Grand Wastewater Designs (Revisited)

A 12-month trial of an Advanced Wastewater Treatment Plant (AWTP), destined for Davis research station, has shown the plant can produce drinking quality water from wastewater, while reducing energy consumption and the amount of waste discharged into the environment.

The success of the trial, conducted at TasWater’s Selfs Point wastewater treatment plant in Hobart (Tasmania), puts Australia’s Antarctic stations a step closer to reliable, self-contained, low maintenance water recycling.

Australian Antarctic Division engineer, Mr Michael Packer, said the new AWTP will take treated effluent from the station’s secondary wastewater treatment plant, installed in December 2015, and improve on its quality.

“The secondary treatment plant is very good at removing most of the nutrients and pathogens but it doesn’t remove all of the chemical contaminants, such as some inorganic compounds, pharmaceuticals and endocrine disrupting chemicals,” he said.

“The AWTP will deal with any residual contaminants and pathogens using seven different treatment barriers. These multiple barriers provide a very high level of protection and surety that the quality of the water is always maintained.”

Second to none

The secondary treatment plant treats kitchen and bathroom waste using a standard ‘membrane biological reactor’ process — using microbes to digest nutrients and filtration to remove solids (Australian Antarctic Magazine 25: 30–31, 2013). The resulting clean water is discharged to the ocean via a pipe at the water’s edge, while the solids are returned to Australia.

The plant was installed in response to an environmental impact assessment conducted by Antarctic Division scientists in 2009–10, which showed that existing waste management practices were causing an accumulation of some contaminants in the environment. Two further secondary treatment plants will be installed at Casey and Mawson stations in future years.

“There are similar membrane biological reactor plants built by German company, Martin Membrane Systems, in Antarctica, however ours is close to the leading edge in technology terms,” Mr Packer said.

“We’ve worked closely with the company to ensure the plant is highly automated, low maintenance and has a lot of monitoring capacity, so that we can continuously confirm we are achieving the standards that we aim for.

“We can also reduce the plant’s operational size over winter, when there are 10 times fewer people on station, and return it to full capacity in the summer.“

One of a kind

When the AWTP is installed at Davis in early 2017 it will be the only one of its kind in Antarctica. The bespoke plant was built at the Australian Antarctic Division, with funding, research, design and testing input from academia and industry partners, including the Australian Water Recycling Centre of Excellence, Victoria University, University of Melbourne, RMIT University, Veolia, AECOM, Curtin University, TasWater and Coliban Water.

The 12-month trial of the plant proved that it works under more demanding conditions than are expected in Antarctica.

“The effluent coming out of TasWater’s Selfs Point secondary treatment plant is not as clean as the effluent from the Davis secondary treatment plant, because it uses a more traditional biological nutrient reduction process than our Antarctic plant,” Mr Packer said.

“However, our AWTP proved quite capable of removing pathogens and chemicals to values well within the standards set by the Australian Drinking Water Guidelines.”

As the AWTP is designed to produce drinking quality water (although there are no immediate plans to use it for this purpose), it aims to achieve up to a 13 ‘log reduction’ in pathogens. To put that in context, a two log reduction kills 99% of pathogens, a three log reduction kills 99.9% of pathogens, and so on to 11 decimal places.

To do this the plant uses an arsenal of germ-killing and molecule-blasting technologies — ozone disinfection, microfiltration, biological activated carbon, reverse osmosis, ultraviolet disinfection and chlorination. These processes kill and/or remove bacteria, viruses and protozoa, and break up large chemical molecules, such as hormones, into smaller ones, which are filtered out later. Throughout the treatment process a range of ‘critical control parameters’ have been defined, to alert the Antarctic Division head office of potential problems, and trigger the shut-down of the plant if the parameters are breached.

While the effluent quality has met expectations, some trial work needs to continue to ensure the plant can operate autonomously, with only annual maintenance required by a skilled operator. As the AWTP’s operation is dependent on the flow of effluent from the secondary wastewater treatment plant, it is designed to shut itself down and go into ‘preservation’ mode — to preserve sensitive filter membranes — when flows are low. The plant then ramps up again when flows increase.

“The AWTP works on a batch basis and will provide up to 22 kilolitres of clean water per day at full capacity,” Mr Packer said.

“But it needs a few hours each day to flush filters and in winter it might only run once every two or three days.

“We’ve shown that the plant can be operated remotely and that it can automatically start and stop routinely, however we still have some work to do to ensure minimal operator input.”

The trial has also shown that if water from the plant was recycled for reuse at Davis station it could reduce energy consumption related to water management by 69%, by reducing the need to desalinate water from a nearby tarn.

“If we reuse the water we’d save more than 33 000 litres of diesel a year, so the potential for energy saving is high,” Mr Packer said.

As well as Antarctica, the AWTP is well suited to potable water production in other remote areas around the world, using source waters from sewer, mining and stormwater systems. As a result, the project has attracted international attention, with institutions in both China and India expressing interest in collaborating in the development of similar treatment systems.

Wendy Pyper
Australian Antarctic Division