Research progress of anaerobic co-digestion of winery waste and residue activated sludge

Abstract: Anaerobic digestion has been widely used in the disposal of various industrial wastes. However, the load shock and microbial loss have been caused by the high chemical oxygen demand (COD) content, low pH, and seasonal production of winery waste. Meanwhile, the low methane production efficiency cannot fully meet the requirements, particularly for the complex components and low hydrolysis rate of the waste activated sludge. Anaerobic co-digestion (AcoD) can be expected to serve a pivotal disposal way for the winery waste and waste activated sludge, due to the balance nutrients, loss inhibitory effects, high microbial synergy, and methane production. A systematic review was made on the research progress in the AcoD process of the wine wastewater and waste activated sludge. Two systems were selected as the wine wastewater and waste activated sludge, as well as the wine solid waste and waste activated sludge. The main factors of two systems were summarized in the AcoD performance. The wine wastewater was mainly from the processes, such as pressing, pouring, filtering, and cleaning. At the same time, there were also the high COD content, low carbon/nitrogen (C/N) ratio, high generation, and seasonal production. Thus, the optimal mixing ratio was performed to determine the suitable contents of nutrients and C/N ratio. An investigation was also made on the impact of the short-term, large-scale high-concentrations wastewater in the AcoD system during the picking seasons (9~11). Three types of substances were consists of the unfermented juice residues (stems) sediments after fermentation (waste yeast), and filters (diatomaceous earth) in the wine lees, which was the main solid waste in the winery production process. Wine lees were characterized by the low pH, low C/N ratio, high total solids, as well as the high-concentrations of K+ and polyphenols. Generally, the hydrolysis was considered as the rate-limiting step for the WAS in the AcoD process. The approach was applied to raise the temperature for the better hydrolysis and solubilization of organic components. The impact of multiple toxic substances were investigated in the AcoD system. The accumulated antibiotics and heavy metals were considered as the negative for the microbes. Secondly, a summary was made on the ethanol-based direct interspecies electron transfer in the AcoD. The extracellular electron transfer system (EET) was involved two main types of mechanisms: the mediated interspecies electron transfer (MIET) and direct interspecies electron transfer (DIET) in the anaerobic digestion. Compared with the MIET, the DIET was considered to be a more efficient electron transfer pathway through the cell components (e-pili or cytochrome OmcS) without relying on the electron carriers. Although the DIET between the bacteria and methanogens was difficult to establish in the conventional anaerobic digestion system, the establishment of DIET can be promoted by adding ethanol or cooperating with the carbon-based materials. Ethanol was set as the substrate in the AcoD system functions, as the precursor to stimulate DIET by enriching the electroactive microbes for the co-digesting complex organic wastes. Therefore, the ethanol was widely applied as the electron donor in the presence of carbon-based materials to induce the DIET. The carbon-based materials presented the high conductivity to promote the DIET, in order to accelerate the substrates degradation for the less enrichment time of functional microbes. Ultimately, the omics technologies were used as the community-substrate metabolic coupling of the AcoD system. The finding can provide a strong reference to clarify the methanogenesis metabolic pathway for the co-digestion models, in order to characterize the metabolic kinetics in the AcoD process.