Water treatment

A project to address conditions at Sydney Water’s Nepean WTP

The current floc strength test is based on turbulence induced shear techDue to the historic low turbidity and colour of many raw surface water supplies, Sydney Water has employed direct/contact filtration systems for drinking water treatment. One challenge for water filtration plants is the rapid deterioration of raw water colour and NOMs during heavy rain events and changes in the dam levels. Removing additional colour introduced under these conditions requires an increase in dose of ferric chloride and polyDADMAC, which has resulted in the reduction of floc strength if the charge of the floc drifts outside the optimum range. niques employing impellers (Jar test). This may not be an accurate representation of the shear conditions in a direct filter operation and cannot be used to define a threshold velocity gradient to prevent the breakthrough of suspended solidsThe membrane technology, developed by Professor Leslie and the University of Sydney’s Professor Bruce Sutton, has been patented by UNSW commercial arm, NewSouth Innovations and commercialization partners are being sought.

Membrane distillation-crystallization (MDC) process has great potential for recovery of high quality water and valuable precipitates from effluents of high salt content such as inland brine water.  Incorporation of submerging membrane in a feed tank provides opportunity for saving of energy consumption by eliminating the need for feed circulation and reduces the loss of heat. The main challenges in submerged vacuum membrane distillation crystallization (SVMDC) are the reduction of feed temperature (temperature polarization) and the enhancement of feed concentration (concentration polarization) adjacent to membrane surface, which can cause reduction of actual driving force for water vapour transport and induce fouling formation on the membrane surface.

Validation of the pathogen removal efficiency in water treatment processes is a critical step in the delivery of water recycling projects. Validation is the process of linking the results of reliable integrity monitoring techniques to the observed removal efficiency for the target contaminants. In the case of membranes, while, existing integrity monitoring methods are adequate for pathogens such as cryptosporidium that are larger than 3 microns, there are limited methods available to quantify integrity for small pathogens such as enteric virus which range from 0.01 – 0.04 μm. Currently, challenge testing with MS2 phage is the best process indicator for virus removal in membrane systems, however incorporating this test in a full scale plant on a regular basis is attended by high costs to cultivate, dose and enumerate the bacteriophage.

The fate of spent reverse osmosis (RO) membranes appears as an emerging challenge faced by the water industry. In this project, alternative and valuable usages of end-of-life desalination membranes will be investigated. Opportunities like cost effective reuse in lower specification applications, potential recycling of valuable materials and conversion of RO into microporous separation devices will be assessed both technically and financially.

Membrane distillation-crystallization (MDC) process has great potential for recovery of high quality water and valuable precipitates from effluents of high salt content such as inland brine water.  Incorporation of submerging membrane in a feed tank provides opportunity for saving of energy consumption by eliminating the need for feed circulation and reduces the loss of heat. The main challenges in submerged vacuum membrane distillation crystallization (SVMDC) are the reduction of feed temperature (temperature polarization) and the enhancement of feed concentration (concentration polarization) adjacent to membrane surface, which can cause reduction of actual driving force for water vapour transport and induce fouling formation on the membrane surface.

Research is being conducted to address the major barriers preventing streamlined implementation of membrane bioreactors (MBRs) in water recycling schemes. As a result, appropriate, transparent and informed validation protocols will be developed for MBRs in Australia.

Within this project, the concept of assisted forward osmosis (AFO) will be applied as a pre-treatment step for reverse osmosis (RO) desalination, resulting in significant dilution of the sea/brackish waters and optimisation of the use of renewable energy. In AFO, a slight pressure is applied to the feed side, resulting in greater dilution of the RO feed, and thus significant reduction in the energy cost for RO operation. In this project, anti-fouling strategies will be investigated to decrease AFO operational costs, detailed modelling will be performed to optimise the process, and novel membranes will be studied for this specific osmotic application.

This project aims to develop a method for detecting changes in the nano-architecture of thin film membranes used in liquid phase separation processes. It builds on recent advances in Electrical Impedance Spectroscopy (EIS) techniques that generate information on the electrical properties across the thin film in situ and in real time. These new techniques to generate and interpret EIS spectra will provide insight, at the nano-scale, into changes (such as engineered surface modifications or fouling) that impact the functionality and performance of polymeric membranes. This will lead to new instrumentation that can be used to improve the performance of industrially important membrane processes such as reverse osmosis and nano-filtration and provide researchers with a tool for rapid screening and characterisation of advanced separation processes such as forward osmosis (FO) and piezoelectric membranes (PEM).

Low-pressure porous membranes are increasingly considered for pre-treatment of sea and brackish waters. However, membrane fouling remains a major drawback, as it results in higher operating, maintenance and cleaning costs. Through the development and validation of techniques for advanced characterisation of the organic compounds present in feedwaters, this project aims to better understand and to optimise the strategies currently used for fouling control. The relative efficiencies of both physical (relaxation, backwashing) and chemical cleanings will be assessed on lab and pilot scales. The organic and inorganic nature of the irreversible fouling formed during long-term filtrations (and repeated cleanings) will be characterised in detail, allowing recommendations for sustainable operation and performance.