Selective nitrate removal by coupling electrodialysis and a bioreactor

Studies have been conduced on a groundwater containing 850–1100 mg/l of total dissolved solids (TDS) and 80 mg/l of nitrate to remove nitrate by coupling electrodialysis and bioreactor. The performances of the pilot plant during the period of the tests (more than one year) were proved. The optimisation of recovery rates was carried out by the study of the influence on the water recoveries of the addition of acid and antiscalant to the brine stream. The moderated performances of the bioreactor were shown.

In the centre of Morocco, especially in the region where the study was conduced (Boujaad), the contamination of groundwater by nitrates becomes worrying. No alternative water supply sources are available near this region and the conventional solutions, as mixing dilution becomes uneconomical and inadequate. So many borings were abandoned. For these reasons, studies were conducted in this region to remove nitrate in groundwater by coupling electrodialysis and a bioreactor, using a pilot plant with a capacity of 24 m3/d. The pilot tests conducted from January 2001 to April 2002 confirm the satisfactory performances and the constancy of results during this period. Moreover, test results indicate the following possible operation and performances: • Recovery rates of up to 98% can be reached using HCl for pH control and antiscalant (Hypersperse AF200) in the brine stream. • Recoveries of up to 97% are possible using only HCl for pH control or up to 95% using only antiscalant. • The consumption of reagents was estimated and the best results were obtained in the cases of combination of acid and antiscalant. By coupling a bioreactor to the brine stream, a significant reduction of nitrate in the brine was observed. Certainly the bioreactor performances must be improved but the preliminary results are encouraging. The study was not stopped and it continues to optimise the bioreactor performances and to evaluate the economical cost of operation.