DENITRIFICATION WITH METHANOL IN TERTIARY FILTRATION AT WASTE-WATER TREATMENT-PLANT ZURICH-WERDHOLZLI

In co-ordination with the EU-guidelines the large wastewater treatment plants in Switzerland have to be extended with enhanced nitrogen remo val. Denitrification in tertiary filtration is a cost-effective altern ative to extended denitrification in the activated sludge system, whic h needs; additional reactor volume. At the wastewater treatment plant Zurich-Werdholzli full-scale experiments of denitrification with metha nol in tertiary filtration were performed during a summer and a winter campaign of 4 months each. For this purpose one of the original 22 fi lter cells was equipped with a methanol dosage. At temperatures of 12- 15 degrees C rates of denitrification of about 1.0 kgN m(-3) d(-1) are attained. After main backwashing, denitrification is significantly re duced. Frequent backwashings (several times per day) led to methanol b reakthroughs due to biofilm loss. The yield coefficient Y-COD was 0.4 kg CODX kg(-1) CODme. In spite of methanol dosage the quality of the f ilter effluent was very good during normal operation in the winter cam paign. Accumulation of the nitrite intermediate product was observed i n summer at temperatures of 20-22 degrees C. (C) 1997 IAWQ. Published by Elsevier Science Ltd.