Application of nanofiltration for removal of pesticides, nitrate and hardness from ground water: rejection properties and economic evaluation

摘要

The drinking water industry faces a growing number of difficulties in the treatment of ground water for drinking water production. Ground water sources are frequently contaminated with pesticides; nitrate concentrations are increasing and are often close to or above the legal standard of 50 mg/l. moreover, partial removal of hardness is desirable for reasons of comfort. Nanofiltration is a process in which pesticides, hardness and nitrates can be simultaneously removed or partly removed, so to make a good control of the membrane unit possible. In the first part of this paper, the removal of four pesticides (atrazine, simazine, diuron and isoproturon), the removal of hardness and the removal of nitrates with the membranes NF70, NF45, UTC-20 and UTC-60 is experimentally studied. The results show that pesticide rejections are satisfactory; hardness is also very efficiently removed, whereas only a small fraction of nitrate is removed for most membranes, except for NF70 where a 76% removal of nitrate was obtained. Rejection characteristics are explained, and used to calculate the properties for a double pass module design with recirculation of the concentrate in the second module to the feed of the first module. When this design is applied with NF70, all pesticide molecules are removed to well below the detection limit. The partial removal of nitrates may help to meet the legal standard of 50 mg/I, but is not a main objective for the filtration process. The hardness of the permeate might be too low, so that hardness should be readded. The second part of the paper discusses the economical side of the implementation of nanofiltration. This is indeed an important factor that has never been evaluated before. The outline of the calculation of the investment costs and the operating costs is summarized, and the calculations were used in an example calculation for a given production of drinking water, based on the experimental results from the first part of the paper. Price calculations at different pressures resulted in an pressure of 8 bar. The final price for treatment of ground water is realistic, showing that nanofiltration is a valuable option for ground water treatment.