Development of a membrane integrity monitoring strategy for the UF/RO Heemskerk drinking water treatment plant

At the Heemskerk water treatment plant of N.V. PWN Water Supply Company North Holland the first full scale integrated membrane system in the Netherlands is realized. The 20 Mm³/year (15 MGD) ultrafiltration (UF)/reverse osmosis (RO) plant servicing IJssel Lake water has been in operation since the second half of 1999. Disinfection is a major objective of the direct surface water treatment plant without chemical disinfection. After UF indicator organisms such as E. coli and Clostridia spores were absent. Integer UF membranes removed MS-2 phage spikes completely (<5.4 log), severely compromised membranes removed 2.7 log only. RO showed a high although incomplete removal of MS-2 phages (up to 4.8 log). Therefore integrity monitoring is a critical issue. Before installation, vacuum testing was applied with a criterion of 10 kPa/min. Many standard modules failed to pass the test. During operation UF is monitored by 1 μm particle counting with 0.05 μm particle counting as a quality control. A 3 log removal can be established. At this moment for RO conductivity measurement is applied enabling a 2 log removal monitoring. Short term monitoring of conductivity will be replaced by sulfate, increasing the monitoring range by 1 log unit. The total monitoring range of 5-6 log units easily satisfies the maximum disinfection requirement for the membrane steps for viruses of 3.6 log. To determine a wider range of disinfection requirements PWN together with Norit Membrane Technology developed the Spiked Integrity Monitoring (SIM®) System. Spiking with 14000 PAC particles/ml combined with 1 μm particle counting increased the potential for log removal monitoring of UF to 5.8 log units. Additionally PAC particle spiking increased the potential to detect UF fiber compromising. During the first 200 days of full scale operation, system performance is excellent. Membrane integrity control is very satisfactory and SIM®-System integrity control has proved to be a valid technique to establish a broader range of required inactivation capacities.