Removal of substituted phenyl urea pesticides by reverse osmosis membranes: Laboratory scale study for field water application

Highlights

• Polyamide membrane was prepared and used for pesticide separation from water.

• Significantly high separation could be achieved for diuron and isoproturon.

• Ion type, concentration and pesticide nature influence membrane rejection property.

• Isoproturon rejection was always higher than that of diuron.

• Diuron and isoproturon modify membrane property which influences membrane flux.

Abstract

Thin film composite polyamide reverse osmosis membrane prepared in laboratory was used for filtration of two phenyl urea pesticides (diuron and isoproturon) dissolved in deionized water, tap water and agriculture field water. Membrane performance in removing pesticides from water was evaluated and compared with commercial membrane data. Membrane fouling was less for diuron and the value was restricted within 11%. Membrane fouling and permeate flux decline depends on water type. For field water flux decline was maximum. The presence of mono- (Na⁺) and bi-valent (Ca^2 +) ions in feed water influences membrane performance. Isoproturon rejection for the membranes was always higher than diuron. Pesticide rejection from field water was more than 95%. The presence of humic acid in water has no significant effect on diuron and isoproturon rejection. Post filtration behavior of membranes reflects hydrophilicity change irrespective of water type. Depending upon the pesticide, membrane property influences permeate flux and water permeability.

Introduction

Modern agriculture practices include use of chemicals in the form of fertilizers and pesticides. Possible runoff of these chemicals into surface water bodies or infiltration of the same in ground water brings about a serious threat to drinking water quality. One of the studies conducted by U.S. Geological Survey (USGS) reported pesticide contamination in 90% or more sample of water and fishes collected from major rivers or water streams particularly in those having influence of agriculture and urban land use [1]. USGS also reported finding of more than a hundred pesticides in ground water. The survey also included report on water sample collected from India. It was reported that ground water samples collected from places around Bhopal were detected contaminated with organo chlorine pesticides at a level higher than the EPA (Environment Protective Agency, US) standard.

Globally 30% of pesticides used are herbicides. Diuron and isoproturon, examples of substituted urea herbicides are the most widely used herbicides in agriculture [2]. Diuron being an algaecide also finds uses in paints, fountains, aquaculture [3]. Since diuron sorption is less in soil, the possibility of leaching into ground water is higher. The situation is further deteriorated due to slow rate of diuron degradation and production of more harmful product during the process of degradation. Isoproturon is frequently used to control and prevent weed development in cereals. Isoproturon and its metabolites are suspected carcinogens and are having harmful effects to invertebrates, freshwater algae and microbial community [4]. Inspite of the restriction imposed on the use of isoproturon in several countries it is still extensively used worldwide.

To address these water pollution issues removal of pesticides is necessary. Reports on application of techniques like activated carbon, ozone and peroxide treatment are there in the literature. The presence of natural organic matter in water incorporates disadvantages to conventional methods of activated carbon treatment, oxidation by ozone and peroxides for removal of such pesticides from water [5], [6]. Frequent activation of carbon also adds cost to the method. Additionally, removal of polar compounds like diuron by adsorption onto activated carbon column was not so efficient [7]. Membrane filtration was envisaged as advantageous over all these conventional techniques.

Till date there have been several reports on the use of membranes for removal of pesticides. In all those investigations the membranes used from commercial suppliers include ultrafiltration membranes like GK, PT, PW and nanofiltration membranes CK, DK and DL from GE, Osmonics [8], PVD1, and ESNA from Hydranautics, NF200, NF270, NF45, and NF70 from Dow/Filmtec [7], [9], [10], NTR7450 from Nitto Denko, and UTC 20 and UTC 60 from Toray Industries [11], [12]. These are membranes having predominantly polypiperazine polyamide top layer with exceptions like PT, PW (polyethersulfone), NTR7450 (sulfonated polyethersulfone) [13], CK (cellulose acetate), PVD1(Polyvinyl alcohol/polyamine copolymer), ESNA and NF70 (fully aromatic polyamide top layer) [14]. Rejection by these membranes was reported to be less than 90% for diuron and within 95% for isoproturon. ESNA and NF70 are fully aromatic polyamide membranes and displayed better rejection for both the pesticides.

In this work removal of diuron and isoproturon, the two widely used substituted phenyl urea pesticides by purely aromatic polyamide thin film composite reverse osmosis membrane prepared in laboratory has been reported. To simulate the real situation pesticide solution prepared in water collected from a well in an agriculture field was also considered in this study. Filtration was carried out in different water types. Since the work was aimed to check the performance of laboratory made thin film composite RO membrane in removing pesticides from agriculture field water in its natural condition, any kind of modification in water properties was avoided. Analysis of membrane performance in different water types and fouling has been reported. To our knowledge there was no previous report on pesticide removal from agriculture field water using membranes from other than commercial sources.