Swine manure treatment technologies as drivers for circular economy in agribusiness: A techno-economic and life cycle assessment approach

Exogenous additive ferric sulfate regulates sulfur-oxidizing bacteria in cow manure composting to promote carbon fixation

Enhancing carbon fixation in the composting process was of great significance in the era of massive generation of organic solid waste. In this study, the experimental results showed that the contents of dissolved organic matter (DOM) in the experimental group (CT) were 37.58% higher than those in the control group (CK). The CO2 emission peaked on day 5, and the value of CK was 1.34 times that of CT. Significant differences were observed between the contents of sulfur fractions in CT and CK. This phenomenon may be due to the suppression of sulfur-reducing gene expression in CT. On day 51 of composting, the abundance of sulfur-oxidizing bacteria (SOB) Rhodobacter (5.33%), Rhodovulum (14.76%), and Thioclava (23.83%) in CT was higher than that in CK. In summary, the composting fermentation regulated by Fe2(SO4)3 increased the sulfate content, enhanced the expression of sulfur-oxidizing genes and SOB, and ultimately promoted carbon sequestration during composting.

Life cycle assessment of biostimulant production from algal biomass grown on piggery wastewater

Piggery wastewater has become a large source of pollution with high concentrations of nutrients, that must be managed and properly treated to increase its environmental viability. Currently, the use of microalgae for treating this type of wastewater has emerged as a sustainable process with several benefits, including nutrient recovery to produce valuable products such as biostimulants, and CO2 capture from flue gases. However, the biostimulant production from biomass grown on piggery wastewater also has environmental impacts that need to be studied to identify possible hotspots. This work presents the life cycle assessment by IMPACT 2002+ method of the production of microalgae-based biostimulants, comparing two different harvesting technologies (membrane in scenario 1 and centrifuge in scenario 2) and two different technologies for on-site CO2 capture from flue gases (chemical absorption and membrane separation). The use of membranes for harvesting (scenario 1) reduced the environmental impact in all categories (human health, ecosystem quality, climate change, and resources) by 30 % on average, compared to centrifuge (scenario 2). Also, membranes for CO2 capture allowed to decrease environmental impacts by 16 %, with the largest reduction in the resource category (∼33 %). Thus, the process with the best environmental viability was achieved in scenario 1 using membranes for CO2 capture, with a value of 217 kg CO2 eq/FU. In scenario 2 with centrifugation, the high contribution of the cultivation sub-unit in all impacts was highlighted (>75 %), while in scenario 1 the production sub-unit also had moderate contribution in the human health (∼35 %) and climate change (∼30 %) categories due to the lower concentration and high flow rates. These results were obtained under a worst-case situation with pilot scale optimized parameters, with limited data which would have to be further optimized at industrial-scale implementation. The sensitivity analysis showed a little influence of the parameters that contribute the most to the impacts, except for the transportation of the piggery wastewater to the processing plant in scenario 2. Because of the relevant impact of biostimulant transportation in scenario 1, centrifugation becomes more favourable when transportation distance is longer than 321 km.

Livestock waste management for energy recovery in Brazil: a life cycle assessment approach

Livestock farming has exerted intense environmental pressure on our planet. The high emissions to the environment and the high demands of resources for the production process have encouraged the search for decarbonization and circularity in the livestock sector. In this context, the objective of this study was to evaluate and compare the environmental performance of two different uses for biogas generated in the anaerobic digestion of animal waste, either for electricity generation or biomethane. For this purpose, a life cycle assessment approach was applied to evaluate the potential of anaerobic digestion as a management technology for three different livestock wastes, related to beef cattle, dairy, and sheep in the Brazilian animal production context. The results suggest that the treatment scenarios focusing on biomethane generation were able to mitigate the highest percentage of damages (77 to 108%) in the global warming category when compared to the scenarios without the use of anaerobic digestion (3.00·102 to 3.71·103 kgCO2 eq) or in the perspective of electricity generation (mitigation of 74 to 96%). In terms of freshwater eutrophication, the generation of electricity (- 2.17·10-2 to 2.31·10-3 kg P eq) is more favorable than the purification of biogas to biomethane (- 1.73·10-2 to 2.44·10-3 kg P eq), due to the loss of methane in the upgrading process. In terms of terrestrial ecotoxicity, all scenarios are very similar, with negative values (- 1.19·101 to - 7.17·102 kg 1,4-DCB) due to the benefit of nutrient recovery, especially nitrogen, associated with the use of digestate as fertilizer, which was one of the critical points in all scenarios. Based on these results, it is evident that proper management of all stages of the treatment life cycle is the key to decarbonization and circularity in livestock waste management. The biogas use does not present different effects on the environmental performance of the scenarios studied, demonstrating that the purpose should be chosen according to the needs of each plant or management system.

A thematic review on livestock manure treatment strategies focusing on thermochemical conversion

Livestock manure (LSM) management is emerging as a challenge due to increasing livestock consumption. Owing to the decreased agricultural land area, it is necessary to ensure LSM utilization in non-agricultural fields. LSM can be a valuable resource if managed as a circulating resource. This study discusses research trends based on a literature review and classifies LSM treatments. The analysis of each treatment is presented according to research trends, and implications for the future LSM processing are discussed. "Biological treatment" accounted for the largest portion at 48%, "manure management," which suggests improvement in manure treatment through systematic thinking or LSM management practices, accounted for 16%, and "thermochemical conversion" accounted for 11%. In addition, "life cycle assessment (LCA) research," "solid-liquid separation approach," and "nutrient-recovery/losses" were derived. Studies on biological treatments are increasing. Although anaerobic digestion (AD) is the most used method, it has the disadvantages of long processing time and waste generation after processing. As a key supplement, thermochemical conversion (TCC) technology, which could overcome the disadvantages of AD, was reviewed.