The feasibility of citric acid as external carbon source for biological phosphorus removal in a sequencing batch biofilm reactor (SBBR)

• SBBR with citric acid as a carbon source was applied for phosphorus removal.
• Phosphates release and uptake rates depended on mixing and aeration phases duration.
• The highest dephosphatation efficiency was observed for phases ratio of 1:3.
• Phosphorus content in dry matter of biofilm reached 4.6%.

The aim of this study was to evaluate the feasibility of citric acid as external carbon source for biological phosphorus removal. Citric acid was the only source of organic carbon and biomass occurred only as a biofilm. The effect of varying the duration of the mixing and aeration phases on the process of dephosphatation and consumption of organic substrate was examined. The operation consisted of filling (0.5 h), mixing (2.75–8.25 h), aeration (2.75–8.25 h) and draw (0.5 h) phases. Total phosphorus and nitrogen influent concentrations were 7.02 mg P L−1 and 2.05 mg N L−1, respectively. Enhanced intracellular accumulation of polyphosphates (poly-P) and their release in reactors with immobilized biomass (SBBR) was stated. The highest rates of phosphates release (0.059 ± 0.004 g P–PO43− m−2 h−1) and phosphates uptake (0.028 ± 0.002 g P–PO43− m−2 h−1) were observed for mixing to aeration phase duration ratio of 1:3. The percentage of phosphorus in dry matter of biofilm reached 4.6%.