The scarcity of water is an intrinsic part of life in most of Australia. Better use and conservation of this vital resource will improve the quality of life for many Australians, especially those who live and work in the semi-arid region surrounding Whyalla in South Australia, where BHP Steel's Long Products Division (LPD) has been operating a steelworks since 1964.
Water is essential to the operations of a steelworks, being used for cooling, cleaning, lubrication and numerous other purposes. In Whyalla it is a scarce and expensive resource. BHP Steel is keen to reduce water consumption and is also aware of the need to efficiently treat waste effluent before it is discharged.
Studies over a number of years have looked into LPD's waste water discharges into the Spencer Gulf. The studies have identified the effluent from coke ovens as a significant source of organic matter and ammonia. BHP Steel needed to reduce and/or eliminate these materials from its waste water prior to discharging it.
Cleaner production initiatives
Within LPD, the reed bed technology was first identified by a Superintendent of the coke ovens, while visiting British Steel's operations at its Llanwern Plant in the UK. The reed bed technology used at British Steel was founded in Germany by Professor Reinhold Kickuth during the 1960s. In Australia, reed beds have been used for stormwater run-off and sewage treatment, but little is known about other uses. The Llanwern plant represented the first reed bed technology trial on coke effluent.
In artificial reed bed systems (also known as constructed wetlands), the effluent to be treated percolates through the soil and roots of a large bed of reeds and then drains through a pipe at the base of the bed. The function of the reeds is to pump oxygen into the soil through the roots. Near the roots, there is an aerobic (oxygen-containing) zone and further away, there is an anaerobic (oxygen-free) zone. Thus, within the soil, a range of processes exist that allow the transformation of environmentally undesirable components of waste water.
BHP Steel hired a consultant to manage the trial and the subsequent full-scale system. BHP commenced construction of the trial beds in February 1993. Surveys of reeds in the surrounding areas were undertaken and information on reeds best suited to waste water treatment was reviewed. Accordingly, five reed varieties, all of Australian native species, were selected to make up the trial. Once the system was established the process of adapting the reeds to the effluent was started.
The aim of the trial is ‘to determine the reed best suited to Australian conditions in Whyalla for BHP Steel's coke oven effluent’. However, other benefits of the trial have become increasingly important, leading to further objectives for a full scale system. These include:
the possibility of producing potable water from the reed beds, thereby improving the quality of the input water and creating a valuable resource for Whyalla; and
investigating the development of an artificial soil, due to lack of suitable soils in the area for a full scale system. Reed bed systems utilising an artificial soil already exist in Europe, making this a viable option.
The trials suggest that the eventual construction and operation of a full-scale system appears to be realistic. This prospect is attracting considerable interest in Whyalla and other surrounding country towns. The Whyalla City Council is now also installing a wetland for stormwater. Regulatory authorities have taken a keen interest in the developments, recognising the significance of this trial for the use of reed bed technology for industrial chemical effluent treatment in Australia.
Advantages of the Process
Potential benefits include:
- improving the quality of LPD's fresh waste water discharges into the Spencer Gulf;
- recovery of a valuable resource of fresh water for recycling on the plant;
- improving the quality of reclaimed land that previously had no value in the coke ovens area, while improving the
- visual appearance of that part of the plant;
- reducing the impact of wind blown dust in an area with no vegetation; and
- providing a shield against the searing hot north winds during the summer months.
Cleaner production incentives
Alternatives to a reed bed system include a conventional biological treatment plant similar to that at BHP Steel's Port Kembla works in New South Wales. Such an approach has a capital cost of $12-14 million and involves greater operating costs. The projected cost of establishing a reed bed at Whyalla is $5 million. Reed beds only require electricity to carry the effluent system, after which nature looks after the rest through naturally occurring processes.
BHP’s publicly declared philosophy is that:
'BHP is committed to continuous improvement in all its activities. As environmental management is an integral part of the way we do business, this commitment manifests itself in our environmental approach to both existing and new facilities. We encourage innovative approaches as well as the use of proven technologies in order to get the best solution for each individual situation.'
This philosophy can be seen in action in the reed bed trials.
Strong winds, dusty conditions, hot summers with high evaporation rates, salts within the soil and water, have all posed problems at various stages. These setbacks have gradually been overcome through modifications to the successful European design to suit Whyalla's environment. The results of the trial to date, to a large extent, reflect the effort which has been put into monitoring and managing the system. These results have been mixed, as would be expected with the first trial application of the reed bed technology to coke effluent in Australia.
Resources similar to those used for the reed bed construction in the UK have not always been easy to source in Australia, particularly those of good-quality land and clay. At the British Steel system site, the soil in the area was excavated, and ponds lined with the excavated soil. Suitable soil for the trial reed bed at Whyalla had to be identified through extensive soil sampling because of the high salinity in the area. Due to the shallow water table in the Whyalla works area, the trial beds had to be built up from ground level. This would also be the case for a full-scale system.