Upflow Anaerobic Floating Filter (UAFF) Improved the Performance of the Anaerobic Treatment of Brackish Aquaculture Waste

Abstract

Highlights Fish hatchery RAS thickened wastewater was successfully treated by anaerobic digestion. Traditional complete mix digester (CSTR) configuration was compared to the UAFF, an upflow anaerobic floating filter. UAFF start-up resulted faster and more productive than in conventional reactors (188 compared to 100 NmL CH4/g VS). At steady conditions, yields of 190.5 and 180.9 NmL CH4/g VS were recorded, for UAFF and CSTR respectively. Abstract. Thickened wastewater from a fish hatchery recirculating water system (RAS) was successfully treated by anaerobic digestion, showing a high methane potential in brackish and marine conditions. To optimize the process and establish operational criteria for a full-scale transfer, pilot-scale tests were carried out in a BioReactor Simulator System (BRS, Bioprocesscontrol, Sweden). The BRS consists of 6 reactors with a volume of 1.8 L each: 3 reactors operated in conventional configuration (CSTR, continuous stirred tank reactor), while the other 3 were modified with an up-flow fixed bed layout, with floating plastic filling elements (UAFF, upflow anaerobic floating filter). The objective of the present paper was the comparison of the performance of the UAFF and the CSTR anaerobic systems both in the initial colonization batch process, and in the following continuous process. The batch test was performed in 72 days by treating aquaculture sludge inoculated with brackish digestate, for the CSTRs, and with the biofilm of the plastic media for the UAFFs. The following continuous loading phase was characterized by start-up and steady steps. The tests were performed in mesophilic conditions. The start-up in the UAFF reactors resulted significantly faster and more productive than in conventional reactors, with specific yields reaching 187.9 NmL CH4/g VS compared to 100.0 NmL CH4/g VS. During the following steady phase, with the retention time of 20 days, the specific yields increased in all digesters but the differences between the 2 types of reactors were not significant, even if favorable for the UAFF (190.5 and 180.9 NmL CH4/g VS, respectively for UAFF and CSTR). Keywords: Anaerobic digestion, Anaerobic filter, Aquaculture, Biogas, Biomethane, Brackish and marine wastewater, Fish farm effluents.