Introduction
Whangamata Marina is a leader for recognising the importance of doing as much as practically possible to protect the receiving environment around the marina – to set new standards for this in NZ.The Whangamata Marina is one of New Zealand’s newest, and one of only three on the popular eastern seaboard of Coromandel Peninsula, catering for predominantly recreational vessels. As with most marinas the site has significant maintenance haul-out area and a hull water blasting facility.
After construction on the Whangamata Marina, which started in 2008, marina management realised that the mixing of boat maintenance wash water, which is high in anti fouling paint contaminants, with stormwater was causing a non-compliant situation. This issue would also cause unnecessary impact on the Whangamata Estuary and the bay.
In 2010 IWS was employed to initially develop, design and have consented a wash water treatment solution. In the IWS's opinion is always good practice to separate industrial wash water from stormwater and to treat these separately. This approach was pursued at the marina with a Wastewater Treatment Plant being installed to sit along-side the existing stormwater treatment measures already in place (a cartridge filtration system).
Design and Construction
In 2014 the project moved on to become a Wastewater Treatment Plant design project. The project had 2 distinct elements – the first being to collect wash water and first flush stormwater from 2 areas on site, transferring these to a storage tank. The second element of the project was to remove the particulate and dissolved contaminants within the wash water into a recovered solid and into a ‘clean’ water stream that could be discharged back into the marine environment, or into the public sewer.
The collection system is set up to take wash water and a reasonable portion of first flush stormwater. The transfer system responds to rainfall depth and to storage capacity remaining in the system. If areas on the hardstand are not being used to bypass the system, meaning that no unnecessary rainfall is treated.
The treatment system starts with a 22 m³ storage tank which is mixed by air to suspend solids and control odour. When there is adequate wash water to treat, which can be up to a batch of 15 m³ in volume, the mixed wash water is transferred to the Chemical Treatment Tank. To control the variable strength of the wash water a batch treatment process has been elected. During the mixing of the batch a flocculation and pH adjustment process takes place. This results in a clear water that is able to be drawn off the tank and returned to the sea or to the sewer, and a wet sludge in a conical base of the CTT.
At this point the wet sludge could have been removed for off-site treatment at a Liquid and Hazardous Waste Facility. This is not practical at a remote town so a dewatering system was also installed. This reduces the wet sludge to a dry filter cake suitable for landfill directly. The control of the system is semiautomatic. The operator is required to check the dosing chemical supply and to initiate the treatment process. The operator also sets up the dewatering device – a Plate filter Press – which in this case uses a pre-coating product. Periodic checking of such things as the pH calibration is required.
Results
Comprehensive analysis has shown very high levels of contaminants in the wash water that comes off antifouled hulls. The range of contaminant concentrations is broad in undiluted wash water. Typical Copper and Zinc levels, measured as total heavy metals, are around 50g/m3 and 70g/m3 respectively. With basic settling alone, this wash water will exhibit a metals load at around 2 to 5g/m3 for both Copper and Zinc. The release of this level of contaminants into the natural environment, and even into some public sewer networks, is not sustainable.
With the forced removal of the paint fines and other contaminants as occurs in the Whangamata Marina plant, the discharge of treated wash water exhibits a total Copper and Zinc heavy metal concentration of less than 0.05g/m3 for both metals. At this level the discharge becomes much more sustainable.
Each 15 m³ batch of wash water at Whangamata Marina produces about 200kg of dry filter cake which originates from 5-10 boats. This best practicable option approach substantially reduces the contaminant load in the water column, and in the bed sediments, of the marina. This also means that a lower level of contaminants passes out into the estuary and further on out to sea with each change of tide at the marina.
"The IWS team were extraordinary in their handling of this project for us. From preliminary testing, to plant design, to Regional Council consent, construction supervision, commissioning and most importantly, ongoing post commissioning support and back up, no one could ask for more."
John Gillooly
Marina Manager
07 865 6274
