Mechanical Dredging
For many years, dredging has been the solution
for dying ponds and rivers. Dredging removes sediment, some excess nutrients,
pollutants and organic matter. By increasing the depth in this way, weed
growth is discouraged, water temperature lowered and oxygen levels increased.
Though dredging can help in these ways, it only solves part of the problem,
and causes some others.
Mechanically removing sediment is extremely
disruptive to the aquatic ecosystem.
Removing sediment and organic matter also removes the plants and animals
of the bottom community, which form the basis of life for higher animals.
Further, dredging does not often consider what the natural contours of a
waterway should be. Near-shore areas are deepened, eliminating shallow habitats,
spawning and rearing grounds, changing natural flow patterns and precluding
recreational uses such as swimming. The sudden increase in turbidity further
degrades water quality, stressing fish and other organisms, sometimes fatally.
The changes in light patterns throw off reproductive cycles. It can take
weeks for the water to settle down, and in the end, the system is completely
unbalanced. |
Bio-Dredging
Using nature to heal itself is a gentle yet
powerful way to treat a disturbed ecosystem. Water quality problems are
often due to a combination of factors and are manifested in a number of
ways. Poor water quality does not end with sludge removal. The water
column may be polluted by industrial effluent containing everything from
table salt to cyanide. Runoff and sewer discharge may contain fertilizer,
pesticides, road salt, oil and gas. It is the combination of these pollutants
in addition to the detriments of sludge that leads to a dying water.
Bacteria have evolved for millions of years,
in any number of habitats, with an appetite for a surprising number of compounds.
Indeed, one of their roles in nature is to turn complex substances, no longer
usable to other life forms, back into simple, usable compounds.
Introducing bacteria in large quantities into
a polluted system merely transplants nature's engineering to the right place
at the right time. Bacteria will degrade sludge and pollutants dissolved
in the water column, turning them into carbon dioxide, water and bacterial
biomass. As the system returns to normal, the water becomes clear, the
sludge disappears, and nature takes over, restabilizing the topography and
ecology. The bacteria themselves will die back to a normal population
once their food source is diminished. If additional polluted influent will
continue to arrive in the environment, a maintenance program will be setup,
following biodredging, to keep the water clean and prevent formation of
future sludge.
Biotechnology is both more complete as a treatment
and far less expensive than mechanical treatment. Wet dredging has been
estimated to cost approximately $40,000 to $150,000 per acre-foot of sludge,
while Alken Clear-Flo® products (1005,
1006 & 1015,
depending on the level of contamination, costs 35 to 50% of the cost of
mechanical dredging, while accomplishing simultaneous water cleanup, the
opposite of mechanical dredging, which usually contributes increased pollution
while buckets of sludge are dug up and dragged from the waterway.
In some cases, additional equipment, such
as aerators and bioreactors, is needed, however, total cost is still well
below that of mechanical dredging. Bacterial treatment avoids unsightly
machinery, ramp building and mounds of sludge. It also avoids creating a
second environmental problem: disposing of the sludge. There are few limitations:
Bacteria cannot degrade dirt, rock, sand or other inorganic substances.
Alken Clear-Flo® cannot survive in fluctuating
extremes of temperature and pH or when high levels of metals or biocides
are present. Otherwise, there are few limitations. |
