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Innovations for reverse osmosis facilities


Reverse osmosis (OR) or nanofiltration (NF) membrane plants equipped with spiral wound elements represent the state of the art in the treatment of water contaminated with organic and inorganic pollutants. This separation technology offers an effective barrier to salts, organics and particles and does not depend on chemicals for treatment. Despite being a mature technology, there are still important opportunities for technological innovation, mainly in OR/NF processes for the treatment of well water, where the chemical composition can vary greatly from one well to another with frequent occurrence of low solubility salts that limit plant productivity. The conventional OR/NF multistage plant configuration is particularly disadvantageous for this market. The need to control scale deposits of poorly soluble salts in the second and third stages can severely limit the yield of the plant and demand the addition of antiscalants, with an important impact on operation costs. Volumetric losses due to significant volumes of concentrate can compromise water supply in communities where water works have little or no reserve well production capacity. An additional disadvantage of the multistage RO plant configuration is its low flexibility for changing the water supply. The replacement of the well that served as the basis for the plant sizing by another one with a slightly different chemical composition can cause hydraulic imbalance and the need for non-trivial adjustments of the operational parameters. The market lacks effective autopsy and chemical cleaning procedures as well as mathematical models for optimal membrane plant sizing that minimizes CAPEX and OPEX. Micro- or ultrafiltration, although state of the art in the pre-treatment of the feed water for these plants, are both unaffordable for small plants and the conventional pre-treatment is rather complex and of low efficiency at this scale. There is a demand for novel compact and efficient pre-treatment technologies. This project aims to develop a complete technological package of innovative solutions for the treatment of well water by RO technology. A new mathematical model will enable a detailed assessment of different scenarios for the insertion of RO plants in water production systems supplied exclusively or partially by well water to identify the options that minimize CAPEX and OPEX. The innovative plant configuration that incorporates continuous recycling of concentrate offers the potential for a more robust operation and greater tolerance to variations in the chemical composition of the feed water. The concentrate intermittently discharged from the recycling loop will be submitted to an innovative process of removing problem compounds (poorly soluble salts or target contaminants) to maximize recycling and thus optimizing plant yield. These measures will be complemented with more effective autopsy and chemical cleaning procedures. The package includes innovative compact slow sand biological filtration systems for pre-treatment, designed to control deposit-forming particles and assimilable organic carbon that promotes the growth of bacteria on the surfaces of membranes. An advanced microbiological characterization technique based on the combination of flow cytometry equipped with cell sorter associated with molecular biology will allow the identification of key organisms for the bioprocesses of relevance to the operational stability of the plant: biofouling (negative) and biofiltration (positive). (AU)

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