Booster Chlorination Research Articles

Adaptative water quality management in water distribution systems by optimizing control valves and chlorination booster stations

ABSTRACT Good water quality in a water distribution system (WDS) can be reached by using flow control valves (FCV) to reduce water residence time (WRT), and chlorine booster stations to maintain acceptable free residual chlorine concentrations (FRCC). The research developed a cost-effective, adaptative approach for managing FCV and chlorine booster stations, while maintaining acceptable pressure and FRCC ranges. The methodology is applied to a real full-scale case study considering three optimization formulations: 1) FCV operation, 2) chlorine booster station operation, and 3) combining them in an adaptive management strategy. Results revealed that chlorine booster stations individually or combined with FCV enhanced water quality significantly at an acceptable cost, while FCV optimization alone or combined with chlorine booster stations reduced WRT by, at most, 3.8%. Chlorine booster stations were thus more effective than FCV in this case study. This formulation can be applied to other WDS to improve water quality cost-effectively.

Optimizing the number, locations, and chlorine dosages of booster chlorination stations in water distribution networks

ABSTRACT Safe and reliable drinking water is essential for sustaining life. Chlorination is widely used for disinfection in water distribution networks (WDNs). A higher dose of chlorine is required in an overhead service reservoir to maintain minimum residual chlorine at the farthest end in WDNs. However, delivering high dosages of chlorine from storage tanks can pose public health issues, especially for the residents living near overhead service reservoirs due to the formation of trihalomethanes, haloacetic acids, and chlorophenols. In addition, a higher dosage will lead to increased chlorine consumption and will accelerate pipe corrosion. Booster chlorination (BC) stations with smaller dosages are a solution to this problem. However, identifying the optimal number, locations, and dosage of each BC station in a cost-effective manner is challenging. This study proposes a methodology for determining the optimal number, locations, and chlorine dosages of BC stations in WDNs using a mixed integer linear programming problem. The methodology is illustrated through a simplified WDN in Holeta town, Ethiopia. The results indicate that if one adds two BC stations beyond the three dosage stations at the source, it will lead to a 49% reduction in chlorine use and a 27% decrease in the life cycle cost.

Optimization of Chlorine Injection Schedule in Water Distribution Networks Using Water Age and Breadth-First Search Algorithm

Chlorine decay over time and distance travelled poses challenges in maintaining consistent chlorine levels from treatment plants to demand nodes in water distribution networks (WDNs). Many studies have focused on optimizing chlorine booster systems and addressing dosage and location. This study proposes a chlorine injection optimization model for maintaining spatial and temporal chlorine residuals within an acceptable range. First, the approach involves identifying potential pathways from the source to demand nodes using a breadth-first search (BFS) algorithm. Subsequently, the required chlorine injection to maintain a 0.2 mg/L residual chlorine level at demand nodes is estimated based on water age. Finally, a single-objective genetic algorithm optimizes the chlorine injection schedule at the source. The results demonstrated that chlorine estimation based on water age exhibited promising results with an average error below 10%. In addition, the four-interval injection scheme performed well in adapting to changing demand patterns, making the method robust to varying demand patterns. Moreover, the model could accommodate fluctuating water temperature conditions according to operating seasons. This study provides valuable insights into effectively managing chlorine levels and operations of WDNs, and paves the way for using water age for chlorine estimation.

Photodegradation of halogenated organic disinfection by-products: Decomposition and reformation

In this study, the photodegradation of 33 different DBPs (trihalomethanes, haloacetic acids, haloacetaldehydes, and haloacetonitriles) and TOX with low pressure UV light and the subsequent reformation of DBPs with chlorine and monochloramine were investigated. Results indicated that photodegradation followed the order of TOI > TOBr > TOCl, and treated surface water with low SUVA254 background did not impact the photodegradation of highly UV susceptible DBPs such as triiodomethane (TIM), diiodobromomethane (DIBM), tribromomethane (TBM). The mass balance results of chloride, bromide and iodide showed that the main photodegradation mechanism of TOBr and TOI was dehalogenation supported by halide releases (i.e., Cl−, Br− and/or I− ion). In addition, the photodegradation removal effect was higher, when brominated DBPs formation was high. Although low pressure UV light effectively removed halogenated organic DBPs, subsequent use of disinfectants (Cl2 and NH2Cl) reformed photodegraded DBPs, and the overall DBPs concentrations were increased, which suggested that the released Br− and I− ions will reform DBPs in distribution systems, with oxidants present or added (e.g., booster chlorination) in distribution systems. This study showed that although UV photodegradation will reduce halogenated organic DBPs in distribution systems, especially more toxic iodinated and brominated DBPs, it will be a more effective technology towards the end of the distribution system or a point of entry solution rather than in distribution system with post-disinfection and residence time.

Bayesian Optimization of Booster Disinfection Scheduling in Water Distribution Networks

Chlorine remains the most widely used disinfectant in drinking water treatment and distribution systems worldwide. To maintain a minimum residual throughout the distribution network, chlorine dosage needs to be regulated by optimizing the locations of chlorine boosters and their scheduling (i.e., chlorine injection rates). Such optimization can be computationally expensive since it requires numerous evaluations of water quality (WQ) simulation models. In recent years, Bayesian optimization (BO) has garnered considerable attention due to its efficiency in optimizing black-box functions in a wide range of applications. This study presents the first attempt to implement BO for the optimization of WQ in water distribution networks. The developed python-based framework couples BO with EPANET-MSX to optimize the scheduling of chlorine sources, while ensuring the delivery of water that satisfies water quality standards. Using Gaussian process regression to build the BO surrogate model, a comprehensive analysis was conducted to evaluate the performance of different BO methods. To that end, systematic testing of different acquisition functions, including the probability of improvement, expected improvement, upper confidence bound, and entropy search, in conjunction with different covariance kernels, including Matérn, squared-exponential, gamma-exponential, and rational quadratic, was conducted. Additionally, a thorough sensitivity analysis was performed to understand the influence of different BO parameters, including the number of initial points, covariance kernel length scale, and the level of exploration vs exploitation. The results revealed substantial variability in the performance of different BO methods and showed that the choice of the acquisition function has a more profound influence on the performance of BO than the covariance kernel.

Robust Optimal Booster Disinfectant Injection in Water Systems under Uncertainty

Water distribution systems (WDSs) require high-quality water for safe consumption. To achieve this, disinfectants such as chlorine are often added to the water in the system. However, it is important to regulate the levels of chlorine to ensure they fall within acceptable limits. The higher limit is to control disinfection by-products, while the lower limit is established to guarantee that the water is free of organic contaminants. The rate at which chlorine reacts within the pipes is affected by various factors, such as the type of pipe, its age, the pH level of the water, the temperature, and others. This variability makes it challenging to accurately model water quality in WDSs, which can impact the optimal rate of booster injection. To address the uncertainty in the chlorine reaction rate, the current research proposes a robust counterpart reformulation of the booster chlorination scheduling problem, which considers the chlorination reaction rate as uncertain. The proposed reformulation was tested on two benchmark WDSs and analyzed with a thorough sensitivity analysis. The results showed that as the size of the uncertainty set increased, the injection mass also increased. This reformulated approach can be applied to any WDS and provides a way to obtain optimal scheduling within the desired protection levels.

Predicting Chlorine and Trihalomethanes in a Full-Scale Water Distribution System under Changing Operating Conditions

Predicting free chlorine residual and Trihalomethanes (THMs) in water distribution systems (DS) is challenging, given the variability and imprecise description of the chlorination conditions prevailing in full-scale systems. In this work, we used the variable reaction rate constant (VRRC) model, which offers the advantage of describing variable applied dosage and rechlorination conditions without the need for model recalibration. The VRRC model successfully predicted chlorine decay and THMs formation in ammonia-containing water at the lab scale. Comparing the goodness of fit results showed a better fit by the VRRC model than the 1st-order and an equally good fit compared to the parallel 1st-order model. However, the independence of the VRRC coefficients upon chlorine dosage made it a better choice for full-scale implementation than the parallel 1st-order model. Chlorine and THMs predictions in the DS were performed in 22 locations from a full-scale DS in southern Quebec (Canada). Chlorine predictions by VRRC were conducted in the spring and fall of 2021 under changing water quality conditions (temperature, DOC, dosage). With a prediction target of 0.1 mg/L absolute error, the VRRC model met this target in 77% of the points in the spring and 73% in the fall. While the predictions were comparable and slightly better than those of the 1st-order model, the main advantage of the VRRC was its applicability under variable dosage and rechlorination conditions (e.g., booster chlorination). THMs predictions in the DS were successfully performed in fall 2021. While 91% of the nodes had less than 5 μg/L of absolute prediction error with the VRRC model, the 1st-order model only met this target in 1 out of 22 points. In addition to its high precision, the VRRC can predict THMs using only the lab scale experiments for model parametrization. This enables small utilities with limited resources to predict the possibility of THMs non-compliances under changing water quality conditions with simple lab-based experiments. Changing climatic conditions can deteriorate drinking water quality, raise regulatory concerns for chlorine and THMs, and threaten public health. Water utilities can use the simple approach proposed in this work to assess the possibility of non-compliance under changing conditions. Moreover, the efficiency of different interventions or mitigation strategies to resolve or avoid non-compliance can be evaluated with this approach.

Exploring Vulnerable Nodes, Impactful Viral Intrusion Sites, and Viral Infection Risk Reductions Offered by Chlorine Boosters in Municipal Drinking Water Networks

The effects of drinking water system infrastructure on water quality and health following intrusion events have not been extensively studied. This study proposes a coupling of hydraulic and water-quality modeling with quantitative microbial risk assessment (QMRA) to characterize microbial infection risks. Two networks were considered based on their network configuration. We assumed a continuous intrusion of enterovirus under three scenarios. The location of vulnerable and influential nodes in a looped and a branched network were compared, followed by a comparison of chlorine booster placement to reduce infection risks. The most vulnerable nodes in the branched network were generally downstream of the intrusion site, whereas those for the looped network were in the middle of the network due to tank dynamics. Influential injection nodes for the looped network were also in the middle of the network but mostly located at the upstream nodes for the branched network. A single chlorine booster yielded a risk reduction (47.6%) for the branched network, greater than for the looped network (nearly none). Two chlorine boosters reduced the looped network risks more notably (63%). The generalizability of these results to other networks likely depends upon specific network hydraulics and variability in municipal drinking water use. This work will help public water system managers in identifying vulnerable points in their distribution system and optimal locations for risk reduction strategy implementation.

Chlorine decay and disinfection by-products transformation under booster chlorination conditions: A pilot-scale study

Booster chlorination was usually employed in water distribution systems with a long hydraulic retention time. The free chlorine decay and disinfection by-products (DBPs) transformation under booster chlorination conditions were investigated within a pilot-scale water distribution system (WDS). Compared with the initial chlorination in water plants, the loss of chlorine was relatively slow and could be described with first-order kinetic model. The rate of chlorine decay and the generation of DBPs in WDS were much greater than those in beaker. High flow rate and the hydraulic transients both promoted chlorine decay and DBPs formation, especially for dichloroacetonitrile (DCAN). The formation of trihalomethanes (THMs) and haloacetic acids (HAAs) was higher in the ductile iron pipe than in the steel pipe. After booster chlorination, THMs, HAAs, and DCAN all climbed up and then declined continuously, but the peak times were different during the reaction process. The results showed the generation period of DBPs followed the order: THMs (27 h) > HAAs (22 h) > DCAN (5 h). DCAN was not stable in WDS and could be decomposed for a long hydraulic retention time (HRT). The decrease of dichloroacetic acid (DCAA) and increase of trichloroacetic acid (TCAA) indicated that DCAA may turn into TCAA. Linear relationships between the free chlorine demand (FCD) and the generation of THMs that considered both buck water and the pipe wall, as well as the different hydraulic conditions, were established to predict the formation of DBPs in WDS after booster chlorination.

Fuzzy credibility-constrained quadratic optimization for booster chlorination of the water distribution system under uncertainty

Abstract To keep chlorine concentration at acceptable levels, chlorine is usually injected into the water distribution system (WDS). To protect the health of human beings, the chlorine concentration at consumers’ nodes should be kept at appropriate levels. However, these levels are difficult to determine due to the presence of fuzzy uncertainties. To deal with fuzziness at both sides of the constraints in the optimization model of booster chlorination, we propose a fuzzy credibility-constrained quadratic programming (FCCQP) model with a consideration of credibility levels and weight coefficients. The proposed model is applied to two WDSs to obtain the booster cost under uncertain conditions. The results indicate that the booster cost increases with the confidence level for lower chlorine concentration ζL. In addition, the booster cost decreases with the weight coefficient w. The booster cost function curves along with the variation of weight coefficients are concave and convex for scenario 1 and scenario 2, respectively. These results can help managers to make informed decisions on disinfection injection under conditions of fuzzy uncertainties.

Insights for booster chlorination strategy based on DBPs control in a large-scale water supply system

Based on a one-year field investigation of disinfection by-products (DBPs) in large scale water distribution system (LSWDS), the various characteristics of DBPs together with their correlation with booster chlorination were elaborated through ArcGIS model. Furthermore, the effects of booster chlorination on DBP formation were investigated through simulated experiments. Residual chlorine showed a strong relationship with occurrence of different DBPs in LSWDS, and the yield of DBPs increased significantly after booster chlorination. The simulated chlorination experiments showed that diminution of the ratio of primary to secondary (booster) chlorination dosage, and delaying the secondary chlorine addition reduced the generation of DBPs during water conveyance. The yield concentrations of THMs and HAAs obviously increased after booster chlorination. The correlation between HAAs and chlorine dosage is weaker in the field research than in the simulation experiment while THMs had a positive correlation with the chlorine addition in both field research and simulation experiment.

Staged energy and water quality optimization for large water distribution systems.

Simultaneous optimization of energy and water quality in real-time large-sized water distribution systems is a daunting task for water suppliers. The complexity of energy optimization increases with a large number of pipes, scheduling of several pumps, and adjustments of tanks' water levels. Most of the simultaneous energy and water quality optimization approaches evaluate small (or hypothetical) networks or compromise water quality. In the proposed staged approach, Stage 1 uses a risk-based approach to optimally locate the chlorine boosters in a large distribution system based on residual chlorine failures and the associated consequences in different land uses of the service area. Integrating EPANET and CPLEX software, Stage 2 uses mixed integer goal programming for optimizing the day-ahead pump scheduling. The objective function minimizes the pumping energy cost as well as the undesirable deviations from goal constraints, such as expected water demand. Stage 3 evaluates the combined hydraulics and water quality performances at the network level. The implementation of the proposed approach on a real-time large-sized network of Al-Khobar City in Saudi Arabia, with 44 groundwater wells, 12 reservoirs, 2 storage tanks, 191 mains, 141 junctions, and 17 pumps, illustrated the practicality of the framework. Simulating the network with an optimal pumping schedule and chlorine boosters' locations shows a 40% improvement in water quality performance, desired hydraulics performance with optimal pump scheduling, and an average 20% energy cost reduction compared to the normal (unoptimized) base case scenario.

Convex Heuristics for Optimal Placement and Operation of Valves and Chlorine Boosters in Water Networks

This paper investigates the problem of optimal placement and operation of valves and chlorine boosters in water networks. The objective is to minimize average zone pressure while penalizing deviations from target chlorine concentrations. The problem formulation includes nonconvex quadratic terms within constraints representing the energy conservation law for each pipe, and discretized differential equations modeling advective transport of chlorine concentrations. Moreover, binary variables model the placement of valves and chlorine boosters. The resulting optimization problem is a nonconvex mixed integer nonlinear program, which is difficult to solve, especially when large water networks are considered. We develop a new convex heuristic to optimally place and operate valves and chlorine boosters in water networks, while estimating the optimality gaps for the computed solutions. We evaluate the proposed heuristic using case studies with varying sizes and levels of connectivity and complexity, including two large operational water networks. The convex heuristic is shown to generate good-quality feasible solutions in all problem instances with bounds on the optimality gap comparable to the level of uncertainty inherent in hydraulic and water quality models.

Optimization of booster chlorination for water distribution system under dual uncertainties

ABSTRACT Chlorine is generally used as disinfectant to sustain water quality in water distribution system (WDS). To prevent the occurrence of disinfectant by-product as well as control the growth of microorganism, the residual chlorine concentration in WDS should be kept between acceptable intervals. However, the chlorine concentration was uncertain due to chlorine decay, imprecise measure, hydraulic and topological conditions. In addition, nodal response coefficients to unit disinfectant mass in the left-hand-side of the constraints were also uncertain, which is affected by uncertain pipe diameter, roughness coefficients, nodal demand, bulk decay coefficient, and wall decay coefficient, etc. Therefore, in this paper a fuzzy chance-constrained optimization model under dual uncertainties was proposed and applied to optimize the chlorine injection mass to maintain chlorine in WDS distributed uniformly with consideration of randomness of chlorine concentration limits as well as uncertainty in response coefficient. The total injection mass decreases with the uncertainty level under possibility of dominance and necessity of dominance indices, while increases with the uncertainty level under possibility of strict dominance and necessity of strict dominance indices, which is effective in chlorine injection management.

Discussion of “Influence of Dead-End Sections of Drinking Water Distribution Networks on Optimization of Booster Chlorination Systems” by Ahmed A. Abokifa, Abhilasha Maheshwari, Ravindra D. Gudi, and Pratim Biswas

Discussion of “Influence of Dead-End Sections of Drinking Water Distribution Networks on Optimization of Booster Chlorination Systems” by Ahmed A. Abokifa, Abhilasha Maheshwari, Ravindra D. Gudi, and Pratim Biswas

Closure to “Influence of Dead-End Sections of Drinking Water Distribution Networks on Optimization of Booster Chlorination Systems” by Ahmed A. Abokifa, Abhilasha Maheshwari, Ravindra D. Gudi, and Pratim Biswas

Closure to “Influence of Dead-End Sections of Drinking Water Distribution Networks on Optimization of Booster Chlorination Systems” by Ahmed A. Abokifa, Abhilasha Maheshwari, Ravindra D. Gudi, and Pratim Biswas

Optimal Placement and Operation of Chlorine Booster Stations: A Multi-Level Optimization Approach

Chlorine demand as a disinfectant for water utility impacts on unintended energy consumption from electrolysis manufacture; thus, diminishing the chlorine consumption also reduces the environmental impact and energy consumption. Problems of disinfectant distribution and uniformity in Water Distribution Networks (WDN) are associated with the exponential urban growth and the physical and biochemical difficulties within the network. This study optimizes Chlorine Booster Stations (CBS) location on a network with two main objectives; (1) to deliver minimal Free Residual Chlorine (FRC) throughout all demand nodes according to country regulations, and (2) to reduce day chlorine mass concentration supplied in the system by applying an hour time pattern in CBS, consequently associated economic, energy and environmental impacts complying with regulatory standards. The application is demonstrated on a real-world WDN modeled from Guanajuato, Mexico. The resulting optimal location and disinfectant dosage schedule in CBS provided insights on maintaining disinfectant residuals throughout all the WDN to prevent health issues and diminishing chlorine consumption.

Relax-tighten-round algorithm for optimal placement and control of valves and chlorine boosters in water networks

In this paper, a new mixed integer nonlinear programming formulation is proposed for optimally placing and operating pressure reducing valves and chlorine booster stations in water distribution networks. The objective is the minimization of average zone pressure, while penalizing deviations from a target chlorine concentration. We propose a relax-tighten-round algorithm based on tightened polyhedral relaxations and a rounding scheme to compute feasible solutions, with bounds on their optimality gaps. This is because off-the-shelf global optimization solvers failed to compute feasible solutions for the considered non-convex mixed integer nonlinear program. The implemented algorithm is evaluated using three benchmarking water networks, and they are shown to outperform off-the-shelf solvers, for these case studies. The proposed heuristic has enabled the computation of good quality feasible solutions in most instances, with bounds on the optimality gaps that are comparable to the order of uncertainty observed in operational water network models.

Development of optimization model for booster chlorination in water supply system using multi-objective optimization method

Development of optimization model for booster chlorination in water supply system using multi-objective optimization method

Regulated disinfection byproduct formation over long residence times

Design and operation of drinking water treatment plants and associated distribution systems with long residence times are complicated by the formation of regulated disinfection byproducts (DBPs), comprised of total trihalomethanes (TTHM) and five haloacetic acids (HAA5). Treated water dissolved organic carbon (DOC) concentrations, the unit processes required to meet those DOC concentrations, and disinfection strategies (e.g., booster chlorination) are the primary design and operational considerations that can require extensive testing or modeling to determine. In this study, twelve different treated drinking waters were generated at the bench-scale using ferric chloride coagulation and granular activated carbon adsorption from four parent raw waters collected from the San Juan River representing spring runoff, monsoon, and low flow events. Treated drinking waters with DOC concentrations of 0.9, 1.4, and 1.9 mg/L were tested for regulated DBP formation under simulated distribution system (SDS) conditions over residence times as long as 56 days and compared to 7-day formation potential (FP) testing. SDS free chlorine concentrations were maintained between 0.2 and 1.0 mg/L as Cl2 through periodic booster chlorination. Maximum SDS TTHM and HAA5 concentrations were 0.208 and 0.074 mg/L, respectively, with formation consistently varying by approximately ±20% across the four different parent raw waters despite having been treated to the same three DOC concentrations. An average of four existing TTHM models consistently underpredicted TTHM formation by approximatively 20%. Long considered a conservative measure of DBP formation, FP testing also underpredicted SDS DBP formation at 56 days by approximately 40% on average. The DBP testing approach presented in this study allowed for the development of several significant linear relationships for predicting DBP concentrations based on treated water ultraviolet light absorbance at 254 nm, water temperature, and cumulative free chlorine demand.