Environmental impact and optimization suggestions of pig manure and wastewater treatment systems from a life cycle perspective

Enhanced lactic acid production through enzymatic hydrolysis: Assessing impact of varied enzyme loadings on co-fermentation of swine manure and apple waste

Anaerobic co-fermentation of swine manure (SM) and apple waste (AW) restricts by the slow hydrolysis of substrates with complex structures, which subsequently leads to low lactic acid (LA) production. Therefore, a novel strategy based on enzymatic pretreatment for improving LA production from anaerobic co-fermentation of SM and AW was proposed in this study. The results indicated that the maximal LA concentration increased from 35.89 ± 1.84 to 42.70 ± 2.18 g/L with the increase of enzyme loading from 0 to 300 U/g VSsubstrate. Mechanism exploration indicated that enzymatic pretreatment significantly promoted the release and hydrolysis of insoluble organic matter from fermentation substrate, thus providing an abundance of reaction intermediates that were directly available for LA production. Additionally, bacteria analysis revealed that the high concentration of LA was associated with the prevalence of Lactobacillus. This study offered an environmental-friendly strategy for promoting SM and AW hydrolysis and provided a viable approach for recovering valuable products.

Insights into the removal of antibiotics from livestock and aquaculture wastewater by algae-bacteria symbiosis systems

With the burgeoning growth of the livestock and aquaculture industries, antibiotic residues in treated wastewater have become a serious ecological threat. Traditional biological wastewater treatment technologies-while effective for removing conventional pollutants, such as organic carbon, ammonia and phosphate-struggle to eliminate emerging contaminants, notably antibiotics. Recently, the use of microalgae has emerged as a sustainable and promising approach for the removal of antibiotics due to their non-target status, rapid growth and carbon recovery capabilities. This review aims to analyse the current state of antibiotic removal from wastewater using algae-bacteria symbiosis systems and provide valuable recommendations for the development of livestock/aquaculture wastewater treatment technologies. It (1) summarises the biological removal mechanisms of typical antibiotics, including bioadsorption, bioaccumulation, biodegradation and co-metabolism; (2) discusses the roles of intracellular regulation, involving extracellular polymeric substances, pigments, antioxidant enzyme systems, signalling molecules and metabolic pathways; (3) analyses the role of treatment facilities in facilitating algae-bacteria symbiosis, such as sequencing batch reactors, stabilisation ponds, membrane bioreactors and bioelectrochemical systems; and (4) provides insights into bottlenecks and potential solutions. This review offers valuable information on the mechanisms and strategies involved in the removal of antibiotics from livestock/aquaculture wastewater through the symbiosis of microalgae and bacteria.

Manure derived hydrochar reduced phosphorus loss risk via an alteration of phosphorus fractions and diversified microbial community in rice paddy soil

Phosphorus (P) loss caused by the irrational use of manure organic fertilizer has become a worldwide environmental problem, which has caused a potential threat to water safety and intensified agricultural non-point source pollution. Hydrothermal carbonization is method with a low-energy consumption and high efficiency to deal with environmental problems. Application of pig manure-derived hydrochar (PMH) to soil exhibited potential of sustainable development compared with the pristine pig manure (PM). However, the effects of PMH on the distribution of P among the fractions/forms and the interaction between microorganisms and P forms and its relevance to the potential loss of P in paddy fields has not been clarified. Therefore, in this study, a soil column experiment was conducted using the untreated soil (control), and the PM, PMH1 (PMH derived at 180 °C), and PMH2 (PMH derived at 260 °C) treated soils (at the dose of 0.05 %) and rice was cultivated to investigate the effects of PM and PMH on the P fractions, mobilization, ad potential loss via the induced changes on soil microbial community after a complete growing season of rice. The trend of P utilization was evaluated by P speciation via continuous extraction and 31P NMR. The addition of PMH reduced the proportion of residual P in soil by 23.8-26.3 %, and increased the proportion of HCl-P and orthophosphate by 116.2-158.6 % and 6.1-6.8 % compared to PM. The abundance of gcd gene developed after the application of PMH2, which enhanced the mobile forms of soil P utilization via secreting gluconic acid. The network diagram analysis concluded that the changes in various P forms were mainly related to Proteobacteria, Bacteroides, Firmicutes and Acidobacteria. The results illustrated that PMH mitigate the potential risk of P loss more than PM by altering P fractions and affecting soil microbial community.

Life-cycle comparisons of economic and environmental consequences for pig production with four different models in China

China, the world's largest consumer and producer of pork in the world, is attracting increasing attention due to the environmental impacts of its pig production. Previous studies seldom comprehensively compare the environmental impacts of the pig production system with different models, resulting in different intensities of environmental impacts. We aim to comprehensively evaluate Chinese pig production with different breeding models and explore a more sustainable way for pig production. We use life cycle assessment (LCA) to evaluate and compare environmental impacts of pig production system with four main breeding models in China from 1998 to 2020: domestic breeding, small-scale breeding, medium-scale breeding, and large-scale breeding. The life cycle encompasses fertilizer production, feed production, feed processing, pig raising, waste treatment, and slaughtering. The impact categories including energy consumption (EN), global warming (GWP), acidification (AP), eutrophication (EU), water use (WD), and land occupation (LO) are expressed with "100 kg live weight of fattening pig at farm gate." The results show that driven by governmental support, growing meat demand, and cost advantage, the scale breeding especially large-scale breeding simultaneously yielded greater net economic benefit and less environmental impact compared to other breeding models especially the domestic breeding. Due to mineral fertilizer application, feed production contributed over 50% of the total environmental impacts. Notably, the composition of feeds exerted significant influence on the environmental impacts arising from fertilizer production and feed processing. Furthermore, attributable to the substantial use of electricity and heat, as well as the concomitant emissions, pig raising contributed the largest GWP, while ranking second in terms of AP and EU. Notably, waste management constituted the third-largest EU, AP, and WD. In addition to promote scale breeding, we put forth several sustainable measures encompassing feed composition, cultivation practices, fertilizer utilization, and waste management for consideration.