A new approach for biogas slurry disposal by adopting CO2-rich biogas slurry as the flower fertilizer of Spathiphyllum: Feasibility, cost and environmental pollution potential

Synergistic removal of total petroleum hydrocarbons and antibiotic resistance genes in Yellow River Delta wetlands contaminated soil composting regulated by biogas slurry addition

The interactive effects between the emerging contaminant antibiotic resistance genes (ARGs) and the traditional pollutant total petroleum hydrocarbons (TPHs) in contaminated soils remain unclear. The synergistic removal of TPHs and ARGs from composted contaminated soil, along with the microbial mechanisms driven by the addition of biogas slurry, have not yet been investigated. This study explored the impact of biogas slurry on the synergistic degradation mechanisms and bacterial community dynamics of ARGs and TPHs in compost derived from contaminated soil. The addition of biogas slurry resulted in a reduction of targeted ARGs and mobile genetic elements (MGEs) by 9.96%-95.70% and 13.32%-97.66%, respectively. Biogas slurry changed the succession of bacterial communities during composting, thereby reducing the transmission risk of ARGs. Pseudomonas, Cellvibrio, and Devosia were identified as core microorganisms in the synergistic degradation of ARGs and TPHs. According to the partial least squares path model, temperature and NO3- indirectly influenced the removal of ARGs and TPHs by directly regulating the abundance and composition of host microbes and MGEs. In summary, the results of this study contribute to the high-value utilization of biogas slurry and provide methodological support for the low-cost remediation of contaminated soils.

Regulating the biodegradation of petroleum hydrocarbons with different carbon chain structures by composting systems

Composting can decrease petroleum hydrocarbons in petroleum contaminated soils, however the microbial degradation mechanisms and regulating method for biodegradation of petroleum hydrocarbons with different carbon chain structures in the composting system have not yet been investigated. This study analyzed variations of total petroleum hydrocarbon concentrations with C ≤ 16 and C > 16, Random Forest model was applied to identify the key microorganisms for degrading the petroleum hydrocarbon components with specific structure in biomass-amended composting. Regulating method for biodegradation of petroleum hydrocarbons with different carbon chain structures was proposed by constructing the influence paths of "environmental factors-key microorganisms- total petroleum hydrocarbons". The results showed that composting improved the degradation rate of C ≤ 16 fraction and C > 16 fraction of petroleum hydrocarbons by 67.88 % and 61.87 %, respectively. Analysis of the microbial results showed that the degrading bacteria of the C ≤ 16 fraction had degradation advantages in the heating phase of the compost, while the C > 16 fraction degraded better in the cooling phase. Moreover, microorganisms that specifically degraded C > 16 fractions were significantly associated with total nitrogen and nitrate nitrogen. The biodegradation of C ≤ 16 fraction was regulated by organic matter, moisture content, and temperature. The composting system modified by biogas slurry was effective in removing of petroleum hydrocarbons with different carbon chain structures in soil by regulating the metabolic potential of the 46 key microorganisms. This study given their expected importance to achieve the purpose of treating waste with waste and contributing to soil utilization as well as pollution remediation.

Spatial distribution and influencing factors of China's household biogas: evidence from provincial-level data

To address the adjustment of the Chinese agricultural industry and to better promote the development of Chinese household biogas, this article summarizes and analyzes the spatial distribution characteristics and influencing factors of the type and number of biogas digesters, biogas production, biogas fermentation materials, and methods of fermentation residue utilization and ecological agriculture with household biogas by compiling a dataset covering 31 provincial administrative regions in China. The results show that hydraulic biogas digesters are distributed mainly in northwestern and northeastern China; in addition, continuously stirred biogas digesters and bottom-discharging biogas digesters are distributed mainly in southern and northern China, respectively. Because of temperature and population, the Sichuan and Henan Provinces have the highest number of biogas digesters and biogas production. The type of biogas fermentation materials depends on the local raw materials. Biogas slurry and residue are widely used as fertilizers; furthermore, biogas slurry is used for seed soaking in northeastern and southern China, and biogas residue is used as feed in central southern and northern China. The "Three-in-one" and "Four-in-one" biogas ecological models are used mostly in southern and northern China, respectively, and both are mainly affected by temperature. Finally, we propose various problems and countermeasures to enhance the development of the household biogas industry in China. Our findings are critical for China's policymakers to adopt effective measures for promoting the development of cleaner energy and the layout of the agricultural industry.

Evaluating the ability of green roof plants in capturing air pollutants using biogas-digestate: Exploring physiological, biochemical, and anatomical characteristics

The undeniable impact of plants in reducing air pollution and the crucial role of nutrition in improving stress tolerance in plants has brought attention to the use of eco-friendly fertilizers. The objective of the study was to investigate how Biogas-digestate (BD) can enhance the tolerance of green roof plants in capturing air pollutants. Four plant species, namely reflexed stonecrop (Sedum reflexum), blue fescue (Festuca glauca), garden mum (Chrysanthemum morifolium), and Peppermint (Mentha piperita) were planted in three urban sites in Mashhad, Iran, with different levels of air pollution. The physiological, biochemical, and morphological characteristics of the treated plants were compared to assess their ability to trap air pollutants. The results showed that the treated M. piperita at Razavi with BD, exhibited the highest level of APTI. Although it was influenced by the site conditions, the determination of the optimum API yielded same results. The F. glauca treated in Khayyam had the highest proline content, while S. reflexum at the Honarestan site had the lowest H2O2 level, without significantly affecting BD. F. glauca, S. reflexum, and M. piperita exhibited the highest levels of SOD, PPO, and GPX activity, respectively, which were significantly increased by the BD treatment. Most of the heavy elements showed increased levels with BD treatment, and M. piperita had the highest concentrations of heavy elements. The leaf surfaces of S. reflexum and M. piperita, had the highest and lowest deposition of particulate matter (PMs), respectively. Carbon and oxygen constituted the majority of PMs on the surface of leaves at all three study locations. The following ranks included the elements Si, Ca, Mg, and Al. BD, particularly in the case of S. reflexum and M. piperita, enhanced the plants' tolerance to air pollution. It is recommended to cultivate S. reflexum using BD on the green roof in polluted areas due to its superior capacity to absorb PMs and the fact that it is not edible.

Biogas slurry purification-lettuce growth nexus: Nutrients absorption and pollutants removal

As a main by-product of anaerobic digestion in biogas plants, biogas slurry contains a high concentration of mineral elements (such as ammonia‑nitrogen and potassium) and chemical oxygen demand (COD). So determining how to dispose the biogas slurry in a harmless and value-added ways is crucial from the perspective of ecological and environmental protections. This study explored a novel nexus between biogas slurry and lettuce, in which the biogas slurry was concentrated and saturated with carbon dioxide (CO2) to serve as a hydroponic solution for lettuce growth. Meanwhile, the lettuce was used to purify the biogas slurry through removing pollutants. Results showed that when concentrating the biogas slurry, the total nitrogen and ammonia nitrogen contents in the biogas slurry decreased with the increase of concentration factor. The CO2-rich 5-time-concentrated biogas slurry (CR-5CBS) was screened as the most suitable hydroponic solution for lettuce growth after comprehensively considering the nutrient element balance, energy consumption of concentrating the biogas slurry and CO2 absorption performance. The quality of lettuce cultivated in CR-5CBS was comparable to that of the Hoagland-Arnon nutrient solution in terms of physiological toxicity, nutritional quality, and mineral uptake. Obviously, the hydroponic lettuce could effectively utilize the nutrients in CR-5CBS to purify CR-5CBS, meeting the standard of reclaimed water quality for agricultural reuse. Interestingly, when the same yield of lettuce is targeted, using CR-5CBS as the hydroponic solution to cultivate lettuce can save about US $151/m3-CR-5CBS for lettuce production compared to the Hoagland-Arnon nutrient solution. This study might provide a feasible method for high-value utilization and harmless disposal of biogas slurry.

Simulation of integrated anaerobic digestion-gasification systems using machine learning models

In this study, the anaerobic digestion model M-ADM1 was integrated with the gasification model T-ANN to form a set of integrated models that can efficiently simulate the biomass AD-GS integration technology. Biogas slurry is used as feedstocks to prepare biogas slurry fertilizer. Solid residue is used feedstocks for gasification reactions. Biogas and syngas from the gasification of solid residue are used for energy. In this process, carbon emission is regarded as an important index for the comprehensive evaluation and optimization of AD-GS integration process. This study found that when the anaerobic digestion duration was 0 to 15 days, the carbon emission reduction increased rapidly. The amount of carbon emission reduction peaks on day 15. The value of carbon emission reduction is 0.1828 gCO₂eq. In addition, when FEAG reached the maximum value at 15 days of anaerobic digestion, the decreasing trend of FEAG rate change value started to become significant.

Response of earthworms to microplastics in soil under biogas slurry irrigation: Toxicity comparison of conventional and biodegradable microplastics

As a reliable environment-friendly alternative, biodegradable plastic mulching films have been introduced into agricultural practice to reduce the adverse threats posed by conventional plastic products. Information regarding whether potential untoward effects of biodegradable plastics exist in soil and how strong are such effects on terrestrial organisms, however, still remains unknown. This study examined differences in the responses of earthworm, represented by Eisenia fetida, to exposure to biodegradable (PLA: polylactic acid) and conventional microplastics (PVC: polyvinylchloride, LDPE: low-density polyethylene) in soil with biogas slurry irrigation. Mortality, growth, histopathology and biochemical enzymes of the earthworms exposed to different concentrations of microplastics (5, 20 and 50 g/kg wet weight of soil, respectively) were investigated after 28 days of incubation in the experiment. The obtained results showed that the ecotoxicity of microplastics (MPs) to earthworms was time-dependent. Regardless of MPs type, continuous exposure to MPs at the concentration of 50 g/kg induced mucous vacuolization, longitude muscle disorder, and granular lipofuscin-like deposits generation in the epithelium. Moreover, tissue fibrosis and cavity formation were also observed in intestinal tissue. The presence of MPs stimulated the oxidative stress system of the earthworms, as indicated by the enhancement of malonaldehyde (MDA) content in vivo. The antioxidative defense system in earthworms was supposed to collapse at the MPs concentration of 50 g/kg after 28 days of exposure. Interestingly, PLA exhibited similar ecotoxicity effects with LDPE, which might violate the original intention of biodegradable plastics with less harmful or nontoxic influence on the terrestrial biotas. Thus, knowledge regarding the molecular and genetic mechanisms of the earthworms in soil containing biodegradable plastics should be further explored to better understand the risk posed by biodegradable plastics in the agroecosystem.

The greenhouse gas emission potential and phytotoxicity of biogas slurry in static storage under different temperatures

With the booming development of biogas industry to treat organic waste in China, the by-product of biogas slurry was accompanied with a huge amount. Static storage process of biogas slurry was normally operated under different seasons before application to land which would cause nutrition decomposition and greenhouse gas emission. Thus, the aim of this study was to investigate the nutrition decomposition, greenhouse gas emission (CH₄ and N₂O), and phytotoxicity of biogas slurry under different static temperatures, furthermore to illuminate the network among them and functional microorganism. According to the results, higher temperature at 30 °C contributed to fast and complete degradation of COD. In addition, more quantity of NH₄⁺ conversion and NO₃^- formation appeared at 30 °C. These factors resulted in relatively less crop toxicity together. CH₄ was the dominant greenhouse gas emission than N₂O and was highest in 30 °C treatment with total emission of 273.7 L/(m³·d) and greenhouse gas emission of 20.01 kg CO₂e (carbon dioxide equivalent). Lower temperature was conductive to N reservation and reduction of greenhouse gas emission, but making against with stabilization of organic matter and crop safety. At the same dilution times (≤3) of biogas slurry with deionized water, higher temperature at 30 °C could reduce 30 days of storage time, but 10 °C was still unsafe for crop. Structural equation model was further illustrated the positive effect of temperature on NO₃^-, CH₄, GI, and N₂O and negative on COD and NH₄⁺. These results could help to monitor the environmental risk, evaluate the maturity, guide the irrigation scheme, and regulate the static storage condition of biogas slurry under different seasons.

Phosphate capture from biogas slurry with magnesium-doped biochar composite derived from Lycium chinensis branch filings: performance, mechanism, and effect of coexisting ions

The performance, mechanisms, and effects of various coexisting ions on phosphorus (P) adsorptive capture in biogas slurry using MgO-doped biochar (MBC) were investigated. The results revealed that in comparison to the pristine biochar, the introduction of MgO significantly improved the P adsorptive capture feasibility of MBC. In addition, the process of P capture by MBC was not affected by the initial pH of the solution. The process of P capture could reach equilibrium within 120 min and be simulated using both the pseudo-first-order and the pseudo-second-order kinetic models. In addition, the highest P capture capacity calculated from the Langmuir isotherm model was approximately 129.35 mg/g. The coexisting of cations including NH₄⁺, Ca²⁺, Cu²⁺, Cd²⁺, Pb²⁺, Zn²⁺, and Cr³⁺ in higher concentrations of promoted P adsorptive capture through precipitation and ionic atmosphere effects. The presence of coexisting ions including SO₄^2-, HCO₃^-, and fulvic acid (FA) had a certain inhibitory effect on the P adsorptive capture through competitive adsorption with phosphate. The existence of monovalent ions such as K⁺, Na⁺, Cl^-, and NO₃^- had no significant effect on P adsorptive capture. The adsorptive capture of P by MBC was affected by various processes including electrostatic attraction and surface complexation, and the presence of different coexisting substances had different impacts on the P adsorption. Adding to these, the P in the biogas slurry was completely adsorbed by the MBC during the experiment, indicating that MBC is a promising composite in the engineering application for the capture of P from wastewater.

Substituting urea with biogas slurry and hydrothermal carbonization aqueous product could decrease NH3 volatilization and increase soil DOM in wheat growth cycle

Biogas slurry (BS) and hydrothermal carbonization aqueous products (HAP), which are rich in nitrogen (N) and dissolved organic matter (DOM), can be used as organic fertilizer to substitute inorganic N fertilizer. To evaluate the effects of co-application of BS and HAP on the ammonia (NH₃) volatilization and soil DOM content in wheat growth season, we compared six treatments that substituting 50%, 75%, and 100% of urea-N with BS plus HAP at low (L) or high (H) ratio, named BCL50, BCL75, BCL100, BCH50, BCH75, BCH100, respectively. Meanwhile, urea alone treatment was set as the control (CKU). The results showed that both BCL and BCH treatments significantly mitigate the NH₃ volatilizations by 9.1%-45.6% in comparison with CKU (P < 0.05), whose effects were correlated with soil NH₄⁺-N content. In addition, the decrease in soil urease activity contributed to the lower NH₃ volatilization following application of BS plus HAP. Notably, BS plus HAP applications increased the microbial byproduct- and humic acid-like substances in soil by 9.9%-74.5% and 100.7%-451.9%, respectively. Consequently, BS and HAP amended treatments significantly increased soil humification index and DOM content by 13.7%-41.2% and 38.4%-158.7%, respectively (P < 0.05). This study suggested that BS and HAP could be co-applied into agricultural soil as a potential alternative of inorganic fertilizer N, which can decrease NH₃ loss but increase soil fertility.

Effect of wheat straw pretreated with liquid fraction of digestate from different substrates on anaerobic digestion performance and microbial community characteristics

The effects of liquid fraction of digestate (LFD) pretreatment on anaerobic digestion (AD) performance and microbial community characteristics were estimated. Prior to AD, LFD (LFD_SM, LFD_FW, and LFD_WS) collected separately from three continuously stirred tank reactors (CSTRs) using swine manure (SM), food waste (FW), and wheat straw (WS) as the mono-substrate was applied to pretreat WS. The results showed that AD with LFD pretreatment resulted in biomethane yields of 240.2-277.9 mL·gVS^-1, a 33.57%-54.54% improvement over the yield of the control, and also produced a time saving of 32.26%-46.77%. The pretreatment parameters were optimized for LFD pretreatment. The enhancement effect was in the order of LFD_FW > LFD_SM > LFD_WS. Simultaneously, the cellulose, hemicellulose and lignin contents in the WS and their characteristics (surface properties, crystallinity index, etc.) varied accordingly. The function of the microbial community was strengthened during the pretreatment stage, but the structure of the microbial community had a clear response to the LFD source substrates. Bacteroidetes was the most dominant phyla and was positively correlated with the hydrolysis rate. Consequently, the LFD from the different substrates used as pretreat agents could improve the AD performance of WS.

Effects of bentonite on antibiotic resistance genes in biogas slurry and residue from thermophilic and mesophilic anaerobic digestion of food waste

Anaerobic digestion (AD) processes of food waste (FW) have potential risk on environments due to the prevalence and dissemination of antibiotic resistance genes (ARGs). This study investigated the effect of bentonite on methane production and the abundance of ARGs in biogas slurry and residue during AD of FW. Results showed that methane production increased by 68.52% and 56.79% with 3 g/L and 5 g/L of bentonite in mesophilic and thermophilic digestion, respectively. Adding 5 g/L of bentonite effectively reduced the genes of ermB, ermF, tetQ, tetX, sul1, sul2 and intI1 with a range of 80.82% - 100.00% in biogas residue under mesophilic reactor. The abundance of ARGs and intI1 in biogas residue were lower than in slurry under both temperatures with 5 g/L of bentonite. Statistical analysis indicated that bentonite and temperature were main driver factors which could impact ARGs by influencing the abundance and structure of microbial communities.