The NRSBU can be proud of a range of initiatives it has undertaken over the past decade, or more, which by today’s standards would be regarded as sustainable development.
Prior to the scheme being in place, there were many point source discharges of partially treated and untreated effluent into the estuary. Monitoring every five years of the receiving environment shows a continual improvement in the water quality and benthic environment since the treatment plant was installed.
The asset management plan for the scheme takes into account sustainability efforts in four areas:
A plant upgrade in 1996 allowed for the application of high quality biosolids to be used as fertiliser on local forest areas. The forests at Rabbit and Bells Islands have experienced wood volume increases between 40 and 50 percent with negligible decrease in wood density. In addition, the soil now has a better structure.
The contracts between NRSBU and its five customers are the first of their kind in New Zealand. The contracts apportion costs, control discharges and minimise environmental and financial risks to the owners. The contracts put in place
In the early 1990s the oxidation ponds at Bells Island Treatment Plant were overloaded because the sludge had built up. As part of an upgrade to the plant in 1993/4, the pond sludge was removed and applied to the sandy, infertile paddocks surrounding the ponds. For the first three years the grass was cut for silage and ever since it has been leased for grazing.
Peak wet weather flow (PWWF) can be up to six times the average daily dry weather flow (ADDWF), so reducing the inflow and infiltration reduces the cost of reticulation and treatment, as well as overflow risks.