|
On
The Mend
 |
 |
| |
Each
of the new plant's twelve egg-shaped "digestors" can breakdown
3 million gallons of sludge |
In
1985, two federal agencies, the EPA and the Department of
Justice, sued the Commonwealth of Massachusetts for non-compliance
with the 1972 Clean Water Act. The Massachusetts Water Resource
Authority (MWRA), charged with the task of getting the state's
sewage treatment system up to federal standards, embarked
on one of the largest public works projects ever- cleaning
up Boston Harbor.
In 1989, construction began on a brand new sewage treatment
plant to replace the badly outmoded plant built two decades
before. Now the second largest treatment facility in the United
States, the Deer Island Sewage Plant sends 380 million gallons
of sewage each day through a series of physical, biological
and chemical purification processes.
The
color and smell of the water improved noticeably, bacterial
levels dropped off, and the harbor-dwelling flounder had
fewer tumors
|
|
First,
about half of the suspended solids, pathogens and toxic contaminants
settle out of the wastewater as it passes through a series
of specially designed troughs. These pollutants, called sludge,
once would have been dumped right into the harbor on the outgoing
tide. But since the 1991 completion of a recycling plant that
turns the nitrogen rich sludge into fertilizer, some 4 million
tons have been diverted from the harbor and put to good use.
Next, waste-loving bacteria consume any remaining organic
matter, leaving the water about 85% clean. Finally, chlorine
is added to kill the bacteria and other pathogens and is then
removed to make the water safe for marine life.
Within a year, conditions in Boston Harbor improved greatly,
thanks to the tides that flush it out twice each day. According
to Andrea Rex, Director of Environmental Quality at the MWRA,
the entire harbor turns over about once a week.
"That's what kept it from becoming an open sewer for
so long," she says. "And that's what helped it recover
so much more quickly than we thought it would."
The
color and smell of the water improved noticeably, bacterial
levels dropped off, and a follow up survey found that the
harbor-dwelling flounder had fewer tumors than before. Moreover,
the pollution-loving capitellid population gave way to amphipods,
an important first link in a much more diverse food chain.
People began to report sightings of fish, seals and porpoises.
"It's succession in action," says Rex. "It's
quite interesting to watch this happen"
-
- - - - - - - - - - -
4
pages: | 1 | 2 | 3
| 4 |
Photos:
MWRA; USGS
|
