Biological nutrient removal by applying SBR technology in small wastewater treatment plants: carbon source and C/N/P ratio effects

Abstract

SBR technology is considered an alternative to conventional processes such as Phoredox, Five-stage Bardenpho, among the others for treating nutrients in wastewaters. It is especially applicable to small communities of a just few people to a population equivalent (p.e) up to 4000. In this paper, biological nutrient removal using SBR technology in a single reactor is presented. Biological nutrient removal requires a sequence of anaerobic–anoxic–aerobic phases with multiple feeding events over one cycle. This filling strategy was adapted to enhance denitrification and phosphate release, using the easily biodegradable organic matter from the wastewater. In spite of using this feeding strategy, the organic matter concentration can be insufficient. The results show that biological nutrient removal was successfully achieved by using only one reactor, working with a low organic matter concentration in the influent (C/N/P ratio of 100:12:1.8). Nevertheless, when the C/P ratio was lower than 36 g COD·g−1 P-PO4, an accumulation of phosphate was observed. After that, the system responded quickly and returned to ideal conditions (C/P ratio of 67 g COD·g−1 P-PO4), taking only 15 days to achieve the complete nutrient removal. Furthermore, the operational conditions and the synthetic wastewater used conferred a selective advantage to polyphosphate accumulating organisms (PAOs) over glycogen accumulating non-poly-P organisms (GAOs) as shown by the FISH analysis performed.