Abstract~ombined ion exchange/biological denitrification is a process for nitrate removal from ground water in which nitrate is removed by an ion exchanger and ...
War. Res. Vol. 22, No. 6, pp. 679--684,1988 Printed in Great Britain.All rights reserved
0043-1354/88 $3.00+0.00 Copyright © 1988PergamonPress plc
COMBINED ION EXCHANGE/BIOLOGICAL DENITRIFICATION FOR NITRATE REMOVAL FROM G R O U N D WATER U N D E R DIFFERENT PROCESS CONDITIONS JAN PETER VAN DER HOEK, PAUL J, M. VAN DER VEN and ABRAHAMKLAPWLIK Department of Water Pollution Control, Wageningen Agricultural University, De Dreyen 12, 6703 BC Wageningen, The Netherlands (Received July 1987; accepted in revised form November 1987) Abstract~ombined ion exchange/biologicaldenitrification 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 SO2- 1-~) was treated with the sulfate selective resin Duolite A 165 and with the nitrate selective resin Amberlite IRA 996. In both cases NaC1 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[- 1-I ) was possible by the combined process with the nitrate selectiveresin. 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%. Key words--nitrate removal, drinking water, ground water, denitrification, ion exchange, sulfate, combined process, biological regeneration, nitrate selective resin
INTRODUCTION
High nitrate concentrations in ground water, used for drinking water, is a problem in several European eounteries (Marsh, 1980; Richard and Lcprince, 1982; Bruyn, 1984; Holtmeier, 1984; Sontheimer and Rohmann, 1984; Furrer and Stauffer, 1986), especially since the European Community introduced a new directive relating to the quality of water intended for human consumption (European Community, 1980). In this directive the maximum admissible concentration of nitrate in drinking water has been decreased from 22.6 to 11.3 mg N O f - N 1-l. The guide level is 5.6 mg N O a - N I-~. To remove nitrate from ground water a new process has been developed recently: combined ion exchange/biological denitrification. The process, including basic design criteria and advantages, has been described previously (van der Hoek and Klapwijk, 1987). In this process nitrate is removed from the ground water by ion exchange. Regeneration of the nitrate-loaded resins is carded out in a closed circuit through a biological denitrification reactor. This reactor removes nitrate from the regenerant so that it can be used again. The process can be operated under different process conditions. Firstly, the regenerant can be varied. Regeneration of anion exchange resins can be achieved with sodium chloride solutions or with sodium bicarbonate solutions as regenerant (Deguin et al., 1978). Secondly, it is possible to vary the resin
type. Strong base anion exchange resins are normally sulfate selective, but recently some nitrate selective resins have been developed (Cuter, 1982) and applied (van der Hoek et al., 1988). Thirdly, the local ground water composition can vary. Especially the presence of high sulfate concentrations can affect the removal of nitrate from the ground water in ion exchange processes (Gauntlet, 1975), thus sulfate will also affect the combined ion exchange/biological denitrification process. The treatment of a Dutch ground water containing a relatively low sulfate concentration (30-31 mg S O 2- ! -~) with a sulfate selective resin (Duolite A 165) and sodium bicarbonate as regenerant has been described previously (van der Hoek and Kiapwijk, 1987). This paper describes the combined ion exchange/biological denitrification process run under three other process conditions. These are treatment of a Dutch ground water with a sulfate selective resin (Duolite A 165) and with a nitrate selective resin (Amberlite IRA 996), both with sodium chloride as regenerant, and treatment of an English ground water containing a high sulfate concentration (18ling SO2-1 - l ) with a nitrate selective resin (Amberlite IRA 996) and sodium chloride as regenerant. Treatment of the sulfate-rich ground water with a sulfate selective resin has not been considered. Previous experiments (van der Hoek et al., 1988) showed that the nitrate capacity of a sulfate selective resin is very low in this situation.
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nitrate rich groundwofer
MATERIALS AND METHODS
Apparatus All experiments were carried out with a laboratory-scale pilot plant (Fig. 1) based on previous research (van der Hoek and Klapwijk, 1987; van der Hock et al., 1987). The duration of both service mode and regeneration mode were different for the two resins used in the experiments. In the description below the values relate to the sulfate selective resin Duolite A 165; the values in parentheses refer to the use of the nitrate selective resin Amberlite IRA 996. Two ion exchange columns are used simultaneously for production of potable water with a run time of 9 h (14 h) each, but a phase shift of 4.5 h (7 h). Meanwhile the third ion exchange column is connected with an upflow sludge blanket (USB) denitrification reactor (Klapwijk et al., 1981) and is regenerated for 3.5 h (6 h) followed by 1 h rinsing. Methanol is the carbon source for the denitrification reactor. The optimal methanol dose has been described elsewhere (van der Hock et al., 1987). During rinsing water is recirculated through the denitrification reactor by means of a by-pass. A sand filter in the regeneration circuit prevents carry-over of sludge particles, washed out o f the denitrification reactor, into the ion exchange columns. With this set-up every 4.5 h (7 h) a regenerated ion exchange column is put into service for nitrate removal from ground water.
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