The dead pig is an organic waste rich in oil and protein, and is an ideal anaerobic digestion raw material. This study based on single factor ANOVA and Modified Gompertz model. It investigated the effects of the ratio of dead pigs on biogas production by middle temperature co-digestion of pig manure and dead pigs. And the biogas production potential was determined. The results showed that there was no significant correlation between the ratio of dead pigs and the biogas production. The ratio would significantly affect the average methane content and degradation rate. When the addition ratio was in the range of 3 to 15%, the biogas production was between 191.39 and 202.44 (L/kg VS). The average contents of methane were 50.67%, 50.35%, 41.83%, 45.53% and 44.57%, respectively. The time required to reach 80% of the biogas production was 28, 34, 36, 65 and 63 days, respectively. The degradation rate of the raw materials was generally decreased with the increase of the addition ratio. The results of Modified Gompertz model fitting showed that the mixed raw materials had a fully anaerobic digestion with high utilization rate and short hysteresis in the range of 0 ~ 9%. Therefore, a hydraulic retention time (HRT) of 30 days and the addition ratio was in the range of 0 to 6% could be recommended for a continuous digester. It could get a better gas production and higher raw material utilization.

The excessive biogas slurry produced by anaerobic fermentation seriously constrains the sustainable development of the biogas industry. It is significantly important to realize the resource utilization of biogas slurry. However, biogas slurry contains abundant weak electrolytes of bicarbonate (HCO₃ ⁻), leading to the negative influence of low conductivity, fouling, and scaling on electrodialysis for nutrient recovery. The synchronous metathesis method was first proposed to prepare humic acid-based nanosized calcium carbonate (HA-NCC) using CaCl₂, CaO, and NaOH reacted with HCO₃ ⁻ and HA in biogas slurry to resolve weak electrolyte problems. HA-NCC was decolored to obtain white NCC by a bleaching method and one-step burning method. The NCC whiteness reached 90.4% through a simple one-step burning method at 700 °C for 2 h, which is superior to the bleaching method. The white NCC was needle-like, rod-like, and spindle-like with preferable dispersion properties and a particle size between nanometer and micrometer. However, the particle size of white NCC was smaller compared to commercial NCC. The NCC was calcite and further confirmed the composition of CaCO₃ by XRF. The results are beneficial for the development of high-end NCC products to realize the high-value utilization of biogas slurry.

Assessments of the spatiotemporal distribution of livestock manure and its risk to the watershed are important to prevent water pollution. In this work, the spatiotemporal livestock manure distribution and its risk for the Chaohu lake basin were evaluated based on the excretion coefficient method and ArcGIS technology. In detail, the amounts of livestock manure and its associated pollutants, including chemical oxygen demand (COD), five-day biochemical oxygen demand (BOD₅), ammonia (NH₄⁺-N), total nitrogen (TN), and total phosphorus (TP), were calculated from 2009 to 2019. Then, the diffusion concentrations of COD, BOD₅, NH₄⁺-N, TN, and TP and the water pollution risk index from livestock manure were estimated and predicted for the Chaohu lake basin. The results indicated that the mean amount of livestock manure had reached 1.04 × 10⁷ t in the Chaohu lake basin in the studied decade. The COD, BOD₅, NH₄⁺-N, TN, and TP from livestock manure in Feixi and Feidong contributed 54.26% and 54.40% of the total in the whole basin. These results demonstrate the potential pollution risk of livestock manure for the Chaohu lake basin. Moreover, the diffusion concentrations of COD, BOD₅, NH₄⁺-N, TN, and TP for the lake basin were from highest to lowest as follows: Feixi > Feidong > Chaohu > Lujiang > Wuwei > Shucheng > Hefei. The water pollution risk index was more than 20 in Feixi and Feidong, indicating that these areas were heavily affected by local livestock manure. The water pollution risk index will be approximately 18 for the Chaohu lake basin in 2030, implying that the Chaohu lake watershed will suffer moderate pollution from animal manure. These results provide scientific support for policymakers to enhance manure utilization efficiency and control livestock manure loss, causing water eutrophication in Chaohu lake basin or other similar watersheds.