Reaction Rates of Photosynthesis
MAN M. VARMA, Director
Sanitary Engineering Design and Research
Green Engineering Affiliates
Somerville, Massachusetts
RICHARD S. TALBOT, Sanitary Engineer
Hercules Powder Company
Parlin, New Jersey
INTRODUCTION
Stabilization ponds, also called bio-oxidation or sewage lagoons, have provided an excellent method for the treatment of wastewater. The main source of
oxygen in a stabilization pond is provided as an end-product of photosynthetic activities of the algae. A much smaller amount, up to about 40 lbs of oxygen per
acre per day is provided by absorption at the air-water interface, aided by wind
action. Carbon dioxide, inorganic salts, water and energy of the sun are used by
algae to produce protoplasm, with oxygen and water released into the surrounding
medium. Oxygen is used by heterotrophic micro-organisms as an ultimate hydrogen ion acceptor as they obtain energy through oxidation of organic matter into
stable end products. With no photosynthesis occurring at night, stabilization ponds
and natural bodies of water tend to become depleted of oxygen during the night
by the biochemical oxygen demand of bacteria and other heterotrophic microorganisms, and also by the algae themselves, as they consume oxygen in the absence of sunlight. Septic conditions in the ponds therefore sometimes result.
This problem may be alleviated somewhat by the installation of artificial lights
to effect photosynthesis and oxygen production through the night hrs. Continuous
illumination may be detrimental to oxygen production (1). An alternation of
light and dark periods is beneficial for algal metabolism and a balance in the illumination may be required which, in a pond, can be achieved by automatic
control. The rate of photosynthesis is affected by (a) intensity of light, (b) pH,
(c) temperature, (d) age of the culture. The rate of photosynthesis is proportional
to the light intensity up to a certain intensity beyond which the rate of photosynthesis is no longer proportional to the increase in the light intensity. It has been
found that the highest photosynthetic rate in direct sunlight is normally about eight
ins. below the pond surface for this reason. The determination of the effect of
light intensity on the rate of photosynthesis would be an important design or criterion for stabilization ponds. To obtain a high rate of photosynthesis, the pH of
stabilization ponds in certain cases may have to be adjusted tor the treatment of
wastes. A variation on either side of the optimum pH would change the rate of
oxygen production by algae. Stabilization ponds and natural bodies of water can
show a diurnal variation in pH that may inhibit or kill the micro-organisms that
stabilize organic materials. Biological systems have a temperature range at which
the metabolism is maximum. The age of algal cells will similarly influence the
rate of metabolism.
If algae are to be relied upon to effect treatment of wastes in stabilization
ponds, a knowledge of their reaction rate to a changing environment is important.
Little or no data is available in the literature to show the effect of changing
intensity of light, pH, temperature, and age of the culture on the rate of photosynthesis  of   Chlamydomonas.      Hence,   investigations  were  made to study the
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