Biogenic waste transformation into resources through anaerobic digestion

A large amount of agricultural byproducts and animal husbandry waste have been produced due to the inevitable agricultural practice for human survival. The utilization of agricultural and animal husbandry residues in waste-to-energy technologies has become an eye-catching issue over years because of the concept of circular economy for sustainable development. These biogenic residues possess a high content of organic carbon such as sugars, proteins, and lipids and are being dumped into landfills or incinerated, causing severe environmental challenges and the waste of available resources. Anaerobic digestion (AD) provides a sustainable route for resource circular utilization in agriculture and husbandry waste. The dry anaerobic digestion process is adopted to treat biogenic waste including outer leaves of cabbage (C), litter (L), and pig manure (PM) in the present study. Different from the main target of past studies to enhance biomethane production, this study aimed to transform the waste into saccharides and organic acids which are the intermediates in AD processes (i.e. hydrolysis and acidogenesis phases) and can be further refined or utilized in various industries. For instance, succinic acid of high economic benefits can be obtained through transforming AD digestate. Hence, Saccharomyces cerevisiae was chosen as the microbial inoculum due to its non-gas-generating characteristic. The results of batch AD experiments for 35 days showed that the optimum feedstock mass mixture ratios are C:L = 2:1, C:L = 3:1, C:PM = 2:1, and C:PM = 3:1 since the observation of more saccharides formation. Moreover, the optimal feedstock-to-inoculum ratio (F/I ratio) is 1:1 and the best AD operation temperature is 50℃. The substance flow analysis was established based on the measurement of key AD products (i.e. saccharides, organic acids, CH₄, CO₂, and digestate). The batch experiments was scaled up to the 10L continuously-stirred reaction tank to determine the feasibility of in situ AD practice. In comparison to the traditional way to deal with agriculture and husbandry waste, AD is promising to be a valorized treatment to convert waste into reusable bioproducts which enables economic and environmental benefits to realize the concept of the circular economy.