Too green, too fast: dry drains
In our rush to adopt water-saving technologies in commercial buildings, many building managers have failed to consider the engineering consequences of sudden drops in water flows, particularly wastewater flows through sewerage pipes. HARTLEY HENDERSON examines the nightmare of ‘dry drains’.
Faced with the effects of climate change and the associated challenges of drought and water shortages, together with the water demands of growing populations, governments around the world are pushing for water consumption to be reined in.
In response to such mandates, the plumbing and building industries have taken action on a number of fronts in recent years to design and produce a range of water-saving appliances and fixtures, including dual-flush toilets, waterless urinals and low-flow shower heads.
These developments, combined with extensive water conservation community education programs and government incentives, have led to significant reductions in water consumption.
Continual reductions of water flows in the plumbing systems of buildings, however, have resulted in ‘dry drains’, whereby flows may be insufficient to effectively flush toilet discharges through the piping system.
The situation is further compounded with a trend to extract greywater from plumbing systems for reuse.
This issue is of international concern, to the extent that the recent ISH Frankfurt trade fair in Germany – the world’s largest plumbing expo – was complemented by a Dry Drains Forum.
Dr Steve Cummings, research and development manager at Caroma, was a speaker at the forum. He outlined the investigations undertaken by the ASFlow (Australasian Scientific Review of Reduction of Flows on Plumbing and Drainage Systems) committee into the influences of reduced flushing volumes from toilets and their compatibility with junction configurations.
“The results show that the design of current drainline systems and fitting configurations will need to be adapted to match the performance of future new ultra low-flow WCs,” says Dr Cummings. “There is a need to develop sustainable plumbing solutions and practices, as a further reduction in flow has potential to change the basic function of plumbing and drainage systems that have been operating effectively since the 19th century. Already the work by the ASFlow committee has brought about changes to the plumbing code.
“It is important that pipework be installed effectively with junctions configured to minimise hydraulic jump. For example, our investigations show that horizontal sweep junctions can dramatically affect WC drainline transportation, creating significant backflow and reducing toilet drainline transportation performance.
“In the case of waterless urinals, two basins installed upstream from a waterless urinal will reduce struvite build-up [formed by crystalline deposits in nutrient-rich wastewater] within the drainline.”
In addition to the development of Smartflush technology for toilet suites, which uses only four litres of water for a full flush and 3.5 litres for a half flush, Caroma also offers the H2Zero Cube waterless urinal. This urinal (pictured above) utilises cartridge technology with a bio-seal, rather than an oil-based seal. The bio-seal acts as a one-way airtight valve to seal the cartridge from the drainage system.
Paul Marsh, managing director of Watersave Australia, supplier of the Danish-designed Uridan waterless urinal, points out that waterless urinals were first developed in Switzerland in 1894 and have been in everyday use in Australia since 2003.
“There are several different types of waterless urinal available today, which can be divided into two groups: those that have been certified to Australian Waterless Urinal Standard ATS 5200.459:2004, and those that are additions to an existing flushing urinal. A flushing urinal that is no longer flushed will effectively leave the user exposed to the urine left in the trap because there is no longer a seal between the user and the sewer system,” Marsh says.
“Certified waterless urinals can also be divided broadly into two groups: those with a mechanical seal, and those with a liquid seal between the user and the sewer system. In both cases, the seal will need replacing or cleaning periodically to ensure the urinal works effectively.
“The Uridan has an in-built water trap and utilises a biodegradable odour-blocking fluid (Urilock), which is poured into the water trap. The Urilock fluid floats on the surface of the urine, creating a seal to block any urine odours. When the urinal is used, the urine drains through the Urilock and into the drainage system. Providing the urinal is cleaned daily according to instructions, the urinal will not smell.”
Marsh says Uridan waterless urinals carry WaterMark certification and have been installed in a wide range of facilities including office buildings, sports centres, public amenities, airports, hotels and schools across Australia and around the world.
MICROBES TO THE RESCUE
Desert Eco Systems markets Desert Cubes that utilise microbial technology and are designed to turn existing trough or bowl facilities into touch-free waterless urinals.
The company’s general manager, Chris Donaldson, says that urine itself is not the main cause of urinal odours. “Urine is almost 98 percent water, mild in odour and usually sterile. The problems begin when bacteria bind with the solids found in urine and create an offensive smell, and bacteria and water scale build up to create lumps of uric acid large enough to block pipes,” Donaldson says.
“The microbial technology incorporated in Desert Cubes, which sit in the bottom of the urinal, interferes with the bacterial digestion that produces unpleasant odours from uric acid. Simply add the cubes to your existing urinal and deactivate the flushing button.
“With the addition of the ‘Smart’ sensor-based flush timer, you can guarantee a small flush of water only on the days when the urinal is being used. This will ensure that the pipes are kept clean and the microbes keep active.
“With the average urinal flushing 151,000 litres each year, this small blue cube could reduce that by up to 98 percent.”
DRY DRAIN SOLUTIONS
Hobart-based company, Ducane Research and Development, has released an in-line flushing device called Drainwave (right), which, the company believes, will play a major role in overcoming the dry drain issue.
Managing director David Fisher says Drainwave is designed to minimise the risk of blockages that may be caused by the use of low-flow fixtures.
“By collecting and combining blackwater and greywater and releasing it in batches, Drainwave provides toilet waste with a minimum 9.5 litres of accompanying water,” Fisher says.
“The device consists of a receptacle with a swinging bucket that holds the wastewater from the various fixtures until the 9.5-litre capacity is reached. The bucket then tips to create a surge through the pipe network.
“Located underground outside a building, Drainwave is easy to install, can be retrofitted, does not require any power and consists of only one moving part.”
A recent study by the UK’s Environment Agency recommends that, for new buildings, a revision of existing drainage design standards be undertaken to accommodate planned reductions in water demand. These alterations could include the use of smaller diameter pipes and pipes with steeper gradients.