Biological nutrient removal efficiency in treatment of saline wastewater

There is very little known about the effectiveness of wastewater treatment systems for saline wastewater generated by seafood processing industries, aquaculture and tourism activities. In particular, the effect of salinity on nitrogen and phosphorus removal in wastewater treatment processes is not well understood. Therefore we devised experiments to examine the treatment of highly saline wastewater, by using artificial seafood processing wastewater, for removal of nitrogen and phosphorus. Lab scale sequencing batch reactors (SBR) were initially operated at low, and then at increasing salt levels, to determine the overall effects of salinity on the nutrient removal performance. The microbial populations during these experiments were monitored to determine the specific effect of salinity on the various bacterial groups responsible for nutrient removal. The methods used were whole cell probing with fluorescently labelled RNA-directed oligonucleotide probes. Experimental data showed that the SBRs achieved good biological nutrient removal (BNR) when salinity levels in the influent were low (0.03% to 0.2% NaCl) but showed difficulties with biological phosphorus removal at salinity levels of 0.5%. It was found that there was a dominance of Gram-positive bacteria with a high mol% G+C in their DNA in the SBR treating wastewater with NaCl at 0.03% to 0.2%. The addition of acetate to improve BNR performance increased the proportion of bacteria from the beta Proteobacterial subclass.