Optimisation Of Membrane Bioreactor Nutrient Removal Performance – Some Practical Examples

Membrane Bioreactors (MBR), are of increased interest in New Zealand, driven largely by tighter effluent consent requirements and greater reuse potential of treated effluent. In Australia, MBR has a more extensive track record and history of application; some recent experiences are presented in this paper.

Experiences and outcomes at Goodna Sewage Treatment Plant (GSTP) and Sarina Water Recycling Facility (SWRF) and provided, with the implementation of:

Ammonia based aeration control (ABAC) utilising on-line ammonia analysers,

Ortho-phosphate analyser based dosing control of aluminium chlorohydrate (ACH) and alum dosing, and,

Enhanced Biological Phosphorous Removal (EBPR) optimisation measures relative to advanced analyser based controls

The Broadspectrum Jacobs JV (Formally Transfield / SKM) delivered the 8,000EP Sarina Water Reclamation Facility (SWRF) in 2015. A 5 Stage Bardenpho configuration incorporating a Membrane Bioreactor (MBR) was selected to meet TN 5, TP 1 and NH3 0.5 criteria.

The 90,000EP Goodna STP was delivered by Thiess and Jacobs (formally SKM) in 2012. This benchmark facility is designed to achieve stringent TN and TP discharge criteria of 3mg/L and 1mg/L respectively. The process configuration integrates an MBR and oxidation ditch within an overall 7 stage BNR and EBPR process.

At both facilities, permeate ammonia and ortho-phosphate concentration is measured by online wet chemistry analysers on a continuous basis and can be used for advanced nutrient removal process control, providing enhanced nutrient removal performance and compliance reliability, and reduced energy and chemical operational costs.

The ABAC is achieved through controlling aeration supply and distribution to the bioreactor relative to measured permeate ammonia concentration and the desired ammonia setpoint. The control philosophy adopts an ammonia controller function which trims the target reactor dissolved oxygen (DO) concentration, and provides protection against analyser failure or incorrect measurement which could result in sub optimal aeration control responses. The resulting control can be optimised in terms of analyser confidence and efficiency gain by the Operator or Engineer. The control has been shown to reduce energy consumption and improve performance and reliability accordingly.

The process design compensates transient EBPR performance associated with catchment and environmental impacts using supplementary chemical phosphorous removal, specifically Alum dosing at GSTP, and ACH dosing at SWRF. An online ortho-phosphate

analyser is used to optimise phosphorous removal and EBPR performance, and reduce chemical dosing dependency and costs. Significant reductions in chemical dosing requirements were achieved, as well as a slight reduction in biosolids generation through reduced precipitated solids production.

Control philosophies and improvements in process performance and savings are presented. Lessons learned in controller set up and operational implications and requirements are also provided. These advanced control methodologies may be applied to larger scale facilities to provide substantial cost savings and improved performance reliability. At GSTP, routine sampling shows the plant consistently achieves effluent TP <1.0 mgP/L, ammonia <0.1 mgN/L, and TN <2.5 mgN/L. Control philosophies and improvements in process performance and savings are presented.