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

Heavy metal(loid)s accumulation and human health risk assessment in wheat after long-term application of various urban and rural organic fertilizers

Composting urban and rural wastes into organic fertilizers for land application is considered the best way to dispose of and recycle waste resources. However, there are some concerns about the long-term effects of applying various organic fertilizers on soils, food safety, and health risks derived from heavy metal(loid)s (HMs). A long-term field experiment was conducted to evaluate the effects of continuous application of chicken manure compost (CM), sewage sludge compost (SSC), and domestic waste compost (DWC) for wheat on the accumulation, transfer, and health risks of HMs. The results revealed that, compared with control or chemical fertilizer treatments, continuous application of CM raised the concentrations of cadmium (Cd), chromium (Cr), copper (Cu), and zinc (Zn) in topsoil by 29 %-38 %, 15 %-16 %,11 %-14 %, and 20 %-36 %, respectively; SSC increased the concentrations of Cd, Cr, Mercury (Hg), arsenic (As), Cu, and Zn by 18 %-26 %, 8 %-9 %, 310 %-329 %, 5 %-8 %, 17 %-21 %, and 19 %-35 %, respectively; and DWC elevated the concentrations of Cd, Cr, Hg, lead (Pb), and Zn by 20 %-28 %, 8 %-9 %, 118 %-118 %, 5 %-10 %, and 3 %-17 %. The HMs concentrations in wheat grain were almost unaffected by the application of the organic fertilizers except for Hg and Pb concentrations. However, the HMs concentrations in both soil and wheat grain remained far below the limits of regulation in China. The long-term application of organic fertilizers did not cause additional noncarcinogenic and carcinogenic risks associated with exposure to HMs. In conclusion, although the long-term application of various urban and rural organic fertilizers increased the concentrations of several HMs in the soil, it almost did not cause any additional adverse effects on wheat grain or increase the health risks.

Biostabilization of fecal sludge and tannery liming sludge: A novel approach

Fecal sludge and tannery liming sludge management is essential for humans and the environment. The emitted amount of waste from two industries is reduced in composting leading to value-added products. This research focused on the effectiveness and feasibility of co-composting fecal sludge and hair-burning liming sludge from tannery. Fecal sludge was intermittently mixed with hair-burning liming sludge which also consisted of chicken manure and sawdust. Five piles (Pile 1, Pile 2, Pil3, Pile 4, and Pile 5) indicated respectively as P#1, P#2, P#3, P#4, and P#5, contained various ratios of composting materials were mixed, piled onto a horizontal bamboo frame, and observed for 120 days. To ensure a suitable oxygen supply, the composting piles were turned on in the thermophilic stage so that pathogens could not survive. The highest temperatures in the thermophilic stage were 39.0°C, 49.2°C, 55.7°C, 41.7°C, and 51.3°C. These referred to the respective piles P#1, P#2, P#3, P#4, and P#5. The Dewar stability index confirmed the stability of each composting pile, and the maximum degradation was found for P#3. The metals chromium (Cr), zinc (Zn), lead (Pb), iron (Fe), and nickel (Ni) in the final compost were found to be 38.1, 144.7, 15.1, 450.5, and 22.7 mg/kg, respectively. TCLP results reveal only an insignificant amount of metal leaching. Fecal coliform of the compost was below the standard level; Helminth eggs and Salmonella spp. were absent. SEM micrographs reflect the decomposition of composting materials. The maximum germination index and germination capacity of compost pile P#3 for compost-soil ratio 1:0 and 1:1 were 90%-92.8% and 100%, respectively. The present approach produced nutrient-enriched compost from fecal sludge and hair-burning liming sludge from a tannery emerges as a suitable solution for reducing solid wastes.

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.

Effects and Mechanisms of Different Types of Biochar on Heavy Metal Passivation during Sludge Composting

The effects and mechanisms of the different types of biochar on heavy metal passivation are still not fully understood. This study compared the effects of three types of biochar on heavy metal passivation during sludge composting. Compared with composting without biochar, rice husk biochar was most effective for the passivation of Zn and Pb, with increased passivation rates of 1.90% and 20.43%, respectively. In contrast, sludge biochar was the most effective for the passivation of Cr and Hg, with increased passivation rates of 28.30% and 3.09%, respectively. Coconut shell biochar showed the best performance for the passivation of Cu, Ni, As, and Cd, and was enriched with micropore structures, which possibly led to the adsorption and reaction of heavy metals, organic matter, and microorganisms. The improved passivation effect of the rice husk and sludge biochar on heavy metals can be attributed to the improved humification of organic matter. This study suggests that specific types of biochar should be considered for the passivation of different types of heavy metals for practical applications.

Effect of thermal treatment of illite on the bioavailability of copper and zinc in the aerobic composting of pig manure with corn straw

The large amount of various types of heavy metals in animal manure applied to agricultural field has caused severe threat to the ecosystems of soil environments. In this study, the effect of thermal treatment of illite on the bioavailability of copper (Cu) and zinc (Zn) in the aerobic composting of pig manure with corn straw biochar was investigated. The objectives of this study were to characterize the variations in the bioavailability of Cu and Zn in the aerobic composting of pig manure added with illite treated with high temperatures and to identify the relatively dominant microbes involved in the formation of humus and passivation of heavy metals in pig manure composting based on 16S rRNA high-throughput sequencing analysis. The results showed that in comparison with the raw materials of pig manure, the bioavailability of Zn and Cu in the control and three experimental composting groups, i.e., group I (with untreated illite), group I-2 (with illite treated under 200°C), and group I-5 (with illite treated under 500°C), was decreased by 27.66 and 71.54%, 47.05 and 79.80%, 51.56 and 81.93%, and 58.15 and 86.60%, respectively. The results of 16S rRNA sequencing analysis revealed that in the I-5 group, the highest relative abundance was detected in Fermentimonas, which was associated with the degradation of glucose and fructose, and the increased relative abundances were revealed in the microbes associated with the formation of humus, which chelated with Zn and Cu to ultimately reduce the bioavailability of heavy metals and their biotoxicity in the compost. This study provided strong experimental evidence to support the application of illite in pig manure composting and novel insights into the selection of appropriate additives (i.e., illite) to promote humification and passivation of different heavy metals in pig manure composting.

Ca(H2PO4)2 and MgSO4 activated nitrogen-related bacteria and genes in thermophilic stage of compost

This study was conducted to investigate the effects of Ca(H2PO4)2 and MgSO4 on the bacterial community and nitrogen metabolism genes in the aerobic composting of pig manure. The experimental treatments were set up as control (C), 1% Ca(H2PO4)2 + 2% MgSO4 (CaPM1), and 1.5% Ca(H2PO4)2 + 3% MgSO4 (CaPM2), which were used at the end of composting for potting trials. The results showed that Ca(H2PO4)2 and MgSO4 played an excellent role in retaining nitrogen and increasing the alkali-hydrolyzed nitrogen (AN), available phosphorus (AP), and available potassium (AK) contents of the composts. Adding Ca(H2PO4)2 and MgSO4 changed the microbial community structure of the compost. The microorganisms associated with nitrogen retention were activated. The complexity of the microbial network was enhanced. Genetic prediction analysis showed that the addition of Ca(H2PO4)2 and MgSO4 reduced the accumulation of nitroso-nitrogen and the process of denitrification. At the same time, despite the reduction of genes related to nitrogen fixation, the conversion of ammonia to nitrogenous organic compounds was promoted and the stability of nitrogen was increased. Mantel test analysis showed that Ca(H2PO4)2 and MgSO4 can affect nitrogen transformation-related bacteria and thus indirectly affect nitrogen metabolism genes by influencing the temperature, pH, and organic matter (OM) of the compost and also directly affected nitrogen metabolism genes through PO43- and Mg2+. The pot experiment showed that composting with 1.5% Ca(H2PO4)2 + 3% MgSO4 produced the compost product that improved the growth yield and nutrient content of cilantro and increased the fertility of the soil. In conclusion, Ca(H2PO4)2 and MgSO4 reduces the loss of nitrogen from compost, activates nitrogen-related bacteria and genes in the thermophilic phase of composting, and improves the fertilizer efficiency of compost products. KEY POINTS: • Ca(H2PO4)2 and MgSO4 reduced the nitrogen loss and improved the compost effect • Activated nitrogen-related bacteria and altered nitrogen metabolism genes • Improved the yield and quality of cilantro and fertility of soil.

Biochemical changes, metal content, and spectroscopic analysis in sewage sludge composted with lignocellulosic residue using FTIR-MIR and FTIR-NIR

The use of lignocellulosic residues, originating from sawdust, in composting sewage sludge for organic fertilizer production, is a practice of growing interest. However, few studies have explored the effect of the proportion of sawdust and sewage sludge raw materials on composting performance in the humification process. This study assessed the addition of sawdust in the sewage sludge composting process, regarding carbon content, presence of heavy metals, and humification of the organic compost. The experimental design employed was a randomized complete block design with five treatments featuring different proportions of organic residues to achieve C/N ratios between 30-1 (T1: 100% sewage sludge and 0% sawdust, T2: 86% sewage sludge and 14.0% sawdust, T3: 67% sewage sludge and 33% sawdust, T4: 55% sewage sludge and 45% sawdust, and T5: 46.5% sewage sludge and 53.5% sawdust) and five replications, totaling 25 experimental units. The addition of lignocellulosic residue in sewage sludge composting increased the levels of TOC and the C/N ratio, reduced the levels of pH, P, N, Na, Ba, and Cr, and did not interfere with the levels of K, Ca, Mg, S, CEC, labile carbon, and metals Fe, Zn, Cu, Mn, Ni, and Pb. The increase in the proportion of sawdust residue favored the degradation of aliphatic groups, increasing the presence of aromatic structures and reducing humification at the end of composting. The use of sawdust as a lignocellulosic residue in sewage sludge composting is a viable and efficient alternative to produce high-quality organomineral fertilizers.

Effect of nitrogen retention composite additives Ca(H2PO4)2 and MgSO4 on the degradation of lignocellulose, compost maturation, and fungal communities in compost

This study investigated the effects of the nitrogen retention composite additives Ca(H2PO4)2 and MgSO4 on lignocellulose degradation, maturation, and fungal communities in composts. The study included control (C, without Ca(H2PO4)2 and MgSO4), 1% Ca(H2PO4)2 + 2% MgSO4 (CaPM1), 1.5% Ca(H2PO4)2 + 3% MgSO4 (CaPM2). The results showed that Ca(H2PO4)2 and MgSO4 enhanced the degradation of total organic carbon (TOC) and promoted the degradation of lignocellulose in compost, with CaPM2 showing the highest TOC and lignocellulose degradation. Changes in the three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM) of dissolved organic matter (DOM) components in compost indicated that the treatment group with the addition of Ca(H2PO4)2 and MgSO4 promoted the production of humic acids (HAs) and increased the degree of compost decomposition, with CaPM2 demonstrating the highest degree of decomposition. The addition of Ca(H2PO4)2 and MgSO4 modified the composition of the fungal community. Ca(H2PO4)2 and MgSO4 increased the relative abundance of Ascomycota, decreased unclassified_Fungi, and Glomeromycota, and activated the fungal genera Thermomyces and Aspergillus, which can degrade lignin and cellulose during the thermophilic stage of composting. Ca(H2PO4)2 and MgSO4 also increased the abundance of Saprotroph, particularly undefined Saprotroph. In conclusion, the addition of Ca(H2PO4)2 and MgSO4 in composting activated fungal communities involved in lignocellulose degradation, promoted the degradation of lignocellulose, and enhanced the maturation degree of compost.

Emerging insights into the impacts of heavy metals exposure on health, reproductive and productive performance of livestock

Heavy metals, common environmental pollutants with widespread distribution hazards and several health problems linked to them are distinguished from other toxic compounds by their bioaccumulation in living organisms. They pollute the food chain and threaten the health of animals. Biologically, heavy metals exhibit both beneficial and harmful effects. Certain essential heavy metals such as Co, Mn, Se, Zn, and Mg play crucial roles in vital physiological processes in trace amounts, while others like As, Pb, Hg, Cd, and Cu are widely recognized for their toxic properties. Regardless of their physiological functions, an excess intake of all heavy metals beyond the tolerance limit can lead to toxicity. Animals face exposure to heavy metals through contaminated feed and water, primarily as a result of anthropogenic environmental pollution. After ingestion heavy metals persist in the body for an extended duration and the nature of exposure dictates whether they induce acute or chronic, clinical or subclinical, or subtle toxicities. The toxic effects of metals lead to disruption of cellular homeostasis through the generation of free radicals that develop oxidative stress. In cases of acute heavy metal poisoning, characteristic clinical symptoms may arise, potentially culminating in the death of animals with corresponding necropsy findings. Chronic toxicities manifest as a decline in overall body condition scoring and a decrease in the production potential of animals. Elevated heavy metal levels in consumable animal products raise public health concerns. Timely diagnosis, targeted antidotes, and management strategies can significantly mitigate heavy metal impact on livestock health, productivity, and reproductive performance.

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.

Impact of grazing around industrial areas on milk heavy metals contamination and reproductive ovarian hormones of she-camel with assessment of some technological processes on reduction of toxic residue concentrations

Heavy metals are one of the most toxic chemical pollutants of the environment. Their hazards not restricted to human but extend to animal productivity and reproductively. The present study aimed to assess the impact of grazing around industrial areas on the levels of copper (Cu) and aluminum (Al) residues in milk samples collected from dromedary she-camels and studying their effects on some ovarian hormones. In addition, the study aimed to investigate methods of removal of the toxic concentrations of these heavy metals in milk by applying different technological processes. Blood and milk samples were collected from 30 dromedary she-camels, 15 grazing in non-industrial areas (group A) and 15 grazing in industrial areas (group B). Detection of the levels of these heavy metals in milk was done. Ovarian hormones investigation on the blood was performed. Different technological processes such as boiling, skimming and fermentation were applied to all contaminated samples to reduce the toxic concentrations of these heavy metals. Results revealed that all examined milk samples in both groups contained Cu, while 40% of group A and 100 % of group B contained Al residues with different concentrations. The levels of Cu and Al residues in samples of group A not exceeded the maximum residual limit (MRL) set by World Health Organization (WHO) while 60% and 100% of milk samples in group B contained Cu and Al residues exceeded MRL, respectively. Technological processes induce variant changes in the levels of these metals in milk. Heat treatment of milk in Al vats leads to leaching of Al from containers to the milk causing significant increase in Al load, while Cu level was not significantly affected. Boiling in stainless-steel containers decreased the levels of Al and Cu but in non-significant levels. Regarding skimming process, small amount of Cu and Al escaped into the skimmed milk while greater amount were recovered in the cream. Fermentation by probiotic bacteria showed that milk fermentation has non-significant effect on Cu and Al levels. Investigation of ovarian hormones (estrogen and progesterone) revealed presence of a signification reduction in the levels of these hormones in group B compared to group A. In addition, a negative correlation was found between these heavy metals and ovarian hormones concentrations in the blood. It is concluded that grazing of dromedary camels around industrial areas induce heavy metals toxicity represented by excretion of these metals in milk and significant reduction on ovarian function showed by reduction of estrogen and progesterone levels. Technological processes such as skimming decreased the levels of Al and Cu residues in milk.

Effects of oyster shells on maturity and calcium activation in organic solid waste compost

With the rapid development of aquaculture, the production of oyster shells has surged, posing a potential threat to the environment. While oyster shell powder is widely recognized for its inherent alkalinity and rich calcium carbonate content, making it a superior soil conditioner, its role in organic solid waste composting remains underexplored. To investigate the effects of varying concentrations of oyster shell powder on compost maturation and calcium activation, this study employed thermophilic co-composting with acidic sugar residue and bean pulp, incorporating 0% (control), 10% (T1), 20% (T2), 30% (T3), and 40% (T4) oyster shell powder. Findings revealed that appropriate proportions of oyster shell powder significantly enhance temperature stability during composting and elevate maturation levels, notably reducing ammonia emissions between 62.5% and 76.7%. Intriguingly, the calcium in the oyster shell powder was significantly activated during composting, with the 40% addition group achieving the highest calcium activation rate of 48.5%. In summation, the inclusion of oyster shell powder not only optimizes the composting process but also efficiently activates the calcium, resulting in an alkaline organic-inorganic composite soil conditioner with high exchangeable calcium content. This research holds significant implications for promoting the high-value utilization of oyster shells.

Determining the extraction conditions and phytotoxicity threshold for compost maturity evaluation using the seed germination index method

The phytotoxicity of the compost aqueous extracts determines the maturity. To improve the accuracy of compost maturity evaluation using the seed germination index (GI) method, different extraction methods (different moisture content and extraction ratio) were designed to obtain samples with various phytotoxic level. This study analyzed the effects of different extraction condition of compost samples on GI, and established the relationship between phytotoxicity and GI. The results showed that the moisture content and extraction ratio of the compost significantly affected the GI. The extraction ratio for the compost with 60-70 % moisture content was 1:10 (ratio of compost mass to extract volume). However, commercial compost, which must have a moisture content of 30-45 %, had an extraction ratio of 1:30 (w:v). More importantly, compost extraction based on dry weight, with a moisture content of 10-15 %, more effectively reflected the phytotoxicity variations during composting. In such cases, the extraction ratio should be at least 1:30 (w:v) but not exceed 1:50 (w:v). The relationship between phytotoxicity and GI showed that dissolved organic carbon and dissolved nitrogen were the most important factors influencing GI, followed by NH4+, electrical conductivity, K, volatile fatty acids, Zn, and Cu. For composts with a GI greater than 70 %, the dissolved organic carbon, dissolved nitrogen, and NH4+ concentrations were below 257, 164, and 73 mg/L, respectively. These findings provide an optimized standard method for compost maturity evaluation using GI and a concentration threshold of key phytotoxicity is proposed to achieve accurate control of compost maturity.

Effects of blast furnace slag on the immobilization, plant uptake and translocation of Cd in a contaminated paddy soil

The potential toxicity of Cd to soil and rice plant severely threaten human health. This study was conducted to investigate the remediation effects of blast furnace slag (BFS) on the bioavailability of Cd in a contaminated paddy soil from a perspective of soil solution chemistry. Batch experiments, pot culture experiments, and principal analysis (PCA) were used to study the effects and mechanisms of BFS addition changing Cd chemical behavior and Cd toxicity. Results indicated that BFS facilitated Cd adsorption in soils, increased pH, Eh, and EC values in soil solution, whereas reduced dissolved Cd content. BFS amendment was efficient in decreasing root Cd intake and Cd upward transport in rice plant, with the Cd translocation factor in brown rice decreased by ∼ 75% (BFS treatment, 6‰ wt) relative to Cd treatment, which in turn increased rice biomass and grain yield. PCA indicated that the dissolved Cd concentration had a close relationship with soil pH and metal concentration in soil solution. Results from this study indicated that BFS had potential ability for either immobilization or remobilization of Cd in soils, and the findings have important implications for Cd-polluted soil remediation or other resource utilization with slag-based materials.

A combined passivator of zeolite and calcium magnesium phosphate fertilizer: Passivation behavior and mechanism for Cd (II) in composting

Passivation of heavy metals is one of the most efficient techniques to improve the quality of compost. Many studies confirmed the passivation effect of passivators (e.g., zeolite and calcium magnesium phosphate fertilizer) on cadmium (Cd), but passivators with single component could not effectively passivate Cd in the long-term operation of composting. In the present study, a combined passivator of zeolite and calcium magnesium phosphate fertilizer (ZCP) was used to explore its impacts of adding at different composting periods (heating period, thermophilic period, cooling period) on the Cd control, compost quality (e.g., temperature, moisture content and humification), microbial community structure as well as the compost available forms of Cd and addition strategy of ZCP. Results showed that Cd passivation rate could be increased by 35.70-47.92% under all treatments in comparison to the control treatment. By altering bacterial community structure, reducing Cd bioavailability and improving the chemical properties of the compost, the combined inorganic passivator could achieve high efficiency for Cd passivation. To sum up, the addition of ZCP at different composting periods has effects on the process and quality of composting, which could provide ideas for the optimization of the passivators addition strategy.

Impacts of adding FeSO4 and biochar on nitrogen loss, bacterial community and related functional genes during cattle manure composting

This study investigated the impacts of adding FeSO₄ and biochar to cattle manure and rice straw composts on functional genes controlling nitrogen loss, bacterial community, nitrification, and denitrification. Four treatments were established, including a control group (CP), and CP mixtures that included 4% biochar (TG1), 4% FeSO₄ (TG2), or 2% FeSO₄ and 2% biochar (TG3). Compared to CP, TG1-3 had a lower total nitrogen loss rate, and TG3 resulted in reduced NH₃ (52.4%) and N₂O (35.6%) emissions to mitigate nitrogen loss. The abundance of amoA and narG gene in TG3 was higher than in the other groups, and TG3 was beneficial to the growth of Proteobacteria and Actinobacteria. According to redundancy and Pearson analysis, TG3 had a positive effect on the nitrification process by increasing the abundance of amoA and narG. Thus, biochar and FeSO₄ addition mitigate nitrogen loss by regulating the nitrification processes.

Industrial-scale composting of swine manure with a novel additive-yellow phosphorus slag: Variation in maturity indicators, compost quality and phosphorus speciation

Composting experiment of swine manure, adding with yellow phosphorus slag(YPS) at 5% (w/w), was conducted in an industrial-scale reactor covered with semi-permeable membrane. During 27 days of composting, the changes in temperature, compost quality and phosphorus(P) speciation of products were monitored. Results indicated that the temperature of compost pile was sharply increased on day 2, and the thermophilic period lasted for 15 days. The dynamics in germination index(GI), pH, nutrient contents, etc. of products were in line with conventional composting process. For P distribution, the contents of total-P and citric acid extracted-P(CAP) of products were increased during composting, while that of Olsen-P was decreased. HCl extracted inorganic P(HCl-Pi), a slowly release fraction of P, was dominated in the product, which showed an increasing trend during the composting. These results suggest that the industrial-scale composting with novel YPS additive can be accomplished, and its product contains abundant slowly released P.

Composting of limed fleshings generated in a tannery: sustainable waste management

In tanneries, limed fleshing is an unavoidable waste generated in beamhouse operation. Proper management of limed fleshing with protein, fat, lime, and sulfide will help to protect the natural environment and at least reduce the pollution that ends up in it. In this study, excluding any pretreatment, limed fleshing is used for compost production. Chopped and mixed limed fleshing with chicken manure, cow dung, and sawdust was heaped onto a horizontal bamboo frame. Three composting heaps were fabricated weighing 720, 700, and 760 kg. The turning of composting materials in the heaps causes temperature changes in the thermophilic range. The thermophilic temperatures in these heaps were 69.07 °C (heap 1), 69.9 °C (heap 2), and 69.19 °C (heap 3) which ensured the death of the pathogenic organism. The quality of compost was assessed based on the nutrients-nitrogen (N), phosphorous (P), potassium (K), and sulfur (S) content. NPKS in the compost fulfils the requirements of the investigated materials as compost. The largest amounts of metals- zinc (Zn), copper (Cu), chromium (Cr), lead (Pb), and nickel (Ni) of the compost detected in the heaps were, respectively, 200.3, 37.4, 20.3, 12.0, and 3.9 mg/kg. Cadmium (Cd) in the compost was below the detection limit. Scanning electron microscope (SEM) photographs show the decomposing of composting materials. This study indicates that limed fleshing can be converted into nutrient-enriched compost without any pretreatment. Using an easy, simple, and adaptable technique could reduce the volume of solid waste generated in the tannery to reduce environmental pollution.

Effects of adding biochar on the preservation of nitrogen and passivation of heavy metal during hyperthermophilic composting of sewage sludge

Hyperthermophilic composting (HTC) is regarded as an effective method for processing sewage sludge. The aim of the study was to investigate effects of using biochar as an amendment on the preservation of nitrogen and passivation of heavy metal during the HTC process of sewage sludge. Results showed that HTC improved the fermentation efficiency and the compost maturity by increases in the temperature and germination index (GI) value, and decreases in the moisture and C/N ratio compared to conventional thermophilic composting. HTC process and the biochar addition resulted in a decrease of the nitrogen loss compared with the control pile during composting by promoting transforming ammonium into nitrite nitrogen. Adding biochar to composting inhibited the transformation of Cu, Zn and Pb into more mobile speciation compared to the control pile although their contents increased during composting, which lead to reduction in availability of heavy metals. Thus, HTC process with the addition of biochar is viable for the reduction of the nitrogen losses and mobility of heavy metal in compost.Implications: The treatment of sewage sludge is imminent due to its threat to general health and ecosystems. This work represents the effects of adding biochar on the preservation of nitrogen and passivation of heavy metal during hyperthermophilic composting of sewage sludge. Our results indicate that the additions of biochar and hyperthermophilic composting engendered the several of positive effects on the preservation of nitrogen and passivation of heavy metal. Thus, HTC process with the addition of biochar is viable for the reduction of the nitrogen losses and mobility of heavy metal in compost.

Simulation, prediction and optimization of typical heavy metals immobilization in swine manure composting by using machine learning models and genetic algorithm

Machine learning (ML) is a novel method of data analysis with potential to overcome limitations of traditional composting experiments. In this study, four ML models (multi-layer perceptron regression, support vector regression, decision tree regression, and gradient boosting regression) were integrated with genetic algorithm to predict and optimize heavy metal immobilization during composting. Gradient boosting regression performed best among the four models for predicting both heavy metal bioavailability variations and immobilization. Gradient boosting regression-based feature importance analysis revealed that the heavy metal initial bioavailability factor, total phosphorus, and composting duration were the determinant factors for heavy metal bioavailability variations (together contributing >75%). After genetic algorithm optimization, the maximum immobilization rates of Cu, Zn, Cd, As, and Cr were 79.53, 31.30, 14.91, 46.25, and 66.27%, respectively, superior to over 90% of the measured data. These findings demonstrate the potential application of ML to risk-control for heavy metals in livestock manure composting.

High nitrogen addition after the application of sewage sludge compost decreased the bioavailability of heavy metals in soil

Nitrogen (N) fertilizer is highly significant in agricultural production, but long-term N addition causes changes in quality indicators, such as soil organic matter (SOM), thus affecting the absorption and accumulation of organic pollutants. Therefore, paying more attention to organic fertilizers in the development of green agriculture is necessary. However, the accumulation of heavy metals (HMs) contained in organic fertilizers (especially sewage sludge compost (SSC)) in the soil can cause environmental contamination, but how this cumulative reaction changes with the long-term N addition remains unclear. Here the SSC impact on the bioavailability of five typical HMs (cadmium-Cd, chromium-Cr, copper-Cu, lead-Pb and arsenic-As) in the soil-plant system before and after SSC application was demonstrated through a field study in soils with different application rates of 0, 100 and 300 kg N ha^-1yr^-1, respectively. Our results showed that SSC application increased the concentration of most HMs in soil profiles and plant systems (wheat roots and grains), but the accumulation rate of HMs and most bioaccumulation values (BAC-bioaccumulation coefficient and BCF-bioconcentration factor) in plant systems were both lower in high-N addition soil than that in the low-N group. Moreover, speciation distribution results further indicated that SSC application increased the LB (liable available form, including F1-water soluble, F2-ion exchangeable, and F3-bound to carbonates) form of HMs and decreased the PB (potentially available form, including F4-humic acids and F6-fraction bound to organic matter) form of HMs in high-N addition soil, respectively. Those results suggested that HM bioavailability in high-N addition soil was lower than that in low-N addition soil when applied with SSC. Overall, this study found that increasing soil N content can inhibit the bioavailability of HMs when applying SSC, providing suggestions for optimizing the trialability and risk assessment of SSC application.

Effects of two types nitrogen sources on humification processes and phosphorus dynamics during the aerobic composting of spent mushroom substrate

Aerobic composting is increasingly regarded as a promising technology for the recycling of spent mushroom substrate (SMS), and an applicable nitrogen source is necessary to improve the process. This study is the first to investigate the effects of protein-like N source (chicken manure, CM) and high-N source (urea, UR) on humification process and P dynamics during SMS composting. The effect of different N sources on microbial succession was also studied. Results showed that CM addition achieved a longer thermophilic phase (16 d vs 9 d), greater germination indices (131.6% vs 106.3%), and higher total phosphorus content (13.1 g/kg vs 6.56 g/kg) in the end products, as compared to UR. The addition of CM showed beneficial effects on humification and stabilization, including decreased weight loss and fluctuations in the level of functional groups. The P produced in the compost was interconverted and leached in the P pool. In this case, the P detected in the compost was in the form of orthophosphate and MgNH₄PO₄⋅6H₂O crystal as inorganic P and orthophosphate monoester as organic P. The most abundant microorganisms at the phylum level mainly include Firmicutes, Actinobacteria, and Proteobacteria, accounting for more than 88% of the total microorganisms. The addition of CM to SMS compost resulted in higher organic matter degradation rates. This work clarified the role of various N sources in SMS composting and presented an appropriate waste management method beneficial to bioresource technology and sustainable development of the edible fungi business.

Effect of superphosphate addition on heavy metals speciation and microbial communities during composting

Superphosphate fertilizer (SSP) as an additive can reduce the nitrogen loss and increase available phosphorus in composting but few studies investigated the effect of SSP addition on heavy metal and microbial communities. In this study, different ratios (10%, 18%, 26%) of SSP were added into pig manure composting to assess the changes of heavy metal (Cu, Mn, As, Zn, and Fe) fractions, bacterial and fungal communities as well as their interactions. SSP addition at 18% had lower ecological risk but still increased the bioavailability of Cu, Mn, and Fe in composts compared to control. Adding 18% SSP into compost decreased bacterial number and increased the fungal diversity compared to CK. Redundancy analysis indicated heavy metal fractions correlated significantly with bacterial and fungal community compositions in composting with 18% SSP. Network analysis showed adding 18% SSP increased microbial interaction and positive cooperation especially enhanced the proportion of Proteobacteria and Ascomycota.

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.

Improving the quality of organic compost of sewage sludge using grass cultivation followed by composting

Composting is one of the main processes of stabilization of sewage sludge and its association with cultivation in this residue has a great potential to produce stabilized organic fertilizer and, or substrate for plant development. The aim of this work was to evaluate the physical, chemical, and microbial attributes of sewage sludge (SS) aerated and cultivated with Pennisetum purpureum or Urochloa brizantha and, later, composted. The study was installed in a 2x2+2 factorial scheme, with four replications. The factors consisted of cultivation of P. purpureum or U. brizantha in SS for 90 days, with or without intermittent aeration for 60 days. The control treatments were SS without cultivation, with the presence or absence of aeration. After 90 days of cultivation, the grass was cut, crushed, and incorporated into the SS for composting for 60 days. The composted sewage sludge showed an increase of 26, 24, 17, 123, 19, 32, and 7.7% in the levels of P, Ca, Cu, Fe, Mn, Zn, and Pb; and a reduction of 22, 5.2, 26, 30, 8.8, and 70% in the levels of C, N, K, Mg, Ni, and Na, respectively. The levels of Cu, Ni, Zn, and Pb remained below the maximum limit allowed by environmental resolution. The degradation of SS decreased the particle diameter, increasing the bulk density and total porosity, improving the physical properties of the compost. The SS cultivation and composting, regardless of the grass, led to a reduction in pH, basal and accumulated respiration, nitrification index, and C/N ratio and an increase in the CEC/C ratio, showing adequate maturation of the compost produced. Thus, the SS cultivation and composting with grasses were effective for producing matured and quality organic compost with low risk of environmental contamination.

Evaluating sewage sludge contribution during co-composting using cause-evidence-impact analysis based on morphological characterization

The pertinent challenges associated with effective treatment of fecal sludge in medium scales necessitate alternative means for land application. The methods of compost preparation from sewage sludge and their modes of application to the agricultural fields have profound impacts on the soil ecology and environment. Besides the chemical conditioning effects on soil organic matter, they also impart physical attributes to the soil texture and structure. Though it is expected that compost addition improves water holding capacity and nutrient sequestration, there is lack of clarity in correlating the field outcomes with conditions of excess nutrient storage/leaching despite the agronomic benefits. In this study, we present a systematic cause-evidence-impact relationship on the feedstock composition, processing, and applications of co-composted sewage sludge. Various analytical tools were compared to elucidate the unique characteristics of co-composted sewage sludge to get a realistic understanding of the complex soil-compost interactions. Results from the spectroscopic characterization reveal the implications of selection of bulking agents and sludge pre-treatment in determining the final quality of the compost. Based on the results, we postulate a unique attribution of parent material influence to the formation of well-defined porous structures which influences the nutrient leaching/sequestrating behavior of the soil. Thus, the compounded impacts of composted organic matter on the soil and crop can be proactively determined in terms of elemental composition, functional groups, and stability indices. The present approach provides good scope for customizing the preparations and applications of aerobic microbial composts in order to derive the preferred field outputs.

Characteristic and mechanism analysis of sludge polymer by adding carboxymethyl cellulose-g-acrylic acid for sludge utilization

Herein, a nutrient water retention agent is prepared by fully mixing sludge with carboxymethyl cellulose-g-acrylic acid (CMC-g-AA) gel and nanoscale zero-valent iron (nZVI) using polymer modifying curing technology. Experimental results show that when CMC:AA = 1:12 and CMC-g-AA gel content is 50%, sludge polymer has better water absorption and retention performance and the water retention time is extended for ∼14 days. At the same time, sludge polymer can preserve the characteristics of nutrient-rich elements and organic matter and promote plant growth. The addition of nZVI has a significant impact on reducing the risk of heavy metal toxic leaching in sludge. Moreover, analysis of variance and multiple comparisons shows that sludge polymer's particle size and water absorption times have significant effects on the water absorption and retention properties of sludge polymer. Scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy and ¹³C-nuclear magnetic resonance analyses show that the addition of an appropriate amount of gel could increase the number of hydrophilic groups and hydrophilic mineral components in sludge polymer, increase its overall porosity and improve its water absorption and retention properties.

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.

Evaluation of the Use of Sewage Sludge Biochar as a Soil Amendment—A Review

In recent decades, minimization and recycling/reuse policies were introduced to reduce the quantities of generated waste and for alternative waste recovery. Organic wastes represent 46% of total global solid waste. Possible uses of organic wastes include using it as fertilizer and amendment for soil, for energy recovery and for the production of chemical substances. Sewage sludge disposal and reuse are identified as future problems concerning waste. The total amount of sludge generated in the entire world has increased dramatically, and this tendency is expected to increase significantly in the years to come. In most developed countries, special attention is given to sewage sludge treatment in order to improve the quality and safety of using it on the ground surface. Sewage sludge pyrolysis is considered an acceptable method, from an economic and ecological perspective, for the beneficial reuse of sewage sludge. This method has many advantages because, during the pyrolysis process, the sludge volume is reduced by 80%, pathogenic agents and hazardous compounds from sewage sludge are eliminated, metals are immobilized in solid residue and organic and inorganic fractions are immobilized in a stabilized form of pyrolytic residues (biochar). The biochar generated by sewage sludge pyrolysis does not contain pathogenic agents and is rich in carbon and nutrients.

Application of Phosphate Materials as Constructed Wetland Fillers for Efficient Removal of Heavy Metals from Wastewater

Constructed wetlands are an environmentally friendly and economically efficient sewage treatment technology. Heavy metals (HMs) removal is always regarded as one of the most important tasks in constructed wetlands, which have aroused increasing concern in the field of contamination control in recent times. The fillers of constructed wetlands play an important role in HMs removal. However, traditional wetland fillers (e.g., zeolite, sand, and gravel) are known to be imperfect because of their low adsorption capacity. Regarding HMs removal, our work involved the selection of prominent absorbents, the evaluation of adsorption stability for various treatments, and then the possibility of applying this HM removal technology to constructed wetlands. For this purpose, several phosphate materials were tested to remove the heavy metals Cu and Zn. Three good phosphates including hydroxyapatite (HAP), calcium phosphate (CP), and physic acid sodium salt hydrate (PAS) demonstrated fast removal efficiency of HMs (Cu²⁺, Zn²⁺) from aqueous solution. The maximum removal rates of Cu²⁺ and Zn²⁺ by HAP, CP, and PAS reached 81.6% and 95.8%; 66.9% and 70.4%; 98.8% and 1.99%, respectively. In addition, better adsorption stability of these heavy metals was found to occur with a wide variation of desorption time and pH range. The most remarkable efficiency for heavy metal removal among tested phosphates was PAS, followed by HAP and CP. This study can provide a basis for the application of HMs removal in manmade wetland systems.

Insight into how fertilization strategies increase quality of grape (Kyoho) and shift microbial community

Organic and bioorganic fertilizers were increasingly used for agricultural soil. However, little is known on what kind of organic fertilizer application strategies can promote grape production well and how appropriate fertilization strategies improve soil properties and shift microbial community. This study investigated the improvement in soil physicochemical properties as well as their relations with microbial community structure and grape quality under different fertilization strategies. Our results found that (bio)organic fertilizer (CF1, CF2, and BF) especially combined application of organic and bioorganic fertilization (CBF) had smaller effects on electrical conductivity (EC) and pH, while it improved soil nutrients including N, P, K, and organic matter (OM) well, thereby promoting the grape quality comparing to the group without any fertilizer (CK) and with chemical fertilizer (NPK). Especially, the concentrations of Cr, Hg, Zn, and Cu were reduced by 13.63%, 12.50%, 12.52%, and 11.75% in CBF, respectively. Additionally, CF1, CF2, and BF, especially CBF, optimized the communities' composition and increased the abundance of some plant probiotics such as Solirubrobacter and Lysobacter. Nevertheless, excessive application of organic fertilizer derived from livestock manure could cause the accumulation of heavy metals such as Zn and Cu in soil and leaves, which could further influence the grape quality. Additionally, the structure of microbial communities was also changed possibly because some bacterial genera showed distinct adaptability to the stress of heavy metals or the utilization capacity of N, P, K, and OM. Our results demonstrated that combined application of organic and bioorganic fertilization showed a great influence on soil physicochemical properties, whose positive changes could further optimize microbial communities and facilitate the promotion of grape quality.

Variation and factors on heavy metal speciation during co-composting of rural sewage sludge and typical rural organic solid waste

In this study, a co-composting of rural organic solid waste (rural sewage sludge, kitchen waste and corn stalks) was conducted to analyze the variation of heavy metals (As, Cu, Cr, Ni, Pb, Hg, and Zn) and their major influencing factors. During composting, significant changes were observed in the total contents of heavy metals (p < 0.01): the total concentrations of As, Cu, Hg, Pb and Zn increased by 7.5%, 54.1%, 26.3%, 15.8%, and 34.2%, whereas that of Cr and Ni decreased by 71.3% and 33.4%, respectively. Heavy metals were mainly bound to the oxidizable and residual fractions. Spearman and Redundancy analysis (RDA) indicated that substances were significantly correlated with the changes in speciation of heavy metals, among all the factors, while pH and temperature were the dominating environmental influencing parameters. Several metal-resistant bacterial genera (Pseudomonas, Paenibacillus, Bacillus, Acinetobacter, Desulfovibrio, and Ochrobactrum, etc) were observed, with significant explanatory capacity for the changes in heavy metals. Composting showed a poor effect on heavy metal passivation, except for that of As. After composting, the heavy metal contents were consistent with the application standards. The evaluation of potential ecological risk showed a high cumulative ecological risk (336.9) of heavy metals. This study provides technical support and practical information for the disposal and safe recycling for rural organic solid waste.

Binding characteristics of humic substances with Cu and Zn in response to inorganic mineral additives during swine manure composting

Composting is suitable for recycling livestock manure into valuable organic fertilizer, which can improve soil quality while mitigating potential risk of heavy metal pollution. Humic substances (HS) in compost have been demonstrated to play a key role in regulating the redistribution of heavy metal fractions. However, limited direct information have been reported on how different components of HS complexes with heavy metals to affect their bioavailability during composting. In this study, sequential extraction procedures (H₂O, KCl, Na₄P₂O₇, NaOH and HNO₃) were used to assess the characteristics that HS bound with Cu and Zn during composting of swine manure and straw added either 5% boron waste (BW) or 5% phosphate rock (PR). Organically complexed fraction extracted by Na₄P₂O₇ contained only 33-41% of the Cu but most of the Zn (81-87%). During composting, initially mobile fractions of Cu and Zn (extracted by H₂O or KCl) changed into more stable fractions (extracted by NaOH and HNO₃), and both organic matter and fulvic acids (FA) were identified as critical factors to explain this redistribution based on redundancy analysis. Over 80% of Cu and Zn were complexed with FA of HS. However, exogenous additives (phosphate rock and boron waste) enhanced Cu conversion by promoting humification (Humic acid/Fulvic acids, HA/FA) whereas they had limited influence on Zn, due to the relatively weak binding relationship between Zn and HA.

Tetracycline hydrochloride-stressed succession in microbial communities during aerobic composting: Insights into bacterial and fungal structures

Available information that whether antibiotics affect the succession in microbial communities during aerobic composting remains limited. Thus, this work investigated the dynamic changes in bacterial and fungal structures during aerobic composting amended with tetracycline hydrochloride (TCH: 0, 50, 150 and 300 mg kg^-1). Composting phases significantly affected bacterial and fungal communities, but only fungi strongly responded to antibiotics, while bacteria did not. Firmicutes, Proteobacteria, Bacteroidota and Actinobacteriota were primary bacterial phylum. Neocallimastigomycota was dominant fungal phylum at temperature-heating phase, then Basidiomycota and Ascomycota became main fungal phylum at thermophilic and temperature-colling phases. Low TCH concentration promoted Chytridiomycota growth, while high TCH concentration inhibited mostly fungal activity in TCH-amended composting. Nitrogen species were critical factors controlling the succession in bacterial and fungal communities during composting process. These results cast a new light on understanding about microbial function during aerobic composting.

Evaluation of the effects of adding activated carbon at different stages of composting on metal speciation and bacterial community evolution

Information on the passivation of heavy metals (HMs) by environmental factors and microbial communities during activated carbon (AC) composting remains limited. Thus, this study elucidated the dynamic changes in HM fractions during chicken manure composting after AC amendment at different periods (initial period: T1, thermophilic period: T2, cooling period: T3). Compared with the initial stage, organic matter concentrations in the control, T1, T2, and T3 groups decreased by 15.9%, 25.8%, 22.6%, and 19.0%, respectively, at the end of composting. The HM-fractions results showed that the passivation sequence of HMs by AC was the highest for Zn, followed by Cu and Pb. AC addition in T2 significantly affected the bacterial community. Variance partitioning analysis indicated that AC accelerated the passivation effect on Zn and Pb by regulating environmental factors, and on Cu by influencing the microbial community. These results are helpful for understanding the mechanism of HM passivation in AC aerobic composting, and are also conducive to the environmentally friendly treatment of livestock and poultry manure.

Treatment processes to eliminate potential environmental hazards and restore agronomic value of sewage sludge: A review

Land application of sewage sludge is increasingly used as an alternative to landfilling and incineration owing to a considerable content of carbon and essential plant nutrients in sewage sludge. However, the presence of chemical and biological contaminants in sewage sludge poses potential dangers; therefore, sewage sludge must be suitably treated before being applied to soils. The most common methods include anaerobic digestion, aerobic composting, lime stabilization, incineration, and pyrolysis. These methods aim at stabilizing sewage sludge, to eliminate its potential environmental pollution and restore its agronomic value. To achieve best results on land, a comprehensive understanding of the transformation of organic matter, nutrients, and contaminants during these sewage-sludge treatments is essential; however, this information is still lacking. This review aims to fill this knowledge gap by presenting various approaches to treat sewage sludge, transformation processes of some major nutrients and pollutants during treatment, and potential impacts on soils. Despite these treatments, overtime there are still some potential risks of land application of treated sewage sludge. Potentially toxic substances remain the main concern regarding the reuse of treated sewage sludge on land. Therefore, further treatment may be applied, and long-term field studies are warranted, to prevent possible adverse effects of treated sewage sludge on the ecosystem and human health and enable its land application.

Effects of Application of Pig Manure on the Accumulation of Heavy Metals in Rice

Pig manure (PM) is often highly enriched in heavy metals, such as Cu and Zn, due to the wide use of feed additives. To study the potential risks of heavy metal accumulation in the soil and rice grains by the application of PM and other organic manure, a four-year field experiment was conducted in the suburb of Shanghai, southeast China. The contents of Cu, Zn, Pb, and Cd in the soils and rice plants by the treatments of PM and fungal culturing residues (FCR) show a trend of annual increase. Those in the soils and rice by the PM treatment are raised even more significantly. Cu and Zn contents in the soil and rice roots by the PM are significantly higher than those by the non-fertilizer control (CK) during the four years, and Pb and Cd also significantly higher than CK in the latter two years. Heavy metals taken up by the rice plants are mostly retained in the roots. Cu and Zn contents in the rice plants are in the decreasing order of roots > grains > stems > leaves, and Pb and Cd in the order of roots > stems > leaves > grains. Cu, Zn, Pb, and Cd contents in the soils by the PM treatment increase by 73%, 32%, 106%, and 127% on annual average, and those in the brown rice by 104%, 98%, 275%, and 199%, respectively. The contents of Cu, Zn, Pb, and Cd in the brown rice of the treatments are significantly correlated with those in the soils and rice roots (p < 0.05), suggesting the heavy metals accumulated in the rice grains come from the application of PM and FCR. Though the contents of heavy metals in the brown rice during the four experimental years are still within the safe levels, the risks of their accumulative increments, especially by long-term application of PM, can never be neglected.

Effects of FeSO4 dosage on nitrogen loss and humification during the composting of cow dung and corn straw

The effects of FeSO₄ on nitrogen loss and humification were investigated in the composting of cow dung and corn straw. The results showed that all groups met the ripening requirements after 50 days: the temperature was above 50 °C for 12- 17 days; the products had pH values of 6.4-7.6, electrical conductivities of 1.06-1.33 ms·cm^-1, NH₄⁺-N contents of 37.2-61.8 mg kg^-1, and the seed germination index of 95%-101%. FeSO₄ reduced nitrogen losses by 9.21-15.65% compared to the control group. FeSO₄ also improved the compost humification process: the humus substances (HS) contents in the compost product with FeSO₄ were 109.82-129.86 g·kg^-1, higher than 106.31 g·kg^-1 in the control group. The compost product in 3.75% FeSO₄ treatment had the highest maturity degree. This study showed that FeSO₄ could inhibit the mineralization of organic matter during the composting and accelerate the formation of HS.

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.

Supplying silicon alters microbial community and reduces soil cadmium bioavailability to promote health wheat growth and yield

Soil amendments of black bone (BB), biochar (BC), silicon fertilizer (SI), and leaf fertilizer (LF) play vital roles in decreasing cadmium (Cd) availability, thereby supporting healthy plant growth and food security in agroecosystems. However, the effect of their additions on soil microbial community and the resulting soil Cd bioavailability, plant Cd uptake and health growth are still unknown. Therefore, in this study, BB, BC, SI, and LF were selected to evaluate Cd amelioration in wheat grown in Cd-contaminated soils. The results showed that relative to the control, all amendments significantly decreased both soil Cd bioavailability and its uptake in plant tissues, promoting healthy wheat growth and yield. This induced-decrease effect in seeds was the most obvious, wherein the effect was the highest in SI (52.54%), followed by LF (43.31%), and lowest in BC (35.24%) and BB (31.98%). Moreover, the induced decrease in soil Cd bioavailability was the highest in SI (29.56%), followed by BC (28.85%), lowest in LF (17.55%), and BB (15.30%). The significant effect in SI likely resulted from a significant increase in both the soil bioavailable Si and microbial community (Acidobacteria and Thaumarchaeota), which significantly decreased soil Cd bioavailability towards plant roots. In particular, a co-occurrence network analysis indicated that soil microbes played a substantial role in wheat yield under Si amendment. Therefore, supplying Si alters the soil microbial community, positively and significantly interacting with soil bioavailable Si and decreasing Cd bioavailability in soils, thereby sustaining healthy crop development and food quality.

Disorders of the Reproductive Health of Cattle as a Response to Exposure to Toxic Metals

The aim of this review is to comprehensively present disorders of the reproductive system in cattle exposed to contact with toxic metals. Toxic metals are a common environmental pollutant and can come from mines, smelters, fossil fuel combustion, or volcanic eruptions. Metals have the ability to bioaccumulate in living organisms, thus contaminating the food chain and may pose a threat to humans. They accumulate mainly in the liver and kidneys, but also in muscles and fat tissue. Toxic metals such as lead (Pb), arsenic (As), mercury (Hg), and cadmium (Cd) have a negative impact on the fertility of animals; they can lead to abortions, premature calving, or oocyte dysfunction. Moreover, in the male reproductive system, they disrupt spermatogenesis, and cause apoptosis of sperm and oxidative damage. The main source of exposure of livestock to toxic metals is through the consumption of feed or contaminated water. It is important to monitor the level of heavy metals in animal products to prevent human poisoning. Toxic metal biomonitoring can be performed by testing urine, blood, milk, plasma, or hair. Chromium (Cr), arsenic (As), and cadmium (Cd) are excreted in the urine, while lead can be detected by examining the blood of animals, while in milk, arsenic (As), cadmium (Cd), nickel (Ni), and lead (Pb) can be detected. Moreover, toxic metals do not biodegrade in the environment. To purify soil and waters, remediation methods, e.g., biological or chemical, should be used.

Additive grain-size: An innovative perspective to investigate the transformation among heavy metal and phosphorus fractions during aerobic composting

Considerable researches have been devoted to ascertain the transformation among heavy metal (HM) or phosphorus (P) fractions during aerobic composting. However, available information that additives with different grain-sizes regulate the activation mechanism on P through influencing the passivation effect on HMs remains limited. Thus, this work aimed to investigate the dynamic changes in HM-fractions and P-fractions, and ascertain the interaction pathway between HMs and P during aerobic composting amended with medical stone (Coarse medical stone, 3-5 mm; Fine medical stone, < 0.1 mm). Medical stone, especially for coarse-grained medical stone, significantly enhanced the HM-passivation and P-activation during the composting (P < 0.05). The bioavailability factor of HMs decreased by 48.05% (Cu), 20.65% (Pb), 15.58% (Cd) and 6.10% (Zn), and the content of labile available P (LAP) increased by 6.45%. HMs, with the explanatory capacity of 65.9%-84.9%, was important parameter superior to temperature (0.8%-5.4%), moisture content (MC, 0.1%-1.7%), pH (0.1%-8.7%), electric conductivity (EC, 0.8%-9.8%), carbon-to-nitrogen (C:N, 0.3%-2.3%) ratio and dissolved organic carbon (DOC, 0.4%-3.1%), to evaluate the transformation among P-fractions. Our results cast a new light on P-activation with respect to HM-passivation during aerobic composting.

Effects of microorganism-mediated inoculants on humification processes and phosphorus dynamics during the aerobic composting of swine manure

There is significant interest in the treatment of swine manure, which is a hazardous biowaste and a source of pathogenic contamination. This work investigated the effects of microorganism-mediated inoculants (MMIs) on nutrient flows related to humification or phosphorus (P) dynamics during the aerobic composting of swine manure. The impact of MMIs on microbe succession was also evaluated. The addition of MMIs had positive effects associated with nutrient flows, including thermal activation, decreases in certain fluorescence emissions, lower mass loss and variations in levels of certain elements and functional groups. MMIs altered the maturation behavior and kinetics of organic matter while improving microbial activity. Phosphorus was found in the compost in the forms of MgNH₄PO₄·6H₂O crystals and Poly-P as the IP species, and Mono-P as the OP species in compost generated from the dissolution or inter-transformation among P pools. These nutrient flows are attributed to changes in the structure of microbial communities as a consequence of introducing MMIs. Diverse microbial compositions were identified in different composting phases, although Bacillus appeared in each phase. This work provides support for the aerobic composting of hazardous biowaste as well as an improved understanding of nutrient flows, as a means of producing higher quality compost.

Effects of multi-phase inoculation on the fungal community related with the improvement of medicinal herbal residues composting

Composting has become the most important way to recycle medicinal herbal residues (MHRs). The traditional composting method, adding a microbial agent at one time, has been greatly limited due to its low composting efficiency, mutual influence of microbial agents, and unstable compost products. This study was conducted to assess the effect of multi-phase inoculation on the lignocellulose degradation, enzyme activities, and fungal community during MHRs composting. The results showed that multi-phase inoculation treatment had the highest thermophilic temperature (68.2 °C) and germination index (102.68%), significantly improved available phosphorus content, humic acid, and humic substances concentration, accelerated the degradation of cellulose and lignin, and increased the activities of cellulase in the mature phase, xylanase, manganese peroxidase, and utilization of phenolic compounds. Furthermore, the non-metric multi-dimensional scaling showed that the composting process and inoculation significantly influenced fungal community composition. In multi-phase inoculation treatment, Thermomyces in mesophilic, thermophilic, and mature phase, unclassified_Sordariales, and Coprinopsis in mature phase were the dominant genus that might be the main functional groups to degrade lignocellulose and improve the MHRs composting process.

Coupling thermophilic composting and vermicomposting processes to remove Cr from biogas residues and produce high value-added biofertilizers

Removing pollutants and producing high value-added products are essential steps for sustainable disposal and utilization of biogas residues. Here, a coupled thermophilic composting and vermicomposting process was used to remove Cr from biogas residues, and the composting products were co-fermented with the plant growth-promoting fungus Trichoderma to produce high value-added biofertilizers. The results showed that thermophilic composting for 37 d markedly increased the total content of Cr but decreased the percentage of available Cr fractions. Synchrotron-radiation-based observations further provided direct evidence of the binding sites to support the results from traditional sequential extraction. At a density of 60 g earthworm/kg biogas residues, vermicomposting removed 23-31% of Cr from biogas residues. After vermicomposting, co-fermentation of biogas residues and Trichoderma was optimized, in which Trichoderma spores were 2-5 × 10⁸ cfu/g substrates. Together, coupling thermophilic composting and vermicomposting processes is a promising technique to remove a portion of heavy metals from biogas residues.

Effect of inorganic additives (rock phosphate, PR and boron waste, BW) on the passivation of Cu, Zn during pig manure composting

The bioavailability of heavy metals in compost is critical for their agronomic value. The effect of inorganic additives (rock phosphate, PR and boron waste, BW) on Copper (Cu) and Zinc (Zn) bioavailability during co-compost of swine manure and rice straw was assessed using sequential extraction procedure (European Community Bureau of Reference). The result showed that both additives, applied at rates of 2.5%-7.5% (w/w) could promote the change of exchangeable Cu and reducible Cu into oxidizable Cu, thereby reducing their bioavailability factor (BF) by 15.5%-47.2%. While additives provided no significant reduction in BF of Zn, the shift from exchangeable Zn into reducible Zn can still reduce the mobility of Zn. Based on redundancy analysis (RDA), organic matter (OM) and electrical conductivity (EC) were identified as the most important controlling factors for redistribution of Cu and Zn fractions during composting. The inorganic additives strengthened the passivation of Cu and Zn bioavailability by stimulating OM degradation. The 7.5% (w/w) rock phosphate showed best passivating effect on the bioavailability of Cu.

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.

Exploring the synergic effect of fly ash and garbage enzymes on biotransformation of organic wastes in in-vessel composting system

The aim of the present work was to study the synergic effect of fly ash (FA) and garbage enzymes (GE) on biotransformation of organic wastes in in-vessel composting system. In-vessel composting of organic waste (household + brown in vessel 1) was performed with fly ash (mixed 5% in vessel 2; 10% in vessel 3; 15% in vessel 4; and 20% in vessel 5) by addition of extra carbon source (5%) and garbage enzyme in a fixed-dose (5%) for 15 days and changes in chemical properties (C: N ratio, nitrates, sulphates, phosphates and macro-elements) were analyzed at maturity. Vessel 5 showed better results in terms of organic matter degradability and C: N ratio (13.68) of mature compost. Principal Component Analysis (PCS) also confirmed vessel 5 as the best performing among other vessels. FTIR analysis indicated a major shift in chemical structure of organic waste due to the composting action.

In-situ immobilization of cadmium-polluted upland soil: A ten-year field study

In-situ immobilization is an effective and economically viable strategy for remediation of soil extensively polluted with heavy metals. The long-term sustainability is critical for the remediation practice. In the present study, a ten-year experiment was performed in a Cd-polluted agricultural field to evaluate the long-term stability of lime, silicon fertilizer (SF), fused calcium magnesium phosphate fertilizer (FCMP), bone charcoal, steel slag, and blast furnace slag with one-off application. All amendments had no significant effect on biomass but significantly reduced Cd uptake by Artemisia selengensis at higher dose. Among them, SF and FCMP applied at 1% could reduce Cd uptake by more than 40% to meet the Chinese maximum permissible limit for Cd content in food products (50 μg kg^-1). These amendments stimulated high Cd immobilization by increasing the soil pH and decreasing the soil acid-extractable Cd content, which were closely associated with Cd uptake. In addition, the two amendments altered the soil microbial structure and stimulated metabolism pathways, including amino acid, carbohydrate, and lipid metabolism, which are beneficial for soil function and quality. The results proved that SF and FCMP at 1% are stable and ecologically safe amendments, suitable for long-term Cd immobilization, and provide a strategy to mitigate the risk of food product contamination in heavy-metal-polluted soil.

The passivation effect of heavy metals during biochar-amended composting: Emphasize on bacterial communities

Available information on passivation effect of biochar on heavy metals (HMs) through regulating bacterial communities remains limited. Thus, this study investigated the correlation between bacterial diversity and HM-fractions (Zn, Cu, Cd, Cr and Pb) during composting with different dose of biochar (5% and 10%, dry weight basis), in order to ascertain the passivation effect on HMs under the influence of bacterial community. The addition of 10% biochar showed better passivation effect with reduction in bioavailability factor (BF) of Zn, Cu, Cd and Pb by 4.10%, 44.12%, 18.75% and 30.06%, respectively. In addition, it brought forward the variation in primary bacterial phylum to the thermophilic phase. The results of redundancy analysis (RDA) and structural equation models (SEMs) indicated that C:N ratio was an important factor in controlling the morphological transformation of HM by affecting the bacterial community structure. Our results maybe provide a novel insight into HM-passivation from an interaction mechanism on C:N ratio and bacterial community.