Graphene oxide-doped organic xerogel and magnetite enhance the anaerobic treatment of winery wastewater

Winery wastewater is a high-strength effluent, which is challenging for anaerobic treatment systems. In this study, magnetite and an organic xerogel doped with graphene oxide (OX-GO) were tested as booster materials (BMs) during the anaerobic treatment of winery wastewater. The enhancing effect was clearly reflected in higher methane production rates (up to 25 % increase) and greater organic matter removal (up to 18 % increase) in amended reactors, as compared to the unamended control. BMs also increased the hydrolysis of proteins coupled to biogas production. Furthermore, the organic acids-enriched composition of winery effluents allowed the production of valuable medium-chain carboxylic acids by tuning operational conditions. Finally, the relative abundance of specialized microbial populations, such as beta-oxidizing/proteolytic bacteria (Syntrophomonas) and hydrogenotrophic methanogens (Methanobacterium) increased in the anaerobic systems. Particularly, the presence of BMs promoted the enrichment of specific bacterial genera, including Rhodopseudomonas, Propionicicella, Acetobacter and Anaerolinea, as well as proteolytic genera like Proteiniborus and Proteiniphilum. Moreover, the genus Caproiciproducens exhibited significant fold-changes when OX-GO was added, which is crucial for organic acids production and chain elongation. These BMs are proposed as potential additives in anaerobic systems to boost their performance during the treatment of high-strength industrial effluents.