Effects of three major nutrient contents, compost thickness and treatment time on larval weight, process performance and residue component in black soldier fly larvae (Hermetia illucens) composting.

The cellulose content in vegetable waste (VW) is high and cannot be directly digested by black soldier fly larvae (BSFL). In this study, in order to treat VW using BSFL composting, kitchen waste (KW) is used as the only nutritional supplement for VW to analyze the effects of the different contents of crude protein (CP), crude fat (EE), carbohydrate (3C), compost thickness (CT), and treatment time on the larval weight (LW), survival rate (SR), dry matter reduction rate (DMR), bioconversion rate (BCR), physical and chemical properties of BSFL sand and changes in the microbial community. Our results showed that when the average 3C content increased by 40%, the average LW increased by 47.6%, and the SR, DMR, BCR, and organic matter (OM) content increased by 16.82%, 8.5%, 4.77%, and 3.86%, respectively. In contrast, when the average compost thickness increased by 5 cm, the average weight of BSFL decreased by 22.64%, while the SR of larvae, DMR, BCR, OM, and total nutrients (TN + P2O5 + K2O) decreased by 5%, 5.2%, 4.42%, 9.6%, and 0.78%, respectively. Germination test showed that BSFL sand alone could not be used as soilless culture substrate. After BSFL treatment, we found that the dominant phyla in BSFL sand were Firmicutes (95.77%), Proteobacteria (2.54%), Actinobacteria (0.74%), and Chloroflexi (0.6%). Our results indicate that BSFL composting is an effective method of treating VW, and 3C content and CT have a significant effect on BSFL composting.

Investigation of physico-chemical properties of hydrochar and composition of bio-oil from the hydrothermal treatment of dairy manure: Effect of type and usage volume of extractant.

Hydrothermal treatment for dairy manure into value-added hydrochar and bio-oil is a potential technology for its resource utilization. During the process of treatment, extractant is applied to the separation of hydrochar and bio-oil. In this study, three polar extractants (ethyl acetate, dichloromethane, diethyl ether) and two nonpolar extractants (n-hexane and petroleum ether) were used, and the physico-chemical properties of hydrochar and the composition of bio-oil were investigated. Compared with nonpolar extractants, polar extractants could extract the bio-oil absorbed on the hydrochar exterior and interior surface, resulting in more mass loss of hydrochar and better extraction performance on the production of bio-oil. The decrease of H/C atomic ratio and the increase of O/C atomic ratio indicated the demethanation tendency to occur during the extraction process, and enhanced the hydrochar stability. The scanning electron microscope and specific surface area analysis revealed that polar extractant had a more positive effect than nonpolar extractant on the occurrence of disperse spherical microparticles and the augment of hydrochar specific surface area. The bio-oil from polar extractant mainly consisted of N-containing compounds, ketones, phenols and acids, while the bio-oil from nonpolar extractant mainly consisted of esters, alkanes and aromatics. These results reveal that the hydrochar extracted by polar solvent exerts a greater potential for the production of carbon-based material.

Effects of process parameters on the distribution characteristics of inorganic nutrients from hydrothermal carbonization of cattle manure.

In this study, dairy manure was converted into solid and liquid products via hydrothermal carbonization (HTC) to determine optimal reaction conditions to retain the greatest amounts of inorganic nutrients. The influence of three parameters, reaction temperature (150-270 °C), residence time (0.5-6 h) and manure/water ratio (5/200-25/200 g/mL), on the total nutrient content (TNC) in the solid and liquid products were investigated using a 5-level, 3-factor orthogonal test and principal components analysis (PCA). Also, the distribution characteristics of inorganic nutrients were determined using single factor tests. The maximum TNC of the solid product was 22.92 mg/g, obtained at manure/water ratio of 20/200 g/mL and performed at 240 °C for 6 h. For obtaining the maximum TNC of liquid product, the most optimal conditions were 150 °C, 1 h and 20/200 g/mL which produced TNC of 1619.55 mg/L. The proportion of ammonium (NH4+-N) and orthophosphate (PO43-) were also analyzed in the liquid product. The amount of NH4+-N increased with reaction temperature increasing and manure/water ratio decreasing, the main form of phosphorus (P) was PO43- in the liquid product, and most of the potassium (K) were also dissolved in the liquid product. These results indicate that the HTC could be a promising approach for the utilization of dairy manure as inorganic fertilizer in the future.