This paper describes a modified version of the IAWPRC model and the techniques used to calibrate it on site. Growth rate of autotrophic bacteria and the inert wastewater fractions were measured by simple methods, both in laboratory pilots and on full scale. Model predictions were compared to full scale results in large plants (> 100 000 P E). Measured autotrophic growth rates ranged from 0.3 to 0.65 1/d, depending on wastewater toxicity. Most model constants compared well with original IAWPRC proposals, and several wastewater types were identified. Parameters to establish a suspended solids balance are given. Different configurations of plants for nitrogen removal were investigated, including conventional recirculation, sludge reaeration (RDN) and step feed alternate zone denitrification.

The aim of this article is to present a new biological aerated filter (BAF) for nitrogen removal based on simultaneous nitrification and denitrification. Contrary to the systems which integrate both an aerated and a non-aerated zone to allow complete nitrogen removal in one compact or two different units (pre-denitrification and nitrification), this upflow BAF system is based on the principle of simultaneous nitrification and denitrification since the filter is completely aerated. The denitrification process is possible due to the diffusion effect which dominates biofilm processes. The real time aeration control allows us to maintain a low dissolved oxygen value (0.5 to 3 mg O2/l). In this case, the biofilm will not be fully (or less) penetrated with oxygen and denitrification will be carried out in a large part of the biofilm. Therefore, nitrification and denitrification is running simultaneously in different depths of the biofilm. By using 50% less air this BAF gave the same results (less than 20 mg TN/l) on pilot plant as a classical nitrification and denitrification BAF (Toettrup et al., 1994). Less recirculation was necessary to achieve the same denitrification.

The wastewater plant Seine Aval (located in Acheres, France) treats 6 million PE (25 m3/s average flow, 570 MGD) with activated sludge. Following a research program called “Azote Acheres” which demonstrated that biofilters are an economical solution, the Paris Metropolitan Area Sewage Service (SIAPP) has tested 3 industrial prototypes during a period of more than 4 years. One of these is an up-flow biofilter using a floating filter bed made of expanded polystyrene beads. This specific process is called BIOSTYR and is used here as a nitrifying tertiary biofilter. The purpose of this paper is to show that the biofilter process achieves very low, steady state, effluent ammonia concentrations with different applied nitrogen loads (0.3 to 2.7 kg NTK/m3.d), even with low temperature and high applied carbonaceous load. During this 4 years period, a model has been developed to explain the hydraulic behavior of the filter. By measuring the operating conditions (temperature, loads), the head loss of the filter can be predicted. After this test period, the prototype has been operated by Seine Aval plant staff. The results obtained have confirmed the previous test results.

The use of a sequencing batch reactor (SBR) for wastewater characterization requires the interpretation of the total respirometric response obtained in batch culture with primary settled water. In a first step and with the aim of understanding this total response, the water was divided by filtration into three fractions, the respirometric responses of which were analysed separately. This paper presents the results of the study of the biodegradability and of the specific respirometric responses of the soluble and colloidal fractions of an urban wastewater during batch cultures with a high concentration in pre-acclimatized activated sludges (low So/Xo ratio). For the water studied, the soluble fraction could be divided in two fractions of equal size : a readily biodegradable fraction and an inert fraction. Ultrafiltration of the soluble fraction during the cultures allowed stating the specific evolution of the soluble organic compounds according to their Molecular Weight. For the colloidal fraction, the observed behaviour was totaly different. Indeed, the colloidal organic matter disappeared very quickly from the liquid phase according to a physical phenomenon but without any important biological oxidation during the first 5 hours of a batch culture. Latest work concerns the study of the particulate organic matter and the interpretation of the total respirometric response knowing the specific response of the three fractions.

Biofilters can be added to existing non-nitrifying activated sludge plants for tertiary ammonia removal and effluent polishing. It is a convenient, efficient, and cost effective way of meeting more stringent consents. In order to prove this technology, a biofilter pilot plant was installed in a large activated sludge plant with challenging conditions, since almost half of the load is industrial effluent and the water temperature can be as low as 7 degrees C. Trials were conducted over a two year period, providing the following information: low water temperature does not affect the process; the optimum rise rate at nominal flow is 8.5 m/h for this wastewater; the consent can be achieved for ammonia loads up to 0.94 kgNH4N/M3 media/day; about 50% of the post-secondary TSS and BOD can be removed in the BAF; a large proportion of industrial effluent has not had any noticeable effect on the beads after two years. A full scale plant with a nominal flow of 8257 l/s was then built and commissioned in summer 1998. Seeding was completed within three weeks of starting the filters. Two months later, a 28 day takeover was started. Results obtained on full scale plant during and after this test confirm the results obtained on the pilot.