Effect of different components of single superphosphate on organic matter degradation and maturity during pig manure composting

A comprehensive review on agricultural waste utilization through sustainable conversion techniques, with a focus on the additives effect on the fate of phosphorus and toxic elements during composting process

The increasing trend of using agricultural wastes follows the concept of "waste to wealth" and is closely related to the themes of sustainable development goals (SDGs). Carbon-neutral technologies for waste management have not been critically reviewed yet. This paper reviews the technological trend of agricultural waste utilization, including composting, thermal conversion, and anaerobic digestion. Specifically, the effects of exogenous additives on the contents, fractionation, and fate of phosphorus (P) and potentially toxic elements (PTEs) during the composting process have been comprehensively reviewed in this article. The composting process can transform biomass-P and additive-born P into plant available forms. PTEs can be passivated during the composting process. Biochar can accelerate the passivation of PTEs in the composting process through different physiochemical interactions such as surface adsorption, precipitation, and cation exchange reactions. The addition of exogenous calcium, magnesium and phosphate in the compost can reduce the mobility of PTEs such as copper, cadmium, and zinc. Based on critical analysis, this paper recommends an eco-innovative perspective for the improvement and practical application of composting technology for the utilization of agricultural biowastes to meet the circular economy approach and achieve the SDGs.

Modifying humus-phosphorus-arsenic interactions in sludge composting: The strengthening of phosphorus availability and arsenic efflux detoxification mechanisms

Arsenic (As) in sewage sludge poses a significant threat to environmental and human health, which has attracted widespread attention. This study investigated the value of adding sodium percarbonate (SP) on phosphorus (P) availability and As efflux detoxification through HS-P-As interactions. Due to the unique structure of humus (HS) and the similar chemical properties of P and As, the conditions for HS-P-As interaction are provided. This study discussed the content, morphology and microbial communities of HS, P and As by using metagenomic and correlation analysis. The results showed that the humification index in the experiment group (SPC) was 2.34 times higher than that in the control group (CK). The available phosphorus (AP) content of SPC increased from 71.09 mg/kg to 126.14 mg/kg, and SPC was 1.11 times that of CK. The relative abundance of ACR3/ArsB increased. Pst, Actinomyces and Bacillus commonly participated in P and As conversion. The correlation analysis revealed that the humification process was enhanced, the AP was strengthened, and the As was efflux detoxified after SP amendment. All in all, this study elucidated the key mechanism of HS-P-As interaction and put forward a new strategy for sewage sludge resource utilization and detoxification.

Enhancing C and N turnover, functional bacteria abundance, and the efficiency of biowaste conversion using Streptomyces-Bacillus inoculation

Microbial inoculation plays a significant role in promoting the efficiency of biowaste conversion. This study investigates the function of Streptomyces-Bacillus Inoculants (SBI) on carbon (C) and nitrogen (N) conversion, and microbial dynamics, during cow manure (10% and 20% addition) and corn straw co-composting. Compared to inoculant-free controls, inoculant application accelerated the compost's thermophilic stage (8 vs 15 days), and significantly increased compost total N contents (+47%) and N-reductase activities (nitrate reductase: +60%; nitrite reductase: +219%). Both bacterial and fungal community succession were significantly affected by DOC, urease, and NH4+-N, while the fungal community was also significantly affected by cellulase. The contribution rate of Cupriavidus to the physicochemical factors of compost was as high as 83.40%, but by contrast there were no significantly different contributions (∼60%) among the top 20 fungal genera. Application of SBI induced significant correlations between bacteria, compost C/N ratio, and catalase enzymes, indicative of compost maturation. We recommend SBI as a promising bio-composting additive to accelerate C and N turnover and high-quality biowaste maturation. SBI boosts organic cycling by transforming biowastes into bio-fertilizers efficiently. This highlights the potential for SBI application to improve plant growth and soil quality in multiple contexts.

Phosphate additives promote humic acid carbon and nitrogen skeleton formation by regulating precursors and composting bacterial communities

This study aimed to compare the effect of different phosphate additives including superphosphate (CP) and MP [Mg(OH)2 + H3PO4] on nitrogen conversion, humus fractions formation and bacterial community in food waste compost. The results showed the ratio of humic acid nitrogen in total nitrogen (HA-N/TN) in CP increased by 49 %. Ammonium nitrogen accumulation was increased by 75 % (CP) and 44 % (MP). Spectroscopic techniques proved that phosphate addition facilitated the formation of complex structures in HA. CP enhanced the dominance of Saccharomonospora, while Thermobifida and Bacillus were improved in MP. Structural equation modeling and network analysis demonstrated that ammonium nitrogen can be converted to HA-N and has positive effects on bacterial composition, reducing sugars and amino acids, especially in CP with more clustered network and synergic bacterial interactions. Therefore, the addition of phosphate provides a new idea to regulate the retained nitrogen toward humification in composting.

Effects of adding steel slag on humification and characteristics of bacterial community during phosphate-amended composting of municipal sludge

This study aimed to investigate the effects of different proportions (0%, 5%, 7.5%, and 10%) of steel slag (SS) on humification and bacterial community characteristics during phosphate-amended composting of municipal sludge. Compared with adding KH2PO4 alone, co-adding SS significantly promoted the temperature, pH, nitrification, and critical enzyme activities (polyphenol oxidase, cellulase, laccase); especially organic matter (OM) degradation rate (25.5%) and humification degree (1.8) were highest in the 5%-SS treatment. Excitation-emission matrix-parallel factor confirmed that co-adding SS could promote the conversion of protein-like substances or microbial by-products into humic-like substances. Furthermore, adding 5%-SS significantly improved the relative abundances of Actinobacteria, Firmicutes and the genes related to carbohydrate and amino acid metabolism, and enhanced the interactions of bacterial community in stability and complexity. The partial least squares path model indicated that OM was the primary factor affecting humification. These results provided a promising strategy to optimize composting of municipal sludge via SS.

Effects of bacterial inoculation on lignocellulose degradation and microbial properties during cow dung composting

Inoculation with exogenous microbial agents is a common method to promote organic waste degradation and improve the quality of compost. However, the biotic effects of different microbial agents are often quite different. To evaluate the potential effects of a complex bacterial agent comprised of three strains (belonging to Bacillus and Geobacillus) on lignocellulose degradation and the underlying microbial mechanisms during cow dung composting, two lab-scale composting experiments, a control and a bacterial inoculation treatment, were established. The results suggest that bacterial inoculation accelerated the rate of temperature increase and extended the thermophilic phase. Compared to those in the negative control group, cellulose, hemicellulose, and lignin degradation rates in the inoculated group increased from 53.3% to 70.0%, 50.2% to 61.3%, and 46.4% to 60.0%, respectively. The microbial community structure and diversity in the compost were clearly changed by the bacterial inoculation. Moreover, stamp analysis showed that inoculation modulated the key compost microbial functional populations linked to the degradation of lignocellulose. Correlation matrix analysis indicated that the expression of bacterial lignocellulolytic enzymes is closely related to key microbial functional populations. Overall, the results confirm the importance of bacterial inoculation, and have important implications for promoting the efficiency and quality of cow dung compost.

Trends in the management of organic swine farm waste by composting: A systematic review

Pig farming contributes to the economic development of nations and supplies human food demand; however, it generates a large amount of organic waste which, if not managed properly, becomes a risk to the environment and human and animal health. Considering the relevance of composting and its usefulness for the use of waste, this study aimed to determine the global trends in the management of composting manure, mortality and other organic waste produced on pig farms over the last five years (2017-2022). Systematic search involved four databases: ISI Web of Science, Scopus, Ebsco and Scielo. Of the total findings, 56 articles were included in the review, further classified into 14 categories for their respective analysis: co-substrates/additives, microbial communities, antibiotic resistance, heavy metals, polycyclic aromatic hydrocarbons, microbiological/parasitological quality, phytopathogens, nitrogen transformation, bioinoculants, comparison/combination with other waste management techniques, factors affecting composting, swine mortality and plant growth promotion/phytotoxicity. The review exemplified the importance of swine mortality composting as an alternative for organic matter management in pig farms, considering that the process also includes manure, vegetable waste and wood chips, among others. Controlled factors throughout the process are a requirement to obtain a stable product with physicochemical and microbiological quality that complies with national and international regulations and that will be useful and safe for application on crops, ensuring environmental, animal, and human health.

Phosphorus transformation behavior and phosphorus cycling genes expression in food waste composting with hydroxyapatite enhanced by phosphate-solubilizing bacteria

This study aimed to explore the effect of phosphate-solubilizing bacteria (PSB) Bacillus inoculation in the cooling stage on hydroxyapatite dissolution, phosphorus (P) forms transformation, and bacterial P cycling genes in food waste composting with hydroxyapatite. Results indicated that PSB inoculation promoted the dissolution of hydroxyapatite, increased P availability of compost by 8.1% and decreased the ratio of organic P to inorganic P by 10.2% based on sequential fractionation and ³¹P nuclear magnetic resonance spectroscopy. Illumina sequencing indicated Bacillus relative abundance after inoculation increased up to one time higher than control after the cooling stage. Network analysis and metabolic function of bacterial community analysis suggested inorganic P solubilizing genes of Bacillus and organic P mineralization genes of other genera were improved after inoculation in the core module. Therefore, bioaugmentation of PSB in the cooling stage may be a potential way to improve P bioavailability of bone and food waste in composting.

The effect of calcium superphosphate addition in different stages on the nitrogen fixation and ammonification during chicken manure composting

Nitrogen losses through ammonia (NH₃) emission were an unavoidable issue during chicken manure composting. Calcium superphosphate can be added to effectively limit the emission of NH₃. The results show that adding calcium superphosphate in the heating, high temperature and cooling stages reduces ammonia emission by 18.48 %, 28.19 % and 0.91 % respectively. Furthermore, adding calcium superphosphate at high temperature stage increased the ammonium nitrogen content (NH₄⁺-N), reducing the conversion of organic nitrogen (HON) to NH₄⁺-N. Network analysis indicated that adding calcium superphosphate during the high temperature stage reduced NH₃-related microorganisms and effectively inhibited ammonification. Moreover, the results of qPCR of the ammonification gene gdh and structural equation model (SEM) verify that adding calcium superphosphate at the high temperature stage reduced ammonification and drove ammonification-related bacterial communities to decrease ammonia emissions. Adding superphosphate at high temperature can effectively increase the nitrogen content and reduce gas pollution during composting.

Decomposition and humification process of domestic biodegradable waste by black soldier fly (Hermetia illucens L.) larvae from the perspective of dissolved organic matter

Black soldier fly larvae (Hermitia illucens L.) (BSFL) bioconversion is a promising technology for domestic biodegradable waste (DBW) management and resource recovery. However, little is known about the DBW biodegradation during the BSFL bioconversion from the perspective of dissolved organic matter (DOM). In the current study, field tests were conducted on a full-scale BSFL bioconversion facility with treatment capacity of 15 tons DBW/day. Composition of DOM in DBW were investigated by spectral analysis (UV-vis, fluorescence, and Fourier Transform Infrared spectroscopy (FT-IR)), coupled with enzyme activity analysis. After BSFL bioconversion, DOM concentrations, total carbon and total nitrogen in residues decreased by 51.5%, 18.3% and 19.9%, respectively. Meanwhile, enzymes like catalase, lipase, protease, sucrase, urease and cellulase significantly increased (9.28%-56.3%). The specific UV absorbance at 254 nm and 280 nm (SUVA₂₅₄, SUVA₂₈₀), the area at 226-400 nm (A_226-400) and slope in the 280-400 nm region (S_280-400) of DOM increased by 230%, 186%, 143% and 398%, respectively. Moreover, the characteristic peaks at 1636, 1077 and 1045 cm^-1 in FT-IR increased continuously, with a significant decrease in peak at 1124 and 1572 cm^-1. DOM spectral data show that BSFL decomposed the carboxylic, cellulose and aliphatic components, resulting in the increase of oxygen-containing functional groups (e.g., hydroxyl, carboxyl, carbonyl) and aromatic compounds. Furthermore, fluorescence profiles show that Region Ⅰ, Ⅱ (aromatic proteins) and Ⅳ (soluble microbial byproducts) decreased while Region Ⅴ (humic-like substances) increased significantly. Humification index increased by 122% while biological index decreased by 18.0%, indicating a significant increase in degree of humification and stabilization of the residues. The current evidence provides a theoretical basis for technical re-innovation and improving economic potential of BSFL technology.

Improving the humification by additives during composting: A review

Humic substances (HSs) are key indicators of compost maturity and are important for the composting process. The application of additives is generally considered to be an efficient and easy-to-master strategy to promote the humification of composting and quickly caught the interest of researchers. This review summarizes the recent literature on humification promotion by additives in the composting process. Firstly, the organic, inorganic, biological, and compound additives are introduced emphatically, and the effects and mechanisms of various additives on composting humification are systematically discussed. Inorganic, organic, biological, and compound additives can promote 5.58-82.19%, 30.61-50.92%, 2.3-40%, and 28.09-104.51% of humification during composting, respectively. Subsequently, the advantages and disadvantages of various additives in promoting composting humification are discussed and indicated that compound additives are the most promising method in promoting composting humification. Finally, future research on humification promotion is also proposed such as long-term stability, environmental impact, and economic feasibility of additive in the large-scale application of composting. It is aiming to provide a reference for future research and the application of additives in composting.

Effect of hydrothermal pretreatment and compound microbial agents on compost maturity and gaseous emissions during aerobic composting of kitchen waste

Though aerobic composting is commonly used in kitchen waste (KW) disposal, the high-oil and high-salt characteristics of KW could affect composting efficiency and lead to the land using risk of produced fertilizer. The impact of hydrothermal pretreatment (HTP) and addition of compound microbial agent (CMA) on compost maturity, greenhouse gas (GHGs) emissions and bacterial community during the kitchen waste composting were evaluated in the present work. Results indicated that N2O, CH4 and CO2 emissions from treatment by HTP and CMA addition were reduced by 82.72%, 13.77% and 20.78 %, respectively, comparing with the control (without HTP and without CMA addition). The seed germination index (GI) value of the HTP and CMA addition treatment was 1.03 and had the highest maturity in all treatments. Furthermore, the bacterial community analysis indicated that CMA inoculation could increase the relative abundance of genus Bacillus at the thermophilic stage of composting to accelerate organic biodegradation. This work provided important insight into mitigating GHGs emissions and improving compost quality in kitchen waste composting.

Isolation and characterization of a novel thermotolerant alkali lignin-degrading bacterium Aneurinibacillus sp. LD3 and its application in food waste composting

The aim of this study was to isolate thermotolerant alkali lignin-degrading bacteria and to investigate their degradation characteristics and application in food waste composting. Two thermotolerant alkali lignin-degrading bacteria isolates were identified as Bacillus sp. LD2 (LD2) and a novel species Aneurinibacillus sp. LD3 (LD3). Compared with strain LD2, LD3 had a higher alkali lignin degradation rate (61.28%) and ligninolytic enzyme activities, and the maximum lignin peroxidase, laccase, and manganese peroxidase activities were 3117.25, 1484.5, and 1770.75 U L^-1, respectively. GC-MS analysis revealed that low-molecular-weight compounds such as 4'-hydroxy-3'-methoxy acetophenone, vanillic acid, 1-(4-hydroxy-3,5-dimethoxyphenyl), benzoic acid, and octadecanoic acid were formed in the degradation of alkali lignin by LD3, indicating the cleavage of β-aryl ether, C_α-C_β bonds, and aromatic rings in lignin. Composting results showed that inoculating LD3 improved the degradation of organic matter by 20.11% and reduced the carbon-to-nitrogen (C/N) ratio (15.66). Additionally, a higher decrease in the content of lignocellulose was observed in the LD treatment. FTIR and 3D-EEM spectra analysis indicated that inoculating LD3 promoted the decomposition of easily available organic substances and lignocellulose and the formation of aromatic structures and humic acid-like substances. In brief, the thermotolerant lignin-degrading bacterium Aneurinibacillus sp. LD3 is effective in degrading lignin and improving the quality of composting.

Natural field freeze-thaw process leads to different performances of soil amendments towards Cd immobilization and enrichment

Cadmium (Cd) soil pollution is a global issue affecting crop production and food safety. Remediation methods involving in-situ Cd immobilization have been developed, but their effectiveness can diminish under seasonal freeze-thaw aging processes. In this study, we assessed the field performance of four soil treatments at a seasonally frozen rice paddy. Amendments were applied at 2 wt%, including: (i) sepiolite (a 2:1 clay mineral), (ii) superphosphate, (iii) biochar (produced by rice husk at 500 °C for 2 h), and (iv) joint application of biochar & superphosphate (1:1 mixture by weight). Immobilization performance was determined as DTPA extractable Cd and plant uptake in various organs. Overall, the four treatments significantly reduced Cd bioavailability during the plant growth period, with average DTPA-extractable concentrations decreasing by 43%, 34%, 39% and 45% for the four treatments, respectively, relative to untreated soil (control). Rice grain yields from the superphosphate and the joint application treatments increased by 8.0% and 11.8%, respectively, and Cd accumulation within those grains reduced by 14.3% and 48.9%, respectively. During the winter non-growth period, freeze-thaw aging facilitated Cd mobilization, with DTPA-extractable Cd increasing by 16.9% in the control soil, relative to the initial period. However, this reduced to 10.9%, 14.4%, 7.6% and 5.0%, for the sepiolite, superphosphate, biochar and joint application treatments, respectively. Overall, the joint application of biochar and superphosphate provided the best performance in terms of both long-term Cd immobilization and rice production enhancement, offering a green remediation option for risk management at Cd contaminated rice paddies in seasonally frozen regions.

Managing Phosphorus Availability from Organic and Inorganic Sources for Optimum Wheat Production in Calcareous Soils

In calcareous soils, wheat productivity is much lower due to improper nutrient management, especially phosphorus (P). Therefore, this study was conducted to manage P availability from various organic (Control, FYM and Sugar cane straw applied at the rate of 10 ton ha−1) and inorganic (Control, 100% rock phosphate (RP), 50% acidulated RP, 100% acidulated RP, single super phosphate (SSP) and diammonium phosphate (DAP)) sources applied at the rate of 90 kg P2O5 ha−1 in calcareous soil while using wheat as test crop. When averaged across the organic sources, SSP performed better in emergence m−2 (126), tillers m−2 (431), spikes m−2 (419), grains spikes−1 (61), plant height (95.1 cm), 1000-GW (40 g), biological yield (11,023 kg ha−1), grain yield (4022 kg ha−1), phosphorus use efficiency (10.5%), phosphorus in leaves at tillering (2.63 mg kg−1) and anthesis stage (2.50 mg kg−1), soil P at heading (1.73 mg kg−1) and post-harvest stage (1.56 mg kg−1) compared to the rest of the mineral sources. Similarly, among the organic sources, FYM performed better than others for all tested traits. Integration of inorganic P sources with organic manures further improved crop performance and post-harvest soil P content. Therefore, using 10 tons FYM ha−1 in integration to SSP or 100% acidulated RP at the rate of 90 kg P2O5 ha−1 is recommended for ensuring optimum wheat productivity under calcareous soils.

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.

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.

Microbial inoculants and struvite improved organic matter humification and stabilized phosphorus during swine manure composting: Multivariate and multiscale investigations

The combined effects of microbial inoculants (MI) and magnesium ammonium phosphate (MAP; struvite) on organic matter (OM) biodegradation and nutrients stabilization during biowaste composting have not yet been investigated. Therefore, the effects of MI and MAP on OM stability and P species during swine manure composting were investigated using geochemical and spectroscopic techniques. MI promoted the degradation of carbohydrates and aliphatic compounds, which improved the degree of OM mineralization and humification. MI and MAP promoted the redistribution of P fractions and species during composting. After composting, the portion of water-soluble P decreased from 50.0% to 23.0%, while the portion of HCl-P increased from 18.5% to 33.5%, which mean that MI and MAP can stabilize P and mitigate its potential loss during composting. These findings indicate that MI can be recommended for enhancing OM biodegradation and stabilization of P during biowastes composting, as a novel trial for the biological waste treatment.

Improving the humification and phosphorus flow during swine manure composting: A trial for enhancing the beneficial applications of hazardous biowastes

Improving the recovery of organic matter and phosphorus (P) from hazardous biowastes such as swine manure using acidic substrates (ASs) in conjunction with aerobic composting is of great interest. This work aimed to investigate the effects of ASs on the humification and/or P migration as well as on microbial succession during the swine manure composting, employing multivariate and multiscale approaches. Adding ASs, derived from wood vinegar and humic acid, increased the degree of humification and thermal stability of the compost. The ³¹P nuclear magnetic resonance spectroscopy and X-ray absorption near-edge structure analyses demonstrated compost P was in the form of struvite crystals, Ca/Al-P phases, and Poly-P (all inorganic P species) as well as inositol hexakisphosphate and Mono-P (organophosphorus species). However, the efficiency of P recovery could be improved by generating more struvite by adding the ASs. The flows among nutrient pools resulted from the diversity in the dominant microbial communities in different composting phases after introducing the ASs and appearance of Bacillus spp. in all phases. These results demonstrate the potential value of ASs for regulating and/or improving nutrients flow during the composting of hazardous biowastes for producing higher quality compost, which may maximize their beneficial benefits and applications.

Response of bacterial community to iron oxide nanoparticles during agricultural waste composting and driving factors analysis

The succession of bacterial communities and their function, and the core microorganisms for water soluble organic carbon (WSC) and organic matter (OM) changes during agricultural waste composting with addition of iron oxide nanomaterials (FeONPs, Fe₂O₃ NPs and Fe₃O₄ NPs) were investigated. Moreover, driving factors for bacterial composition and metabolism were analyzed. Results showed that FeONPs treatments increased the relative abundance of thermophilic microorganisms for OM degradation. Most of the core genera were responsible for decomposition of OM and synthesis of WSC. Additionally, FeONPs promoted the metabolism of amino acids. The most significant factors for dominant genera in control, Fe₂O₃ NPs and Fe₃O₄ NPs group were moisture (62.1%), moisture (62.0%) and OM (58.2%), respectively. For metabolism, the most significant factors in control, Fe₂O₃ NPs and Fe₃O₄ NPs group were temperature (57.2%), NO₃^--N (60.5%), NO₃^--N (62.6%), respectively. The relationships between compost properties, bacterial community and metabolism were changed by FeONPs.

Give priority to abiotic factor of phosphate additives for pig manure composting to reduce heavy metal risk rather than bacterial contribution

Phosphate additives especially superphosphate can reduce nitrogen loss, and increase phosphorus availability in composting. This study investigated the changes of different heavy metals fractions and their relationship with bacterial community and abiotic factors during pig manure composting with adding equimolar H₃PO₄, H₂SO₄ and K₂HPO₄. Results showed that both acidic and alkaline labile phosphate increased the potential ecological risk of heavy metals compared to control, but K₂HPO₄ decreased the accumulation of exchangeable Zn and Mn by 12% and 15% than that with H₃PO₄ and H₂SO₄ addition. Network analysis showed that K₂HPO₄ enhanced the proportion of negative links in bacterial species with heavy metals, but H₃PO₄ decreased the stability of bacterial network. Redundancy analysis demonstrated that pH was the key factor on metal speciation and risk with phosphate additives than bacterial role. The study presented theoretical basis for additive selection in controlling composting nitrogen fixation and environmental risk.

Inoculation of phosphate-solubilizing bacteria (Bacillus) regulates microbial interaction to improve phosphorus fractions mobilization during kitchen waste composting

Bacillus presents in most composts as core microbial taxa and is widely used as inoculant in composting. However, the role of Bacillus as phosphate-solubilizing bacteria (PSB) inoculant in composting and the response of indigenous bacterial community are unclear. This study used redundancy analysis (RDA), network analysis and structural equation model (SEM) to investigate the dynamics of phosphorus (P) fractions, bacterial community, and microbial interaction in composting with PSB (Bacillus sp. P6) inoculation. Results indicated that Bacillus inoculation increased Olsen P content, organic matter degradation, and bacterial diversity, benefiting P fractions mobilization during composting. RDA showed that pH was the main factor influencing P fractions transformation and bacterial taxa. Network analysis and SEM revealed that Bacillus indirectly improved the contribution of bacterial community on P mobilization by enhancing microbial interactions. Therefore, Bacillus with P solubilizing function may be a potential inoculant to regulate the biotic process of P transformation.

Phosphorus excess changes rock phosphate solubilization level and bacterial community mediating phosphorus fractions mobilization during composting

This study investigated the changes of phosphorus (P) fractions, bacterial community and their response to available P or carbon (C):P during composting with different rock phosphate (RP) addition levels. Results showed that adding RP at 10% or 15% promoted the rise of temperature, maturity and Olsen P accumulation in composting, which had a higher amount of RP solubilization than other groups. Available P changed bacterial composition and decreased diversity in composts. RP solubilization efficiency was negatively correlated to C:P ratio and the highest (22.7%) when 10% RP was added, in which bacterial community changed from "function redundancy" to "intensive P-solubilization". Low C:P ratio (〈300) increased the RP solubilization ratio especially within 135-160. Therefore, this study proposed that adding P-rich substrates to decrease C:P ratio could regulate P-solubilizers' activity for increasing RP solubilization efficiency during composting.

Bamboo charcoal enhances cellulase and urease activities during chicken manure composting: Roles of the bacterial community and metabolic functions

Microbial enzymes are crucial for material biotransformation during the composting process. In this study, we investigated the effects of adding bamboo charcoal (BC) (i.e., at 5%, 10%, and 20% corresponding to BC5, BC10, and BC20, respectively) on the enzyme activity levels during chicken manure composting. The results showed that BC10 could increase the cellulose and urease activities by 56% and 96%, respectively. The bacterial community structure in BC10 differed from those in the other treatments, and Luteivirga, Lactobacillus, Paenalcaligenes, Ulvibacter, Bacillus, Facklamia, Pelagibacterium, Sporosarcina, Cellvibrio, and Corynebacterium had the most important roles in composting. Compared with other treatments, BC10 significantly enhanced the average rates of degradation of carbohydrates (D-xylose (40%) and α-D-lactose (44%)) and amino acids (L-arginine (16%), L-asparagine (14%), and L-threonine (52%)). We also explored the associations among the bacterial community and their metabolic functions with the changes in the activities of enzymes. Network analysis demonstrated that BC10 altered the co-occurrence patterns of the bacterial communities, where Ulvibacter and class Bacilli were the keystone bacterial taxa with high capacities for degrading carbon source, and they were related to increases in the activities of cellulase and urease, respectively. The results obtained in this study may help to further enhance the efficiency of composting.

Recycling of nutrients from organic waste by advanced compost technology- A case study

Composting is widely used as an easily operated and economical method to manage organic wastes. However, the long residence time of composting impedes the recycling nutrients from large amounts of organic wastes produced every day. In this study, the intelligent biodrying + continuous dynamic trough (IB + CDT) was created and used in China's first urban and rural organic waste treatment and utilization demonstration center in Suzhou city. Results showed that IB + CDT composting had higher temperature, more reduction of moisture than windrow composting, enhancing 40% of composting efficiency. Primary fermentation of the IB + CDT composting in the indoor conditions could achieve the harmless treatment (GI > 80%) of compost within 12 days. The IB + CDT composting product enhanced 17% soil organic matter and 11% available nitrogen. The IB + CDT composting mode could earn 57.6 USD/ton by recycling organic waste and producing organic fertilizer, leading to a sustainable and profitable mode.

Moisture-Induced Pattern of Gases and Physicochemical Indices in Corn Straw and Cow Manure Composting

This study investigated the altering effect of moisture on the emission pattern of gases and the evolutionary dynamics of physicochemical indices in corn straw and cow manure composting. Exploring this effect was reasonable to unravel the use of moisture as a cheap alternative to control gaseous emissions and improve the final properties of compost. The nutrient dynamics of the compost showed 21.6% losses in total organic carbon content, with a 33.3% increase in total nitrogen content at the end of composting. All the gases (CH4, CO2, N2O and NH3) yielded a common emission pattern despite the differences in moisture content. Except for CH4, the peak and stable emission periods of all the gases were observed on the 5th day (thermophilic phase) and after the 27th day (late mesophilic phase) of composting, respectively. Emission reductions of 89%, 91%, 95% and 100% were recorded for CH4, CO2, N2O and NH3, respectively, during the late mesophilic phase of composting. From the study, the 65% moisture content was efficient in reducing the loss rate of the gasses and nutrient contents of the compost. This study would enable farmers to channel organic residues generated into compost while minimizing pollution and nutrient losses associated with the composting process.

Role of phosphorous additives on nitrogen conservation and maturity during pig manure composting

This study compared different types and addition amounts of phosphorous additives on nitrogen conservation and maturity during pig manure composting. Phosphogypsum and superphosphate were applied with the same amount of phosphorus (5% of the initial total nitrogen, molar basis) or weight (10% of initial dry matter) and compared to a control treatment without additives. Results show that phosphorous additives could effectively conserve nitrogen. Adding phosphogypsum could significantly reduce NH₃ emission and total nitrogen loss, but increase N₂O emission. Application of 10% superphosphate mitigated NH₃ emissions and total nitrogen loss but inhibited the organic matter degradation and compost maturity. More importantly, with the addition of 5% initial total nitrogen (i.e., 2.5% dry matter), superphosphate could synchronously reduce NH₃ and N₂O emissions and improve compost quality by introducing additional nutrients into the compost. In comprehensive evolution of gaseous emissions, nitrogen loss, and compost maturity, superphosphate addition with 2.5% of initial dry matter was suggested to be used in practice.

Acetobacter orientalis XJC-C with a high lignocellulosic biomass-degrading ability improves significantly composting efficiency of banana residues by increasing metabolic activity and functional diversity of bacterial community

Banana residues are an important energy resource after fruit harvesting. The optionally dumping and burning causes severely environmental problems. Traditional compost efficiency was limited by lignocellulosic composition of banana residues. Inoculation with cellulase-producing microbes provides an efficient strategy for improving degradation of lignocellulosic materials. In our study, a newly isolated cellulolytic bacterium Acetobacter orientalis XJC-C with a salt and high temperature resistance was identified from a marine soft coral. By contrast, the strain can biodegrade different lignocellulosic agricultural residues, especially banana straw. The highest cellulolytic and ligninolytic enzyme activities were detected during composting at 40 days. Compared with the negative and positive control groups, the lignin degradation rate reached 76.24% in the A. orientalis XJC-C group, increased by 47.08% and 21.85%, respectively. Moreover, the strain improved significantly the metabolic activity and functional diversity of bacterial community. Hence, A. orientalis XJC-C will be a promising candidate for degrading lignocellulosic agricultural residues.

Insight into the mechanisms of insoluble phosphate transformation driven by the interactions of compound microbes during composting

Phosphate-solubilizing (PS) microbes are important to improve phosphorus availability and transformation of insoluble phosphate, e.g., rock phosphate (RP). The use of phosphate solubilizing bacteria (PSB) as inoculants have been proposed as an alternative to increase phosphate availability in RP and composting fertilizers. In this study, the effect of compound PSB coinoculation and single-strain inoculation on the transformation of insoluble phosphate were compared in a liquid medium incubation and RP-enriched composting. The goal of this study was to understand the possible mechanisms of insoluble phosphate transformation driven by the interactions of compound PS microbes during composting. The correlations between organic acids production, P-solubilization capacity and bacterial community with PSB inoculation were investigated in the RP-enriched composting by redundancy analysis (RDA) and structural equation models (SEM). Results showed that both single-strain and compound PSB inoculants had a high P-solubilization capacity in medium, but the proportion of Olsen P to total P in composts with inoculating compound PS microbes was 7% higher than that with single strain. PS inoculants could secrete different organic acids and lactic was the most abundant. However, RDA and SEM suggested that oxalic might play an important role on PS activity, inducing RP solubilization by changing pH during composting. Interaction between compound microbes could intensify the acidolysis process for insoluble P transformation compared to the single strain. Our findings help to understand the roles of complex microbial inoculants and regulate P availability of insoluble phosphate for the agricultural purposes.

Aerobic composting remediation of petroleum hydrocarbon-contaminated soil. Current and future perspectives

This article provides a comprehensive review on aerobic composting remediation of soil contaminated with total petroleum hydrocarbons (TPHs). The studies reviewed have demonstrated that composting technology can be applied to treat TPH contamination (as high as 380,000 mg kg^-1) in clay, silt, and sandy soils successfully. Most of these studies reported more than 70% removal efficiency, with a maximum of 99%. During the composting process, the bacteria use TPHs as carbon and energy sources, whereas the fungi produce enzymes that can catalyze oxidation reactions of TPHs. The mutualistic and competitive interactions between the bacteria and fungi are believed to sustain a robust biodegradation system. The highest biodegradation rate is observed during the thermophilic phase. However, the presence of a diverse and dynamic microbial community ensures that TPH degradation occurs in the entire composting process. Initial concentration, soil type, soil/compost ratio, aeration rate, moisture content, C/N ratio, pH, and temperature affect the composting process and should be monitored and controlled to ensure successful degradation. Nevertheless, there is insufficient research on optimizing these operational parameters, especially for large-scale composting. Also, toxic and odorous gas emissions during degradation of TPHs, usually unaddressed, can be potential air pollution sources and need further insightful characterization and mitigation/control research.

Phosphate: Coupling the functions of fertilization and passivation in phytoremediation of manganese-contaminated soil by Polygonum pubescens blume

Phosphate (P) fertilization is a commonly used agronomic practice. However, research on bioremediation is very limited. This study's principal objective was to evaluate the role of P in the growth and heavy metals (HMs) accumulation of Polygonum pubescens Blume cultured in Mn-contaminated soil. To this end, the effects of sodium dihydrogen phosphate (SDP) and single superphosphate (SSP) on the growth, Mn bioremediation efficiency, organ HMs, and physiological parameters related to antioxidant stress of P. pubescens were examined. The results showed that both SDP and SSP increased soil pH and available P but decreased available HMs. Phosphate significantly (P < 0.05) promoted P. pubescens height and biomass. Average height increased by 36.1% and 32.6% with SDP and SSP, respectively, with corresponding biomass increases of 71.8% and 135%. Phosphate significantly (P < 0.05) reduced Mn concentrations, especially in leaves, where the values decreased by >50.0% for DSP and SSP. Total Mn significantly (P < 0.05) decreased with DSP amendment but significantly (P < 0.05) increased by 38.5% with SSP (200 mg kg^-1) through an increase in biomass. Phosphate significantly (P < 0.05) decreased all organ HM concentrations and translocation, indicating that less HM stress occurred with P amendment. The changes in reactive oxygen species, antioxidants and non-antioxidant materials further supported these results. Pearson correlation analysis revealed negative relationships between soil available P and HMs, indicating a novel role of P in HM passivation. The uncommonly high Ca concentrations in leaves suggested that Ca plays a vital role in promoting growth and alleviating HM stress in P. pubescens, which warrants further study.

Phosphate-solubilizing Pseudomonas sp., and Serratia sp., co-culture for Allium cepa L. growth promotion

Different genus of bacteria has been reported with the capacity to solubilize phosphorus from phosphate rock (PR). Pseudomonas sp., (A18) and Serratia sp., (C7) isolated from soils at the “Departamento de Boyacá” Colombia, where Allium cepa is cultivated. Bacteria were cultured in MT11B media and evaluated as a bio-fertilizer for A. cepa germination and growth during two months at greenhouse scale. Pseudomonas sp., and Serratia sp., cultured at 30 °C, 48 h in SMRS1 agar modified with PR, (as an inorganic source of phosphorus), presented a phosphate solubilization index (SI) of 2.1 ± 0.2 and 2.0 ± 0.3 mm, respectively. During interaction assays no inhibition halos were observed, demonstrating there was no antagonism between them. In MT11B media growth curve (12 h) demonstrated that co-culture can grow in the presence of PR and glucose concentrations 7.5-fold, lower than in SMRS1 media and brewer's yeast hydrolysate; producing phosphatase enzymes with a volumetric activity of 1.3 ± 0.03 PU at 6 h of culture and 0.8 ± 0.04 PU at 12 h. Moreover, co-culture released soluble phosphorus at a rate of 58.1 ± 0.28 mg L⁻¹ at 8 h and 88.1 ± 0.32 mg L⁻¹ at 12 h. After five days of evaluation it was observed that germination percentage was greater than 90 % of total evaluated seeds, when placing them in contact with the co-culture in a concentration of 1 × 10⁸ CFU mL⁻¹. Furthermore, it was demonstrated that co-culture application (10 mL per experimental unit to complete 160 mL in two months) at 8.0 Log₁₀ CFU mL⁻¹ twice a week for two months increased A. cepa total dry weight (69 ± 13 mg) compared with total dry weight (38 ± 5.0 mg) obtained with the control with water.

Effect of clay on greenhouse gas emissions and humification during pig manure composting as supported by spectroscopic evidence

To evaluate the effect of clay on greenhouse gas (GHGs) emissions and humification during pig manure (PM) composting, two lab-scale composting experiments, a control and a 10% clay treatment, were established. The results showed that adding clay reduced the emissions of CH₄ and N₂O by 45.88% and 86.79%, respectively, promoted the degradation of organic matter (OM) and facilitated the synthesis of humic acid (HA). The spectrum of dissolved organic matter (DOM) indicated that adding clay promoted the formation of aromatic carbon compounds and the degradation of aliphatic carbon. Furthermore, compared with the control, the spectral parameters including the specific UV absorbance at 254 nm (SUVA₂₅₄), the specific UV absorbance at 280 nm (SUVA₂₈₀) and the ration of the area at 435-480 nm and at 300-345 nm (A₄/A₁) of DOM were increased by 5.45%, 3.66% and 29.26%, respectively. Combined with the excitation - emission matrix (EEM) and the percentage fluorescence response (Pi,n), the clay amendment promoted the decomposition of tyrosine and Tryptophan and the formation of humic-like substances, and thus increased humification. The variation in the HA/fulvic acid and the humification index confirmed these results. Therefore, clay amendment is beneficial for reducing GHG emissions, promoting humification and aromatization during pig manure composting.

Effects of calcium magnesium phosphate fertilizer, biochar and spent mushroom substrate on compost maturity and gaseous emissions during pig manure composting

This study used a laboratory-scale system to investigate the effects of calcium magnesium phosphate fertilizer (CaMgP), biochar, and spent mushroom substrate (SMS) on compost maturity and gasous emissions during pig manure composting. The results showed that the addition of CaMgP, Biochar or SMS had no negative effect on the quality and maturity of compost, and all three additives could reduce the emissions of ammonia (NH₃), hydrogen sulfide (H₂S), dimethyl sulfide (Me₂S) and dimethyl disulfide (Me₂SS). Among them, the effect of adding CaMgP on NH₃ emission reduction was the most obvious, reduced 42.90%. The emission reduction of CaMgP to H₂S was similar to that of SMS, which decreased by 34.91% and 32.88% respectively. The emission reduction effects of the three additives on Me₂S and Me₂SS were obvious, all of which were over 50%. However, only adding SMS reduced the N₂O emission by 37.08%.

Acidification of manure reduces gaseous emissions and nutrient losses from subsequent composting process

Manure acidification is recommended to minimize ammonia (NH₃) emission at storage. However, the potential for acidification to mitigate NH₃ emission from storage and the impact of manure acidification (pH range 5-8) on composting have been poorly studied. The effects of manure acidification at storage on the subsequent composting process, nutrient balance, gaseous emissions and product quality were assessed through an analysis of literature data and an experiment under controlled conditions. Results of the data mining showed that mineral acids, acidic salts and organic acids significantly reduced NH₃ emission, however, a weaker effect was observed for organic acids. A subsequent composting experiment showed that using manure acidified to pH5 or pH6 as feedstock delayed organic matter degradation for 7-10 days, although pH6 had no negative effect on compost maturity. Acidification significantly decreased NH₃ emission from both storage and composting, however, excessive acidification (pH5) enhanced N₂O emissions (18.6%) during composting. When manure was acidified to pH6, N₂O (17.6%) and CH₄ (20%) emissions, and total GHG emissions expressed as global warming potential (GWP) (9.6%) were reduced during composting. Acidification of manure before composting conserved more N as NH₄⁺ and NO_x^- in compost product. Compared to the control, the labile, plant-available phosphorus (P) content in the compost product, predominately as water-soluble inorganic P, increased with manure acidification to pH5 and pH6. Acidification of manure to pH6 before composting decreases nutrient losses and gaseous emissions without decreasing the quality of the compost product. The techno-economic advantages of acidification should be further ascertained.

Passivation of lead and cadmium and increase of the nutrient content during sewage sludge composting by phosphate amendments

As an efficient and cost-effective biological treatment method for sewage sludge, composting has been widely used worldwide. To passivate heavy metals and enhance the nutrient content in compost, in the present study, phosphate rock, calcium magnesium phosphate, and monopotassium phosphate were added to the composting substrate. According to the Community Bureau of Reference sequential extraction procedure, phosphate rock and monopotassium phosphate amendments exhibit a good passivation effect on Cd and Pb. The X-ray diffraction patterns proved the formation of Pb₃(PO₄)₂ and Cd₅(PO₄)₂SiO₄ crystals, and X-ray absorption near-edge structure spectroscopy illustrated the change in P speciation after phosphate amendment. Furthermore, phosphate amendment increased the contents of total P and available P, and it reduced the loss of N during sewage sludge composting. The germination index showed that the target phosphate amendments in sewage sludge compost had no negative effects on seed germination, and this method has great potential to be used as a soil amendment.

Effects of external additives: Biochar, bentonite, phosphate, on co-composting for swine manure and corn straw

Composting is an acceptable and economically feasible process for recycling agricultural biomass waste. The addition of external additives to adjust the process of composting has been attracted lots of research attention. To investigate the effects of external additives on nutrients transformation process of composting, a laboratory reactors scale co-composting based on swine manure and corn straw (CK) with the additives of phosphate (MP), calcium bentonite (CB) and biochar (BC) were performed for 30 days. The results showed the addition of phosphate and biochar could contribute to accelerating temperature rise and shorten the thermophilic phase. The germination index (GI) of MP and BC achieved 180% and 150%, respectively. The excitation-emission matrix (EEM) demonstrated the intensities of the peak C (humic acids) of the MP treatment was 829.5, and the P_V,n/P_III,n value (9.59) of MP treatment was particularly higher compared to other three treatments according to the fluorescence regional integration (FRI) analysis. The Fourier Transform Infrared spectroscopy (FTIR) indicated the rate of decomposition of aliphatic C substances was higher than that of aromatic C substances. According to the X-ray diffraction (XRD) spectra results, characteristic peaks at both 16° and 22° were decreased, indicating cellulose and amorphous components were degraded. It further proved the formation of struvite component in MP treatment. Therefore, based on the maturity indicators, EEM and XRD results, phosphate is an efficient additive and recommended for swine manure and corn straw co-composting.

Effect of bean dregs amendment on the organic matter degradation, humification, maturity and stability of pig manure composting

The purpose of this study was to effectively dispose of bean dregs (BD) using composting technology, which could provide a theoretical basis for the disposal of BD. Therefore, the influence of different quantities of bean dregs (BD) (0%, 5%, 10% and 15%, w/w with a dry base of pig manure (PM)) on the decomposition and humification of organic matter during PM-composting was investigated, and a 0% BD amendment was used as the control (CK). Wheat straw was used as a bulking agent. Compared to the CK, the BD amendment promoted the degradation of organic matter. The degree of organic matter degradation increased by 16.46-25.04% upon BD amendment. Furthermore, the BD amendment improved humification and increased indices of the humification ratio (HR), percentage of humic acids (PHA), degree of polymerization (DP) and the humification index (HI). Furthermore, Fourier transform infrared (FTIR) spectroscopy indicated that the aromatic structure was enhanced with the BD amendment, and excitation-emission matrix (EEM) fluorescence spectra showed increased humic-like substance production. Additionally, the dissolved organic carbon (DOC), germination index (GI), electrical conductivity (Ec) and carbon/nitrogen (C/N) influenced the maturity and stability of composting. Comparatively, a 10% BD addition showed the optimal performance among all PM-composting treatments.

Hyperthermophilic composting of sewage sludge accelerates humic acid formation: Elemental and spectroscopic evidence

Application of thermophilic composting (TC) is limited due to poor efficiency and long composting period. Hyperthermophilic composting (HTC) could effectively overcome this defect. Here, the transformation of humic acid (HA) in both HTC and TC was characterized and compared to investigate the roles of HTC toward accelerating the formation of HA. In HTC, the highest temperature was 96.6 °C, and the hyperthermophilic and thermophilic phases exceed 18 days. The degree of polymerization (DP) in HTC increased to 1.27 on day 27, while it only increased to 1.15 at the end of TC. The elemental composition of the HA in HTC showed higher O atomic content (36.3%) and lower C/N atomic ratio (6.5) compared with TC. These changes indicated that HTC could significantly accelerate oxidized and polycondensed reactions for HA formation, which resulted in the shortening of composting period to 27 days. The maximum fluorescence intensity (F_max) of humic-like components were achieved faster in HTC (F_max = 1649.9) than in TC (F_max = 1316.9), implying that HTC promoted the polycondensation of small molecular components to form HA with larger molecular weight and higher degree of aromatization. Two-dimensional FTIR correlation spectroscopy (2D-FTIR-COS) analysis demonstrated that HTC prevented the HA precursor from condensing before it was deeply oxidized, and increased the content of small molecules rich in carboxyl moieties. Based on the evolution of the molecular structure of HA, the level of oxidation of HA precursors was a key factor to determine the degree of polymerization and the degree of HA humification.

Preservation of nitrogen and sulfur and passivation of heavy metals during sewage sludge composting with KH2PO4 and FeSO4

Composting is an effective method for treating sewage sludge. The aim of this work was to study preservation of nitrogen and sulfur and passivation of heavy metals during sewage sludge composting with KH₂PO₄ and FeSO₄. The results show the loss rate of N decreased by 27.5% while that of S was increased by 32.1% compared with the control treatment during composting when KH₂PO₄ and FeSO₄ were added. X-ray absorption near-edge structure spectra show that S was converted to a highly oxidizable state during sewage sludge composting with added KH₂PO₄. The mobility factors of Cu, Zn, and Pb after composting were found to decrease by 13.6%, 21.6%, and 3.8%, respectively, compared with those before composting when KH₂PO₄ was added. Adding these two materials to Cu and Zn inhibits Zn₃(PO₄)₂(H₂O)₄ and Cu₅(PO₄)₂(OH)₄ from transforming into more mobile forms, while adding these materials to Pb promotes Pb₃(PO₄)₂ formation.

Pilot-scale composting of typical multiple agricultural wastes: Parameter optimization and mechanisms

In this work, pilot-scale (100 kg of mixed wastes each time) composting of typical agricultural wastes, including chicken manure, vegetable leaves and rice husks with a mass ratio of 6:3:1, was studied. Effects of thermal phases and transformation time on performance, including moisture, nutrient, and carbon contents and C/N ratios of compost, were investigated. The optimal parameters were 75 ± 5 °C and 18 h; the compost met the requirements of Chinese National Agricultural Organic Fertilizer Standard (NY525-2012). Mechanisms investigations demonstrated that, Bacillus and Sinibacillus played key roles in degrading high-molecular-weighted organic substances into small-molecular-weighted humic- and fulvic-acid-like matters, resulting in smaller particle size and loose structure of the product; rice husk particles acted as a conditioning agent and remained their originally morphology. The mechanism provided informative guidance for optimizing the process in practical application.

Impacts of iron oxide nanoparticles on organic matter degradation and microbial enzyme activities during agricultural waste composting

The effects of iron oxide nanoparticles (IONPs, including Fe₂O₃ NPs and Fe₃O₄ NPs) on composting were investigated through evaluating their influences on organic matter (OM) degradation, dehydrogenase (DHA) and urease (UA) activities, and quality of the final compost product. Results showed that composting amended with Fe₂O₃ NPs was more effective to facilitate OM degradation. At the end of composting, the total OM loss in T-C, T-Fe₂O₃ NPs and T-Fe₃O₄ NPs was 66.19%, 75.53% and 61.31%, respectively. DHA and UA were also improved on the whole by the amendment of IONPs, especially Fe₂O₃ NPs. Although relationships between enzyme activities and environmental variables were changed by different treatments, temperature was the most influential to variations of both DHA and UA in all treatments, which independently explained 75.1%, 34.7% and 38.4% of variations in the two enzyme activities in T-C, T-Fe₂O₃ NPs and T-Fe₃O₄ NPs, respectively. Compared with DHA, UA was more closely related to the environmental parameters. The germination index in T-C, T-Fe₂O₃ NPs and T-Fe₃O₄ NPs was 134.49%, 153.64% and 146.76%, and the average shoot length was 3.16, 3.87 and 3.45 cm, respectively, indicating that amendment of IONPs, especially Fe₂O₃ NPs, could promote seed germination and seedling growth. Therefore, composting amended with IONPs was a feasible and promising method to improve composting performance, enzyme activities as well as quality of the final compost product.

The potential of ryegrass (Lolium perenne L.) to clean up multi-contaminated soils from labile and phytoavailable potentially toxic elements to contribute into a circular economy

Aided phytoremediation was studied for 48 weeks with the aim of reducing extractable and phytoavailable toxic elements and producing potential marketable biomass. In this sense, biomass of ryegrass was produced under greenhouse on two contaminated garden soils that have been amended with two successive additions of phosphates. After the first addition of phosphates, seeds of ryegrass were sown and shoots were harvested twice. A second seedling was performed after carefully mixing the roots from the first production (used as compost), soils and phosphates. Forty-eight weeks after starting the experiments, the concentrations of Cd, Pb, Zn, Cu, Fe, and Mn extracted using the rhizosphere-based method were generally lower than those measured before the addition of phosphates and cultivation (except for Pb and Fe in the most contaminated soil). The concentrations of metals in the shoots of ryegrass from the second production were lower than those from the first (except for Al). The best results were obtained with phosphates and were the most relevant in the lowest contaminated soil, demonstrating that the available metal concentrations have to be taken into account in the management of contaminated soils. In view of the concentration of metals defined as carcinogens, mutagens, and reprotoxics (e.g., Cd, Pb) and those capable to be transformed into Lewis acids (e.g., Zn, Fe), the utilization of ryegrass in the revegetation of contaminated soils and in risk management may be a new production of marketable biomass. The development of phytomanagement in combination with this type of biomass coincided with the view that contaminated soils can still represent a valuable resource that should be used sustainably.

Impact of phosphate additive on organic carbon component degradation during pig manure composting

Phosphate, as an additive to composting, could significantly reduce ammonia emission and nitrogen loss but may also cause adverse effects on the degradation of organic matter. However, there is little information about the influence of pH change, salt content, and phosphate on different organic fraction degradation during composting with the addition of phosphate at a higher level. In this study, the equimolar phosphoric acid (H₃PO₄), sulfuric acid (H₂SO₄), and dipotassium phosphate (K₂HPO₄) were added into pig manure composting with 0.25 mol mass per kilogram of dry matter basis addition amount to evaluate the effect of H⁺, PO₄^3-, and salinity on carbon component transformation and organic matter degradation. The results showed that both H₃PO₄ and K₂HPO₄ additives could lead to shorter duration in the thermophilic phase, lower degradation of lignocellulose, and lesser carbon loss compared to CK, even though had different pH, i.e., acidic and alkaline conditions, respectively. Besides, the addition of H₃PO₄, H₂SO₄, and K₂HPO₄ could increase the degradation of soluble protein and lipid during composting. Redundancy analysis demonstrated that the variation in different organic carbon fractions was significantly correlated with the changes of pH and the presence of PO₄^3-, but not with SO₄^2- and electrical conductivity, suggesting that pH and phosphate were the more predominant factors than salinity for the inhibition of organic matter degradation. Taken together, as acidic phosphate addition produces a true advantage of controlling nitrogen loss and lower inhibition of organics transformation during composting, the expected effects may result in more efficient composting products.

Effect of phosphate amendments on improving the fertilizer efficiency and reducing the mobility of heavy metals during sewage sludge composting

Composting has been globally applied as an effective and cost-efficient process to manage and reuse sewage sludge. In the present study, four different phosphates as well as a mixture of ferrous sulfate and monopotassium phosphate were used in sewage sludge composting. The results showed that these phosphate amendments promoted an increase in temperature and the degradation of organic matter as well as reduction on nitrogen loss during 18 days of composting. In addition, ferrous sulfate and phosphate had a synergistic effect on reducing nitrogen loss. The contents of total phosphorus and available phosphorus in the compost with addition of 1% phosphate were 40.9% and 66.1% higher than the compost with control treatment. Using the BCR (Community Bureau of Reference) sequential extraction procedure, the addition of calcium magnesium phosphate significantly reduced the mobility factor of Cd, Zn and Cu by 24.2%, 1.7% and 18.8%, respectively. The mobility factors of Pb were increased in all samples, but the monopotassium phosphate treated sample exhibited the greatest Pb passivation ability with the lowest mobility factor increase (1.8%) among all treatments. The X-ray diffraction patterns of compost samples indicated that the passivation mechanism of Cu and Zn may be the forming CuFeS₂ and ZnCu(P₂O₇) crystals during sewage sludge composting. The germination index showed that the compost of all treatments was safe for agricultural application; the germination index of the calcium magnesium phosphate treatment was 99.9 ± 11.8%, which was the highest among all treatments.