FAVOURITES – 18 October 2010 – AIRAH conference – There was no shortage of cutting edge technology discussed at AIRAH’s Achieving the green dream conference- tomorrow’s technology today. An impressive array of technologies and their practical applications were presented by speakers over two days.
There was solar cooling, blackwater and greywater reuse, change phase materials that increased buildings’ thermal mass, co- and tri-generation, airconditioning systems using ammonia and CO2, cool roof technology, cooling buildings using seawater….. and the list goes on.
We look at two of these and lessons learnt in practice in two parts. First is blackwater and greywater reuse systems.
Nicki Colls, environmental engineer with Sustainable Built Environment, presented the findings of a survey that aimed to discover just how successful blackwater and greywater treatment systems are in practice. And the results showed that despite the high cost of the systems and problems with design, those who use these systems feel considerable pride in “doing the right thing”.
The aim of the survey was to use the information to improve design, commissioning, legislation and maintenance of these systems. Colls says there is significant variation in both uptake of both greywater and blackwater systems across Australia and in the legislation controlling their use. (see table below)
Legislation has been developed on a state-by-state basis with some recent cohesion provided by the development of the Australian Guidelines for Water Recycling, 2008.
“There is a small uptake of onsite blackwater treatments in Victoria and in Australia,” said Colls. “We’re dealing with multiple regulatory bodies and there is ad hoc approach across the states. There are also gaps in the legislation.”
Despite these difficulties, uptake and interest in the systems as well as in reuse of rainwater has increased significantly in the past five years, said Colls. This could be attributed to greater community awareness of potable water scarcity through drought, subsequent water restrictions and regulatory requirements.
“Government tenants, local authorities and development authorities have helped to move the market in the direction of increased water efficiency as do voluntary environmental assessment tools such as Green Star,” said Colls.
Greenstar does not specifically require onsite treatment and reuse of greywater and blackwater, but instead awards points for potable water savings and reduced discharge to the sewer system, which provides incentive for designers to consider onsite treatment.
Given that government tenancies had set minimum Green Star targets, it was important to review how effective wastewater treatment systems were in practice, said Colls.
Respondents to the survey were facilities managers and other professionals on buildings with onsite greywater and sewage treatment systems. The system capacities ranged from 1.2 L to 100kL and the treatment technologies varied.
Survey questions and interviews focused on the following areas:
- maintenance arrangements
- system specifics
- percentage of time the system is operating effectively
- upfront and maintenance costs incurred to date
- monitoring and reporting
- operational issues and advice for design
The key finding of the survey, said Colls, were that water treatment systems that were installed prior to 2006 had significant operational problems, while those installed after 2007 have had comparatively minor problems in becoming fully operational. The systems were expensive to run and did not pay back over their lifetime (see table below)
Average as-built capital cost and maintenance costs
System Type Average capital (cost/kL) Annual maintenance (cost/kL)
Greywater $39,000 $2,200
Sewage $31,000 $1,500
All $34,000 $2,000
Net Present Value of Systems to building owners
Average NPV Minimum NPV Maximum NPV
Per kL Capacity $44,000 $8,500 $53,000
Per person equivalent $9,000 $1,600 $10,600
Other findings included:
- large variability in length of time taken between installation of system and effective operation with those prior to 2006 taking longer
- delays in commissioning caused by membranes clogging, pump needing replacement, change in chemical dosing and installation of improved monitoring equipment
- on average treatment systems were oversized by 11%
- usage patterns and daily rainfall forecasts need to be used to size systems more accurately
- all systems used external contractors for ongoing maintenance
- main maintenance problems –membranes clogging and fouling, equipment failure and lack of contingency in design
- systems do not pay back over their lifetime because of low cost of mains water and high running costs of the systems
- user perception – building operators felt users were mostly unaware of the reuse systems on a day to day basis. Most common complaints were smell, noise and straw coloured water.
Irrespective of these problems, “building operators still expressed a sense of pride in the systems and felt that it was the right thing to be doing,” Colls said.
“But there is a need to reduce the overall maintenance on water re-use systems. Right now it is negating the positive cost benefits of using less water.”