1.1 Wastewater characterization and treatment

Tilapia fish processing wastewater used in the experiment was donated by Tilapia do Brasil Inc. (Buritama City, SP, Brazil) and was made up of effluents from killing, scaling, gutting, cleaning, skinning, filleting and freezing operations, and also from cleaning operations, which were gathered and roughly filtered (grating), averaging 10,000 L h-1.

Crude wastewater was analyzed for turbidity, total solids (TS), pH, total nitrogen (TN) and oils and greases (OG), according to standard methods (American Public Health Association, American Water Works Association, Water Pollution Control Federation [APHA, AWWA and WPCF], 2005). Chemical Oxygen Demand (COD) was determined by chemical digestion (HR digestion solution for COD 0-1500 ppm; DRB200; DR2800; Hach), based on the protocol developed by Jirka & Carter (1975).

Before being used as a substrate for the bacterial growth, the wastewater was filtered in a 50 pm mesh fast filter (Gardena 1731; 3,000 L h-1) for the withdrawal of gross particles and heat treated (Incomar LTLT tank) at 65oC/30 min to eliminate pathogenic agents and repress the level of competing microorganisms. After that, wastewater was cooled to room temperature and so it was ready to receive the bacterial inoculum.

Microbiological analyses of crude and heat treated wastewater comprised mesophilic aerobic bacteria, total and fecal coliforms, molds and yeasts, Aeromonas spp and Salmonella spp, and were performed according to standard methodology (APHA, AWWA and WPCF 2005).