Color and COD retention by nanofiltration membranes

In the present study the application of the nanofiltration process was investigated mainly in the retention of color and chemical oxygen demand (COD) present in textile industry wastewater. Nanofiltration experiments were carried out in a pilot unit, operating in crossflow. Three different types of spiral wound membranes, DK 1073, NF 45 and MPS 31 were used simultaneously in the same unit. The results of the tests showed that for color retention, the values were around 99% for the DK 1073 and NF 45 membranes and the 87% for COD retention for the DK 1073. The permeate flux for the different wastewaters varied from 30.5 to 70 L/h.m2. Fouling was observed in all membranes due to the accumulation of molecular species close to the filtering surface. The process was efficient and promising for the reuse of wastewater from this type of industry.

• • We can consider that the nanofiltration process, with the membranes and the conditions used, proved to be efficient for the retention of dyes, COD and color present in textile wastewaters. The process allowed the production of a permeate with great reutilization possibilities, and the permeate fluxes can be con- • • • sidered compatible with the industrial reality. In a general sense, membrane fouling was not severe and occurred mainly due to the accumulation of dye and other organic materials on the membrane surface. This accumulation, in its turn, leads to a permeate flux reduction during the process. With the exception of COD removal, the membrane MPS 31 showed the best performance in terms of color removal, permeate flux, and fouling resistance. Taking into account the great amount of water used by textile industries and the expectations of an increase in the price of this resource in the near future, membrane technology represents a promising method that could be used by the textile industries in the reuse of wastewaters.