Using broiler litter and swine manure lagoon effluent in sawdust-based swine mortality composts: Effects on nutrients, bacteria, and gaseous emissions

Development of a microbial protease for composting swine carcasses, optimization of its production and elucidation of its catalytic hydrolysis mechanism

BACKGROUND

Dead swine carcass composting is an excellent method for harmless treatment and resource utilization of swine carcass. However, poor biodegradation ability of traditional composting results in poor harmless treatment effect. Researches report that the biodegradation ability of composting can be improved by inoculation with enzyme-producing microorganisms or by inoculation with enzyme preparations. At present, the researches on improving the efficiency of dead swine carcass composting by inoculating enzyme-producing microorganisms have been reported. However, no work has been reported on the development of enzyme preparations for dead swine carcass composting.

METHODOLOGY

The protease-producing strain was isolated by casein medium, and was identified by 16 S rRNA gene sequencing. The optimal fermentation conditions for maximum protease production were gradually optimized by single factor test. The extracellular protease was purified by ammonium sulfate precipitation and Sephadex G-75 gel exclusion chromatography. The potential for composting applications of the purified protease was evaluated by characterization of its biochemical properties. And based on amino acid sequence analysis, molecular docking and inhibition test, the catalytic hydrolysis mechanism of the purified protease was elucidated.

RESULTS

In this study, a microbial protease was developed for swine carcass composting. A protease-producing strain DB1 was isolated from swine carcass compositing and identified as Serratia marcescen. Optimum fermentation conditions for maximum protease production were 5 g/L glucose, 5 g/L urea, 1.5 mmol/L Mg²⁺, initial pH-value 8, inoculation amount 5%, incubation temperature 30 °C and 60 h of fermentation time. The specific activity of purified protease reached 1982.77 U/mg, and molecular weight of the purified protease was 110 kDa. Optimum pH and temperature of the purified protease were 8 and 50 °C, respectively, and it had good stability at high temperature and in alkaline environments. The purified protease was a Ser/Glu/Asp triad serine protease which catalyzed substrate hydrolysis by Glu, Arg, Ser, Asp and Tyr active residues.

CONCLUSIONS

In general, the microbial protease developed in this study was suitable for industrial production and has the potential to enhance composting at thermophilic stage. Moreover, the catalytic hydrolysis mechanism of the protease was further analyzed in this study.

Lagoon water quality monitoring based on digital image analysis and machine learning estimators

Lagoon has been widely used to treat animal wastewater. However, because lagoon effluent often fluctuates in water quality, land application of the effluent may pose a risk to the environment and/or public health. It is necessary to monitor the quality of lagoon water to reduce the risk of its land application. This paper proposes an innovative monitoring method for animal wastewater in lagoons. We implemented spectral processing techniques to analyze the reflectivity of wastewater samples from lagoons, and applied machine learning methods to estimate the water quality parameters of the effluents, including the levels of nitrogen, phosphorus, bacteria (total coliform and E. Coli), and total solids. This study found significant correlations between the spectral rate of emission and above water quality parameters. We used machine learning to train three types of estimators, normal equation linear regression (LR), stochastic gradient descent (SGD), and Ridge regression to quantify these relations. The model performance was evaluated by weight coefficient, function intercept, and mean squared error (MSE). The model showed that TS level and the blue band of spectral reflectance of samples have a relatively good linear relationship, and the MSE of prediction set and decision coefficient were 0.57 and 0.98, respectively. For bacteria level, the MSE of prediction set was 0.63, and coefficient R² was 0.96. The results from this study could provide a versatile method for remote sensing of animal waste water.

Effect of Substrate on Identification of Microbial Communities in Poultry Carcass Composting and Microorganisms Associated with Poultry Carcass Decomposition

Three composting systems, which consisted of different ratios of chicken manure, sawdust, and poultry carcasses, were used to investigate the effect of substrate on the identification of microbial communities and microorganisms associated with poultry carcass decomposition by characterizing the microbial communities and physicochemical parameters. The physicochemical and Miseq Illumina sequencing results showed the composition of substrate had a significant effect on the identification and metabolic capabilities of microbial communities in decomposting process. Poultry carcasses might be the potential driver for the identification of bacterial communities in poultry carcass composting, whereas the initial C/N ratio may mainly contribute to the diversity of fungal communities and the similar dominant microbial communities in treatments. Poultry carcasses and initial C/N ratio could respectively affect the composition and abundance of microorganisms associated with the decomposition of poultry carcasses. Understanding the potential composting driver could allow development of an efficient carcass degradation system.

Feasibility study of recycling cephalosporin C fermentation dregs using co-composting process with activated sludge as co-substrate

Composting is a potential alternative for cephalosporin C fermentation dregs (CCFDs) compared with incineration process or landfill because of its advantage of recovering nutrients. In this research, CCFDs and activated sludge (AS) were co-composted to analyze the feasibility of recycling the nutrients in CCFDs. A pilot-scale aerobic composting system with an auto-control system was used in this research, and the maturity and security of the compost product were evaluated. The temperature of the composting mixtures was maintained above 55°C for more than 3 days during the composting, indicating that co-composting of CCFDs and AS could reach the compost maturity standard, and the seeds germination index (GI) increased from 17.61% to 68.93% by the end of the composting process (28 days). However, the degradation rate of cephalosporin C (CPC) was only 6.58% during the composting process. Monitoring the quality of antibiotic resistance genes (ARGs) in the composts showed that the log copy of blaTEM in the composts increased from 2.15 in the initial phase to 6.37 after 28 days. Long-term investigation of CPC degradation and ARGs variation was conducted for the composts; CPC could still be detected after the maturity phases. A removal efficiency of 49.10% could be achieved in 110 days, while the log copy of ARGs increased to 7.93. Although a higher GI value (>80.00%) was observed, the risk of recycling the CCFDs compost product into land is still high.