Determining algal-available phosphorus in pulp and paper mill effluents: Algal assays vs routine phosphorus analyses

We determined the potentially algal-available P (Paa) in pulp and paper mill effluents by two bioassay techniques (a dual-culture assay and a batch approach) and compared it with chemically analysed P (total P, total dissolved P, reactive P, dissolved reactive P and dissolved hydrolysable P). The mean Paa given by the dual-culture assay was within a 40% range of that given by the batch approach. The Paa obtained by both bioassays differed from total P. Dissolved reactive P appeared to be the most readily available chemical P fraction, but other P fractions also contributed to Paa. The analysis of reactive P, which involves direct staining of an unfiltered sample, best approximated the Paa given by the dual-culture assay (relative error 9%). The results suggest that assessment of eutrophying effluent P can be improved by analysing simple chemical P fractions in wastewater. The fractions to be analysed, however, may be site specific.