(311e) Comprehensive Integrity Verification System for Low Pressure Membrane Systems

Low pressure membranes are used for water treatment as well as pre-treatment in water reclamation plants and desalination.

The main advantage of using MF or UF in the drinking water treatment is their high level of microbial pathogen removal to meet stringent water quality regulations. However, pathogens will pass through the membrane system and contaminate the product if the membrane integrity is compromised. The Membrane Filtration Guidance Manual published by the USEPA details both direct and continuous integrity testing for water treatment plants.

Any process in a water treatment system is assigned a log removal value (LRV). Depending on the quality of the source water, different LRV targets are assigned to various plants. The maximum removal credit that a membrane filtration process may receive is the lower value of either:

• The removal efficiency demonstrated during challenge testing; OR
• The maximum log removal value that can be verified by the direct integrity test used to monitor the membrane filtration process

Hence, the ability of a plant to accurately monitor the integrity of the plant directly affects the design and cost of the plant.

Wastewater reclamation via nanofiltration (NF) or reverse osmosis (RO) requires pre-treatment of the feed water using microfiltration (MF) or ultrafiltration (UF) membrane modules. The performance of these pre-filtration modules is critical to maintaining efficient operation of the NF or RO membrane modules. Any compromised pre-filtration modules can cause fouling of the NF or RO membrane modules via the deposition of particulate materials that would otherwise have been removed by the upstream modules. This fouling of the NF or RO membrane modules causes increased energy usage per unit product which can cause the plant to shut down for cleaning or replacement. Higher module replacement rates will also lead to high operating, maintenance cost and unit cost of water. 

This paper describes a comprehensive integrity management system that helps plant operators determine the health of their membrane systems as well as the LRV credit. The system has three components

• LRV Determination
• Integrity Monitoring
• Diagnostic Testing

The backbone of this system is the Membrane Integrity Sensor (MIS) developed at the Nanyang Technological University.