Total organic carbon rejection

Softening and raising the pH level of the RW tends to increase the rejection rate of silica, boron, and total organic carbon (TOC). It also tends to increase silica solubility, thus reducing the risk of silica deposition on the membrane. 

Vourch et al49 studied the applicability of the RO process for the dairy industry wastewater. The treated wastewater total organic carbon (TOC) was <7 mg/L. It was found that in order to treat a flow of 100 m3/d, 540 m2 of the RO unit is required with 95% water recovery. Dead-end NF and RO were studied for the treatment of dairy wastewater.50 Permeate COD, monovalent ion rejection, and multivalent ion rejection for the dead-end NF were reported as 173-1095 mg/L, 50-84%, and 92.4-99.9%, respectively. When it comes to the dead-end RO membranes, the values for permeate COD, monovalent ion removal, and multivalent ion removal were 45-120 mg/L, >93.8%, and 99.6%, respectively. Membrane filtration technology can be better utilized as a tertiary treatment technology and the resultant effluent quality will be high. There can be situations where the treated effluents can be reused (especially if RO is used for the treatment). 

The results of field trials, based on total organic carbon (TOC) levels, show excellent recovery of the majority of organics present (21). Recovery data from a typical field RO concentration are shown in Table XIII. These results reflect high membrane rejections and recoveries found with higher molecular weight organics. Reductions in the total amount of adsorbed material in relation to the total sample... 

To determine the organic rejection by the FO process, the total organic carbon (TOC) concentration was measured. The initial TOC concentration in the feed was 130 mg/L and the final concentration (after approximate 50% volnme reduction) was 235 mg/L. The TOC concentration in the draw solution was less than 1 mg/L this indicates that the FO membrane can effectively reject the organics in the feed water. Table 1 shows the concentration for the anions and cations present in the feed and draw solutions. 

The heavy vacuum bottoms stream is fed to a Flexicoking unit. This is a commercial (125,126) petroleum process that employs circulating fluidized beds at low (0.3 MPa (50 psi)) pressures and intermediate temperatures, ie, 480—650°C in the coker and 815—980°C in the gasifier, to produce high yields of hquids or gases from organic material present in the feed. Residual carbon is rejected with the ash from the gasifier fluidized bed. The total Hquid product is a blend of streams from Hquefaction and the Flexicoker. 

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. 

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