Techno-economic assessment of industrial food waste composting facility: Evaluating bulking agents, processing strategies, and market dynamics.

Techno-economic assessment (TEA) of a valorization of bulking agent (BA) ratios on the food waste compost value chain is made to assess economic feasibility. TEA was performed with two plans (Plan A: existing composting facilities; Plan B: new composting facilities) and each plan was under four scenarios. The BA (i.e. corn stalks, garden waste, and watermelon seedlings) ratio of 5 % (S1), 10 % (S2), 20 % (S3), and garden waste with a ratio of 20 % (S4). Results indicate that S2, with a net present value (NPV) of 128.9 million, represents Plan A's most economically viable scenario. Although the total operating costs of S4 were 18.9 %-23.5 % higher, 25.6 %-42.2 % higher total revenue made S4 have an NPV of 92.9 million, making it the most viable scenario in Plan B. All scenarios show positive NPV within a ± 20 % fluctuation range. Organic fertilizer price, government subsidies, and processing capacity were the key factors influencing NPV.

Temperature affects variations of class 1 integron during sludge anaerobic digestion.

Revealing class 1 integron characteristics under different operating conditions is of great importance to control antibiotic resistance genes (ARGs) during sludge anaerobic digestion (AD). This study investigated the variations of class 1 integrons and the ARGs carried by class 1 integrons in anaerobic sludge digesters under 25 °C, 35 °C, and 55 °C. The results showed lower intI1 abundance and fewer class I integrons with long gene cassette arrays at 55 °C than at 25 °C and 35 °C. Multi-resistance gene cassette arrays were observed in the digesters at 25 °C and 35 °C. Abundant ARGs were detected on class 1 integrons in all digesters with aminoglycosides as the dominant class. The abundance of ARGs on class 1 integrons in digesters at 55 °C was lower than that at 25 °C and 35 °C. Thermophilic AD is better than mesophilic ones in the control of ARGs carried by class 1 integrons.

Thermophilic rather than mesophilic sludge anaerobic digesters possess lower antibiotic resistant genes abundance.

For exploring the impact of temperature on antibiotic resistant genes (ARGs) during sludge anaerobic digestion (AD), the dynamic variations of sludge ARGs, plasmid ARGs, and cell-free ARGs in mesophilic (25 °C and 35 °C) and thermophilic (55 °C) digesters were investigated. The study revealed that the abundance of sludge ARGs and plasmid ARGs in thermophilic sludge AD was significantly lower than that in mesophilic digesters, while the cell-free ARGs abundance of the thermophilic digesters was similar to mesophilic digesters. Higher archaea abundance, lower bacteria abundance, and different microbial community were found in thermophilic digesters compared to that of mesophilic ones. Firmicutes might be a main group of potential hosts of ARGs in sludge AD. The distinct microbial community was the main contributor to the low ARGs abundance in thermophilic sludge AD. Thermophilic operation at 55 °C rather than mesophilic operation is more conducive to control ARGs in sludge anaerobic digestion.

[Interference of Dead Cell DNA on the Analysis of Antibiotic Resistance Genes and Microbial Community in Anaerobic Digestion Sludge].

To investigate the potential interference of dead bacteria DNA on the analysis of antibiotic resistance genes (ARGs) and microbial communities in anaerobic digestion sludge, three different types of anaerobic digestion sludge were treated with propidium monoazide (PMA) in this study, and the results of subsequent ARGs and microbial community analysis with the interference of dead cell DNA blocked by PMA was compared to that without PMA treatment. It was found that after PMA treatment, the absolute abundance of the ARGs in the anaerobic digestion sludge from self-anaerobic digestion system of excess sludge and from high solid sludge anaerobic digestion system decreased by 41%-86%, and 74%-98%, respectively. ARGs abundance in the sludge from the anaerobic digestion system with sludge hydrolyzate as a substrate and anaerobic granular sludge as inoculum after 15 days of digestion considerably decreased with PMA treatment. However, its ARGs abundance still declined by up to 34%. PMA treatment influenced the analysis of microbial community of the three types of anaerobic digestion sludge to different degrees, in which the influence was the highest on the community structure analysis of the sludge from high solid anaerobic digestion system. The results of the correlation analysis between the ARGs abundance and the microbial community composition were completely different in the case with PMA treatment and without PMA treatment. This study proved the potential interference of dead cell DNA on the analysis of ARGs and microbial community in anaerobic digestion sludge. PMA pretreatment could achieve a more accurate analysis of the microbial community and ARGs characteristics in anaerobic digestion sludge.