Conventional Chlorination Research Articles

Homogeneous versus heterogeneous Mn(II) oxidation in peroxymonosulfate assisting chlorination: Synergistic role for enhanced Mn(II) oxidation in water treatment

Removal of Mn(II) is an essential step for addressing water discoloration in water treatment utilities worldwide. However, conventional chlorination suffers from poor oxidation of Mn(II) due to its low homogeneous oxidation kinetics. This study explored the oxidation capability of a new chemical dosing strategy employing peroxymonosulfate (PMS) to assist the chlorination process (PMS@Cl2) for effective Mn(II) oxidation. The study comprehensively explored both oxidation kinetics and underlying mechanisms associated with homogeneous and heterogeneous oxidation within the PMS@Cl2 system. At an [Mn(II)]0 of 1 mg/L, chlorination demonstrated inability in oxidizing Mn(II), with <10 % oxidation even at an elevated [Cl2] of 150 μM (∼10 mg/L). By contrast, PMS completely oxidized 100 % Mn(II) within a 30-minute reaction at a much lower [PMS] of 60 μM (kobs = 0.07 min−1 and t1/2 = 9 min), demonstrating its superior Mn(II) oxidation kinetics (over one order of magnitude faster than conventional chlorine). PMS@Cl2 exhibited an interesting synergistic benefit when combining a lower dose PMS with a higher routine dose Cl2 (loPMS@hiCl2), e.g. [PMS]:[Cl2] at 15:30 or 30:30 μM. Both conditions achieved 100 % Mn(II) oxidation, with even better values of kobs and t1/2 (0.16–0.17 min−1 and ∼4 min) relative to PMS alone at 60 µM. The synergic benefit of PMS@Cl2 was attributed to distinct functions played by PMS and Cl2 in both homogeneous and heterogeneous oxidation processes. Reactive species identification excluded the possible involvement of SO4•−, OH•, or chlorine radicals in the homogeneous oxidation of the PMS@Cl2 system. Instead, the dominant species was O2•− radical generated during the reaction of Mn(II) and PMS. Furthermore, the heterogeneous oxidation emphasized the important role of combining Cl2 dosing, which demonstrated an increased reactivity and electron transfer with the Mn−O−Mn complex, surpassing PMS. Overall, heterogeneous oxidation accelerated the oxidation kinetics of the PMS@Cl2 system by 1.1–2 orders of magnitude relative to the homogeneous oxidation of Cl2 alone. We here demonstrated that PMS@Cl2 could offer a more efficient mean of soluble Mn(II) mitigation, achieved with a relatively low routine dose of oxidant in a short reaction period. The outcomes of this study would address the existing limitations of traditional chlorine oxidation, minimizing the trade-offs associated with high residual chlorine levels after treatments for soluble manganese-containing water.

Comment on “Approaching easy water disinfection for all: Can in situ electrochlorination outperform conventional chlorination under realistic conditions?, published by Atrashkevich et al. [Water Research 250 (2024) 121,014]”

Comment on “Approaching easy water disinfection for all: Can in situ electrochlorination outperform conventional chlorination under realistic conditions?, published by Atrashkevich et al. [Water Research 250 (2024) 121,014]”

Influence of physical and water quality parameters on residual chlorine decay in water distribution network

Chlorine is the most common disinfectant in drinking water distribution practice. World Health Organization recommends 0.2–5.0 mg/l of residual chlorine in drinking water. This paper analyzed influence of physical and water quality parameters on chlorine decay in drinking water distribution. Principal component analysis, directed tree and regression were used to investigate influence of these parameters on chlorine from water treatment plant to water consumption points. Results show that initial chlorine, electrical conductivity and distance explain 62 % of chlorine decay with estimated error of 0.045 mg/l. The decision-tree feature importance scores of initial chlorine and electrical conductivity were 0.47 and 0.23 respectively. The combined feature importance scores of physical parameters of distance (0.09), pipe diameter (0.06), flow velocity (0.03), pressure (0.02) and travel time (0.046) were less than that for initial chlorine concentration (0.47) alone. These results show that conventional chlorination at water treatment plants removes largely fast inorganic reactants leaving traces of slow organic reactants as the dominant secondary contaminants in water distribution system. The key policy recommendation is to use water quality parameters more than physical parameters in order to enable water utility managers maintain residual chlorine within safe public health standards.

Advanced oxidation of recalcitrant chromophores in full-scale MBR effluent for non-potable reuse of leachate co-treated municipal wastewater

Wastewater non-potable reuse involves further processing of secondary effluent to a quality level acceptable for reuse and is a promising solution to combating water scarcity. Recalcitrant chromophores in landfill leachate challenge the water quality for non-potable reuse when leachate is co-treated with municipal wastewater. In this study, we first use multivariate statistical analysis to reveal that leachate is an important source (with a Pearson's coefficient of 0.82) of recalcitrant chromophores in the full-scale membrane bioreactor (MBR) effluent. We then evaluate the removal efficacies of chromophores by chlorination, breakpoint chlorination, and the chlorination-UV/chlorine advanced oxidation treatment. Conventional chlorination and breakpoint chlorination only partially remove chromophores, leaving a colour level exceeding the standards for non-potable reuse (>20 Hazen units). We demonstrate that pre-chlorination (with an initial chlorine dosing of 20 mg/L as Cl2) followed by UV radiation (with a UV fluence of 500 mJ/cm2) effectively degraded recalcitrant chromophores (>90%). By quantifying the electron donating capacity (EDC) and radical scavenging capacity (RSC) of the reclaimed water, we demonstrate that pre-chlorination reduces EDC and RSC by up to 64%, increases UV transmittance by 32%, and increases radical yields from UV photolysis of chlorine by 1.7–2.2 times. The findings advance fundamental understanding of the alteration of dissolved coloured substances by (photo)chlorination treatment and provide implications for applying advanced oxidation processes in treating wastewater effluents towards sustainable non-potable reuse.

Approaching easy water disinfection for all: Can in situ electrochlorination outperform conventional chlorination under realistic conditions?

Electrochlorination has gained research interest for its potential application as decentralized water treatment. A number of studies have displayed promising efficiency for water disinfection. However, a comprehensive comparison of in situ electrodisinfection to existing disinfection techniques, particularly under realistic water composition and flow rates, still needs additional research efforts. The aim of this study is to evaluate in situ electrochlorination while comparing the treatment with conventional chemical chlorination for point-of-entry decentralized disinfection at the household level. An electrochemical flow cell reactor was operated in a single pass mode considering water flow and water consumption for a household of four family members. Disinfection efficiency assessment of both electrochemical and chemical chlorination was conducted using bacterial and viral surrogates, E. coli and MS2 bacteriophage. Furthermore, a techno-economic analysis was conducted, using the levelized cost of water, to compare two electrochemical chlorination scenarios (i.e., electrical grid energy use, and solar panel powered system) and benchmarked against the baseline treatment of chemical chlorination. The findings revealed increased inactivation efficiency of in situ electrochlorination over conventional chlorination (p-value < 0.05). The synergetic impact of radicals and chlorine, and/or contribution of high chlorine concentration at acidic pH near anode surface were identified as key factors that could enhance disinfection performance of in situ electrochlorination. The techno-economic analysis demonstrated that electrochemical treatment, when operated using renewable energy sources, is not only a more environmentally sustainable approach, but also emerges as a more economically feasible solution for decentralized water treatment application. The results highlight that in situ electrochlorination is a more advanced alternative to decentralized water chlorination. However, further fundamental research on products and by-products formation under various water matrices is required.

Nanowire electroporation-induced cell pores on antibiotic-resistant bacteria to promote chlorine permeation for eliminating intracellular antibiotic resistance genes

Conventional chlorination (Cl2) is inefficient to eliminate intracellular antibiotic resistance genes (i-ARGs) of antibiotic-resistant bacteria (ARB) due to the chlorine permeation barrier and oxidative competition of cell wall/membrane. Herein, we proposed an efficient strategy by constructing synergistic nanowire-induced electroporation (DC-EP) and Cl2 (DC-EP/Cl2) with H2-reduced TiO2 nanowire (TiOxNW) electrodes, attempting to promote i-ARG removal via DC-EP-induced cell damage for chlorine permeation and i-ARG leakage. DC-EP/Cl2 (∼3.7 log and ∼ 60.5 J/L/log) exhibited excellent synergistic effects for ARB inactivation (Escherichia coli) and i-ARG removal (tet(W), aac(3)-II, and blaTEM–1), which achieved much larger i-ARG removal and lower energy consumption than the individual 1.5 V-DC-EP (∼0.05 log) and 10 mg/L-Cl2 (∼0.5 log and ∼ 262.0 J/L/log). Analyses of i-ARG/e-ARG abundances, bacterial cell integrity, and cell morphology indicated that DC-EP-induced cell pores provided channels of chlorine permeation, which was accompanied with oxidative enlargement of cell pores for i-ARG leakage and subsequent degradation. DC-EP/Cl2 exhibited 15–90 times lower frequency of horizontal gene transfer than the individual Cl2 disinfection. The TiOxNW-based DC-EP/Cl2 exhibited excellent stability of i-ARG removal (undetectable ARG abundance and ∼ 20.3 J/L/log) for treating 103 CFU/mL ARB-contaminated tap water within 7-day continuous operation, suggesting its great application potential to alleviate ARG dissemination risk for drinking water.

Oxidative Chlorination: A Sustainable Alternative for the Preparation of Chloroarenes

Abstract: Chloroarenes are important from both academic and industrial points of view. They are useful intermediates and building blocks in manufacturing a range of bulk and fine aromatic chemicals, dyes, flame retardants in electronic boards, disinfectants, and pharmaceutical drugs. In addition, diverse agrochemicals, synthetic drugs, and natural products are chloroarenes. Although conventional chlorination of arenes is a well-established transformation that has been studied in detail in many textbooks, current challenges have driven scientists to design new strategies that can address the need for efficiency and sustainability. The oxidative chlorination reaction proceeds via an oxidation step of the chloride ion to generate the active electrophilic chlorenium species in situ. In these regards, the present review focused on the main achievementsof the oxidative chlorination of arenes, with special focus on their generality and green aspects. Therefore, the use of different oxidants (hydrogen peroxide, oxygen, iodine(III) reagents, enzymes) and conditions of electrochemistry and photocatalysis are presented.

Improvement of chlorination and sterilization of pathogenic bacteria by natural products

There are many highly resistant pathogenic bacteria in the environment that cannot be removed by conventional chlorination disinfection. This study demonstrated a combined sterilization strategy for combating the extension of pathogenic bacteria by enhancing the bactericidal ability of sodium hypochlorite at subinhibitory concentrations with the utilization of the natural antimicrobial molecule cinnamaldehyde. The results indicated that treatment of cinnamaldehyde enhances the effect of chlorination disinfection, leading to an increase in concentration-dependent inactivation efficiency from 33.5 to 86.1%. Our results also proved that the combined sterilization strategy showed an inhibitory and destructive effect on the hazardous biofilm formed by Pseudomonas aeruginosa. Additionally, the cell membrane permeability and reactive oxygen species (ROS) levels were 1.8-fold and 2.3-fold increased compared with the controls, respectively, which revealed the synergistic effect and hypothetical mechanisms of natural antimicrobial products treatment to chlorination disinfection. This study provides further research for the control of drug-resistant bacteria in water treatment systems and contributes to combating the growing threat of antibiotic resistance.

Correlation Analysis of the Experimental Data for In-Situ Chlorine Generation in Electrochlorination Process

Even though chlorination is a widely used disinfection technique, it has several disadvantages, such as formation of chlorates during prolonged storage, requirement for skilled supervision during operations, risk of leakage, and related accidents during transport and storage. Electrochlorination (EC) is one of the novel technologies generating in-situ chlorine, thereby limiting most of the disadvantages of conventional chlorination treatment for water disinfection. The correlation between the various influencing parameters for EC, which is important for achieving the optimal conditions for in-situ chlorine generation, is still unclear. The major objective of the present study is to provide a detailed correlation analysis between the parameters influencing the EC process based on the extensive experimental data generated from the developed lab-scale setup for electrochlorination using graphite electrodes and titanium electrodes separately. The present study also examined the rate of loss of the electrode materials to check the longevity of electrodes. The experimental results generated were used for comparative analysis of the EC process for maximum in-situ chlorine generation. A detailed principal component analysis (PCA) was performed for the data generated during experimentation to understand the correlation between the influencing parameters for optimum in-situ chlorine generation. The optimum conditions for maximum in-situ chlorine generation obtained from the experiments were 10 V electric voltage, 60 min electrolysis time, 4 cm distance between electrodes, and 3.5 g/L electrolyte concentration, with maximum chlorine generation of 15.95 mg/L obtained for titanium electrodes using NaCl electrolytes for the developed lab setup. The results of PCA established the correlation between the influencing parameters and concluded that the most significant parameter influencing chlorine generation was electrolyte concentration and electrochlorination time, and electric potential was moderately influential, whereas distance between electrodes was least influential. The rate of material loss was 15.3 mg/min for titanium electrodes and 24 mg/min for graphite electrodes, indicating titanium electrodes are more durable than graphite electrodes during a prolonged EC process. The applicability of the generated chlorine stock solution was also examined for drinking water sample disinfection and found to be effective.

Evaluation of algaecide effectiveness of five different oxidants applied on harmful phytoplankton

Harmful algal blooms (HABs) in coastal areas similarly impact both ecosystems and human health. The translocation of phytoplankton species via maritime transport can potentially promote the growth of HABs in coastal systems. Accordingly, ballast water must be disinfected. The main goal of this study is to assess the effectiveness of different emerging biocides, including H2O2, peracetic acid (PAA), peroxymonosulfate (PMS), and peroxydisulfate (PDS). The effectiveness of these biocides is compared with that of conventional chlorination methods. Their effects on two ichthyotoxic microalgae with worldwide distribution, i.e., Prymnesium parvum and Heterosigma akashiwo, are examined. To ensure the prolonged effectiveness of the different reagents, their concentration–response curves for 14 days are constructed and examined. The results suggest a strong but shorter effect by PMS (EC50 = 0.40–1.99 mg·L-1) and PAA (EC50 = 0.32–2.70 mg·L-1), a maintained effect by H2O2 (EC50 = 6.67–7.08 mg·L-1), and a negligible effect by PDS. H. akashiwo indicates higher resistance than P. parvum, except when H2O2 is used. Based on the growth inhibition performance and consumption of the reagents as well as a review of important aspects regarding their application, using H2O2, PAA, or PMS can be a feasible alternative to chlorine-based reagents for inhibiting the growth of harmful phytoplankton.

Identification of β-lactam-resistant coding genes in the treatment plant by activated sludge process

Wastewater treatment plants are the most important release source of antibiotic-resistance genes (ARGs) into the environment. This study aimed to identify β-lactam-resistance genes in Qom province municipal wastewater and also to determine the effect of municipal wastewater treatment plants with different processes on reducing these pollutants. Sampling was performed according to the standard protocol and at constant temperature conditions. Nine genes resistant to the six groups of β-lactam antibiotics were selected, and polymerase chain reaction (PCR) test was performed to identify the presence/absence of ARGs. At the same time, real-time PCR test was also carried out to quantitatively measure three ARGs in wastewater and effluent samples. The obtained results showed that the highest and the lowest removal were related to blanps-1 (90.61%) and blaCTX-M-32 (65.93%), respectively; however, a decreasing trend in these two genes were showed in to blaoxa-1 with an increase in effluent unit (45.12%). The results showed that conventional biological wastewater treatment processes not only have little potential to reduce antibiotic-resistance genes during the treatment process but also these processes sometimes increase resistant genes. The results of the oxa-1 gene in this study are consistent with this trend. In addition, the sludge treatment unit was based on the results of sequencing Salmonella enterica and Klebsiella pneumoniae. Our study suggests that wastewater treatment plants using conventional chlorination do not favor the proliferation of antibiotic resistance bacteria and ARGs during wastewater treatment. Thus, equipping treatment plants with advanced processes will be efficient in reducing bacterial resistance.

Studies in instant water disinfection using natural oils

The present research reveals an instant and simple process for drinking water treatment by employing specific natural oils having antimicrobial properties to ensure complete elimination of harmful bacteria. The disinfection was studied for two different model bacteria, Gram-negative E. coli and Gram-positive, S. aureus. Seven natural oils, ajwain, thyme, oregano, peppermint, harsingar, cinnamon leaf and black pepper oil were evaluated and were found to yield 100% water disinfection within 1 min except for harsingar and black pepper oil. The process was also effective for the instant and 100% disinfection of real well water. The methodology for altering zeta potential, to an extent of 130%, for instant disinfection in drinking water treatment helps in selecting natural oils. Molecular docking studies indicated natural oils action as potential inhibitors of bacterial DNA gyrase. The studies indicate one of the lowest operating costs comparable to conventional chlorination. The simple methodology not requiring complex equipment has the potential to provide many options for implementations- from portability, household application to large scale water treatment plants.

Co-chlorination of low-density polyethylene in paraffin: An intensified green process alternative to conventional solvent-based chlorination

Abstract This study experimentally demonstrates the potential of co-chlorination as a green process alternative to conventional independent chlorination of polyolefins, which involves the use of non-environment-friendly solvents like carbon tetrachloride (CCl4). Low-density polyethylene (LDPE) was used as a representative polymer in this study and co-chlorinated with paraffin. Apart from being a reactant, the paraffin also acts as a solvent, thus eliminating the need for using CCl4 during the reaction. Test runs were first conducted to measure LDPE-paraffin solution viscosities at different LDPE concentrations to investigate the solubility of LDPE in paraffin. Co-chlorination experiments were then carried out covering a range of temperatures (100–130°C), chlorine flow rates (150–350 mL·min−1), LDPE concentrations in paraffin (10–30%) and agitation speeds (100–400 rpm). The chlorinated LDPE and paraffin products were subsequently characterized post separation using FTIR/1H NMR spectroscopy and differential scanning calorimetry. Specific properties of these two co-chlorinated products were compared with independently chlorinated LDPE and paraffin. The co-chlorinated products were found to compare well in terms of chlorine content and quality. A preliminary comparative study from a process perspective between co-chlorination and conventional chlorination of LDPE is also reported. The results obtained confirm the potential of co-chlorination as an environmentally friendly alternative.

The fate of tolfenamic acid in conventional chlorination and UV/chlorination process

The fate of tolfenamic acid in conventional chlorination and UV/chlorination process

Removal of dexamethasone by oxidative processes: Structural characterization of degradation products and estimation of the toxicity

Dexamethasone (DEX) belongs to a class of steroid hormones that can potentially be harmful due to their endocrine disrupting properties. The efficient elimination of DEX during the treatment of drinking water is needed to ensure that the health of both human and aquatic species are protected. Thus different oxidative processes were investigated in order to assess the effect of these procedures and conditions on DEX. Aqueous solutions of DEX were treated by conventional chlorination ([NaClO]=10 mg L−1) and advanced oxidative processes (ozonation – [O3]=8 mg L−1; photocatalysis – [TiO2]=120 mg L−1 and UV-C; photolysis – UV-C). The most and least efficient processes for DEX removal were ozonation (95%) and chlorination (54%), respectively. In total, 16 degradation products were identified and characterized by high-resolution mass spectrometry and only two have been proposed in previous reports. Chemical structures of the degradation products were proposed and alcohol oxidation, ozonolysis and decarboxylation were the main chemical transformations observed. The toxicities of DEX and its derivatives were evaluated by following methods: MTT assay (HepG2 cell), ECOSAR (acute and chronic toxicity) and molecular docking (AutoDock). MTT assay results demonstrated that only a mixture DEX and the chlorinated derivative were toxic at high concentrations. ECOSAR analysis showed that products formed from dehydration and fluoride elimination were more toxic than intact DEX, mainly for fish and Daphnid and to a lesser extent for green algae. The docking study revealed that these degradation products were not capable of making hydrogen bonds with residual amino acids GLN570, GLN642 and CYS736, but were stable at the glucocorticoid receptor indicating the possibility of being toxic to humans.

Assessing the Impact of DMAs and the Use of Boosters on Chlorination in a Water Distribution Network in Greece

Disinfection is one of the most important water treatment processes as it inactivates pathogens providing safe drinking water to the consumers. A fresh-water distribution network is a complex system where constant monitoring of several parameters and related managerial decisions take place in order for the network to operate in the most efficient way. However, there are cases where some of the decisions made to improve the network’s performance level, such as reduction of water losses, may have negative impacts on other significant operational processes such as the disinfection. In particular, the division of a water distribution network into district metered areas (DMAs) and the application of various pressure management measures may impact the effectiveness of the water chlorination process. Two operational measures are assessed in this paper: (a) the use of inline chlorination boosters to achieve more efficient chlorination; and (b) how the DMAs formation impacts the chlorination process. To achieve this, the water distribution network of a Greek town is chosen as a case study where several scenarios are being thoroughly analyzed. The assessment process utilizes the network’s hydraulic simulation model, which is set up in Watergems V8i software, forming the baseline to develop the network’s water quality model. The results proved that inline chlorination boosters ensure a more efficient disinfection, especially at the most remote parts/nodes of the network, compared to conventional chlorination processes (e.g., at the water tanks), achieving 100% safe water volume and consuming almost 50% less chlorine mass. DMAs’ formation results in increased water age values up to 8.27%, especially at the remote parts/nodes of the network and require more time to achieve the necessary minimum effective chlorine concentration of 0.2 mg/L. However, DMAs formation and pressure management measures do not threaten the chlorination’s efficiency. It is important to include water age and residual chlorine as criteria when optimizing water pressure and the division of DMAs.

Biomaterial based shrink resist treatment of wool fabric: A sustainable technology

Shrinkage in the wool fabric is a practical limitation with reference to its dimensional stability, mechanical properties, and service life. The conventional processes of shrink resist finish to the wool fabric are not eco-friendly and they also deteriorate the fabric quality. This study reported an effective and eco-friendly treatment to impart shrink resistance to wool fabric. The sequential combination of enzymes followed by polysaccharide-based biopolymers obtained good shrink resistance and retained the original attributes of the wool fabric. The fabric was initially treated with laccase and protease enzymes separately. Following enzyme, fabrics were coated with three polysaccharide biopolymers (chitosan, wheat starch, and gum arabic) using the pad-dry-cure technique. The protease-chitosan combination showed the least area shrinkage (3.57%) as compared to the untreated fabric (16.37%). The effectiveness of the treatment was evaluated and validated on wool tops using the felt ball density test. The treated fabrics were characterized using FE-SEM, EDS, and FTIR. The tensile, frictional, and bending properties were analyzed against the untreated fabric. Except for friction, tensile and bending properties remain unaffected after the shrink resist treatment. The combination of treatment retained similar whiteness and also reduced yellowness of the wool fabric. A sustainable approach of biological macromolecules-based shrink resistance treatment has an advantage over the conventional chlorination process regarding eco-friendliness, yellowness reduction, and better handle of the wool fabric at comparable shrinkage.

Simultaneous Disinfection and Organic Microcontaminant Removal by UVC-LED-Driven Advanced Oxidation Processes

This work presents the comparison of four advanced oxidation processes driven by UVC-LED radiation (278 nm—2 W/m2) for simultaneous bacteria inactivation (Escherichia coli—106 CFU/mL) and microcontaminant removal (imidacloprid—50 µg/L) in simulated wastewater secondary effluent. To this end, the activation of H2O2 and S2O82− as precursors of HO• and SO4•−, respectively, by UVC-LED and UVC-LED/Fe3+–NTA (ferric nitrilotriacetate at 0.1 mM) has been studied at different oxidant concentrations. For the purpose of comparison, conventional chlorination was used as the baseline along with bacterial regrowth 24 h after treatment. Disinfection was achieved within the first 30 min in all of the processes, mainly due to the bactericidal effect of UVC-LED radiation. UVC-LED/H2O2 did not substantially affect imidacloprid removal due to the low HO• generation by UVC irradiation at 278 nm, while more than 80% imidacloprid removal was achieved by the UVC-LED/S2O82−, UVC-LED/Fe3+–NTA/S2O82−, and UVC-LED/Fe3+–NTA/H2O2 processes. The most efficient concentration of both oxidants for the simultaneous disinfection and microcontaminant removal was 1.47 mM. Chlorination was the most effective treatment for bacterial inactivation without imidacloprid removal. These findings are relevant for scaling up UVC-LED photoreactors for tertiary wastewater treatment aimed at removing bacteria and microcontaminants.

Comparison between a Conventional Anti-Biofouling Compound and a Novel Modified Low-Fouling Polyethersulfone Ultrafiltration Membrane: Bacterial Anti-Attachment, Water Quality and Productivity.

In this work, the efficiency of a conventional chlorination pretreatment is compared with a novel modified low-fouling polyethersulfone (PES) ultrafiltration (UF) membrane, in terms of bacteria attachment and membrane biofouling reduction. This study highlights the use of membrane modification as an effective strategy to reduce bacterial attachment, which is the initial step of biofilm formation, rather than using antimicrobial agents that can enhance bacterial regrowth. The obtained results revealed that the filtration of pretreated, inoculated seawater using the modified PES UF membrane without the pre-chlorination step maintained the highest initial flux (3.27 ± 0.13 m3·m−2·h−1) in the membrane, as well as having one and a half times higher water productivity than the unmodified membrane. The highest removal of bacterial cells was achieved by the modified membrane without chlorination, in which about 12.07 × 104 and 8.9 × 104 colony-forming unit (CFU) m−2 bacterial cells were retained on the unmodified and modified membrane surfaces, respectively, while 29.4 × 106 and 0.42 × 106 CFU mL−1 reached the filtrate for the unmodified and modified membranes, respectively. The use of chlorine disinfectant resulted in significant bacterial regrowth.

Enhanced electrochemical oxidation process with hydrogen peroxide pretreatment for removal of high strength ammonia from semiconductor wastewater

Electrochemical oxidation (EO) process was investigated for decomposing ammonia in wastewater from semiconductor industry. This wastewater typically contains high concentration of hydrogen peroxide as well as ammonia in nature. As results of lab test, the presence of hydrogen peroxide exhibited a significant negative effect on ammonia removal efficiency, which was described by an oxidant-scavenging reaction pathway with recurrence relationship. Hydrogen peroxide removal by activated carbon was proposed as a pretreatment of EO process not only for the enhancement of reaction rate but also for the stability of effluent quality. As results of pilot test, ammonia removal rates were enhanced 2 ∼ 3.5 times after pretreatment. In addition, economic analysis results indicated that operating expense with pretreatment was about 60 % of that without pretreatment, which was about 30 % less than that in conventional chlorination without addition of hazardous chemicals. The suggested process has great potential for alternative to conventional chlorination in treatment of high strength ammonia wastewater from semiconductor industry.