Aerated Biofilters for Nitrification and Effluent Polishing

Abstract

To comply with new effluent discharge standards of 10 mg TKN/l, different upgrading methods for a highly loaded activated sludge plant were explored. As a conclusion, demonstration units were tested to assess process feasibility and performance data of an innovative technology. The Achères Treatment plant of the city of Paris is currently being extended to purify a flow of about 2 700 000 m3/d, corresponding to 8 Million population equivalents. Conventional activated sludge, loaded at about 0.6 kg BOD/kg SS d, delivers an effluent of 30 mg/l for both BOD and SS. To achieve nitrification, a considerable multiplication of basin volume and clarifier area would be required. In the densely urbanised Paris area, insufficient space is available for a such an extension. Therefore, new technology for plant upgrading was tested on industrial scale. Biological aerated filters combine aerobic degradation of pollutants with physical retention of suspended solids in one reactor. A high concentration of active biomass can be retained in the packed bed, and nitrifying bacteria can be attached to the filter media. Removal efficiency becomes thus independent of clarification and sludge settling, and ammonia oxidation can be achieved without sludge age requirements. Four parallel units were installed on the Colombes research platform, handling a total flow of 3000 m3/d. An extensive demonstration test program was carried out over a period of five years to assess the feasibility and performances of the process in line with a conventional activated sludge plant. The limits of loading to achieve different residual ammonia concentrations were studied, and the influence of temperature on biological and hydraulic parameters was verified. Backwash requirements and residual values of carbonaceous and suspended matter were explored in dependence on influent values and filtration velocity. At 13 °C, an ammonia load of 0.5 kg N/m3 d was completely oxidized. A concentration of 20 mg/l N-NH4 can thus be totally converted with an empty bed contact time of 1 hour. The Arrhenius temperature coefficient for nitrification was measured as 1.05. Biodegradable carbonaceous and suspended matter was completely removed at filtration velocities higher than 4 m/h, yielding an effluent of less than 5 mg/l for both SS and BOD. Backwash frequency was less than once per day, and a maximum of 5 % of the filter flowrate was used for backwashing.

Studies in nitrification of municipal sewage in an upflow biofilter

“…which shows a linear variation of eliminated ammonium load with the applied ammonium load. Similar tendency was observed in literature for full-scale sewage treatment plants [2,13,14].…”

“…The nitri®cation requirements usually lead to a reactor volume four times larger than that for carbon removal only. To comply with new ef¯uent discharge standards of <10 mg TKN/l, different upgrading methods for a highly loaded activated sludge plant were explored [2]. Fixed ®lm systems as tertiary add-on systems were thus developed to provide higher treatment standards on a limited area [3].…”

“…Because of high speci®c surface area and intensely aerated environment, granular ®lters provide favorable conditions for autotrophic bacteria attachment and so nitri®cation becomes independent of sludge age requirement [4]. The slow growth rate of nitri®ers is counterbalanced by their attachment on media [2]. Tertiary activated sludge may produce a diffuse¯oc dif®cult to settle [5].…”

“…Tertiary activated sludge may produce a diffuse¯oc dif®cult to settle [5]. Biological aerated ®lters combine aerobic degradation of pollutants with physical retention of suspended solids in one reactor [2]. The nitrifying ®lters were supposed to nitrify and polish the residual organic pollution contained in the secondary puri®ed water [6].…”

Inhibitory effects of ammonium, lipids, and salt on anaerobic digestion of food waste

“…Their ability to sustain shock loadings because of high bacterial concentrations also makes them ideal for pretreatment of industrial wastewaters. Pilot-scale studies (Paffoni et al, 1990;Dillion and Thomas, 1990;Vedry et al, 1994;Tschui et al, 1994) have confirmed the suitability of using aerated submerged filters for carbonaceous oxidation of settled sewage and tertiary nitrification of secondary effluent. Full-scale applications of biological aerated filters in conventional wastewater treatment facilities have also been reported (Rogalla and Sibony, 1992;Pujol et al, 1994).…”