Algal production 251protein biomass in the fish tissue. However, fish cannot effectively graze all the
algal cells and will also discharge fish feces, causing the pond water to still
contain high algal contents and organic matters. Details about fish production in
wastewater can be found in Chapter 6.
5.3.5 Comparison of alternative algal harvesting methods
The literature on algal harvesting contains numerous studies and discussion of
various harvesting methods (Golueke and Oswald 1965; Middlebrooks et al.
1974; Parker and Uhte 1975; Benemann et al. 1980). Besides the 4 harvesting
methods listed above, there are other methods that can be used to separate algal
cells such as centrifugation, fine-weave belt filtration and sand filtration.
However there does not appear to be any method, which is clearly superior for a
"typical" application. Due to the very wide range of conditions and objectives
encountered, the selection of an algal harvesting technology and its application
should be approached as a distinct case, weighing the merits/drawbacks of each
method for the particular circumstances.
Factors to be considered in the selection of a harvesting method include
wastewater and HRAP effluent characteristics, treatment objectives (in terms of
harvested effluent quality for different water reuse applications or discharge
requirements), algal product quality, capital and operating costs, energy
requirements, level of operator skill required, and availability of equipments and
chemicals. The specific physical properties of algae also directly affect the
selection of a harvesting method, e.g. the motile euglenoids may resist
sedimentation or flotation because they can swim away from the process
effluent or the unicellular green algae will have sizes too small for the
conventional microstrainers. It is apparent that laboratory- or pilot-scale
experiments with that particular HRAP water should be conducted and the data
thoroughly analyzed prior to the selection of an algal harvesting method.
5.4 Utilization of waste-grown algae
Besides the benefits in wastewater treatment gained from waste-grown algae,
these algae, depending on their characteristics, can be further used according to
the applications shown in Figure 5.2.