Pilot-scale Water Distribution System Research Articles

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.

Degradation of sulfapyridine antibiotics by chlorination in a pilot-scale water distribution system: kinetics, THMs, and DFT studies

Sulfonamides (SAs) have been proved to damage organisms if the contact time last over the long term.

Chlorination contributes to multi-antibiotic resistance in a pilot-scale water distribution system

Abstract The generation and dissemination of antibiotic resistance bacteria (ARB) and antibiotic resistance genes (ARGs) in the environment has become a critical risk to human health. This study is based on a pilot-scale simulated water distribution system to understand the effects of chlorine disinfection treatment (without free chlorine) on ARB and ARGs in biofilms. The hydraulic parameters and pipe materials of the system were simulated based on a drinking water system. The results of the colony counts showed that bacterial multi-antibiotic resistance could be enhanced 13-fold in the biofilms of the pipeline. The use of high-throughput qPCR (HT-qPCR) indicated that the total relative abundance of ARGs in biofilm samples increased significantly (p < 0.05), while the diversity of bacteria was shown to be reduced via taxonomic analysis of the V3–V4 region of 16S rRNA. The prominent types of ARGs were conferred resistance by aminoglycoside and β-lactam after the chlorine disinfection treatment, and antibiotic deactivation was the main mechanism. Phyla Proteobacteria had the highest abundance in both treatment and control groups but decreased from 70.81% (initial biofilm sample) to 26.09% (the sixth-month biofilm sample) in the treatment groups. The results show that the chlorine disinfection plays a role in the risk of development of bacterial antibiotic resistance in pipe networks owing to bacteria in biofilms. This study was the first to investigate the contribution of chlorination without free chlorine to the bacterial community shift and resistome alteration in biofilms at a pilot-test level.

Degradation of estriol by chlorination in a pilot-scale water distribution system: Kinetics, pathway and DFT studies

Estriol (E3) is a potent intracellular estrogen and endocrine disruptor that has been frequently detected in surface water in recent years. We investigated the degradation kinetics of E3 during chlorination in a pilot-scale water distribution system (WDS), and found that its degradation followed second-order kinetics. Higher concentrations of bromide and neutral acids promoted the degradation of E3. In addition, the degradation of E3 was higher at higher water velocity in WDS. This study further compared the degradation of E3 in different pipe materials and the results indicated that the degradation of E3 was most efficient in stainless-steel pipe, followed by the polyethylene pipe and then ductile iron pipe. To gain more insights into the mechanisms of E3 degradation, intermediate products from E3 degradation were analyzed. Five intermediates were identified, and a possible pathway was proposed by combining the experimental observations with the density functional theory (DFT) calculation. Four types of disinfection byproducts (DBPs) in ductile iron pipe were detected from E3 degradation during chlorination, confirming that DBPs are generated by E3 during the free chlorine oxidation, which pose a greater safety threat to drinking water.

Evidence-based analysis on the toxicity of disinfection byproducts in vivo and in vitro for disinfection selection

Disinfection is a key step in drinking water treatment process to prevent water-borne infections. However, reactions between chlorine, one of the most common disinfectants, and natural organic matter (NOM) often lead to the formation of hazardous disinfection byproducts (DBPs). However, the cytotoxicity of some DBPs is still poorly understood. Such knowledge is critical for proper selection of disinfection processes. We investigated the effects of DBPs on mouse acute liver injury. The exacerbation of liver damage increased with the DBPs concentrations, likely due to the increased hepatic macrophages. Haloacetonitriles (HANs) and haloketones (HKs) are more toxic to Human Hepatocellular (Hep3B) cells than trihalomethanes (THMs). Cytotoxicity of DBPs were governed by the halogen type (brominated DBPs > chlorinated DBPs) and the numbers of halogen atoms per molecule. Then, we used the pilot-scale WDS to study the best conditions for reducing the formation of DBPs. The result showed that the formation of DBPs followed the order: stainless-steel (SS) > ductile iron (DI) > polyethylene (PE) pipe. Higher flowrate promoted the formation of DBPs in all three pipes. The results suggest that the formation of DBPs in chlorine disinfection can be reduced by using PE pipes and low flow rate in water distribution systems (WDS).

Chlorination of enoxacin (ENO) in the drinking water distribution system: Degradation, byproducts, and toxicity

Chlorine is widely used as a drinking water disinfectant to ensure water security. However, the transformation mechanisms of its degradation of emerging pollutants within the water distribution system (WDS) is insufficiently understood. Thus, the kinetics, degradation byproducts, and toxicity of the chlorination of enoxacin (ENO, a type of emerging pollutant) were explored in a pilot-scale WDS for the first time. It was found that the chlorination rate of ENO was higher in deionized water (DW) than in the pilot-scale WDS, and the degradation followed second-order kinetics in DW. The degradation efficiency was found to be sensitive to pH, and was highest at a pH of 7.4. The chlorination rate of ENO increased with increasing temperature in both DW and WDS. For different pipe materials, the relative performance of ENO chlorination efficiency followed the order of steel pipe > ductile iron pipe > polyethylene (PE) pipe. Seven intermediates were identified during ENO chlorination, and the primary oxidation reaction involved the cleavage of the piperazine group. Finally, it was found that the potential for chlorine toxicity in treated drinking water in the presence of ENO is higher than it is without this pollutant.

SExploring integrated impact of temperature and flow velocity on chlorine decay for a pilot-scale water distribution system

sExploring integrated impact of temperature and flow velocity on chlorine decay for a pilot-scale water distribution system

Sulfadiazine destruction by chlorination in a pilot-scale water distribution system: Kinetics, pathway, and bacterial community structure.

Sulfadiazine (SDZ) has been frequently detected in surface waters in recent years. We evaluated the kinetics, mechanisms, intermediate products and bacterial community structure that result from the reaction of SDZ with free chlorine (HOCl/OCl-). We examined this in a pilot-scale water distribution system. Neutral pH had the fastest rate of destruction of SDZ. A second-order reaction constant for the destruction of SDZ by chlorine increased with increasing concentration of free chlorine (FC). For different pipe materials, the rate of SDZ degradation decreased as follows: stainless steel (SS) pipe > polyethylene (PE) pipe > ductile iron (DI) pipe. Based on the less complex bacterial diversity and more chlorine-resistant by 16S ribosomal ribonucleic acid (rRNA) gene analysis, SS pipe and PE pipe were more suitable in SDZ degradation in water distribution system (WDS) than DI pipe. In addition, the transformation products from SDZ chlorination were identified by gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry, and the products included SO2 extrusion products, haloacetic acids and trihalomethanes. Toxicity tests further confirmed that the toxicity of SDZ chlorination was higher both in low FC (0.7 mg/L) and high FC (1.3 mg/L) in WDS.

Effect of pipe materials on disinfection by-products and bacterial communities during sulfamethazine chlorination in a pilot-scale water distribution system

Water research is usually done using simplified devices, e.g., beakers, in laboratory glassware, and thus may yield results that are not representative of real wastewater treatment plants that use complex pipe systems made of various materials. Therefore, here we studied for the first time the effect of different pipe materials on sulfamethazine chlorination and formation of disinfection by-products. We also studied the relationships between bacterial communities, pipe materials, sulfamethazine degradation, free chlorine decay and formation of disinfection by-products. Results show that the degradation of sulfamethazine was faster in pipes than in batch tests, due to the influences of sediment, iron and bacterial communities. Specifically, the total concentration of disinfection by-products after 22 h followed the order: 49.43 μg/L for stainless-steel pipe, 46.76 μg/L for ductile iron pipe, 39.12 μg/L for polyethylene pipe, and 19.22 μg/L for batch tests. 16S rRNA microbial analysis showed that ductile iron and stainless-steel pipes had the highest operational taxonomic unit (OTU) richness. Microbial communities between polyethylene and ductile iron pipe had a relatively higher similarity. Sphingomonas and Actinobacteria slowed down the decay of free chlorine in the stainless-steel pipe, which promoted the degradation of sulfamethazine. Mycobacterium and Pseudomonas are the dehalogenation-related bacteria, which reduced the formation of distribution by-products in polyethylene pipe.

A comparative study for the decay of chlorine residual using EPANET2.0 and an experimental pipeline system

The residual chlorine concentration is an essential factor to secure reliable water quality in the water distribution systems. The chlorine concentration decays along the pipeline system and the main processes of the reaction can be divided into the bulk decay and the wall decay mechanisms. Using EPANET 2.0, it is possible to predict the chlorine decay through bulk decay and wall decay based on the pipeline geometry and the hydraulic analysis of the water distribution system. In this study, we tried to verify the predictability of EPANET 2.0 using data collected from experimental practices. We performed chlorine concentration measurement according to various Reynolds numbers in a pilot-scale water distribution system. The chlorine concentration was predicted using both bulk decay model and wall decay model. As a result of the comparison between experimental data and simulated data, the performance of the limited 1st-order model was found to the best in the bulk decay model. The wall decay model simulated the initial decay well, but the overall chlorine decay cannot be properly predicted. Simulation also indicated that as the Reynolds number increased, the impact of the wall

Degradation of chloramphenicol by chlorine and chlorine dioxide in a pilot-scale water distribution system

This paper presents the degradation of chloramphenicol (CAP) by chlorine and chlorine dioxide (ClO2) in tap water in a pilot-scale water distribution system (WDS) containing loops of three different pipe materials (stainless steel, ductile iron, and polyethylene). Greater degradation of CAP was seen with chlorine than with chlorine dioxide. After 180 min in the ductile iron loop of the WDS, the percent degradation of CAP by 2.0 mg/L of chlorine or ClO2 was 76% and 52%, respectively. The degradation of CAP by chlorine in the WDS was investigated under various conditions, including chlorine concentrations of 1.0–4.0 mg/L, and varying pipe materials, flow velocity, and temperature. Degradation of CAP under different conditions could be fitted by first-order kinetics, and the determined first-order rate constants (k, min−1) increased with an increase in chlorine concentration, flow velocity, and temperature. The degradation of CAP in different pipes followed the order stainless steel loop > ductile iron loop > polyethylene loop. Identified oxidized products of the chlorination of CAP were in agreement with proposed reaction pathways, which were also theoretically confirmed by quantum chemical calculations. Formation of three disinfection byproducts (chloroform, bromodichloromethane, and dibromochloromethane) was observed, with increases of 7.7, 0.76, and 0.39 µg/L, respectively, after 160 min.

Kinetics and degradation pathway of sulfamethazine chlorination in pilot-scale water distribution systems

As a new type of environmental micro-organic pollutant, sulfonamides (SAs) have been shown to damage organisms if they are exposed to them over the long term. Moreover, an increasing number of SAs has been detected in natural water and urban water supply systems in recent years because they cannot be completely removed through conventional water treatment processes. Therefore, sulfamethazine (SMZ) in urban water systems was selected as a target to be investigated. The reaction kinetics of sulfamethazine chlorination were studied in a pilot-scale water distribution system (WDS) under the influence of different factors, including pH, temperature, flow rate and pipe materials, to determine the optimal factors for removing SMZ and to provide a reference for water quality in urban drinking water systems.According to the experimental results, the kinetics models of SMZ chlorination fitted a second-order reaction in pure water. The degradation of SMZ was not only affected by the water quality conditions but also the operating temperatures, flow rates and pipe materials. The rate constants of SMZ chlorination under different temperatures were related to the Arrhenius equation. Different flow rates had little effect on SMZ degradation. In different pipes, the degradation rates of SMZ followed the order stainless-steel pipe>polyethylene pipe (PE)>ductile iron pipe. Moreover, eight reaction intermediates during SMZ degradation were observed and identified, and a degradation pathway was proposed. The concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs) during the degradation of SMZ in WDS were also determined.

Kinetics and mechanism of 17β-estradiol chlorination in a pilot-scale water distribution systems

The kinetics and mechanisms of 17β-estradiol (E2) chlorination in water distribution systems (WDS) were studied. We examined the impacts of different factors, including pH, temperature, humic acid concentration and type, and flow velocity. The experimental results showed that the rate constants in beaker tests and WDS were described by a pseudo-first-order model. pH had the greatest impact on E2 chlorination in the beaker tests. However, temperature had the greatest impact on E2 chlorination in WDS. Mechanistic analysis of E2 chlorination showed that chlorine attacked E2 in three stages: 1) halogenation of the aromatic ring, 2) cleavage of the benzene moiety and chlorine or bromine substitution formation, and 3) formation of trihalomethanes (THMs) and halogenated acetic acids (HAAs) from phenolic intermediates through benzene ring opening with chlorine and/or bromine substitution of hydrogen on the carbon atoms. In the third stage, the concentrations of THMs and HAAs increased rapidly.

Behaviour of Haloacetic Acids in Drinking Water Distribution Systems

To guarantee the safety of drinking water quality after chlorination, the formation, distribution and factors influencing the concentrations of haloacetic acids (HAAs) in a water distribution system (WDS) were investigated both on a full-scale WDS (FWDS) and pilot-scale WDS (PWDS) within a city in northern China. The results of both investigations showed that trichloroacetic acid (TCAA) and dichloroacetic acid (DCAA) were the dominating types of HAAs. In the FWDS, variations in the HAA content showed negative correlations with total residual chlorine, pH and non-purgeable organic carbon (NPOC) and positive correlations with temperature and UV254. In the PWDS, the concentration of HAAs after rechlorination followed the rule of ‘first rise and then fall’; therefore, locating an appropriate rechlorination point and lowering the single chlorine dosage could be used as effective measures to control the HAA content in WDSs.

Transformation of bisphenol A during chloramination in a pilot-scale water distribution system: Effect of pH, flow velocity and type of pipes

Chloramination of bisphenol A (BPA) in a pilot-scale water distribution system (WDS) was investigated to assess factors that influence degradation rate and degradation products. In deionized water (DW) and in the WDS, complete degradation of BPA after chloramination required >9h. At Cl/N mass ratios of 3, 4 or 6, the degradation rate was appreciably greater in the WDS than in the DW. In both the DW and WDS, the bromide ion concentration had little influence on BPA degradation. The BPA degradation rate was greatly affected by pH and temperature in both the DW and in the WDS. The rate of BPA degradation by chloramination increased with increasing flow velocity, but the increase was limited. The BPA degradation rate in different pipes followed the order: ductile iron pipe>polyethylene (PE) pipe>stainless steel pipe. Twelve specific degradation products of BPA that were produced following chloramination were tentatively identified, with 2-chloro-BPA as the main byproduct. One nitrogenous byproduct produced following chloramination was detected for the first time, and appeared at 15min, indicating that nitrogen from the chloramine participated in the BPA degradation reaction at the beginning of the experiment. In the presence of chloramines and BPA, the formation of trihalomethanes (THMs), haloacetic acids (HAAs) and halogenated nitromethane (HNMs) occurred primarily in the initial 3h. The intermediates of BPA that were formed during chloramination had relatively little influence on THM, HAA and HNM formation. The degradation pathways for BPA during chloramination in the WDS are proposed.

Effect of pipe materials on chlorine decay, trihalomethanes formation, and bacterial communities in pilot-scale water distribution systems

In this study, the influence of pipe materials on chlorine decay, trihalomethanes formation, as well as on microbial community composition of the biofilms formed on the pipe walls in a model full-scale water distribution system was investigated. The chlorine decay experiment showed that the turbulent flow model fitted the experiment data of chlorine decay well, with stainless steel pipe that had the highest rate constant of chlorine decay, and followed by ductile iron pipe and polyethylene pipe. Meanwhile, the formation of trihalomethanes under the three different pipe materials followed the order as: polyethylene pipe > ductile iron pipe > stainless steel pipe. Microbial community analysis showed that biofilm from polyethylene pipe had much higher diversity than that from the ductile iron pipe and stainless steel pipe. In addition, clear differences in the bacterial community structure among biofilms of different pipe materials were observed. The ductile iron pipe biofilm was mainly composed of Enhydrobacter (33.84%), Propionibacterium (8.08%) and Acinetobacter (5.59%). The polyethylene pipe biofilm contained Sphingomonas (25.25%), Streptococcus (7.64%), Ralstonia (4.83%), Pseudomonas (4.63%), and Escherichia–Shigella (4.71%). The stainless steel pipe biofilm was abundant with Flavobacterium (24.76%), Arcicella (12.03%), and Acidovorax (8.98%). Moreover, the occurrence of opportunistic pathogens was detected, especially in the biofilm of polyethylene pipe, followed by ductile iron pipe and stainless steel pipe. The integrated findings in this study suggest that ductile iron pipe and stainless steel pipe are more suitable as plumbing material than polyethylene pipe in drinking water distribution systems.

Chloramines in a pilot-scale water distribution system: Transformation of 17β-estradiol and formation of disinfection byproducts

The degradation and transformation products of 17β-estradiol (E2) by chloramines in a pilot-scale water distribution system (WDS) were investigated using varying conditions including multiple mass ratios of chlorine to nitrogen (Cl/N), changing concentrations of chloramines, and different pH and pipe materials. The degradation of E2 was complete in ≤9 h in both deionized water (DW) and in the WDS under studied conditions. When the degradation rate of E2 was compared in WDS and DW, the degradation rate was appreciably greater in the WDS than in the DW at Cl/N mass ratios of 3, 4 and 6. However, at Cl/N mass ratios of 8 and 9, degradation was faster in the DW than in the WDS. The degradation rate of E2 was greatly affected by the initial total chloramine concentration, and the degradation of E2 in DW was consistent with second-order kinetics. The degradation rate of E2 in both the DW and the WDS increased with increasing pH. The order of degradation rate of E2in different pipes was: ductile iron loop (loop A) > polyethylene (PE) loop (loop B)> stainless steel loop (loop C). Ten specific degradation products of E2, produced by chloramination, were identified. Most of the degradation products of E2 chloramination were stable for more than 10 h. The degradation pathways of E2 in the WDS are proposed and briefly discussed. The concentrations of trihalomethanes (THMs), haloacetic acids (HAAs), and halogenated nitromethane (HNMs) during the degradation E2 in WDS were also determined.

Desalinated seawater into pilot-scale drinking water distribution system: chlorine decay and trihalomethanes formation

Residual chlorine decay and trihalomethanes (THM) formation of desalinated seawater by ultrafiltration (UF) and nanofiltration (NF) membranes in a pilot-scale water distribution system (DWDS) were investigated. Three-dimensional fluorescent features of two source waters including NF permeate and municipal water were studied. Sixteen groups of data-sets were obtained to explore the effects of initial chlorine concentration (ICC), dissolved organic carbon (DOC), and temperature on chlorine decay and THM formation in laboratory conditions and pilot-scale DWDS, respectively. A first-order model was applied to evaluate the chlorine decay of desalinated seawater and a new model combining ICC, DOC concentration, and temperature was obtained to determine the first-order decay coefficient. Other seven models describing the kinetics of chlorine decay were also applied and compared in this study. Total trihalomethanes (TTHM) formation kinetics was studied and first-order model was suggested to describe this formation. The relationship between TTHM formation and chlorine demand was demonstrated and the results showed that second-order polynomial model better described the relationship.

Transformation of bisphenol A in water distribution systems: A pilot-scale study

Halogenations of bisphenol A (BPA) in a pilot-scale water distribution system (WDS) of a cement-lined ductile cast iron pipe were investigated. The water in the pilot-scale WDS was chlorinated with a free chlorine concentration of 0.7mgL−1 using sodium hypochlorite, and with an initial BPA concentration of 100μgL−1 was spiked in the WDS. Halogenated compounds in the BPA experiments were identified using EI/GC/MS and GC. Several BPA congeners, including 2-chlorobisphenol A (MCBPA), dichlorobisphenol A (D2-CBPA), 2,2′,6-trichlorobisphenol A (T3CBPA), 2,2′,6,6′-tetrachlorobisphenol A (T4CBPA), 2-bromobisphenol A (MBBPA), and bromochlorobisphenol A (MBMCBPA) were found. Moreover, further halogenation yielded other reaction intermediates, including 2,4,6-trichlorophenol (T3CP), dichlorobisphenol A, bromodichlorophenol, and dibromochlorophenol. After halogenation for 120min, most of the abovementioned reaction intermediates disappeared and were replaced by trihalomethanes (THMs). Based on these experimental findings, the halogenation process of BPA oxidation in a WDS includes three stages: (1) halogenation on the aromatic ring; (2) chlorine or bromine substitution followed by cleavage of the α-C bond on the isopropyl moiety with a positive partial charge and a β′-C bond on the benzene moiety with a negative partial charge; and (3) THMs and a minor HAA formation from phenolic intermediates through the benzene ring opening with a chlorine and bromine substitution of the hydrogen on the carbon atoms. The oxidation mechanisms of the entire transformation from BPA to THM/HAA in the WDS were proposed.

A general framework of chlorine decay modeling at a pilot-scale water distribution system

Understanding the variation of chlorine concentrations in water distribution systems is important for determining the schedule of rechlorination. Maintaining an appropriate chlorine concentration in domestic tap water and a sustainable residual chlorine in water distribution systems is an important commitment to ensure high drinking water quality. A generic modeling framework is proposed to amalgamate most widely used existing chlorine decay models. This framework gives rise to 14 distinct model structures. A pilot-scale water distribution system was designed and fabricated to investigate the performance of the proposed modeling framework. A hybrid calibration algorithm, obtained using a combination of the genetic algorithm and the particle swarm optimization, was introduced to rigorously calibrate the parameters of the various models. The adequacy of the performance of the various models was evaluated using both the Akaike information criterion and the Bayesian information criterion. A reliable relationship between the Reynolds numbers and the model parameters was obtained for the relatively simple model structure. The parameter spaces of several chlorine decay models can be configured, and equations of parameters for corresponding flow condition can be delineated. The generic model robustly predicted the chlorine concentration when the Reynolds numbers were between 15,000 and 40,000.