Removal of nitrate by modified pine sawdust: Effects of temperature and co-existing anions

• Sorption capacities of 22.2–32.8 mg N/g were obtained at 5–70 °C.
• Nitrate removal was inhibited at S and P concentrations of 100 and 50 mg/l.
• Sulphate and phosphate were also successfully removed.
• Nitrate was completely eluted in column using about 80 bed volumes of 0.1 M NaCl.

The effect of temperature, sulphate and phosphate, and the initial nitrate concentration on nitrate removal was studied with synthetic solutions. Chemically modified pine sawdust (Pinus sylvestris) anion exchange resin (MPSD) was used in the sorption studies. The resin was synthesized by reacting pine sawdust with epichlorohydrin, ethylenediamine and triethylamine in the presence of N,N-dimethylformamide. Nitrate removal was successful at 5–70 °C. Higher temperatures caused nitrate removal to decrease moderately, but sorption capacities of 22.2–32.8 mg/g for NO3–N were achieved. The removal of nitrate in the presence of sulphate or phosphate was studied at concentrations of 30 mg N/l, 10–500 mg S/l and 1–50 mg P/l. A significant decrease in nitrate reduction was observed at sulphate and phosphate concentrations of 100 mg S/l and 50 mg P/l, respectively. The effect of initial nitrate concentration was studied in column. Nitrate sorption was clearly dependent on the initial concentration. Desorption of nitrate in column was completed using about 80 bed volumes of 0.1 M NaCl solution. The sorption data were fitted to the Langmuir, Freundlich and Redlich–Peterson adsorption models. The Redlich–Peterson and Langmuir models gave the best fit, which suggests monolayer sorption. Thermodynamic studies revealed that the sorption of nitrate was spontaneous and exothermic in nature. The results imply that modified pine sawdust could be a feasible alternative in the treatment of real industrial wastewaters.