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doi: 10.1177/014233128400600302pmid: N/A
In general, studies of the control of the activated sludge process have focused on the design of single-loop controllers able to suppress higher-frequency disturbances and provide minimum-variance performance about a precisely-defined, constant set-point. This paper addresses some of the complementary problems of control. It considers the slower dynamical components of activated sludge process behaviour, the detection of and response to conditions of process failure, control within imprecisely-defined 'domains' of performance, and (by implication) the concept of switching performance from one such domain to another. For these purposes the paper discusses the construction of a relatively complex microbiological model for the activated sludge process. The results of using this model in simulation studies of a fuzzy controller are then presented. These preliminary results are encouraging and suggest that, in spite of the substantial current limitations on process knowledge, there are many novel aspects of activated sludge process control yet to be explored.
doi: 10.1177/014233128400600303pmid: N/A
The oxidation ditch is becoming increasingly popular in the United Kingdom for comparatively low-load domestic waste treatment situations. It has found widespread use for larger-scale waste treatment in Europe, especially in Holland. The original oxidation ditch concept is over 20 years old, and much research work has been carried out on the sludge characteristics and chemical processes. As a result of ever-increasing operational costs and more stringent effluent quality standards, the need has now arisen for a detailed study of the dynamics of the oxidation ditch process.This paper forms part of an overall model identification study and intends to examine the possibility of on-line parameter estimation using the Extended Kalman Filter. The first part of the paper develops a non- linear, conceptual, dynamic model of dissolved oxygen (DO)/biological oxygen demand (BOD) interaction in the oxidation ditch. The model is employed together with an arbitrary set of parameters, in the synthesis of a series of noise-corrupted process data. The second part of the paper gives the Filter equations and the third part presents the results of the parameter estimation study.
doi: 10.1177/014233128400600304pmid: N/A
The general theme of water quality management is to reduce a primary health risk to a residual risk and induced secondary risks. The paper considers UK residual health risks, sources of instability in water resource systems and the control of complex river basins.
doi: 10.1177/014233128400600305pmid: N/A
This paper assesses the potential benefits of optimal control applied to the activated sludge wastewater treatment process. The optimal control approach is motivated by the need to compromise between treatment efficiency and operational costs. In this sense this approach differs from a previous activated-sludge control scheme, in which only control effectiveness was taken into account. Two separate control problems are addressed, with differing scope and methodologies, but still in the optimality context. Dissolved oxygen control is considered first, and a discrete-time optimal output regulator is designed. Then the attention is focused on recycle sludge manipulation for which two different feedback schemes are evaluted. From the simulations it appears how the effectiveness of a control scheme depends almost entirely on a proper choice of the cost functional.
doi: 10.1177/014233128400600306pmid: N/A
A simple digester model considering the degradation of carbohydrates to acetic acid by acetogenic bacteria and the subsequent production of CH4 and CO2 by acetoclastic methanogens was used to simulate the effects of organic ramp overload waves. Process-control strategies based on pH or bicarbonate-concentration monitoring and alkali addition were simulated and compared. CO2 partial pressure as indicator of process stability was also tested.
doi: 10.1177/014233128400600307pmid: N/A
The theory behind the dynamics of the final clarifier of the sludge plant is reviewed and the corresponding distributed parameter model is discussed. Since this full model is too complicated for on-line use, a simplified, lumped-parameter model is derived, which has the following three state variables : sludge blanket height and mean sludge concentrations above and below the sludge blanket height. It has been calibrated and validated with routine measurements from a real clarifier. The conclusion is drawn that the simplified model describes well the dynamics of the clarifier and, therefore, may be used for various real-time control purposes. For example, when combined with an adaptive parameter estimation algorithm, the model can be used to monitor the settling characteristics of the sludge without measuring sludge volume index.
doi: 10.1177/014233128400600309pmid: N/A
In this paper, variable operation of the plant is studied through a model previously developed for simulating steady-states and optimising the total design cost of a treatment plant. In particular, various possible designs of a plant are considered; for each of them, a set of steady-state values for the effluent quality level, compatible with the initial design, are simulated and the total variable operating costs are optimised. In this way the dependence of the variable operating costs on both the design and operating effluent quality levels can be analysed.
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