Liquid hot water pretreatment to enhance the anaerobic digestion of wheat straw-effects of temperature and retention time.

Wheat straw is an abundant agricultural waste that is rich in lignocellulose. However, its waxy surface, highly crystallized structure, and limited surface area make it difficult to be hydrolyzed and used efficiently by microorganisms. Liquid hot water (LHW) pretreatment was studied to explore the feasibility of improving the methane yield of wheat straw in anaerobic digestion (AD). The results showed that the crosslinking structure of wheat straw was broken by LHW pretreatment. Some pores and cracks appeared on the surface of the pretreated wheat straw, increasing the microbial attachment sites. Under different hydrothermal temperatures (150-225 °C) and retention times (5-60 min), the degradation of hemicellulose ranged from 27.69 to 99.07%. The maximum methane yield (201.81 mL CH4/g volatile solids) was achieved after LHW pretreatment at 175 °C for 30 min, which was a 62.9% increase compared with non-treated straw. LHW at high temperatures such as 225 °C was not suitable for the AD of wheat straw. Methane yield results were fitted with the first-order and modified Gompertz equations to evaluate the hydrolysis rate and inhibitory effects of the pretreated materials in AD.

Performance of Anaerobic Digestion of Chicken Manure Under Gradually Elevated Organic Loading Rates.

Poultry manure is the main source of agricultural and rural non-point source pollution, and its effective disposal through anaerobic digestion (AD) is of great significance; meanwhile, the high nitrogen content of chicken manure makes it a typical feedstock for anaerobic digestion. The performance of chicken-manure-based AD at gradient organic loading rates (OLRs) in a continuous stirred tank reactor (CSTR) was investigated herein. The whole AD process was divided into five stages according to different OLRs, and it lasted for 150 days. The results showed that the biogas yield increased with increasing OLR, which was based on the volatile solids (VS), before reaching up to 11.5 g VS/(L·d), while the methane content was kept relatively stable and maintained at approximately 60%. However, when the VS was further increased to 11.5 g VS/(L·d), the total ammonia nitrogen (TAN), pH, and alkalinity (CaCO3) rose to 2560 mg·L-1, 8.2, and 15,000 mg·L-1, respectively, while the volumetric biogas production rate (VBPR), methane content, and VS removal efficiency decreased to 0.30 L·(L·d)-1, 45%, and 40%, respectively. Therefore, the AD performance immediately deteriorated and ammonia inhibition occurred. Further analysis demonstrated that the microbial biomass yield and concentrations dropped dramatically in this period. These results indicated that the AD stayed steady when the OLR was lower than 11.5 g VS/(L·d); this also provides valuable information for improving the efficiency and stability of AD of a nitrogen-rich substrate.

Environmental Assessment of a Hybrid Solar-Biomass Energy Supplying System: A Case Study.

Local energy supply by renewable energy, such as solar energy and biomass, using distributed energy systems plays an important role in global energy structure. This study investigated the environmental performance of a hybrid solar-biomass energy supplying system by life-cycle assessment method. The results showed that in terms of environmental and energy impacts, the construction stage and the disassembly and recycling stage of the system contribute little to the whole life-cycle environmental impacts. According to the results of most of the selected impact categories, the solar subsystem contributed the most environmental emissions during construction stage, followed by the two anaerobic reactors; therefore, the excessive pursuit of high solar energy proportion can correspondingly lead to even more serious environmental problems. The integrated energy supplying system significantly reduces non-renewable energy consumption, climate change impacts, acidification as well as eutrophication effects due to the replacement of alternatives such as lignite coal, and from fertilizer production. The present hybrid solar-biomass energy supplying system not only produces clean thermal energy but also reduces the disposal of organic wastes and produces valuable agricultural products.

Effects of biogas residues containing antibiotics on soil enzyme activity and lettuce growth.

To investigate the effects of biogas residues containing antibiotics on lettuce growth and soil enzyme activity, the antibiotics oxytetracycline and sulfadiazine were used as additives; two kinds of feedstocks including pig manure and straw were chosen. Results showed that the higher the concentrations of the antibiotics are, the stronger the inhibition of soil sucrase activity becomes. The activity of sucrose enzyme in the test group with a single concentration of 60 mg/kg was significantly lower than the group that was treated with 0 mg/kg. In the mass, the organic fertilizer containing antibiotics can improve the soil urease activity and increase the urease activity of the soil. In the growth phase, urease activity increased by 27% from 0.85 mg NH3-N/(g day) in the blank group to 1.08 NH3-N/(g day) in the 0-mg test group. During all growing stages of lettuce, though the effects of the biogas residues containing oxytetracycline and sulfadiazine on the soil catalase activity were not obvious, the field application could inhibit the activity of soil catalase to some extent.