243
SUMMARY AND CONCLUSIONS
An experimental facility was built to test the feasibility of recovering nutrients and
energy from swine manure. A source of industrial waste heat was simulated to enhance the
biological processes involved. Algae and bacteria were used to convert nutrients into biomass
and to generate biogas.
Manure was removed from the animal quarters by a gutter flushing system and solids were
separated from liquids by gravity settling. Solids were subjected to anaerobic digestion in a
14 m 3 digester to release plant nutrients, reduce the volume of the solids, stabilize the manure
biologically to reduce odor problems, and recover energy in the form of methane gas.
The liquid phase of the manure was used as a nutrient substrate for the growth of algae
and bacteria in 12 outdoor basins with a combined surface area of 24 m 2 and a combined volume of 6,000 I.
The waste heat needed to maintain above-ambient temperatures in the bioconversion
units was simulated by heating water in heat exchangers with electrical resistance heaters. An
accurate heat balance for digester and basins was obtained by using kWh meters.
The experimental facility was designed so that the waste water could either be recycled
for flushing or discharged into a neaby lagoon. In the latter case, only fresh water was used for
flushing of the animal quarters.
The experimental facility was used to study:
1. the functioning of the digester and the algal growth basins,
2. the degree of nutrient removal,
3.
dry matter and protein yields,
4. production of methane gas,
5. the energy requirements of the digester and the outdoor basins,
6. the quality of the waste water after removal of the biomass,
7. the biological stability of the conversion units,
8. the practical and economical feasibility of the nutrient recovery system,
9. the development of design criteria for a full-scale operation, and
10. the formulation of other bioconversion processes which might improve the recovery
of nutrients as well as the quality and quantity of end products from swine manure.
Growth of Algae
In early laboratory tests, the high temperature strain 211/8K of Ch/orella vulgaris was
found to grow better in swine waste than Scenedesmus obliquus Sc D 3 WT, Scenedesmus
quadricauda, Selenastrum capricornutum, Spirulina major, and Botyrococcus, and was therefore selected for use in the field experiments.
244
Experiments were designed to test the ability of Chlorella vulgaris 211/8K to establish
itself as the predominant algal species and to find the combinations of culture depth, retention
time, and temperature which produce the highest cell concentrations under prevailing climatic
conditions.
It was determined that the fresh manure must be diluted before the liquid phase is suitable for algal growth. In terms of inorganic nitrogen the manure must be diluted to contain
150 to 250 mg of elemental nitrogen in the ammonium form per liter. This is achieved by a
50-fold dilution of the volume of manure excreted by the animals, including liquids and solids.
When the manure is not sufficiently diluted, the high concentration of organic matter
promotes bacterial growth over algal growth.
Light Requirements
It was found that Chlorella vulgaris 211/8K requires a monthly average of the daily rate
of solar radiation in excess of 2,000 kcal/m 2 day and a photoperiod of at least 11 h, in order
to maintain a sufficiently high concentration of cells for harvesting at retention times of 8 days
or less. Growth continues at less than 2,000 kcal/m 2 day but at a reduced rate, so that adjustments in the retention time and/or culture depth are necessary to prevent depletion of the
algae and eventual predominance of bacterial growth.
Adjustments in retention time and/or culture depth are also necessary whenever a prolonged period of cloudiness occurs during which the rate of solar radiation remains below
2,000 kcal/m 2 day, although the monthly average of the daily rate may still be above 2,000
kcal/m 2 day.
Culture Depth
The highest concentrations of algae were found at the culture depth of 10 cm. Increasing
the culture depth to 20 cm reduced the concentration of algae by 50 percent. However, the
total biomass, including algae and bacteria, was nearly the same at either depth.
Temperature
The use of waste heat to maintain a culture temperature of at least 25 C was essential in
achieving high concentrations of algae, except during the summer months when the monthly
average of the daily maximum air temperature was 25 C and the monthly average of the daily
minimum air temperature was not less than 10 C. The statement assumes continuous mixing
of the algae and equilibrium of temperature between the culture medium and air.
Maximum concentrations of Chlorella were obtained at 30 C or 35 C. However, the contribution made by the algae to the total biomass, including bacteria, was higher at the temperature of 35 C than at 30 C. This was attributed to the production of anti-bacterial substances
by Chlorella at 35 C but not at 30 C.
245
Retention Time
The concentration of algal cells was found to increase with retention time. Maximum
concentrations were obtained at retention times of 6 to 8 days, indicating a generation time of
Ch/ore//a of 72 to 96 h under field conditions.
Concentrations of Algal Cells
Concentrations of cells of Ch/ore//a greater than 10 7/ml could be maintained in the
properly diluted waste water at retention times of 3 to 8 days, temperatures of 25 to 35 C,
and culture depths of 7.5 to 20 cm when the monthly average of the daily rate of solar radiation was at least 2,000 kcal/m 2 day.
Experiments conducted during the months of October through December showed that a
culture temperature of 35 C, a shallow culture depth of 10 cm, and a retention time of 8 days
do not compensate for the loss in algal growth due to the short photoperiod of less than 11
h/day and a monthly average of the daily rate of solar radiation of less than 2,000 kcal/m2
day. Under these conditions, a retention time of 8 days exceeds the generation time of
Ch/ore//a vulgaris 211/8K, so that the harvesting process depletes the algal population and
bacterial growth dominates.
When the cell density of Ch/ore//a could be maintained above 10 7/ml, the culture fluid
had a deep green color which was used as visual evidence of algal growth. The typical odor of
swine manure was absent. The photosynthetic activity of the algae caused daily changes in the
pH and the dissolved oxygen content of the swine waste substrate. The magnitude of these
changes was a function of the intensity of solar radiation, culture depth, and temperature. In
general, the photosynthetic activity of the algae, as measured by the DO content of the
culture, increased soon after sunrise and reached a maximum value sometime between 13:00
and 16:00 h. The DO concentration frequently rose above 20 mg/I and the pH rose as high as
9 in the 20 cm deep cultures and above 10 in the 7.5 cm deep basins. Nighttime respiratory
activity of algae and bacteria increased the concentration of dissolved CO2 and reduced the pH
to about 8 by early morning. During the same time the DO decreased to concentrations
between 4 and 6 mg/I. Periods of prolonged cloudiness reduced the photosynthetic activity of
the algae so that the pH fluctuated only between 7.8 and 8.5 and the DO content between 4
and 8 mg/I. Temperatures of less than 25 C also reduced photosynthetically induced changes in
pH and DO concentrations.
Cultures with cell densities of less than 10 6/ml showed no visual evidence of algal growth.
The medium had the appearance of activated sewage and the odor was that typical of swine
manure. The pH in these cultures remained at 7.6 and the DO concentrations at less than 1
mg/I. This condition was favored at radiation intensities of less than 2,000 kcal/m 2 day in
combination with short retention times of 2 to 3 days and culture depths greater than 10 cm.
It was concluded that the most effective way of maintaining a high density of Ch/ore//a cells
during prolonged periods of low intensity of solar radiation was to lower the culture depth to
10 cm or less, to stop harvesting, and to stop the addition of fresh substrate to the culture.
246
Contribution of Algal Cells to Total Biomass
Efforts were made to distinguish between the contribution made by algal cells and the
contribution made by bacterial cells to the total biomass. Algal cell counts were made using a
hemocytometer and Coulter counter. Concentrations of algal dry matter were estimated as
the product of mean cell volume and algal cell counts, taking into consideration a moisture
content of 75 percent w/w and a specific gravity of the algae of 1.1 g/cm 3 . The mean cell
volume was determined by a MCV-computer attached to the Coulter counter. It was assumed
that the difference between the concentrations of total dry matter obtained by the Millipore
filter technique and the estimated concentrations of algal dry matter represented the contribution made by the bacterial cells to the total biomass.
In sufficiently diluted waste containing 150 to 250 mg NH4-N/I, the highest concentration of algal dry matter, namely 0.70 g/I, was obtained in 10 cm deep basins when the retention time was 6 days, the temperature of the culture was 35 C, and the mean of the intensity
of solar radiation was 3,000 kcal/m 2 day. Essentially all of the biomass consisted of algae
under these conditions. In contrast, the concentration of algal dry matter was 0.36 g/I in the
20 cm deep basins and the algae were estimated to have contributed about 50 percent to the
concentration of total biomass of 0.74 g/I.
The total biomass harvested per day from either 10 cm or 20 cm deep basins would thus
be the same in a large scale operation. But the product recovered from the 10 cm deep basins
would be algae whereas the product recovered from the 20 cm deep basins would consist of an
equal mixture of algae and bacteria. Given a constant volume of waste which must be treated
each day, the recovery of an exclusively algal product from 10 cm deep basins would require
twice as much surface or land area than the recovery of a mixture of algae and bacteria from
20 cm deep basins.
At either depth, the concentration of 1,600 mg COD/I of waste water was reduced by 80
percent, the concentration of 900 mg BOD/I by 90 percent, and 30 percent of the inorganic
nitrogen in the waste was recovered as organic nitrogen in the biomass.
When the retention time was 4 days instead of 6 days, the concentration of algal dry
matter was reduced from 0.70 g/I to 0.45 g/I in the 10 cm deep basins and the algae contributed between 40 and 70 percent of the dry matter to the total biomass. The concentration of
algal dry matter was reduced from 0.36 g/I to 0.22 g/I in the 20 cm deep basins and the algae
contributed between 20 and 40 percent of the dry matter to the total biomass.
Yields of Algal Biomass
Maximum yields of 10 to 12 g/m 2 day of algal dry matter were obtained in 10, 15, and
20 cm deep basins when the retention time was 4 to 6 days, the temperature of the cultures 30
to 35 C, and the mean rate of solar radiation 3,000 kcal/m 2 day. Under these conditions,
Chlorella vulgaris 211/8K converted 1 to 2 percent of the total radiation into chemical energy.
Although the yields in g/m 2 were similar in the 10, 15, and 20 cm deep basins at both the
4-day and the 6-day retention times, operation of the basins at a depth of 10 cm and a retention time of 6 days would be preferred, because the concentration of algal dry matter and the
247
percentage of contribution by the algae to the total biomass were higher for this combination
of parameters than for the other combinations of culture depth and retention time.
When the quantity of algal dry matter recovered from the waste was related to the live
weight of the animals which produced the waste, maximum yields of 2 to 3 g/kg pig per day
were obtained in 7.5 and 10 cm deep basins operated at 6-day and 8-day retention times.
Recovery of Nitrogen
The nitrogen balance in the outdoor basins showed that 21 to 47 percent of the ammonium nitrogen available to the algae was converted into harvested biomass. The biomass contained 6 to 11 percent nitrogen on a dry matter basis.
The low percentage of conversion of ammonium nitrogen into organic nitrogen was
undoubtedly due in part to the need of the algae to make continuous physiological adjustments in response to the daily variations in the intensity of the solar radiation and the pH and
DO content of the medium. High concentration of oxygen and pH values above 8 favor photorespiration, a process which reduces biomass production by inhibiting protein synthesis. High
concentrations of OH- ions also cause the precipitation of micro- and macronutrients such as
iron, magnesium, manganese, and calcium which are essential for photosynthesis and protein
synthesis. It is therefore essential to control the pH, preferably in the range between 7.5 and
7.9, to improve the recovery of nitrogen from swine waste. This range of pH enhances the
activity of the enzymes responsible for the fixation of CO2, in particular ribulose-1,5-diphosphate carboxylase.
Control of the pH is essential for another reason: 50 to 75 percent of the ammonium
nitrogen in the waste could not be accounted for in the biomass and in the effluent of the
basins. This loss in N was in part attributed to volatilization as NH3 at pH values above 8,
induced by the photosynthetic activity of the algae. The remainder of the N not accounted
for settled to the bottom of the basins as sludge.
The bottom sediment or sludge is considered a desirable source of nitrogen and other
nutrients when algae are grown in dilute waste such as domestic sewage. In contrast, swine
manure is a rich source of nitrogen so that the layer of sludge no longer serves a useful purpose. In fact, the sludge was found to reduce the efficiency of heat transfer from the heat
exchanger pipes placed near the bottom of the basins to the culture medium and, more importantly, it served as an ideal environment for the proliferation of algal predators such as Vorticella spp. Furthermore, the sludge not only represented a loss of harvestable biomass but also
an inefficient use of energy because its organic nitrogen had to be recycled again, first into
inorganic nitrogen by bacterial ammonification and then back into organic nitrogen by algal
and bacterial assimilation.
Quality of Treated Waste Water
The water quality of the liquid swine waste was measured in terms of chemical and
biological oxygen demands. Rapid removal of COD and BOD occurred at retention times of
2 to 4 days. Thereafter, further increases in the retention time had only a small effect on the
reduction of COD and BOD.
248
The COD of the waste pumped into the basins ranged from 700 to 4,800 mg/I and the
BOD ranged from 340 to 2,300 mg/I. Algal-bacterial growth reduced the COD by 80 percent,
leaving a COD of 140 to 960 mg/I in the effluent after removal of the biomass by centrifugation. The BOD was reduced by 90 percent, leaving 34 to 230 mg/I in the effluent. These
levels of COD and BOD are acceptable in a system where the water is recycled for flushing.
The residual COD and BOD is too high to permit discharge of the centrifuged waste water into
public waters.
Stability of Algal Cultures
Continuous mixing, at least during daylight hours, was found to be essential for maintaining a predominant and competitive Chlorella population. Chlorella vulgaris 211/8K was able
to dominate the cultures to the practical exclusion of other algal species. Only small numbers
of Euglena, Ankistrodesmus, Oscrnatoria, and Scenedesmus spp. as well as diatoms, in particular Nitzchia sp., were observed.
However, an ever present threat to the dominance of the non-motile Chlorella were cells
of Chlamydomonas spp. in both the motile and palmaloid stages. It was not established why
the number of Chlamydomonas did not increase as long as mixing continued. The paddle
wheels turned at 5 rpm, imparting the culture fluid a speed of about 15 cm/sec. When the
mixing action was stopped, Chlamydomonas cells usually covered the entire basin surface in a
thick layer of scum within two to three days, thus excluding most of the light from the
Chlorella population below. A return to mixing would simply move the entire layer along the
surface of the cultures. Attempts to remove the Chlamydomonas by skimming were found to
be ineffective. The layer of cells broke up easily and the cells dispersed into the culture
medium only to form another layer a few hours later. Because of the reduced availability of
light and perhaps the production of antagonistic substances by the Chlamydomonas, the
Chlorella population declined rapidly.
The opportunistic invasion of Chlamydomonas occurred most often during the months of
May and June. The organism is a common inhabitant of soil. Its prevalence during these two
months may have been related to the plowing and tilling activities in the farmlands adjacent to
the experimental facility.
Invasion by predatory rotifers was • not observed, but protozoa occurred in large numbers.
Those in the circulating culture fluid consisted mostly of ciliates and flagellates which were
non-predatory to the algae. In the accumulating bottom sediment, however, Vorticella,
Amoeba, and Paramecium spp. were found to feed on Chlorella. Of these three algal predators, Vorticella was found to be most numerous and voracious when in the actively reproducing stage of its life cycle. It was not established why the number of Vorticella did not increase
sufficiently to threaten the survival of the Chlorella population.
Another threat to the stability of the algal population was the apparently random invasion of a fungus. During July, 1976, when all 12 basins were operated under identical conditions, five basins became infested with a fungus which formed star-shaped particles ranging in
size from 5 to 20 mm in diameter. These particles tended to form floating patches of aggregated clumps. The infection disappeared on its own within 10 days after its onset.
249
A complete loss of the Chlorella populations was experiences at all culture depths when
the basins were operated at a retention time of 6 days and received rates of solar radiation in
excess of 4,000 kcal/m 2 day. Autoflocculation was avoided at a retention time of 4 days. The
spontaneous clumping and settling of the algal cells was attributed to the precipitation of
essential nutrient elements and changes in cell surface charges at pH values above 8.5, induced
by the photosynthetic activity of the algae.
The loss of Chlorella vulgaris 211/8K by autoflocculation can be prevented by controlling the pH of the culture fluid. Control should be exercised between pH 7.5 and 7.9 by CO2
injection to keep micro- and macronutrient elements available to the algae in soluble form and
to maximize production of the enzyme ribulose-1,5-disphosphate carboxylase in the carbon
reduction cycle for maximum photosynthesis. Although total quantities of essential elements
such as iron, magnesium, manganese, calcium, and sulfur were found to be adequate in the
swine manure for algal growth, the availability of these elements to the algae in a metabolically
suitable form may actually be less than indicated, so that the supplemental addition of a mixture of minerals may be advisable.
The loss of cultural stability due to the invasion of predators, fungi, and undesirable
species of algae remains unpredictable until research determines which factors enable Chlorella,
or any other chosen alga, to maintain predominance. Continuous mixing and control of pH
are but two such factors. A third factor may be the recycling of a portion of the harvested
algae to increase the concentration of Chlorella in the basins.
Harvesting of Algae
The algal-bacterial biomass in the basin effluents was concentrated to a paste with a solids
content of 15 to 20 percent on a dry matter basis. The centrifuge which was selected for harvesting the biomass is commonly used in industry to separate crystals and other heavy particles
from solutions. It was acquired for the experimental facility because of its low cost of $6,800
relative to a cost of $13,000 to $15,000 for the smallest centrifuges available on the market
for concentrating single cell protein. The centrifuge was adequate for harvesting the algae for
feeding trials but it was found impractical for large scale harvesting. Its disadvantages include a
fairly large motor of 2.2 kW, a low centrifugal force of 2,000 x G, and the necessity to stop
operations periodically to scrape the algal paste from the centrifuge bowl.
At a flow rate of 5 1/m in, the centrifuge removed about 75 percent of the algal cells while
most of the bacterial cells passed through because of the low centrifugal force. At a flow rate
of 3 l/min, approximately 85 percent of the algae were recovered. Given the highest concentration of algal dry matter produced in the outdoor basins, namely 0.70 g/I, and a cost of
50/kWh of electricity, the cost of concentrating the algae was $0.69 to $1.02 per kg.
If a centrifuge specifically designed to harvest single cell protein had been available, the
cost of concentrating the algae would have been $0.07 per kg algae or $0.13 per kg of crude
protein. This compares with a cost of $0.50 to $0.70 per kg of soybean meal protein, F.O.B.
Portland, Oregon, 1977. To be competitive with soybean meal as a protein supplement in
livestock rations, the cost of producing and processing the algae, in addition to the cost of harvesting should therefore not exceed $0.40 to $0.60/kg.
250
The most efficient and reliable methods of harvesting micro-algae, but also the most
expensive ones, are centrifugation and chemical flocculation. As compared to centrifugation,
chemical flocculation has the disadvantage of contaminating the algal product with the coagulating chemical, usually alum. This makes the use of the algae as a feed supplement questionable because of possible toxicity effects as well as reduced digestibility and palatability.
The least expensive but also the least efficient methods of harvesting algae are sedimentation, autoflocculation, and filtration through microstrainers. The efficiency of microstrainers
could be improved significantly by growing filamentous algae instead of single-celled or
colonial algae such as Chlorella and Scenedesmus and by increasing the concentration of the
filamentous algae. Treatment ponds with continuous flow-through of waste water usually
contain mixed populations of algae. At short retention times, single-celled or colonial type
green algae predominate over slower growing, filamentous blue-green algae such as Oscillatoria. By lengthening the retention time and recycling a portion of the harvested algae to the
pond it may be feasible to establish the slow growing filamentous algae as the predominant
species over the fast growing unicellular algae.
The selection of filamentous algae for the purpose of decreasing the cost of harvesting has
several disadvantages, however. Filamentous algae are most often blue-green algae, many of
which are known to produce potent toxins lethal to both man and animal. Strict operational
controls as well as product quality controls must therefore be maintained to ensure the safe
use of the final product as a protein supplement in livestock rations. Furthermore, the long
retention time needed to assure the predominance of filamentous algae, as compared to the
short retention time needed to maintain the predominance of unicellular algae such as
Chlorella, will require a correspondingly larger surface area of the algae pond in order to treat
the same volume of waste water each day.
Thus trade-offs have to be considered in evaluating the cost of harvesting algae. Microstraining filamentous blue-green algae is less costly than centrifuging unicellular green algae
such as Chlorella and Scenedesmus, but some blue-green algae are known to produce deadly
toxins whereas green algae are not known to produce toxins and, given a fixed volume of waste
which needs to be treated each day, the filamentous algae require more surface/land area for
growth than the unicellular algae because of the difference in growth rates.
Growing Chlorella or some other green algae and harvesting them by centrifugation may
therefore be more cost effective for a large scale operation than growing filamentous algae and
concentrating them by microstrainers.
Nutritional Value of Algae
The harvested biomass was freeze-dried and its nutritional value determined in feeding
trials with Long-Evans rats. It was found that the raw algae had a low protein efficiency ratio
(PER) of 0.84 which improved to 131 by steam autoclaving for 30 min at 120 C. The digestibility of the raw algae was 59 percent which improved to 68 percent after autoclaving. In
comparison, the digestibility of soybean meal is 85 percent.
Although the PER was low, when used as a protein supplement to corn, the algae gave
favorable growth and feed efficiency responses. At a dietary level of 18 percent, the algal
protein performed as well as fish and soybean meal at a dietary level of 13 percent.
251
Amino acid supplementation of a corn diet containing autoclaved algae, indicated that
lysine was the first-limiting amino acid while methionine was present in adequate quantities.
A corn-algae diet supplemented with 0.3 percent lysine gave a growth rate of 5.5 g/day,
exceeding a growth rate of 5 g/day obtained with a corn-soybean meal diet at the same protein
level.
Because the lysine content of the raw algae was high, namely 4.83 percent on a dry
matter basis, further study is needed to identify the reasons for its low availability. Lysine
inactivation during heat processing and lysine "tie-up" as constituent of the indigestible cell
wall are two possibilities to consider. Development of processing methods to increase protein
digestibility and the availability of lysine are needed before the algae can be used successfully
as a replacement for soybean meal in swine rations.
Bacterial Growth
Batch cultures of mixed populations of bacteria indigenous to the liquid phase of swine
manure reached maximum concentrations in 6 h, at which time the cells could be harvested.
Temperatures in the range between 15 and 35 C did not influence maximum concentrations of
bacterial dry matter but determined which species of bacteria were present.
Maximum concentrations of bacterial dry matter increased linearly as a function of the
concentration of ammonium N in the range from 100 to 800 mg/I. The crude protein content
was quite variable and often below 50 percent of the dry matter. This was attributed to the
occurrence of autolysis. Maximum concentrations of bacteria in batch cultures are obtained
near the stationary phase of growth when many species of bacteria undergo autolysis.
The recovery of nutrients from swine waste by bacteria would be more efficient in a
continuous culture system which maintains the bacterial populations at an exponential rate of
growth. Autolysis would be largely avoided and a crude protein content of 50 to 75 percent
of the dry matter could be expected. Yields of 0.38 g cells/g COD and yields of 2.2 g cells/kg
pig per day appear feasible.
The continuous culture of bacteria is probably the simplest biological method of recovering nutrients from swine waste. Many of the different genera and species of bacteria indigenous to the swine waste tolerate or can adapt to a wide range of pH, temperature, and nutrient
concentrations. The need to control particular environmental and nutritional conditions is
therefore reduced to a minimum and the system can be operated throughout the year. Automated systems for the continuous culture of bacteria are commercially available.
However, given the genera and species of bacteria present in swine waste, it is conceivable
that toxic substances and organisms which are potentially pathogenic to both man and animal
can be produced. The harvested biomass may therefore have to be processed to eliminate the
potential problems of toxicity and pathogenicity before the bacteria can be used as a protein
supplement in livestock feed. This aspect of nutrient recovery by bacteria from swine waste
needs support for further research.
252
Anaerobic Digestion
Operational Characteristics
The settled manure solids from 50 pigs were loaded into an underground, concrete
digester with a volume of 14 m 3 at a rate of 0.96 kg VS/m 3 day (0.06 lb VS/ft3 day). The
digester content was continuously mixed and maintained at a temperature of 37 C. Its pH
stabilized at 7.2. The hydraulic residence time was 47 days. The digester influent had a
COD/VS ratio of 1.5 and a VS/TS ratio of 0.8.
Gas Production
The digestion process removed 55 percent of the total solids from the swine manure.
The destruction of the volatile solids averaged 56 percent, and the COD was reduced by 41
percent. These values are in general agreement with values cited in the literature for small
laboratory digesters ranging in size from a few liters to several hundred liters.
The daily gas production averaged 8.4 m 3 (300 ft3 ), containing 68 percent CH4 and 32
percent CO2. Based on the destruction of volatile solids, the production of biogas corresponded to 1.06 m 3/kg VS removed (17.2 ft3/Ib VS). This value is consistent with values
obtained for laboratory sized digesters.
Energy Requirements
The energy requirements for heating the digester ranged from 13,000 kcal/day during the
summer to 64,000 kcal/day during the winter. These values are greatly exaggerated because of
the unusual arrangement of placing two concrete tanks side by side into the ground and connecting them to make a single functional unit, and because the top surfaces of the tanks were
used as work areas and left exposed to the air without insulation.
Potential for Improving Yields of Biogas
The production of biogas may be enhanced by the following methods:
1. The loading rate may be increased from 0.96 kg VS/m 3 day to 3.8 kg VS/m3 day
while decreasing the hydraulic residence time from 47 days to 10 to 17 days.
2. The production of biogas with a high fuel value is favored when the C/N ratio is near
30. Swine manure has a C/N ratio of approximately 10. By adding properly pretreated cellulosic wastes to the digester, such as grass and cereal straws as well as other crop residues, the
C/N ratio of the swine manure may be raised to 30 and the yield of CH 4 by 0.44 m 3/kg of
cellulose.
Pure cellulose is readily digested under anaerobic conditions. However, in its natural state
it is chemically bound to hemicellulose and lignin in a complex structure which is largely
inaccessible to the extracellular enzymes of the bacteria in the digester. Pretreatment of the
cellulosic waste is therefore necessary.
253
The practical feasibility of pretreating cellulosic wastes and adding them to manure to
improve the yield of biogas remains to be determined.
3. The growth of yeast or microfungi in the liquid phase of diluted manure would generate considerable quantities of heat which could be diverted to the anaerobic digester. By
coupling the heat producing aerobic fermentation of yeast or microfungi in the liquid phase of
the manure with the heat requiring anaerobic digestion of the manure solids, the energy
requirements normally expected for cooling of the yeast fermenter can be eliminated while at
the same time the energy requirements of the digester for heating can be reduced, if not eliminated also. Most of the biogas could then be used for purposes other than heating the digester.
4. At present, the anaerobic digestion of organic wastes is practiced most often in a
single vessel. However, the digestion process itself is mediated by two distinct populations of
bacteria which differ from each other in growth characteristics and sensitivity to environmental stress.
Separating the acidogenic and methanogenic populations of bacteria and permitting them
to grow in separate reactors under environmental and nutritional conditions most suitable for
each group, may optimize the anaerobic digestion of organic matter. Phase separation may be
expected to provide substantial benefits, including greater removal of volatile solids and therefore higher yields of biogas as well as reduced digester volume and capital cost requirements.
Problems
An important element in the development of the anaerobic digester for farm use is the
acceptance of the technology by the farmer. The probability of acceptance is increased if the
digester system returns a profit, which may not necessarily be a monetary one, if the digester
system is easy to understand, install, and operate, and if adequate service is available.
The quantity and quality of manure available for digestion from a livestock operation or
farming enterprise are likely to vary during the year. The energy needs also vary from season
to season. An important research need is therefore the development of systems of waste
management which aim at the full utilization of organic wastes from all sources, including
manure and crop residues, and find a continuous use for the gas.
Energy Balance of Basins
Solar radiation, atmospheric radiation, back radiation, convection, evaporation, precipitation, and the addition of cold water to replace losses due to harvesting and evaporation contributed to the energy balance of the basins.
Equations for each component of heat transfer were developed and programmed into a
computer to predict the net energy requirements of outdoor basins under varying environmental conditions.
Energy requirements measured for outdoor basins at 30 C ranged from 27.8 mcal/cm2sec
in February to an average of 10.6 mcal/cm 2sec in August. Energy requirements for cultures
maintained at 15 C ranged from 9.8 mcal/cm 2 sec in February to 4.8 mcal/cm 2 sec in April.
254
The computer model predicted the energy requirements within 10 percent of the measured values. The model indicated that 73 to 115 percent of the net energy loss was due to
evaporation and convection for the 30 C cultures. The relative contribution made by radiation
to the total loss of energy varied from a net energy gain of 20.3 percent in July to a net energy
loss of 17 percent in January. An average of 5.6 percent of the loss in energy was due to the
addition of make-up water.
Methods of Nutrient and Energy Recovery
The necessity to dilute the swine waste with large volumes of water in order to make the
liquid phase of the manure suitable for algal growth, and the potentially high cost of harvesting and processing the algae prompted further considerations of the biological recovery of
nutrients and energy from swine manure.
To reduce the large volumes of dilution water, it is proposed to pretreat the liquid waste
by first using it as a substrate for the growth of selected heterotrophs such as yeasts and microfungi. As an alternative to harvesting the algae by centrifugation and to avoid the potentially
high cost of processing the algae to improve their low digestibility and the low availability of
lysine, it is proposed to use a polyculture of fish, thereby gaining a high quality protein which
is easy to harvest and already accepted as a supplement in livestock feed.
An effort was made to bring the several possible bioconversion processes together into
functional management systems, which have in common that the solids are treated by anaerobic digestion to recover biogas, to solubilize nutrients, and to reduce the solid waste by 40 to
60 percent. Most also conserve water by recycling the waste water to flush the animal quarters
and dilute the manure. The harvested protein is recycled as a supplement in livestock feed.
The proposed bioconversion methods include:
OPTION A: Methane and Fertilizer
The manure is digested to produce gas and a biologically stabilized waste for use as a
fertilizer.
OPTION B: Methane and Algae
The manure is digested to produce gas and to solubilize plant nutrients. The nutrients in
the liquid phase of the digested manure are recovered by algae.
OPTION C: Methane, Yeast, Microfungi, and Algae
The manure solids are digested to produce gas. Yeast, microfungi, and algae are cultivated in the liquid phase of the manure.
OPTION D: Methane and Fish
The manure is digested to produce gas. The digester effluent is used as a source of nutrients for fish.
255
OPTION E: Methane and Bacteria
The manure is digested to produce gas from the solids. The liquid portion of the manure
and the supernatant liquid from the digester are treated in aeration basins, operated to maximize the production of bacteria.
Architectural perspectives and plan views were developed together with schematic diagrams showing the flow of energy and materials through each system based on the feed and
energy needs and the waste discharge of 100 pigs.
The quantities of biogas and protein which can be recovered from swine waste are limited
by the availability of carbon and nitrogen. Algae, yeast, or microfungi could recover about 5
percent of the digestible energy present in the feed or replace 30 to 60 percent of the soybean
meal protein. About 90 percent of the combustible energy present in the manure could be
recovered. However, yields of each bioconversion process can be increased as desired by
supplying the bioconversion units with additional sources of carbon and nitrogen. Technical
difficulties need to be overcome, principally the conversion of cellulosic wastes to reducing
sugars, the stability of the algal cultures under field conditions, the efficient transfer of oxygen
to growing cells of yeast, bacteria, or microfungi, and improvement of the anaerobic digestion
process by phase separation. No new technologies need be developed.
257
REFERENCES
Abeliovich, A. and Y. Asov. 1976. Toxicity of ammonia to algae in sewage oxidation ponds.
Applied and Environmental Microbiology 31(6):801-806.
Allen, M.D.B. and M.K. Garrett. 1976. Effects of the culture of Chlorella upon the bacterial
flora of the liquid phase of animal slurry. Proc. Soc. General Microbiology 3:130-131.
Allen, M.B. 1955. General features of algal growth in sewage oxidation ponds. Publication
No. 13, State Water Pollution Control Board, State of California, Sacramento, California.
American Association for the Advancement of Science. 1974. Energy: Use, Conservation,
and Supply. P.H. Abelson (ed.). AAAS, Washington, D.C. 154 p.
American Association for the Advancement of Science. 1975. Food: Politics, Economics,
Nutrition, and Research. P.H. Abelson (ed.). AAAS, Washington, D.C. 202 p.
American Public Health Association, American Water Works Association, Water Pollution Control Federation. 1971. Standard Methods for the Analysis of Water and Wastewater,
12th edition. American Public Health Association, Inc., New York, New York. 874 p.
Anonymous. 1974. Energy down on the farm. Rural Research 85:4-14.
Asplund, J.M. and W.H. Pfander. 1973. Production of single-cell protein from solid wastes.
In: Alternative sources of protein for animal production. National Academy of Sciences,
Washington, D.C. 183 p.
Bain, R.C., Jr. 1969. Algal growth assessments by fluorescence techniques. pp. 39-55. Proc.
Eutrophication-Biostimulation Assessment Workshop, June 19-21. Berkeley, California.
281p.
Bardach, J.E., Ryther, J.H., and W.O. McLarney. 1972. Aquaculture. The Farming and
Husbandry of Freshwater and Marine Organisms. Wiley lnterscience, New York, New
York. 868 p.
Barlow, E., Boersma, L., Phinney, H.K., and J.R. Miner. 1975. Algal growth in diluted pig
waste. Agriculture and Environment 2:339-355.
Bassham, J.A. 1976. Mechanism and efficiency of photosynthesis in green plants. pp. 205228. Proc. Symp. "Clean Fuels from Biomass, Sewage, Urban Refuse, Agricultural
Wastes", January 27-30, Orlando, Fla. Institute of Gas Technology, Chicago, Illinois.
459 p.
Bates, E.M. and W. Calhoun, Jr. 1976. Local climatological data for Oregon State University,
1975. Special Report 277. Agricultural Experiment Station, Oregon State University,
Corvallis, Oregon.
Bates, EM. and W. Calhoun, Jr. 1977. Local climatological data for Oregon State University,
1976. Special Report 277. Agricultural Experiment Station, Oregon State University,
Corvallis, Oregon.
Beale, S.I. and D. Appleman. 1971. Chlorophyll synthesis in Chlorella. Regulation by degree
of light limitation on growth. Plant Physiology, Lancaster 47:230-235.
Boersma, L., Davis, L.R., Reistad, G.M., and W.E. Schmisseur. 1974. A systems analysis of
the economic utilization of warm water discharge from power generating stations. pp. 1014. Bulletin No. 48, Engineering Experiment Station, Oregon State University, Corvallis,
Oregon. 257 p.
258
Boersma, L., Barlow, E., Miner, J. R., Phinney, H.K., and J.E. Oldfield. 1975. Protein produc
tion rates by algae using swine manure as a substrate. pp. 475-493. In: W.J. Jewell (ed.),
Energy, Agriculture, and Waste Management. Ann Arbor Science Publishers, Inc., Ann
Arbor, Michigan. 540 p.
Bremner, J.M. and D. R. Keeney. 1966. Determination of isotope-ratio analysis of different
forms of nitrogen in soils. Soil Sci. Soc. Amer. Proc. 30:577-582.
Brenner, W., Rugg, B., and C. Rogers. 1977. Utilization of waste cellulose for production of
chemical feedstocks via acid hydrolysis. pp. 201-212. Proc. Symp. "Clean Fuels from
Biomass and Wastes", January 25-28, Orlando: Fla. Institute of Gas Technology, Chicago,
Illinois. 521 p.
Casey, R.P. and J.A. Lubitz. 1963. Algae as food for space travel. A review. Food Technology 17:1386.
Cook, B.B. The nutritive value of waste-grown algae. Amer. J. Public Health 52:243.
Davis, E., Dedrick, J., French, C., Milner, H., Myers, J., Smith, J., and H. Spoehr. 1953.
Laboratory experiments on Chlorella culture at the Carnegie Institute of Washington. pp.
105-153. CIW Publication No. 600. Carnegie Institute of Washington, Washington, D.C.
357 p.
Dieckamp, H. 1971. The fast breeder reactor. A source of abundant power for the future.
EOS, Transactions Amer. Geo. Union 52:756-763.
Edinger, J.E. and J.C. Geyer. 1965. Heat exchange in the environment. Edison Electric Institute Publication No. 65-902. Edison Electric Institute, New York, New York.
Environmental Protection Agency. 1971. Algal Assay Procedure. Bottle Test. National
Eutrophication Research Program, Pacific Northwest Water Laboratory, Corvallis, Oregon.
Farm Electrification Council. 1975. Food and energy. Des Moines, Iowa.
Finney, C.D. and R.S. Evans II. 1975. Anaerobic digestion: the rate-limiting process and the
nature of inhibition. Science 190:1088-1089.
Forss, K., Passinen, K., and E. SjostrOm. 1974. Utilization of the spent sulfite liquor components in the Pekilo protein process and the influence of the process on the environmental problems of the sulfite mill. Presented at Symposium "Wood Chemistry, Pure and
Applied", March 31-April 5, American Chemical Society National Meeting, Los Angeles,
California.
Fowden, L. 1962. Amino acids and proteins. pp. 189-209. In: R.A. Lewin (ed.), Physiology
and Biochemistry of Algae. Academic Press, New York, New York. 929 p.
Fraser, M.D. 1977. The economics of SNG production by anaerobic digestion of specially
grown plant matter. pp. 425-439. Proc. Symp. "Clean Fuels from Biomass and Wastes",
January 25-28, Orlando Fla. Institute of Gas Technology, Chicago, Illinois. 521 p.
Fukui, W.S. 1975. An engineering design of a swine waste management and nutrient conversion system utilizing thermal discharges. Engineering report in partial fulfillment of a
Master of Science degree. Department of Civil Engineering, Oregon State University,
Corvallis, Oregon.
Garrett, M.K., Strain, J.J., and M.D.B. Allen. 1976. Composition of the product of algal culture in the liquid phase of animal slurry. J. Sci. Food and Agriculture 27:603.
Gaudet, J. L. 1966. The status of warm water pond fish culture in Europe. FAO Fisheries
Reports 44(2):70-87.
259
Ghosh, S. and D.L. Klass. 1977. Two-phase anaerobic digestion. pp. 373-415. Proc. Symp.
"Clean Fuels from Biomass and Wastes", January 25-28, Orlando, Fla. Institute of Gas
Technology, Chicago, Illinois. 521 p.
Gianelli, W.R., Pafford, R.J., DeFalco, P., and J.R. Teerink. 1971. Removal of nitrate by an
algal system. Phase II. Bioengineering aspects of agricultural drainage, San Joaquin
Valley. Report No. 13030 ELY 06/71-13. California Department of Water Resources,
Fresno, California. 132 p.
Goldman, J.C., Oswald, W.J., and D. Jenkins. 1974. The kinetics of inorganic carbon limited
algal growth. J. Water Pollution Control Federation 46(3):554-574.
Goldstein, A. 1965. Biostatistics. The MacMillan Company, New York, New York. 272 p.
Gramms, L.C., Polkowski, L.B., and S.A. Witzel. 1971. Anaerobic digestion of farm animal
waste (dairy, bull, swine, and poultry). Transact. Amer. Soc. Agric. Engineers 14:7-11,13.
Han, Y.W. and A.W. Anderson. 1974. The problem of rice straw waste: a possible feed
through fermentation. Economic Botany 28(3):338-344.
Han, Y.W., Lee, J.S., and A.W. Anderson. 1975. Chemical composition and digestibility of
ryegrass straw. J. Agric. Food Chemistry 23(5):928-931.
Hargett, N. L. 1975. Fertilizer summary data. U.S. National Fertilizer Development Center,
Tennessee Valley Authority, Muscle Shoals, Alabama.
Hazen, T.E. 1973. Manure handling by hydraulic flushing. pp. D1-D11. In: Proceedings,
Livestock Waste Management Conference. University of Illinois, Urbana, Illinois.
Hegewald, E. 1972. Untersuchungen des Zeta-Potential von Planktonalgen. Arch. Hydrobiol.
Suppl. 42:14-90.
Heichel, G.H. and C.R. Frink. 1975. Anticipating the energy needs of American agriculture.
J. Soil and Water Conservation 30:48-53.
Heitman, H., Jr., and H. Hintz. 1967. Sewage grown algae as a protein supplement for swine.
Animal Production 9:135-140.
Hellebust, J.A. 1974. Extracellular products. pp. 838-863. In: W.D.P. Stewart (ed.), Algal
Physiology and Biochemistry, Botanical Monographs, Vol. 10. University of California
Press, Berkeley, California. 989 p.
Hemens, J. and G. Stander. 1969. Nutrient removal from sewage effluents by algal activity.
pp. 701-715. In: S.H. Jenkins (ed.), Advances in Water Pollution Research. Proceedings, 4th International Conference on Water Pollution Research, Prague. Pergamon Press,
London. 936 p.
Hemerick, G. 1973. Mass culture. pp. 255-267. In: J.R. Stein (ed.), Handbook of Phycological methods; culture methods and growth measurements. Cambridge University
Press, London. 448 p.
Hendrix, S.B. 1969. Food from the land. In: Resources and Man, National Academy of Sciences, National Research Council. W.H. Freeman and Co., San Francisco, California.
259 p.
Hepher, B. 1966. Some limiting factors affecting the dose of fertilizers added to fish ponds,
with special reference to the Near East. FAO Fisheries Reports 44(3):1-6.
Heydeman, M.T. 1973. Protein production by unicellular organisms. pp. 303-321. In:
J.G.W. Jones (ed.), The Biological Efficiency of Protein Production. Cambridge University Press, London. 385 p.
260
Hickling, C.F. 1962. Fish Culture. Faber and Faber, London. 317 p.
Hickling, C.F. 1968. The farming of fish. Pergamon Press, London. 88 p.
Hirst, E. 1974. Food related energy requirements. Science 184:134-138.
Hogan, T.T., Leipins, A.A., and E. Reid. 1970. An engineering economic study of cooling
pond performance. EPA Water Pollution Control Research Series, Report No. 16130DFXD5/70. Prepared by Littleton Research and Engineering Corp.
Hugli, T.E. and S. Moore. 1972. Determination of the tryptophan content of proteins by ion
exchange chromatography of alkaline hydrolysates. J. Biol. Chemistry 247(9):2828-2834.
Humphrey, A.E. 1974. Current developments in fermentation. Chemical Engineering 81(26):
98-112.
lfeadi, C.N. and J.B. Brown, Jr. 1975. Technologies suitable for recovery of energy from livestock manure. pp. 373-396. In: W.J. Jewell (ed.), Energy, Agriculture, and Waste Man
agement. Ann Arbor Science Publishers, Inc., Ann Arbor, Michigan. 540 p.
Jewell, W.J. 1976. Bioconversion of agricultural wastes for pollution control and energy conservation. Final Report No. TID-27164. Contract No. ERD-NSF-741222A01, United
States Energy Research and Development Administration, Oak Ridge, Tennessee. 321 p.
Jewell, W.J. and P.L. McCarty. 1968. Aerobic decomposition of algae and nutrient regeneration. Technical Report No. 91. Department of Civil Engineering, Stanford University,
Stanford, California.
Jiler, H. 1972. Commodity Yearbook. pp. 252-253. Commodity Research Bureau, Inc., New
York, New York.
Jones, J.H. and C. Foster. 1942. A salt mixture for use with basal diets either high or low in
phosphorus. J. Nutrition 24:245.
Kauffman, M.D. and E.H. Gardner. 1976. Methods of Soil Analysis Used in the Soil Testing
Laboratory at Oregon State University. Special Report 321. Agricultural Experiment
Station, Oregon State University, Corvallis, Oregon. 40 p.
Kessler, E. 1964. Nitrate assimilation by plants. Ann. Rev. Plant Physiology 15:57-71.
Knudson, J.G., Boersma, L., Davis, L.R., Reistad, G.M., Schmisseur, W.E., and J.C. Ringel.
1975. Future developments in waste heat utilization. Circular No. 49, Engineering
Experiment Station, Oregon State University, Corvallis, Oregon. 110 p.
Koberg, G.E. 1964. Methods to compute long wave radiation from the atmosphere and
reflected solar radiation from a water surface. U.S. Geological Survey Professional Paper
No. 272-F, Washington, D.C.
Kowallik, W. 1962. Ober die Wirkung des blauen und roten Spektralbereichs auf die Zusammensetzung und Zellteilung synchronisierter Chlorellen. Planta 58:337-365.
Krauss, R.W. and W.H. Thomas. 1954. The growth and inorganic nutrition of Scenedesmus
obliquus in mass culture. Plant Physiology 29:205-214.
Krenkel, P.A. and F.L. Parker. 1969. Engineering aspects, sources, and magnitude of thermal
pollution. pp. 10-51. In: P.A. Krenkel and F.L. Parker (eds.), Biological Aspects of
Thermal Pollution. Vanderbuilt University Press, Nashville, Tennessee. 407 p.
Lambeth, C. L. and D.W. Seckler. 1975. Practical evaluation of recycled animal waste protein
in feedlot steers. Feedstuffs 47(331:23.
Leopold, L.B. 1974. Water. W.H. Freeman and Company; San Francisco, California. 172 p.
261
Lima, D.O. 1936. Pond cooling by surface evaporation. Power (March).
Ling, S.W. 1966. Feeds and feeding of warm water fishes in ponds in Asia and the Far East.
FAO Fisheries Reports 44(3):284.
Lipinsky, E.S. and J.H. Lichtfield. 1970. Algae, bacteria, and yeasts as food or feed. CRC
Crit. Rev. Food Technology 1:581.
Loehr, R.C. 1974. Agricultural waste management: problems, processes, and approaches.
Academic Press, New York, New York. 576 p.
Lorenzen, C.J. 1966. A method for the continuous measurement of in vivo chlorophyll concentration. Deep-Sea Research 13:223-227.
Mandels, M., Hontz, L., and J. Nystrom. 1974. Enzymatic hydrolysis of waste cellulose.
Biotech. Engineering 16:1471-1493.
Mandeville, R.T. 1976. Fuel gas from landfill. pp. 197-204. Proc. Symp. "Clean Fuels from
Biomass, Sewage, Urban Refuse, Agricultural Wastes", January 27-30, Orlando, Fla.
Institute of Gas Technology, Chicago, Illinois. 459 p.
Maughan, P.M. 1966. Measurement of radiant energy over a mixed water body. Ph.D. Thesis;
Oregon State University, Corvallis, Oregon.
McCarty, P. L. 1970. Chemistry of nitrogen and phosphorus in water. J. Amer. Water Works
Association 62(2):127-140.
McGarry, M.G. and C. Tongkasame. 1971. Water reclamation and algae harvesting. J. Water
Pollution Control Federation 43(5):824-835.
McGriff, E.C. and R.E. McKinney. 1971. Activated algae: a nutrient removal process. Water
and Sewage Works 118(2):377-379.
McLachlan, J. 1963. Some effects of tris-(hydroxymethyl)-aminomethane on the growth of
Haematococcus pluvialis Flotow. Can. J. Botany 41:35.
Meadows, D.H., Meadows, D.L., Randers, J., and W.W. Behrens. 1972. The Limits of Growth.
Potomac Associates, Washington, D.C. 205 p.
Meek, B., Chesnin, L., Fuller, W., Miller, R., and D. Turner. 1975. Guidelines for manure use
and disposal in the western region, USA. Bulletin 814. College of Agriculture Research
Center, Washington State University, Pullman, Washington. 18 p.
Meeks, J.C. 1974. Chlorophylls. pp. 161-175. In: W.D.P. Stewart (ed.), Algal Physiology
and Biochemistry, Botanical Monographs, Vol. 10. University of California Press,
Berkeley, California. 989 p.
Meyrath, J. 1975. Production of feed yeast from liquid wastes. Process Biochemistry 10(3):
20-22.
Midwest Plan Service. 1975. Livestock Waste Facilities Handbook. MWPS-18, July. Iowa
State University, Ames, Iowa. 94 p.
Millet, M.A. 1974. Pretreatments to enhance chemical, enzymatic, and microbiological attack
of cellulose materials. Forest Products Laboratory, June. U.S. Dept. of Agriculture,
Madison, Wisconsin.
Miner, J.R. and R.J. Smith (eds.). 1975. Livestock waste management with pollution control.
North Central Region Research Publication 222. Midwest Plan Service Handbook MWPS19, Iowa State University, Ames, Iowa. 89 p.
Morris, G.R., Jewell, W.J., and G.L. Casler. 1975. Alternative animal waste anaerobic fermentation designs and their costs. pp. 317-335. In: W.J. Jewell (ed.), Energy, Agriculture,
and Waste Management. Ann Arbor Science Publishers, Inc., Ann Arbor, Michigan.
540 p.
262
Morris, I. 1974. Nitrogen assimilation and protein synthesis. pp. 583-609. In: W.D.P.
Stewart (ed.), Algal Physiology and Biochemistry, Botanical Monographs, Vol. 10. University of California Press, Berkeley, California. 989 p.
Myers, J. 1963(a). Algal cultures. pp. 649-668. In: R.E. Kirk and D.F. Othmer (eds.),
Encyclopedia of Chemical Technology, Volume 1, 2nd edition. lnterscience Publishers,
New York, New York.
Myers, J. 1963(b). Enhancement. pp. 301-317. In: B. Kok and A. Jagendorf (eds.), Photosynthetic Mechanisms of Green Plants. National Academy of Sciences, National Research
Council Publication No. 1145. Washington, D.C. 766 p.
Myers, J. 1971. Enhancement studies in photosynthesis. Ann. Rev. Plant Physiology 22:289312.
National Academy of Sciences. 1969. Resources and Man. W.H. Freeman and Co., San
Francisco, California. 143 p.
National Research Council. 1956. Handbook of Biological Data. W.S. Spector (ed.), W.B.
Saunder Company, Philadelphia, Pennsylvania. 584 p.
National Research Council. 1971. Atlas of nutritional data on United States and Canadian
Feeds. National Academy of Science. Washington, D.C. 772 p.
Nelson, L.F., Burrows, W.C., and F.C. Stickler. 1975. Recognizing productive, energyefficient agriculture in the complex U.S. food system. Paper No. 75-7505, American
Society of Agricultural Engineers, St. Joseph, Michigan.
Nobel, P. 1974. Introduction to biophysical plant physiology. W.H. Freeman and Co., San
Francisco, California. 488 p.
Oswald, W.J. and C.G. Golueke. 1960. Biological transformation of solar energy. Adv.
Applied Microbiology 2:232.
Oswald, W.J. and S.A. Gaonkar. 1969. Batch assays for determinations of algal growth
potential. pp. 23-37. In: Proc. Eutrophication-Biostimulation Assessment Workshop,
June 19-21. Berkeley, California. 281 p.
Overcash, M.R. and F.J. Humenik. 1976. State of the Art: Swine Waste Production and Pretreatment Processes. Environmental Protection Technology Series, EPA-600/2-76-290,
December. R.S. Kerr Environmental Research Laboratory, Office of Research and
Development, USEPA, Ada, Oklahoma. 171 p.
Payne, W.J. 1970. Energy yields and growth of heterotrophs. Ann. Rev. Microbiology 24:17.
Person, H.L. and J.R. Miner. 1971. A dosing siphon for discharging cleaning water into flushing gutters. Paper No. MC-71-105, Mid-Central Region Meeting, April 16-17. American
Society of Agricultural Engineers, St. Joseph, Michigan.
Picket, J. 1971. Effects of flashes of red or blue light on the composition of starved Ch/ore//a
pyrenoidosa. Plant Physiology 47:226-229.
Pimentel, D., Hurd, L.E., Bellotti, A.C., Forster, M.J., Oka, I.N., Shores, 0.D., and R.J.
Whitman. 1974. Food production and the energy crisis. pp. 41-47. In: P.H. Abelson
(ed.), Energy: Use, Conservation, and Supply. American Association for the Advancement of Science, Washington, D.C. 154 p.
Pimental, D., Dritschillo, W., Krummel, J., and J. Kutzman.1975. Energy and land constraints
in food production. Science 190:754-791.
263
Pigg, D. L. 1977. Commercial size anaerobic digester performance with dairy manure. Paper
No. 77-4055, American Society of Agricultural Engineers, St. Joseph, Michigan.
Prowse, G.A. 1966. A review of the methods of fertilizing warm water fish ponds in Asia and
the Far East. FAO Fisheries Reports 44(3):7-12.
Rappaport, A., Sarig, S., and M. Marek. 1976. Results of tests of various aeration systems on
the oxygen regime in the Genosar experimental ponds and growth of fish there in 1975.
Bamidgeh 29(3):35-49.
Rappaport, U. and S. Sarig. 1975. The results of tests in intensive growth of fish at the
Genosar (Israel) station ponds in 1974. Bamidgeh 27(3):75-82.
Reich, K. 1975. Multispecies fish culture (polyculture) in Israel. Bamidgeh 27(4):85-99.
Sarig, S. and M. Marek. 1974. Results of intensive and semi-intensive breeding techniques in
Israel in 1971-1973. Bamidgeh 26(2):28-48.
Schroeder, G.L. 1975. Some effects of stocking fish in waste treatment ponds. Water
Research 9:591-593.
Scrimshaw, N.S., Wang, D.I.C., and M. Milner. 1975. Protein Resources and Technology:
Status and Research Needs. Summary and research recommendations prepared for
National Science Foundation, Research Applications Directorate, RANN, NSF RA-T-75037. Stock No. 038-000-00251-1, Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.
Seckler, D. 1975. The CERECO process. Ceres Ecology Corporation, 1860 Lincoln Street,
Denver, Colorado.
Seward, R.A. 1976. The growth of Ch/ore//a vulgaris 211/8K in diluted swine manure as a
function of temperature, light intensity, depth, and retention time. M.S. Thesis, Department of Microbiology, Oregon State University, Corvallis, Oregon. 171 p.
Snedecor, G.W. and W.G. Cochran. 1967. Statistical Methods, 6th edition. Iowa State University Press, Ames, Iowa. 593 p.
Soeder, C. and E. Stengel. 1974. Physico-chemical factors affecting metabolism and growth
rate. pp. 714-740. In: W.D.P. Stewart (ed.), Algal Physiology and Biochemistry, Botanical Monographs, Vol. 10. University of California Press, Berkeley, California. 989 p.
Sorokin, C. 1971. Calefaction and phytoplankton. Bioscience 21:1153-1159.
Sorokin, C. and R. Krauss. 1962. Effects of temperature and illuminance on Ch/ore//a growth
uncoupled from cell division. Plant Physiology 37:37-42.
Spackman, D.H., Stein, W.H., and S. Moore. 1958. Automatic recording apparatus for use in
the chromatography of amino acids. Anal. Chemistry 30(7):1190-1206.
Spans, L.A. 1976. Enzymatic hydrolysis of cellulosic wastes to fermentable sugars for alcohol
production. pp. 325-348. Proc. Symp. "Clean Fuels from Biomass, Sewage, Urban
Refuse, Agricultural Wastes", January 27-30, Orlando, Fla. Institute of Gas Technology,
Chicago, Illinois. 459 p.
Spataru, P. 1976. Natural feed of Tilapia aurea Steindachner in polyculture, with supplementary feed and intensive manuring. Bamidgeh 28(3):57-63.
Spoehr, H. and H. Milner. 1949. The chemical composition of Ch/ore//a; effect of environmental conditions. Plant Physiology 24:120-149.
Spoehr, H.A., Smith, J.H.C., Strain, H.H., Milner, H.W. and G.J. Hardon. 1949. Fatty acid
antibacterials from plants. Carnegie Inst. Wash. Publ. No. 586:1-67.
264
Starr, C. 1975. A strategy for national electricity production. pp. 217-247. In: W.D. Loveland
(ed.), Magnitude and Deployment Schedule of Energy Resources. Oregon State University, Corvallis, Oregon. 284 p.
Steel, R.G.D. and J.H. Torrie. 1960. Principles and Procedures of Statistics. McGraw-Hill
Book Co., New York, New York. 481 p.
Subbulakshmi, G., Backer, W.E., and L.V. Venkataraman. 1976. Effect of processing on the
nutrient content of the green alga Scenedesmus acutus. Nutrition Reports International
14:581.
Sykes, R. 1975. Theoretical heterotrophic yields. J. Water Pollution Control Federation
47(3):591-600.
Syrett, P.J. and I. Morris. 1963. The inhibition of nitrate assimilation by ammonium in
Chlorella. Biochim. Biophys. Acta 67:566-575.
Tal, S. 1974. Preliminary observation on new methods of fish culture in Israel. Bamidgeh
26(3):51-56.
Tolbert, N.E. 1974. Photorespiration. pp. 474-504. In: W.D.P. Stewart (ed.), Algal Physiology and Biochemistry, Botanical Monographs, Vol. 10. University of California Press,
Berkeley, California. 989 p.
Trukhin, N. 1968. Effect of the carbon supply on the response of Chlorella pyrenoidosa to
blue and red light. Fiziologiya rastenii 15:652-657.
Tubb, J.A. 1966. Status of fish culture in Asia and the Far East. FAO Fisheries Reports
44(2) :45-53.
United States Department of Agriculture. 1975 (January). Statistical Reporting Service,
Crop Reporting Board, Da 1-1. Washington, D.C.
United States Department of Commerce. 1969. Census of Agriculture. Social and Economic
Statistics Administration, Bureau of Census, Washington, D.C.
United States Department of Commerce, Bureau of the Census. 1972. 1969 Census of Agriculture. U.S. Government Printing Office, Washington, D.C.
Vitkevich, V.I. (ed.). 1963. Agricultural Meterology. Translated from Russian by Israeli Program for Scientific Translations, Jerusalem. OTS 63-11075. IPST Cat. No. 876.
National Science Foundation and U.S. Department of Agriculture, Washington, D.C.
320 p.
Ward, G.M., Johnson, D.E., and R.D. Boyd. 1975. Nutritional value for steers of Cereco silage
and Cereco protein produced from feedlot manure. Feedstuffs 47(March 24):19.
Warren, K.S. 1962. Ammonia toxicity.and pH. Nature 195:47-49.
Wilson, M. and J.A. Houghton. 1974. Growth of algae on pig manure. Irish J. Agric.
Research 13:49-60.
Wolny, P. 1967. Fertilization of warm water fish ponds in Europe. J. Water Pollution Control Federation 3:64-81.
Woodward, F.N. 1952. Industrial utilization of agricultural wastes. Chemistry and Industry
71:844.
Worgan, J.T. 1973. Microbial protein from carbohydrates. pp. 339-361. In: J.G.W. Jones
(ed.), The Biological Efficiency of Protein Production. Cambridge University Press,
London. 385 p.
Yentsch, C.S. and D.W. Menzel. 1963. A method for the determination of phytoplankton
chlorophyll and phaeophytin by fluorescence. Deep-Sea Research 10:221-231.