Study of the behaviour of a reverse osmosis membrane for wastewater reclamation — influence of wastewater concentration

Water scarcity is becoming a serious problem in the Mediterranean countries. To minimize negative effects, wastewater reclamation can be one of the possible solutions. Reverse osmosis (RO) is the process that ensures the highest water quality. Thus, the required quality goal can be reached adjusting the wastewater portion to be treated and the portion directed to the blending tank. In this work, a study with a low-pressure RO pilot plant was conducted in the laboratory. A spiral wound composite polyamide membrane (ESPA1-2540, Hydranautics) with an active area of 2.59 m2 was tested for increasing volume concentration factors (VFC). Thus, the membrane elements behaviour within a pressure vessel in a full-scale plant was simulated. The experiments were run three times to confirm statistically the results. These ones showed an almost constant permeate flux (17 L m−2 h−1) while keeping the transmembrane pressure constant at 6.8 bar with a VCF of 2.5. Concerning the salt retention, it was observed a slightly reduction on increasing the VFC. However, the permeate conductivity was lower than 80 µS/cm in all cases.

In order to study the membrane elements behaviour in a pressure vessel of an industrial plant, experiments with only one element with increasing VCF can be performed in laboratory scale. This is possible if the element conversion is kept approximately constant. Although ESPA1-2540 is not a low fouling membrane but a standard thin film composite membrane, no fouling problems were detected in the performed experiments for increasing VCF up to 3. Thus, the water membrane permeability hardly decreased although no chemical cleaning was carried out. Since there was no addition of antiscaling chemicals, higher VCF values (6.0) entailed a significant transmembrane pressure increase to keep the conversion and a salts retention reduction.