Determination of biological nutrient removal performance in biofilm-based sequencing batch reactors

In this study, the effect of sludge age, hydraulic retention time, wastewater composition and ratio of carrier element to the reactor volume on the organic matter, nitrogen and phosphorus removal were investigated in moving bed sequencing batch biofilm reactors. A conventional sequencing batch reactor (CSBR) was also operated under same operating conditions, except for the ratio of carrier element to the reactor volume. The study was carried out in four sequencing batch reactors, which were -R1 reactor without carrier element. R2 reactor with %30 carrier ratio, R3 reactor with %50 carrier ratio and R4 reactor with %65 carrier ratio.The best removal efficiencies were obtained at the sludge age of 10 days when the cycle time of anaerobic/aerobic/anoxic was kept at 12-h, in the case of that acetate-containing feed was of 1000 mg/L COD, 50 mg/L NH4-N and 15 mg/L PO4-P. COD removal was found to be %93, %95, %94 and %94 in R1, R2, R3 and R4 reactors, respectively. TIN (total inorganic nitrogen) and PO4-P removal was observed to be %69 in R1, %88 in R2, %87 in R3, %89 in R4 and %13 in R1, %23 in R2, %19 in R3 and %17 in R4. COD removal decreased dramatically to %85 in the case of 8-h cycle time. The removals of PO4-P were respectively %23, %22, %21, %11 in R1, R2, R3 and R4 as NH4-N declined sharply to %31, %20, %17, %11 and %23, %22, %21, %11 in R1, R2, R3 and R4, respectively. When the reactors were fed with an influent having 500 mg/L COD, 50 mg/L NH4-N and 15 mg/L PO4-P, COD removal varied in the range of %85-94, %88-92, %84-92 and %84-92 in R1, R2, R3 and R4, respectively. NH4-N removal was quite a low efficiency except for R2 reactor. PO4-P efficiency was also low. In the case of that influent was changed as 250 mg/L COD, 50 mg/L NH4-N and 10 mg/L PO4-P, COD removal varied in the range %80-93 and %57-89 in R1 and R2 reactors, respectively. NH4-N removal dropped to %6. PO4-P removal was found below %12 and %17. At the cycle time of 8 h, when the influent contained 125 mg/L COD, 50 mg/L NH4-N and 5 mg/L PO4-P, COD removal varied in the range of %33-64 in R3. NH4-N and PO4-P removal was below %14 and %16, respectively. COD and NH4-N removal varied respectively in the range of %82-91 and %15-43 in R4 when the influent contained 500 mg/L COD, 25 mg/L NH4-N and 15 mg/L PO4-P.COD removal was %88, %85, %76 and %83 in R1, R2, R3 and R4, respectively when the cycle time was kept at 6-h, in the case of that glucose-containing feed was of 1000 mg/L COD, 500 mg/L NH4-N and 15 mg/L PO4-P. NH4-N and PO4-P removal were found %79 in R1, %79 in R2, %76 in R3, %72 in R4 and %50 in R1, %52 in R2, %53 in R3, %51 in R4, respectively. COD removal was found to be %59, %58, %67 and %62, respectively when NH4-N concentration was increased to 100 mg/L. NH4-N removal decreased to %10. PO4-P removal was %20.NH4-N removal was %96 in all of the reactors when the cycle time of anaerobic/aerobic/anoxic was kept at 8-h and reactors were fed with domestic wastewater. PO4-P removal was higher in MBSBBRs than that of CSBR. NH4-N removal was above %99 in all of the reactors when the cycle time of anaerobic/aerobic/anoxic/aerobic was kept at 8-h. Effluent NO3-N concentration decreased below 1 mg/L when sufficient carbon source existed in anoxic phase. PO4-P removal varied in the range of %81-85, %88-95, %94-95 and %70-90 in R1, R2, R3 and R4, respectively. At the cycle time of 6 h, NH4-N removal was above %99 in all the reactors. PO4-P removal varied in the range of %50-93, %78-94, %89-95 and %84-94 in R1, R2, R3 and R4 reactors, respectively. The removal efficiencies obtained by anaerobic/aerobic/anoxic/aerobic phases were better than anaerobic/aerobic/anoxic phases. Required C/N ratio for denitrification was found to be 4 g COD/g NO3-N.Keywords: moving bed sequencing batch biofilm reactor, nutrient removal, wastewater