Adjusting N:P ratios in liquid dairy manure through nitrification and chemical phosphorus removal to match crop fertilizer requirements

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Adjusting NP ratios in liquid dairy manure
through nitrification and chemical phosphorus
removal to match crop fertilizer requirements
J. DeBusk1, J. Arogo1, N. Love2, and K.F.
Knowlton3
Results The 100, 75, and 50 aeration
strategies have been tested to date. Table 2
shows the average characteristics of both the
influent and effluents. Although the effluent
total nitrogen (TN) was lowest at the 50
aeration treatment, the low nitrate concentration
indicates nitrification was not the reason for
nitrogen reduction. Ammonia stripping was the
most likely cause of such significant nitrogen
loss.
Background Nutrient recycling through
land-application of manure is an economical and
practical farming practice. A nitrogen to
phosphorus (NP) ratio of 51, which is suitable
for crop application, is typical in fresh manure.
If left untreated, nitrogen (N) in the manure is
subject to loss via volatilization,
denitrification, and runoff. Conservation of
nitrogen in a non-volatile form will help
maintain the fertilizer value of manure.
Phosphorus-based nutrient management plans help
prevent phosphorus (P) loss via runoff which can
occur as P accumulates in soil over time. As the
amount of cropland available for manure
application decreases, it is important that
manure be treated for phosphorus removal so that
more liquid manure can be utilized and nitrogen
needs can be met without the risk of over
applying phosphorus.
A significant reduction in total ammonia nitrogen
(TAN) was observed in all three reactors, but
only the higher aeration strategies achieved the
goal of nitrogen conservation as nitrate (Figure
4). Further analysis is needed to determine the
means of total nitrogen losses.
Methods Three 30 L attached growth reactors were
constructed (Figure 1). The reactors are filled
with 16 mm diameter Norpac media (Figure 2) and
each contains two diffuser stones providing air
at approximately 2 L/min.

• Objectives
• Develop a cost effective treatment strategy to
  conserve nitrogen in liquid dairy manure by
  determining (1) the most cost-effective aeration
  strategy to concentrate nitrogen in the manure
  and (2) the effects of recycled flush water on
  bio-available N during nitrification.
• Evaluate the use of chemicals to reduce
  phosphorus concentrations in the treated dairy
  manure to achieve suitable NP ratios for crop
  production.

• Work to be done
• The aeration strategies previously described will
  be repeated using scraped/separated dairy manure.
  The goal is to determine if flush water affects
  the bio-availability of nitrogen during
  nitrification.
• NP ratios will be adjusted by phosphorus
  removal. Reactor effluent will undergo batch
  tests for phosphorus removal by chemical
  precipitation using aluminum- and iron-based
  salts and polymers. Efficiency of phosphorus
  recovery and sludge production will be quantified.

Once steady state was reached, the 100 and 75
reactors performed similarly in terms of nitrate
production. The 75 intermittent aeration
strategy appears to be a viable and economical
option for liquid manure treatment (Figure 3).
Flushed and separated liquid dairy manure is
obtained from the Virginia Tech dairy complex.
The manure is stored in a 120 L anaerobic stirred
tank prior to being fed to the reactors. The
reactors are maintained at a hydraulic retention
time of approximately 3.75 d. Analysis is done on
reactor influent and effluents effluents are
sampled three times per week. The reactors are
aerated according to the aeration schemes shown
in Table 1.
Strategy Nitrification is the oxidation of
ammonia to nitrate by aerobic autotrophic
bacteria. This process is used to conserve
nitrogen in a non-volatile form. NH4 2O2 ?
NO3- 2H H2O The goal is to maximize
nitrogen conservation while minimizing nitrogen
loss and energy usage through the use of various
intermittent aeration strategies.
1 Biological Systems Engineering 2 Civil and
Environmental Engineering 3 Dairy Science