H. Søeberg

External carbon source addition as a means to control an activated sludge nutrient removal process

Abstract In alternating type activated sludge nutrient removal processes, the denitrification rate can be limited by the availability of readily-degradable carbon substrate. A control strategy is proposed by which an easily metabolizable COD source is added directly to that point in the process at which denitrification momentarily occurs. This approach serves to increase the denitrification rate on demand, thereby allowing the accumulation of nitrate and nitrite during periods of peak nitrogen loading to be reduced or avoided. A pilot plant demonstration of the control strategy using acetate as COD source is provided, showing a marked improvement in effluent water quality as compared to the uncontrolled case. An examination of the resulting denitrification rates illustrates the direct proportionality between these rates and the rate of COD addition.

Mathematical model describing dispersion in free solution capillary electrophoresis under stacking conditions

Abstract From experiments a mathematical model is derived that quantitatively describes the dispersion processes in free solution capillary electrophoresis (FSCE) under both stacking and non-stacking conditions. The dispersion is subdivided into an axial, a radial and an introduction term. The last term includes an eventual stacking process, extraneous injection and diffusion during sample introduction. Each of the dispersive terms is derived and discussed. Guidelines for improved peak efficiency during FSCE analysis with stacking conditions are presented.

Temperature elevations of the sample zone in free solution capillary electrophoresis under stacking conditions

Abstract The combination of a low specific conductivity ratio of sample solution to surrounding running buffer (under stacking conditions) and high applied potentials can result in high power inductions and high temperatures of the sample zone. Eventually boiling occurs. Calculations of the sample zone and running buffer temperatures are based on changes in viscosity, relative permittivity, zeta potential and specific conductivity of the buffer solutions as a function of temperature. The temperature gradients across the capillary inner radius, the glass wall, the polyimide coating and the ldthermo layer” from the capillary outer coating to the surroundings are estimated. Heat-transfer coefficients for liquid- and air-cooled capillaries were obtained.

Monitoring and control of biological removal of phosphorus and nitrogen by flow-injection analysers in a municipal pilot-scale waste-water treatment plant.

Abstract A flow-injection system is used for monitoring and control of a biological waste-water treatment plant with biological removal of phosphate and nitrate. The waste-water treatment plant is an activated sludge type on a pilot scale, with municipal waste water as the influent. The flow-injection system monitors the concentrations of phosphate, ammonia and nitrate in four places: in the inlet, in the outlet of the anaerobic pretreatment tank, in one of the aeration tanks and in the outlet of the plant. Sampling is carried out via a cross-flow filter system, based on an ultra-filtration membrane. The analysers employ highly pulsating, single-piston liquid chromatographic pumps. Synchronization of injection time and pump pulses eliminates the need for pulse-damping devices and ensures high reproducibility. The chemical methods are based on classical colorimetric methods. The measurement system has been designed with emphasis on long-term stability, low reagent consumption and minimum maintenance. To maintain stable, low flow-rates, on-line degassing has been installed for each reagent. Further, on-line standard calibration is being used to compensate for drift in the sensitivity of the analysers. The system is controlled by a PC, programmed in ASYST. The calibrated data is fed to a programmable logic controller (PLC), which also controls the pilot plant. A supervisory PC, programmed in Factory Link, stores and presents data. The measurements will be used for studies of different control strategies for the plant, e.g., rule-based control.

An analysis of nitrogen removal and control strategies in an alternating activated sludge process

Abstract The biological nitrogen removal in an alternating activated sludge process is described and analyzed using a simplified model of the IAWQ activated sludge model No. 1. In face of the alternating nature of the process, a new analytical approach is developed by introducing the nitrification capacity and denitrification potential concepts into the alternating process analysis. This facilitates a more obvious insight into the nitrogen removal with the development of mathematical relationships between the nitrogen removal efficiency and the process operational conditions. The process performances with different operational conditions and control strategies are presented using this approach. The results show that the total nitrogen removal is strongly dependent on the process load, nitrification rate, denitrification rate, cycle length and DO setpoint etc. and an optimal operation requires a proper match between the nitrification and denitrification. In addition, the different control strategies are evaluated using the new analytic technique and through this their mechanism and effectiveness are better understood.

Monolithic flow sensor for measuring millilitre per minute liquid flow

Abstract A flowmeter based on a monolithic integrated flow sensor has been developed for measuring liquid flows as small as 0.1 ml/min in microchannels. The flowmeter is able to operate in thermal transit-time mode and thermal dilution mode. Diodes on the silicon chip are used both as the heating device and as the temperature detectors. When operating in thermal transit-time mode, the flowmeter has an accuracy better than 0.2% (at a flow rate of 0.2 ml/min) and a 90% response time less than 1 s. While operating in thermal dilution mode, the flowmeter has an accuracy of about 1%, but features an excellent dynamic performance with a —3 dB frequency cutoff up to 5 Hz. A dynamic model has also been developed for the interpretation of the mechanism of the flow sensor and for the calibration of the flowmeter. Simulation based on the model shows good agreement with the experimental results. The flowmeter will be used to monitor and control the liquid flow in FIA (flow injection analysis) systems.

A novel control strategy for improved nitrogen removal in an alternating activated sludge process—part I. Process analysis

Abstract Increasing demands on discharged water quality have led to the development of activated sludge processes which incorporate the biologically mediated removal of nitrogen and phosphorus. A major obstacle in the development of new control strategies for such processes is the lack of variables which can effectively alter process behavior and can feasibly be manipulated. This two part paper deals with a novel means to improve the nitrogen removal in an alternating type nutrient removal activated sludge process through control of the cycle length. In this first part, an analysis of process dynamics is undertaken. Using a simple model to describe the nitrogen dynamics in the alternating process, the existence of an optimal cycle length as a function of process conditions is demonstrated and explained. A graphical technique is developed which allows quick visualization of nitrogen dynamics under constant process conditions. This also serves as a means to assess whether a selected cycle length is optimal, too long, or too short for a given set of conditions. Based on the findings of this first part, the second part of the paper develops and demonstrates control strategies which serve to automatically adjust the cycle length to compensate for changing process conditions.

A novel control strategy for improved nitrogen removal in an alternating activated sludge process—part II. Control development

Abstract The first part of this two part contribution dealt with an analysis of nitrification and denitrification in an alternating activated sludge nutrient removal process for the case of constant process conditions. The existence of an optimal cycle length, which is a function of the process conditions, was demonstrated and discussed. Based on these findings, this paper examines a control strategy by which the cycle length of an alternating activated sludge nutrient removal process is automatically adjusted in order to compensate for changing process conditions. Two control algorithms are proposed. One involves proportional-integral-derivative (PID) control which requires minimal process information and computational effort. The second is a model based predictive control (MBPC) technique, which introduces a feedforward element into the control strategy. The MBPC technique is examined using a relatively simple process model. The results of experimental demonstrations of these two algorithms in a pilot plant facility indicate their potential towards improving nitrogen removal in the alternating process.

Identification of aprotinin degradation products by the use of high-performance capillary electrophoresis, high-pressure liquid chromatography and mass spectrometry

A preparation of bovine aprotinin, bovine pancreatic trypsin inhibitor, was subjected to high-performance capillary electrophoresis (HPCE) analysis and the purity was calculated to be approximately 80%. The two dominating contaminants were integrated to approximately 7% each as compared to the intact molecule. Characterization by high-pressure liquid chromatographic (HPLC) and mass spectrometric analysis was carried out on digests of the reduced and alkylated molecules. The contaminants were identified as truncated aprotinin, missing one and two amino acids, respectively, at the C-terminus. No such structures were identified in similar amounts in preparations of recombinant aprotinin by HPLC or HPCE.

Monitoring and Control of a Biological Nutrient Removal Process: Rate Data as a Source of Information

Abstract A means for obtaining rates of nitrification, denitrification and phosphate uptake/release in a nutrient removal waste water treatment process from FIA measurements is demonstrated. These rates provide useful information for understanding and modelling the process, and for the development of control strategies.