自来水厂后臭氧投加复合控制

Composite control of post-ozone dosing in waterworks

摘要:

后臭氧化工艺是臭氧—生物活性炭深度处理工艺的重要环节,自来水厂的后臭氧投加控制直接关系到后臭氧化工艺的运行效率,以及深度处理工艺出水水质是否达标和优质.水源水质受上游来水水质、气候及气象条件、突发污染事故的影响非常大,而且自来水厂制水工艺各个环节影响因素较为复杂,后臭氧化工艺进水水质和水流量变化较为频繁.因此,当进水水质和水流量变化时,如何实时调整臭氧投加量以保证臭氧化效能和控制溴酸盐生成是后臭氧化工艺运行优化的难点.本文以CT值（即C和T的乘积,C为水中余臭氧质量浓度,T为臭氧与水接触时间）为控制目标,在水流量比例控制的基础上,提出一种基于干扰观测器（disturbance observer,DOB）和模型预测控制（model predictive control,MPC）的复合控制方法.MPC用于臭氧投加的反馈控制,DOB用于估计进水水质和水流量变化引起的模型失配和外部干扰,并将估计值用于臭氧投加的前馈控制中.仿真和实验验证结果表明,与MPC反馈控制相比,所提的后臭氧投加DOB-MPC复合控制具有更优异的控制性能和干扰抑制效果,能够有效提高后臭氧化工艺的运行效率和深度处理工艺出水水质的稳定性.

Abstract:

Post-ozonation is an important step during advanced water treatment by ozone-biological activated carbon. Post-ozone dosing control in waterworks is directly related to the operation efficiency of post-ozonation and the treated water quality of advanced water treatment. Source water quality is highly affected by the upstream water quality, climate, and weather conditions, as well as sudden pollution accidents. The influential factors of each link in water treatment plant are complicated. Thus, the influent water quality and water flow of post-ozonation change frequently. When the influent water quality and water flow change, how to adjust the ozone dosage in time to ensure ozonation efficiency and restrict bromate formation is a challenge in operation optimization of post-ozonation. A composite control method consisting of disturbance observer (DOB) and model predictive control (MPC) was proposed based on the control objective of CT value (i.e., product of C and T, Cis the concentration of ozone residual in water, T is the contact time of ozone and water) and proportional control of water flow. MPC was employed for the feedback control of ozone dosing. DOB was adopted to estimate the model mismatch and external disturbance of ozonation caused by the change of influent water quality and water flow. The estimated values were applied for the feed-forward control of ozone dosing. Both simulations and experimental results show that compared with MPC feedback control, the proposed DOB-MPC composite control of post-ozone dosing has better control performance and disturbance rejection effect, which can effectively improve the operation efficiency of post-ozonation and the stability of treated water quality of advanced water treatment.