DENITRIFICATION OF TRICKLING FILTER EFFLUENTS USING EXTERNAL CARBON-SOURCES

To upgrade existing trickling filter systems to comply with the Pi effluent standard of 1.0 mg/l as P and with pending N standards, a comprehensive system comprising chemical treatment for P removal and biological treatment for N renoval was considered. Pilot plant experiments were carried out to study the suitability of primary sludge and raw and settled sewage as C and energy sources for biological denitrification in such schemes. Using settled sewage from the Daspoort Sewage Works [South Africa], an average of 15 mg/l NO3-N was removed from biological filter effluent. The denitrification rate was 17 mg NO3-N/g volatile suspended solids/h; all systems suffered from poor sludge settleability. This problem is considered inconsequential in terms of full-scale application, where chemical addition should ensure good settleability.