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A pot experiment was conducted on arsenic (As) and cadmium (Cd) co-contaminated soil to discern the influence of varying proportions of pig manure compost (PM) vis-à-vis chemical fertilizers (NPK) on the mitigation of Cd and As absorption by rice. Our findings illustrated that by increasing the PM proportions from 25 to 100%, it manifested a statistically significant reduction in the mobilized fractions of Cd, accounting for up to 77% reduction in soil CaCl 2 -Cd concentrations. Conversely, the NaHCO 3 -As reactions were contingent on the distinct PM application rates. Furthermore, augmented PM application rates correlated with a substantial surge in Cd and As concentrations within the iron (Fe) and manganese (Mn) plaques, ranging from up to 116.6% and 85.9%, respectively. This led to a concomitant decline in Cd and As concentrations within the grains, up to 72.6% and 74.5%, respectively. Notably, grain concentrations of As and Cd diminished progressively with increased PM application, reaching a nadir with the 75% PM treatment. In summary, the observed mitigation in contamination is postulated to stem from the modulation of soil attributes via PM addition, which curtails Cd availability, combined with the bolstered immobilization of As and Cd by the Fe/Mn plaques.

Methane production characteristics of anaerobic co-digestion of pig manure (PM) and fermented liquid feed (FLF) were investigated in a continuous digester under mesophilic conditions. The experiment followed three phases. PM alone was digested in phase I. In phases II and III, PM and FLF were mixed in a ratio of 95:5 and 90:10 (% v/v), respectively. The specific methane yields (SMYs) during phases I, II, and III were 238, 278, and 326.8 mLCH4·gVS−1-added, respectively. It was due to the effect of balancing the feedstock carbon-to-nitrogen ratio by adding FLF. This improvement can also be attributed to the readily biodegradable compounds in the FLF. The higher SMY obtained in this study showed a positive synergistic effect in the anaerobic co-digestion of PM and FLF. The results also indicate that adding the FLF positively affected and maintained a constant pH level, avoiding volatile fatty acid accumulation and ammonia inhibition in the anaerobic digestion (AD). Thus, this study provides valuable information regarding the usage of unused or wasted FLF as a co-substrate for the practical AD of PM. The production of fermented liquid additives such as FLF to improve the methane production from the AD of PM is a potential novel alternative to food waste recycling in Japan, besides compost and animal feeding.

A pot experiment and a leaching experiment were conducted to investigate the effects of earthworms and pig manure on heavy metals (Cd, Pb, and Zn) immobility, in vitro bioaccessibility and leachability under simulated acid rain (SAR). Results showed manure significantly increased soil organic carbon (SOC), dissolved organic carbon (DOC), available phosphorus (AP), total N, total P and pH, and decreased CaCl 2 -extractable metals and total heavy metals in water and SAR leachate. The addition of earthworms significantly increased AP (from 0.38 to 1.7 mg kg −1 ), and a downward trend in CaCl 2 -extractable and total leaching loss of heavy metals were observed. The combined earthworm and manure treatment decreased CaCl 2 -extractable Zn, Cd, and Pb. For Na 4 P 2 O 7 -extractable metals, Cd and Pb were decreased with increasing manure application rate. Application of earthworm alone did not contribute to the remediation of heavy metal polluted soils. Considering the effects on heavy metal immobilization and cost, the application of 6% manure was an alternative approach for treating contaminated soils. These findings provide valuable information for risk management during immobilization of heavy metals in contaminated soils.

The pig industry generates copious amounts of liquid pig manure (LPM), which poses a great challenge to the environment; conventional treatment of the manure is often time-consuming and inefficient. We developed a novel technique for converting LPM into liquid microbial fertilizer with two steps: (1) screened ammonia nitrogen-degrading strains and synthetic microbial communities (SynCom) were used in combination with H 2 O 2 for the biological deodorization of LPM; and (2) the bio-deodorized and autoclaved LPM was then inoculated with screened SynCom2 to produce liquid microbial fertilizers. The results of bio-deodorization demonstrated that both single ammonia nitrogen-degrading strains and SynCom1 reduced over 90% of the odor and GHGs emissions (NH 3 , H 2 S, CO 2 and CH 4 ) from LPM, and decreased the pH, chemical oxygen demand (COD), ammoniacal nitrogen (NH 4 + -N) and EC to varying extents. The SynCom1 was able to completely eliminate malodorous volatile organic compounds (p-methyl phenol) from LPM, outperforming single ammonia nitrogen-degrading strains. The deodorized LPM treated with SynCom2 exhibited high levels of nutrient concentration (31.58 g/L of total carbon and 3.81 g/L of total nitrogen), microbial biomass (up to 1.92 × 10 10 CFU/mL), plant safety and maturity (germination index > 100%), indicating suitability as microbial fertilizer. Cultivation experiments demonstrated a significant increase of over 70% in shoot length, root length, fresh weight and dry weight of rice seedlings when microbial fertilizers were applied in black soil. Overall, our study provided a valuable direction for the development of potential industrial applications.

The synergistic remediation of heavy metal-contaminated soil by functional strains and biochar has been widely studied. However, the mechanisms by which urease-producing bacteria combine with pig manure biochar (PMB) to immobilize Cd and inhibit Cd absorption in vegetables are still unclear. In our study, the effects and mechanisms of PMB combined with the urease-producing bacterium TJ6 (TJ6 + PMB) on Cd adsorption were explored. The effects of TJ6 + PMB on the Cd content and pH of the leachate were also studied through a 56-day soil leaching experiment. Moreover, the effects of the complexes on Cd absorption and microbial mechanisms in lettuce were explored through pot experiments. The results showed that PMB provided strain TJ6 with a greater ability to adsorb Cd, inducing the generation of CdS and CdCO 3 , and thereby reducing the Cd content (71.1%) and increasing the pH and urease activity in the culture medium. TJ6 + PMB improved lettuce dry weight and reduced Cd absorption. These positive effects were likely due to (1) TJ6 + PMB increased the organic matter and NH 4 + contents, (2) TJ6 + PMB transformed available Cd into residual Cd and decreased the Cd content in the leachate, and (3) TJ6 + PMB altered the structure of the rhizosphere bacterial and fungal communities in lettuce, increasing the relative abundances of Stachybotrys , Agrocybe , Gaiellales , and Gemmatimonas . These genera can promote plant growth, decompose organic matter, and release phosphorus. Interestingly, the fungal communities were more sensitive to the addition of TJ6 and PMB, which play important roles in the decomposition of organic matter and immobilization of Cd. In conclusion, this study revealed the mechanism by which urease-producing bacteria combined with pig manure biochar immobilize Cd and provided a theoretical basis for safe pig manure return to Cd-polluted farmland. This study also provides technical approaches and bacterial resources for the remediation of heavy metal-contaminated soil.

Phosphogypsum (PG) has the potential to elevate phosphorus levels in compost; however, it may also retard the composting maturation process, and its underlying mechanism for phosphorus activation remains unclear. In this study, sawdust was mixed with pig manure or chicken manure at a ratio of 1:4 (m:m, fresh weight) and added 10% PG as the treatment group, and added no PG as control treatment. The entire composting process lasts for 60 days. During the composting process, temperature was monitored daily, pH, electrical conductivity (EC), germination index (GI), phosphorus and its distribution were measured to monitor the composting process, and bacterial communities and predict phosphate-solubilizing genes and bacteria through the KEGG database. Pearson correlation analysis between phosphate-solubilizing bacteria and phosphorus components was conducted. The results demonstrated that (1) PG supplementation delayed the temperature rise and humification during composting, yet the final compost maturity was maintained (GI ≈ 90%). (2) PG addition increased the abundance of the ppx-gppa and phoR genes in pig manure compost, while enhancing the phnE and phoP genes in chicken manure compost. (3) In pig manure composting, Dietzia and Clostridium sensu stricto_1 were identified as key bacteria responsible for phosphorus activation, and promoting their growth favored phosphorus mobilization. (4) In chicken manure compost, Lactobacillus and Pseudomonas played crucial roles in phosphorus activation, though inhibiting their growth was found to enhance phosphorus availability. Overall, PG addition promoted phosphorus activation in compost, significantly increasing the NaHCO3-P content in both pig manure and chicken manure composts (by 9.36 and 17.86 percentage points, respectively).

Hydrothermal treatment (HTT) of sewage sludge (SS) with pig manure biochar (PMB) addition at 160–200 °C was conducted in this study. The effects of PMB addition on the dewaterability of SS and the speciation evolution, leaching toxicity, and potential ecological risk of heavy metals were investigated. The results showed that the solid contents of the filter cakes after adding PMB increased from 20.24%, 24.03%, and 28.69% to 21.57%, 27.69%, and 32.91% at 160, 180, and 200 °C, respectively, compared with traditional HTT of SS. Furthermore, PMB could reduce the bioavailable fractions of Cr, Ni, As, and Cd in the filter cakes obtained at 160 and 180 °C compared with the theoretical value. The leaching toxicity of heavy metals in the filter cakes after adding PMB decreased significantly at 160 and 180 °C and the potential ecological risk index ( RI ) declined from 62.13 and 44.83 to 55.93 and 42.11, respectively. The obtained filter cake had low potential ecological risk when used in the environment. The mechanisms on the improvement of the dewaterability and heavy metals immobilization were related that PMB acted as the skeleton builder providing the outflow path for free water and implanting heavy metals into SS structure. And the optimal results were obtained at 180 °C during HTT of SS with PMB addition. This work provides a novel and effective method for the treatment of SS.

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.

Due to the development of urbanization and industrialization, a large amount of cultivated land resources has been occupied, while new reclamation land could expand the supply of usable land for food security. Organic fertilizers, such as crop residues, biosolids, sheep manure, mushroom residue, and biogas liquid, have been considered as an effective amendment in immature soil to improve its quality. Recently, two kinds of commercial organic fertilizers, pig manure and mushroom residue organic fertilizer (PMMR-OF), and sheep manure organic fertilizer (SM-OF), have been more regularly applied in agriculture production. However, the information available on effect of the two kinds of fertilizers on plant growth and rhizosphere soil properties in immature field is very limited. In order to evaluate PMMR-OF and SM-OF on immature soil, the soil quality and microbial community structure of corn rhizosphere soil samples under the two kinds of organic fertilizers at different concentrations was investigated. The results revealed a significant difference between commercial organic fertilizers (especially SM-OF) and chemical compound fertilizers (CCF) in soil properties and microbial community structure. Indeed, compared with the control based on16S and ITS amplicon sequencing of soil microflora, SM-OF caused a 10.79–19.52%, 4.33–4.39%,and 14.58–29.29% increase in Proteobacteria, Actinobacteria, and Ascomycota, but a 5.82–20.58%, 0.53–24.06%, 10.87–16.79%, 2.69–10.50%, 44.90–59.24%, 8.88–10.98%, and 2.31–21.98% reduction in Acidobacteria, Gemmatimonadetes, Bacteroidetes, Verrucomicrobia, Basidiomycota, Mortierellomycota, and Chytridiomycota, respectively. CCF caused a 24.11%, 23.28%, 38.87%, 19.88%, 18.28%, and 13.89% reduction in Acidobacteria, Gemmatimonadetes, Bacteroidetes, Verrucomicrobia, Basidiomycota, Chytridiomycota, but a 22.77%, 41.28%, 7.88%, and 19.39% increase in Proteobacteria, Actinobacteria, Ascomycota, and Mortierellomycota, respectively. Furthermore, redundancy discriminant analysis of microbial communities and soil properties of PMMR-OF, SM-OF, CCF, and the control treatments indicated that the main variables of bacterial and fungal communities included organic matter content, available P, and available K. Overall, the results of this study revealed significant changes under different fertilizer conditions (PMMR-OF, SM-OF, CCF, under different concentrations) in microbiota and chemical properties of corn soil. Commercial organic fertilizers, particularly SM-OF, can be used as a good amendment for the new reclamation land.

Preventing loss of nitrogen during aerobic manure composting is a critical challenge, and introducing microbial agents with specific functions offers a promising solution. This study aimed to explore how Bacillus subtilis F2 (a thermotolerant nitrifying bacterium) affects nitrogen conservation, microbial dynamics, and nitrogen conversion-associated gene abundance during pig manure composting. Relative to the uninoculated controls, adding F2 markedly raised the germination index, nitrate content, and total nitrogen in the final compost, resulting in reduced nitrogen loss. The inoculation led to a distinct succession of bacterial communities, enriching microorganisms associated with fermentation and hydrocarbon degradation, while the fungal communities did not change significantly between the control and treated compost. Furthermore, inoculation markedly increased amoA gene levels and decreased nirK abundance during the cooling and maturation phases. Significant relationships were detected between nitrogen content, microbial composition, and nitrogen conversion genes in correlation analyses. In summary, the addition of F2 is recommended for bolstering nitrogen retention in the context of composting.