534
Discussion
pond strata receiving virtually no light. However, the introduction of irradiance incident on the pond
surface per volume of pond water may also render the prediction of algal yields erroneous, especially
in ranges of pond depth and algal concentration not covered by the experiments described in the
paper. For example, during high detention periods, algal concentration will tend to increase, leaving a
relatively shallow strata of pond water photosynthetically active. The bulk of the pond water,
especially in relatively deep ponds, will have a high algae concentration with decay occuring due to
lack of light energy. Similarly, the authors failed to take into consideration the problems of
differential algae growth in various different zones of the pond cross-section, such as the light
inhibition zone at the surface, the light saturation zone and the zone in which algae growth will be
almost proportional to the incremental increase of irradiance levels.
The authors failed to take into account the decreases in algae concentration due to wash-out of
algae due to short detention periods, and when the dilution rate surpasses the net algae production
rate.
The above-mentioned limitations severely restrict use of the proposed method of prediction to
gross estimations of algal yields, and only under a given set of conditions.
REFERENCES
SHELEF, G., OSWALD, W.J., and GOLUEKE, CG., "Kinetics of Algal System in Wastewater
Treatment" San. Eng. Res. Lab. Report No. 68-4, Univ. of California, Berkeley (1968).
SHELEF, G. and HALPERIN, R., in: Developments in Water Quality Research (editor H.I. Shuval) pp.
211-228, Ann Arbor-Humphrey Sei. pub., Ann Arbor (1970).
SHELEF, G., SCHWARTZ, M. and SCHECHTER, H., Proc. 6th Int. Conf. Wat. Poll. Res. A/5/9/1,
Jerusalem (1972).
Israel Unger, Canada
What techniques were employed in the determination of light absorbed? The figure showing algae
yield vs k cal/1 of light absorbed would be better expressed as a quantum yield. The algae can absorb
one, two or more quanta of a given wavelength; it does not absorb 20 k cal or 40 k cal. I should also
like to point out that the Beer Lambert Law does not hold for this type of system.
N.A. Lever, South Africa
What was the nitrogen content of the treated effluent from the high rate ponds, after algal growth
but before irrigation? Did the authors use artificial fertilizers, particularly nitrogen, to increase the
yield of algae?
Aaron Moron, Israel
To increase algal yields how successful are depth, mixing and nutrient balance in addition to light?
H. Leclerc, France
Is the author aware of the cultures of Spirullius prepared for experimental purposes, particularly in
Mexico? Industries based on algae may be useful in sunny countries but are they of any use in
northern climates? Our experimental work in the north of France shows that algae make little
contribution towards reoxygenation, still less as a source of production.
Reply
I concur with the discussor's comments underlining the potential value of the sewage treatment -
protein production system and that it has strong applicability to the developed arid regions. However,
I cannot agree with the statement that the communities of south east Asia are not yet aware of the
need to cope with the growing water pollution problems that could benefit from an algal treatment
system. Although many of these countries have not yet well developed pollution abatement programs
it is not that they are unaware, rather it is that there is a severe shortage of funds for large capital
intensive programs. Indeed, it was the Bangkok Municipality's awareness which caused them to
provide substantial financial support for the research reported in the above paper.
Dr. Shelefs discussion related to the nitrogen removal capacity of the pond system is well taken; it
is to this aspect that most of our current research work is related. As stressed in the paper, the cost of
treatment may well be covered by the value of the algae alone. In tropical developing countries of
South East Asia algae may compete with fish-meal as having a higher nutritional value than soybean
or rice. Although the latter crops have up to this time benefited by recent technological developments
in agriculture our fish-meal market is beset with quality control problems, the fish-meal price
continues to rise.
Discussion
pond strata receiving virtually no light. However, the introduction of irradiance incident on the pond
surface per volume of pond water may also render the prediction of algal yields erroneous, especially
in ranges of pond depth and algal concentration not covered by the experiments described in the
paper. For example, during high detention periods, algal concentration will tend to increase, leaving a
relatively shallow strata of pond water photosynthetically active. The bulk of the pond water,
especially in relatively deep ponds, will have a high algae concentration with decay occuring due to
lack of light energy. Similarly, the authors failed to take into consideration the problems of
differential algae growth in various different zones of the pond cross-section, such as the light
inhibition zone at the surface, the light saturation zone and the zone in which algae growth will be
almost proportional to the incremental increase of irradiance levels.
The authors failed to take into account the decreases in algae concentration due to wash-out of
algae due to short detention periods, and when the dilution rate surpasses the net algae production
rate.
The above-mentioned limitations severely restrict use of the proposed method of prediction to
gross estimations of algal yields, and only under a given set of conditions.
REFERENCES
SHELEF, G., OSWALD, W.J., and GOLUEKE, CG., "Kinetics of Algal System in Wastewater
Treatment" San. Eng. Res. Lab. Report No. 68-4, Univ. of California, Berkeley (1968).
SHELEF, G. and HALPERIN, R., in: Developments in Water Quality Research (editor H.I. Shuval) pp.
211-228, Ann Arbor-Humphrey Sei. pub., Ann Arbor (1970).
SHELEF, G., SCHWARTZ, M. and SCHECHTER, H., Proc. 6th Int. Conf. Wat. Poll. Res. A/5/9/1,
Jerusalem (1972).
Israel Unger, Canada
What techniques were employed in the determination of light absorbed? The figure showing algae
yield vs k cal/1 of light absorbed would be better expressed as a quantum yield. The algae can absorb
one, two or more quanta of a given wavelength; it does not absorb 20 k cal or 40 k cal. I should also
like to point out that the Beer Lambert Law does not hold for this type of system.
N.A. Lever, South Africa
What was the nitrogen content of the treated effluent from the high rate ponds, after algal growth
but before irrigation? Did the authors use artificial fertilizers, particularly nitrogen, to increase the
yield of algae?
Aaron Moron, Israel
To increase algal yields how successful are depth, mixing and nutrient balance in addition to light?
H. Leclerc, France
Is the author aware of the cultures of Spirullius prepared for experimental purposes, particularly in
Mexico? Industries based on algae may be useful in sunny countries but are they of any use in
northern climates? Our experimental work in the north of France shows that algae make little
contribution towards reoxygenation, still less as a source of production.
Reply
I concur with the discussor's comments underlining the potential value of the sewage treatment -
protein production system and that it has strong applicability to the developed arid regions. However,
I cannot agree with the statement that the communities of south east Asia are not yet aware of the
need to cope with the growing water pollution problems that could benefit from an algal treatment
system. Although many of these countries have not yet well developed pollution abatement programs
it is not that they are unaware, rather it is that there is a severe shortage of funds for large capital
intensive programs. Indeed, it was the Bangkok Municipality's awareness which caused them to
provide substantial financial support for the research reported in the above paper.
Dr. Shelefs discussion related to the nitrogen removal capacity of the pond system is well taken; it
is to this aspect that most of our current research work is related. As stressed in the paper, the cost of
treatment may well be covered by the value of the algae alone. In tropical developing countries of
South East Asia algae may compete with fish-meal as having a higher nutritional value than soybean
or rice. Although the latter crops have up to this time benefited by recent technological developments
in agriculture our fish-meal market is beset with quality control problems, the fish-meal price
continues to rise.