Evaluation of the Algal System

 The feeding operation at the Swine Research Unit presently averages about
 300 animals with short lapses of near zero between cycles. Taking 300 as a
 starting figure, the feed input amounts to some 450 kg of corn and soybean meal
 per day during mid cycle. Present cost for the mixed feed is $108 per day.
 The largest daily crops of algae contained some 30 kg of ash free dry weight.
 Substituting for soybean meal at $0.22 per kg, their value equates to $6.60
 per day, or 6% of the total feed bill. The average algae crop amounted to
 1/3 of the maximum crops and thus had a value of 2% of the total feed costs.

 Evaluated in this manner, the algal system could be seen as worthwhile
only under the optimum conditions, and even then only for conserving materials,
since the cost of harvesting essentially negates the gain in dollars. However,
if the leaks in the system are eliminated, and it is evaluated from the
standpoint of its potential, the outlook is more encouraging.

 The primary objective of the algal system is to recycle as algal protein
the nitrogen wasted in the feeding operation. Analysis of the lagoon effluent
indicated that an average of 4.5 kg of nitrogen, largely in the form of ammonia,
entered the algal culture daily. Since the calculated output of waste nitrogen
from 300 animals is about 15 kg per day, some 2/3 of the nitrogen never got to
the algal culture. This loss can be accounted for by precipitation, settling,
and volatilization of ammonia from the lagoon during the long detention time.
The result was that the algal culture serviced the equivalent of 100 animals,
rather than 300. On the basis of 100 animals, the best crops were then
returning 18$ of the feed bill, and the average crop 6%.

 The loss of nitrogen can be eliminated almost entirely by replacing the
lagoon by an anaerobic digester, something we are now doing. In addition to
saving nitrogen, this will provide an estimated 30 m3 of methane a day (about
$4 worth of fuel).

 The relative potential of the algal system becomes apparent when one
compares it to conventional agriculture on the basis of land area. If the
0.1 ha area of the culture were planted in soybeans, the expected annual yield
of 2.5 tons per ha would average 0.7 kg per day and have a value of $0.15,
or 7% of the average algae crop. Soybeans are ranked highest among conventional
crops in protein yield per unit of land area (Leesley 1980).

 With respect to energy flow, the algal culture is considered here strictly
as an autotrophic converter of solar energy. Calculated on the basis of our
present system, at a yield of 30 kg per day, the preharvest return in algal
energy is 165,000 kcal per day (5500 kcal/kg x 30 kg). Assuming a flocculant
cost of 12,000 kcal (400 kcal/kg x 30 pg) and a pumping cost of 10,000 kcal
(16 hph x 641 kcal/hph) the resulting gain is 143,000 kcal per day. This is
30% as much as the estimated 380,000 kcal contained in the daily manure
output. In combination with an anaerobic digester, an additional 250,000
kcal/day should be obtained from the waste stream. The total of nearly
400,000 kcal compares favorably with 1.9 million kcal of combustible energy
in the daily input of feed.