Pyrolysis recycling of pig manure biochar adsorption material for decreasing ammonia nitrogen in biogas slurry.

Biochar adsorption materials have a good removal effect on ammonia nitrogen in piggery biogas slurry. However, the cost of biochar adsorption material is still high. If these materials can be recycled several times, the cost can be significantly reduced. Therefore, this paper investigated a new process of biochar adsorption material (C@Mg-P) pyrolysis cycle for reducing ammonia nitrogen in piggery biogas slurry. The effects of pyrolysis process conditions (pyrolysis temperature and pyrolysis time) and number of recycling times on reducing ammonia nitrogen in biogas slurry by C@Mg-P were studied, a preliminary investigation on the reaction mechanism of C@Mg-P for reducing ammonia nitrogen in biogas slurry was conducted, and the economic feasibility of the pyrolysis recycling process was analyzed. It was found that the NH3-N elimination efficiency by C@Mg-P was 79.16 % under the optimal conditions of 0.5 h and 100 °C. Second, C@Mg-P removed 70.31 % NH3-N after recycling 10 times. Chemical precipitation, ion exchange, physical adsorption and electrostatic attraction were the potential reaction mechanisms for NH3-N reduction by C@Mg-P. Moreover, C@Mg-P had a good decolorization effect on piggery biogas slurry with a 72.56 % decolorization rate. Compared with the non-pyrolyzed recycling process, the proposed process saved 80 % of the cost, thus representing an economically possible approach for pig manure biochar application in wastewater denitrification treatment.

Ultrafiltration concentrated biogas slurry can reduce the organic pollution of groundwater in fertigation.

Biogas slurry has the problems of having a low concentration, having a large production volume, and containing many small-molecule organic pollutants. During the fertigation process of biogas slurry, many small-molecule organic pollutants may pose potential pollution risks to groundwater. In this study, the ultrafiltration membrane technology was used to separate small-molecule organics in the biogas slurry to prepare ultrafiltration concentrated biogas slurry (UCBS). To research the impact of UCBS and raw biogas slurry (RBS) on the small-molecule organic pollution of groundwater, a laboratory soil column simulation leaching device was used to conduct leaching experiments with 4 types of UCBS and RBS in acric ferralsols and hydragric anthrosols for two quarters (8 fertilization periods). The results of the study show that both UCBS and RBS caused nitrate pollution to groundwater. UCBS has a lower risk of organic pollution to groundwater than RBS. Irrigating UCBS in hydragric anthrosols has a higher risk of organic pollution of groundwater than that in acric ferralsols. Analysis of the molecular weight distribution of dissolved organic matter (DOM) in the leaching solution showed that the organic pollutants were mainly small molecules <10 kDa. According to 3D excitation-emission matrix (3D-EEM) analysis, the main organic pollutants in the leaching solution were fulvic acid, microbial protein metabolites and humic acid organic compounds. The research results show that the pretreatment of biogas slurry by ultrafiltration can reduce the risk of small-molecule organic pollution of groundwater in land application, which can provide a new scientific basis to standardize biogas slurry land application technical guidelines and reduce groundwater pollution.