All Purpose Pumps was approached to audit a domestic bore water reverse osmosis application located in the western suburbs of Melbourne. The plant had not been performing well and was showing signs of:

• Short membrane life
• Poor rejection and recovery
• Requirement for a membrane change out

The plant in question is a small, common design brackish water reverse osmosis process built by a local supplier in about 2016. The system comprises independent bore control, backwashing media filter, cartridge filters, antiscalant dosing and a 4 x 4040 BW membrane RO system. Feedwater salinity is approximately 4,000 mg/L TDS so significant but not daunting. The client has had irregular and less than perfect support in the past resulting in a degree of a lack of confidence in the process overall.

All Purpose Pumps has over 30 years of membrane and separation application experience, specifically with hollow core and flat sheet membranes and all the supporting apparatus.

The plant was audited by All Purpose Pumps and found to have several typical design and process faults:

• Media filter backwash was incorrectly set up and was causing a significant impact on the efficiency of the backwash cycle. So much so that initially, the media filter DP was more than 160 kPa
• The antiscalant dosing was set up incorrectly resulting in intermittent and incorrect operation of the dosing pump.
• This led to the RO membranes being scaled to the point where permeate flow was negligible and salt rejection was around 50%. This scaling had led to scale forming on various pieces of components as well – for example, all concentrate flow lines including the VA flow meters.
•  The owner was at the point of discontinuing the plant and shutting it down permanently due to the lack of return with this process over the cost of Mains water and it was not economically sustainable.

All Purpose Pumps have a long history of designing, maintaining and troubleshooting bore water separation processes throughout the region. The problems identified in this instance were not complex, but insidious and, over a long interval, led to the situation that we ascertained.

All Purpose Pumps generated a report for the owner, explaining each and every aspect of the process, the shortcomings and the rectification of these issues.

Subsequently, the process has been modified and attended to in the form of:

• Pre-treatment backwash is no longer compromised by the RO cycles. Media filter backwash cycle is now effective and has no tangible impact on the RO performance in the form of poor backwash performance and media filter DP is now 20 kPa
• Antiscalant dosing was rectified with the correct setting and tuning of the dosing pump, two long term minor leaks leading to partial cavitation of the dosing pump were also rectified. Dosing is now consistent in delivery.
• Membranes were replaced as they were scaled beyond recovery.