The Challenge
In Australia, natural water resources are increasingly under the twin pressures of climate change and population growth. Wider use of water recycling is one measure available as a response to these pressures, and a spectrum of small scale water recycling plants suitable for single dwellings to full sized remote communities is now available for study. This project comprises a review of current water quality monitoring technology and its application in a sample of nine small scale water recycling plants.
The Project
The project consisted of a literature review to identify current best practice in monitoring techniques for water recycling, followed by nine case studies of small scale water recycling plants.
These plants recycle both grey water and wastewater for various end uses. The systems selected are all capable of unmanned operation and were designed to treat between 2.5 kilolitres and 1000 kilolitres per day.
The project objectives were to:
- Identify current best practice and emerging monitoring technologies for control of health risks in small scale wastewater recycling systems.
- Provide an overview of the strengths and weaknesses of the monitoring approaches and the treatment technologies to which they could be applied.
- Provide a practical overview of the monitoring approaches with consideration of the need for specialist services such as maintenance and calibration.
- Provide information on data collection for integration into centralised monitoring and response systems.
- Provide indicative costs associated with the application of the monitoring approaches.
- Provide an indication of the ability of monitoring to identify reductions in treatment plant performance.
The literature survey covered new techniques for process and verification monitoring including:
- Biosensors,
- Microelectrode and chemical sensor arrays,
- Optical and fluorescence methods,
- Flow injection analysis, and
- Remote monitoring.
Common measurements in water recycling plants were found to include:
- Residual chlorine levels,
- pH,
- Dissolved oxygen,
- Electrical conductivity, and
- Suspended solids and turbidity.
Other parameters less commonly measured included oxidation reduction potential, temperature and particle counts.
The Outcome
A number of current best practices and emerging monitoring technologies found in the literature survey were subsequently identified in the case studies. This included the use of networks and remote control to centrally operate systems. Additionally, robust system design with plant components fit-for-purpose, regular calibration of sensors and planned plant maintenance schedules were found to contribute to reliable performance.
A Hazard Analysis Critical Control Point (HACCP) risk management methodology allows development of appropriate risk management strategies and leads to enhanced operating reliability. HACCP plans are long established in food technology applications and this report recommends their use in all water recycling systems. Online monitoring is a key component of HACCP and allows: operation within defined limits, the effective use of remote alarms and automated plant shutdown when required.
Further research is recommended to investigate the benefit of monitoring UV transmission now commonly used to reduce biological load, and the feasibility of online remote monitoring for systems designed for individual households. The report recommends monitoring networks should be further explored, as this presents a cost effective solution for monitoring and maintaining a large number of systems through a centralized facility.
