Comparison of biological and chemical phosphorus removal in wastewater

Phosphorus has been found to be the main culprit in eutrophication of lakes and water ways which is a major international environmental problem. Two methods are currently being used around the world to remove phosphorus in wastewater: biological and chemical phosphorus removal. Presently, most plants in the world with phosphorus removal use chemical phosphorus removal but the tendency is that an increasing number of plants are built or reconstructed in order to use biological phosphorus removal. The software EFOR which is a computer tool for predicting operating results from wastewater treatment is used to compare between chemical and biological phosphorus removal. Results obtained from the study demonstrate that chemical phosphorus removal yields better and more stable results as far as effluent quality of treated wastewater is concerned. Chemical phosphorus removal produces a lot more sludge than biological phosphorus removal and the difference is dependent on the type of chemical used. Biological phosphorus removal consumes more energy in terms of the aeration capacity of the process than chemical phosphorus removal. Moreover, biological phosphorus removal needs a lot more volume or space than the chemical process as the anaerobic unit of the latter process is not necessary and can be omitted. An economic evaluation in terms of sludge production and chemical cost only, revealed that about 602.000 SEK (if FeCl3 is used) and 343.000 SEK (if Fe2(SO4)3 is used) can be saved if biological phosphorus removal is used instead of chemical phosphorus removal. It was noted that it is not a good idea to conclude that any of the treatment methods is better than the other as each one has its advantages and disadvantages and the choice of which method should be used would depend on the priority that society places on the wastewater treatment and the costs they are ready to incur. A final remark is that the winning concept these days should not be based on which process should be used in isolation to the other, but rather using the advantages of both processes together to obtain ‘best’ results, while at the same time minimizing their disadvantages.