Optimising wastewater treatment plant performance

Wastewater treatment processes have been driven to reduce nutrient concentrations over the past couple of decades to improve receiving water quality, particularly in inland waterways. This has led to the installation of complex and often energy-intensive processes. Recently, focus has been on optimising existing treatment processes both in terms of energy usage and plant performance to maximise performance, capacity and operation of the plants.

Aurecon Associate - Water & Wastewater Treatment Susan Kitching will be presenting a paper on optimising Sydney Water’s wastewater treatment plant performance at Ozwater’15 on 12-14 May in Adelaide. The paper discusses a program of work that commenced in 2011 with Aurecon to audit 11 anaerobic digestion facilities. Following successful results from this program, a second program was established to assess the capacity and capability of their water and wastewater facilities focusing on the performance of the system and operation and maintenance. The objectives of the program are to:

• standardise operations where possible on good practice to optimise maintenance requirements;
• consistently comply with effluent and biosolids land application guidelines/standards;
• improve biosolids and effluent quality; and
• improve operational efficiency.

Case study: Liverpool Water Recycling Plant

One of the plants that was audited within the anaerobic digestion audits is Liverpool Water Recycling Plant (WRP). The plant treats wastewater from the South Western Suburbs of Sydney around Liverpool.

The plant consists of an inlet works, primary sedimentation and secondary treatment in a conventional activated sludge plant. Solids are collected from the primary and secondary treatment and treated in anaerobic digesters prior to dewatering and being taken off-site for beneficial re-use.

The Liverpool WRP audit and BioWin modelling identified a number of short-, medium- and long-term modifications to improve digester performance. From these findings a number of modifications have been made to the plant to trial some of the recommendations, specifically that relating to recuperative thickening.

The initial changes resulted in improvements to biosolids product quality, increased gas production and a reduction in operating costs. Following on from the initial success, between October and early 2014, the recuperative thickening has been optimised on-site to stabilise the thickening performance and hence the digester operation within the limits of the existing equipment. The increase in gas production can be seen in Figure 1 (approximately 30%).

Figure 1.

Conclusion

The auditing process as applied to Sydney Water treatment plants allows understanding of influent characteristics, overall plant mass balance and process unit performance. Examination of these, alongside operations and maintenance practices, and comparison to good practice can lead to optimisation of treatment facility assets and maximising available treatment capacity.