Nutrient (sulphate) removal from wastewater in inverse fluidized bed biofilm reactor

Abstract

Sulphate is one of the inorganic nutrient pollutants present in wastewater which needs to be treated due to present day global stringent emission norms. Among the several available biological means to treat industrial wastewaters, the use of inverse fluidized bed biofilm reactors (IFBBRs) has gained much attention in recent years over other fluidized bed reactors. In this work, the feasibility of removal of sulphate from synthetic wastewater having initial concentrations of 13.096, 32.74, and 65.48 mg/l was studied using mixed bacterial culture. Spherical polypropylene balls were taken as biomass support particles having density of 920 kg/m3 and diameter of 5.63 mm. Three different bed-volume to reactor-volume (Vb/Vr) ratios i.e., 0.304, 0.380, & 0.445 and three different superficial air velocities i.e., 0.0065, 0.0085, & 0.0106 m/s were considered for experimental runs. The reactor inoculum was prepared from the sludge collected from local steel industry’s wastewater treatment plant. The effects of different input parameters such as Vb/Vr ratio, superficial air velocities, and initial concentration of sulphate in synthetic wastewater on the output sulphate concentration were studied. Temperature of 30–32 °C and pH of 8.3–8.8 were maintained throughout the degradation studies. The reactor was operated in semi-batch recirculation mode with superficial water velocity of 0.0021 m/s. Sulphate concentration was measured by turbidity method using UV spectrophotometer at 420 nm which is as per APHA standards. The maximum removal efficiency of sulphate was found to be 72–75% which was achieved at a Vb/Vr ratio of 0.380 and the superficial gas velocity of 0.0085 m/s observed at a time of 40 h. Higher sulphate reduction was not achieved due to presence of more inorganic salts in the synthetic wastewater. At higher initial sulphate concentration, reactor operational difficulties were observed.