3 questions from Queensland's water recycling guidelines

    Friday, July 03, 2015

    The completion of the Western Corridor Recycled Water Project marked a monumental time in South East Queensland's water engineering history. 

    A $2.5 billion project, the Queensland Department of State Development lauded it as the largest recycled water scheme ever built in Australia. The system is an impressive feat, capable of supplying up to 232 megalitres of purified, recycled water on a daily basis. 

    To fully appreciate the expertise and insights applied to this project, we'll answer three key questions engineers ask themselves when developing recycled water schemes: 

    1. What should be detailed in a recycled water management plan? 

    A recycled water management plan (RWMP) must detail the systems that produce and/or supply recycled water to a distribution network, according to Section 201 of the Water Supply (Safety and Reliability) Act 2008. In addition, the RWMP must describe:

    • How the infrastructure will be maintained
    • Any possible hazards and dangerous events that could impact the recycled water's quality
    • The manner in which any risks will be addressed and resolved

    2. Does Queensland classify recycled water? 

    The Queensland Department of Energy and Water Supply (DEWS) assigns recycled water either A+, A, B, C or D classifications if the liquid is sourced from a utility's sewage system. The same categorisation also applies when a water provider uses sewage or effluent to produce recycled water.

    DEWS uses log reduction metrics (percentage of microorganisms eliminated or mollified via a certain process) to develop classifications. So, when a recycled water scheme's virus filtration system receives a '4-log' rating, it means the solution removed 99.99 per cent of viruses. 

    3. What classification must drinking water receive? 

    When recycled water is delivered for potable uses, the contents must meet the following minimum log reductions for indicator organisms and pathogens:

    • Bacteria (Salmonella, Escherichia colia, etc.) must register an 8-log valuation.
    • Viruses (Adenovirus, Hepatitis A and Coronavirus) must receive a 9.5-log rating.
    • Protozoa (Cryptosporidium, Naeglergia fowleri) requires an 8-log appraisal.
    • Helminths (parasites or worms) must receive an 8-log appraisal. 

    In this regard the A+, A, B, C and D categories do not apply, as the aforementioned valuations exceeded the standards highlighted in each of these classifications. 

    Given the effects of climate change, concerns regarding devastating droughts and other such issues, recycled water will likely become an integral part of Queensland's metropolitan infrastructures and rural communities.