Biological Nutrient Removal Plants: Review of Full-Scale Operation

This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.

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Report no. UWRAA 94

May 1995

Synopsis

Biological nutrient removal (BNR) is a relatively new technology and only a limited number of full-scale plants are operating in Australia. The aim of this study was to review the operating experience at the first seven Australian BNR plants (all continuous flow format) and four intermittent process plants in the USA. These plants were located at Albury, Ballarat, Bendigo, Brendale, Penrith, South Windsor and West Wodonga in Australia, and Flushing, Dundee, Catawba and Foxwood in the USA.

Each of the Australian plants was visited for discussion with operators and collection of data. Daily operating data for the 1993 year were then analysed in detail. Information on the US plants was supplied by US consultant CH2MHill.

Biological phosphorus removal capacity was found to be fairly consistent between plants and averaged about 0.017 times biodegradable COD in the wastewater, declining slightly as feed TKN/COD ratio increased. Of the intermittent plants, data from only one was useful in this evaluation and performance of that plant was comparable with the continuous flow plants.

Effluent variability was high. Geometric standard deviation for effluent quality parameters averaged: COD or BOD 1.7, SS 2.0, total P 2.0, total N 1.7, NH3-N2.9.

RBCOD data measured by aerobic batch test method were available for three plants. Phosphorus removals calculated from these RCOD concentrations using the UCT model were consistent with plant performance. At three plants, short sludge age pre-fermentation appeared to enhance phosphorus removal to a limited degree.

Guidelines were developed for operational, staffing and cost parameters. Capital cost of existing BNR plants was more sensitive to effluent phosphorus concentration than nitrogen concentration. Cost of a new BNR plant was 30% higher than a secondary treatment plant at mean effluent phosphorus of 2 mg/L and at lower concentrations was inversely proportional to the 0.5 power of the mean phosphorus concentration.

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