Burst Detection by Water Demand Nowcasting Based on Exogenous Sensors

Bursts of drinking water pipes not only cause loss of drinking water, but also damage below and above ground infrastructure. Short-term water demand forecasting is a valuable tool in burst detection, as deviations between the forecast and actual water demand may indicate a new burst. Many of burst detection methods struggle with false positives due to non-seasonal water consumption as a result of e.g. environmental, economic or demographic exogenous influences, such as weather, holidays, festivities or pandemics. Finding a robust alternative that reduces the false positive rate of burst detection and does not rely on data from exogenous processes is essential. We present such a burst detection method, based on Bayesian ridge regression and Random Sample Consensus. Our exogenous nowcasting method relies on signals of all nearby flow and pressure sensors in the distribution net with the aim to reduce the false positive rate. The method requires neither data of exogenous processes, nor extensive historical data, but only requires one week of historical data per flow/pressure sensor. The exogenous nowcasting method is compared with a common water demand forecasting method for burst detection and shows sufficiently higher Nash-Sutcliffe model efficiencies of 82.7% - 90.6% compared to 57.9% - 77.7%, respectively. These efficiency ranges indicate a more accurate water demand prediction, resulting in more precise burst detection.

     

Monitoring Support for Water Distribution Systems based on Pressure Sensor Data

Water Resources Management - The increasing age and deterioration of drinking water mains is causing an increasing frequency of pipe bursts. Not only are pipe repairs costly, bursts might also lead...     

Modelling and controller design for distributed parameter systems via residence time distribution

For chemical reactors with non-linear fluid dynamics, a linear model realisation is proposed. The inputs are the ingoing concentration of a certain component in the fluid, and the reaction rate. The output is the outgoing concentration. The realisation makes use of a first-order reaction equation, and the residence time distribution of the fluid particles inside the reactor. Also dead time is incorporated in the modelling. The method is tested on two non-linear models for which the residence time distributions are known analytically. The first model is a series of mixed tanks, and it is shown by simulation that the method gives an accurate approximation of the original model. The second model is a UV disinfection reactor, which has a dead time. For this model, the residence time distribution is first fitted by a form that is suitable for our realisation method. Simulations show that for realistic disturbances a high-performance linear controller can be designed. After that, the residence time distribution of a real life UV reactor (for which we have no model) is fitted by a suitable form. The fit is of the same quality as for the UV reactor model. This indicates that also for the real life UV reactor a high-performance controller can be designed.     

Numerical modeling of piezoelectric transducers using physical parameters

Design of ultrasonic equipment is frequently facilitated with numerical models. These numerical models, however, need a calibration step, because usually not all characteristics of the materials used are known. Characterization of material properties combined with numerical simulations and experimental data can be used to acquire valid estimates of the material parameters. In our design application, a finite element (FE) model of an ultrasonic particle separator, driven by an ultrasonic transducer in thickness mode, is required. A limited set of material parameters for the piezoelectric transducer were obtained from the manufacturer, thus preserving prior physical knowledge to a large extent. The remaining unknown parameters were estimated from impedance analysis with a simple experimental setup combined with a numerical optimization routine using 2-D and 3-D FE models. Thus, a full set of physically interpretable material parameters was obtained for our specific purpose. The approach provides adequate accuracy of the estimates of the material parameters, near 1%. These parameter estimates will subsequently be applied in future design simulations, without the need to go through an entire series of characterization experiments. Finally, a sensitivity study showed that small variations of 1% in the main parameters caused changes near 1% in the eigenfrequency, but changes up to 7% in the admittance peak, thus influencing the efficiency of the system. Temperature will already cause these small variations in response; thus, a frequency control unit is required when actually manufacturing an efficient ultrasonic separation system.     

Adsorption of Phosphonate Antiscalant from Reverse Osmosis Membrane Concentrate onto Granular Ferric Hydroxide

Adsorptive removal of antiscalants offers a promising way to improve current reverse osmosis (RO) concentrate treatment processes and enables the reuse of the antiscalant in the RO desalination process. This work investigates the adsorption and desorption of the phosphonate antiscalant nitrilotris(methylenephosphonic acid) (NTMP) from RO membrane concentrate onto granular ferric hydroxide (GFH), a material that consists predominantly of akaganéite. The kinetics of the adsorption of NTMP onto GFH was predicted fairly well with two models that consider either combined film-pore or combined film-surface diffusion as the main mechanism for mass transport. It is also demonstrated that NTMP is preferentially adsorbed over sulfate by GFH at pH 7.85. The presence of calcium causes a transformation in the equilibrium adsorption isotherm from a Langmuir type to a Freundlich type with much higher adsorption capacities. Furthermore, calcium also increases the rate of adsorption substantially. GFH is reusable after regeneration with sodium hydroxide solution, indicating that NTMP can be potentially recovered from the RO concentrate. This work shows that GFH is a promising adsorbent for the removal and recovery of NTMP antiscalant from RO membrane concentrates.     

Pathways of sulfide oxidation by haloalkaliphilic bacteria in limited-oxygen gas lift bioreactors

Physicochemical processes, such as the Lo-cat and Amine-Claus process, are commonly used to remove hydrogen sulfide from hydrocarbon gas streams such as landfill gas, natural gas, and synthesis gas. Biodesulfurization offers environmental advantages, but still requires optimization and more insight in the reaction pathways and kinetics. We carried out experiments with gas lift bioreactors inoculated with haloalkaliphilic sulfide-oxidizing bacteria. At oxygen-limiting levels, that is, below an O(2)/H(2)S mole ratio of 1, sulfide was oxidized to elemental sulfur and sulfate. We propose that the bacteria reduce NAD(+) without direct transfer of electrons to oxygen and that this is most likely the main route for oxidizing sulfide to elemental sulfur which is subsequently oxidized to sulfate in oxygen-limited bioreactors. We call this pathway the limited oxygen route (LOR). Biomass growth under these conditions is significantly lower than at higher oxygen levels. These findings emphasize the importance of accurate process control. This work also identifies a need for studies exploring similar pathways in other sulfide oxidizers such as Thiobacillus bacteria.     

On feedback identification of unknown characteristics: a bioreactor case study

The problem of dynamical identification of unknown characteristics (states/parameters) in a biochemical model of a fed-batch bioreactor system given observations of some states is considered. An algorithm that solves this simultaneous state and parameter estimation problem and that is stable with respect to bounded informational noises and computational errors is presented. The algorithm is based on the principle of auxiliary models with adaptive controls. Convergence of the algorithm is proven and a convergence rate is derived. The performance of the algorithm is illustrated to a typical single-species bioreactor example.     

Optimal parametric sensitivity control of a fed-batch reactor

The paper presents an optimal parametric sensitivity controller for estimation of a set of parameters in an experiment. The method is demonstrated for a fed-batch bioreactor case study for optimal estimation of the half-saturation constant K_S and the parameter combination μ_maxX/Y in which μ_max is the maximum specific growth rate, X is the biomass concentration, and Y the yield coefficient. The resulting parametric sensitivity controller for the parameter K_S is utilized in two sequential experiments using a ‘bang-bang-singular’ control strategy. Comparison with an optimal solution for the weighted sum of squared sensitivities for both parameters are compared with the individual cases where only one specific parametric output sensitivity is controlled. The parametric uncertainty is handled in a completely deterministic way as to arrive at a control law that maximizes the parametric output sensitivity.     

Bit-rate control for MPEG encoders

Bit-rate control is a central problem in designing image sequence compression systems. In this paper we describe a new approach to bit-rate control for inter-frame encoders such as MPEG encoders. This approach uses concepts from control theory. Its central feature is a surprisingly simple but effective model for the encoder, which consists of a gain element, a delay element and additive noise. In our system we control the bit-rate with a PI-controller which is set to achieve two objectives: (1) we want the picture quality to be as uniform as possible, and (2) we want to use as closely as possible the available amount of bits. It is demonstrated in the paper that these two objectives, when considered separately, lead to contradictory settings of the controller. This dilemma can be solved by using Bit Usage Profiles that indicate how the bits have to be spread over the pictures. The effectiveness of the approach is demonstrated by designing a bit-rate control for an MPEG encoder that has a nearly constant bit-rate per group of pictures (GOP). Such a bit-rate control is of high value for applications like magnetic recording, where a constant bit-rate per GOP is required in order to realize playback trick modes, e.g. the fast forward mode.     

Nitrogen dynamics in flooded soil systems: an overview on concepts and performance of models

Extensive modelling studies on nitrogen (N) dynamics in flooded soil systems have been published. Consequently, many N dynamics models are available for users to select from. With the current research trend, inclined towards multidisciplinary research, and with substantial progress in understanding of N dynamics in flooded soil systems, the objective of this paper is to provide an overview of the modelling concepts and performance of 14 models developed to simulate N dynamics in flooded soil systems. This overview provides breadth of knowledge on the models, and, therefore, is valuable as a first step in the selection of an appropriate model for a specific application. © 2017 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.