A. Klapwijk

Nitrate removal from ground water

In the new E.C. directive relating to the quality of water intended for human consumption the maximum admissable concentration of nitrate in drinking water is decreased from 22.6 mg N03 --N/l to 11.3 mg N03 --N/l. The guide level is 5.6 mg N03 --N/l (1). At the same time, in many European countries an increasing nitrate concentration in ground water is observed. High nitrate concentrations in ground water are a consequence of fertilizer activities in agriculture. Both artificial fertilizers and animal manure cause nitrate problems (2, 3, 4, 5, 6, 7).

Combined ion exchange/biological denitrification for nitrate removal from ground water under different process conditions

Combined ion exchange/biological denitrification is a process for nitrate removal from ground water in which nitrate is removed by an ion exchanger and the resins are regenerated in a closed circuit through a biological denitrification reactor. On laboratory-scale the process was run under three process conditions. Ground water with a relatively low sulfate concentration (31 mg SO42− 1−1) was treated with the sulfate selective resin Duolite A 165 and with the nitrate selective resin Amberlite IRA 996. In both cases NaCl was used as regenerant. Although the nitrate concentration in the treated water was hardly influenced by the different resin types, chloride and sulfate concentrations were clearly affected. With the nitrate selective resin sulfate concentrations were higher and chloride concentrations were lower as compared with the sulfate selective resin. Treatment of ground water containing a very high sulfate concentration (181 mg SO42− 1−1) was possible by the combined process with the nitrate selective resin. In all three cases sulfate accumulated in the regeneration circuit without imparing the nitrate removal in the service mode. The regenerant was renewed every 2 weeks under one process condition. Compared with conventional ion exchange regeneration this results in a reduction of brine production of 95%.

Effect of copper on nitrification in activated sludge

Abstract The concentration of free copper in activated sludge with copper added is strongly influenced by pH. For example, at pH 6.5 with 9.13 × 10 −5 mol Cu l −1 , the free copper concentration is 4.0 × 10 −7 mol l −1 (pCu = 6.4) and at pH 8.4 this concentration is 10 −8 mol l −1 (pCu = 8.0). In both cases the activated sludge concentration is 0.7 g MLSS l −1 . The free copper concentration is also affected by the concentration of mixed liquor suspended solids (MLSS). In batch experiments with constant pH, the effect of copper on the nitrification rate was not regulated by total copper concentration but by copper/sludge ratio or by free copper concentrations. Experiments at different pH showed a linear correlation between nitrification capacity and free copper concentration, suggesting that the pH effect on nitrification below 8.3 is in fact a copper effect. Activated sludge with copper did not become acclimatized to the copper in a period of three days. Addition of nitrilotriacetic acid (NTA) within one day did cancel the copper inhibition. The results were compared with the effect of copper on acetate removal by heterotrophic micro-organisms. The nitrifiers proved to be no more susceptible to copper than heterotrophic micro-organisms.

Denitrification with methanol in the presence of high salt concentrations and at high pH levels.

SummaryIn the combined ion exchange/biological denitrification process for nitrate removal from ground water, in which nitrate is removed by ion exchange, the resins are regenerated in a closed circuit by a biological denitrification reactor. This denitrification reactor eliminates nitrate from the regenerant. Methanol is used as electron donor for biological denitrification. To obtain sufficient regeneration of the resins within a reasonable time, high NaCl or NaHCO3 concentrations (10–30 g/l) in the regenerant are necessary. High NaHCO3 concentrations affected the biological denitrification in three ways: a) a slight decrease in denitrification capacity (30%) was observed; b) the yield coefficient and CH3OH/NO3-−N ratio decreased. When high NaHCO3 concentrations (above 10g NaHCO3/l) were used, the yield coefficient was 0.10–0.13 g VSS/g NO3-−N and the CH3OH/NO3-−N ratio was 2.00–2.03 g/g; c) high NaHCO3 concentrations influenced nitrite production. Nitrite is an intermediate product of biological denitrification and with rising NaHCO3 concentrations nitrite accumulation was suppressed. This was explained by the effect of high NaHCO3 concentrations on the pH in the microenvironment of the denitrifying organisms. High NaCl concentrations also resulted in a slight decrease in denitrification capacity, but the second and third effects were not observed in the presence of high NaCl concentrations.Although the pH in the regenerant will rise as a result of biological denitrification, the capacity of a denitrification reactor did not decrease significantly when a pH of 8.8–9.2 was reached.

Nitrate removal from ground water — use of a nitrate selective resin and a low concentrated regenerant

A new, strong base, macro-porous anion exchange resin, Amberlite IRA 996, appeared to be more nitrate selective than sulfate selective in treating high nitrate concentrations (18 mg NOinf3sup−-N L−1) in potable water. When regeneration is carried out in a closed circuit in which a biological denitrification reactor is incorporated to remove nitrate from the regenerant, regeneration salt requirement and brine production can be minimized. In this combination of ion exchange and biological denitrification, regeneration with 30 g NaHCO3 L−1) is possible in 6 hr at a flow rate of 11 BV hr−1. Accumulation of sulfate in the closed regeneration circuit does not affect the nitrate capacity of the resin.

Reduction of regeneration salt requirement and waste disposal in an ion exchange process for nitrate removal from ground water

Abstract Due to the use of fertilizer and manure in agriculture, nitrate concentrations in ground water are increasing. The maximum admissible concentration of nitrate in drinking water is 11.3 mg NO3−/L (as N/L). Hence, several water supply companies will have to remove nitrate from ground water. Ion exchange is a relatively simple technique for this purpose, but is characterized by two important disadvantages: regeneration of the ion exchange resins requires large quantities of salt while a voluminous brine is produced which is difficult to dispose of. Regeneration in a closed circuit including a biological denitrification reactor can avoid these drawbacks. During regeneration the regenerant, containing a high sodium chloride or sodium bicarbonate concentration, is recirculated through the ion exchange column and the biological denitrification reactor. Bacteria in this reactor convert nitrate to nitrogen gas and thus the regenerant can be used again. As a result of this regeneration procedure, waste production is minimized and the excess of salt, needed for regeneration, is kept within the system. The process has been tested successfully with a laboratory-scale plant. With the use of a nitrate selective resin high sulfate concentrations in the ground water did not affect the process negatively. As compared with conventional regeneration procedures it was possible to reach a reduction of 95% in waste volume and a reduction of 80% in regeneration salt requirement.