur compounds (VSCs), including hydrogen sulfide (H2S), and methyl mercaptan (CH4S), primarily contributed to the malodorous gases emission during the entire composting process due to their low olfactory threshold. These compounds are mainly emitted at the thermophilic phase, accounting for over 70% of total gas emissions during the whole process, whereas methane (CH4) and nitrous oxide (N2O) are commonly detected during the mesophilic and cooling phases. Therefore, the human health risk assessment of malodorous gases using various indexes such as ECi (maximum exposure concentration for an individual volatile compound EC), HR (non-carcinogenic risk), and CR (carcinogenic risk) has been evaluated and discussed. Also, several strategies such as maintaining optimal operating conditions, and adding bulking agents and additives (e.g., biochar and zeolite) to reduce malodorous emissions have been pointed out and highlighted. Biochar has specific adsorption properties such as high surface area and high porosity and contains various functional groups that can adsorb up to 60%-70% of malodorous gases emitted from composting. Notably, biofiltration emerged as a resilient and cost-effective technique, achieving up to 90% reduction in malodorous gases at the end-of-pipe. This study offers a comprehensive insight into the characterization of malodorous emissions during composting. Additionally, it emphasizes the need to address these issues on a larger scale and provides a promising outlook for future research.

Effects of Bacillus-based inoculum on odor emissions co-regulation, nutrient element transformations and microbial community tropological structures during chicken manure and sawdust composting

This study aims to evaluate whether different doses of Bacillus-based inoculum inoculated in chicken manure and sawdust composting will provide distinct effects on the co-regulation of ammonia (NH3) and hydrogen sulfide (H2S), nutrient conversions and microbial topological structures. Results indicate that the Bacillus-based inoculum inhibits NH3 emissions mainly by regulating bacterial communities, while promotes H2S emissions by regulating both bacterial and fungal communities. The inoculum only has a little effect on total organic carbon (TOC) and inhibits total sulfur (TS) and total phosphorus (TP) accumulations. Low dose inoculation inhibits total potassium (TK) accumulation, while high dose inoculation promotes TK accumulation and the opposite is true for total nitrogen (TN). The inoculation slightly affects the bacterial compositions, significantly alters the fungal compositions and increases the microbial cooperation, thus influencing the compost substances transformations. The microbial communities promote ammonium nitrogen (NH4+-N), TN, available phosphorus (AP), total potassium (TK) and TS, but inhibit nitrate nitrogen (NO3--N), TP and TK. Additionally, the bacterial communities promote, while the fungal communities inhibit the nitrite nitrogen (NO2--N) production. The core bacterial and fungal genera regulate NH3 and H2S emissions through the secretions of metabolic enzymes and the promoting or inhibiting effects on NH3 and H2S emissions are always opposite. Hence, Bacillus-based inoculum cannot regulate the NH3 and H2S emissions simultaneously.

Synthetic microbial consortia to enhance the biodegradation of compost odor by biotrickling filter

Composting generates odorous gases, including ammonia (NH3), hydrogen sulfide (H2S), and volatile organic compounds (VOCs). The Biological Trickling Filter (BTF) is effective for odor treatment, but it may have limitations with hydrophobic VOCs. In this study, a strain of Bacillus subtilis with ammonia-reducing ability, a strain of Bacillus cereus with desulfurization ability and a strain of Schizophyllum commune with the ability to degrade dimethyl disulfide were isolated and screened. The three strains were combined to create synthetic microbial consortia for enhancing odor treatment in the BTF. Compared to the activated sludge control, the BTF with synthetic microbial consortia removed 92.43% ammonia, 92.75% hydrogen sulfide. Furthermore, it demonstrated a significant improvement in the removal rates of p-methyl mercaptan, methyl sulfide, and dimethyl disulfide. High-throughput sequencing was conducted on the fillers of the synthetic microbial consortia-inoculated BTF to analyze the microbial community composition.

Comparative genomic analysis of Cohnella hashimotonis sp. nov. isolated from the International Space Station

A single strain from the family Paenibacillaceae was isolated from the wall behind the Waste Hygiene Compartment aboard the International Space Station (ISS) in April 2018, as part of the Microbial Tracking mission series. This strain was identified as a gram-positive, rod-shaped, oxidase-positive, catalase-negative motile bacterium in the genus Cohnella, designated as F6_2S_P_1T. The 16S sequence of the F6_2S_P_1T strain places it in a clade with C. rhizosphaerae and C. ginsengisoli, which were originally isolated from plant tissue or rhizosphere environments. The closest 16S and gyrB matches to strain F6_2S_P_1T are to C. rhizosphaerae with 98.84 and 93.99% sequence similarity, while a core single-copy gene phylogeny from all publicly available Cohnella genomes places it as more closely related to C. ginsengisoli. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values to any described Cohnella species are <89 and <22%, respectively. The major fatty acids for strain F6_2S_P_1T are anteiso-C15:0 (51.7%), iso-C16:0 (23.1%), and iso-C15:0 (10.5%), and it is able to metabolize a wide range of carbon compounds. Given the results of the ANI and dDDH analyses, this ISS strain is a novel species within the genus Cohnella for which we propose the name Cohnella hashimotonis, with the type strain F6_2S_P_1T (=NRRL B-65657T and DSMZ 115098T). Because no closely related Cohnella genomes were available, this study generated the whole-genome sequences (WGSs) of the type strains for C. rhizosphaerae and C. ginsengisoli. Phylogenetic and pangenomic analysis reveals that F6_2S_P_1T, C. rhizosphaerae, and C. ginsengisoli, along with two uncharacterized Cohnella strains, possess a shared set of 332 gene clusters which are not shared with any other WGS of Cohnella species, and form a distinct clade branching off from C. nanjingensis. Functional traits were predicted for the genomes of strain F6_2S_P_1T and other members of this clade.

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.

Effects of microbial inoculum on microbial community and enzyme activity involved in nitrogen-sulfur metabolism during sewage sludge composting

The purpose of this study was to access the effects of thermotolerant nitrifying microorganisms and sulfur-oxidizing bacteria on microbial community and enzyme activity involved in nitrogen‑sulfur metabolism during laboratory-scale sewage sludge (SS) composting，and to do a microbial-environmental factor association analysis to promote composting key species for nitrogen‑sulfur transformation in the body. The microbial community structure and the activities variation of six key enzyme involved were detected. The microbial inocula added had little impact on the diversity of the microbial community but changed its succession direction, and the abundance of Actinobacteria was decreased obviously of inoculation treatment (TR). The three dominant genera and indicator species in TR were significantly correlated with the conversion of nitrogen and sulfur. The addition of microbial inocula promoted the conversion of nitrogen and sulfur in SS compost, and increased the activities of the key enzymes and the microbial genera involved in nitrogen‑sulfur conversion. In other words, the nitrification and sulfur oxidation were enhanced simultaneously in the later stage of composting in TR.

Nitrogen loss, nitrogen functional genes, and humification as affected by hydrochar addition during chicken manure composting

This study investigated the effect of hydrochar addition on nitrogen (N) transformation, N functional genes, and humification during chicken manure composting. The addition of 10 % hydrochar reduced cumulative ammonia (NH₃) and nitrous oxide emissions by 55.24 % and 45.30 %, respectively, and N losses by 32.07 %. Further, it increased the relative abundance of amoA while decreasing that of nirK, nirS, and nosZ in compost. Hydrochar reduces NH₃ emissions during composting owing to its acid-carbon properties that lower the pH of the composting pile and promote ammonia oxidation. Moreover, hydrochar addition enhances the humification of the composting pile and significantly increases the content of humic substances. Moreover, after hydrochar addition, the germination index of the compost product reached >80 % 10 days earlier. The results demonstrate that hydrochar is a suitable composting additive for reducing N loss and shortening the composting time.

The Comparison of Biotreatment and Chemical Treatment for Odor Control during Kitchen Waste Aerobic Composting

Odor ΨΩγemission has become mathvariant="normal" mathvariant="sans-serif-bold-italic" an important issue in kitchen waste management. Ammonia and hydrogen sulfide are the two most important odor sources as they contribute malodor and can cause health problems. As biotreatment and chemical treatment are two majorly applied technologies for odor control, in this study, they were used to remove ammonia and hydrogen sulfide and the performance of each process was compared. It was found that chemical absorption could efficiently eliminate both ammonia and hydrogenmathvariant="script" sulfide, and the removal efficiencies of ammonia and hydrogen sulfide highly depended on the pH of the adsorbent, contacting time, and gas and solution ratio (G/S). The ammonia-removal efficiency reached 100% within less than 2 s at G/S 600 and pH 0.1. The complete removal of hydrogen sulfide was achieved within 2 s at G/S 4000 and pH 13. Biotrickling filter showed better ability for hydrogen sulfide removal and the removal efficiency was 91.9%; however, the ammonia removal was only 73.5%. It suggests that chemical adsorption is more efficient compared to biotreatment for removing ammonia and hydrogen sulfide. In the combination of the two processes, biotrickling filter followed by chemical adsorption, the final concentrations of ammonia and hydrogen sulfide could meet the Level 1 standard of Emission Standards for Odor Pollution (China). The study provides a potential approach for odor control during kitchen waste aerobic composting.

Isolation and application of a thermotolerant nitrifying bacterium Gordonia paraffinivorans N52 in sewage sludge composting for reducing nitrogen loss

A thermotolerant strain with heterotrophic nitrification capability obtained from sludge composting was identified as Gordonia paraffinivorans N52. Strain N52 utilized 51.8% of ammonium nitrogen (NH₄⁺-N) at 60℃, and the nitrogen balance results indicated that 25.5% of the consumed NH₄⁺-N was changed into nitrification intermediates, 53.0% to intracellular nitrogen, and only 5.2% was lost. The successful detection of enzymes related to nitrification and PCR amplification of functional genes further demonstrated nitrification ability of the isolated strain. Moreover, orthogonal test indicated that conditions for the optimal nitrification performance were C/N 15, 50℃, 150 rpm and pH 8. Compared with the control group, the addition of Gordonia paraffinivorans N52 to sewage sludge composting reduced 27.6% of ammonia emissions, accelerated the conversion from NH₄⁺-N to nitrate nitrogen and decreased the total nitrogen loss. These results suggested that inoculation of Gordonia paraffinivorans N52 effectively controlled ammonia emissions and reduced nitrogen loss in composting.

Evaluation of bacterial agent/nitrate coupling on enhancing sulfur conversion and bacterial community succession during aerobic composting

This study evaluated the coupling effects of sodium nitrate (SN) and sulfur-oxidizing bacterial agent (BA) on oxidizing reduced-state sulfur and altering the bacteria community in SN, BA, and SN + BA treatments, respectively. Results revealed that bacterial inoculation prolonged the thermophilic period, facilitated organics degradation and compost humification. Compared to the control group, SN + BA treatment reduced the cumulative H₂S emissions and sulfur loss rate by 55.1 % and 15.7 %, respectively, and the nitrate reduction (used as electron donors) efficiency was enhanced by 7.8 % during the first week of composting. Bacterial inoculation altered the diversities and structure of the bacterial community by increasing the relative abundances of thermotolerant bacteria. Correlation analyses showed that the dominant phyla involved in nitrate-based sulfur-oxidizing reactions could be Firmicutes and Synergistota. These findings suggested the application viability of SN and BA to regulate the sulfur biotransformation and bacterial community in composting.

Inhibitory Effects of the Addition of KNO3 on Volatile Sulfur Compound Emissions during Sewage Sludge Composting

Odor released from the sewage sludge composting process often has a negative impact on the sewage sludge treatment facility and becomes a hindrance to promoting compost technology. This study investigated the effect of adding KNO₃ on the emissions of volatile sulfur compounds, such as hydrogen sulfide (H₂S), dimethyl sulfide (DMS), and carbon disulfide (CS₂), during sewage sludge composting and on the physicochemical properties of compost products, such as arylsulfatase activity, available sulfur, total sulfur, moisture content, and germination index. The results showed that the addition of KNO₃ could inhibit the emissions of volatile sulfur compounds during composting. KNO₃ can also increase the heating rate and peak temperature of the compost pile and reduce the available sulfur loss. The addition of 4% and 8% KNO₃ had the best effect on H₂S emissions, and it reduced the emissions of H₂S during composting by 19.5% and 20.0%, respectively. The addition of 4% KNO₃ had the best effect on DMS and CS₂ emissions, and it reduced the emissions of DMS and CS₂ by 75.8% and 63.0%, respectively. Furthermore, adding 4% KNO₃ had the best effect from the perspective of improving the germination index of the compost.