Mitigating inhibition of undissociated volatile fatty acids (VFAs) for enhanced sludge-rice bran composting with ferric nitrate amendment

Correlations between sewage sludge composting physicochemical parameters and emissions of greenhouse gases and ammonia: A statistical analysis

Mitigating the environmental impact of composting by the reduction of greenhouse gases (N2O, CH4) and ammonia (NH3) emissions is a major challenge. To meet this challenge, the understanding of the relationships between composted substrates initial physicochemical parameters and gas emissions is essential. From a long-term perspective, it will allow to guide the recipe formulation of the initial mixture to be composted, with a view to reducing gas emissions during composting. This study gathered literature data targeting sewage sludge composting and performed statistical correlation analyses between cumulative gas emissions and the following parameters: sewage sludge, bulking agent and composted mixture initial physicochemical parameters (pH, dry matter, total carbon, total nitrogen, C/N), the dry mass ratio of sewage sludge to bulking agent and the duration of composting. The average values of cumulative emissions show a large variability: 1.37 ± 2.71 gC.kg initial mix DM-1, 0.13 ± 0.17 gN.kg initial mix DM-1 and 2.23 ± 2.79 gN.kg initial mix DM-1 for CH4, N2O and NH3 emissions respectively. Although the correlation analysis highlighted some significant interesting correlations between initial physicochemical parameters and gas emissions (p.value < 0.05), reliable multiparametric model could not fit the data, meaning that the actual literature data are not sufficient to explain most part of gas emissions. Among the most interesting relationships, the study showed that the dry matter of the composted mixture is negatively correlated to N2O emissions, while the ratio of sewage sludge to bulking agent and the duration of composting are positively correlated to N2O emissions. It was also shown that the pH of the bulking agent is positively correlated to NH3 emissions. Considering the large part of the emission variability that is not explained and the difficulty to link the correlation with their causality, it will be interesting to improve composting gas emissions knowledge in future research by analyzing free air space, bulking agent adsorption capacity and available and biodegradable organic matter. These parameters are of particular interest in solving the main problems associated with sewage sludge composting, namely porosity and nitrogen retention. This study also highlighted the necessity to extend the duration of the composting studies over 40 days in order to measure possible N2O late release and better identify parameters influencing N2O emissions.

Optimization of organic solid waste composting process through iron-related additives: A systematic review

Composting is an environmentally friendly method that facilitates the biodegradation of organic solid waste, ultimately transforming it into stable end-products suitable for various applications. The element iron (Fe) exhibits flexibility in form and valence. The typical Fe-related additives include zero-valent-iron, iron oxides, ferric and ferrous ion salts, which can be targeted to drive composting process through different mechanisms and are of keen interest to academics. Therefore, this review integrated relevant literature from recent years to provide more comprehensive overview about the influence and mechanisms of various Fe-related additives on composting process, including organic components conversion, humus formation and sequestration, changes in biological factors, stability and safety of composting end-products. Meanwhile, it was recommended that further research be conducted on the deep action mechanisms, biochemical pathways, budget balance analysis, products stability and application during organic solid waste composting with Fe-related additives. This review provided guidance for the subsequent targeted application of Fe-related additives in compost, thereby facilitating cost reduction and promoting circular economy objectives.

The efficient solution to decline the greenhouses emission and enrich the bacterial community during pig manure composting: Regulating the particle size of cornstalk

In present study, four lengths of chopped cornstalks were amended with pig manure respectively for 100 days aerobic fermentation, which aimed to evaluate the impact of different length of agricultural solid wastes on gaseous emission and dominating bacterial community succession and connection. The result revealed that the maximum ammonia volatilization was observed in 5 cm of straw samples attributed to the prominent mineralization, which was opposite to the emission of CH4 and N2O. As for global warming potential, the minimum value was detected in 5 cm of straw samples, which decreased by 5.03-24.75% compared with other samples. Additionally, the strongest correlation and complexity of bacterial community could be detected in 5 cm of straw treatment, representing the most vigorous bacterial metabolic ability could be recorded by optimizing the microbial habitat. Therefore, in order to decline the greenhouse effect in livestock manure composting, the 5 cm of corn straw was recommended.

Exploring gaseous emissions and pivotal enzymatic activity during co-composting of branch and pig manure: The effect of particle size of bulking agents

The purpose of current study was to probe the effect of various length of branch on gaseous emissions and vital enzymatic activity. Four lengths (< 2 cm, 2 cm, 5 cm, and > 5 cm) of clipped branch were mingled with collected pig manure for 100 days aerobic fermentation. The consequence demonstrated that the amendment of 2 cm of branch showed conducive to decline the greenhouse gas emissions, which the CH4 emissions decreased by 1.62-40.10%, and the N2O emissions decreased by 21.91-34.04% contrasted with other treatments. Furthermore, the peak degree of enzymatic activities was also observed in 2 cm of branch treatment by the optimizing living condition for microbes. In view of microbiological indicators, the most abundant and complex bacterial community could be monitor in 2 cm of branch composting pile, which verified the microbial facilitation. Summing up, the strategy of 2 cm branch amendment would be recommended.

Phytotoxicity of farm livestock manures in facultative heap composting using the seed germination index as indicator

Static facultative heap composting of animal manure is widely used in China, but there is almost no systematic research on the phytotoxicity of the produced compost. Here, we evaluated the phytotoxic variation in compost produced by facultative heap composting of four types of animal manure (chicken manure, pig manure, sheep manure, and cattle manure) using different plant seeds (cucumber, radish, Chinese cabbage, and oilseed rape) to determine germination index (GI). The key factors that affected GI values were identified, including the dynamics of the phytotoxicity and microbial community during heap composting. Sensitivity to toxicity differed depending on the type of plant seed used. Phytotoxicity during facultative heap composting, evaluated by the GI, was in the order: chicken manure (0-6.6 %) < pig manure (14.4-90.5 %) < sheep manure (46.0-93.0 %) < cattle manure (50.2-105.8 %). Network analysis showed that the volatile fatty acid (VFA) concentration was positively correlated with Firmicutes abundance, and NH₄⁺-N was correlated with Actinobacteria, Proteobacteria, and Bacteroidetes. More bacteria were stimulated to participate in conversions of dissolved organic carbon, dissolved nitrogen, VFA, and ammonia-nitrogen (NH₄⁺-N) in sheep manure heap composting than that in other manure. The GI was most affected by VFA in chicken manure and cattle manure heap composting, while NH₄⁺-N was the main factor affecting the GI in pig manure and sheep manure compost. The dissolved carbon and nitrogen content and composition, as well as the core and proprietary microbial communities, were the primary factors that affected the succession of phytotoxic substances in facultative heap composting, which in turn affected GI values. In this study, the key pathways of livestock manure composting that affected GI and phytotoxicity were found and evaluated, which provided new insights and theoretical support for the safe use of organic fertilizer.

Effects of phosphate-containing additives and zeolite on maturity and heavy metal passivation during pig manure composting

This study investigated the effects of the combination of phosphogypsum with calcium oxide (PPG + CaO), superphosphate with calcium oxide (SSP + CaO) and zeolite (Zeolite) on composting maturity and heavy metal passivation in pig manure composting. The results showed that all treatments reached the maturity requirements and the phosphorus-containing additive treatments had higher final germination indices (GIs). Compared with CK, additive treatments enhanced the compost maturity by promoting volatile fatty acids (VFAs) decomposition (26.4%-30.5%) and formation of stable humus substances. All additive amendment treatments increased humic acid-like substances by over 20%, and the PPG + CaO treatment had the highest level of humus. Composting process reduced the bioavailability of Cu (49.2%), Cd (5.0%), Cr (54.3%), and Pb (26.6%). Correlation analysis found that the heavy mental passivation rate was significantly negatively correlated with the contents of VFAs and nitrogenous substances, and positively correlated with the pH, GI, humic acid content and the ratio of humic acid to fulvic acid (HA/FA). Therefore, the PPG + CaO treatment further increased the passivation rates of Cu (65.6%), Cd (21.7%), and Pb (48.7%) and decreased the mobilization of Zn by promoting maturity and humification during composting.

Impact of biochar, calcium magnesium phosphate fertilizer and spent mushroom substrate on humification and heavy metal passivation during composting

The effects of exogenous additives (biochar, calcium magnesium phosphate fertilizer, and spent mushroom substrate) on humification process and heavy metal passivation during pig manure composting were investigated. The aerobic composting trial were carried out in 60 L reactors for 49 d. The calcium magnesium phosphate fertilizer, biochar, and spent mushroom substrate amendment treatments all accelerated the organic matter degradation and increased the temperature, decreased the volatile fatty acid content by 45%-49.0% and promoted humification of the compost (increasing the humic acid content and humus index). The biochar passivated Cu best, calcium magnesium phosphate fertilizer passivated Zn best (passivation rate 13.85%), and spent mushroom substrate passivated Cd, Cr, and Pb best (passivation rates 25.47%-47.91%). The additives amendment improved Cu, Zn, Cd, Cr, and Pb passivation performance by promoting composting humification process.

Insights into the effect of iron-carbon particle amendment on food waste composting: Physicochemical properties and the microbial community

The effects of iron-carbon (Fe-C) particle amendment on organic matter degradation, product quality and functional microbial community in food waste composting were investigated. Fe-C particles (10%) were added to the material and composted for 32 days in a lab-scale composting system. The results suggested that Fe-C particle enhanced organic matter degradation by 12.3%, particularly lignocellulose, leading to a greater humification process (increased by 15.5%). In addition, NO₃^--N generation was enhanced (15.9%) by nitrification with more active ammonia monooxygenase and nitrite oxidoreductase activities in the cooling and maturity periods. Fe-C particles not only significantly increased the relative abundances of Bacillus and Aspergillus for organic matter decomposition, but also decreased the relative abundances of acid-producing bacteria. RDA analysis demonstrated that the bacterial community was significantly influenced by dissolved organic matter, C/N, NO₃^--N, humic acid, volatile fatty acids and pH, while electrical conductivity was the key factor affecting the fungal community.

Bioaugmentation mitigates ammonia and hydrogen sulfide emissions during the mixture compost of dewatered sewage sludge and reed straw

This study investigated the effectiveness of bio-augmenting aerobic cell culture to mitigate ammonia and hydrogen sulfide emission in sewage sludge composting amended with reed straw (with the weight ratio of 1:0.3-0.4). During the 20-day aerated lab-scale composting, adding 200-mL culture (56.80 NTU) reduced ammonia and hydrogen sulfide emissions by 38.00% and 54.32%, and conserved total nitrogen and sulfate by 39.42% and 70.75%, respectively. Organic matters degradation was quick started 1 day ahead. Comparing to the control, nitrate content increased 38.75% at the end of the compost. Bioaugmentation evened the distributions of bacterial communities in the thermophilic phase. The shift was mainly due to 22.97% of relative abundance of Proteobacteria depressed and 157.16% of Bacteroidetes increased, which were beneficial for nitrogen conservation and glycan breakdown, respectively. In summary, the results demonstrated that bioaugmentation addition could be an effective strategy for enhanced sludge composting.

Links between microbial compositions and metabolites during aerobic composting under amoxicillin stress was evaluated by 16S rRNA sequencing and gas chromatography-mass spectrometry: Benefit for the plant growth

The purpose of this study was to identify the relationship between core bacteria and metabolites during aerobic composting and analyze the effects of metabolites on plant growth. The results revealed that amoxicillin might affect the generation and transformation of metabolites by reconstructs the bacterial communities. The peak area ratios (PAR) of esters and fatty acids (FAs) were increased, while sterols decreased during composting. Furthermore, the correlation analysis showed that the production of FAs, esters and sterols is strongly correlated with Oceanobacillus, Corynebacterium, Psychrobacter, Xanthomonadaceae, Pusillimonas and Gracilibacillus. Moreover, 36 key metabolites were screened out, the PAR of the propanoic acid ethyl ester and oleic acid that benefit plant growth were increased in amoxicillin groups. However, the PAR of environmental pollutants, such as n-hexadecanoic acid and 3β, 5β-Cholestan-3-ol is the opposite. Therefore, composting can eliminate the environmental risks caused by antibiotic residues in feces and promote plant growth.

Improvement of two-stage composting of green waste by addition of eggshell waste and rice husks

With the development of urban greening and increases in the human population, the production of green waste (GW) has been increasing in China. Although GW is biodegradable, its composting is difficult because of its low degradation rate. This study focuses on how addition of eggshell waste (ESW; at 0, 10, and 20%) and/or rice husks (RH; at 0, 15, and 25%) affects the two-stage composting of GW on the basis of temperature, bulk density, particle-size distribution, pH, nitrogen changes, carbon dioxide emission, organic matter degradation, humic substances, the activities of microorganisms and enzymes, and the phytotoxicity to germinating seeds. The combined addition of 10% ESW and 25% RH produced the highest quality compost in the shortest time. To produce a stable and mature product, two-stage composting of GW required 30 days without additives but only 20 days with the combined addition of 10% ESW and 25% RH.

Influence of fine coal gasification slag on greenhouse gases emission and volatile fatty acids during pig manure composting

This study was evaluated industrial waste fine coal gasification slag (FCGS) as an additive on pig manure composting by parameters of greenhouse gases, NH3, volatile fatty acids (VFAs) and maturity. Six treatments of FCGS (0%, 2%, 4%, 6%, 8% and 10%) were added into the mixture raw material and composted 42 days. Results illustrated that the FCGS amendment could prolong sanitation stage and promote the degree of maturity, germination index and C/N ratio during composting. With the increasing amendment of FCGS, GI was increased from 9.97 to 28.45%. Compared with control, increasing of FCGS proportion could reduce the mitigation of global warming potential (N2O and CH4), NH3 and cumulative of VFAs from 8.89-77.04%, 3.81-71.65%, 5.18-28.02% and 8.79-83.33%. Finally, present study results revealed that 10%FCGS could improve composting and reduced the maturity period as well as compost quality, thus recommended as effective dosage for efficient pig manure composting.

The effect of sulfate on nitrite-denitrifying anaerobic methane oxidation (nitrite-DAMO) process

Sulfate is generally found in natural water and wastewater. Nitrite-DAMO bacteria live in natural water or wastewater containing different sulfates. To determine the effect of sulfate on the nitrite-DAMO process, we conducted batch tests and continuous tests to investigate the performance and microbial structure of the nitrite-DAMO system at different sulfate concentrations. The results indicated that the nitrogen removal performance of the nitrite-DAMO system was initially promoted and then inhibited at 0-200 mg SO₄^2-/L, and the denitrification rate was highest at 80 mg SO₄^2-/L which was 1.26 mgN/(L·d). When stimulated by sulfate, protein stabilized nitrite-DAMO bacteria. The denitrification kinetics conformed to the Edward equation, and the initial inhibitory concentration of the nitrite-DAMO system was 189.70 mg SO₄^2-/L. Changes in the proportion of unclassfied_c_ABY1 of the phylum Patescibacteria and norank_f_LD-RB-34 of the phylum Bacteroidetes were the main factors influencing how the nitrogen removal rate of the nitrite-DAMO system responded to sulfate.

Insights into Anaerobic Co-Digestion of Lignocellulosic Biomass (Sugar Beet By-Products) and Animal Manure in Long-Term Semi-Continuous Assays

Biogas production through anaerobic digestion has proven to be one of the most important pillars of the transition into the circular economy concept, a sustainable approach for biorefinery. This work aims to extend and improve knowledge in the anaerobic co-digestion of complementary substrates, given insights into wastes biodegradability and the influence of manure composition on the anaerobic process stability. Anaerobic co-digestion of sugar beet by-products with two kinds of animal manure (pig and cow) was investigated in semi-continuous assays, analyzing both common and non-classical parameters. Co-digestion with manure clearly mitigated the inhibitory effect of volatile fatty acids at high organic loading rates, leading to increases in methane production by 70% and 31% in comparison with individual digestion of sugar beet by-products, for co-digestion with pig and cow manure, respectively. Non-classical parameters could give more insight into the coupling/uncoupling of the anaerobic digestion phases and the involved microorganisms. Indirect parameters indicated that the process failure at the critical organic loading rates was mainly due to methanogenesis inhibition in the co-digestion with pig manure, while in co-digestion with cow manure or in individual digestion of sugar beet by-products, both hydrolysis–acidogenesis and methanogenesis phases were affected. Biomethanation degree refers to the maximum methane potential of organic wastes. Sugar beet by-products required a long digestion-time to reach high biodegradability. However, short digestion-times for co-digestion assays led to a high biomethanation degree.

Response of bamboo biochar amendment on volatile fatty acids accumulation reduction and humification during chicken manure composting

Present study was focused on to evaluate the effectiveness of increasing bamboo biochar (BB) (0%, 2%, 4%, 6%, 8% and 10%) amendment on volatile fatty acids (VFAs) degradation and humification, as well as correlation with interrelated physicochemical parameters during chicken manure (CM) composting. The results showed that the extended thermophilic period and higher humic acid/fulvic acid ratio as well as richness bacteria community during CM composting. In addition, lower quantities of VFAs and odor generation with elevated biochar concentration. Redundancy analysis also supported that 10% BB has strong correlation with physicochemical parameters than other treatments. Overall, the 10% BB amendment could stimulate microbial activities to accelerate the organic waste degradation, reduced VFAs and odor emission so that improve hygiene and end product quality. It is notably assessed that application of 10% BB additive were optimal feasible and effectively channel for disposal of manure.

Application of ceramsite and activated alumina balls as recyclable bulking agents for sludge composting

Composting is a major sludge-treatment method and bulking agents are very important in sludge composting. In this study, ceramsite and activated alumina balls were chosen as recyclable bulking agents for sludge composting. Variations in the temperature, pH, electrical conductivity, organic matter, dissolved organic carbon, moisture content, and heavy metals were detected during composting with different bulking-agent treatments as well as differences in the germination index values. The results showed that both bulking agents could ensure the maturity of the compost; further, ceramsite treatment resulted in the best water removal efficiency. According to the sequential extraction procedure, both ceramsite and activated alumina balls could stabilize Cd but they also increased the mobility of Zn. After comparing the effects of different particle sizes of ceramsite on composting, 20 mm was determined to be the most optimal value. Additionally, the recovery rates of ceramsite and activated alumina balls were 96.9% and 99.9%, respectively.

New insight of tertiary-amine modified bentonite amendment on the nitrogen transformation and volatile fatty acids during the chicken manure composting

In this study, the main objective was to investigate the potential effect of tertiary-amine modified bentonite (TAMB) on the nitrogen transformation and the volatile fatty acids (VFAs) degradation during the chicken manure (CM) composting. Six dosages of TAMB (0%, 2%, 4%, 6%, 8% and 10%) were amended into the mixture of CM and wheat straw and then composted for 50 days. The results revealed the TAMB amendment could prolong the thermophilic phase and enhance the organic matter (OM) degradation. With the increasing dosage of TAMB, the ammonia volatilization was reduced by 15.41%-65.35%. Meanwhile, the TAMB addition had a positive effect on VFAs degradation and reducing odor unitMAX (OUMAX) by 17.61%-59.24%. Moreover, CH4 was reduced by 12.15%-32.78% in TAMB applied treatments compared to control. Finally, combined with all results, it indicated that TAMB amendment could reduce VFAs, CH4 emission and nitrogen loss to improve the compost quality.

Nitrogen loss reduction by adding KH2PO4-K2HPO4 buffer solution during composting of sewage sludge

Nitrogen loss through gaseous emission, mainly ammonia emission, was an inevitable problem during sewage sludge composting. In this study, MgSO₄ + K₃PO₄ (Run A), K₂SO₄ + KH₂PO₄-K₂HPO₄ (Run B) and MgSO₄ + KH₂PO₄-K₂HPO₄ (Run C) were mixed with mixtures before composting, aiming at researching the effects of buffer solution on reducing nitrogen loss during composting. Ammonia loss of Run C was reduced by 53.8% and 45.5%, and nitrogen loss of Run C was decreased by 61.2% and 67.1%, compared to that of Run A and Run B, respectively. Besides, organic matter degradation of Run C was 36.8%. Among the three amended treatments, nitrogen loss in Run C was effectively reduced and organic matter degradation was slightly improved. The addition of MgSO₄ and KH₂PO₄-K₂HPO₄ was confirmed to be effective to maintain a desired pH range for struvite precipitation as well as to reserve more ammonia in the compost to promote the formation of struvite.