Waste stabilisation ponds are perhaps the most common type of sewage treatment system in Australia, based on the total number of sewage plants operating around the country (many which are small regional systems).
The reason for Waste Stabilisation Ponds prevalence is their operational simplicity and low mechanical requirements, including low power demand. This makes them an attractive solution for remote, regional and privately operated treatment facilities.
Unfortunately performance issues with Waste Stabilisation Ponds are common, and the technology is often dismissed, even though easy remedies exist to rectify and enhance performance. The main water quality failures that occur in Waste Stabilisation Ponds are generally associated with BOD, SS, and pH. Failures are largely down to several common problems:
- Algae. Algae affects the pH (increasing pH to 8.5-10.5 during natural photosynthesis) and also suspended solid loading
- Sludge accumulation in ponds: although ponds are simple to operate, unfortunately many are left without ANY operation and maintenance. If sludge accumulation in the ponds is not periodically removed (e.g. 5-10 years), it can build up and start to entrain into the effluent stream, especially during peak wet weather flows. Failures in water quality are often the direct result of not desludging, rather than a failure of the technology itself.
- Hydraulic short circuiting: although Waste Stabilisation Ponds may have theoretically large retention times (i.e large ponds with small flows through them), their general design can limit mixing and subsequently cause flows to fast track through the pond; sometimes using less than 10% of the total available volume.
Several straight forward solutions to these common problems exist, without having to build new mechanical package plants. Apart from the first step of “desludging the pond” if needed, two improvement strategies that the Water and Carbon Group undertook for QUU to improve the performance of their Helidon Waste Stabilisation Ponds which services a community of 500EP in QLD, was to:
- Improve the hydraulic retention of the Waste Stabilisation Ponds by installing stub baffles and redirect the influent pipework in the primary pond to improve mixing in the pond and avoid water “tracking” around the side.
- Construct a high density wetland at the end of the ponds to polish the water and deliver year round license compliance. The wetland effectively removed algae (hence Suspended Solids), stabilised pH and reduced variable BOD.
These works were successfully implemented for the least cost per EP available on the market, improving the final water quality to below the required license limits. A joint paper with QUU was written discussing the Helidon Waste Stabilisation Ponds upgrade project for the AWA regional conference in Mackay in July 2014 (see link).
How Can the Water and Carbon Group Support Waste Stabilisation Ponds Projects
The Water and Carbon Group is able to support Waste Stabilisation Ponds projects in a number of ways, including:
- Performance and operational assessments of ponds.
- Waste Stabilisation Ponds pond process modelling.
- Detailed design.
- Tracer studies – hydraulic assessment.
- Improvement strategies e.g. baffles, enhancements.
- Integration with other technologies.
Additional reference papers / information about Waste Stabilisation Ponds