Study on the Inactivation of Pseudomonas Sp and the Degradation of Trichloroethylene by Fenton-Like Reaction

water

Article Study on the Inactivation of Pseudomonas sp and the Degradation of Trichloroethylene by Fenton-Like Reaction

Dan Zhong, Fu He, Wencheng Ma * , Yixing Yuan * and Ziqiang Wang

School of Environment, Harbin Institute of Technology, Harbin 150090, China; [email protected] (D.Z.); [email protected] (F.H.); [email protected] (Z.W.) * Correspondence: [email protected] (W.M.); [email protected] (Y.Y.); Tel.: +86-0451-8628-2104 (W.M.); +86-0451-8628-2735 (Y.Y.) Received: 20 August 2018; Accepted: 27 September 2018; Published: 1 October 2018

Abstract: The present work intended to use goethite, one of the main compositions of pipe deposit, to combine with H2O2 to degrade TCE or disinfect drinking water. Goethite exhibited excellent degradation performance for TCE, outstanding inactivation ability for Pseudomonas and the disinfection effect for filter water of water treatment plants. The TCE degradation efficiency could reach 87.4%, while the inactivation efficiency of Pseudomonas and the bacterial mortality rate in filtered water were more than 99.9% in this study. In order to effectively reduce the disinfection by-products (chlorine-resistant bacteria) and conduct permanent disinfection, the Fenton-like and chlorine combined disinfection method was also investigated. Experimental results indicated that the bacteria could be effectively killed by this combined method and the chlorine residual was 0.41m g/L, ensuring sustainable disinfection. This work verified that the pipe deposit from the water distribution network is multifunctional, which is a potential candidate for pollutant removal and sterilization. The results could also offer theoretical support for water quality security in water distribution networks in the future.

Keywords: water distribution network; growth ring; Fenton-like; disinfection; trichloroethylene

1. Introduction The water distribution network (WDN) is vital for transporting safe, clean and ideal drinking water. However, these networks are huge, complex and can be influenced by nature and operational conditions. The microbial communities in WDN also vary [1]. Microorganism contamination of WDN could damage the water services and the safe use of drinking water. It is also harmful to the human body [2]. Disinfection is an essential step to protect people from waterborne diseases [3]. At present, the addition of chlorine-containing disinfectant and maintaining a certain amount of chlorine residual is the most common method for controlling the regrowth of bacteria in WDN [4]. However, some bacteria still survive even under the condition of a high chlorine residual level. These bacteria can form biofilm on the wall of the network, which is a source of microbial contamination, and slowly release microorganisms into the WDN, posing a serious threat to human health. And when the water quality and hydraulic conditions change, the biofilm may fall off and enter the water resulting in pollution. In addition, exfoliated biofilm can accelerate the corrosion of growth ring and form red water, causing deterioration of water’s smell and taste [5,6]. In recent years, volatile organic compounds (VOCs) have become dangerous to the environment and human health, including alcohols, mercaptans, ketones, and halogenated hydrocarbons [7]. Trichloroethylene (TCE) is widely used as a cleaning and degreasing agent in industries. TCE is

Water 2018, 10, 1376; doi:10.3390/w10101376 www.mdpi.com/journal/water Water 2018, 10, 1376 2 of 13 considered one of the most toxic and carcinogenic VOCs, and it has been easily found in the waste byproducts of chemical processes, dumping grounds, the indoor air and even in groundwater remediation sites [8]. The removal of TCE has been an urgent problem to explore. Several methods have been used to reduce VOCs, including TCE, such as combustion [9], adsorption [10], advanced oxidation processes [11] and biological methods [12]. Advanced oxidation processes (AOPs) is an effective way for water purification and recovery [13–17]. The Fenton reaction is an effective, inexpensive and environmentally friendly method to degrade pollutants [18–20]. In 2012, Oliveira et al. successfully used pipe deposits from water networks as novel catalysts to remove the pesticide paraquat in water by Fenton reaction [21]. In 2013, Gosselin et al. added H2O2 into the actual pipe network, and the corrosive growth ring combined with H2O2 to form Fenton-like system for the disinfection of drinking water and biofilm, and it has achieved a good disinfection effect. Gosselin et al. believed that the Fenton-like reaction is a promising alternative disinfection method [2]. However, very few studies simultaneously focus on the pollutant degradation and the disinfection of drinking water. In this study, we analyzed the actual pipe growth ring and prepared one main composition of the actual pipe growth ring and characterized it by X-ray diffraction (XRD), X-ray fluorescence (XRF), Automatic Specific Surface Area and Porosity Analyzer (BET) and so on. These results demonstrated that the main composition of the pipe growth ring, goethite, could be used as a catalyst in active H2O2 to produce •OH radical. The ability of goethite to facilitate the Fenton-like oxidation of TCE and bacteria inactivation were tested under varying conditions. The Fenton-like and chlorine combined disinfection method and the related mechanism were also discussed.

2. Materials and Methods

2.1. Preparation of Goethite According to the alkaline precipitation method [22], the prepared process of goethite (α-FeOOH) was as follows: First, 1 mol/L KOH (Sinopharm Chemical Reagent Co., Ltd, Shanghai, China) was added dropwise to Fe(NO3)3 (Sinopharm Chemical Reagent Co., Ltd, Shanghai, China) solution (20 mL, 1 mol/L), and was stirred with a magnetic stirrer until the pH reached 7. Then, the mixed solution was centrifuged (4000 r/min, 4 min; Eppendorf, Shanghai, China) to obtain goethite, and the goethite was washed several times with deionized water. Finally, the prepared goethite was dissolved into a certain amount of deionized water and dried in a drying oven at 333 K for 12 h. The goethite crystal was ground uniformly and preserved for next use.

2.2. TCE Degradation Experiments by Fenton-Like Reaction

50 mL deionized water, 50 µL TCE, 3.33 g/L goethite and 11.5 g/L H2O2 were added into a 100 mL beaker, which formed a Fenton-like system. The residual TCE at different times was measured by using the gas chromatography-headspace sampling method. In order to study the degradation efﬁciencies at different conditions, adjusted pH, changed goethite dosage and H2O2 concentration were used. 25 mL methanol was used to terminate the Fenton-like reaction for better TCE concentration detection. All the catalytic degradation experiments were conducted in triplicate.

2.3. Microbiology Experiments

2.3.1. Microbial Enrichment Culture The microorganism culture operation steps were as follows: (1) the contained bacteria samples were cultivated by the streak plate method (303 K, 24 h) and the target colonies were selected; (2) the target colonies were inoculated into the R2A liquid medium, which has been sterilized at high temperature; (3) the conical ﬂask containing the culture medium was shaken into an oscillation Water 2018, 10, 1376 3 of 13 incubator for fostering (303 K, 5–7 days); (4) a small amount of the liquid medium was taken and cultured by the streak method (303 K, 24 h).

2.3.2. Bacterial Counting Method The method for counting bacteria in the microbiology experiment was the ﬂat colony counting method. The speciﬁc steps were as follows: (1) sample dilution: Dilute the bacterial sample until the bacterial concentration was about 105 CFU/L (CFU, Colony-Forming Units); (2) bacterial inoculation: Use a pipette to draw a certain amount of bacterial dilution into the plate, and then coat it evenly with a coating bar; (3) constant temperature culture: Place the plate in a 303 K constant temperature incubator and incubate for 2–3 days; (4) colony count: Observe the growth of bacterial colonies in the plate and calculate the number.

2.3.3. Sterilization Experiments by Fenton-Like Reaction The bacteria were inoculated into an Erlenmeyer flask containing about 40 mL of R2A liquid medium using an inoculating loop. The conical flask was placed in a constant temperature shaking incubator and cultured at 303 K for 3–4 days. The culture was dealt with using a high-speed centrifuge (5000 r/min, 5 min). Then the supernatant was removed, followed by washing the precipitate three times with a phosphate buffer solution (pH = 7.2). Finally, it was diluted to the required concentration for the next experiment. The sterilization experiments were performed in a dark test tube. A certain amount of above-prepared bacterial suspension, goethite and H2O2 (Shanghai Aladdin Bio-Chem Technology Co., LTD, Shanghai, China) were added into the test tube. 1 mL reaction solution was quenched by 9 mL, 1.5% Na2S2O3 (Tianjin Guangfu Technology Development Co., Ltd., Tianjin, China). The mixed solution was diluted several times, then 0.5 mL sample was inoculated into R2A solid medium, inverted, and incubated at 303 K for 48 h. The colonies in the culture dish were counted, then positive control experiments and parallel experiments conducted. The experimental sample was cultured at 303 K for 48 h in a constant temperature incubator. The obtained data by counting were the final result of the experiment. Experimental procedures for disinfection of filtered water by Fenton-like reaction were similar to the abovementioned processes.

2.4. The Fenton-Like and Chlorine Combined Disinfection Method

90 mL ﬁltered water added into a dark conical ﬂask, then a certain amount of goethite and H2O2 solution was added. In order to terminate the reaction, 1 mL reaction solution mixed with 9 mL, 1.5% Na2S2O3. 0.5 mg/L chlorine was put into the above system and repeated with a quenching operation. The Fenton-like and chlorine disinfection mixture was diluted several times. 0.5 mL sample mixture was pipetted, inoculated into R2A solid medium, inverted, incubated at 303 K for 48 h. The colony growth was observed and the number calculated.

2.5. Determination Method of H2O2 Concentration

10 mL H2O2 transferred into a 50 mL Erlenmeyer ﬂask, then added 10 mL of 20.0% H2SO4 (Sinopharm Chemical Reagent Co., Ltd, Shanghai, China). Titrating with KMnO4 (CKMnO4 = 0.1 mol/L, Sinopharm Chemical Reagent Co., Ltd, Shanghai, China) standard solution until the solution was light pink and kept at 30 s. According to the equation to calculate the concentration of H2O2, the equation was as the following [23]:

2KMnO4 +5H2O2 + 3H2SO4 = 2MnSO4+ K2 SO4 + 5O2↑+ 8H2O (1)

CH2O2 = 0.025VKMnO4 CH2O2—the concentration of H2O2, mol/L VKMnO4—used KMnO4 volume, mL Water 2018, 10, 1376 4 of 13

2.6. Characterization The crystal structures of the pipe growth ring and goethite were obtained by X-ray diffraction (XRDWater 2018 (Rigaku, 10, x FOR Corporation, PEER REVIEW Japan) Rigaku D/max-RB with Ni-filtered Cu Kα radiation (λ = 1.54056)). 4 of 13 The BET method was used to calculate the specific surface area. The pore-size distribution was measuredmeasured byby usingusing ASAPASAP 2020M2020M analyzeranalyzer (Micromeritics(Micromeritics InstrumentInstrument Corp,Corp, Beijing,Beijing, China).China). TheThe typetype andand content of of each each element element in ingrowth growth ring ring were were confirmed confirmed by X-ray by X-ray fluorescence fluorescence spectrometer spectrometer (XRF, (XRF,AXIOS-PW4400, AXIOS-PW4400, PANalytical PANalytical B.V. B.V. Beijing, Beijing, China). China). TCE TCE concentration concentration was was detected detected by Gas Gas chromatographychromatography (Agilent(Agilent 6890,6890, AgilentAgilent TechnologiesTechnologies Inc., Inc., Shanghai, Shanghai, China). China).

3.3. ResultsResults andand DiscussionsDiscussions

3.1.3.1. CharacterizationCharacterization ofof thethe ActualActual GrowthGrowth RingRing AndAnd GoethiteGoethite

3.1.1.3.1.1. CompositionComposition AnalysisAnalysis ofof thethe GrowthGrowth RingRing ofof WDNWDN AA sectionsection ofof pipepipe waswas taken,taken, whichwhich waswas fromfrom anan actualactual WDNWDN inin aa certaincertain citycity inin HeilongjiangHeilongjiang Province.Province. The The pipe pipe growth growth ring ring was was stripped. stripped. The compositions The compositions of the pipe of the growth pipe ring growth were ring analyzed were throughanalyzed the through following the following methods. methods. The speciﬁc The conditions specific conditions of the pipe: of Castthe pipe: iron Cast pipe, iron the pipe, pipe agethe pipe was 20age years, was 20 and years, the disinfectant and the disinfectant was chlorine was dioxide.chlorine dioxide. TheThe majormajor compositionscompositions ofof thethe strippedstripped growthgrowth ringring werewere detecteddetected byby XRD.XRD. FigureFigure1 1aa was was the the relevantrelevant spectra. The The main main compositions compositions were were lepidocrocite lepidocrocite (γ-FeOOH) (γ-FeOOH) and and goethite goethite (α-FeOOH), (α-FeOOH), and andtheir their diffraction diffraction peaks peaks were were consistent consistent with with the the previous previous published published result result [24]. [24]. The The contents contents of of lepidocrocitelepidocrocite andand goethitegoethite werewere 55.9%55.9% andand 44.1%,44.1%, respectively, respectively, closing closing to to 1:1. 1:1.

FigureFigure 1.1. XRD patternspatterns ofof ((aa)) thethe actualactual pipepipe growthgrowth ringring andand ((bb)) thethe preparedprepared goethite.goethite.

TheThe types and contents of of each each element element contained contained in in the the pipe pipe growth growth ring ring were were determined determined by byquantitative quantitative analysis analysis and and semi-quantitative semi-quantitative analysis. analysis. According According to to Table Table 1 1,, the the elements elements and and compoundscompounds inin thethe growthgrowth ringring accountedaccounted forfor 55.6%55.6% andand 50.4%,50.4%, respectively,respectively, closingclosing toto 1:1.1:1. TheThe mainmain chemicalchemical elementselements inin thethe growthgrowth ringring werewere FeFe andand O,O, inin whichwhich thethe proportionsproportions areare 24.0%24.0% andand 29.3%29.3% ofof thethe totaltotal weightweight ofof thethe growthgrowth ring,ring, respectively.respectively. ItIt waswas verifiedverified thatthat thethe mainmain compositioncomposition ofof thethe growthgrowth ringring isis ironiron oxide.oxide. There was a small amount of Si (1.2%) and Al (0.2%) in the growth ring. TheThe mainmain existentexistent formsforms ofof SiSi and and Al Al were were SiO SiO2 2and and Al Al22OO33.. TheThe mainmain reasonreason forfor thethe existenceexistence ofof SiOSiO22 mightmight bebe thatthat thethe waterwater plantplant usesuses aa sandsand filter,filter, thethe finefine particlesparticles andand thethe SiOSiO22 inin thethe soilsoil cancan enterenter WDNWDN toto formform aa sectionsection ofof pipepipe growthgrowth ring. ring. TheThe reasonreason forfor the the existence existence of of Al Al22OO33 couldcould bebe attributedattributed toto tracetrace amountsamounts ofof coagulant.coagulant.

Water 20182018,, 1010,, 1376x FOR PEER REVIEW 55 of of 13

Table 1. The analysis result of XRF. Table 1. The analysis result of XRF. Analytical Element Concentration (%) Analytical Compound Concentration (%) AnalyticalO Element Concentration29.320 (%) Analytical- Compound Concentration- (%) OCl 0.042 29.320 -- -- Cl 0.042 -- Na 0.138 Na2O 0.212 Na 0.138 Na2O 0.212 MgMg 0.121 0.121 MgO MgO 0.231 0.231 2 3 AlAl 0.224 0.224 Al Al2OO3 0.4910.491 SiSi 1.211 1.211 SiO SiO22 3.0183.018 PP 0.060 0.060 P P22OO55 0.1630.163 S 0.028 SO3 0.083 S 0.028 SO3 0.083 K 0.031 K2O 0.044 CaK 0.031 0.212 K CaO2O 0.044 0.358 TiCa 0.212 0.057 CaO TiO2 0.3580.116 MnTi 0.057 0.091 TiO MnO2 0.116 0.151 FeMn 0.091 24.021 MnO Fe2O3 0.15145.365 Zn 0.058 ZnO 0.103 SumFe 24.021 55.614 Fe Sum2O3 45.365 50.335 Zn 0.058 ZnO 0.103 Sum 55.614 Sum 50.335 The catalytic activity of the catalyst is related to the active site on the surface of the catalyst. The amountThe catalytic of active activity site directlyof the catalyst determines is related the catalytic to the active activity. site Specificon the surface surface of area, the porecatalyst. volume The andamount pore of size active of thesite growth directly ring determines were confirmed the catalytic by the activity. BET method. Specific surface It can be area, seen pore that volume the growth and ringpore hassize aof large the growth specific ring surface were area, confirmed which by led the to itsBET good method. catalytic It can capacity. be seen Thethat detailedthe growth data ring is shownhas a large in Table specific2. surface area, which led to its good catalytic capacity. The detailed data is shown in Table 2. Table 2. Specific surface area, pore volume and pore size of the growth ring and goethite. Table 2. Specific surface area, pore volume and pore size of the growth ring and goethite. Samples Specific Surface Area Pore Volume Pore Size Samples Specific Surface Area Pore Volume Pore Size 2 3 The growth ring 397.06 m /g2 0.51 cm /g³ 44.52 Å The growth ring 397.06 m /g 0.51 cm3 /g 44.52 Å Goethite 146.85 m2/g 0.15 cm /g 35.38 Å Goethite 146.85 m2/g 0.15 cm³/g 35.38 Å

3.1.2. Morphology Analysis of the Prepared Goethite Scanning electron microscopy (SEM) was used to observe the prepared goethite morphology at different magnification, magnification, as as shown shown in in Figure Figure2a,b. 2a and Goethite Figure showed 2b. Goethite a flocculent-like showed a structure. flocculent-like This structurestructure. hasThis a structure large specific has a surface large specific area, which surface is beneficial area, which for is enriching beneficial pollutants. for enriching pollutants.

Figure 2. SEM images of the prepared goethite, (a) 5 magniﬁcation,magnification, (b)) 200200 magniﬁcation.magnification.

3.1.3. Composition Analysis of the Prepared Goethite

Water 2018, 10, 1376 6 of 13

Water 2018, 10, x FOR PEER REVIEW 6 of 13 3.1.3. Composition Analysis of the Prepared Goethite TheThe crystalcrystal formform ofof thethe preparedprepared goethitegoethite waswas analyzedanalyzed byby XRD,XRD, andand thethe XRDXRD spectrumspectrum waswas shownshown in Figure1 1b.b. ComparedCompared the diffraction peaks with with the the standard standard card card (JCPDS (JCPDS 29-0713) 29-0713) [24], [ 24 ],it itcould could be be seen seen that that the the prepared prepared goethite goethite had had good good crystallinity, crystallinity, and its compositioncomposition waswas indeedindeed mainlymainly goethite.goethite. TableTable2 2summarized summarized the the results results of the of porethe pore structure structure analysis analysis of the preparedof the prepared goethite. goethite. The speciﬁc The surfacespecific area surface of the area actual of the growth actual ringgrowth was ring much was larger much than larger the than prepared the prepared goethite. goethite. This might This be might that thebe that growth the growth ring contains ring contains pipe rust, pipe and rust, the and rust the structure rust structure is loose andis loose porous. and porous.

3.2.3.2. TCETCE DegradationDegradation byby Fenton-LikeFenton-Like ReactionReaction

3.2.1.3.2.1. TheThe ContrastContrast ofof RemovalRemoval EfficiencyEfficiency ofof TCETCE byby AdsorptionAdsorption andand DegradationDegradation AccordingAccording toto thethe previousprevious researchresearch reportsreports ofof ourour groupgroup [[25],25], goethitegoethite hashas an adsorption capacity toto pollutants.pollutants. TheThe removalremoval efficiencyefficiency ofof TCETCE byby adsorptionadsorption andand Fenton-likeFenton-like degradationdegradation waswas 15.6%15.6% andand 58.5%,58.5%, respectively.respectively. TheThe detaileddetailed conditionsconditions werewere shownshown inin FigureFigure3 3.. The The removal removal efficiency efficiency of of TCETCE byby Fenton-likeFenton-like waswas almostalmost fourfour timestimes asas muchmuch asas adsorption.adsorption. AfterAfter 100100 min,min, adsorptionadsorption reachedreached saturation,saturation, but but the the Fenton-like Fenton-like degradation degradation was was still still effective.effective. The removal efficiencyefficiency of TCE TCE by by Fenton-likeFenton-like waswas almostalmost sixsix timestimes asas muchmuch asas adsorption afterafter 480480 min.min. Therefore, Fenton-like reactionreaction waswas aa moremore effectiveeffective methodmethod toto removeremove TCE.TCE.

FigureFigure 3. 3. The The contrast contrastof of adsorption adsorption and and degradation. degradation. Reaction Reaction conditions: conditions:[H [H22OO22]]00 = = 11.5 11.5 g/L, g/L, [Goethite][Goethite] == 3.333.33 g/L,g/L, pH pH = = 4, 4, T T = = 293 293 K. K.

3.2.2.3.2.2. TCETCE DegradationDegradation byby Fenton-LikeFenton-Like ReactionReaction underunder DifferentDifferent ConditionsConditions 1.1. EffectEffect of ofthe the initial initial pH pH pHpH isis anan importantimportant influencinginfluencing factorfactor ofof thethe FentonFenton reaction.reaction. TheThe effecteffect ofof pHpH waswas investigatedinvestigated atat pHpH valuesvalues atat 3,3, 44 andand 55 (Figure(Figure4 4a).a). The The degradation degradation efficiencyefficiency decreaseddecreased withwith thethe pHpH increasing.increasing. This may be attributed to two reasons: Firstly, H O is not stable with the pH increasing. Secondly, the This may be attributed to two reasons: Firstly, 2H22O2 is not stable with the pH increasing. Secondly, • leachingthe leaching iron iron ions ions can graduallycan gradually form form iron hydroxideiron hydroxide sludge, sludge, which which reduces reduces the production the production of OH of radical.•OH radical. The optimum The optimum pH for pH degradation for degradation TCE was TCE 3.0, was which 3.0, was which in agreement was in agreement with the previous with the classicalprevious Fenton classical reaction Fenton studies reaction [26 studies,27]. [26,27]. 2. Effect of the H O concentration 2. Effect of the H2O2 concentration2 The effect of H O concentration on the degradation of TCE was shown in Figure4b. When the The effect of H22O22 concentration on the degradation of TCE was shown in Figure 4b. When the dosage of H O was in the range of 1.7–11.5 g/L, the removal efficiency of TCE increased gradually, dosage of H22O2 was in the range of 1.7–11.5 g/L, the removal efficiency of TCE increased gradually, and the TCE removal efficiency could attain 91.3%. It could be seen that the dosage of H2O2 has a significant effect on the removal of TCE in water. However, when the concentration of H2O2 was 16.7 g/L, the removal efficiency went down. This was because the H2O2 concentration was increased to a

Water 2018, 10, 1376 7 of 13

and the TCE removal efficiency could attain 91.3%. It could be seen that the dosage of H2O2 has a Watersignificant 2018, 10, x effectFOR PEER on theREVIEW removal of TCE in water. However, when the concentration of H2O2 was 7 of 13 16.7 g/L, the removal efficiency went down. This was because the H2O2 concentration was increased to certaina certain extent, extent, and and the thegenerated generated •OH•OH cannot cannot react react with with the the TCE TCE in time, whichwhich led led to to self-quenching self-quenching of of•OH.•OH. And And the the inhibition inhibition of of iron iron corrosion corrosion by H22O2,, which which hadhad thethe samesame effect effect [ 28[28,29].,29].

3. Effect3. Effect of the of catalyst the catalyst dosage dosage According to the previous study [25], the catalyst dosage was set at 1.67 g/L, 3.33 g/L and 6.67 According to the previous study [25], the catalyst dosage was set at 1.67 g/L, 3.33 g/L and g/L6.67 to study g/L to the study effect the of effect catalyst of catalyst dosage dosage on the onTCE the degradation, TCE degradation, Figure Figure 4c. As4c. the As catalyst the catalyst dosage increaseddosage increasedfrom 1.67 fromg/L to 1.67 3.33 g/L g/L, to the 3.33 TCE g/L, removal the TCE efficiency removal efficiencyincreased increasedfrom 28.75% from to 28.75% 95.9%,to but when95.9%, the but catalyst when the dosage catalyst exceeded dosage 6.67exceeded g/L, 6.67 the g/L,TCE the removal TCE removal efficiency efficiency was only was only42.2%. 42.2%. More goethiteMore goethitecould increase could increase the total the area total of area the ofsolid-liquid the solid-liquid contact contact surface, surface, increase increase the theenrichment enrichment rate 2 2 2 2 of rateTCE ofand TCE H andO , Haccelerate2O2, accelerate the decomposition the decomposition rate of rate H ofO H and2O2 generateand generate a large a large number number of •OH of radical,•OH radical,leading leading to a better to a better degradation degradation effect. effect. However, However, excessive excessive catalyst catalyst would consumeconsume• OH,•OH, whichwhich was was harmful harmful to to degrading degrading TCE TCE [30]. [30]. The The decrease decrease of degradationdegradation efficiencyefficiency of of TCE TCE may may be be attributedattributed to to the the agglomeration agglomeration ofof catalyst catalyst and and the the•OH •OH self-quenching self-quenching or quenching or quenching of •OH of by •OH excess by excessFe2+ Fe[282+, 31[28,31].].

FigureFigure 4. 4.EffectEffect ofof (a ()a )the the initial initial pH, pH, ( (bb)) the the H2O2 concentrationconcentration andand ((cc)) thethe catalyst catalyst dosage dosage on on TCE TCE degradation.degradation. Reaction Reaction conditions: conditions: (a) ([TCE]a) [TCE]0 =0 1.46= 1.46 g/L, g/L, [Goethite] [Goethite] = 3.33 = 3.33 g/L, g/L, [H2O [H2]02 O= 28] 0g/L,= 8 T g/L, = 293 K; T(b =) 293[TCE] K;(0 =b )1.46 [TCE] g/L,0 =[Goethite] 1.46 g/L, = [Goethite] 3.33 g/L, pH = 3.33 = 4, g/L, T = 293 pH K; = 4,(c)T [TCE] = 2930 K=;( 1.46c) [TCE]g/L, [H0 =2O 1.462]0 = g/L,8 g/L, pH[H = 24,O 2T] 0= =293 8 g/L, K. pH = 4, T = 293 K.

3.3. The Microorganism Identification Results of Filtered Water in a Water Plant Six strains of bacteria were isolated from the filtered water of a water plant, and one of them failed to be identified, while the 16S rDNA sequences of the other five strains were obtained. The phylogenetic tree of related bacteria and comparison result were shown in Figure 5 and Table 3. The obtained microorganisms could be divided into two major categories. One major is γ-proteobacteria including 1-2, 1-5, they were all Pseudomonas. The other category included 1-1, 1-3, and 1-4. 1-1 belongs to the Bacteroides. 1-3 and 1-4 belong to Proteobacteria. According to Figure 5 and Table 4,

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3.3. The Microorganism Identification Results of Filtered Water in a Water Plant Six strains of bacteria were isolated from the filtered water of a water plant, and one of them failed to be identified, while the 16S rDNA sequences of the other five strains were obtained. The phylogenetic tree of related bacteria and comparison result were shown in Figure5 and Table3. The obtained Watermicroorganisms 2018, 10, x FOR PEER could REVIEW be divided into two major categories. One major is γ-proteobacteria including 8 of 13 1-2, 1-5, they were all Pseudomonas. The other category included 1-1, 1-3, and 1-4. 1-1 belongs to the relativethe Bacteroides. abundance 1-3 andof Proteobacteria 1-4 belong to Proteobacteria. was 80% when According microorganisms to Figure5 wereand Table classified4, the relative by phylum. The relativeabundance abundance of Proteobacteria of Pseudomonas was 80% when was microorganisms 40%. were classified by phylum. The relative abundance of Pseudomonas was 40%.

99 1-2

100 Pseudomonas fluorescens(HQ874650) 1-5 92 100 Pseudomonas sp. F15(KF573430) 46 Flavobacterium cheonhonense(NR_125552) Agrobacterium tumefaciens(FJ639330) Sphingomonas sp. HX-H01(KF501484) 1-3

100 1-1 58 1-4

FigureFigure 5. 5. TheThe phylogenetic phylogenetic treetreeof of related related bacteria. bacteria. Table 3. Comparison of bacteria isolated from filtered water in a water plant and related microorganisms. Table 3. Comparison of bacteria isolated from filtered water in a water plant and related microorganisms.No. Sequence Length/bp Related Bacteria Name Related Strain Number Similarity/% 1-1 1403 Flavobacterium cheonhonense NR_125552 98 No. 1-2 Sequence Length/bp 1438 RelatedPseudomonas Bacteria ﬂuorescens Name RelatedHQ874650 Strain Number Similarity/% 98 1-1 1-3 1403 1452 FlavobacteriumSphingomonas cheonhonense sp. HX-H01 KF501484NR_125552 99 98 1-4 1418 Agrobacterium tumefaciens FJ639330 99 1-2 1-5 1438 1459 PseudomonasPseudomonas fluorescens sp. F15 KF573430HQ874650 99 98 1-3 1452 Sphingomonas sp. HX-H01 KF501484 99 1-4 1418 AgrobacteriumTable 4. Filtered tumefaciens water microorganisms. FJ639330 99 1-5 1459 Pseudomonas sp. F15 KF573430 99 No. Phylum Class Order Family Genus 1-2 Proteobacteria γ-proteobacteriaTable 4. FilteredPseudomonas water microorganisms.Pseudomonadaceae Pseudomonas 1-5 Proteobacteria γ-proteobacteria Pseudomonas Pseudomonadaceae Pseudomonas No. Phylum Class Order Family Genus 1-23.4. Inactivated Proteobacteria Pseudomonas γ-proteobacteria by Fenton-Like Reaction Pseudomonas Pseudomonadaceae Pseudomonas 1-5 Proteobacteria γ-proteobacteria Pseudomonas Pseudomonadaceae Pseudomonas The typical chlorine resistant bacteria, Pseudomonas, was separated from the water distribution network and studied Pseudomona’s inactivated effect by Fenton-like reaction. According to the 3.4. InactivatedFigure6, the Pseudomonas rapid sterilization by Fenton-Like stage occurred Reaction at 0–60 min and the relative number of Pseudomonas declinedThe typical from chlorine 1 to 0.867, resistant the inactivation bacteria, Pseudomonas, rate was 86.7%. was The separated inactivation from rate the slowed water down distribution at network60–180 and min studied because Pseudomona’s H2O2 was consumed. inactivated After effect 180 min, by Fenton-like the inactivation reaction. rate attained According 99.9%. to the FigureThis 6, resultthe rapid indicated sterilization that Fenton-like stage occurred reaction at has0–60 outstanding min and the effects relative on thenumber Pseudomonas of Pseudomonas that are inactivated. declined from 1 to 0.867, the inactivation rate was 86.7%. The inactivation rate slowed down at 60– 180 min1. becauseEffect of H the2O catalyst2 was consumed. dosage on Pseudomonas After 180 min, inactivated the inactivation rate attained 99.9%. This result indicated that Fenton-like reaction has outstanding effects on the Pseudomonas that are inactivated. The control variate method was used to study the effect of catalyst dosage on Pseudomonas that were inactivated. The catalyst dosage was 0.89, 4.45, 8.9 g/L (Figure7a) and the concentration of H 2O2 was 5 g/L. The inactivation rate of Pseudomonas increased with the increase of catalyst dosage, and the

Water 2018, 10, x FOR PEER REVIEW 8 of 13

the relative abundance of Proteobacteria was 80% when microorganisms were classified by phylum. The relative abundance of Pseudomonas was 40%.

99 1-2

100 Pseudomonas fluorescens(HQ874650) 1-5 92 100 Pseudomonas sp. F15(KF573430) 46 Flavobacterium cheonhonense(NR_125552) Agrobacterium tumefaciens(FJ639330) Sphingomonas sp. HX-H01(KF501484) 1-3

100 1-1 58 1-4

Figure 5. The phylogenetic tree of related bacteria.

Table 3. Comparison of bacteria isolated from filtered water in a water plant and related microorganisms.

No. Sequence Length/bp Related Bacteria Name Related Strain Number Similarity/% 1-1 1403 Flavobacterium cheonhonense NR_125552 98 1-2 1438 Pseudomonas fluorescens HQ874650 98 Water 20181-3, 10, 1376 1452 Sphingomonas sp. HX-H01 KF501484 99 9 of 13 1-4 1418 Agrobacterium tumefaciens FJ639330 99 1-5 1459 Pseudomonas sp. F15 KF573430 99 inactivation time shortened. The increased inactivation efﬁciency may be attributed to introducing more active sites, which allow forTable producing 4. Filtered more water•OH microorganisms. radical that promotes the inactivation reaction. No. Phylum Class Order Family Genus 2. Effect of H2O2 concentration on Pseudomonas inactivated 1-2 Proteobacteria γ-proteobacteria Pseudomonas Pseudomonadaceae Pseudomonas

1-5The effect Proteobacteria of H2O2 on the γ-proteobacteria inactivation rate of Pseudomonas Pseudomonas was Pseudomonadaceae shown in Figure7 b. PseudomonasThe inactivation rate of Pseudomonas in the Fenton-like system increased with the increase of H2O2 concentration. However,3.4. Inactivated when Pseudomonas the dosage by exceeded Fenton-Like a certain Reaction amount, the inactivated effect gone down. Because • H2O2Theconcentration typical chlorine was over-high, resistant bacteria, the generated Pseudomonas,OH radical was cannot separated react from with Pseudomonasthe water distribution in time which leads to a self-quenching of •OH. At the rapid sterilization stage (0–90 min), Pseudomonas networkWater 2018 , 10 and, x FOR studied PEER REVIEW Pseudomona’s inactivated effect by Fenton-like reaction. According 9 toof 13 the wereFigure rapidly 6, the killed,rapid sterilization and the total stage number occurred of bacteria at 0–60 decreasedmin and the rapidly. relative 90–180 number min of wasPseudomonas the slow sterilization stage, that because H O was consumed. At same time, when the H O was higher, declinedFigure 6. Inactivatedfrom 1 to 0.867,effect of the Fenton-like inactivation2 2 reaction rate onwas typical 86.7%. chlorine-resistant The inactivation bacteria. rate slowedReaction2 2 downconditions: at 60– the Pseudomonas inactivation rate was faster. The inactivation efﬁciency of Pseudomonas could reach 180[Goethite] min because = 0.89 g/L; H 2[HO2O was2]0 = consumed.0.50 g/L. After 180 min, the inactivation rate attained 99.9%. This result 99.9%indicated or more. that Fenton-like reaction has outstanding effects on the Pseudomonas that are inactivated. 1. Effect of the catalyst dosage on Pseudomonas inactivated The control variate method was used to study the effect of catalyst dosage on Pseudomonas that were inactivated. The catalyst dosage was 0.89, 4.45, 8.9 g/L (Figure 7a) and the concentration of H2O2 was 5 g/L. The inactivation rate of Pseudomonas increased with the increase of catalyst dosage, and the inactivation time shortened. The increased inactivation efficiency may be attributed to introducing more active sites, which allow for producing more •OH radical that promotes the inactivation reaction.

2. Effect of H2O2 concentration on Pseudomonas inactivated

The effect of H2O2 on the inactivation rate of Pseudomonas was shown in Figure 7b. The inactivation rate of Pseudomonas in the Fenton-like system increased with the increase of H2O2 concentration. However, when the dosage exceeded a certain amount, the inactivated effect gone down. Because H2O2 concentration was over-high, the generated •OH radical cannot react with Pseudomonas in time which leads to a self-quenching of •OH. At the rapid sterilization stage (0–90 min), Pseudomonas were rapidly killed, and the total number of bacteria decreased rapidly. 90–180 min was the slow sterilization stage, that because H2O2 was consumed. At same time, when the H2O2 Figure 6. Inactivated effect of Fenton-like reaction on typical chlorine-resistant bacteria. Reaction was higher, the Pseudomonas inactivation rate was faster. The inactivation efficiency of conditions: [Goethite] = 0.89 g/L; [H2O2]0 = 0.50 g/L. Pseudomonas could reach 99.9% or more.

FigureFigure 7.7. EffectEffect of (a) the catalyst dosage dosage and and ( (bb)) the the H H22OO2 2concentrationconcentration on on Pseudomonas Pseudomonas inactivated. inactivated. ReactionReaction conditions:conditions: (a)) [H[H2O22]]00 == 5 5g/L; g/L; (b ()b [Goethite]) [Goethite] = 0.89 = 0.89 g/L. g/L.

3.5.3.5. StudyStudy onon BacteriaBacteria InactivationInactivation in Filtered Water by Fenton-Like Method Method ActualActual waterwater qualityquality afterafter ﬁltrationfiltration was shown at Table 55..

Table 5. Actual water quality after filtration.

Temperature Turbidity NH4+ Cl− SO42− TOC Total Iron Total Alkalinity pH (K) (NTU) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (CaCO3, mg/L) 302 0.51 6.83 0.17 8.36 3.49 2.12 0.16 22.3

Disinfection experiments were carried out by adding goethite and H2O2 into the actual filtered water. The experimental results were shown in Figure 8. The total number of bacteria increased rapidly at the initial 20 min, and the relative bacteria total number increased from 1 to 2.67. Because the main catalytic species was Fe3+, while the catalytic efficiency of Fe3+ to H2O2 was low, this resulted in producing less •OH radical. The bacteria had adapted to the environment to enter the logarithmic growth period, so the total number of bacteria had increased at the beginning of the reaction. 20–60

Water 2018, 10, 1376 10 of 13

Table 5. Actual water quality after ﬁltration.

Temperature Turbidity NH4+ Cl− SO 2− TOC Total Iron Total Alkalinity pH 4 (K) (NTU) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (CaCO3, mg/L) 302 0.51 6.83 0.17 8.36 3.49 2.12 0.16 22.3

Disinfection experiments were carried out by adding goethite and H2O2 into the actual filtered water. The experimental results were shown in Figure8. The total number of bacteria increased rapidly at the initial 20 min, and the relative bacteria total number increased from 1 to 2.67. Because the 3+ 3+ Watermain 2018, catalytic10, x FOR speciesPEER REVIEW was Fe , while the catalytic efficiency of Fe to H2O2 was low, this resulted 10in of 13 producing less •OH radical. The bacteria had adapted to the environment to enter the logarithmic min growthwas the period, rapid so sterilization the total number stage, of bacteriathe total had number increased of at bacteria the beginning decreased of the reaction.rapidly, 20–60and minthe total numberwas theof bacteria rapid sterilization decreased stage, to 0 theat 60 total min. number This result of bacteria illustrated decreased that rapidly, the Fenton-like and the total reaction number has a goodof disinfection bacteria decreased effect toon 0 actual at 60 min. filtered This resultwater, illustrated and the bacteria that the Fenton-likeinactivation reaction rate was has aover good 99.9% [32].disinfection effect on actual filtered water, and the bacteria inactivation rate was over 99.9% [32].

FigureFigure 8. 8.Fenton-likeFenton-like system system for disinfectiondisinfection of of ﬁltered filtered water. water.

3.6. Fenton-Like and Chlorine Combined Disinfection Method 3.6. Fenton-Like and Chlorine Combined Disinfection Method Due to •OH being easily quenched, the Fenton-like disinfection method does not have the continuousDue to •OH disinfection being easily characteristic. quenched, A new the method Fenton-like is proposed, disinfection which puts method the Fenton-like does not reaction have the continuousand chlorine disinfection disinfection characteristic. together. According A new to method Figure9 , is The proposed, total number which of bacteria puts the increased Fenton-like reactionrapidly and at thechlorine beginning, disinfection because only together. Fe3+ was According presentin to the Figure solution 9, at The the total intial numberstage, and of ferric bacteria 3+ 3+ 2+ increasedoxide wasrapidly less at efﬁcient the beginning, in catalyzing because H2O2 .only The Fe transition was present of Fe ininto the Fe solutionwas the at controlthe intial step, stage, and resultingferric oxide in the was amount less ofefficient generated in catalyzing•OH radical H being2O2. smallerThe transition than the growthof Fe3+ rateintoof Fe bacteria.2+ was the It was control step,not resulting enough in to the kill amount the bacteria, of generated so the total •OH number radical of bacteria being smaller increased. than At the 20–45 growth min, rate the relative of bacteria. 2+ It wastotal not number enough of bacteriato kill the decreased bacteria, rapidly so the from total 1.15 number to 0.03. Fe of bacteriairons appeared increased. in the At solution 20–45 at min, the the • relativemoment, total which number could of catalyze bacteria H 2 decreasedO2 to decompose. rapidly A from large number1.15 to of 0.03.OH Fe were2+ irons generated, appeared so the in the bacteria were quickly killed. At 45 min, •OH was consumed in a large amount, the sterilization rate solution at the moment, which could catalyze H2O2 to decompose. A large number of •OH were of •OH was less than the rate of bacteria growth, and the total number of bacteria began to increase generated, so the bacteria were quickly killed. At 45 min, •OH was consumed in a large amount, the slowly. The total number of dead bacteria was very small through the Fenton-like system, so the total sterilizationnumber ofrate bacteria of •OH grew was slowly. less than At 60 the min, rate 0.5 of mg/L bacteria chlorine growth, was addedand the into total above number sterilization of bacteria beganreaction, to increase and total slowly. bacteria The rapidly total number decreased. of dead At this bacteria stage, chlorine was very participated small through in the disinfectionthe Fenton-like system,process. so the The total total number number ofof bacteriabacteria was grew 0 at slowly. 180 min, At the 60 bacteria min, 0.5 were mg/L completely chlorine killed, was andadded the into abovechlorine sterilization residual reaction, in water was and 0.41 total mg/L. bacteria These rapidly results demonstrateddecreased. At that this the stage, Fenton-like chlorine and participated chlorine in thecombined disinfection disinfection process. method The could total by number continuous of disinfection, bacteria was reduce 0 at the 180 disinfection min, the by-products. bacteria were completely killed, and the chlorine residual in water was 0.41 mg/L. These results demonstrated that the Fenton-like and chlorine combined disinfection method could by continuous disinfection, reduce the disinfection by-products.

Water 2018, 10, 1376 11 of 13 Water 2018, 10, x FOR PEER REVIEW 11 of 13

Figure 9. Fenton-likeFenton-like and chlorine combined disinfection experiment results.

3.7. The Disinfection Mechanism of Fenton-Like Reaction

H2OO22 cancan destroy destroy the the barrier barrier structure structure of of bacteria bacteria and and change the osmotic pressure and permeability ofof bacteria,bacteria, which which is is conducive conducive to to the the other other substances substances entering entering the bacteriathe bacteria [33]. The[33].• TheOH •OHcan oxidize can oxidize amino amino acids, proteins,acids, proteins, sugars, sugars, lipids, andlipids, nucleic and nucleic acids in acids bacterial in bacterial cells by additioncells by addition reaction, reaction,electron transfer,electron andtransfer, dehydrogenation and dehydrogenation to attain the to aimattain of killingthe aim the of bacteria. killing the Bacteria bacteria. inactivation Bacteria inactivationinvolved the involved following the several following processes several [34 processes]: [34]: First, when •OH•OH radical entered the bacteria, it could inhibit the synthesis of alanine aminotransferase. TheThe proteinprotein couldcould be be destroyed destroyed by by oxidizing oxidizing the the unsaturated unsaturated functional functional group group in the in theprotein, protein, and and•OH •OH could could also also directly directly act on act the on hydrogen the hydrogen atom atom on the on surface the surface of the of polypeptide the polypeptide chain chainto inactivate to inactivate the protein. the The protein.•OH radical The •OH could radical also cause could polymerization also cause polymerizationbetween macromolecular between macromolecularproteins to form anproteins acid, whichto form loses an aacid, metabolic which function,loses a metabolic resulting function, in bacterial resulting metabolic in bacterial disorder metabolicand achieving disorder the purpose and achieving of sterilization. the purpose Second, of• sterilization.OH could take Second, away the•OH hydrogen could take atoms away pentose the hydrogensugars and atoms basic pentose groups ofsugars the DNA and basic to form groups free of radicals, the DNA resulting to form in free the radicals, DNA pentose resulting and in basic the DNAgroups pentose becoming and unsaturated, basic groups destroying becoming the unsaturated, DNA backbone. destroying The genetic the DNA information backbone. was The destroyed, genetic informationeventually leading was destroyed, to bacterial eventually lysis and death.leading Third, to bacterial•OH could lysis alsoand oxidizedeath. Third, unsaturated •OH could fatty acids also oxidizein bacteria. unsaturated Because the fatty phospholipids acids in bacteria. of the cell Because membrane the compositionphospholipids contain of the unsaturated cell membrane acids, composition•OH could destroy contain the unsaturated structure of acids,the cell •OH membrane, could causingdestroy the the cell structure membrane of the to lose cell the membrane, selective causingpermeability, the cell the membrane osmotic pressure to lose the of theselective bacteria permeability, to become unbalanced,the osmotic andpressure the toxic of the and bacteria harmful to becomesubstances unbalanced, entering theand bacteria, the toxic thereby and harmful destroying substances the bacterial entering metabolism, the bacteria, ﬁnally thereby causing destroying lysing theand bacterial death. metabolism, finally causing lysing and death.

4. Conclusions 4. Conclusions The main compositions of the actual pipe growth ring were analyzed and prepared with one The main compositions of the actual pipe growth ring were analyzed and prepared with one main composition, goethite. Goethite Goethite was was used used as as catalyst catalyst or or bactericidal agent to degrade TCE or purify water distribution network by the Fenton-like reaction. Studies on the degradation efﬁciency purify water distribution network by the Fenton-like reaction. Studies on the degradation efficiency of goethite for TCE showed that goethitegoethite hashas aa goodgood abilityability toto removeremove pollutants.pollutants. pHpH == 3,3, 3.333.33 g/Lg/L goethite and 11.5 g/L H2O2 were the best degradation conditions. Moreover, goethite could activate goethite and 11.5 g/L H2O2 were the best degradation conditions. Moreover, goethite could activate H2O2 to generate •OH, which could kill bacteria. Nearly 100% of Pseudomonas could be inactivated H2O2 to generate •OH, which could kill bacteria. Nearly 100% of Pseudomonas could be inactivated at the conditions of 0.5 g/L H2O2 and 0.89 g/L goethite. Goethite was also used to disinfect the actual at the conditions of 0.5 g/L H2O2 and 0.89 g/L goethite. Goethite was also used to disinfect the actual filterﬁlter water from a water plant, which obtained outstanding effects. These results indicated that the pipe growth ring had great potential toto repairrepair waterwater pollutionpollution andand disinfectdisinfect drinkingdrinking waterwater inin situ.situ.

Water 2018, 10, 1376 12 of 13

Author Contributions: D.Z. designed the all experimental processes, F.H. completed degradation experiments, analyzed all data and wrote this paper. Z.W conducted sterilization experiments. W.M. and Y.Y. discussed the first review comments and the second review comments. All authors completed the final manuscript proofreading. Funding: This study was financially supported by National Natural Science Foundation of China (51578180); National Natural Science Foundation of China (51778177). Conflicts of Interest: The authors declare no conflict of interest.

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