Biological reactors using a culture fixed on a fluidized bed are suitable for many applications in waste water treatment. A large number of studies have been carried out at the pilot-plant scale but none exists at the industrial scale for municipal waste water treatment. Examples are: - Dorr Oliver (Sutton + Mishra) (1) - The Biolex process developed by EBARA (2) - The reactor described by Heijnen (Holland) (3) In the latter two processes, fluidization and aeration are provided by an air-lift system inside the reactor. This article describes the Biolift process whose original feature is that the air-lift system is outside the reactor and is assisted by a system to inject secondary air (process air) into the reactor. This combination allows tight control of fluidization and aeration factors.

The new European Guideline on municipal wastewater discharges will require nitrogen removal in all sensitive areas below 15 mg TN/l. To achieve this limit within reasonable time and budget, infrastructure cost has to be minimised. To construct new sewage treatment plants close to urban neighborhoods or to upgrade existing facilites within current plant boundaries, high-rate reactors for nitrogen were investigated. The retained option was an upflow aerated filter on a floating granular media. The lightweight media facilitates backwashing, and an anoxic zone at the filter bottom achieves denitrification. After extensive pilot tests to quantify the performance of the reactor, a demonstration plant of one full-scale filter cell was constructed and operated for two years to verify technological as well as process options. The dynamic behaviour of the reactor could be assessed by continuous reading of ammonia and carbon pollution. This paper describes the results obtained and the observed system limits. The reactor was fed with primary settled wastewater containing about 450 mg COD/l and 65 mg TKN/l. Filtration velocity was varied between 1 and 2 m/h, and 100 to 300 % of the feed flow was recirculated. The removal rates at different temperatures were measured, under an applied load of 5 kg COD/m3 d, nitrification and denitrification capacities in the respective zones were around 1 kg N/m3 d at 15 °C. Up to 50 mg TN/l could be removed and the required effluent quality of the EC guideline could thus be achieved with an empty bed contact time of 2 hours. An additional on-site pilot test showed that within this same detention time, total nitrogen residuals down to 5 mg/l could be achieved at 10 °C.

Biological filters with fixed submerged beds are normally used for secondary or tertiary treatment and are recognized for their good performance. These processes are designed to meet, simultaneously, strict requirements of quality and operation. The achievement of the discharge consent requires the use of fine media which features a large support surface for the growth of biomass. On the other hand, the achievement of long filter run times is intrinsically related to the use of coarse media. Nowadays, all biological filters have mono‐media, which offers a compromise between these two conflicting criteria. The B2A process is a newly developed compact filter which ensures high filtration performance and long filter run times, even when used for crude sewage. The technology has been in use since 1992 for nitrification/ denitrification using an applied load of 0.7 kg/m3. d to obtain an effluent quality of 20 mg/l total nitrogen. Further tests have proved its efficiency in the removal of carbonaceous pollution. The B2A process is the first compact filter capable of treating screened crude sewage yet producing effluent qualities which are equal to that from conventional biological filters receiving settled sewage.

No abstract