High rate aerated biofilters for plant upgrading

Abstract

Biocarbone aerated biofilters were developed more than ten years ago. Almost one hundred plants worldwide provide complete treatment in very short hydraulic retention time. This allows to construct compact plants in sensitive areas such as inner cities, sea or mountain resorts. The filters can be adapted to high effluent qualities expected by the European directive on wastewater treatment. Full oxidation of ammonia can be achieved in less than two hours. A plant for complete removal of nitrogen has been operated for more than a year in Denmark to meet Europe's most stringent effluent requirements by using an anoxic biofilter in series with the Biocarbone. A new aerated biofilter, turning the Biocarbone principle upside down, is presented : a synthetic floating material allows enhanced performance, simplified backwash and a combination of anoxic and aerobic zones in one reactor. Effluent quality of less than 10 mg/l for all components (BOD, SS, TN) was demonstrated in a one-year long on-site test in Denmark and the first facility for 60 000 population equivalents is under startup. Full scale results of the upflow floating filter, Biostyr, are presented for nitrogen and phosphorus removal according to the European directive.

Studies in nitrification of municipal sewage in an upflow biofilter

“…11. As the HRT decreased from 24 to 6 hour, the ef®ciency decreased from 98 to 96% for the average inlet suspended solids concentration of 428 mg/l, compared to the investigations of Rogalla et al [3] and Desbos et al [14] where, for the inlet suspended solids concentration of 335 mg/l, the suspended solids removal ef®ciencies of 89 and 93% respectively were reported with less than 1 h and 4 h HRTs for the domestic municipal sewage system.…”

“…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].…”

Integration of high-rate DAF technology within a municipal biofiltration plant for the treatment and thickening of backwash wastewaters

“…Submerged biological aerated filtration (BAF) is one of the most compact technologies for wastewater treatment. One of the major interests in using BAF for wastewater treatment is its small footprint, which is of great interest for new projects in dense urban areas, as well as for the extension and upgrading of existing works (Rogalla et al 1994), especially those in built-up areas where limited space is available for expansion (Pujol et al 1994). When used as a secondary treatment step, BAF backwash water represents 12 to 35% of the total treated water volume (Mendoza-Espinosa & Stephenson 1999), which is usually returned at the head of the works, thus impacting the hydraulic design of the BAF units.…”