Recognition on characteristics and applicability of typical modes for manure & sewage management in pig farming: A case study in Hebei, China

Comparative efficacy of anaerobic digestion systems in removing antimicrobial resistance genes from swine wastewater

Swine farm wastewater is a major reservoir of antimicrobial resistance genes (ARGs). Anaerobic digestion (AD), widely implemented in farms, has been extensively studied for ARG removal. However, a comparative study on ARG removal efficiency across the four principal AD systems - up-flow anaerobic sludge blanket (UASB), continuous stirred tank reactor (CSTR), buried biogas digester (BBD), and septic tank (SPT) - is lacking. Herein, we employed metagenomic sequencing, ultra-performance liquid chromatography-tandem mass spectrometry, as well as atomic absorption spectrometry/atomic fluorescence spectrophotometry, and revealed that UASB and CSTR achieved higher removal efficiencies for both ARGs (67% and 57%) and antibiotic residues (100% and 90%) compared to BBD and SPT. Acinetobacter, Escherichia, Pseudomonas and Streptococcus were the primary ARG hosts, comprising over 65% of the total abundance in influent samples. UASB and CSTR systems demonstrated superior removal efficiencies for both mobile genetic elements (MGEs) and antibiotic residues, both of which had essential impacts on ARG profiles. In addition, heavy metals might contribute to variation in ARGs through horizontal gene transfer. Collectively, the variation in microbial communities and better removal of both MGEs and antibiotic residues contribute to the remarkable ARG removal efficiency of UASB and CSTR, therefore, advocating for the widespread adoption of these two AD systems in swine farms.

Methodological study on carbon sequestration accounting for emission reductions from the whole-chain utilization of livestock and poultry manure

Effective livestock manure management is crucial for carbon neutrality. Scientific accounting methods and integrated management strategies can help guide reductions in carbon emissions and promote green development. To reduce greenhouse gas emissions by livestock manure, this study analyzed current accounting systems and focused on the complete chain of "collection-treatment-storage-use-returning" of manure based on the theoretical framework of greenhouse gas emissions accounting in the IPCC 2019 Guidelines. Combined with a life cycle assessment, the accounting list and boundaries were clarified, and the whole chain of livestock and poultry manure greenhouse gas accounting methodology system was proposed. Using swine breeding as a case study, this study evaluated the carbon emission reduction and sequestration effect of the whole manure chain using a typical technology model and a typical technological framework. It predicted the carbon reduction potential and sequestration benefits of utilizing swine manure in 2025 and 2030 in four scenarios. The findings indicated that the greenhouse gas emission factor of the whole chain of the six typical swine manure utilization modes in China was -48.82-40.54 kgCO2et-1. In 2022, the net greenhouse gas emissions from swine manure in China totaled approximately 2.0 × 107 tCO2e, with manure resource utilization reducing emissions by 3.2 × 107 tCO2e. Our projections suggest that emissions from swine manure in China may range from -1.8 × 107 to 1.3 × 107 tCO2e by 2025 and from -3.1 × 107 to 4.5 × 106 tCO2e by 2030. This can help guide optimal greenhouse gas emission reduction pathways for livestock and poultry farming and aid in the formulation of policies.

From manure to megawatts: Navigating the sustainable innovation solution through biogas production from livestock waste for harnessing green energy for green economy

This article aims to provide a systematic review of the literature on animal biomass and biogas plants through an analysis of externalities and benefits in economic, social, and environmental terms. In recent years, the spread of biogas plants has played an important role, especially in rural areas, generating benefits not only for the individual farm but for entire communities, contributing to the reduction of energy poverty and, at the same time, promoting the production of energy and organic manure. In light of the findings, the study argues that: (a) more public subsidies are needed; (b) the deployment of an appropriate policy mix would encourage the spread of small and medium-sized plants, with a reduction in road transport; and (c) targeted and diversified investments are needed on a geographic-by-geographic basis.

Mobile genetic elements mediate the cross-media transmission of antibiotic resistance genes from pig farms and their risks

Manure composting in traditional small-scale pig farms leads to the migration and diffusion of antibiotics and antibiotics resistance genes (ARGs) along the chain of transmission to the surrounding environment, increasing the risk of environmental resistance. Understanding the transmission patterns, driving factors, and health risks of ARGs on small-scale pig farms is important for effective control of ARGs transmission. This study was conducted on a small pig farm and its surrounding environment. The cross-media transmission of ARGs and their risks in the farming habitat were investigated using Metagenomic annotation and qPCR quantitative detection. The results indicate that ARGs in farms spread with manure pile-soil-channel sediment-mudflat sediment. Pig farm manure contributed 22.49 % of the mudflat sediment ARGs. Mobile genetic elements mediate the spread of ARGs across different media. Among them, tnpA and IS26 have the highest degree. Transmission of high-risk ARGs sul1 and tetM resulted in a 50 % and 116 % increase in host risk for sediment, respectively. This study provides a basis for farm manure management and control of the ARGs spread.

Effect of biochar with various pore characteristics on heavy metal passivation and microbiota development during pig manure composting

Understanding the porosity of biochar (BC) that promotes the heavy metal (HM) passivation during composting can contribute to the sustainable management of pig manure (PM). The current work aimed to explore the influence of BC with varying pore sizes on the physicochemical properties and morphological changes of HMs (including Zn, Cu, Cr, As, and Hg), and microbiota development during PM composting. The various pore sizes of BC were generated by pyrolyzing pine wood at 400 (T1), 500 (T2), 600 (T3) and 700 (T4) °C, respectively. The results revealed a positive correlation between specific surface area of BC and pyrolysis temperature. BC addition contributed to a significantly extended compost warming rate and duration of high-temperature period, as well as HM passivation, reflected in the decrease in Exc-Zn (63-34%) and Red-Cu (28-13%) content, and the conversion of Oxi-Cr (29-21%) and Red-Hg (16-5%) to more stable forms. Moreover, BC at T4 exhibited the best effect on Zn and Cu passivation due to the highest specific surface area (380.03 m2/g). In addition to its impact on HM passivation, BC addition improved the microbial environment during PM composting, leading to enhanced microbial diversity and richness. Notably, Chloroflexi and Bacteroidota played key roles in promoting the transformation of Exc-Cu and Red-Hg into stable forms. This phenomenon further stimulated the enhanced decomposition of organic matter (OM) when BC prepared at 600-700 °C was added. Therefore, it can be concluded that the regulation of BC porosity is an effective strategy to improve HM passivation and the overall effectiveness of PM composting.

How environmental decentralization affects the synergy of pollution and carbon reduction: Evidence based on pig breeding in China

Reducing pollution and carbon is essential to achieve China's goal of "carbon peaking and carbon neutrality"; however, the collaborative paths of pollution and carbon reduction remain vague and worth exploring. This paper analyses panel data from 30 provinces in China from 2002 to 2017 to determine the impact of environmental decentralization on the synergy of pollution and carbon reduction in pig farming. The result shows that environmental decentralization has a significant 'carbon reduction effect' and 'pollution reduction effect' on pig farming; it is also conducive to promoting the synergistic effect of reducing pollution and carbon emissions through supporting environmental facilities and industrial organisations. Various types of environmental decentralization have significant differences in the synergy of pollution and carbon reduction. The scale of pig breeding plays a positive regulatory role in the impact of environmental decentralization on the synergy of pollution and carbon reduction while showing regional heterogeneity. This research is crucial for advancing the green transformation of pig breeding.

Microplastic pollution in organic farming development cannot be ignored in China: Perspective of commercial organic fertilizer

Commercial organic fertilizer, an essential fertilizer for developing organic farming in China, has been identified as a potentially important source of microplastics (MPs) on farmland. However, little is known about the occurrence of MPs in commercial organic fertilizers and their potential ecological risks nationwide. Here, stereoscopy and laser-infrared imaging spectrometry were used to comprehensively investigate the abundance, size, type and morphology of MPs in commercial organic fertilizers collected from mainland China, assess the ecological risks, and predict MP contamination. Commercial organic fertilizers contained many MPs (8.88 ×103 to 2.88 ×105 items/kg), especially rich in small-size MPs (<100 µm), accounting for 76.53%. The highest MP pollution load value was observed in fertilizers collected from East China. Chlorinated polyethylene, polyurethane, polyethylene and polypropylene were the dominant MPs with the shape of film and fragment, concentrated in small sizes (<100 µm). The risk index (H-index) of the MPs was used to quantify the ecological risk of the MPs in the different samples, and most of the fertilizers were at level Ⅲ with high risk. Predictably, 2.32 × 1013 - 2.81 × 1016 MPs will accumulate in orchard soils after five years of fertilization, especially in South, Southwest and East China. This study provides primary scientific data on MP pollution in commercial fertilizer and the health development of organic farming.

Opportunities for centralized regional mode of manure and sewage management in pig farming: The evidence from environmental and economic performance

Pig breeding is moving toward more intensive development and is accompanied by the integrated generation of pig waste. This has disrupted the synergy between the original manure and sewage management mode and corresponding farmland at the household level. Centralized bio-energy mode is proposed to relieve environmental pressure, increase the resource recovery efficiency and rebuild the breeding and cropping. However, there is a lack of comprehensive information on a regional scale, particularly regarding evaluation, applicability and feasibility. Therefore, compared to the individual and traditional mode at the household level, this study was conducted using life cycle assessment and life cycle cost analysis, systematically assessed the environmental performance and economic viability of the centralized bio-energy mode at the regional scale, and further explored the adaptability of multi-subjects (various pig farms and biogas enterprise) and regional feasibility. Results revealed that the centralized bio-energy mode appeared to be a better alternative in terms of global warming, terrestrial acidification and marine eutrophication, with the significant reductions of 49.49 %, 6.8 % and 4.67 % respectively. Moreover, the study demonstrated a substantial profit of 48.5 CNY1 per ton of managed pig waste. Furthermore, both environmental and economic performance could be improved through scale expansion and transport optimization, with an optimal collection radius of less than 31.45 km. Conclusions clarified the potential of centralized bio-energy mode and provided valuable references for its implementation in various regions. Ultimately, further contributing to a more efficient, cost-effective, and regulated manner for resource recovery, culminating in the sustainability of pig farming and achieving environmental-friendly agriculture practices in regional contexts.