Herwig Bogaert

A titrimetric respirometer measuring the nitrifiable nitrogen in wastewater using in-sensor-experiment

Measurement of nitrifiable nitrogen contained in wastewater by combining the existing respirometric and titrimetric principles is reported. During an in-sensor-experiment using nitrifying activated sludge, both the dissolved oxygen (DO) and pH in the mixed liquor were measured, and the pH was controlled at a set-point through titration of base or acid. A combination of the oxygen uptake rate (OUR), which was obtained from the measured DO signal, and the titration data allowed calculation of the nitrifiable nitrogen and the short-term biological oxygen demand (BOD) of the wastewater sample that was initially added to the sludge. The calculation was based solely on stoichiometric relationships. The approach was preliminarily tested with two types of wastewaters using a prototype sensor. Good correlation was obtained.

Reducing the size of a nitrogen removal activated sludge plant by shortening the retention time of inert solids via sludge storage

Spare nitrification capacity is usually needed for a nitrifying activated sludge plant to counter nitrogen shock loads and/or toxicity incidents. The traditional way to provide this capacity is to apply a sludge retention time that is much longer than needed for treating ordinary loads, resulting in over-designed plants. The approach investigated in this paper is to store the spare biomass in a separate sludge storage tank and return it to the main stream process when a shock nitrogen load or an inhibition/toxicity incident occurs. Model-based analysis reveals that, in such a plant, inert solids stay significantly shorter than the active biomass. This implies that one may extend the retention time of the active biomass to the required level without raising the retention time of the inert solids to the same level, giving rise to the possibility of reducing the size of the plant. Savings on tank volume are estimated to be typically around 20%. Experimental studies carried out on a pilot plant confirmed the theoretical results. Furthermore, they revealed that the decay rate of the nitrifiers in the storage tank could be maintained at a low level by intermittently aerating the sludge, so that an even smaller storage tank is required.

Sensors to monitor biological nitrogen removal and activated sludge settling

Abstract A brief overview of methods and sensors to characterize activated sludge is presented, summarizing techniques related to two important activated sludge processes: biological nitrogen removal (nitrification and denitrification) and sludge settling. Traditional off-line methods, typically applied in a laboratory environment to determine nitrifying/denitrifying sludge activities and sludge settling properties are briefly described. The main part of the paper covers a more detailed description of on-line sensors which were recently developed to continuously provide information about important activated sludge properties in a full-scale plant. The most important future work in this research field is the development of control strategies based on the data provided by these sensors.

Sludge storage for countering nitrogen shock loads and toxicity incidents

Spare nitrification capacity is usually needed for a nitrifying activated sludge plant to counter nitrogen shock loads and/or toxicity incidents. The traditional way to provide this capacity is to apply a sludge retention time which is much longer than what needed to obtain a stable nitrification, resulting in over designed plants. Another approach, which is investigated in this paper, is to store the spare biomass in a separate sludge storage tank and return it to the main stream process when a shock nitrogen load or a toxicity incident occurs. Model based analysis reveals the unique feature of the scheme: different particulate components in the sludge have a different retention time, and more specifically, active biomass stays longer in the plant than inert solids. This results in that a plant with a storage tank can have the same amount of active biomass as a traditional plant but less sludge, opening the potential of reducing the volume of the plant. Analysis shows that a plant with a sludge storage tank can be about twenty percent smaller than a traditional plant that has the same treatment capability. Analysis is verified by simulation studies.

Design and verification of a model secondary clarifier for activated sludge

A model clarifier was designed using conventional methods for the surface calculation and an alternative pathway for the determination of the height and constructed accordingly. In addition, a new approach was used to evaluate the necessary scraper speed in comparison to full-scale clarifiers. Scaling effects were taken into account. The model clarifier was first tested by tracer experiments. Conductivity measurements were used for the clarification zone, whereas the thickening zone was tested using pyrene as an organic tracer compound. Finally, the behaviour of the model clarifier was compared with a full-scale settler. The results indicated that operation of the model clarifier was representative of full-scale behaviour, except for severe overloads. Hence, the small-scale clarifier qualified as a model for small-scale studies and could be installed on large-scale plants to monitor more transparently plant performance and sludge behaviour