Two-step heating mode with the same energy consumption as conventional heating for enhancing methane production during anaerobic digestion of swine wastewater

Recent advances in swine wastewater treatment technologies for resource recovery: A comprehensive review

Swine wastewater (SW), characterized by highly complex organic and nutrient substances, poses serious impacts on aquatic environment and public health. Furthermore, SW harbors valuable resources that possess substantial economic potential. As such, SW treatment technologies place increased emphasis on resource recycling, while progressively advancing towards energy saving, sustainability, and circular economy principles. This review comprehensively encapsulates the state-of-the-art knowledge for treating SW, including conventional (i.e., constructed wetlands, air stripping and aerobic system) and resource-utilization-based (i.e., anaerobic digestion, membrane separation, anaerobic ammonium oxidation, microbial fuel cells, and microalgal-based system) technologies. Furthermore, this research also elaborates the key factors influencing the SW treatment performance, such as pH, temperature, dissolved oxygen, hydraulic retention time and organic loading rate. The potentials for reutilizing energy, biomass and digestate produced during the SW treatment processes are also summarized. Moreover, the obstacles associated with full-scale implementation, long-term treatment, energy-efficient design, and nutrient recovery of various resource-utilization-based SW treatment technologies are emphasized. In addition, future research prospective, such as prioritization of process optimization, in-depth exploration of microbial mechanisms, enhancement of energy conversion efficiency, and integration of diverse technologies, are highlighted to expand engineering applications and establish a sustainable SW treatment system.

Treatment and utilization of swine wastewater - A review on technologies in full-scale application

The management of swine wastewater has become the focus of attention in the farming industry. The disposal mode of swine wastewater can be classified as field application of treated waste and treatment to meet discharge standards. The status of investigation and application of unit technology in treatment and utilization such as solid-liquid separation, aerobic treatment, anaerobic treatment, digestate utilization, natural treatment, anaerobic-aerobic combined treatment, advanced treatment, are reviewed from the full-scale application perspective. The technologies of anaerobic digestion-land application is most appropriate for small and medium-sized pig farms or large pig farms with enough land around for digestate application. The process of "solid-liquid separation-anaerobic-aerobic-advanced treatment" to meet the discharge standard is most suitable for large and extra-large pig farms without enough land. Poor operation of anaerobic digestion unit in winter, hard to completely utilize liquid digestate and high treatment cost of digested effluent for meeting discharge standard are established as the main difficulties.

Effect of temperature on the persistence of fecal bacteria in ambient anaerobic digestion systems treating swine manure

This study aimed to explore the effect of temperature on the persistence of fecal bacteria by multiple approaches in ambient anaerobic digestion systems treating swine manure. Both lab-scale (15 °C, 20 °C, and 25 °C) and field (26 °C on average) studies were conducted by high-throughput sequencing and culture-based methods. A community-wide Bayesian SourceTracker method was used to identify and estimate the fecal bacterial proportion in anaerobic effluent. High proportional contributions of fecal bacteria were observed in effluent at 15 °C (73%) and 20 °C (75%), while less was found at 25 °C (19%). This was further verified by a field study (23%) and an anaerobic reactor study at 37 °C (0.01%). To explore the potential reasons for differences in fecal bacterial proportions, bacterial taxa were divided into "lost" and "survivor" taxa in manure waste by LEfSe. The "survivor" taxa abundance was positively correlated with SourceTracker proportion (r = 0.913, P = 0.001), but negatively correlated with temperature (r = -0.826, P = 0.006). In addition, biomarkers in effluent were divided into "enriched" and "de novo" taxa. "Enriched" taxa, including acidogenic and acetogenic bacteria, were found at all temperatures, whereas taxa related to organic degradation were multiplied "de novo" at 25 °C. Variation partition analysis showed that temperature could explain 30% of variations in effluent bacterial community. Moreover, coliforms isolated from the manure and effluents at 15 °C and 20 °C were also phylogenetically related. This study provided comprehensive insight into the impact of temperature on the persistence of fecal bacteria in anaerobic effluent, with temperatures over 25 °C recommended to reduce fecal pollution.

Intermittent air mixing system for anaerobic digestion of animal wastewater: Operating conditions and full-scale validation

An air mixing system for anaerobic digestion has been proved to be beneficial for methane production. The aim of the present study was to further investigate the appropriate conditions for air mixing. The effective methane production time (EMPT) was defined to determine the air mixing time in the article. The results indicated that the appropriate aeration intensity was 66.7 mL air per volume of reactor per min and mixing time was 1.5 min. When air mixing time exceeded 3 min on each occasion, total CH₄ production was less than that achieved under the no mixing condition due to a decrease in the EMPT. In addition, the possibility of air mixing was evaluated in an anaerobic full-scale plant comprising a continuous stirred tank reactor. One year of operating data validated the feasibility of air mixing during the anaerobic digestion of swine wastewater.

Recent advancement on biological technologies and strategies for resource recovery from swine wastewater

Swine wastewater is categorized as one of the agricultural wastewater with high contents of organics and nutrients including nitrogen and phosphorus, which may lead to eutrophication in the environment. Insufficient technologies to remove those nutrients could lead to environmental problems after discharge. Several physical and chemical methods have been applied to treat the swine wastewater, but biological treatments are considered as the promising methods due to the cost effectiveness and performance efficiency along with the production of valuable products and bioenergies. This review summarizes the characteristics of swine wastewaters in the beginning, and briefly describes the current issues on the treatments of swine wastewaters. Several biological techniques, such as anaerobic digestion, A/O process, microbial fuel cells, and microalgae cultivations, and their future aspects will be addressed. Finally, the potentials to reutilize biomass produced during the treatment processes are also presented under the consideration of circular economy.