The Possible Future of Septic Systems
By CYNTHIA DRUMMOND/ecoRI News contributor
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| An advanced nitrogen-removing septic system at a home near the coast in Charlestown. The town is working with researchers at the University of Rhode Island to develop a less-expensive and energy-efficient system to remove nutrients before they enter local waters. (Cynthia Drummond/for ecoRI News) |
A simpler, less-expensive, advanced on-site wastewater treatment system will soon be undergoing field tests in Rhode Island.
In the coming weeks, the
Rhode Island Department of Environmental Management (DEM) is expected to
approve a pilot project to test an experimental nitrogen-removing septic system
known as “layered soil treatment area” — or LSTA for short.
Proposed by a consortium
of the town of Charlestown and the University of Rhode Island’s Laboratory of
Soil Ecology and Microbiology and New England On-Site Wastewater Training
Program, the non-proprietary septic system would put nitrogen-removing
technology within reach for more coastal homeowners.
Since 2008, the state
has required that failing septic systems in the coastal zone be replaced with
advanced nitrogen-removing wastewater treatment systems. The requirement also
applies to new construction and to major rebuilds.
However, despite the
more-stringent regulations, nitrogen pollution, which causes algal blooms,
oxygen depletion, and fish kills, continues to be a problem.
A 2016 study, funded by
a $674,000 grant from the Environmental Protection Agency, $20,000 from the
town, and in-kind contributions from the Salt Ponds Coalition and Save The Bay,
showed that even with advanced treatment systems, nitrate levels in groundwater
in some Charlestown neighborhoods and in the town’s salt ponds remained high.
Now, armed with a
$250,000 grant from the town, the consortium is proposing to replace several
failing conventional septics with LSTA systems, which will be monitored for
several years to determine their efficacy.
DEM supervising
environmental engineer Mohamed Freij said the LSTA system, which uses gravity
and a single, small pump, has several advantages over conventional advanced
treatment systems.
“The typical
denitrification system relies on pumping and circulating the water in different
tanks to do denitrification, so there is a pumping process going on
constantly,” he said. “It takes power, and there’s a vent and there’s a fan and
there’s all kinds of stuff.”
As expensive as they are
to install, conventional denitrification systems can also be expensive to
operate. In addition to regular maintenance, they can add $50-$100 a month to a
homeowner’s electric bill.
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| Views of the prototype advanced on-site wastewater treatment system to be tested in Charlestown. (Alissa Cox/URI) |
The LSTA process is simpler. The effluent first passes through a layer of sand and then moves down to a second layer, which, in addition to sand, contains sawdust and mulch.
Freij explained that the
second layer removes the nitrogen.
“When the nitrates hit
that layer, the bacteria strips the oxygen from the nitrates and the nitrogen
gas escapes into the soil and you will have less nitrogen-loading to the water
table,” he said.
Consortium member Alissa
Cox, program director at URI’s New England On-Site Wastewater Training Program,
noted that the LSTA system is non-proprietary, one of the reasons it costs
thousands less than a conventional system.
“Nobody owns a patent to
this,” she said. “We don’t have to put R and D [research and development]
dollars into this.”
Matt Dowling, the town’s
on-site wastewater manager, noted that he has these systems budgeted at $20,000
each for installation, components, engineering, and design.
“They are highly
effective, and they’re simple and they’re passive and they’re cheap,” the
environmental scientist said.
The LSTA concept has been around for a while, and was first proposed in Canada in the mid-1990s by University of Waterloo professor Will Robertson. The system is already approved for use in Connecticut and is currently being tested in Massachusetts by the Barnstable County Department of Health and the Environment and in Suffolk County, N.Y.
Professor José Amador,
of URI’s Laboratory of Soil Ecology and Microbiology, said it was time to begin
testing LSTA systems here in Rhode Island.
“It’s going to be a
while before we know everything we need to know about it, and that’s why the
project that the town of Charlestown wants to carry out and fund is really
important,” he said. “Because it’s a non-proprietary technology, nobody’s going
to make any money selling these things and so what’s the incentive, other than
universities and towns interested finding out how well they perform.”
Dowling said four experimental
LSTA systems would be installed at homes with failing septics near Green Hill
Pond.
“We did an analysis to
find the most densely developed area of Charlestown, meaning the most densely
OWTS [on-site wastewater treatment system]-heavy portion of Charlestown within
proximity to the most impacted salt pond, which is Green Hill Pond and eastern
Ninigret Pond,” he said.
Eastern Ninigret Pond is
closed to shellfishing.
Conventional denitrification septic systems can be expensive to operate. (Cynthia Drummond/for ecoRI News)
Cox said she appreciates
the simplicity of the LSTA treatment system.
“I’m interested in
sustainable infrastructure related to wastewater treatment, and so, these LSTA
systems provide a really exciting option in certain parts of the landscape … to
provide a low-cost alternative to some of the more-expensive proprietary
technology that we’re now relying on, especially in coastal areas, to reduce
the nitrogen-loading that’s going into our watersheds and putting human and
environmental health at risk,” she said.
Freij said the LSTA
system, if approved for general use, might encourage private companies to
develop similar low-tech systems.
“I’m hoping this
technology will kind of introduce this option that’s lower in price to
encourage other technologies, maybe, to compete a little bit,” he said.
