New measurement techniques for secondary settlers: a review.

In activated sludge wastewater treatment research, most of the attention has been devoted to the biodegradation process. However, in terms of effluent quality, the final settling and clarification processes are at least as important because any particle carried over the overflow weir brings with it not only COD, but also nitrogen and phosphorus. In recent years we see indeed increased attention on this separation step, and alternatives such as membrane separation are increasingly introduced. Still, a large installed base of settlers exists, whose operation could/should be optimised. The measurement techniques presented in this contribution each focus on one of the key processes in the secondary settler: hydrodynamics, particle aggregation and breakage, hindered settling and compression. For each technique, the measuring principle is explained and a typical data set shown.

Estimating costs and benefits of advanced control for wastewater treatment plants--the MAgIC methodology.

This paper discusses a methodology to estimate the costs and benefits of advanced control for wastewater treatment plants. The methodology has been applied to four wastewater treatment plants, representing four standard types of plants built in Flanders, Belgium. The paper outlines the methodology and illustrated results from one of the four design cases. General results are shown and contrasted with full-scale experience. The methodology appears to give realistic results and will be used for further refinement of default control algorithms for certain types of plants. A preliminary analysis indicates that on-line control can become cost-effective for plant sizes above 50,000 population equivalents.

Non-contact measurement of wastewater polluting load--the Loadmon project.

A new approach to the measurement of polluting load in crude wastewaters is described. The Loadmon project has developed an optical technique which enables suspended solids and organic load of a crude wastewater to be measured in an open channel. There is no requirement for any sampling equipment or sensor contact of any kind. The paper covers the laboratory study of wastewater optical properties,the prototype development, testing in the laboratory and field trials. Future plans for product development are outlined.

A new one-dimensional clarifier model--verification using full-scale experimental data.

A new one-dimensional clarifier model was developed, including components of existing models, and extended with a height-dependent cross-sectional area and two flowrate-dependent dispersion coefficients. This model is evaluated using data from a detailed one-month measuring campaign on a full-scale wastewater treatment plant. The data included hourly sludge concentration profile, sludge heights at 10 minute intervals, sludge concentrations in inlet, effluent and recycle flows and regular settling properties characterised by batch setting tests. Due to the poor quality concentration measurements at the surface of the clarifier, the model was not calibrated to perform well in concentration predictions at this surface. However, excellent descriptive capabilities were obtained for sludge profiles and blanket level. The Cho et al. setting velocity function was found to be significantly better in terms of description capability than the more traditional Vesilind function.

Feasibility of automatic chemicals dosage control--a full-scale evaluation.

This contribution discusses the feasibility of automatic control for chemicals dosing in activated sludge systems. The evaluation is made on the basis of a full-scale implementation at the Lommel WWTP (Belgium) of an on-line controlled dosage system for iron chloride and external carbon source. The control laws are very simple and allow intuitive adaptation by the plant operators. The control system results in a significant reduction of the chemicals dosage, better effluent results and a lower sludge production. The implementation is furthermore cost-efficient.

On-line control of biological nutrient removal processes in practice: a cost-benefit analysis.

On-line control is able to boost process efficiency and optimise effective capacity of nutrient removal plants. In this paper, costs and benefits of on-line control are presented and economical feasibility is analysed using a simple economical cost-benefit analysis. These concepts are illustrated by a number of full-scale case studies. The on-line control of ferric dosage is illustrated by the case of the Lommel WWTP, and the Harelbeke WWTP and Houthalen WWTP illustrate advanced on-line control of aeration for nitrogen removal.

On-line estimation of the maximum specific growth rate of nitrifiers in activated sludge systems.

The on-line estimation of the maximum specific growth rate of autotrophic biomass is addressed in this article. A general nitrification process model, which is valid for any realistic flow pattern, is used to develop the estimation algorithm. Depending on the measurements available, two estimation equations are derived. While both require measuring the nitrification activity of the activated sludge, one requires the additional measurement of the nitrifiable nitrogen concentrations at the two ends of the bioreactor, and the other requires the nitrate nitrogen concentrations at the same locations. The algorithm also requires some stoichiometric and kinetic parameters. However, sensitivity analysis shows that the estimate is insensitive to the parameters other than the autotrophic decay rate. Compared to the existing algorithms, the algorithm developed in this article does not rely on the assumption of ideal flow pattern in the plant and does not require an error-prone estimate of the autotrophic biomass concentration. Experimental and simulation studies show that the algorithm performs well and is robust to influent variations and accidental sludge losses.