the borderline economics of the system could become real profitability
if the cost of chemicals, calculated at 80% of the operating expenses, could
be eliminated.

 Bioflocculation, the autoflocculation of algal bacterial suspensions,
is economically the most promising means of primary concentration of the cells.
This has been used consistently for decades in the activated sludge process
for removal of bacterial solids from sewage, and depends on the maintenance of
turbulence under aerobic condition. Recently, it has been found that low
velocity mixing of wastewater algal cultures with a paddlewheel will induce
bioflocculation (Oswald 1977, Koopman et al. 1979, 1981). Concentration of the
cells can then be achieved by settling or microstraining (Dodd 1980). In
this process, the necessary aerobic conditions are maintained by photosynthetic
production of oxygen, rather than by forced aeration, as in the activated sludge
process. Zoogleal bacteria and exocellular polymers, which are instrumental in
floc formation, are common to both processes. Bioflocculation has thus far
been limited to cultures of the green algae Scenedesmus sp. and Micractinium
pusillium, but there is reason to believe that other algae may behave similarly,
since the process is largely bacterial in its mechanism. Research is now
needed into the chemical and physical parameters that are associated with the
formation of biofloc particles. Among the control parameters are cell
concentration, dilution rate, depth, and loading of organic wastes. In judging
the overall economics of bioflocculation, it should be noted that while
paddlewheel mixing does consume energy, the amount consumed is on the order of
2% of that fixed by the algae. An important consideration is that the process
does not depend on the high technology and proprietary information of the
chemical industry.

 Another approach to economic algal recovery is the use of filamentous
blue-green algae, such as Arthrospira (Spirulina), Oscillartoria, or other
members of the Oscillatoriaceae. which can be skimmed or strained by mechanical
means at very low energy cost. These algae have been grown on digester effluent
(Seshadri 1980, Soong 1980), as well as in alkaline and saline waters supplemented
with nitrates (Richmond 1980, Sanitillan 1974, Clement 1967). The filamentous
blue-greens are not as productive as the other microalgae, having a maximum
productivity of 10 to 15 g/m2 per day, but the protein content is generally
in the range of 60 to 65% of the dry weight, and the product is somewhat more
digestible than green algae. Use of Spirulina for large scale recycling of
swine wastes is now under investigation in Taiwan (Soong 1980).

 The economics of protein production with Spirulina has recently been
evaluated by Leesley (1981). Spirulina protein was compared with 15 other
sources of protein for seven parameters including production cost per ton and
energy output-input ratio. The cost per ton of Spirulina protein is given as
$399 versus $794 for soybean protein. Energy output/input ratio is 4.33 for
Spirulina and 1.18 for soybean. By comparison, the cost per ton for pork
protein is $20,258 and the energy ratio is 0.17. While these figures do not
take into account the biological feasibility of extensive Spirulina production,
they do point to an economy of energy and land use that is too significant to
ignore.

 It is worth noting that Spirulina has been made available as a health food
in the U.S. with current retail price of slightly more than $100 per kg. While
this is a specialty market of limited importance, it nonetheless represents