Is grey the new black?
With rain being so scarce in many parts of Australia and water charges envisaged to increase, it’s important we all make the most of what little water we have and take the pressure off our existing infrastructure at the same time.
Green Star and NABERS focus on reducing a facility’s water footprint, resulting in numerous innovative water conservation practices. But what more can we do to future- proof existing facilities? The answer lies in greywater.
Reusing the waste stream relates to black water or greywater systems. Significant benefits can be achieved by reusing the water within a facility, reducing the carbon footprint, plus achieving maximum credits for Green Star/NABERS related projects.
Black water recovery can assist in earning green credibility. In Australia, however, recycling from the waste stream is a relatively taboo subject. People’s perception of reusing wastewater generally creates that ‘yuck’ factor.
Within any commercial building, the mechanical cooling towers usually consume the majority of water in any building, followed by WC flushing and showering from end- of-trip facilities. Just picture the water and sewerage charges that could be potentially be saved within your facility, if this was recycled.
A RAW DEAL
Greywater can be defined as any domestic wastewater produced, excluding sewage. The main difference between greywater and sewage or black water is the organic loading, which is much larger in sewage.
But how effective can these types of systems really be in reducing overall water consumption and can they be retrofitted in an existing building?
In a conventional plumbing system, the waste entering the sewer system is not segregated in any way. However, if considering a grey or black water system, differentiating between these waste streams is crucial at an early stage. The additional sewer drainage pipework to separate the source must be taken into account, as well as the storage and treatment necessary. The treated water being distributed throughout the building also needs to be clearly labelled.
In a typical greywater system, the waste is collected and treated to purify the water. Several stages are involved:
- filtration of solids (lint and hair)
- removal of pathogens and unwanted chemicals (such as salts and nutrients) using either micro-organisms or chemical treatment, and
- disinfection by chlorination or UV light, (though not all systems do this).
With proper treatment both black and greywater can be put to good use within and around the building. This includes utilising the water for laundry and toilet flushing, irrigation and cooling towers.
BACK TO BLACK
Black water can be classified as any waste stream that contains water discharged from a toilet. Compared to greywater recycling, it’s usually easier to recycle black water – generally because most plumbing systems don’t separate the greywater stream, such as that discharged from showers and basins. Sewage is different from greywater and requires further treatment, because it contains bacteria, pathogens and food particles, which can rot.
The main benefit of a black water treatment plant is that it can be retrofitted to an existing facility, or installed in new build applications, without involving complex plumbing pipework configurations. Once the system is installed and commissioned, the facility will be provided with unlimited recycled water, saving extensively on all non-potable water requirements.
A typical black water treatment plant consists of the following stages:
- Aerobic screening – this process reduces insoluble material to a negligible residue.
- Biological treatment – air is diffused into the water to make ideal conditions for bacteria to consume impurities. A sustainable biomass concentration is maintained, which metabolises all the incoming waste. This means there’s negligible sludge and 99.9 percent of the incoming water is reused.
- Ultrafiltration – this occurs through a special membrane of microscopic pores that stop particles, bacteria and viruses from passing through.
- Ultraviolet disinfection – as a precaution, ultraviolet lamps are included for the protection against pathogens.
- Chlorination – a chlorine residual is added to protect the water while in storage and the reticulation system. This is the only time any chemicals are used in the treatment process.
- Treated water storage – the result is safe water, kept in storage for immediate use for non-potable applications, including surface irrigation, toilet flushing and cooling towers.
MAKING A SPLASH
Sounds too good to be true… or does it? In Europe and the US, both black and greywater treatment systems are installed extensively and becoming far more frequent.
What about a little closer to home? Commissioned in May 2011, 1 Bligh Street in Sydney, a 29-level office tower overlooking Sydney Harbour, captures nearly 100 percent of its wastewater and successfully reuses it within the building.
Recycling via the black water treatment plant treats approximately 100,000 litres on-site daily, the vast majority of the waste stream. Building owner, Dexus Property Group avoids sewer capacity issues and has reduced the building’s potable cold water demand by approximately 90 percent. It’s a fascinating building that incorporates numerous green plumbing initiatives,being one of the first six-Star Green Star buildings constructed in Australia.
In addition, a 65,000-litre rainwater harvest tank recycles it for irrigation. Water-efficient appliances are used throughout, using three- star WELS-rated showerheads, five-star rated hand wash basin taps and four-star rated toilets. All water use is closely monitored via the building management system. As a result of these systems being implemented, reliance on municipal potable water sources has been reduced by more than 90 percent.
It’s surprising to learn that not all of the wastewater reused at Bligh Street comes from the building itself. Calculations revealed the building’s total waste stream would not meet the non-potable demand for cooling tower make-up and toilet flushing (the desired reuse applications). Rather than supplementing this demand with potable water from Sydney Water, the development has engaged in ‘sewer mining’, which involves tapping into the city’s sewer main, as a source of waste stream that is treated and reused within the building.
The benefits of a black/greywater system outweigh the costs associated with the water supply, sewage and stormwater fees, plus connection and meter charges from the utility providers. These systems conserve not only water, but also energy, while reducing the stress of ageing infrastructure.
Although these systems require a significantcapitalinvestment,plusoperational and maintenance costs, the payback in
the majority of cases can be significantly accelerated and will greatly assist in buildings of the future reaching net-zero water.
Paul Angus is an associate director – Hydraulic Services at AECOM, based in Sydney. Paul has strong commercial and technical capability in developing and delivering hydraulic design strategies and solutions. He specialises in providing a sustainable approach to system design, including water conservation, recycling and generating innovative engineering solutions. He has extensive experience in the hydraulic design, pre-acquisition and condition surveys, including all forms of specialist client advisory work. He also has extensive experience in expert witness reporting, taking part in adjudications, mediations, negotiations and arbitrations.
This article also appears in the December/January issue of Facility Management magazine.
Image courtesy Aquacell Pty Ltd