Phosphorus recovery from biogas fermentation liquid by Ca-Mg loaded biochar

Shortage in phosphorus （P） resources and P wastewater pollution is considered as a serious problem worldwide. The application of modified biochar for P recovery from wastewater and reuse of recovered P as agricultural fertilizer is a preferred process. This work aims to develop a calcium and magnesium loaded biochar （Ca-Mg/biochar） application for P recovery from biogas fermentation liquid. The physico-chemical characterization, adsorption efficiency, adsorption selectivity, and postsorption availability of Ca-Mg/biochar were investigated. The synthesized Ca-Mg/biochar was rich in organic functional groups and in CaO and MgO nanoparticles. With the increase in synthesis temperature, the yield decreased, C content increased, H content decreased, N content remained the same basically, and BET surface area increased. The P adsorption of Ca-Mg/biochar could be accelerated by nano-CaO and nano-MgO particles and reached equilibrium after 360min. The process was endothermic, spontaneous, and showed an increase in the disorder of the solid-liquid interface. Moreover, it could be fitted by the Freundlich model. The maximum P adsorption amounts were 294.22, 315.33, and 326.63 mg/g. The P adsorption selectivity of Ca-Mg/biochar could not be significantly influenced by the typical pH level of biogas fermentation liquid. The nano-CaO and nano-MgO particles of Ca-Mg/biochar could reduce the negative interaction effects of coexisting ions. The P releasing amounts of postsorption Ca-Mg/biochar were in the order of Ca-Mg/B600 〉 Ca-Mg/B4S0 〉 Ca-Mg/B300. Results revealed that postsorption Ca-Mg/biochar can continually release P and is more suitable for an acid environment.

Design and preliminary experimental research on a new biogas fermentation system by solar heat pipe heating

Biogas fermentation requires appropriate temperature,while the biogas fermentation can be affected by the low ambient temperature in winter.In order to overcome the negative effects of low temperature fermentation,a new type of solar heat pipe biogas fermentation heating system was designed and a preliminary experiment research on this system was conducted using cow manure as the raw material at 6%concentration and total fermentation volume of 175 L.The experimental results showed that when the system was in normal operation,the fermentation temperature rose every day by gradient.This gradient will gradually become smaller with the increase of fermentation liquid temperature,and the temperature can reach 38°C after stability.Using this solar heat pipe heating system,the fermentation liquid temperature can be increased by 5°C every sunny day.This solar heat pipe heating system plays a significant role in biogas fermentation.The results of economic analysis show that the system can realize the fermentation at constant temperatures of 25°C and 35°C respectively,and it can also save standard coal equivalent of 40 kg and 80 kg in winter and spring,respectively.

Microbial Community Dynamics During Biogas Slurry and Cow Manure Compost

This study evaluated the microbial community dynamics and maturation time of two compost systems： biogas slurry compost and cow manure compost, with the aim of evaluating the potential utility of a biogas slurry compost system. Denaturing gradient gel electrophoresis （DGGE）, gene clone library, temperature, C/N ratio, and the germination index were employed for the investigation, cow manure compost was used as the control. Results showed that the basic strip and dominant strips of the DGGE bands for biogas slurry compost were similar to those of cow manure compost, but the brightness of the respective strips for each system were different. Shannon-Weaver indices of the two compost systems differed, possessing only 22% similarity in the primary and maturity stages of the compost process. Using bacterial 16S rRNA gene clone library analysis, 88 bacterial clones were detected. Further, 18 and 13 operational taxonomic units （OTUs） were present in biogas slurry and cow manure compost, respectively. The 18 OTUs of the biogas slurry compost belonged to nine bacterial genera, of which the dominant strains were Bacillus sp. and Carnobacterium sp.; the 13 OTUs of the cow manure compost belonged to eight bacterial genera, of which the dominant strains were Psychrobacter sp., Pseudomonas sp., and Clostridium sp. Results demonstrated that the duration of the thermophilic phase （more than 50°C） for biogas slurry compost was 8 d less than the according duration for cow manure compost, and the maturation times for biogas slurry and cow manure compost were 45 and 60 d, respectively. It is an effective biogas slurry assimilate technology by application of biogas slurry as nitrogen additives in the manufacture of organic fertilizer.