Benthic Ecology Research Programme - Ashblocks

Bermuda has historically disposed of waste such as trash from homes and businesses by burying it in a landfill.  However, the landfill was nearly full by the late 1980's and there was no room to expand it.  No one wanted, on this small crowded island, to provide the land for another landfill.  The government decided that the best solution was to burn the waste in an incinerator on the North Shore of the island. 

When you burn something, there is always some ash left over.  Just imagine what would be left over if you burned the trash from your house, including the old toaster, that toothpaste tube and other stuff that do not  really burn!  You are left with piles of ash that must go somewhere.  You might wonder what the advantage of using an  incinerator is if there is so much stuff left over. But really only about 5 to 10 percent  is left so you can greatly reduce the amount of trash that needs to be disposed of by using an incinerator.   Still, there is the problem of what to do with the residual ash which has high amounts of poisonous metals and other compounds.

The solution was to mix the ash with concrete and make large square blocks that could be dumped into the ocean and used to form new "land".  In fact, the blocks could be used as a retaining wall for trash that could not go in the incinerator, such as cars, refrigerators and other big hunks of metal or concrete!  The blocks would go into the ocean and other trash would be dumped into the water as well. Then everything would be covered with dirt when it got near the surface.

Before going ahead with the plan, the government decided to study what would happen to the blocks once they were in the ocean.  What could happen to concrete blocks?  Concrete is very similar to the material that forms the coral reef  (calcium carbonate) and there are many organisms that can bore into, or eat the surface of the reef.   If these organisms did eat the blocks, the toxic metals and other chemicals could kill these organisms or become part of the food chain and eventually end up threatening the health of other animals including humans! 

This picture shows a pile of the ash blocks set down at about 30 ft in Castle Harbour near the airport where the landfill for the large items is located.  You can see that the blocks are covered with what looks like fuzz which is really a wide range of organisms that have colonized the surface, especially algae. 

Artificial ash block (impact) and concrete-only (control) reefs were set up in Castle Harbour and in Tynes Bay near the incinerator and continue to be monitored on an annual basis.  Two aspects of the potential fate of chemicals from the blocks and effects on organisms have been studied since they were installed in the winter of 1992.  So far there has been no clear evidence of increases in the levels of trace metals (copper, cadmium, lead, zinc and nickel) in sediments adjacent to the ash reefs compared to the concrete-only control reefs in either Castle Harbour or Tynes Bay. These results would indicate that the ash blocks may be only very slowly releasing contaminants into the environment

Using photographs, we have monitored the community of organisms living on the artificial reefs.  At present, the abundance and diversity of animals (sponges, tunicate and corals) living on the surfaces of the Castle Harbour and Tynes Bay ash blocks are comparable to the concrete-only control reefs.  This suggests that the  toxicity of the ash blocks is low,  allowing more animals to colonize the reefs as well as for more growth of organisms that have been present on the blocks for some time, e.g.  encrusting sponges

Since the original blocks were made from ash from incinerators off the island (ours wasn't working yet ), in 1996 we had the opportunity to create an artificial reef made from Tynes Bay incinerator ash.  Very little colonization took place over the summer months except for minute algae.  Based on the results of the original sets of ash reefs made from imported ash in 1991, it may take one to two years before significant numbers of organisms begin to appear on the new reef

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