Anaerobic Digestion of Brackish and High Salinity Aquaculture Sludges

The development of intensive fish production is facing the challenge of the sustainable management of effluents. Aquaculture reproductive sectors (i.e., hatcheries) in most cases implement water recirculation systems (RAS), which discharge a portion of the produced wastewater. Anaerobic digestion (AD) process could mitigate the environmental impact of this waste stream while producing fuel in the form of biogas. The present research represents a further development of previous tests conducted in the framework of the AdriaAquaNet Interreg Project. The anaerobic digestion tests were conducted using a pilot scale Bioreactor simulator system (BRS, Bioprocess Control, Sweden). This apparatus can operate with semi continuous loading, simulating a full scale reactor in order to study the optimal process layout and the optimal substrate retention time. The system was initially loaded with an inoculum derived from anaerobically treated brackish aquaculture sludges and with digestate originated from a full scale anaerobic reactor operating with animal manure and corn silage. The incubation period lasted 20 days, and from the 21st day, aquaculture sludges were loaded with organic loading rates (OLR) varying from 0.16 to 0.64 g VS/L day, with hydraulic retention times (HRTs) shortened from 30.0 days to 12.9 days. The tests were performed with salt concentration established at 35 g/L (high salinity conditions) and 12 g/L (original brackish water conditions). Specific methane productions were fairly good (278.9 300.3 NL/kg VS input), resulting higher in brackish conditions than in marine conditions, and in correspondence of retention times of about 20 30 days.