Genevieve Petch and crew visit the microfiltration units.

Australian Vinyl’s move to recycle its wastewater secured both its water supply and its water quality. But what about downstream? Richard Collins and George Smith report.

Water in Melbourne’s western suburbs has gotten a little worse over the last decade, at least according to the highly refined tastes of Australia’s only large-scale PVC maker. This decline, probably due to falling reservoirs levels, was reinforced the decision to recycle its wastewater on-site, a bid to secure not just the company’s water supply but also its water quality.

Australian Vinyls’ Altona plant is one of the few in the world that has relied on mains water. Following the launch of its $5.5 million Water Recycling Plant (WRP) by Premier John Brumby, it is also one of the few to recycle its wastewater.

PVC manufacture is notoriously fickle, a suspension process highly sensitive to fluctuations in everything from its base material, vinyl chloride monomer, to the water supply.

“We have two main water supplies and we can tell when they switch dams – usually a bit before summer – because the reaction process gets a bit upset for a few days,” said Genevieve Petch, the process engineer in charge of the recycling project.

Contaminants such as metals alter the properties of the PVC powder, increasing its porosity among other things, so Australian Vinyls monitors its water very closely, measuring for conductivity, turbidity, pH and dissolved oxygen.

“We noticed conductivity, which is a measure of dissolved salts, has been increasing over 10 years. [Total dissolved solids] used to be 60-80ppm, now it is about 120ppm,” said Petch.

“The water quality has deteriorated, [where] the Water Recycling Plant produces a consistent quality of water to the spec that we want [of 40-60ppm].”

The WRP has also halved the company’s mains water use, from 640ML a year, and slashed trade waste discharges by an impressive 70 per cent. We’ll come back to trade waste, however, because the impacts of climate change on the sewerage system have “blindsided” the water industry, said Water Services Association of Australia chief, Ross Young.

Targeting savings
Australian Vinyls was one of Melbourne’s top 20 water users, making it an obvious target when City West Water started looking for savings four or five years ago. Water restrictions, or at least a cap on growth, were very much on the cards.

“We use quite a lot of water to make PVC, so we basically had to come up with an alternative water supply for our plant,” said Petch.

“We thought the best way to do that was to recycle our own water to get to a quality we needed and go from there. The production process requires pure water, while for sections like cooling towers, water quality is not quite so important.”

Easier said than done. They’ve learned a lot along the way and the first step, Petch reckons, is to determine the reuse options and required water quality parameters.

“If you do not identify your reuse options, you have a million scope changes throughout the project, because everyone wants their pet thing done,” she said.

“We did not work with the chemists early enough to define exactly what water was needed and ended up doing another project to cool the water down. We knew we would have to do that but we did not scope it out enough at the start.”

Consult widely, particularly with production staff on how to integrate the treatment plant with the rest of the process, and with chemists to determine quality needs and treatment issues.

“If we did it again, we would define the water quality and draw a line to make sure there are no changes; then build back from that,” Petch said.

They also developed a hierarchy of reuse according to water quality, firstly in process, then in the boilers and finally blended with mains water for the cooling towers.

Investigate, then implement
Another tip is don’t shirk the hard yards in pre-project investigation, particularly if there is a high degree of technical risk. For Australian Vinyls, a six-month pilot revealed a flaw in the original plan to take water straight from the effluent ponds – trace amounts of PVC quickly blinded the microfiltration membranes.

The pilot cost $400,000 but ultimately saved time, disruption, frustration and ongoing operating costs. As a result the first treatment train worked so well when commissioned in September they brought the second one forward and have not looked back. It employs a three-stage process.

“Hydrocyclones remove the larger 100 micron particles that are in the water,” explained Petch.

“Then we are in the next step in the process with 20 micron particles in the water, and that’s removed through microfiltration. Microfiltration basically removes all suspended solids from the water; we reuse the concentrate from microfiltration elsewhere in the plant so we recover that stream.

“The permeate, the clean water from microfiltration, then goes through to reverse osmosis, which removes dissolved salts from the water, the same as desalination technology.”

Finally, the water is neutralised because it is highly acidic at pH 3, then stored before being distributed for reuse.

The company expects a net saving of nearly $800,000 a year through reduced water and wastewater costs. That equates to a payback of six years, though with water prices to rise 20 per cent annually for the next two years the return in investment will come in further.

The figure does not include energy as the WRP is almost energy neutral, with heat extracted and reused from the 60?C wastewater before treatment and the recycled water produced still at 40?C when fed to the boilers.

Blindsided by recycling
While officially opening the WRP in early February, the premier said recycled water was a core component in the next stage of the government’s Water Plan.

“Melbourne already uses almost three times more recycled water than any other major Australian city and this project will help further reduce our reliance on drinking water supplies,” said Premier Brumby.

“We can save billions of litres of drinking water each year by substituting treated wastewater for a range of industrial, commercial and business applications.”

It sounds undeniably beneficial. However, the rise of recycling has created a range of issues that will require careful balancing, says Ross Young, head of the WSAA and one of the industry’s most thoughtful advocates.

One is that while wastewater volumes entering the sewers may reduce, contaminant loads will not, resulting in higher concentrations and slower flows. And that poses challenges.

“Some people say the water conservation measures have gone that little bit too far,” Young told WME. “There is no turning around, of course… but this can be a significant issue with corrosion, it can be a significant issue with the utilities complying with their EPA discharge licences.”

Canberra utility ACTEW, for example, is contemplating adding a desalination plant on its wastewater treatment plant because of the salt loads discharging into the Murrumbidgee River.

Industrial recycling is not the only contributor to the slow sewer issue. The popularity of water efficient appliances and ad hoc greywater recycling and the reduction of rain and groundwater infiltration into the sewers contribute too.

“This is an issue we are all working through at the moment,” said Young. “It is one of the unintended consequences of climate change that no one ever predicted. We were blindsided on this one.”

While it’s early days, he is already speculating about radical solutions, including the “absolute heresy” of reconnect stormwater to sewers, “at the right time and the right place”. There is also a bigger game afoot.

“I have a particular view that in 20 years’ time, our wastewater treatment plants will be better known as generators of green electrons than pollution cleaning devices. Once there is a price on carbon, green energy will become very valuable,” said Young.

“If you think about the wastewater system, the infrastructure is already in place and it is largely gravity fed, so it is very easy to convey material through that you can convert to biogas in a treatment plant.

“Once you think of your wastewater system in that regard, you virtually throw all the balls up in the air. Maybe the utilities should be buying waste from breweries and asking them to put it in the sewer because it is really good carbon to turn into biogas. Maybe insinkerators are a good idea after all. It really does revolutionise you.”

But real revolutions come when a single idea excites a critical mass, so government, industry and the water sector must soon get on the same page about wastewater recycling.