Reverse osmosis wastewater treatment

In this treatment process, unit operations such as chemical coagulation, flocculation, and sedimentation followed by filtration, activated carbon, ion exchange, and reverse osmosis are employed to remove significant amounts of nitrogen, phosphorus, heavy metals, organic matters, bacteria, and viruses present in wastewater.2 It is always the last process step in the wastewater treatment plant that finally renders the treated wastewater reusable and disposable into the environment without any adverse effect (Figure 22.1). 

Vourch, M., Balannec, B., Chaufer, B., and Dorange, G., Treatment of dairy industry wastewater by reverse osmosis for water reuse, Desalination, 219, 190-202, 2008. 

Configurations used include tubes, plate-and-frame arrangements and spiral wound modules. Spiral wound modules should be treated to remove particles down to 20 to 50. im, while hollow fiber modules require particles down to 5 im to be removed. If necessary, pH should be adjusted to avoid extremes of pH. Also, oxidizing agents such as free chlorine must be removed. Because of these restrictions, reverse osmosis is only useful if the wastewater to be treated is free of heavy contamination. The concentrated waste material produced by membrane processes should be recycled if possible but might require further treatment or disposal. 

Treatment of dye wastewater involves physical, physico-chemical, chemical, and biological methods. Physical processes are dilution, filtration, and gamma radiation. Physico-chemical includes adsorption, coagulation, flocculation, precipitation, reverse osmosis, ion exchange, etc. 

Wastewater reverse osmosis reclamation systems, 26 79-80 Wastewater treatment, 25 882-920 advances in, 25 910-912 alternative biological technologies in, 25 902-905... 

Beier S, Koster S, Veltmann K, Schroder HFr, Pinnekamp J (2010) Treatment of hospital wastewater effluent by nanofiltration and reverse osmosis. Water Sci Technol 61 1691-1698... 

Advanced wastewater treatment techniques, for example oxidation processes, can achieve up to 100% removal for diclofenac [52,53], Reverse osmosis, activated carbon and ozonation have been shown to significantly reduce or eliminate antibiotics from wastewater effluents [32], The efficiency of two tertiary treatments, chlorination and UV disinfection, was compared and chlorination led to lower quantities of antibiotics [54],... 

Reverse osmosis can remove dissolved metals to very low levels. It can also remove a variety of pollutants such as cyanide and residual organics from refinery wastewater. However, because it is an expensive process, it would be competitive only if removal of total dissolved solids is also required. It also requires extensive pretreatment to prevent membrane fouling and deterioration [52]. The pretreatment processes may include filtration to remove suspended solids, pH adjustment, softening, and activated carbon treatment to remove organics and chlorine. A major drawback of the RO process is the handling and disposal of the reject stream, which can amount to 20-30% of the influent flow. 

Sierka, R.A. Cooper, S.P. Pagoria, P.S. Ultrafiltration and reverse osmosis treatment of an acid stage wastewater. Water Sci. Technol. 1997, 35 (2-5), 155-161. 

The wastewater at an aircraft-component manufacturing plant contained free and emulsihed oil. The water was treated using 454 kg of organoclay followed by a reverse-osmosis system. The organoclay portion of the treatment train cost 5000. The organoclay was replaced once a year. Replacement and disposal costs was approximately 3000 (D17267S, p. 30). 

In 1996, costs for SLM technology treatment of a wastewater system typical of that found in the nickel-plating industry were compared to those for reverse osmosis treatment of the same amount of wastewater. It was assumed that wastewaters would be processed at a feed rate of 30/gal min, 15 hr/day, and 20 days/month. It was also assumed that a total of 175 lb of nickel sulfate, 45 lb of nickel chloride, and 225 lb of chromium salts would be removed. 

A conventional wastewater treatment system with an average flow rate of 160,000 gpd produces effluent suitable for NPDES discharge. Metal hydroxide sludges are dewatered in a 15 cu. ft filter press producing more than one half ton of filter cake per day. The filter cake is further dewatered in a 7 cu. ft, batch-type sludge dryer. Based upon recommendations by their consultant, the firm also uses the sludge dryer to dehydrate nickel strip solutions. Two reverse osmosis systems are used for partial nickel recovery. Trivalent chromium is recovered by drag-out control and evaporation. 

One can also recognize that application of sufficient pressure (above the equilibrium osmotic pressure n) to the right-hand chamber in (7.67) must cause the solvent flow to reverse, resulting in extrusion of pure solvent from solution. This is the phenomenon of reverse osmosis, an important industrial process for water desalination. Reverse osmosis is also used for other purification processes, such as removal of H20 from ethanol beyond the azeotropic limit of distillation (Section 7.3.4). Reverse osmosis also finds numerous applications in wastewater treatment, solvent recovery, and pollution control processes. 

Reverse osmosis is nsed as a method of desalting seawater, recovering wastewater from paper mill operations, pollution control, industrial water treatment, chemical separations, and food processing. This method involves application of pressure to the surface of a saline solution, thus forcing pure water to pass from the solution through a membrane that is too dense to permit passage of sodium and chlorine ions. Hollow fibers of cellulose acetate or nylon are used as membranes, since their large surface area offers more efficient separation. 

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