This research project focused on nitrogen removal in activated sludge systems used for treating saline industrial wastewater. A team of three industrial partners (Shell, Heiploeg and Ecco) and two knowledge partners (IHE Delft and TUD) were involved in the project. The project was initiated at IHE Delft with partial support from Shell on March 1998.
The official project subsidised by BTS/Senter started on 1/9/1999 and continued for a period of three years.
There is an increasing concern for the future availability of fresh water of good quality, which is leading to a policy of more economic usage of water and water reuse. This will result in an increase of salt content of the ultimately produced wastewater. On the other hand, effluent criteria are becoming more stringent especially with respect to the discharge of nutrients such as nitrogen.
These two developments may interfere because high salt levels may negatively affect nitrification, which is the rate-limiting step in biological nitrogen removal. This means that there is a need for clear understanding of the precise effects of salt on the nitrification process. Therefore a research project had been set up at IHE Delft.
This project concentrated on establishing fundamental relationships between salinity, pH, temperature and ionic strength on the kinetics of nitrification.
The research concept was based on a close and direct connection between the theoretical and experimental work at IHE and the practical problems in operation of industrial large-scale treatment works of the industrial partners.
The aim of this project was to generate an understanding, based on laboratory scale experiments and modelling, of the sensitivity of the nitrification process to sub-optimal salt concentrations in combination with other sub-optimal environmental conditions expected to occur in full scale treatment plants.
Activities and Outputs
Two phases were involved in the research project. The first phase incorporated laboratory scale and field-work research, the second phase covered the modelling part of the research topics. The main research topics can be summarised as follows:
- Determination of the qualitative and quantitative effect of the salt level on nitrification.
- Determination of the effect of different types of salt on the nitrification activity.
- Identification and quantification of the effects of salt in combination with other destabilising factors (pH and temperature) on the stoichiometry and kinetics of nitrification.
- Investigation of shifts in the microbial populations of nitrifying micro-organisms as a result of the prevailing salt level.
- Incorporation of the salt effect on nitrification in the existing activated sludge model (ASM 2).
- Considering the effect of salinity on technological and physico-chemical parameters.