Nitrate removal from drinking water using combined ion exchange/ resin bioregeneration
Nitrate contamination is a drinking water concern in many areas in the world, especially rural communities. Excess nitrate can cause several environmental and health problems. The maximum acceptable concentration of nitrate in drinking water is set to be 45 mg /L as nitrate by USEPA. One of the most common methods for nitrate removal from water is ion exchange using nitrate selective resins. Although these resins have a great capacity for nitrate removal, they are considered non regenerable. The ability to regenerate these resins multiple times will increase the environmental and economic sustainability of nitrate-contaminated water treatment processes. This dissertation tests the hypothesis that multi-cycle exhaustion/ bioregeneration of resin enclosed in a membrane is feasible and temperature and salt concentration in the medium will have an influence on the processes involved. The results showed that this method is an effective and innovative resin regeneration method. Applying 6 cycles of resin exhaustion/ regeneration showed that resin could be used for 4 cycles without a loss of capacity, after 6 cycles only 6% of the capacity was lost. A pseudo-second order kinetic equation described the nitrate desorption analysis well. The initial desorption rates of nitrate from the resin in a membrane were significantly different at different salt concentrations and temperatures; maximum of 306±21 mg of nitrate/g of resin. h for 6% at 35 °C and minimum of 42±3 mg of nitrate/g of resin. h at 2% salt and 12 °C . The effect of different salt concentrations on the biological nitrate removal rate was dependent on the temperature; within each group of temperatures, the nitrate degradation rate decreased with increasing the salt concentration. ( / .ℎ )=0.0102+(0.00114× )−(0.000291× ) fit the data for the effect of salt concentration and temperature on nitrate degradation rate with the best correlation (R² = 0.93). The results from the kinetic studies were used to develop a mathematical model which incorporated physical desorption process with biological removal kinetics. The model fit well to experimental data (R²= 0.94±0.06 for 6 bioregeneration cycles) and was applied in the design of a bioreactor for a local nitrate contaminated drinking water source.