3.- Water recycling of contaminated water used in cleaning hulls of boats

ENVIRONMENTAL PROJECT AT MAJOR MARINA IN VICTORIA B.C.

CASE STUDY N°.: 3

Like many marinas around the country, The Royal Victoria Yacht Club in Victoria has facilities to allow members to bring their boats out of the water on a slipway where they can clean and repaint the hulls of their vessels.

This involves considerable quantities of water which can be contaminated with oil, pain solvents, copper residues and sludge.

For years, this contaminated water was disposed of into the sea with the potential to harm aquatic life.

Over the past 2 years, the majority of marinas in British Columbia were visited by inspectors from Environment Canada who, together with the Department of Fisheries and Oceans has the responsibility for ensuring that contaminated water do not exit into rivers, lakes and oceans. The purpose of this 2 year program was to indicate to the marina operators and users that past practices of disposing of contaminated waters into the water systems were no longer permitted. All marinas were given until March 2007 to comply with the permissible levels of contaminants stipulated in the legislation. These limits included heavy metals such as copper, zinc, lead, mercury and iron. Chemical Oxygen Demand (COD), Biological Oxygen (BOD) and Total Extractable Hydrocarbons (THE).

In December 2006 an Environmental Canada inspector visited the marina, investigating a reported disposal of contaminated wash water into the sea. It was indicated to the marina personnel that this action was no longer permissible and the facility was given until the end of March to remedy the situation.

Petro Barrier Systems Inc. (PBSI) had already announced that a comprehensive system was available to treat and clean contaminated waters to meet the requirements of the Federal regulations for COD, BOD, and TEH. PBSI also believed that a new filtration system for heavy metals would significantly alleviate the metal problem, even achieving clean-up levels as low as 5ppb copper.

The marina approached PBSI requesting a review of their problems, indicating that they would be interested in a solution that would allow them to recycle their wash water and use it for watering the lawns around the property.

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Description of Process

The boats are raised from the water either along a slipway or using a lifting crane for smaller vessels and suspended above a sump which collects all the wash water containing grit, silt, oil and paint residues from the washing of the hulls.

The solids are allowed to settle and the supernatant liquid is pumped into a second sump. From there, the wash water is pumped through the pre-screen filter and into the first chamber of the 4-compartment oil-water separator. Any residual oil floats to the surface and when a sufficient layer accumulates, the oil is removed for safe disposal.

The water continues to overflow through 2 more compartments into the 4th compartment. From this chamber, it is pumped through a polishing pressure filter to remove any oil remaining and subsequently through a second pressure filter to remove any copper and other heavy metals in the water.

The treated water is fed into a holding tank for later use.

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Commissioning and Test Results

After installation, water samples from the first sump under the boat, and the exiting stream after the pressure filters were analyzed for a variety of properties as shown in Table A. These results showed a dramatic difference in the oil and copper levels.

After 2 weeks of operation, the flow of water slowed appreciably and the pumping pressure showed levels as high as 60psi, indicating some type of partial blockage. Isolating each filter in turn showed that the second filter was the culprit. On disassembling, this filter revealed a partially blocked exit pipe caused by the movement of some of the polyester felt packing. In addition, some ot the filter media had been washed away.

Although the oil filter was functioning satisfactorily, it was decided to replace both filters.

Almost immediately, the water exiting from the replacement filters was clear and colourless and the levels of oil and copper were well below the lower permissible amounts. The operating pressures were around 5psi for both filters and the water flow was 5-6 gallons/minute.

The original filters were dismantled and the absorbents examined. There was evidence of small amounts of oil in the oil polishing filter and the absorbent was quite dirty but still functioning satisfactorily.

The metal polishing filter had lost a fair amount of its absorbents and there was evidence that the colour of the contaminated water, caused by the pigmentation from the paints was being removed.

These filters, which were much larger in capacity than the replacements, were repacked and re-installed. The performance of both filters was good with pressures below 10 psi and no colour in the exiting water.

Analysis of the water before and after treatment showed how effective the system is at removing contaminants down to acceptable.

Tables B and C show the results of the testing of water samples.

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The system has been in operation for nearly 6 weeks with 1-2  boats/day being cleaned. The discharged water (2-300 gallons/day) remains clear and colorless. The copper levels are around  1ppm and the oil testout at N/D (less than 1ppm).

Discussion of Results

The complete system is proving very effective in removing oil down to very acceptable levels of less than 1ppm.

The metal removal filter is designed to remove copper, but it will also remove other metals. While this is totally acceptable, it can have an effect on the life span of the filter reactant if there are large amounts of other metal components present.

Table C shows that the total heavy metals content of the sump water was as high as 14,280 ppm with the exiting sample educed to less than 10ppm.

In this particular test, the copper content in the exit sample was higher than desired, probably due to the very high levels of metals in the original water. Subsequent testing showed the copper to be around 1-2 ppm which satisfies the current local requirements. It is believed that by some minor changes in the filtration components, it is possible to remove the copper to much lower levels.