Automatic control for do and pH in the activated sludge process in a coke wastewater treatment plant

The objective of this study is to develop an automatic control system for dissolved oxygen (DO) and pH of the activated sludge process in a coke wastewater treatment plant. A discrete type autotuned proportional-integral (PI) controller using an auto-regressive exogenous (ARX) model as a process model was developed to maintain the DO concentration in aerators by controlling the speed of surface aerators. Also a nonlinear pH controller using the titration curve was used to control the pH of influent wastewater. This control system was tested in a pilot scale plant. During this pilot plant experiment, there was small deviation of pH and the electric power consumption of surface aerators was reduced up to 70% with respect to the full operation when the DO set point was 2 mg/1. For real plant operation with this system, the discrete PI controller showed good tracking for set point change. The electricity saving was more than 40% of the electricity consumption when considering surface aerators. As a result of maintaining the DO constantly at the set point by the automatic control system, the fluctuation of effluent quality was decreased and overall improvement of the effluent water quality was achieved.     

Model-based control of the substrate concentration in an aeration basin using the wastewater level

This paper deals with the minimal-cost control of the modified activated sludge process with varying level of wastewater in the aerator tank. The model-based adaptive controller of the effluent substrate concentration, basing on the substrate consumption rate and manipulating the effluent flow rate outcoming from the aerator tank, is proposed and its performance is compared with conventional PI controller and open loop behavior. Since the substrate consumption rate is not measurable on-line, the estimation procedure on the basis of the least-square method is suggested. Finally, it is proved that cooperation of the DO concentration controller with the adaptive controller of the effluent substrate concentration allows the process to be operated at minimum costs (low consumption of aeration energy).     

Use of modelling to evaluate best control practice for winery-type wastewaters.

Winery wastewaters are high strength, and readily biodegradable, making them perfect for application of anaerobic digestion. However, inherent buffering against pH changes also requires some process knowledge and monitoring. They are therefore an important target for anaerobic process control. This has had limited application, but is emerging as an important research and development area. In this paper, we evaluate the use of model-based control analysis of a heavily loaded vinasse-fed reactor. Two controllers--both proportional-integral (PI)--on total volatile fatty acids (VFA) (< 500 mg/L), alkalinity (VFA/Total Alkalinity < 0.2) were evaluated in a fitted model, against the actual control mechanism used, which was model-based adaptive control. The two controllers were both less aggressive than the adaptive controller, producing less gas overall, but also using more caustic for pH control. The controllers were also evaluated against their ability to deal with noise, as PI controllers are relatively poor for controlling non-linear processes. The VFA controller was very poor with noise added, proving difficult to tune, and oscillatory. The alkalinity controller was effective with moderate detuning. This emphasizes the need to use effective controller inputs, when applying simple, linear controllers. Overall, use of a model was an effective method to evaluate the different controllers in a competitive way, in a standardized environment.     

Improvement of ammonia removal in activated sludge process with feedforward-feedback aeration controllers.

In the paper three linear aeration controllers that can be easily implemented are presented and evaluated on the activated sludge process pilot plant. Controllers differ according to the information that is used about the process, which can be oxygen in the last aerobic reactor, ammonia in the last aerobic reactor and ammonia in the influent. The aeration controllers that are addressed are: oxygen cascade PI controller, ammonia cascade PI controller and ammonia feedforward-cascade PI controller. Experiments show that, in comparison with the oxygen cascade PI controller, the ammonia cascade PI controller allows better control of effluent ammonia and airflow savings of around 23%, while the ammonia feedforward-cascade PI controller gives the best reduction of ammonia peaks and can save up to 45% of the airflow.     

Multivariable modeling and control of an activated sludge process

This paper contains two contributions. First it is shown, in a simulation study using the IAWQ model, that a linear multivariable time-invariant state-space model can be used to predict the ammonium and nitrate concentration in the last aerated zone in a pre-denitrifying activated sludge process. Secondly, using the estimated linear model, a multivariable linear quadratic (LQ) controller is designed and used to control the ammonium and nitrate concentration.     

基于节能的鼓风曝气系统溶解氧稳定智能控制方法

目前,国内大多数采用活性污泥法的城市污水处理厂的曝气控制系统普遍存在着溶解氧浓度波动大、曝气量冗余大、曝气单元能耗高等问题。介绍了一种基于气量动态变化反馈控制原理与PID反馈控制原理的鼓风曝气系统溶解氧稳定智能控制方法,该方法可以使曝气池适应污水处理厂进水水量和水质的变化,保持溶解氧浓度的稳定,对污水处理厂稳定安全的运行和降低系统能耗均有显著效果。该方法对于采用鼓风曝气的活性污泥法工艺具有良好的普适性和有效性,并在实际应用中取得了很好的效果。     

The application of model predictive control of ammonia nitrogen in an activated sludge process

In this paper a model predictive controller (MPC) for ammonia nitrogen is presented and evaluated in a real activated sludge process. A reduced nonlinear mathematical model based on mass balances is used to model the ammonia nitrogen in the activated sludge plant. An MPC algorithm that minimises only the control error at the end of the prediction interval is applied. The results of the ammonia MPC were compared with the results of the ammonia feedforward-PI and ammonia PI controllers from our previous study. The ammonia MPC and ammonia feedforward-PI controller give better results in terms of ammonia removal and aeration energy consumption than the ammonia PI controller because of the measurable disturbances used. On the other hand, with the ammonia MPC, comparable or even slightly poorer results than with the ammonia feedforward-PI controller are obtained. Further improvements to the MPC could be possible with an improved accuracy of the nonlinear reduced model of the ammonia nitrogen, more sophisticated control criteria used inside the controller and the extension of the problem from univariable ammonia to multivariable total nitrogen control.     

水处理过程中DO值控制的研究

通过采用一种先进的控制策略——基于径向基函数神经网络,利用T I公司的TM S320LF 2407型DSP作为中央处理器,选择磁场导向控制(FOC)算法,对用于驱动鼓风机的异步交流电动机的转速实施控制,从而实现了对采用活性污泥法水处理过程中一重要指标——生化反应池中的溶解氧(DO)进行准确实时控制,达到较好的水处理效果。     

Knowledge-based control and case-based diagnosis based upon empirical knowledge and fuzzy logic for the SBR plant.

Because biological wastewater treatment plants (WWTPs) involve a long time-delay and various disturbances, in general, skilled operators manually control the plant based on empirical knowledge. And operators usually diagnose the plant using similar cases experienced in the past. For the effective management of the plant, system automation has to be accomplished based upon operating recipes. This paper introduces automatic control and diagnosis based upon the operator's knowledge. Fuzzy logic was employed to design this knowledge-based controller because fuzzy logic can convert the linguistic information to rules. The controller can manage the influent and external carbon in considering the loading rate. The input of the controller is not the loading rate but the dissolved oxygen (DO) lag-time, which has a strong relation to the loading rate. This approach can replace an expensive sensor, which measures the loading rate and ammonia concentration in the reactor, with a cheaper DO sensor. The proposed controller can assure optimal operation and prevent the over-feeding problem. Case-based diagnosis was achieved by the analysis of profile patterns collected from the past. A new test profile was diagnosed by comparing it with template patterns containing normal and abnormal cases. The proposed control and diagnostic system will guarantee the effective and stable operation of WWTPs.     

A hybrid respirometric method for more reliable assessment of activated sludge model parameter

A novel hybrid respirometric principle is proposed that is particularly suited to sludge and wastewater characterisation in the context of activated sludge process models. Advantages of two respirometric principles are combined and their disadvantages eliminated to increase measuring frequency and precision. Emphasis is put on decreasing the bias in parameter estimates that results from the use of unreliable sensor constants in the calculation of respiration rates. To this end checks for dissolved oxygen probes, aeration systems and pumps are built into the respirometer's operation. Checks are to be run while the respirometric batch experiment is conducted so that between-experiment variation is eliminated and within-experiment variation is minimised. It is also stressed that a combined sensor/process model should be used to estimate the process parameters rather than a sequential procedure in which the sensor constants are first used to calculate respiration rates, that are subsequently used for sludge and wastewater characterisation. Finally, three possible practical implementations of the new principle are discussed in relation to maximising parameter estimation accuracy.     

潘家口水库热分层期溶解氧垂向分布及影响因素

为探究水库热分层对溶解氧垂向分布的影响,2019年8月在潘家口水库设置监测平台,分别采用YSI-EXO2监测仪和NISKIN采样器进行监测和水样采集,测定库区水温、溶解氧、pH、浮游植物等水质指标的垂向分布,分析水体热分层期溶解氧垂向分布的影响因素及溶解氧极小值（MOM）的形成原因。结果表明：潘家口水库8月存在显著热分层现象,水温呈混合层-温跃层-滞温层结构。混合层溶解氧浓度大于6.5 mg/L;温跃层受热分层等影响显著,层内出现MOM,梯度明显增大,浓度显著减小;滞温层溶解氧逐渐恢复。相关性分析表明：溶解氧与水温和浮力频率显著相关,热分层是MOM形成的主要物理因素;溶解氧与浮游植物生物量和pH呈正相关,温跃层浮游植物的呼吸作用、营养物质的积累和有机物质的氧化分解等生物和化学因素在一定程度上促进了MOM的发展。     

风电机组的积分模糊滑模变桨距控制

针对变桨距风力发电机组具有参数变化、强干扰、建模困难等特性,设计出了一种积分模糊滑模变桨距控制器。通过在传统滑模控制器中采用状态变量代替误差项的导数并引入误差项的积分来设计切换函数,消除了传统变结构控制需要已知期望输出信号导数的假设;利用模糊推理动态地调节切换增益,并采用积分的方法对切换增益上界进行估计,避免了传统滑模控制器需要选取不确定因素上界,同时采用合适的连续函数来代替切换增益中的符号函数,有效地削弱了系统的抖振。仿真结果表明:该控制器应用在风速高于额定风速以上的变桨距控制系统中,对系统参数的不确定性和外部干扰均具有很强的鲁棒性,能够有效地改善风电机组变桨距系统的控制性能。     

Use of a dynamic gassing-out method for activity and oxygen diffusion coefficient estimation in biofilms

p-toluenesulphonic acid degradation by Comamonas testosteroni T-2 in multi-species biofilms was studied in a fixed bed biofilm reactor. The polypropylene static mixer elements (Sulzer Chemtech Ltd., Switzerland) were used as a support matrix for biofilm formation. Biofilm respiration was estimated using the dynamic gassing-out oxygen uptake method. A strong relation between oxygen uptake and reactor degradation efficiency was observed, because p-toluenesulphonate degradation is a strictly aerobic process. This technique also allowed us to estimate the thickness of the active layer in the studied system. The mean active thickness was in order of 200 μm, which is close to maximum oxygen penetration depth in biofilms. A transient mathematical model was established to evaluate oxygen diffusitivity in non-steady-state biofilms. Based on the DO concentration profiles, the oxygen diffusion coefficient and the maximum respiration activity were calculated. The oxygen diffusion coefficient obtained (2 10^-10-1.2 10^-9 m² s^-1) is in good agreement with published values. The DO diffusion coefficient varied with biofilm development. This may be, most likely, due to the biofilm density changes during the experiments. The knowledge of diffusivity changes in biofilms is particularly important for removal capacity estimation and appropriate reactor design.     

Modelling of long-term simultaneous nitrification and denitrification (SNDN) performance of a pilot scale membrane bioreactor

Nutrient removal capability of the MBR process has attracted more attention than organics removal in the past few years. Apart from the conventional schemes for nitrogen removal in MBR process, simultaneous nitrification-denitrification (SNDN) requires the most attention for further research. In order to fully understand the fundemantals and mechanism of SNDN in MBRs, a pilot plant was set up. A mathematical model was adopted for investigation and calibration against the observed values. This paper reports a study focusing on evaluating major mechanisms that govern nitrogen removal from domestic wastewater in membrane bioreactors. Two items need to be emphasized in this evaluation: (i) an MBR is basically regarded as an activated sludge process-a suspended growth bioreactor with total biomass recycle and substantially higher biomass concentration; (ii) in this context an AS model, namely ASM1R modified for endogenous respiration, is used for dynamic modelling and calibration of experimental results. The impact of diffusion through biomass which obviously exerts a significant effect on system performance and denitrification is evaluated with success using the adopted model by means of switch functions that regulate nitrification-denitrification with respect to dissolved oxygen concentration in the bulk liquid.     

Theoretical analysis and experimental study of oxygen transfer under regular and non-breaking waves

The dissolved oxygen concentration is an important index of water quality, and the atmosphere is one of the important sources of the dissolved oxygen. In this paper, the mass conservation law and the d...     

Fault detection in a real-time monitoring network for water quality in the lagoon of Venice (Italy).

In the context of monitoring water quality in natural ecosystems in real time, on-line data quality control is a very important issue for effective system surveillance and for optimizing maintenance of the monitoring network. This paper presents some applications of recursive state-parameter estimation algorithms to real-time detection of signal drift in high-frequency observations. Two continuous-discrete recursive estimation schemes, namely the Extended Kalman Filter and the Recursive Prediction Error algorithm, were applied to assuring the quality of the dissolved oxygen (DO) time series, as obtained from the Lagoon of Venice (Italy) during August 2002, through the real-time monitoring network of the Magistrato alle Acque (the Venice Water Authority). Results demonstrate the effectiveness of the methodology in early detection of a probable drift in the DO signal. Comparison of these results with those obtained from the application of a related recursive scheme (a Dynamic Linear Regression procedure) suggests the strong benefits of approaching the problem of on-line data quality control with several (not merely a single) independent such estimation methods.     

Predictive control of irrigation canals – robust design and real-time implementation

Predictive control is one of the most commonly used control methods in a variety of application areas, including hydraulic processes such as water distribution canals for irrigation. This article presents the design and application of predictive control for the water discharge entering into an irrigation canal located in Spain. First, a discrete time linear model of the process is described and its parameters are experimentally identified. The model is well validated within the usual canal operating range and is used to formulate a predictive control law with an incremental formulation. Finally, experimental and simulation results are presented in which predictive control has shown better performance than a well-tuned proportional, integral and derivative controller to automatically manage demanded water discharges.     

A nitrate biosensor based methodology for monitoring anoxic activated sludge activity.

An improved methodology based on a nitrate biosensor is developed and applied successfully for in-depth monitoring and study of anoxic activated sludge activities. The major advantages of the methodology are its simplicity, reliability and high data quality. The resulting data allowed for the first time to monitor anoxic respiration rate of activated sludge (nitrate uptake rate (NUR)) at a high time resolution making it clearly comparable with high frequency oxygen uptake rate (OUR) measurements obtained under aerobic conditions. Further, the anoxic respiration data resulting from a pulse addition of carbon source to endogenously respiring anoxic activated sludge shows a clear start-up phenomenon and storage tail that is usually also observed in high-frequency OUR measurements. Finally, the improved methodology can be expected to serve as an anoxic respirometer for activated sludge treatment plants where denitrification process occurs in single-step. Further, it can be used for a variety of purposes e.g. for toxicity and activity monitoring, process control and parameter estimation of the activated sludge process, similar to the aerobic respirometers.     

Iterative design of a nitrate controller using an external carbon source in an activated sludge process

More stringent effluent and cost requirements are increasing the need for better control of wastewater treatment plants. In an activated sludge process, the nitrogen removal efficiency may be improved by adding an external carbon source. In this paper, automatic control of the nitrate level by regulating external carbon flow is discussed. More specifically, an iterative tuning procedure for the controller is outlined. Iterative controller design schemes aim at tuning high performance controllers of low complexity using closed loop data. The basic strategy used in this paper is an iterative pole placement controller design procedure. The suggested approach is compared with conventional design in a simulation study.     

风力发电机的最优控制

在对定速风力发电机建模的基础上,针对大型风力发电机功率控制中相互矛盾的要求,结合PI控制器,采用了线性二次最优控制,对仿真与传统的PI控制进行了对比,仿真结果表明:运用此控制器,控制效果要好于单独的PI控制器。同时,对桨矩角采用不同的权重时,输出功率、发电机转速、输出转矩都将发生变化。