Membrane treatment of high turbidity water - pilot studies on New Zealand river water

The use of low-pressure (LP) membrane systems (microfiltration/ultrafiltration - MF/UF) to produce potable water has become increasingly common, over the last 15 years. Due to the absolute pore size of the membranes used in LP membrane filtration, high-quality water is guaranteed regardless of raw water turbidity. This has enabled municipalities and industries to utilise more challenging water sources, such as very turbid river water, while providing higher quality water to their townships and processing sites. LP membrane filtration is also effective in removing microbial pathogens such as protozoa and bacteria. High quality water is verified automatically, both indirectly with an inline turbidity meter and directly through a daily pressure-decay integrity test. When the LP membrane system is coupled with pre-treatment process trains such as coagulation, membrane filtration is able to remove significant amounts of disinfection-by-product (DBP) precursors, and remove other contaminants such as iron, manganese, arsenic and colour. Excellent filtrate quality coupled with the ability to handle varying water conditions makes LP membrane filtration an excellent treatment option to ensure compliance with increasingly stringent drinking water regulations.

Pall Corporation has conducted several hundred LP membrane filtration pilot studies around the world. Both MF and UF systems have been piloted, on various water sources and integrated into treatment processes to target contaminants of concern. For example, naturally occurring organic mater can be removed from surface water with proper pre-treatment and MF. Microbial pathogens are effectively removed from all water sources solely with MF alone.

The aim of this pilot study was to prove that MF can be used successfully on high turbidity feed waters in New Zealand conditions, where conventional filtration practices have proven troublesome.

This paper presents results from pilot studies undertaken on highly variable, turbid river water in New Zealand, with naturally occurring high organic matter levels. The LP MF system continuously provided excellent filtrate water quality, while handling turbidity spikes of up to 450 NTU without the need to shut down. The MF system reliably removed the targeted contaminants of concern, as well as demonstrating low rates of fouling over months of continuous operation.

The project background, water quality, membrane performance data, and projected full-scale plant designs derived from the pilot study are presented.