Waste Management In Action

Looking ahead pays dividends

organic waste

Wastewater specialist Aerofloat won a tender for Shellharbour Council not only based on experience, but having foresight. It explains how.

Like any local authority, the Shellharbour Resource Recovery facility needed to reduce costs in its operations, which is why it decided to commission a report to consider alternative options to its current offsite treatment arrangements – due to ever increasing disposal costs.

Historically, leachate produced from the Dunmore Recycling and Waste Deposit Depot was collected in 200,000L of onsite tanks, and then disposed of by either onsite irrigation, or trucking to a third-party for treatment. The outcomes of the commissioned report showed that onsite pre-treatment and connection to sewer was a good value option for disposal of the leachate.

Council identified the nearest existing sewer and began developing concept designs with the assistance of external consultants.

Through an expressions of interest process prior to the design and construction tender, Shellharbour Council staff leveraged the expertise of several companies to understand the risks and benefits of several concept process designs. It eventually selected a two-staged process design to proceed with and construct tender.

The plant was required to achieve an effluent quality suitable for discharge to Sydney Water’s sewer with a design capacity of 65m3/day based on an ammonia concentration of 1200mg/L. The nearest sewer main capable of accepting the discharge was some 1.2km away. The land zoning and size of the treatment plant meant it could be delivered under the State Environmental Planning Policy (Infrastructure) 2007 as development permitted without consent, whereas the pipeline required development consent due to parts of the alignment being with the proximity area of a coastal wetland. As such, the works were delivered as separate projects and under separate contracts.

Even during tender stage, one of the key elements, and something that helped the company get over the line in terms of securing the contract, was having foresight. Something that Aerofloat’s Managing Director Ray Anderson had when reviewing the design of the system.

“I anticipated there would be more nitrogen in the future and it wouldn’t cost much more if we modified the design to account for this from the start,” Ray says. “Which, as it turns out was a good move, as the concentration changed throughout the course of the project but design changes were not necessary half way through the project.

“We tend to be a little bit more conservative with our designs. The plant was designed for 65m3 per day, with an average ammonia concentrate of about 1250mg/L. The testing that we have been doing over the past few weeks of commissioning has shown it has been up around the 1500 to 1800mg/L, or up to 50 per cent higher than the original design concentration. Due to our conservative design, the plant has the capacity to handle this higher load.”

It was this attention to detail and critical thinking that led to Aerofloat being awarded the contract and ultimately resulted in delivering a successful project.

The scope of the build included preparation of the site, constructing piles under concrete tanks, slabs, and bund walls, as well as installing two new leachate tanks. There were also three large concrete tanks that had to be installed that comprised an anoxic reactor, a nitrifying reactor, and a sequence batch reactor (SBR).

To complete the build there are internal recycle sludge pumps between the nitrifying reactor and anoxic reactor, and between the SBR and nitrifying reactor. The treated effluent is decanted into a treated effluent tank prior to being pumped to the sewer. Different chemicals are added to optimise the process performance, including sucrose as a carbon source and caustic soda for pH correction. Excess biosolids are pumped to a thickening tank for disposal back into the landfill.

The plant is contained within a concrete bund and has a purpose-built mezzanine floor that was installed to ensure critical mechanical and electrical componentry is positioned above the top of the bund wall level. The entire system is PLC controlled and automated with remote monitoring capabilities.

“The site also required a different approach to that of many other leachate treatment plants,” says Council Project Manager James Brumpton. “The common approach usually consists of large upstream leachate storage ponds to provide balancing and mixing, feeding a relatively consistent leachate into one or more sequence batch reactors.

“One of the issues was that the site does not have any upstream storage, so the leachate quality is highly variable, with ammonia occasionally as high as 2000mg/L,” says James.

Mick Anderson, Aerofloat’s General Manager of Engineering and Projects, knew the challenges of removing the main contaminant, ammonia, from the leachate and the impact the resultant nitrate formation, can have on the stability of the treatment process.   “In other leachate treatment plants, ammonia levels are often around 300 to 500mg/L. Shellharbour is vastly different from a typical leachate treatment plant where ammonia concentrations up to 2000mg/L can occur,” says Anderson.

“Understanding the nitrification and denitrification process is extremely important in treating leachate with such high ammonia levels to ensure the treated effluent quality consistently meets the acceptable limits for discharge to sewer. It is these in-house process skills from years of experience that Aerofloat prides itself on,” says Anderson.

Project Delivery

Due to the high disposal costs, Shellharbour staff had a desire to promptly deliver a treatment facility. Following an extensive tender review process, the contract was awarded to Aerofloat at the end of November 2020 with a practical completion date of 30 June 2021. Detailed design started immediately with preliminary earth works commencing in early January.

“Throughout the project we had weekly meetings between Council and Aerofloat to constantly challenge the timeframe and work out ways to bring forward the completion date,” says James. “The initial scope of the project did not include the hot commissioning of the plant. However, Aerofloat agreed to seed the plant with biomass, prior to practical completion to enable the biosolids to acclimatise and to ensure that the plant could treat and commence discharging the treated effluent to sewer as soon as possible. There was a high level of collaboration between Council and Aerofloat as well as key subcontractors Dynamic Civil and Panthers Tanks to ensure the project was completed on time, on budget and to a high standard of quality.”

Mick Anderson and Aerofloat Project Manager Nick Lowe are happy with the way the plant is functioning through its commissioning phase. “Having only been running for a few weeks it has already reached its designed capacity, which means Ray’s intuition was right when he insisted more capacity should be built in,” says Lowe. “We were producing an effluent quality that met discharge requirements early in the commissioning phase.”

Aerofloat has a strong aftersales business and will continue to have a long-term relationship with the council and its operator, Innaco, during the ongoing operations contract.

“We have good relationships with our clients,” says Mick. “We will have production managers, commissioning engineers, and process engineers dial in remotely to the plant to review trends and advise if needed.”

And what does the council think of the end result?

“From the beginning, Aerofloat critically analysed the process design by leveraging its in-house knowledge and experience in treating industrial wastewaters,” says James. “[Its] attention to detail and passion for excellence was evident throughout the entire design, manufacture, construction, testing and commissioning phases. Aerofloat truly has been fantastic and a real pleasure to work with.”

Once the civil works and large tanks were constructed, Aerofloat made the build seem simple, despite being a very complex project. Completing the project ahead of schedule enabled council to commence discharging treated effluent to sewer much sooner than expected. Needless to say they were satisfied with the result.

For more information, visit www.aerofloat.com.au

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