EFFECT OF FOUR PRETREATMENTS IN THE NITROGEN AND PHOSPHORUS MASS BALANCE FROM EFFLUENTS OF A RECIRCULATING AQUACULTURE SYSTEM

Aquaculture is a fast growing activity. However, the effluents generated by this activity are generally discharged directly into the water body becoming a potential environmental risk.  The advantages of using recirculating aquaculture systems (RAS) are their low water replacement and concentration of the solid waste in small flows. Anaerobic digestion is used to treat the effluents of a RAS and decrease the amount of sludge and nutrient concentrations. The objective of this work was to evaluate the effect of four pretreatments: chemical (NaOH 0.8Mmol), mechanical (5000 rpm for 30 min), thermal (100˚C for 30min.), biological (80:20, secondary and primary sludge) on nitrogen (N) and phosphorus (P) removal through a mass balance approach. Anaerobic batch digestion was performed for 15 days from March to September at ambient temperature without pH control.

Significant differences (P<0.0001) were detected in total nitrogen and total phosphorus concentrations among months, pretreatments, and the interaction between months and pretreatments. In all four pretreatments N was transformed by denitrification, and an increment in both, N and P by sludge mineralization were detected. The highest removal of organic N was obtained in control and biological pretreatments. Phosphorus was removed only in the chemical pretreatment. The mechanical pretreatment removed the highest concentration of N. In all pretreatments an increment in P was observed. The lowest P concentration was observed in the chemical pretreatment (Figure 1).