Semi-continuous anaerobic co-digestion of flotation sludge from broiler chicken slaughter and sweet potato: Nutrients and energy recovery

Comprehensive experiences on the operation of a full-scale continuous dry anaerobic digestion plant treating mechanically sorted OFMSW

Anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) is a crucial waste management method for the diversion of organics from landfills to decrease greenhouse gas emissions while enabling energy recovery. A number of dry AD systems treating OFMSW have notably increased over the last two decades. In this study, mono-digestion of mechanically sorted OFMSW and co-digestion of OFMSW, chicken manure and WWTP sludge were evaluated using triplicate full-scale digesters. Results demonstrated that 5-6.6 m3biogas/m3reactor.day biogas could be produced at an organic loading rate (OLR) of 10.5-12 kg TVS/m3.day, with an HRT of 16-18 days. Beyond this threshold, further increases in OLR resulted in reduced gas production due to ammonia inhibition as a result of broiler chicken manure overload. Biogas yield decline started when the chicken manure content of the feed was increased to 10% (w/w) and accompanied with the VFA/TA ratio rising above 0.8. Process instability and a sharp drop in biogas productivity were observed when the feed contained more than 20% (w/w) chicken manure, where VFA/TA ratio exceeded 1.0. Results underline the importance of balancing different properties (e.g., degradability, carbon to nitrogen (C/N) ratio) of co-substrates to optimize the biogas yield and to ensure process stability.

Switching from wet to dry anaerobic digestion of food waste with different dilution times under no mechanical mixing condition

Previous research on anaerobic digestion of food waste has primarily focused on either wet or dry anaerobic digestion (AD), typically accompanied by continuous mechanical mixing. However, the necessary dilution rates and the extent of mixing required have yet to be addressed. In this study, we investigated switching from wet to dry AD of food waste without mechanical mixing, employing different dilution rates. Lab-scale anaerobic reactors were operated with dilution rates of 10, 5, and 2 times during Phases I (0-56 days), II (57-121 days), and III (122-209 days), respectively. The methane production rates were not significantly different (p > 0.05) across the dilution rates decreased from 10 to 2 times. Remarkably, the methane production in the anaerobic reactors exhibited fluctuations due to variations in feeding, with the methane production rate ranging from 2.0 to 2.7 g CH4-COD/(L d), without mechanical mixing, as the solids content transitioned from wet to near-dry digestion conditions (15 %, food waste). The distribution of sludge volatile solids concentrations remained uniform in the reactor, even at high solids concentrations of up to 15 %. A dynamic microbial community response to changes in dilution rates, with a shift from aceticlastic to hydrogenotrophic methanogenesis pathways. Syntrophic acetate oxidization bacteria (the genus Syner-01 (4.2-8.9 %) and f_Synergistaceae (3.6-4.2 %)) were highly enriched as switching from wet AD to dry AD. The study's findings provide crucial operational insights for anaerobic food waste treatment, potentially resulting in decreased water usage and operational costs, particularly in scenarios with low dilution rates and without mechanical mixing.

Biowastes of slaughterhouses and wet markets: an overview of waste management for disease prevention

Slaughterhouse and wet market wastes are pollutants that have been always neglected by society. According to the Food and Agriculture Organization of the United Nations, more than three billion and nineteen million livestock were consumed worldwide in 2018, which reflects the vast amount and the broad spectrum of the biowastes generated. Slaughterhouse biowastes are a significant volume of biohazards that poses a high risk of contamination to the environment, an outbreak of diseases, and insecure food safety. This work comprehensively reviewed existing biowaste disposal practices and revealed the limitations of technological advancements to eradicate the threat of possible harmful infectious agents from these wastes. Policies, including strict supervision and uniform minimum hygienic regulations at all raw food processing factories, should therefore be tightened to ensure the protection of the food supply. The vast quantity of biowastes also offers a zero-waste potential for a circular economy, but the incorporation of biowaste recycling, including composting, anaerobic digestion, and thermal treatment, nevertheless remains challenging.

Combination of biological processes for agro-industrial poultry waste management: Effects on vermicomposting and anaerobic digestion

This study evaluated the combination of bioprocesses to increase the utilization of agro-industrial poultry wastes. Composting piles were submitted to hydration and fraction separation (FS) and then, the solid fraction was vermicomposted and the liquid fraction was anaerobically digested. Composting followed by hydration and FS prior to vermicomposting enhanced earthworm adaptation and survival by reducing salt levels (50%), total organic carbon, and total nitrogen which may be limiting to vermicomposting at high concentrations. These strategies providing the production of up to 300 new cocoons and 360 young earthworms more than the control treatment. In addition to providing a favorable environment for earthworm growth, the combination of bioprocesses resulted in a high-quality organic fertilizer free of phytotoxic compounds and with phytostimulant properties (germination index higher than 100%). Energy recovery was greater in the treatment without the precomposting step (T₀) (461.8 L CH₄ kg^-1. Volatile Solids_added). The results show that combining the bioprocesses is a sustainable alternative for managing poultry wastes not only in terms of the recycling of nutrients but also by providing a clean source of energy.