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Low-tech A to B cycle method improves upon traditional
recirculating gravel filters.
By Peter Hildebrandt
For 15 years, Al Privette, marketing manager for BioConcepts
Inc., worked as the director of horticulture at a large
botanical garden in Huntsville, AL. The botanical gardens
owned a 17-acre “borrow pit” from which soil
was taken to cover and cap a landfill. The hole was
used for the botanical garden’s maintenance facilities,
but its septic tanks had a major problem percolating;
for over three years, the tanks were pumped and the
effluent hauled away.
Privette began to search for an answer to the problem
of leftover soil and discovered that the Tennessee Valley
Authority (TVA) had done work in constructive wetlands.
Privette met with the TVA’s Team Leader for Water
Process Research Les Behrends and learned about a new
technology—one that would in due course be called
ReCip (reciprocating water technologies).
“They allowed me to install one of these systems,”
says Privette. “It was the first permitted in Alabama.
After 10 years this same system is still operating with
basically no oversight. If a pump fails, a plumber or
electrician is called.”
Privette is now back in his native North Carolina,
but he never lost his fascination with ReCip technology.
“It was one of the most amazing things I’ve
ever seen,” says Privette. “I decided to approach
the TVA about marketing the technology in eastern North
Carolina. In the 1990s the new technology had been patented
but for some time remained nameless.”
Privette formed BioConcepts Inc. and ended up purchasing
the rights to market the technology for the State of
North Carolina. This was a first: According to Privette,
no one had ever bought a patented technology from the
TVA.
The Tennessee Valley Authority’s Groundbreaking
Technology
The ReCip technology developed by the TVA involves treating
clarified wastewater from something—such as a septic
tank—wherein cells are backfilled with various
sizes of aggregates, starting with the largest. They’re
designed a lot like recirculating gravel filters, except
water is pumped from cell A to cell B and then back
to cell A from cell B. On a recurrent basis that process
may take place anywhere from six to 24 times per day
depending on the strength of the wastewater.
One of Bioconcepts’ projects, an operation in
Aliceville, AL, involves treating wastewater from a
commercial swine growing operation. At the Aliceville
facility the wastewater is pumped back and forth between
paired wetland cells every hour.
“This is a very fast rate,” says Behrends.
“For municipal wastewater where the BOD [biological
oxygen demand] may be only 200, we might reciprocate
six to eight times per day.
“The process of pumping it back and forth doesn’t
really re-aerate the water as much as pump the water
away from the rocks, leaving them exposed to atmospheric
oxygen. Therefore the biofilm that’s on the rocks
is given air. During that process we have a lot of nitrification
going on,” continues Behrends.
ReCip avoids leaching soil.
Unexpectedly, the ammonia in the water is attracted
to the rocks. Bacteria, ammonia, and oxygen are all
available for nitrification, when the water is pulled
away from the rock. When it refills, the ammonia has
been converted to nitrate, and if there’s any residual
BOD, denitrification takes place.
“That’s really the strength of that system,”
says Behrends. “It does a great job of removing
BOD and nitrogen. It does not, conversely, do much for
phosphorous.”
During the course of the process, the biofilm coats
the gravel substrate. That’s why there are gradations.
Toward the top of the system very fine pea gravel provides
a lot of surface area in which the biofilms may develop.
“The downside is, as the biofilms age and die,
they slough, adding to the buildup of sludge in the
system,” adds Behrends. “The sludge itself
is very recalcitrant. It doesn’t have a high oxygen
demand and just kind of sits there. But it fills in
the void spaces.
“We spent about two years doing research on how
to handle that and think we have a fairly good handle
on things,” explains Behrends, “either through
the design of the system or using chemical treatment
where we add concentrated hydrogen peroxide, which attacks
the sludge material. It chemically chews it up so that
it’s available again for the bacteria as a carbon
source. When the sludge is simply dead bacterial cells,
it is difficult to degrade.”
This is a problem with all sludge and all wastewater
treatment processes, according to Behrends. The sludge
accumulates and then something must be done with it.
“Most people either pump it out onto sand drying
beds or put it through a digestion process before placing
it out on land. Our system is no different; we also
have to deal with the sludge.”
Periodically, depending on the load, hydrogen peroxide
is added to the system’s under-drain. Water is
still pumped from cell A to cell B, but as this occurs
the water actually goes down into the under-drain, filling
from the bottom up.
This method allows for the easy introduction of any
chemical into the system. The chemical can be placed
into the pump chamber of one full cell and pumped over,
diluting and distributing the chemical across the bottom
of the cell. As the chamber fills, the water interacts
with the added chemical.
“The interesting thing is when we add the hydrogen
peroxide, it attacks the organic matter but it doesn’t
seem to affect the wastewater treatment process at all,”
says Behrends. “Therefore the bacteria which are
living don’t seem to be impacted whatsoever, only
the dead organic matter. It’s a neat process, but
we haven’t tried it on a commercial size yet. We’re
still tweaking it in the lab; but I think it’s
going to be more cost-effective than actually having
to dig the stuff out.”
The TVA is currently focusing on power generation,
including coal-fired, nuclear plants and hydropower.
Consequently, the TVA has become involved with issues
of water quality, specifically how such issues affect
the Tennessee Valley. Understandably, the TVA is interested
in maintaining the quality of the river, and it does
this by making certain all wastewater is adequately
treated so as not to degrade current water conditions.
“Some biofilms are good; some are bad; it all
mainly depends on where they are,” says Behrends.
“The thing making our system most unique is that
we can control the aerobic versus anoxic conditions.
By doing that we can maintain a really high diversity
in the biofilms, some that do nitrification and some
performing denitrification.
“It’s the same way with sulfate reduction.
A lot of the constructed wetlands in the past started
out with water entering the system as highly anaerobic
and as it moved down through the system became more
aerobic. You did not have the opportunity to expose
the wastewater to both aerobic and anoxic conditions
alternately.”
Behrends has been involved in this work on ReCip since
1993. Recently low-wattage, low-pressure UV lamps have
been integrated in the pump cycle so that each time
the water is pumped from one cell to the other all of
the water is exposed to UV and any free-living bacteria
are killed.
“We’re getting very good removal of any kinds
of pathogens which might be in the wastewater, opening
things up to the possibility of reusing the wastewater
after it’s treated,” says Behrends.
In a nutshell, ReCip eliminates the need for the in
situ soil to treat the wastewater through percolation
or leaching. ReCip treats water to tertiary level quality.
Once it’s clean it comes under a different auspice
or criterion, according to Privette: The soil only needs
to have a hydraulic capacity to absorb the water per
location regulations.
“The beauty of ReCip is that it both nitrifies
and denitrifies,” says Privette. “We not only
convert ammonia and nitrogen to nitrate and nitrite,
but we also take those and further convert or denitrify
by taking it out to nitrogen dioxide or dinitrogen gas,
which forms 80% of our atmosphere.
“This fact is important especially in some areas
like around the Chesapeake Bay where even though the
water will percolate, the septic systems contribute
a lot of nitrates to that particular watershed.”
All of this treatment or remediation is done without
any chemicals as well as with low-energy and low-tech
equipment. The water is simply moved from one cell to
the other periodically. Privette compares it to breathing.
When air is taken in through the mouth into the lungs,
capillaries there are exposed directly to atmospheric
oxygen, immediately absorbing it.
When the cell is drained, it actually breathes in air.
The bacteria in the biofilm have an instantaneous exposure
to atmospheric oxygen, just like in the lungs. When
the lungs exhale and when the cells in the system fill
up, it’s basically carbon dioxide.
“The environment in there is very stable,”
adds Privette. “Just like in the wintertime when
typically a lot of bugs are killed, in the summertime
we’re not overrun with bugs. The environment, as
in real life, is constantly being upset. The constant
flooding or saturating and draining of the cells means
no one bacteria can predominate over another,”
says Privette. “The biofilms are also simply doing
what they naturally do, attaching to surfaces where
their needs for oxygen, moisture, low light, and nutrients
can be met.”
In normally constructed wetlands the base of the roots
of the plants is the only primary place for the bacteria
to receive oxygen; therefore, the bacteria cling to
the roots. This works fine for a vast amount of area.
But if an onsite water treatment system is limited,
there must be another way to get oxygen into the system.
The draining and filling works wonderfully, contrasting
with the stirring and spraying that occurs during such
processes as bulk aeration.
The ReCip system includes a variety of ancillary benefits
that make it a viable treatment option. Due to the engineering
and overflow setting measures, ReCip allows the water
to flow through the system even when no power is available
or when no water is visible. In addition, the ReCip
installations are filled with rock and therefore can
literally be walked upon. Finally, the process guarantees
that no offensive odors will seep out of the system.
This is due to the fact that as water travels up and
down a cell, bacteria scrub it and the hydrogen sulfate
and sulfide are converted to carbon dioxide.
“The water coming from our hog farm operations
was clean and totally odorless,” says Privette.
“We use it to flush the barns because in these
big concentrated operations the flushing is done with
anaerobic lagoon water. We clean it up and flush the
barns with it, and they started smelling like barns,
not like ammonia.
“We don’t bulk aerate anything,” says
Privette. “All we do is to expose the bacteria
to oxygen. A ReCip may take a little bit more space
because it uses less energy in addition to being a bit
more time-consuming in time required to treat the effluent.
The more energy, generally, that you throw at wastewater
treatment, the faster you’ll accomplish treatment,
but at a cost, especially in operations and maintenance.
“But if you’re living in a coastal area on
a quarter-acre plot, this is the solution. It’s
less costly and more energy-efficient and requires less
oversight. If the power is lost for some reason, there
is not a panic situation whereas with bacteria being
pumped up artificially with aeration, when power’s
lost then you have a problem.”
From an Engineering Standpoint
When North Carolina–based McKim & Creed Project
Manager Chuck Donnell, P.E., first met and had discussions
with Privette, they spent a lot of time discussing the
possibility of eliminating the anaerobic lagoons for
hog farms in North Carolina. In a settlement with the
State of North Carolina, Smithfield Foods offered $15
million to have the state evaluate candidate wastewater
treatment technologies whose purpose was to eliminate
the anaerobic lagoons.
The state asked North Carolina State University (NC
State) to be the agency that would monitor that program
and allocate funds. NC State’s committee of some
30 individuals, including environmentalists, evaluated
all the proposals, approximately 116 to 120 in all.
Donnell and Privette were chosen to receive funds. “We’ve
installed a ReCip facility on a farm, Corbett Farm 2,
near Rose Hill, North Carolina. Essentially it was very
successful,” says Donnell.
“Subsequently we’ve gotten a lot of good
experience designing and studying all aspects of running
and monitoring the operation of the system with such
things as Webcams. Webcams can monitor operations for
us very inexpensively.”
Corbett Farm 2 includes an outdoor control panel enabled
to run all the pumps, timers, and other equipment. The
next logical step was to set up a Webcam aimed at the
control panel in order to remotely monitor operations.
The installation of an auto-dialer in the control panel
allows for the Webcam to be accessed via the Internet
to check which pump has a red light, indicating it needs
attention. A quick look could instantly determine whether
the pump in question is critical or whether it is just
one of the four contained within each of the cells that
can be dealt with at a later time. “This wasn’t
a real-time feed,” says Donnell. “But it was
close enough for the work we were doing.
“In the meantime we started a project at Holden
Beach, North Carolina,” says Donnell. “This
was our first commercial system to be permitted in North
Carolina. The hog farm installation was permitted but
it was more of an experiment or study. The Holden Beach
shopping center site was actually permitted by the state
as a normal project that was not connected to an experiment.
It became something of a showcase, as there were those
concerned about Recip’s ‘permit-ability.’”
The Holden Beach project is still running after some
four years, but because a municipal sewer line is soon
to move into the area, it will be taken out of service.
The flow equalization tank will now be used as a lift
station charged with changing the direction of the force
main from the wastewater treatment plant back to a gravity
sewer manhole.
Most ReCip units are reminiscent of the traditional
wetland treatment units, built at or near ground level.
But due to size constraints at the condo association’s
OWT development in Atlantic Beach, NC, it is actually
built in a 12-foot-high concrete tank.
A main concern in eastern North Carolina is that many
of the traditional or extended aeration wastewater treatment
or package plants are good at nitrifying but poor at
denitrifying. “But this technology, in and of itself,
without any other processes does a good job of denitrifying,”
adds Donnell. “This is why it’s become so
attractive to people here in the state.”
Not all treatment situations lend themselves easily
to ReCip systems. Donnell believes this technology works
best for small to medium-sized plants, rather than large
facilities processing 1 million gallons per day. Sometimes
the nature of the treatment makes ReCip prohibitive.
For example, for a food processing or rendering plant
with a high fats, oils, and grease load, ReCip may not
be the most appropriate technology because the pore
space between the aggregate needs to stay unclogged.
For pre-treatment applications, there may be simpler
solutions.
Maintenance Ease
Wayne Britt, owner of Britt and Britt Environmental
Services, the private contractor who’s handled
the maintenance on BioConcepts’ Holden Beach, NC,
system for four years now, has worked with a wide variety
of OWT systems since 1975, from antiquated aerobic digesters
to the latest technology. He likes the simplicity of
the ReCip system as well as its lack of mechanical and
moving parts.
“Things just go from one chamber to another in
this system and there is very little maintenance involved,”
says Britt. “The water coming out is clean enough
to be used for the highest-quality reclaimed water,
close to drinking-water levels. The system is also very
efficient with its four separate chambers and four separate
1.5-horsepower pumps, housed within a 24-inch pipe with
holes in the bottom so the water can come in and out
efficiently.”
The pump itself is easy to access. It can be easily
pulled in and out. If power goes out there’s a
backup generator onsite, yet even this is not critical.
There is so much redundancy that the system can go several
hours without power. “Also, it’s designed
much bigger than it has to be so that if something did
happen it could handle it, most definitely. It’s
going to take a lot to foul it up,” says Britt.
The system is checked five days per week, taking approximately
one half-hour per day to make sure everything’s
working properly. UV lights are used for a final disinfection
step. The water then travels into a drip irrigation
system on 1.5 acres of forested land. The piping, specially
designed to keep the holes from getting stopped up,
is above the ground.
The system, according to Britt, is odor-free. It’s
located under a bed of rock with vegetation growing
on top for aesthetics, as it’s located near the
shopping area’s parking lot. The system has small
gravel just below beach sand, on top of which grows
the grass.
“The ReCip unit is a neat system,” adds Britt.
“It is very easy to operate and would be perfect
for something like condominium units or small developments
such as 100 or so homes. With low upkeep and maintenance
you don’t have to worry about much. As the word
gets out I can see them being a perfect fit especially
for many OWT situations in rural areas.”
From the Contractor’s Perspective
Robert Eberhart, owner of Eberhart Construction in Raleigh,
NC, has been involved in the construction of the OWT
system at A Place at the Beach II in Atlantic Beach,
NC. “ReCips tend to be simple projects,” says
Eberhart. “It’s a simple treatment process
with few moving parts, which is the beauty of it.
A Place at the Beach II is a 60,000-gallon-per-day
system with 15-inch-thick concrete walls, 12 feet tall
atop a 30-inch-deep foundation slab. “This all
involved a lot of concrete pouring with much piping
constructed on the bottom. The media in the bottom is
class I riprap, which must be placed, as well as washed,
by hand. It’s bucket-loaded in and then hand-unloaded
from the bucket and placed around the piping on the
bottom. There are a lot of different options with how
these can fit the site. This particular one was designed
to have its wall 12 feet above grade.”
The site had a footprint requirement of approximately
100 by 30 feet. The size is flexible, according to Eberhart,
as long as the storage/operating volume designed into
the system is accomplished. Due to a lower water table
than expected, Eberhart was able to place this system
slightly deeper than originally planned. He is impressed
with the versatility of these systems on each site they’re
installed. The water table is something to be aware
of no matter where the ReCip system’s set up.
As the media get smaller they can be loaded with machines,
mechanically, sometimes using equipment as big as a
trackhoe in order to walk around this large box. But
the bigger stuff must be loaded by hand.
“The most expensive part of the job for Eberhart
was the casting in place of the concrete,” says
Eberhart. “The parts and motors are small and with
simple logic running them. There is a control panel
looking for a float to tell what your water elevation
is, and then you may have a simple processor doing a
timed dosing, pumping one side down at one time and
the other at another time or vice versa.
“The treatment process consists of taking bacteria,
exposing them to air and submerging them in wastewater,
and continually stirring all this up. I like building
these systems, despite the high amount of labor involved.
You must have a lot of hand laborers ready.
“Our company’s set up so we have lots of
those people available, such as carpenters, electricians,
and others. After 15 years these projects tie together
a lot of what we’ve always done. Though this would
probably not appeal to a wide variety of contractors
out there, it’s a real good fit for our company.
“For the amount of water that you can treat with
this ReCip process and for the quality obtained from
it, I think it’s head and shoulders above the other
15 or 16 technologies out there mainly because of how
simple it is.
“They’re all going to take time to build
and this one might be more labor-intensive than the
others, but once it’s in the ground it has a lot
fewer motors running, requiring less energy, and it’s
much simpler to control. Also, it’s ‘bullet-proof’
because of all the materials it’s constructed of.”
Peter Hildebrandt writes extensively on engineering
and scientific subjects.
OW - July/August 2007
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