Full Scale Experience with Biological and Chemical Phosphorus Removal
According to the latest Danish legislation, effluent demands regarding discharge of treated wastewater have to fulfil a standard of 8 mg/l total nitrogen and 1.5 mg/l total phosphorus. These requirements are minimum requirements and certain countries even go down to 6 mg/l nitrogen and 0.6 mg/l phosphorus because of the recipients involved. There is full confidence that these demands can be met before 1993 as there is already today operating experience from more then 50 plants operated with nitrogen and phosphorus removal. The most extensively used plants for nitrogen removal are using the BIO-DENITRO process. For phosphorus removal a combination of chemical and biological processes are being used. The characteristic features of the various processes will be described in more detail, examples will be given of time series analyses, and probability quantile diagram for effluent parameters for a number of these plants from which the operational stability can be evaluated. A comparison is made between plants with pure chemical, pure biological, and combined chemical/biological phosphorus removal. Utilization of contact filtration process as further polishing is evaluated and the influence of chemicals addition to the filtration plant is presented. On the basis of the available material, the processes appear to be equally good, however, a two step precipitation — pre-precipitation combined with a post-precipitation — has proved to lie in the low end of the scale. Similar or even better results can, however, be obtained by using a contact filtration process as the final treatment step.
KeywordsHydrolysis Phosphorus Filtration Sludge Lime
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