| The toxicity of reverse osmosis (RO) brine rejects may impose a significant barrier in implementing the RO technology in water recycling applications. This research discusses several bio-physicochemical processes for removing ammonia, nitrate and sulfate from RO brine rejects.; The first stage involved optimizing a laboratory-scale fluidized bioreactor and a pilot-scale rotating biological contactor with to achieve maximum biological nitrification efficiencies. In the second stage, a series of batch studies were conducted to determine the effects of temperature, pH, total dissolved solids (TDS) and carbon-to-nitrogen (C:N) ratio on the denitrification process. The maximum specific denitrification rates were obtained at a temperature of 35°C, pH of 8.0 and C:N of 1.8:1, while little or no effect of TDS on the denitrification rate was found. In the third stage, a series of chemostat tests were conducted under nitrogen- and carbon-limited conditions to determine the Monod biokinetic parameters. It was found that nitrate was far more favorable as the main substrate for the denitrifying culture than nitrite, and that insufficient carbon source caused instability of the system due to inhibitory effect of nitrate and/or nitrite accumulation. The fourth stage involved conducting fluidized bioadsorber reactor (FBAR) denitrification experiments at different GAC quantities, hydraulic retention times and nitrate concentrations. Nitrate removal efficiencies as high as 96 to 100% were obtained. Similar FBAR experiments conducted with sand showed that (i) completion of denitrification process took much longer time than with GAC with substantial nitrite accumulation, and (ii) significantly smaller biomass concentrations were obtained with sand as compared to GAC. Following the FBAR studies, a mathematical model was developed for predicting the dynamic behavior of the FBAR denitrification process. Model simulations demonstrated good agreement between the experimental data and model predictions. Sensitivity analyses indicated that growth yield and maximum substrate utilization rate coefficients had the utmost influence on the process. In the last stage, simultaneous denitrification and sulfate removal processes were investigated using a similar FBAR process. A second FBAR employed to remove the remaining sulfate from the first FBAR successfully reduced sulfate to almost zero. The hydrogen sulfide gas generated by this process was effectively removed by biofiltration. |
