PHOTOSYNTHETIC YIELDS AND
BYPRODUCT RECOVERY FROM
SEWAGE OXIDATION PONDS
M.G. McGAPRY, CD. LIN and J.L. MERTO
Division of Environmental Engineering, Asian Institute of Technology,
PO Box 2754, Bangkok, Thailand
INTRODUCTION
Conservation of resources is essential to the economies of developing countries of Asia.
In many ways wastewater may be considered as a resource. Livestock and human excreta
are commonly used to fertilize ponds for fish culture. The Taiwanese fish farmer pays
$NT 25* per cubic metre of fresh nightsoil which, in some cases, is carted over distances
of up to 40 km to fish ponds surrounding the city of Tainan. Naturally, the municipal
authorities of Tainan look upon excreta as a resource of monetary value which should not
be wasted. Likewise, excreta has been used for centuries as a source of nutrients for the
production of vegetable crops in Europe and Asia.
More efficient use of otherwise wasted nutrients may be made through cultivation of
algae in sewage oxidation ponds. Algae have the advantage of having higher specific
growth rates and protein contents than higher plants. On an areal basis sewage grown
algae are capable of producing 127 times more protein per year than normal yields of the
conventional crop soy bean. Fortunately algae grow naturally in aerobic oxidation ponds;
the high rate oxidation pond as a means of sewage treatment and algal production has
been described in the literature (Oswald and Golueke, 1968, McGarry, 1971 and McGarry
and Tongkasame, 1971). Total reuse of wastewater may be achieved if the algae
byproduct is sold as a livestock feed protein concentrate and the effluent used for
irrigation or as a potable water supply after further treatment (Tuntoolavest, 1971).
The Asian Institute of Technology in cooperation with the Applied Scientific Research
Corporation of Thailand is conducting a study of the high rate oxidation pond as a low
cost sewage treatment system applicable to the developing nations of Asia. This paper
describes sewage treatment and algal growth under tropical conditions as affected by
pond mixing, solar radiation and diurnal variations in pond loading. Research into
processing the algal byproduct and its market value is also discussed.
SEWAGE TREATMENT AND ALGAL GROWTH
As a sewage treatment device the high rate pond has been shown to be very effective;
its ability to aerobically degrade organics is relatively unaffected by detention period and
depth at BOD loadings below 350 kg ha"
1 day"
1 . The filtered effluent BOD is normally
well below 20 mg Γ
1 . Emphasis in research has been laid upon growth characteristics of
algae in order to improve the quality and quantity of yields which may be used to offset
sewage treatment costs.
Pond mixing
Five outdoor experimental ponds (Fig. 1) were operated at 224 kg BOD ha"
1 day
-1
loading, 45 cm depth and 1.5 days detention period. Each had a surface area of 9m
2 , and
*$NT 25 -US$0,625
521
BYPRODUCT RECOVERY FROM
SEWAGE OXIDATION PONDS
M.G. McGAPRY, CD. LIN and J.L. MERTO
Division of Environmental Engineering, Asian Institute of Technology,
PO Box 2754, Bangkok, Thailand
INTRODUCTION
Conservation of resources is essential to the economies of developing countries of Asia.
In many ways wastewater may be considered as a resource. Livestock and human excreta
are commonly used to fertilize ponds for fish culture. The Taiwanese fish farmer pays
$NT 25* per cubic metre of fresh nightsoil which, in some cases, is carted over distances
of up to 40 km to fish ponds surrounding the city of Tainan. Naturally, the municipal
authorities of Tainan look upon excreta as a resource of monetary value which should not
be wasted. Likewise, excreta has been used for centuries as a source of nutrients for the
production of vegetable crops in Europe and Asia.
More efficient use of otherwise wasted nutrients may be made through cultivation of
algae in sewage oxidation ponds. Algae have the advantage of having higher specific
growth rates and protein contents than higher plants. On an areal basis sewage grown
algae are capable of producing 127 times more protein per year than normal yields of the
conventional crop soy bean. Fortunately algae grow naturally in aerobic oxidation ponds;
the high rate oxidation pond as a means of sewage treatment and algal production has
been described in the literature (Oswald and Golueke, 1968, McGarry, 1971 and McGarry
and Tongkasame, 1971). Total reuse of wastewater may be achieved if the algae
byproduct is sold as a livestock feed protein concentrate and the effluent used for
irrigation or as a potable water supply after further treatment (Tuntoolavest, 1971).
The Asian Institute of Technology in cooperation with the Applied Scientific Research
Corporation of Thailand is conducting a study of the high rate oxidation pond as a low
cost sewage treatment system applicable to the developing nations of Asia. This paper
describes sewage treatment and algal growth under tropical conditions as affected by
pond mixing, solar radiation and diurnal variations in pond loading. Research into
processing the algal byproduct and its market value is also discussed.
SEWAGE TREATMENT AND ALGAL GROWTH
As a sewage treatment device the high rate pond has been shown to be very effective;
its ability to aerobically degrade organics is relatively unaffected by detention period and
depth at BOD loadings below 350 kg ha"
1 day"
1 . The filtered effluent BOD is normally
well below 20 mg Γ
1 . Emphasis in research has been laid upon growth characteristics of
algae in order to improve the quality and quantity of yields which may be used to offset
sewage treatment costs.
Pond mixing
Five outdoor experimental ponds (Fig. 1) were operated at 224 kg BOD ha"
1 day
-1
loading, 45 cm depth and 1.5 days detention period. Each had a surface area of 9m
2 , and
*$NT 25 -US$0,625
521