Towards Zero Liquid Discharge in drinking water production

Nanofiltration (NF) and reverse osmosis (RO) membranes are used to produce clean water, but also produce a concentrate stream which contains most of the contaminants. Discharging concentrate streams to the environment is hindered by regulations, which are becoming more strict, and by the desire of recovering every single valuable atom. Therefore, the minimization of the concentrate volume to almost zero, is required in order to make treatment of the concentrate feasible. Currently several research studies are being conducted to find smart zero liquid discharge (ZLD) strategies in water desalination. In this PhD work the feasibility of reaching very high recovery (which equals a very low volume of concentrate) in a system consisting of cation exchange pretreatment, NF and RO (with the RO implemented on the NF concentrate to increase feed water recovery) was studied. The outcome of this research indicates that the nearly ZLD concept is technically possible, with the right combination of techniques. The studied system could be applied for the production of drinking water from ground water or surface water with high concentrations of bivalent cations, silica and/or organic micropollutants.BiotechnologyApplied Science

Amorphous aluminosilicate scaling characterization in a reverse osmosis membrane

This paper describes the results of experiments performed in a high-recovery system to elucidate the silica scaling phenomenon and characterize the scaling. In this research, cation exchange pretreatment is used to reduce Ca2+, Ba2+, and Mg2+ levels to prevent scaling during subsequent nanofiltration (NF) and reverse osmosis (RO) filtration, in which RO is fed with NF concentrate. In a pilot plant, a series of experiments were carried out at a total (NF + RO) recovery of 91, 94, 96 and 98% with locally available tap water as feed water. Autopsy studies were performed with the RO membranes after each experiment. The fouling layer was studied using SEM-EDX, ATR-FTIR and fouling extraction to determine the structure and the composition of the fouling deposits. A thin dense fouling layer was observed, which covered approximately half of the membrane surface, after operating for 20 days at 91 and 94% recovery. At 96 and 98% recovery, the fouling layer was thicker and completely covered the membrane surface. The scaling layer was mainly composed of Si, Al, Fe and O. The amount of Si increased with increasing recovery. To work at these high recoveries for an extended period, further measures need to be taken to prevent silica scaling