Insight into effects of electro-dewatering pretreatment on nitrous oxide emission involved in related functional genes in sewage sludge composting

Study on the effect of biochar combined with Fenton oxidation on the aerobic composting of sludge

Biochar was derived from rice straw pyrolyzed at 400°C, and biochar was added to the excess sludge at the ratio of 10% DS, 25% DS, and 50% DS as a supplementary skeleton for sludge Fenton pre-treatment. Rice husk biochar mixed with fungus residue as compost conditioner. In this study, we explored the effects of seven groups of composting materials on the composting effect and fertilizer quality under different pre-treatment methods of Fenton-pretreated sludge cake and conventional dewatered sludge cake, and different biochar additions. Specifically, we conducted a 22-day composting experiment using a composting reactor to investigate the effect of rice husk biochar combined with Fenton oxidation on the physicochemical properties of sludge composting. The results of this study showed that the FB50 group significantly increased the composting rate. Nutrient analysis showed that the FB50 group was rich in fertilizer nutrients, such as available phosphorus, and alkali-hydrolyzable nitrogen content increased. Heavy metals (Cu, Cd, Cr, Pb, Zn, Ni) met China's 'Agricultural Sludge Pollutant Control Standard' GB 4284-2018 Grade A standard, with obvious passivation and significantly reduced bioavailability. All these results suggested that biochar coupled with Fenton oxidation was more beneficial to sludge composting.

Nitrogen (N) "supplementation, slow release, and retention" strategy improves N use efficiency via the synergistic effect of biochar, nitrogen-fixing bacteria, and dicyandiamide

Irrational nitrogen (N) fertilizer management and application practices have led to a range of ecological and environmental problems that seriously threaten food security. In this study, an effective N fertilizer management strategy was established for improving N fertilizer utilization efficiency (NUE). Biochar, N2-fixing bacteria (Enterobacter cloacae), and a nitrification inhibitor (dicyandiamide, DCD) were simultaneously added to the soil during maize cultivation. The goal was to increase soil ammonium nitrogen content and NUE by regulating the relative abundance, enzyme activity, and functional gene expression of N conversion-related soil microbes. Biochar combined with E. cloacae and DCD significantly increased soil N content, and the NUE reached 46.69 %. The relative abundance of Burkholderia and Bradyrhizobium and the activity of nitrogenase increased significantly during biological N2 fixation. Further, the abundance of the nifH gene was significantly up-regulated. The relative abundance of Sphingomonas, Pseudomonas, Nitrospira, and Castellaniella and the activities of ammonia monooxygenase and nitrate reductase decreased significantly during nitrification and denitrification. Moreover, the abundance of the genes amoA and narG was significantly down-regulated. Correlation analyses showed that the increase in soil N2 fixation and the suppression of nitrification and denitrification reactions were the key contributors to the increase in soil N content and NUE. Biochar combined with E. cloacae and DCD synergistically enabled the supplementation, slow release, and retention of N, thus providing adequate N for maize growth. Thus, the combination of biochar, E. cloacae, and DCD is effective for mitigating the irrational application of N fertilizers and reducing N pollution.

The combined action of biochar and nitrogen-fixing bacteria on microbial and enzymatic activities of soil N cycling

This study aims to investigate the positive effects of the combined use of Enterobacter cloacae and biochar on improving nitrogen (N) utilization. The greenhouse pots experimental results showed the synergy of biochar and E. cloacae increased soil total N content and plant N uptake by 33.54% and 15.1%, respectively. Soil nitrogenase (NIT) activity increased by 253.02%. Ammonia monooxygenase (AMO) and nitrate reductase (NR) activity associated with nitrification and denitrification decreased by 10.94% and 29.09%, respectively. The relative abundance of N fixing microorganisms like Burkholderia and Bradyrhizobium significantly increased. Sphingomonas and Ottowia, two bacteria involved in the nitrification and denitrification processes, were found to be in lower numbers. The E. cloacae's ability to fix N₂ and promote the growth of plants allow the retention of N in soil and make more N available for plant development. Biochar served as a reservoir of N for plants by adsorbing N from the soil and providing a shelter for E. cloacae. Thus, biochar and E. cloacae form a synergy for the management of agricultural N and the mitigation of negative impacts of pollution caused by excessive use of N fertilizer.

Influence of thermally activated peroxodisulfate pretreatment on gaseous emission, dissolved organic matter and maturity evolution during spiramycin fermentation residue composting

Aerobic composting combined with appropriate pretreatment is promising to achieve the utilization of antibiotics fermentation residues (AFRs). This research studied the effect of thermally activated peroxodisulfate (TAP) pretreatment on greenhouse gas (GHGs) emission, dissolved organic matter (DOM) and maturity evaluation during spiramycin fermentation residue (SFR) composting. Three treatments were conducted from co-composting of SFR and wheat straw, while 90% and 99.9% residual spirmycin removal pretreatment SFR by TAP were provided and compared with raw SFR. The cumulative CO₂ and NH₃ emissions increased by 17.2% and 30.8% after TAP pretreatment removed 99.9% residual spiramycin in SFR, while the cumulative CH₄ and N₂O emission decreased by 34.0% and 5.27%, respectively. The DOM, humic acid (HA)/fulvic acid (FA) and NH₄⁺/NO₃^- analysis confirmed that the composting maturity was improved with the increasing of HA and NO₃^- content by TAP pretreatment.

Long-term metal pollution shifts microbial functional profiles of nitrification and denitrification in agricultural soils

The increasing contamination of heavy metals in agricultural soils and its impact on the nitrogen (N) cycle and N use efficiency have attracted considerable attention in recent years. In this study, agricultural soils neighboring the Dabaoshan copper mining area (DBS) and Qingyuan electronic-waste recycling area (QY), in Guangdong, China, were sampled to study the interaction between heavy metals and nitrification/denitrification processes, especially the related microbial functional profiles. Results showed that the contamination of heavy metals affected nitrifiers and denitrifiers differently. The potential nitrification activity was about four times lower in metal-polluted soils compared with the unpolluted ones, with a significant decrease in the abundance of amoA and nxrB (p < 0.05) in the polluted samples. On the other hand, the potential denitrification activity was more metal-resistant, which attributed to its complex species composition as shown by a slightly higher α-diversity index, and was slightly higher (p > 0.05) in the polluted samples. Among the five denitrifying genes tested, nosZ gene had the highest increase and the nirK gene the most decrease in numbers and in the polluted soils. The metal-polluted soils had fewer correlations among N functional genes based on the co-occurrence network analysis. In addition, the core taxa of the whole bacterial community changed from copiotrophic to oligotrophic bacteria in the presence of heavy metals. Mantel test indicated that heavy metals were the dominant factors determining N-related genes while the bacterial community composition was due to a combination of heavy metal presence and soil properties such as TOC, NO₂^-, and pH. It is concluded that long-term heavy metals pollution potentially affected nitrifiers and denitrifiers differently as indicated by the shift in N functional genes and the change in nitrification/denitrification processes.

Process control for improving dewatering performance of sewage sludge based on carbonaceous skeleton-assisted thermal hydrolysis

The poor dewaterability of sewage sludge is a major obstacle to its disposal and utilization. Our previous study developed a novel method of carbonaceous skeleton-assisted thermal hydrolysis to achieve good performance of sludge dewatering. This work was conducted for further improving the efficiency through investigating the effects of the properties of sludge, skeleton, and key process parameters. A dewatering model was also established based on Darcy's Law and experimental results from a self-designed computer control on-line filter press system. The experimental results showed that the water content can all be reduced by about 36% for sludge with the varying organic content from 35% to 60%. Lignocellulosic skeleton had better assistive capabilities than skeleton with high content of hemicellulose, lipid, and chitin, and the appropriate dosage was 0.2-0.5 g/g DS. Satisfied reduction of about 30% in water content can be obtained when sludge was assisted-hydrolyzed at a moderate temperature of 180 °C only within 5 min and dewatered at 0.4-1.0 MPa for 10-20 min. By using self-developed dewatering model, the filtrate mass with time under any mechanical pressure can be obtained and the theoretical value fit the actual value very well. Based on this, excellent dewatering performance can be achieved through process control of assisted thermal hydrolysis and mechanical dewatering.

In-situ electrolytic oxygen is a feasible replacement for conventional aeration during aerobic composting

Aerobic composting is an effective recycling method for the disposal and resource utilization of organic solid waste. However, the inappropriate aeration mode used during conventional aerobic composting (CAC) often results in low oxygen utilization efficiency and loss of temperature, which further leads to a long maturation period and large odorous gas (NH₃) pollution. Herein, a novel electrolytic oxygen aerobic composting (EOAC) process was invented first using in-situ oxygen generation for aeration by the electrolysis of water in compost. Our results demonstrated that the germination index (GI) significantly increased during EOAC, and the maturation time of compost was shortened by nearly 50% during EOAC compared to CAC, indicating higher oxygen utilization efficiency during EOAC. Meanwhile, NH₃ emissions, N₂O emissions, and nitrogen loss during the EOAC process decreased by 61%, 46%, and 21%, respectively, compared to CAC. The total relative abundance of thermophilic and electroactive bacteria during EOAC increased remarkably. EOAC inhibited ammoniation, nitrification, and denitrification, and weakened N-associated functional genes. A techno-economic analysis indicated that EOAC had greater technical superiority and cost advantages compared to CAC. This study represents proof-of-principle for EOAC and suggests that in-situ electrolytic oxygen is a feasible replacement for conventional aeration during aerobic composting.

Microbial community competition rather than high-temperature predominates ARGs elimination in swine manure composting

Aerobic composting is commonly used in pig manure treatment, however, antibiotic resistance genes (ARGs) and their unclear transformation during composting process make the treated manure land using risky. The effects of enhanced thermophilic phase strategy (external heating (HTC) and thermophiles inoculation (MC)) on ARGs removal and the underlying mechanisms were investigated during swine manure composting. HTC increased the total relative abundance (RA) of ARGs by 32.38%, and MC decreased by 21.50% compared to CK by the end of the composting. Mantel test indicated that it was not temperature (P > 0.05), but environmental parameters (pH, Electric Conductivity (EC), etc.) and metabolic products (nitrogen forms) significantly affected the ARGs profile. Partial least-squares path modeling (PLS-PM) suggested that microbial community structure (bacterial abundance and diversities) was the main factor for ARGs evolution. Co-occurrence analysis revealed that HTC could promote the propagation of ARG hosts in later stage of the composting because the strong selection of thermophiles resulted in ecological niches vacancy, and MC enhanced the competition between hosts and nonhosts for ecological niches by increasing thermophiles diversities. These results suggested that competitive inhibition to potential ARGs hosts could be a helpful strategy in ARGs threaten elimination during composting.

Effects of bulking agents on greenhouse gases and related genes in sludge composting

The effect of organic bulking agents on CO₂, NH₃, N₂O and CH₄ emission and related genes was evaluated in 40 days sludge composting with wood chip, wheat straw and rice husk, respectively. The results showed wood chip had the highest C/N of 111.3, total porosity of 93.13% and aeration porosity of 78.98% among three bulking agents. Wheat straw had the highest water-holding porosity of 25.62%, which could be critical factor increasing CH₄ production and reducing NH₃ emission. Moreover, there was no significant difference in N₂O emission rates in three composting systems with three bulking agents. RDA analysis showed a negative correlation between mcrA and NH + 4-N. Nitrate content in raw feedstock was dominant factor limiting N₂O yield due to low amoA. The continuous increase of oxidation-reduction potential was significantly positive correlated with pmoA and negative correlation with nirK and norB, which reduced N₂O and CH₄ production in the curing period.

Insights into influences of sucrose amendment on nitrification and denitrification in sewage sludge composting

Sucrose amendment could promote ammonia assimilation and reduce nitrogen loss in sewage sludge (SS) composting, but the effects of sucrose amendment on nitrification and denitrification are still unknown that were firstly researched in present paper. Result showed that sucrose amendment reduced 33.0% of N₂O emission by changing the physicochemical indexes, nitrogen forms, related bacteria and functional genes. In the sucrose treatment, the higher nitrifying bacteria community, amoA and nxrA genes abundance were, the lower hao, narG、nirS、nirK and norB genes abundance were. Based on the correlation analysis, the number of nitrifying bacteria was significantly positively correlated with NO₃^- and nxrA abundance, indicating that sucrose amendment promoted the growth of nitrifying bacteria, the contents of NO₃^- and the activity of nitrite oxidation. Moreover, contents of NO₂^- were positively correlated with N₂O emission, narG, nirS and norB abundance, indicating that denitrification was the main path of N₂O generated.

Alternating magnetic field mitigates N2O emission during the aerobic composting of chicken manure

Nitrous oxide (N₂O) emission is an environmental problem related to composting. Recently, the electric field-assisted aerobic composting process has been found to be effective for enhancing compost maturity and mitigating N₂O emission. However, the insertion of electrodes into the compost pile causes electrode erosion and inconvenience in practical operation. In this study, a novel alternating magnetic field-assisted aerobic composting (AMFAC) process was tested by applying an alternating magnetic field (AMF) to a conventional aerobic composting (CAC) process. The total N₂O emission of the AMFAC process was reduced by 39.8% as compared with that of the CAC process. Furthermore, the results demonstrate that the AMF weakened the expressions of the amoA, narG, and nirS functional genes (the maximum reductions were 96%, 83.7%, and 95.5%, respectively), whereas it enhanced the expression of the nosZ functional gene by a maximum factor of 36.5 as compared with that in CAC. A correlation analysis revealed that the nitrification and denitrification processes for N₂O emission were suppressed in AMFAC, the main source of N₂O emission of which was denitrification. The findings imply that AMFAC is an effective strategy for the reduction of N₂O emission during aerobic composting.

Microbial driving mechanism of biochar and bean dregs on NH3 and N2O emissions during composting

In this study, the effect of biochar (BC) and bean dregs (BD) on nitrifiers and denitrifiers as well as the contributions to the NH₃ and N₂O emissions were investigated. Compared with the BD treatment, the maximum value of NH₃ and N₂O emission was decreased by 32.92% and 46.61% in the BD + BC treatment, respectively. The production of NH₃ and N₂O was closely associated with the abundance and structure of nitrogen functional genes. BD + BC increased the abundance of AOB amoA gene to decrease the NH₃ emission. The abundance of nirS was more closely associated with N₂O. The abundance of nirS in the BD + BC was lowered by 18.93% compared with the BD treatment, thereby decreasing the N₂O emission after composting. Besides, the nosZ-type gene was the more functional denitrification bacterial communities to effect the N₂O emissions.

Influence of spent mushroom substrate and molasses amendment on nitrogen loss and humification in sewage sludge composting

The present study included lab-scale sewage sludge (SS) composting amended by molasses and spent mushroom substrate (SMS) in 5 L composting reactor system. The influence of molasses and SMS amendment on nitrogen loss and humification of SS composting was evaluated. The results showed that SMS amendment, especially combination with molasses raised composting temperature, increased CO₂ volatilization, promoted organic matter degradation, improve germination index and humification process. The addition of SMS and molasses contain carbohydrates used as carbon source and energy substance by microorganisms could increase microbial activity and ammonia assimilation. In the SMS + molasses treatments, NH₃ volatilization was reduced by 33.1%–37.3% and N₂O volatilization was only 17.8%–25.4% of that in the control treatment, furthermore, the nitrogen loss rate was reduced by 27.2%–32.2%. Consequently, the addition of SMS and molasses improved the compost maturity and reduced nitrogen loss in the SS composting process.

Microbial driven reduction of N2O and NH3 emissions during composting: Effects of bamboo charcoal and bamboo vinegar

In this study, we systematically analyzed the microbial-driven effects of bamboo charcoal (BC) and bamboo vinegar (BV) on reducing NH₃ and N₂O emissions during aerobic composting. The results showed that BC and BV improved the nitrogen conversion and compost quality, but the combined BC + BV treatment obtained the best improvements. The BC, BV, and BC + BV treatments reduced the NH₃ emissions by 14.35%, 17.90%, and 29.83%, respectively, and the N₂O emissions by 44.83%, 55.96%, and 74.53%. BC and BV reduced the NH₃ and N₂O emissions during composting by controlling ammonia oxidation, where napA, nirK, and nosZ served as useful indicators of the N₂O emissions from compost, especially the nirK gene. The dominant nitrifying and denitrifying bacteria belonged to Proteobacteria, and the changes in environmental factors during composting significantly affected the succession of the nitrifying and denitrifying bacterial communities. Nitrosomonas was a key nitrifying bacterial genus in the mesophilic composting period, and BC and BV may have reduced the NH₃ emissions by enhancing its conversion to NH₄⁺-N by Nitrosomonas. In addition, norank_p__environmental_samples, unclassified_k__norank_d__Bacteria, and unclassified_p__Proteobacteria were jointly responsible for driving the production of N₂O during the compost maturity stage.

Insight into the effects of sulfamethoxazole and norfloxacin on nitrogen transformation functional genes during swine manure composting

The effects of sulfamethoxazole and norfloxacin on nitrogen functional genes were investigated in four composting treatments of swine manure: CK (no antibiotics), SMZ (spiked with 5 mg kg^-1 dry weight (DW) sulfamethoxazole), NOR (spiked with 5 mg kg^-1DW norfloxacin), and SN (spiked with 5 mg kg^-1DW sulfamethoxazole and 5 mg kg^-1DW norfloxacin). Antibiotics decreased relative abundance of bacterial amoA and nxrA, while increased nosZ/nirK. The decline in amoA/16S rRNA increased the total NH₃ emission in SMZ and NOR from 1027.05 to 1144.39 and 1278.22 mg kg^-1DW. The decrease of nxrA/16S rRNA enhanced the NO₂^--N content and N₂O emission in SMZ in the initial composting. Additionally, the increase in nosZ/nirK probably was the main reason for the lower N₂O emission in SN than other treatments in the cooling phase. The inhibition on nitrification process and increase in NH₃ emission resulted from antibiotics is worthy of attention in the future.

Nitrification plays a key role in N2O emission in electric-field assisted aerobic composting

Nitrous oxide (N₂O) emission is a serious environmental problem in composting. Previous studies have indicated that electric field assistance results in lower N₂O emissions in aerobic composting; however, the exact mechanisms involved in electric-field assisted aerobic composting (EAAC) are not clear. In this study, the biological N transformation processes and the N-associated genes were investigated. The results demonstrated that electric field application inhibited nitrification, weakened the nitrifying functional genes (the hao and nxrA genes declined maximally by 86% and 86.8%, respectively), and increased the N₂O consumption-related gene (nosZ) by a maximum factor of 2.76 compared with that in CAC. The correlation analysis demonstrated that nitrification was the main source of N₂O emission in EAAC. The findings imply that EAAC is a promising process for mitigating N₂O emission at the source during aerobic composting.

Biochar combined with montmorillonite amendments increase bioavailable organic nitrogen and reduce nitrogen loss during composting

This study aimed to compare the effects of biochar, montmorillonite and their mixture on nitrogen availability and nitrogen loss during chicken manure composting. Four lab-scale composting experiments, the control (CK), 5% biochar addition (BC), 5% montmorillonite addition (M) and 2.5% biochar + 2.5% montmorillonite addition (BCM), were established. Results showed that the addition of BC, M and BCM significantly improved the contents of bioavailable organic nitrogen and NH₄⁺-N in composts. In addition, BC and BCM reduced N loss by 19.2% and 12.2%, respectively, in comparison with CK. Significant shift of key bacterial communities associated with N transformation were also found in four treatments. Redundancy analysis and structural equation models indicated different additives changed the correlation among bacterial communities, environmental factors and organic N fractions. Comparison of N availability and N loss indicated that the combination of biochar and montmorillonite are more effective than that of separate application during composting.

Biodegradation of volatile solids and water mass balance of bio-drying sewage sludge after electro-dewatering pretreatment

Using pressurized electro-osmotic dewatering (PEOD) as the pretreatment process for sewage sludge (SS) bio-drying can improve the dewatering performance, but the kinetics of volatile solids biodegradation and the water mass balance are still unknown. These processes were first investigated in this study. Experiments were conducted with three different initial materials, which were composed of SS, bio-dried product and SS dewatered by PEOD (EDSS) as different mass ratios. Six kinetic models and a nonlinear regression method were used to estimate the kinetic parameters, and the models were analyzed using four statistical indicators. Satisfactory fitting of the proposed kinetic model to the experimental data was achieved. Through the water mass balance, the results showed that EDSS had the best dewatering performance for bio-drying. EDSS provided the most appropriate conditions for the bio-drying process; the highest correlation coefficient was 0.9291 and the total water removal rate was 51.13% in the bio-drying of all EDSS.

Electric field induces electron flow to simultaneously enhance the maturity of aerobic composting and mitigate greenhouse gas emissions

The long maturation period and greenhouse gas (GHG) emission are two major problems that arise during aerobic composting, mainly due to the low efficiency of O₂ transmission and utilization. In this study, a novel electric-field-assisted aerobic composting (EAC) process was tested by simply applying a direct-current voltage of 2 V to a conventional aerobic composting (CAC) process. Compared with the CAC process, the maturation time and the total GHG for the EAC process were reduced by 33% and 70%, respectively. Furthermore, the analyses of O₂ consumption and microbial communities demonstrated that the electric field had enhanced O₂ utilization by 30 ± 9% and increased the relative abundance of electroactive bacteria by about 3.4-fold compared to CAC. This work has represented a proof of principle for EAC and suggests that the electric field is an effective and environmentally friendly strategy for enhancing compost maturity and mitigating GHG emissions during aerobic composting.

Electro-dewatering pretreatment of sludge to improve the bio-drying process

In this study, the feasibility of electro-dewatering (EDW) as a pretreatment of the subsequent bio-drying process (EB process) was investigated from the point of view of the influence of EDW on the microbial biodegradability of sludge. The results showed that suitable EDW pretreatment was beneficial for microbial growth in the sludge cake, and in the subsequent bio-drying process it increased the metabolic activity of microorganisms. However, electric field strength impacted microbial activity and soluble chemical oxygen demand (SCOD) of the sludge. As the applied electric field strength increased from 20 to 60 V cm⁻¹, the microbial activity of sludge decreased gradually but SCOD of sludge increased. The specific oxygen uptake rate (SOUR) at electric field strength of 20 V cm⁻¹ was 8.7% higher than that of raw sludge. EDW pretreatment accelerated the drying rate of bio-drying process, and the final water content of sludge (44%) was 6.3% lower than that of non-pretreated sludge. It was observed that in the bio-drying process with an EDW pretreatment, the first peak temperature of the sludge pile was 58.7 °C at 36 h and the second peak temperature was 48.7 °C at 56 h, whereas that of the non-pretreated sludge was only 46.5 °C at 42 h and 40.3 °C at 62 h, respectively. The EDW sludge incorporating straw as a bulking agent showed promising results during bio-drying. In addition, EDW pretreatment of sludge to improve the bio-drying process showed lower energy consumption and cost.

The feasibility of electro-dewatering (EDW) as a pretreatment of the subsequent bio-drying process was investigated in this study.

Hyperthermophilic composting significantly decreases N2O emissions by regulating N2O-related functional genes

This study reported for the first time that hyperthermophilic composting (HTC) could mitigate 90% of the cumulative amount of N₂O emissions compared to traditional composting (TC) in a full-scale experiment. The concentrations of NO₂^--N and NO₃^--N in HTC were significantly lower than those in TC, which may be the main reason for the reduced N₂O emissions. Furthermore, this study found that the decrease in N₂O emissions in HTC compared to TC was mainly due to the inhibition of the abundance of the bacterial amoA and norB genes, which could decrease the nitrification rate and control N₂O formation, respectively. Partial least squares path modeling revealed that a high temperature was the key factor in lowering N₂O emissions in HTC, while physicochemical properties were the dominant factor in enhancing N₂O emissions in TC. These results suggested that HTC is a promising technique for reducing N₂O emissions in manure composting.

Succession of bacterial community function in cow manure composing

Succession of bacterial community, metabolism function and substrate utilization capacity in 60 days composting of cow manure were analyzed by 16S rRNA pyrosequencing, PICRUSt and Biolog method, respectively. The results showed that the number of bacterial OTUs increased from 176 in raw cow manure to 203 on Day-10, 220 on Day-30 and 313 on Day-60 of the composting, respectively. The PICRUSt analysis showed that the relative abundances of genes involved in lipid and carbohydrate metabolism increased by 28.5% and 22.4% during the incubation, respectively, but the abundances of the genes involved in nucleotide and amino acid metabolism decreased by 21.6% and 2.1%. Furthermore, the average well color development (AWCD) of carboxylic acids (0.99-0.48) and amino acids (1.61-0.89) in Biolog Eco-microplate displayed a steady downtrend through the composting process. Redundancy analysis showed that ORP, moisture and temperature could explain 68.1%, 17.6% and 14.2% of the variation in bacterial genera, respectively.

Effects of bioleaching pretreatment on nitrous oxide emission related functional genes in sludge composting process

The effect of bioleaching pretreatment on N₂O generation in sludge composting process was firstly investigated in this study. The relationships among physicochemical factors, N₂O and NH₃ emission and related functional genes were analyzed in 60 days composting of bioleaching dewatering sludge (BDS) and filter press dewatering sludge (FDS), respectively. The results showed the cumulative amounts of NH₃ and N₂O emission from the BDS composting system were reduced by 83.52% and 54.76% after bioleaching pretreatment, respectively. The lower moisture and pH, and the higher ORP and the concentrations of NH₄⁺-N, NO₃^--N and NO₂^--N were observed in BDS during the composting compared to FDS. Furthermore, bioleaching pretreatment improved the relative abundance of hao but reduced amoA, nirK and norB in the BDS during the composting. The low pH level and the reduction of nirK and norB in BDS were the main reasons mitigating NH₃ and N₂O emissions, respectively.