Studies on Removal of Ammonia-Nitrogen from Industrial Wastewater using Inverse Fluidized Bed Biofilm Reactor

Abstract

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. Compared to conventional fluidized bed reactors, IFBBRs have many unique benefits due to which these are widely used nowadays for the treatment of pollutants like ferrous iron, aniline, phenol, and sulphate. In the current work, nutrient pollutants of industrial wastewater particularly ammonia-nitrogen is treated for which hydrodynamics of an IFBBR were studied at first. Hydrodynamics with respect to phase holdups was studied by varying different parameters such as ratio of bed volume to reactor volume (Vb/Vr ratio) and superficial gas velocity. The developed correlations for the gas phase holdup have average absolute percent deviations of 7.90 & 7.39 suggesting good agreement of the predicted values with the experimentally observed values. Synthetic wastewater was treated in the present IFBBR using polypropylene balls and mixed culture. The inoculum was prepared from the sludge taken from the local steel industry’s wastewater treatment plant. The effects of different input parameters such as Vb/Vr ratio, superficial air velocity, initial concentration of NH4+-N, C/N ratio, temperature, and pH were studied. The output in terms of final concentration of NH4+-N in the wastewater was measured as per APHA standards for each experiment at pre-determined time intervals. Optimum operating condition was found to be at Vb/Vr ratio of 0.380, pH of 8.3, temperature of 300C, superficial gas velocity of 0.0085 m/s, and C/N ratio of 0.0. Complete removal of NH4+-N is achieved in this IFBBR at a faster rate. However, with the increase of C/N ratio from 0.0 to 2.5, the NH4+-N removal reduces by 30.96% to 52.18% for initial NH4+-N concentrations of 40 to 200 mg/l respectively. Percentage nitrification was found to be 96.2% for initial NH4+-N concentration of 40 mg/l which reduces with the increase of C/N ratios and initial NH4+-N concentrations. Fractional Factorial Design analysis has been used to predict the removal of NH4+-N and the rate of reaction of NH4+-N. In these cases the average absolute percent deviations were 11.75 and 7.89 respectively suggesting the proposed correlations to be better validated with the experimentally observed values. The kinetic parameters obtained were also found to be in the acceptable range. The performance of the present IFBBR was further found to be stable for semi-batch operations with NH4+-N loading rate of 40 to 200 mg/l/d. The local pond water was also treated in this IFBBR. The results obtained from the experiments were also found to be satisfactory implying the effectiveness of the IFBBR for wastewater treatment in general.