E U T R O P H I C A T I O N A N D E C O S Y S T E M S
PREDICTION OF PHOTOSYNTHETIC BIOMASS
PRODUCTION IN ACCELERATED ALGAL-BACTERIAL
WASTEWATER TREATMENT SYSTEMS
G. SHELEF, M. SCHWARZ and H. SCHECHTER
The Environmental Health Laboratories, Department of Medical Ecology,
The Hebrew University, Jerusalem, Israel
INTRODUCTION
The use of symbiotic activity of algae and bacteria for treatment of wastewater in
more controllable and intensified systems than stabilization of oxidation ponds, was
sought after in many regions of the world where conditions of ample sunlight exist. The
work of Oswald and co-workers in California (1, 2, 3), McGarry et al (4, 5) in Thailand
and Shelef et al (6, 7) in Israel serve as examples of such attempts and their objectives
were to exert the full capacity of the bacterial phase in the breakdown of organic matter,
as in activated sludge systems, and simultaneously to provide conditions for maximum
photosynthetic activity, similar to those encountered in mass cultures of algae. By
maximizing algal net production photosynthetic oxygen production and the
incorporation of nutrients into the algal biomass would be maximised, thus removing the
nutrients from the aqueous phase. Clearly, the separation of the algae frorn the water is
essential in order to produce a suitable effluent. The separated algae can be disposed of or
might be utilized as a source of protein for animal feed (8,9).
A few methods for the separation of algae have been proposed, among them alum
coagulation and flotation, which was first demonstrated in South Africa by Van Vuuren
et al (10, 11).
This paper describes experiments conducted in a 300 m
2 accelerated photosynthetic
pond at the Environmental Health Laboratories of the Hebrew University of Jerusalem, in
order to determine the relationship between the dilution rate (or detention period) and
the photosynthetic activity, as expressed by the net production of algae biomass. The
kinetics of algae production with respect to solar incident irradiance served for the
construction of a mathematical model for predicting algae biomass production as a
function of the hydraulic dilution rate under given levels of solar irradiance. Some of the
perfomance data of the accelerated photosynthetic wastewater treatment system in
Jerusalem are also given.
THE ACCELERATED PHOTOSYNTHETIC POND
The photosynthetic pond in Jerusalem (Figs. 1 and 2) is a system of meandering 1.20
m (4 ft) wide channels with a total area of 300 m
2 (3200 ft
2 ). The pond is 50 cm (20
inches) deep and is lined with concrete.
The pond is equipped with a mixing-aeration pump (or alternatively a cage aerator)
which provides the necessary aeration when the dissolved oxygen falls below 1.5 mg/1,
which usually occurs only at night time. This mechanism also provides the necessary
mixing and recirculation of water in the channels at a velocity of about 30 cm/sec (1.0
ft/sec). During night time operation the process resembles a Pasveer oxidation ditch,
Pasveer (12). During daytime a specially designed mixer-agitator is operated. This
181
PREDICTION OF PHOTOSYNTHETIC BIOMASS
PRODUCTION IN ACCELERATED ALGAL-BACTERIAL
WASTEWATER TREATMENT SYSTEMS
G. SHELEF, M. SCHWARZ and H. SCHECHTER
The Environmental Health Laboratories, Department of Medical Ecology,
The Hebrew University, Jerusalem, Israel
INTRODUCTION
The use of symbiotic activity of algae and bacteria for treatment of wastewater in
more controllable and intensified systems than stabilization of oxidation ponds, was
sought after in many regions of the world where conditions of ample sunlight exist. The
work of Oswald and co-workers in California (1, 2, 3), McGarry et al (4, 5) in Thailand
and Shelef et al (6, 7) in Israel serve as examples of such attempts and their objectives
were to exert the full capacity of the bacterial phase in the breakdown of organic matter,
as in activated sludge systems, and simultaneously to provide conditions for maximum
photosynthetic activity, similar to those encountered in mass cultures of algae. By
maximizing algal net production photosynthetic oxygen production and the
incorporation of nutrients into the algal biomass would be maximised, thus removing the
nutrients from the aqueous phase. Clearly, the separation of the algae frorn the water is
essential in order to produce a suitable effluent. The separated algae can be disposed of or
might be utilized as a source of protein for animal feed (8,9).
A few methods for the separation of algae have been proposed, among them alum
coagulation and flotation, which was first demonstrated in South Africa by Van Vuuren
et al (10, 11).
This paper describes experiments conducted in a 300 m
2 accelerated photosynthetic
pond at the Environmental Health Laboratories of the Hebrew University of Jerusalem, in
order to determine the relationship between the dilution rate (or detention period) and
the photosynthetic activity, as expressed by the net production of algae biomass. The
kinetics of algae production with respect to solar incident irradiance served for the
construction of a mathematical model for predicting algae biomass production as a
function of the hydraulic dilution rate under given levels of solar irradiance. Some of the
perfomance data of the accelerated photosynthetic wastewater treatment system in
Jerusalem are also given.
THE ACCELERATED PHOTOSYNTHETIC POND
The photosynthetic pond in Jerusalem (Figs. 1 and 2) is a system of meandering 1.20
m (4 ft) wide channels with a total area of 300 m
2 (3200 ft
2 ). The pond is 50 cm (20
inches) deep and is lined with concrete.
The pond is equipped with a mixing-aeration pump (or alternatively a cage aerator)
which provides the necessary aeration when the dissolved oxygen falls below 1.5 mg/1,
which usually occurs only at night time. This mechanism also provides the necessary
mixing and recirculation of water in the channels at a velocity of about 30 cm/sec (1.0
ft/sec). During night time operation the process resembles a Pasveer oxidation ditch,
Pasveer (12). During daytime a specially designed mixer-agitator is operated. This
181