مدیریت بروز آلودگی درشبکه‌های توزیع آب شهری: مطالعه موردی

نویسندگان

چکیده

درسال‌های اخیر توجه روز افزون به ایمن نگاه داشتن شبکه‌‌های آب شهری از خطرات احتمالی طیف وسیعی از مطالعاتی را به دنبال داشته است که مهم‌‌ترین هدف آن‌ها، کمینه کردن اثرات مخرب این خطرات بر سلامت عموم بوده است. یکی از مهم‌ترین خطرات تهدید کننده شبکه‌های آب شهری، حملات عمدی ‌به‌منظور آلوده کردن آب شبکه با آلاینده‌های شیمیایی است. به دلیل اهمیت بروز آلودگی در شبکه آب شهری بر سلامت مردم وهمچنین زمان بسیار مهم از هنگام تشخیص و تأیید آلودگی تا شروع فعالیت-های واکنشی در کاهش اثرات مخرب آلودگی بر سلامت مردم ضروری است اقدامات مناسبی در این خصوص اندیشیده شود. از جمله اقدامات انجام شده در این تحقیق ایزوله کردن ناحیه آلوده شده توسط شیرهای موجود در شبکه به منظور‌جلوگیری از گسترش آلودگی و تخلیه آب آلوده از طریق شیرهای آتش‌نشانی می‌باشد. این مسئله با استفاده از الگوریتم ژنتیک بررسی شد. نتایج نشان داد که با انتخاب تعداد جمعیت ?? و نسل ???، نرخ تزویج ??/? و جهش ??/? کمترین آلودگی در شبکه مصرف شده است. در این تحقیق آنالیز حساسیت بر روی زمان شروع مدیریت پیامد از ساعت ?? الی ?? انجام شد که نتایج نشان داد، کاهش زمان شروع مدیریت پیامد درکاهش آلودگی نقش بسزایی دارد.

کلیدواژه‌ها


عنوان مقاله [English]

Consequence Management of Pollution Injection in Water Distribution Networks: A Case Study

چکیده [English]

Introduction:
Water Distribution Networks (WDNs) are one the most important infrastructures that very vulnerable to accidental or deliberate contamination intrusion due to their accessibility and extension over urban areas. In recent years, there has been increased interest on protecting these networks from possible contamination risks with the aim of mainly minimizing the harmful effects on public health and security. Attacks on WDNs can be divided into three categories of cyber-attacks, physical attacks and biological and chemical attacks. One of the most important threat to WND is a deliberate chemical or biological contamination injection due to uncertainty on both location injection and consequences. Therefore, it is essentially required to take optimal activities for minimizing public health and economic consequences and restoring the system to normal operation conditions. These activities mainly consist of any combination of system isolation, public notification, flushing and finally providing short-term and long-term alternative domestic water supply.
Methods:
In this study, an embedded approach consists of EPANET simulation model and multi-objective optimization model namely Non-dominated Sorting Genetic Algorithm-II (NSGA-II) is used to derive the optimal operational response actions following the contamination detection in the network. EPANET ?.? simulation model is used to calculate the spatial variation of contamination in the network at different time step. EPANET is an open free software that easily linked with optimization model via its toolkit. NSGA-II optimization model develops a trade-off between two common objectives functions in consequence management modeling. NSGA-II optimization model sorts the population of different chromosomes based on their non-dominance over the other solutions. According to the number of dominated solutions, a rank is assigned to a particular chromosome in the current population. Moreover, a crowding distance is considered to preserve diversity among chromosomes in a population.
In this research, to illustrate the performance of the proposed methodology, Net? from EPANET ? is employed. This system consists of ??? pipes, ?? nodes, three tanks, two pumps, a lake and a river. A deliberate contamination is injected into the network at node ??? for six hours (??:?? to ??:??). As suggested in Ostfeld and Salomons (????) study, five sensors at nodes ??, ??, ???, ??? and ??? are considered for early warning contamination detection. The first sensor is detected the contamination about ??:?? and one hour is assumed for initiating response actions. Therefore, optimal operational response actions are started at ??:?? and will continue until the end of simulation time (??:??). It is assumed that all hydrants are class C (red) with discharge rate of less than ???? liter/min (proposed by National Fluid Power Association).
Two main objective functions are considered in this study for NSGA-II multi-objective optimization model. The first objective is to minimize the number of operational activities that include open or close the valves and hydrants in the network. To control the consequences of contamination in the network, the polluted area is isolated by the valves to prevent the spread of contamination and the discharge of contaminated water through fire hydrants. Hence, the optimization model has binary decision variables including hydrant opening and valve closing. Total number of decision variables are equal to the potential number of valves and hydrants. In this study, optimal operation activities should be selected among ?? potential valves and hydrants. The number of operational activities was limited to ?? activities. The second objective is minimization of consumed contaminated water by multiplying the concentration of pollutants in consumed contaminated water volume.
Results:
Obtained results show that without any operational response action, consumed contamination mass is equal to ??.?? kg. Whereas, consumed contamination mass is decreased to ??.?? kg with ?? optimal response actions. Optimal values for different parameters of multi-objective model are obtained by sensitivity analysis through the number of populations and genes, as well as crossover and mutation rates. The optimal selected values for the optimization model are ?? populations, ??? genes with a crossover and mutation rate of ?.?? and ?.??, respectively. Moreover, in this study, sensitivity analysis was carried out on start time of consequence management (between ??:?? to ??:?? with one hour time interval) for evaluation of its effect on the second objective function. Consumed contamination mass at different start time of consequence management between ??:?? to ??:?? with hourly time step are equal to ??.??, ??.??, ??.??, ??.??, ??.?? and ??.?? kg, respectively. As it is illustrated, the earlier the operational activities starts, the more the consumed contamination mass decreases.

کلیدواژه‌ها [English]

  • Contamination
  • Consequences Management
  • Genetic Algorithm
  • Simulation
  • Optimization