Wetlands as water treatment

wetland is a distinct ecosystem that is flooded by water, either permanently or seasonally. Wetland species such as rushes and reeds are known to absorb nutrients from the water, and filter oil and bacteria.

A wetland can be designed and planted for the purpose of treating grey water (sewerage effluent), such as that which is proposed to be pumped out to sea at Merimbula.

Wetlands are part of the wastewater management strategy for Byron Bay’s Sewage Treatment Plant (STP), in what is called the Integrated Water Management Reserve (Byron Wetlands). These wetlands not only minimise the impact of sewage on surrounding ecosystems, but enhance the natural environment, supporting a diversity of native fauna, including threatened species of birds, mammals and amphibians.

“There’s no such thing as wastewater in Byron Bay – only resource water,” quipped wetland designer Dr Keith Bolton.

Why have the Bega Council ruled out Wetlands?
The BVSC’s project manager said; “There is no problem with having wetlands per se. The issue at least in NSW is that the wetlands won’t be licenced by the EPA as part of an engineered treatment process because the wetland may take up pollutants at times and then shed them at others (i.e. it’s inconsistent). So the discharge parameters (water quality) is set at the inlet to the wetland and the wetland is treated as the receiving water from a licencing perspective.”

BVSC Water and sewer engineer, Chris Best said “Byron only reuse 40 per cent of their treated wastewater in reuse schemes. The rest falls through the wetland and into groundwater or the creek which goes to the ocean. They are getting 30 per cent reuse and have a lot of farms on flat land within easy reach but they are spending another $30m and hoping to reach 80 per cent reuse. They have already spent over $100m for a sewage treatment plant upgrade but they still have to keep their outfall.
“Constructed wetlands are a valuable way of encouraging wildlife and polishing treated effluent under some circumstances. Unfortunately, the Merimbula and Pambula areas are highly constrained, and wetlands are unsuitable for the following reasons.
“If constructed wetlands were to be utilised, the outflow from them would need to be directed to Merimbula and/or Pambula Lakes posing an added risk to oyster farming, and to the recreation and aquatic ecosystem values associated with those lakes. Likewise, constructed wetlands present a risk to natural pristine wetlands such as Panboola.
“Significantly, wetlands have variable performance due to seasonal/climatic factors and consequently they fall outside NSW EPA licencing provisions. This means that NSW EPA will prescribe treatment performance (via Licence conditions) at the end of the man-made treatment process and exclude any notional benefit that wetlands may provide.
Furthermore, using our pristine lake and wetland environments as receiving waters for treated effluent is unlikely to be supported by the NSW Office of Environment and Heritage (OEH) or its successor because such a use is not aligned with the aims of the Coastal Management Act 2016.
“Wetlands require a large land area and a suitable discharge location for water flowing from them. There is no identified available land or suitable discharge location for a constructed wetland near Merimbula STP.”

BVSC Director Assets and Operations added, “Whilst the Pambula/Merimbula area is unsuitable for constructed wetlands, a large area of Council owned land adjacent to Bega STP may provide an opportunity for a constructed wetland. In this situation there may be significant environmental gains particularly since the reuse scheme associated with the adjacent dairy is no longer in operation. A scoping assessment is currently being undertaken by specialist wetland consultants. From a practical perspective, Wetlands in the Merimbula STP context will not remove the need for a sustainable disposal system and they will simply add a cost overhead to any treated effluent disposal solution.”

Why SWAMP questions BVSC’s explanation:
Byron Bay receives almost double the rainfall of Merimbula, so 40% of their treated waste water equates to almost 100% of Merimbula’s volume of wastewater.
If a wetland system is not possible near Merimbula/Pambula, then it could be situated in Wolumla or Lochiel, and the outflow used for irrigation.
As the wetlands are NOT part of a treatment process, occurring after the grey water has left the treatment plant, the EPA licencing issue will be eliminated. This is similar to the constructed wetlands at Byron Bay and East Gippsland.
In BVSC’s community consultation Factsheets, it says “AECOM consultants have undertaken a desktop review of soil data and conducted water balance modelling to optimise the irrigation potential across the four Wolumla properties. Modelling estimated that around 1,036 ML or 3.7 ML/ha/year could be sustainably used on an average year. This would equate to about 148% of the total existing volume of effluent discharged from the STP per annum.”
Therefore, all the recycled water produced by Merimbula STP could be directed and reused in the combination of wetlands, water storage and irrigation in the Wolumla and or Lochiel areas, thereby helping our dairy industry to minimise the impact of drought conditions.
All successful water-recycling schemes are seldom achieved by one single solution Often a combination of systems will be required. While a Byron style wetlands might not be a perfect solution for Merimbula, we need to learn from other shires in providing a solution for the South Coast.