Addition Of Chlorine Research Articles

Mechanical alloying and characterization of chlorine doped hydroxyapatite nanopowders

Chlorine-doped Hydroxyapatite (ClHA)(Ca10(PO4)6(OH)2-xClx) nanopowders were successfully synthesized using high planetary ball mill. Milling was carried from 1 to 8 h in order to study the effect of milling time on the doped powders. Additionally, a study on the effect of chlorine addition to HA was also done. XRD results confirmed that all the milled powders consisted apatite as main phase. A significant increase in the unit cell parameters of ClHA nanopowders was observed in contrast to pure HA. However, in doped powders the size decreased with an increase in milling time with a minimal change in the lattice parameters. Microscopic observations also revealed an overall increase in the particle size due to Cl− addition. FTIR results confirmed the incorporation of Cl ions into HA lattice. Hemocompatibility of the synthesized powders (pure HA and ClHA8) was investigated using bovine blood. It was seen that hemolysis ratios for both the samples were below 2%, indicating that the synthesized powders of HA and ClHA are hemocompatible and can be used in various biomedical applications.

Formation and control of C- and N-DBPs during disinfection of filter backwash and sedimentation sludge water in drinking water treatment

Drinking water treatment plants (DWTPs) produce filter backwash water (FBW) and sedimentation sludge water (SSW) that may be partially recycled to the head of DWTPs. The impacts of key disinfection conditions, water quality parameters (e.g., disinfection times, disinfectant types and doses, and pH values), and bromide concentration on controlling the formation of trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and haloacetamides (HAMs) during disinfection of FBW and SSW were investigated. Concentrations of most disinfection byproducts (DBPs) and associated calculated toxicity increased with extended chlorination for both FBW and SSW. During chlorination of both FBW and SSW, elevated chlorine doses significantly increased THM yields per unit dissolved organic carbon (DOC), but decreased HAN and HAM yields, with minimum effect on HAA yields. Chloramine disinfection effectively inhibited C-DBP formation but promoted N-DBPs yields, which increased with chloramine dose. Calculated toxicities after chloramination increased with chloramine dose, which was opposite to the trend found after free chlorine addition. An examination of pH effects demonstrated that C-DBPs were more readily generated at alkaline pH (pH=8), while acidic conditions (pH=6) favored N-DBP formation. Total DBP concentrations increased at higher pH levels, but calculated DBP toxicity deceased due to lower HAN and HAM concentrations. Addition of bromide markedly increased bromo-THM and bromo-HAN formation, which are more cytotoxic than chlorinated analogues, but had little impact on the formation of HAAs and HAMs. Bromide incorporation factors (BIFs) for THMs and HANs from both water samples all significantly increased as bromide concentrations increased. Overall, high bromide concentrations increased the calculated toxicity values in FBW and SSW after chlorination. Therefore, while currently challenging, technologies capable of removing bromide should be explored as part of a strategy towards controlling cumulative toxicity burden (i.e., hazard) while simultaneously lowering individual DBP concentrations (i.e., exposure) to manage DBP risks in drinking water.

On-site chlorination responsible for effective disinfection of wastewater from hospital.

Both hospital effluent and a model sewage treatment plant (STP) wastewater prepared by mixing STP influent and STP secondary effluent at a volume ratio of 1:9 were directly treated with chlorine for investigation of their effects on disinfection of antimicrobial-resistant bacteria (AMRB) and antimicrobial-susceptible bacteria (AMSB). The overall results indicate that the chlorine disinfection effectively inactivated the majority of AMRB and AMSB, expect for MRSA and Staphylococcus aureus in both wastewaters. No significant differences could further be observed in the taxonomic diversity of micro-organisms after the treatment. The degrees of disinfection given by the direct chlorination were comparable to those attained by combination of conventional activated sludge process and additional chlorine treatment at the STP. The results of this study evoked a recommendation to operate local chlorination treatment directly for the wastewater from medicinal facilities prior to its flow into the STP as sewage. Although additional disinfection treatment at the STP seems necessary to remove the recalcitrant MRSA and Staphylococcus aureus, the present study desirably contributes to a great reduction of the loads of STP and urgent prevention of spreading of infectious diseases in the present state.

Isolation and Structural Determination of a Hexacoordinated Antimony(V) Dication.

Invited for the cover of this issue are Masato Sakabe and Soichi Sato at Tokyo Metropolitan University. The image depicts the new hexacoordinated dicationic antimony species reported in this work. Read the full text of the article at 10.1002/chem.202004659.

Water quality in the municipalities of Sincerín and Gambote, Bolívar, Colombia (2017-2018

This study evaluates the water quality for human consumption in the municipalities of Sincerín and Gambote. It was measured through physico-chemical (color, turbidity, conductivity, pH, dissolved oxygen, hardness, and heavy metals) and microbiological (total coliforms, Escherichia coli) parameters before and after a partial form of water treatment was used (alum and chlorine addition in Gambote and Sincerín municipalities, respectively). This investigation was done in accordance with the maximum permissible values established by the Resolution 2115 of 2007 of the Ministry of Environment, Housing, and Territorial Development of Colombia (MAVD in Spanish). Additionally, the IRCA (Water Quality Risk Index) was calculated to determine the degree of risk of disease occurrence. The results indicated concentrations higher than the recommended values for: (a) hardness (in Sincerín); (b) iron (Fe), turbidity (only before being treated), E. coli (in Gambote); and (c) mercury (Hg), and total coliforms. The water supplies of the municipalities presented unsafe IRCA. Therefore, it is expected that the results of this study could be used for proposing strategies for improving these conditions by means of the design and implementation of an adequate treatment system.

N-Nitrosodimethylamine Formation during UV/Hydrogen Peroxide and UV/Chlorine Advanced Oxidation Process Treatment Following Reverse Osmosis for Potable Reuse.

Chloramines applied to control microfiltration and reverse osmosis (RO) membrane biofouling in potable reuse trains form the potent carcinogen, N-nitrosodimethylamine (NDMA). In addition to degrading other contaminants, UV-based advanced oxidation processes (AOPs) strive to degrade NDMA by direct photolysis. The UV/chlorine AOP is gaining attention because of its potential to degrade other contaminants at lower UV fluence than the UV/hydrogen peroxide AOP, although previous pilot studies have observed that the UV/chlorine AOP was less effective for NDMA control. Using dimethylamine (DMA) as a model precursor and secondary municipal wastewater effluent, this study evaluated NDMA formation during the AOP treatment via two pathways. First, NDMA formation by UV treatment of monochloramine (NH2Cl) and chlorinated DMA (Cl-DMA) passing through RO membranes was maximized at 350 mJ/cm2 UV fluence, declining at higher fluence, where NDMA photolysis outweighed NDMA formation. Second, this study demonstrated that chlorine addition to the chloramine-containing RO permeate during the UV/chlorine AOP treatment initiated rapid NDMA formation by dark breakpoint reactions associated with reactive intermediates from the hydrolysis of dichloramine. At pH 5.7, this formation was maximized at a chlorine/ammonia molar ratio of 3 (out of 0-10), conditions typical for UV/chlorine AOPs. At 700 mJ/cm2 UV fluence, which is applicable to current practice, NDMA photolysis degraded a portion of the NDMA formed by breakpoint reactions. Lowering UV fluence to ∼350 mJ/cm2 when switching to the UV/chlorine AOP exacerbates effluent NDMA concentrations because of concurrent NDMA formation via the UV/NH2Cl/Cl-DMA and breakpoint chlorination pathways. Fluence >700 mJ/cm2 or chlorine doses greater than the 3:1 chlorine/ammonia molar ratios under consideration for the UV/HOCl AOP treatment are needed to achieve NDMA control.

The roles of added chlorine and sulfur on ash deposition mechanisms during solid fuel combustion

The focus of this paper is on effects of chlorine and sulfur on coal ash deposition rates, under practically relevant but systematically controlled combustion conditions. This problem is important, not so much for coal, but to understand and predict deposition rates for biomass combustion where chlorine contents can be high. To this end, ash deposition rates on a controlled temperature surface were measured for controlled amounts of chlorine and sulfur added to a pulverized coal, doped with potassium and burned in a 100 kW rated combustion rig. Previous work with 35 tests on 11 coal, biomass and petroleum coke fuels burned under a range of operating conditions had strongly suggested that the deposition rate of the tightly bound inside deposits was independent of the ash aerosol composition, and depended only on PM1 in the flue gas. The loosely bound outside deposition rate was dependent primarily on the total alkali content in the flue gas. The new results using chlorine added to the fuel (in the form of ammonium chloride) required these previous conclusions to be drastically revised. They showed that chlorine, not alkali alone, had large effects on the deposition rate of the inside deposits, which now were orders of magnitude higher than without chlorine addition, and did not fit previous (multi-fuel) correlations with PM1. Sulfur addition, together with chlorine, did not affect deposition rates much, although it did lower the chlorine content of the deposit. These results are interpreted in terms of the ash aerosol size segregated composition, which was also measured, and potential sulfation reactions within the deposit.

Wastewater Treatment on Shrimp Processing Industry

Increasingly rapid industrial development poses serious environmental problems such as wastewater.The higher the number of production, the more waste that wasted and can decrease the environment quality. Fieldwork practice activity is carried out starting from the date of January 20, 2014, until February 15, 2014. The purpose of this fieldwork practice is to acquire knowledge and skills on the field of wastewater treatment technique and to know the parameters of the wastewater inlet and outlet channels in comparison with wastewater quality standards. The method that used in Field Work Practice This is descriptive, the method to describe the circumstances or events in a particular region. The result obtained from fieldwork practice known that wastewater treatment techniques consist of preliminary treatment activities, primary treatment, secondary treatment, sedimentation, and disinfection. Preliminary treatment activities is a filtering process substantial in the wastewater that comes out of the inlet channel using four mesh size of the net. The primary treatment for separating solids that escaped from the screening process and disposed to wastewater reservoirs. Secondary treatment activity including Aerobacter sp., Nitrosomonas sp., Nitrobacter sp., Bacillus sp. of bacteria and oxygen addition inside of wastewater. Sedimentation phase separation process is carried out suspended solids in wastewater using clarifier pond. Disinfection stage which activities the addition of chlorine with 222 ppm of doses to kill harmful pathogens. The final stage test to determine the parameters of wastewater effluent quality by using living fishes and taking the sample from another institution.

Molecular characterization of transformation and halogenation of natural organic matter during the UV/chlorine AOP using FT-ICR mass spectrometry

UV/chlorine process, as an emerging advanced oxidation process (AOP), was effective for removing micro-pollutants via various reactive radicals, but it also led to the changes of natural organic matter (NOM) and formation of disinfection byproducts (DBPs). By using negative ion electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS), the transformation of Suwannee River NOM (SRNOM) and the formation of chlorinated DBPs (Cl-DBPs) in the UV/chlorine AOP and subsequent post-chlorination were tracked and compared with dark chlorination. In comparison to dark chlorination, the involvement of ClO•, Cl•, and HO• in the UV/chlorine AOP promoted the transformation of NOM by removing the compounds owning higher aromaticity (AImod) value and DBE (double-bond equivalence)/C ratio and causing the decrease in the proportion of aromatic compounds. Meanwhile, more compounds which contained only C, H, O, N atoms (CHON) were observed after the UV/chlorine AOP compared with dark chlorination via photolysis of organic chloramines or radical reactions. A total of 833 compounds contained C, H, O, Cl atoms (CHOCl) were observed after the UV/chlorine AOP, higher than 789 CHOCl compounds in dark chlorination, and one-chlorine-containing components were the dominant species. The different products from chlorine substitution reactions (SR) and addition reactions (AR) suggested that SR often occurred in the precursors owning higher H/C ratio and AR often occurred in the precursors owning higher aromaticity. Post-chlorination further caused the cleavages of NOM structures into small molecular weight compounds, removed CHON compounds and enhanced the formation of Cl-DBPs. The results provide information about NOM transformation and Cl-DBPs formation at molecular levels in the UV/chlorine AOP.

Hot Carrier Cooling and Recombination Dynamics of Chlorine-Doped Hybrid Perovskite Single Crystals

Controlling the photoexcited properties and behavior of hybrid perovskites by halide doping has the potential to impact a wide range of emerging technologies, including solar cells and radiation detectors. Crystalline samples of methylammonium lead bromide substituted with chlorine (MAPbBr3-xClx) were examined by transient reflectivity spectroscopy and nonadiabatic molecular dynamics simulations. At picosecond time scales, the addition of chlorine to the perovskite crystal increased the observed rate of hot carrier cooling and the calculated electron-phonon coupling constants. Chlorine-doped samples also exhibit a slower surface recombination velocity and a smaller ambipolar mobility.

Isomerization of n-heptane on platinum-zeolite catalysts promoted by chlorine and fluorine

The isomerization of n-heptane on BEA supported platinum catalysts with the addition of chlorine and fluorine as promoters was studied. The use of the halides decreased the operating temperature of the n-heptane conversion. The samples prepared at the stage of peptization showed an increase in the total conversion accompanied by a decrease in the yield of heptane isomers of 6 for chlorine and 27 wt.% for fluorine. Promotion by the halides at the stage of platinum application led to an increase in the catalyst activity without decrease in the selectivity values.

Larvicidal activity of substituted chalcones against Aedes aegypti (Diptera: Culicidae) and non-target organisms.

The expansion of Aedes aegypti (Diptera: Culicidae) population has increased the number of cases of arboviruses, in part due to the inefficiency and toxicity of the chemical control methods available to control this vector. We synthesized 19 chalcone derivatives and examined their activity against Ae. aegypti larvae in order to select larvicidal compounds that are non-toxic to other organisms. Seven chalcone derivatives (3a, 3e, 3f, 6a, 6c, 6d, and 6f) had lethal concentrations of substituted chalcones capable of killing 50% (LC50 ) values lower than 100 mg mL-1 at 24 h post-treatment, which is the dose that the World Health Organization recommends for the selection of promising larvicides. The type of substituent added to (E)-1,3-diphenylprop-2-en-1-one (3a) markedly affected the larvicidal activity. Addition of chlorine, bromine and methoxy groups to the aromatic rings reduced the larvicidal activity, while replacement of the B-ring (phenyl) by a furan ring significantly increased the larvicidal activity. The furan-chalcone (E)-3-(4-bromophenyl)-1-(furan-2-yl)prop-2-en-1-one (6c) killed Ae. aegypti larvae (LC50 = 6.66 mg mL-1 ; LC90 = 9.97 mg mL-1 ) more effectively than the non-substituted chalcone (3a) (LC50 = 14.43 mg mL-1 ; LC90 = 20.96 mg mL-1 ), and was not toxic to the insect Galleria mellonella, to the protozoan Tetrahymena pyriformis, and to the algae Chorella vulgaris. The substitution pattern of chalcones influenced their larvicidal activity. In the set of compounds tested, (E)-3-(4-bromophenyl)-1-(furan-2-yl)prop-2-en-1-one (6c) was the most effective larvicide against Ae. aegypti, with no clear signs of toxicity to other animal models. Its mechanism of action and effectiveness under field conditions remain to be determined.

Application of UV/chlorine pretreatment for controlling ultrafiltration (UF) membrane fouling caused by different natural organic fractions

In this study, the effects of UV/chlorine pretreatment on ultrafiltration (UF) membrane fouling derived from different fractions of natural organic matter (NOM) were studied and compared. Three model organic compounds including humic acid (HA), sodium alginate (SA) and bovine serum albumin (BSA) were employed to represent different NOM fractions in natural surface water. The results suggest that membrane fouling induced from HA, SA and HA-SA-BSA mixture could be effectively mitigated by UV/chlorine pretreatment, which could be further improved by increasing the chlorine dose. Although UV irradiation alone severely aggravated BSA fouling, the addition of chlorine (0.0625 mM) to the pretreatment process could effectively avoid the fouling. The alleviation of membrane fouling is primarily ascribed to the reduction of molecular weight (MW) of organic compounds, and the decomposition of unsaturated organic species, thereby reducing the accumulation of organics on the membrane surface and pores. This is confirmed by the reduction of UV254 and fluorescent components in the feed solution and the increase of DOC in the permeate after UV/chlorine pretreatment. Membrane fouling during the filtration of untreated HA, SA, and HA-SA-BSA mixture was occupied by cake filtration and intermediate pore blocking, while UV/chlorine pretreatment led to the exacerbation of pore blocking at the initial filtration stage. The initial fouling mechanism of untreated BSA was mainly governed by complete blocking, which shifted to intermediate pore blocking after UV/chlorine pretreatment.

The role of chlorine oxide radical (ClO•) in the degradation of polychoro-1,3-butadienes in UV/chlorine treatment: kinetics and mechanisms

Polychoro-1,3-butadienes (CBDs) were widely found in aqueous environment and resistant to conventional water treatment. In this study, the abatement of CBDs during UV/chlorine treatment was investigated. In comparison to UV irradiation alone, free chlorine addition brought benefits for the reduction of tetra-CBDs (TCBDs), but to lesser extent for penta-CBDs (PCBDs), and virtually no benefit for hexa-CBD (HCBD). At a UV dose of 128 mJ cm−2 and a chlorine dose of 10 mg L−1, about 71.7–97.8% CBDs were degraded by UV/chlorine treatment within 10 min. UV irradiation contributed 32.8%–97.6%, HO• contributed 2.6%–14.4%, and reactive chlorine species (RCS) contributed less than 0.5%–42.3% to CBDs degradation. The percentages of RCS contribution generally followed the order of TCBDs (except (Z,Z)-1,2,3,4-TCBD) > PCBDs > HCBD. The chlorine oxide radical (ClO•) was the dominant RCS contributing to the degradation of CBDs. The second-order reaction rate constants of ClO• with CBDs (kClO•,CBDs) were at ∼ 107 M−1s−1 except (Z,Z)-1,2,3,4-TCBD and HCBD (<106 M−1s−1). kClO•,CBDs generally decreased with increasing numbers of chlorine atoms and was also affected by the positions of chlorine atoms in CBDs. A distinct reaction pathway of ClO•, with (Z)-1,1,2,3,4-PCBD as a representative CBD, was proposed. Photoisomers of CBDs from Z or E configuration were observed at lower concentrations in UV/chlorine treatment than under UV irradiation alone due to the radical-involved oxidation, but more organic acids including oxalic acid were observed. In a natural water sample, UV/chlorine treatment also exhibited a good performance in abatement of TCBDs and PCBDs, but not in abatement of HCBD.

Towards a Predictive Model for Initial Chlorine Dose in Humanitarian Emergencies

Free chlorination is a widely employed disinfection method in humanitarian water provision due to its many advantages. However, its effective application is hindered by the challenge in determining adequate initial doses to achieve free chlorine residuals that satisfy both health and aesthetic requirements. Current guidelines show varying recommended dosing strategies, and many do not adequately consider chlorine decay mechanisms that occur during water storage. Even though turbidity is commonly used as a criterion for deciding chlorine dose, it may not be an adequate proxy for the water quality in many cases. This paper addresses the fundamental relationships between chlorine decay kinetics and selected key water parameters (i.e., natural organic matter, water temperature, chlorine demand) by conducting chlorine decay tests in controlled conditions and in jerrycans (i.e., simulating humanitarian water treatment conditions). Chlorine decay constant from the Feben and Taras’s empirical model and first order model formed linear and exponential relationships with two water parameters (UVA254 and 30-min chlorine demand). With these relationships, the two chlorine decay models can be calibrated quickly and frequently in the field, allowing effective determination of initial chlorine dose. These two models calibrated based on the suggested water parameters from the study could predict chlorine decay in water having a main chlorine demand-inducing constituents as natural organic matter. However, they underpredicted chlorine decay in surface water with additional chlorine reactants. Further research on additional chlorine decay mechanisms is needed to expand the applicability of the models.

DESENVOLVIMENTO DE CITRONELA (CYMBOPOGON WINTERIANUS) IRRIGADA COM ESGOTO DOMÉSTICO TRATADO E COM ÁGUA DE ABASTECIMENTO

Este trabalho teve como objetivo avaliar o desenvolvimento de capim citronela (Cymbopogon winterianus) irrigado com água de abastecimento fornecida pela concessionária (TA), esgoto doméstico tratado, após a adição de cloro (TB), e esgoto doméstico tratado, antes da adição de cloro (TC). Utilizou-se o efluente de uma estação de tratamento de esgoto (ETE) do tipo reator anaeróbio de fluxo ascendente (RAFA). A irrigação, com cada efluente, foi realizada em sete vasos, cada vaso com duas mudas do vegetal, totalizando14 plantas. Analisaram-se: índice de clorofila nas folhas (IC); teor de massa seca (MS); teor de massa inerte (MI). Para o IC, os resultados, em Soil Plant Analysis Development (SPAD), foram: 18 (TA), 31,73 (TB) e 37,03 (TC). Para o MS, os resultados, em %m/m, foram: 86,14 (TA), 83,75 (TB) e 82,18 (TC). Para o MI, os resultados, em %m/m, foram: 2,25 (TA), 1,71 (TB) e 1,63 (TC). Percebeu-se que plantas regadas com efluentes tratados apresentaram visualmente um melhor desenvolvimento foliar e tonalidade mais escura deverde. O efluente oriundo do tratamento TC proporcionou a maior produção de clorofila, indicando um maior potencial de aproveitamento. O tratamento TA proporcionou a produção de maiores quantidades de massa seca e de massa inerte.

Temporal release behavior of potassium during pyrolysis and gasification of sawdust particles

The potassium release from sawdust in pyrolysis and gasification was studied using an online measurement method. The final results suggested that the potassium releases more in pyrolysis than that in CO2 gasification environment at 800-900 °C. The overall activation energies and pre-exponential factors of potassium release in pyrolysis and gasification were further derived. In addition, the additive chlorine influence on potassium release had been evaluated, and the results showed that the promoting effect of chlorine during pyrolysis was higher than the case during CO2 gasification. Thermodynamic calculations were done to predict the possible potassium species during pyrolysis and gasification. The K2CO3 (s) formation mostly contributed to the higher potassium release proportion in pyrolysis than that during CO2 gasification.

Influence of Chloride/Iodide Ratio in MAPbI3-xClx Perovskite Solar Devices: Case of Low Temperature Processable AZO Sub-Layer

A significant current challenge for perovskite solar technology is succeeding in designing devices all by low temperature processes. This could help for both rigid devices industrialisation and flexible devices development. The depositions of nanoparticles from colloidal suspensions consequently emerge as attractive approaches, especially due to their potential for low temperature curing not only for the photoactive perovskite layer but also for charge transporting layers. Here, NIP solar cells based on aluminium doped zinc oxide (AZO) electron transport layer were fabricated using a low temperature compatible process for AZO deposition. For the extensively studied perovskites based on methylammonium lead halides (MAPbI3-xClx), the chloride/iodide equation is widely proposed to follow an optimal value corresponding to an introduced MAI:PbCl2 ratio of 3:1. However, the perovskite formulation should be considered as a key parameter for the optimization of power conversion efficiency when exploring new perovskite sub-layers. We here propose a systematic method for the structural determination of the optimal ratio. It may depend on the sublayer and results from structural changes around the optimal value. The functional properties gradually increase with the addition of chlorine as long as it remains intercalated in a single phase. Above the optimal ratio, the appearance of two phases degrades the system.

Shedding light on the governing mechanisms for insufficient CO and H2 burnout in the presence of potassium, chlorine and sulfur

Based on the experiences of insufficient burnout in industrial fluidized bed furnaces despite adequate mixing and availability of oxidizer, the influence of potassium on CO and H2 oxidation in combustion environments was investigated. The combustion environments were provided by a laminar flame burner in a range relevant to industrial furnaces, i.e. 845 °C to 1275 °C and excess air ratios ranging from 1.05 to 1.65. Potassium, in the form of KOH, was homogeneously introduced into the hot gas environments to investigate its effect on the radical pool. To quantitatively determine key species that are involved in the oxidation mechanism (CO, H2, KOH, OH radicals, K atoms), a combination of measurement systems was applied: micro-gas chromatography, broadband UV absorption spectroscopy and tunable diode laser absorption spectroscopy. The inhibition effect of potassium on CO and H2 oxidation in excess air was experimentally confirmed and attributed to the chain-terminating reaction between KOH, K atoms and OH radicals, which enhanced the OH radical consumption. The addition of chlorine or sulfur could reduce the concentrations of KOH and K atoms and consequently eliminated the inhibition on CO and H2 oxidation. Existing kinetic mechanisms underestimate the inhibiting effect of potassium and they fail to predict the effect of temperature on CO and H2 concentration when potassium and sulfur co-exist. This work advances the need to revise existing kinetic mechanisms to fully capture the interplay of K and S in the oxidation of CO and H2 in industrial fluidized bed furnaces.

Solar irradiation combined with chlorine can detoxify herbicides

The solar/chlorine process is an energy-efficient advanced oxidation process that can produce reactive species such as hydroxyl radical, reactive chlorine species and ozone. This study investigated the process’ ability to detoxify the typical herbicides atrazine and mecoprop (methylchlorophenoxypropionic acid). Both herbicides are resistant to direct solar photolysis or chlorination alone, but they can be degraded by the solar/chlorine process effectively. Atrazine inhibited the development of Arabidopsis thaliana, but such inhibition was negligible after solar/chlorine treatment of an atrazine solution. The transformation of atrazine in the process was shown to be through hydroxylation, hydrogen abstraction and dechlorination but did not involve chlorine substitution or addition. Cl• reacts with atrazine and mecoprop with rate constants of 6.87 × 109 M−1s−1 and 1.08 × 1010 M−1s−1, respectively, while ClO• reacts with mecoprop with a rate constant of 1.11 × 108 M−1s−1. The degradation kinetics of atrazine and mecoprop by solar/chlorine was simulated by modeling, which fitted the experimental results well. Hydroxyl radicals (HO•) mainly contributed to the degradation of atrazine by solar/chlorine at pH 7 with the contribution of 65%, whereas ClO• and O3 were main species responsible for the degradation of mecoprop with the contribution of 72% and 17%, respectively. The pseudo-first-order rate constants (k′s) of the two degradations increased substantially (by 28.8% for atrazine and by 198% for mecoprop) when the chlorine dosage was increased from 50 μM to 200 μM. The k′s decreased with increasing pH. The presence of natural organic matter inhibited the degradation of both herbicides, while the presence of bromide enhanced their degradation. This work reveals a feasible method for the detoxifying herbicides by combining chlorine with solar radiation.