Blackwater treatment systems, designed for the recycling of water from toilets and kitchens etc, are becoming more cost-effective and technically viable with every passing year. HARTLEY HENDERSON outlines the workings of typical modern systems in different commercial situations.
Continuing water shortages in many parts of Australia mean that greater attention is being directed at alternative water sources, including the capture, treatment and recycling of blackwater from sewer systems.
Blackwater can include wastewater discharged from various fixtures in a building including the bathroom, laundry, kitchen and toilet, and treatment systems can range from simple trickling filters, aeration and nitrogen bio-reactors, to more sophisticated membrane bio-reactor (MBR) systems. The applications, capacity, cost and output quality of systems, however, can vary greatly.
WJP Solutions, based in the Melbourne suburb of Doncaster, is a major designer and supplier of MBR blackwater treatment systems for use in commercial buildings. Engineering manager, Glen Millot, says the company is experiencing increasing demand for its systems, which can be custom designed and are compliant with relevant Australian and state regulations.
“These MBR systems can convert sewage (black or grey) to Class A water standard, suitable for reuse applications such as toilet flushing, wash-down, irrigation and industrial use. With additional add-on treatment, the system can produce water that can also be used for heating and cooling processes,” Millot says.
“The MBR core process utilises an immersed hollow fibre membrane technology capable of removing pathogens, including viruses, and all our plants have on-board monitoring (including touch screen SCADA control and remote monitoring) and fail safe capabilities to ensure that clean, safe water is delivered for reuse.
“Prior to focusing on MRB-based systems we trialled a number of alternative blackwater treatment systems. These included trickle filter, which did not perform to an acceptable level. Others have tried mechanical filtration, but it kept clogging up and could not operate for long periods of time.
“When considering the installation of a blackwater treatment system it is important to consult relevant authorities about local requirements. Sometimes it is hard to get clear directions from authorities and there can be a lack of consistency. Each state has its own way of interpreting the National Recycled Water Guidelines.
“Where the use of recycled blackwater includes higher risk applications, such as above ground irrigation, it is critical that the treatment system be fully validated, challenge tested and monitored in real time. There is potential for litigation if systems are not designed, installed and operated properly.
“It is also important to establish the viability of a proposed installation in relation to both capital and operating costs and the potential cost/benefits. At the same time, however, the benefits of future-proofing a building should be taken into account as well as the projected future cost of mains water.
“Blackwater treatment systems can be retrofitted, but they are generally more expensive because the existing site may need to be altered. Available space with a high roof line will be needed – perhaps in a basement or loading dock area.”
WJP Solutions has completed a number of major blackwater treatment system installations including at the CBW Building in Melbourne, which accommodates a population of 7462 people. The system has a capacity of 100 kilolitres per day and the recycled water is used for both toilet flushing and cooling towers.
ANAEROBIC AND AEROBIC SYSTEMS
Diston Sewage Purification, based at Lilydale in Melbourne, specialises in small- to medium-sized sewage treatment plants for commercial applications based on a combination of anaerobic and aerobic technology.
According to managing director Matthew Diston, system designs can vary depending on the site and type of application. “We deal with a wide variety of sites – from golf courses and resorts like Uluru to remote locations such as outback mining communities, and even a base in the Antarctic,” Diston says. “As a result, our systems are often custom designed and site specific, and output capabilities range from 3000 to 300,000 litres per day depending on the requirements of the site.
“In the case of remote locations, systems are sometimes designed to be installed in shipping containers, while in more developed urban areas systems they are likely to be larger and can be capable of producing up to 300,000 litres per day of high quality treated blackwater.
“In urban areas sewer mining is also becoming more prevalent, but this needs to be carefully managed as it has the potential to lead to an increased concentration of waste and a reduced hydraulic loading, which in turn can adversely impact community treatment plant operations.”
Diston Sewage Purification provides complete wastewater treatment turnkey packages including site evaluation, consulting services, EPA Environmental Improvement Plans and Works Approvals, site works and installation, commissioning and ongoing maintenance services.
Sydney-based company Aqua Clarus offers the compact Ultra-flo 5000 system that can treat up to 10,000 litres of blackwater per day and is suitable for a range of applications, including small apartment blocks with around 40 residents. In addition, larger commercial systems based on the same technology, but with a capacity of up to 300,000 litres per day, are also available.
Company director Roy Ames says the Ultra-flo 5000 is a modular membrane bio-reactor unit 1.4 by three by 2.2 metres that can be skid mounted and consists of anaerobic and aerobic chambers, filtration and backwash pumps, and ultra-fine membranes. The liquid to be treated is collected in a feed tank, then screened and pumped to the membrane bio-reactor unit.
“On entering the bio-reactor, the liquid is treated in the anaerobic chamber and then flows to the second chamber where it is treated under aerobic conditions. During the filtration cycle, the liquid from the second chamber is pumped through a strainer to the membrane cartridges and then to the product backwash tank. This is followed by membrane backwash, with the backwash returning to the first chamber.
“After some time the membranes will foul, causing a drop in product flow and requiring a regeneration procedure to be carried out. This can be done automatically by dosing the backwash water as it is pumped to the membranes.
“The membrane bio-reactor process can be followed by UV treatment and some chlorine dosing if required by authorities. No pump-out, de-sludging or physical removal of solids is required, and proper operation and maintenance of the system can result in up to 60 percent reduction in mains water usage.”