Methane Digester Odor Reduction by mto13086


									Methane Digester:
Odor Reduction
Prototype earthen, covered lagoon system destroys
offending compounds.

By Joe Vansickle                              solids separation settling basin that
Senior Associate Editor                       would reduce the loadings into the
                                              lagoon. But that called for a significant

         unique, low-cost methane             amount of cropland for manure applica-
         digester may just be the “silver     tion. Acreage is limited at the finishing
         bullet” for odor control that some   site, explains Feldmann.
lagoon owners have been seeking.                 Instead, Saline settled on a more
   For Glenn Saline of Apex Pork it sig-      aggressive plan – an anaerobic methane
nals the end of a long road of soul-search-   digester designed just for odor control.
ing and neighbors’ complaints that the        Feldmann believes it is the only operating
single-cell lagoon at his 8,600-head fin-     pig manure digester in Illinois and one of    The 40-ml.-thick, floating cover from
ishing site gave off offensive odors.         a few in the Midwest. And uniquely            Environmental Fabrics, Gaston, SC, was
   The Rio, IL, pork producer observes,       because it is earthen, mixed, covered and     installed in late December 1998. To
“We had some significant startup odor         heated, it provides year-around digestion     prevent the wind from lifting it at the
coming off our lagoon (that was) con-         of manure solids and a constant reduction     perimeter, the edges of the cover for the
structed in 1995. Most of those odors         of odor-causing compounds.                    120 x 160 ft., 17-ft.-deep digester are
started in spring 1996.                          “We have such low concentrations that      buried in a 2-ft. trench, explains
   “I think we’ve dramatically reduced        there is virtually no odor coming off the     Feldmann. The digester began full oper-
those odors and we’re ex-                                  lagoon,” attests Feldmann,       ation this past winter.
pecting that to continue to                                standing downwind on the            Digester startup has been a big part of
improve because we’ve                                      lagoon’s neatly trimmed          its success, say both Saline and
reduced loading into our                                   berm.                            Feldmann. There were two keys. First,
storage lagoon with the con-                                                                “good” bacteria was pumped over from
struction of our digester.”                                 Digester Design                 the lagoon at the sow farm which has
   Of the three production                                    To build the methane          been working well. Second, using
sites at Apex Pork, only the                                digester, Saline and            propane to start heating the digester, the
finishing site has had any                                  Feldmann turned to the          temperature was raised just 2º/day so that
major lagoon odor problems.                                 Environmental Pollution         other factors like pH and carbon dioxide
                                                            Agency’s (EPA) AgSTAR           in the slurry could be properly monitored
Detours Along The Way                                       program to provide technical    and maintained, says Saline. At the start,
   There’s no doubt the                Glenn Saline         aid and support for the         digester temperature was in the 50-60º F
lagoon was under-sized                                      design. AgSTAR is a volun-      range. The goal is to maintain digester
when it was built, remarks consulting          tary, federal EPA program aimed at           temperature at 95-105º F.
agricultural engineer Terry Feldmann,          promoting recovery and use of methane
Feldmann & Associates, East Peoria, IL.        from animal manure. (For more infor-         Processing The Manure
“It has a large, 6-acre surface area but it is mation, call (800) 95AgSTAR.) Actual            Apex Pork is a three-site, 2,500-sow,
only 13-ft. deep. It wasn’t pre-charged        digester design for Apex Pork was devel-     farrow-to-finish operation. On the
with enough fresh water. The result of all     oped by Mark Moser, Resource Con-            methane digester site are nine, grow-fin-
this was that it emitted pretty excessive      servation Management, Berkeley, CA.          ish (50-250 lb.) buildings, featuring 2-ft.,
odors,” adds Feldmann, who assisted               Installation began in the fall of 1997,   pull-plug manure pits with pit recharge.
with construction of the methane digester      and was completed in the spring of              Normally, one building per day is
and periodically returns to gauge its          1998, recalls Feldmann.                      drained by pulling the plug on the shal-
progress.                                         But the project was dealt a serious       low manure pits. The manure drains to
   Saline and Feldmann tried several           blow when a windstorm struck the site,       the end of the buildings, is piped through
options over the years. First was a micro-     blowing down a nearby barn, ripping the      a central line and into the digester. The
bial additive product which Feldmann           digester cover and compromising its          digester is sized to hold roughly 20
says did reduce lagoon odors but not to an     gas-collection capabilities.                 days’ worth of manure. Once full, it
acceptable level.                                 The easiest solution seemed to be to      maintains a static volume with 2 ft. of
   Then the pair looked seriously at a         add another cover over the original.         freeboard. Digested manure trickles over

10    August 15, 1999                                                                                               National Hog Farmer
                                                                                                         At left, Terry Feldmann
                                                                                                         takes a slurry sample from
                                                                                                         the main lagoon to
                                                                                                         develop a nutrient profile
                                                                                                         and monitor levels of
                                                                                                         odorous compounds.
                                                                                                         Excess methane is flared
                                                                                                         off into the atmosphere.

into the corner of the digester. When the      so you end up flaring off a lot of it,”
level of slurry reaches the “T” of a 10-in.-   points out Feldmann. In winter, most (80-     cheap system but it is pretty much self-
diameter PVC pipe, the effluent trickles       100%) of the gas is used to heat the          sufficient,” remarks Saline. About all he
through the pipe underwater into the           digester.                                     does to maintain it is to daily check the
main storage lagoon, explains Feldmann.           The black digester cover also absorbs      temperature level of the water returning
The hope is that by releasing the effluent     heat from the sun and keeps heat in with      to the digester and make sure all the
underwater, freezing is prevented and          2 in. of foam insulation that is sand-        pumps are operating smoothly.
odors are minimized. The lagoon is             wiched in between the original and the           For his part, Feldmann used to rou-
located adjacent to the digester and they      new digester cover.                           tinely test the finishing site for odor lev-
share the same berm.                              “One of the neat advantages of a           els. He recalls using a scentometer,
   Aiding the digester “processing” of the     heated and mixed digester like this is we     recording smells up to a half mile away.
manure is a mechanical mixer. An 8-hp.,        are able to maintain these high tempera-      Now he doesn’t even use the device
submersible, propeller mixer, located          tures year-around,” says Feldmann. “So        because the odor levels are so low.
near the bottom of the digester, is on a       we don’t have much problem with those            Saline places the total digester cost at
timer that once a day mixes and suspends       sensitive methanogens (methane-pro-           $150,000. Plus, there is a small electric-
manure solids. The digester breaks down        ducing bacteria) that like it warm and        ity cost to run the pumps. The boiler itself
these “volatile solids” and converts them      keep lagoon odors at a constant low           is heated by the methane gas.
into methane, carbon dioxide and water         level.”                                          That’s a big investment these days to
through bacterial digestion. Moser esti-          Those low odors are also a big plus for    most producers. But Saline smiles and
mates that only 20-40% of solids remain.       land application of effluent, he com-         shrugs and remarks it’s still a small price
   In the process, the methane gas bub-        ments. “We’ve converted a lot of the          to pay for piece of mind and the right to
bles toward the top and the biogas is col-     organic nitrogen into the ammonium            coexist in this west central Illinois com-
lected into PVC pipes with holes in it just    form so it is more readily available to the   munity where his dad and uncle have
under the cover of the digester. The bio-      crops.”                                       raised hogs in confinement for the past 30
gas produced is about 60-65% methane                                                         years.
and 30-35% carbon dioxide. The biogas          Cost Control                                     “We think our approach is very
is sucked through pipes using a vacuum            Saline wanted to keep digester costs       aggressive and proactive,” stresses
pump into a small building. There the gas      down but he also wanted to ensure its         Saline. “We feel like we have tried hard
is burned in a boiler (like a hot water        success. Instead of building a typical,       and we feel good about what we have
heater), heating water that is pumped          total concrete methane digester, he opted     done here,” he comments.
back into the digester through a network       for an earthen lagoon with a 22- x 56-ft.        And Feldmann adds a methane diges-
of over 650 ft. of specially designed, 3-in.   concrete bottom to maintain structural        ter is a viable option of odor control for a
black steel heat pipes designed to main-       integrity of the cavity during mixing.        large-scale operation (4,000- to 6,000-
tain the temperature of the slurry.               A typical methane digester is coupled      head finishing and up). Sure, the initial
   Separately, excess methane gas is           with an electrical generator for producing    cost of the system is on the high side, but
pumped out and flared off into the             electricity from methane. Eliminating the     that can be balanced off by the less acres
atmosphere, explains producer Saline.          generator saved about $100,000.               needed to apply the low-odor lagoon
“In the summer, it doesn’t take a whole           That leaves the “boiler room” and the      effluent and a smaller storage basin
lot of biogas to keep the digester warm,       digester itself. “I wouldn’t say it is a      rather than a large treatment lagoon.

National Hog Farmer                                                                                                 August 15, 1999   11

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