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

Abstract

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 SO 4 2− 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 SO 4 2− 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%.