Time filter

Source Type

Seine, France

This paper aims to provide information about the conditions for the occurrence of nitrites upon the wastewater downstream denitrification through biofillration. More specifically, it addresses the issue of nitrogen load handling. The study has shown that nitrogen loading is a key factor to be taken into account to prevent the occurrence of residual nitrites. An excessive nitrogen loading will inevitably bring about the emergence of residual nitrites in the treated water, even though the operating conditions are optimized (optimized C/N and P/N). In the light of the outcomes, it appears that the maximum load beyond which a residual nitrite level is likely to be hardly kept under 1 mg N.t' ranges from 2.5 to 2,8kgN-NO3:m5.d -1. More precisely assessing that upper loading limit is an awkward task, since the occurrence of nitrites additionally depends on such factors as the water temperature.

This paper aims to provide information about the conditions for the occurrence of nitrites upon the wastewater downstream denitrification through biofiltration. More specifically, it addresses the issue of the handling of carbon-containing substrate inputs. Our results have demonstrated that the nitrites emerge when a C/N ratio ranging from 2 to 3 is applied, a peak concentration being recorded at 2.4-2.5. Under such methanol underdosing conditions, the carbon input is sufficient to cause nitrites to be generated in the lower layers of the filter media but insufficient for fully removing them from the upper part of the media. The most suitable ratio for completely removing the nitrates without any emergence of nitrites and without any significant increase in residual BOD is about 3-3.2. This study has also highlighted the need for injecting the methanol in order to keep a constant C/N ratio within the biofilter, a fluctuating ratio inevitably causes the nitrite to emerge. Now, the methanol control pattern as a function of the desired nitrogen concentration in the effluent, which is typically used in the treatment plants, is inadequate for stabilizing the C/N ratio when the concentration of nitrates of the effluent being treated in the plants is highly variable.

This paper aims to provide information about the conditions for the occurrence of nitrites upon the wastewater downstream denitrification through biofiltration. More specifically, it addresses the issue of the effects of phosphate inputs on the occurrence of nitrites in denitrified water. Our results have demonstrated that the biomass consumes on average 0.02-0.03 mg P.permg removed N-NOx. Thus, keeping a P-PO4 -3/N-NO 3 - ratio of 0.03 in the nitrified water as supplied for the denitrification step makes it possible to achieve an efficient denitrification while limiting the concentrations of residual phosphates in denitrified water. A closer look at the phosphate consumption has shown that the biomass may behave like a genuine « phosphate sponge » quite efficiently retaining the phosphates when they occur in an excessive amount in the reaction medium; the consumptions can reach as much as 0.05-0.06 mg P.permg removed N-NOx in these conditions of excess. Conversely, experiments conducted in a laboratory pilot plant have shown that the biomass can remove a large amount of nitrogen in the absence of dissolved phosphates. The purifying biomass is then not very responsive to the phosphate variation in the reaction medium. Unstable phosphate inputs, inducing periods of temporary phosphate deficiency, will not necessarily impair the denitrification nor generate nitrites in the effluent. The phosphate deficiency, however, may be a compounding factor if too high nitrogen loads are applied to the denitrification units. In this situation, slower denitrifkation kinetic processes caused by restrkted phosphorus inputs enhance the phenomenon of nitrite emergence as caused by an excessive nitrogen loading.

Pham H.N.,University Of Technologique Of Complegne | Mottelet S.,University Of Technologique Of Complegne | Schoefs O.,University Of Technologique Of Complegne | Pauss A.,University Of Technologique Of Complegne | And 5 more authors.
Eau, l'INDUSTRIE, les Nuisances | Year: 2010

Pursuant to the EU Water Framework Directive, the member states must restore a good ecological and chemical status of the surface water bodies within 15 years. As regards the nitrogen compounds, the threshold values not to be exceeded in the natural environment have been set to 2 mg.L-1, 0.5mg.L-1, 0.3 mg.L-1 et 50 mg.L-1for Kjeldahl nitrogen (NK), ammonia nitrogen (NH4 +), nitrite nitrogen (NO2 -) and nitrate nitrogen (NO3 -) respectively. Achieving these quality objectives implies that the wastewater treatment plant operators can control and monitor the concentrations of both nitrate and nitrite nitrogen in discharged water. Now, whereas the UV-type measuring apparatuses in current use enable to record the values for both species, they are not suitable for discriminating them. Against that background, the scientists from the Université Technologique de Compiègne and the Syndicat Interdépartemental pour l'Assainissement de l'Agglomération Parisienne have launched a study for testing and improving the on-line measuring apparatuses for NO3 -/NO2+ - As a matter of fact, a prototype on-line spectrophotometer discriminating the specific concentrations of nitrates and nitrites was tested and validated under actual operating conditions in a SIAAP's treatment plant (Seine Centre - Colombes - 800000 equivalent inhabitants). As evidenced by the results, there were good correlations between the estimated and experimental values ranging from 0.5 to 18 mg-N.L-1 for nitrates and from 0.5 to 5 mg-N.L-1 for nitrites. The discrimination between the nitrate and nitrite contents stems from the mathematical treatment of the UV spectrum rather than the resolution of the spectrophotometer. The outcome of the optimization and improvement of the spectral identification software has been weighed against the globally similar results given by such identification methods as PCR (Principal Component Regression) and PLS (Partial Least Squares).

Rocher V.,SIAAP | Paffoni C.,SIAAP | Goncalves A.,SIAAP | Azimi S.,Usine Seine Center | Legaigneur V.,SIAAP Usine Seine Gresillons
Eau, l'INDUSTRIE, les Nuisances | Year: 2010

Water treatment through biofiltration is a technology which is integrated into most of the sewage plants in the Paris area. Due to the development of that process within the Paris area plants, the SIAAP task forces were prompted to get into the refinements and problems related to the use of such fixed beds. To that purpose, the control of the biofilter restarting periods was investigated. What is desired is coming up with strategies for restarting the biofiltration units in order to provide for a quick restoration of the nominal treatment performance. Such an early restoration of performance is essential, since running in degraded conditions will bring about an altered quality of water flowing back to the natural environment.

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