Main disadvantages of state of the art membrane techniques are discussed with respect to the problem of concentrate disposal. Possible ways to improve conventional membrane techniques and to radically decrease the number of effluents discharged are proposed. Application of newly developed “open channel” membrane modules that do not contain “dead” areas enables us to develop and implement into practice new techniques to reduce and even utilize concentrates of membrane units. Experiments demonstrated a possibility to reduce concentrate flow due to deposition of excessive calcium as calcium carbonate on seed crystals in the reactor. Flow diagrams for different cases of natural water composition are described and discussed that demonstrate newly developed techniques to produce drinking quality water using reverse osmosis and nanofiltration membrane facilities with high recoveries.

Aspects of the interaction of organic pollutants of natural water with nanofiltration and reverse osmosis membranes have been considered on the basis of experimental results and summarized literature data. Experimental studies have been carried out to determine the rates of membrane fouling by various organic substances including humic acids (imparting the color) and low-molecular-weight organics (responsible for the oxygen demand) during the treatment of river water and pretreated water. The effect of membrane material on the rate of organic deposition on them has been studied. Relationships have been obtained for calculating the rates of buildup of organics on membranes depending on their concentration in the feed water, the nature and molecular weight of foulants, the membrane material, the flow rates in device channels, and the recovery. Experimental determination of the rates of adsorption of organic substances of various natures has made it possible to measure the sorption capacity of the membrane surface. It is likely that in the case of simultaneous fouling of the membrane with poorly soluble salts (calcium carbonate), colloidal and organic substances, iron compounds, etc., the effect of the set of foulants and scalants on the membranes surface may differ significantly from the results obtained in this study. Predicting the amount of organic foulants will help to correctly select the composition of solutions for chemical cleaning of membranes and eliminate the influence of organics on scale dissolution.

Introduction. In this paper, we investigate the interaction of organic pollutants with nanofiltration and reverse osmosis membranes in natural water on the basis of experimental data and available literature information. The rates of formation of various organic deposits (humic acids changing the water colour and forming low-molecular organic compounds characterised by an oxidation index) on membranes during purifying river and pre-treated water are presented. Aim: To determine the required efficiency of removing organic substances from surface waters at the pre-treatment stage prior to water treatment by reverse osmosis on the basis of measuring the rates of adsorption of organic substances on membranes and predicting the amount of as-formed organic deposits. Methods and materials. Methods for determining the adsorption rate of organic pollutants using gas-liquid chromatography and total carbon determination are described. The advantages of spectrogram analysis in assessing water quality are specified. The formation rates of high- and low-molecular organic substances, which produce colouring and characterise water oxidisability, respectively, were determined using a membrane test unit. Results. According to the rates of forming organic deposits on membranes both during the processing of river water with a colour of 60 PCU and purified (tap) water with a colour of 18 PCU, organic substances adsorbed on membranes are shown to have little effect on the efficiency of the reverse osmosis process. In addition, the rate of depositing organic substances on the membranes under study is established to be significantly lower than that using sparingly soluble salts (calcium carbonate). Conclusion. Our results demonstrate that organic deposits formed on the membranes under study have an insignificant effect on the membrane performance. Therefore, pre-treatment aimed at removing organic substances when purifying natural waters with colour indices of up to 60 PCU is not required.