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Summary
Algal assays were performed with effluent water from 21 Swedish municipal wastewater treatment plants together with chemical analyses of the water during 1972–78. The AGP (algal growth potential)-variation obtained with a mixed algal culture was correlated with the content of P in the water.
The availability of P for algal growth was estimated by comparing the measured algal yield (obtained in algal assay) with calculated algal yield (using a factor for the P content in the cells). Phosphate phosphorus (soluble reactive phosphorus) normally showed an availability of over one hundred percent, indicating that more P than phosphate phosphorus could be utilized by the algae. Availability of total phosphorus was normally below one hundred per cent but in some samples it was found to be over one hundred per cent, indicating presence of algal growth-stimulating substances in the water.
The regression analyses and calculation of availability of P also gave information about inhibitory effects. Algal yields were in some cases not as high as expected from the content of P. This was interpreted as an inhibition of the algal growth by some compounds in the wastewater sample. In exceptional cases this inhibition was so strong that the algal assay showed negative values compared to the control.