Zeolites in a permeable reactive barrier (PRB): One year of field experience in a refinery groundwater—Part 1: The performances
Post on 04-Sep-2016
Embed Size (px)
Chemical Engineering Journal 178 (2011) 204 209
Contents lists available at SciVerse ScienceDirect
Chemical Engineering Journal
jo u r n al hom epage: www.elsev ier .c
Zeolite Onrener es
Rodolfo V AuDanila Ga Department o Novab Department oc eni S.p.A., Re Departd Studies & Res e E. M
a r t i c l
Article history:Received 3 August 2011Received in revised form 14 October 2011Accepted 18 October 2011
Keywords:ZeoliteZSM-5MordeniteWater treatmeAdsorption pr
es ofreactive barrier (PRB) located under a coastal renery. The average organic contamination was 5 mg/L oftotal petroleum hydrocarbons, whose toxic constituents are aromatic (BTEX) and polynuclear aromatichydrocarbons (PAHs), and 5 mg/L of MTBE, specic gasoline additive, while the average concentrationsof more representative inorganic ions were: Na+, 8537 mg/L; Cl, 10,700 mg/L. The target of the entireprocess was: hydrocarbons, 350 g/L; MTBE, 10 g/L; and BTEX, 1, 15, 50 and 10 g/L, respectively.Two working tests of six months each were performed. In the rst phase two zeolite lters, constituted by
A permepermeable versely to tremoving cnatural movare favourain which thand then senormally ucontinuousimpermeab(gate), whilacross the want of the f
ZSM-5 (120 kg) and mordenite (150 kg), were used to treat water with a ow (Q) kept xed at 4 m3/d. Inthe second phase next each lter a new one of same material has been added to have a total of four lters,two of ZSM-5 (120 kg each) followed by two of mordenite (150 kg each), while the ow was doubled. Inboth tests the concentration of the organic contaminants in the outlet water remained constantly underthe limits. Between the two phases, the test was interrupted for six months for removing by backwashingthe inorganic and biological deposits formed on the lters. The performances of zeolites were evaluated onthe basis of the composition of both water sampled at the outlet of zeolite lters (by gas-chromatographicanalysis, GCMS) and contaminants adsorbed in the zeolite channels (by thermogravimetric analysis, TGAand GCMS).
2011 Elsevier B.V. All rights reserved.
able reactive barrier (PRB) consists essentially of adiaphragm of a reactive material, placed in situ trans-he ow of a polluted plume, capable of degrading orontaminants, transported by groundwater during itsement. This technology replaces, where the conditionsble, the conventional pump and treat technology,e plume is extracted from groundwater by pumpingnt to a dedicated water treatment. The congurationstilized in PRB technology are funnel and gate and
barrier. In the rst case the water is conveyed by anle diaphragm (funnel) to the permeable reactive zonee in the second one the reactive material is distributedidth of the contaminated groundwater plume. A vari-
unnel and gate consists of the drain and gate, where
ding author. Tel.: +39 0321447310; fax: +39 0321447506.ress: firstname.lastname@example.org (R. Bagatin).
a drain captures the portion of groundwater containing the plume,including the conveyance, and facilitates the test area, thus allow-ing a reduction of the extent of the barrier itself.
The key component in PRB technology is constituted by the reac-tive material, which should be selected on the basis of the natureof the contaminants to be removed and on the hydro-geologicalconditions of the site. Zero-valent iron (ZVI) is the most commonmaterial used in PRBs, followed by granulated activated carbon(GAC). Other examples of reactive materials include microorgan-isms, natural zeolites, peat, phosphates, limestone and amorphousferric oxide .
Depending on the nature of the material, the elimination of thecontaminants occurs by different processes such as degradation,adsorption or precipitation. In any case, the effectiveness of thematerials depends on their physicalchemical properties as well ason the nature of the compounds to be removed.
Particularly important is the problem related to the decon-tamination of groundwater from hydrocarbons, chlorinatedhydrocarbons and oxygenates (e.g. MethylTertButylEther, MTBE).For such kind of compounds the most widely used reactive
see front matter 2011 Elsevier B.V. All rights reserved.cej.2011.10.050s in a permeable reactive barrier (PRB):y groundwaterPart 1: The performanc
ignolaa, Roberto Bagatina,, Alessandra De Folly Dhisletti c, Roberto Millini c, Raffaello Sistod
f Environmental Technologies, eni S.p.A., Istituto eni Donegani, Via G. Fauser 4, I-28100f Chemistry, La Sapienza Universit di Roma, Piazzale A. Moro 5, I-00185 Roma, Italyning & Marketing Division, San Donato Milanese Research Center, Physical Chemistry earches Department, Renewable Energy & Environment Technologies, eni S.p.A. Piazzal
e i n f o a b s t r a c t
This paper describes the performancom/ locate /ce j
e year of eld experience in a
risb, Cristina Flegoc, Massimo Nalli c,
ment, Via F. Maritano 26, I-20097 S. Donato Milanese, Italyattei 1, I-00144 Roma, Italy
zeolites utilized for one year as adsorbents in a permeable
R. Vignola et al. / Chemical Engineering Journal 178 (2011) 204 209 205
materials seem to be ineffective. For instance, ZVI, used in PRBtechnology since the years 1990s, directly degrades several con-taminants, but appears to be ineffective on irreducible compoundssuch as 1,2-dichloroethane (1,2-DCA), chlorobenzenes as well ashydrocarboaged by ecoof contaminmetal ions.the physicainteractionspresent in gorganics tive in treatas oxygenatas vinyl chl
Removaticularly rechemical, pscarcely efflevels requwhether trefor its olfac
Surfactahighly effewastewater(with negattection) [6,7
This papPRB in drations of theow of watebeing remocrossed a ga drain anbelow the gwater ew by the passing the desreduced to the possiblity needed an existingment) was an adsorbendifferent clathe adsorptsecond zeofour lters treat a rangadvantagestaminant sewith salt aneffective capounds preHowever, story works,duration artiveness of selectively comparableSpecic zeoDCA and Valiphatic, has BTEX an
Table 1Main characteristics of zeolites utilized.
Characteristics ZSM-5 Mordenite
decoe barningformers cnite utedent
of remmpostratatedratioifferece ats, a als wf conthe mof th
litesterisoth cir hidersnite.lite sB fro
. 1 an, resptem s ou
ion, r doe. Sipte neth obes neet,honer wmenon is controlled by a vacuum chamber equipped with ahat provides both the emptying regular of the formed gase initial priming of the siphon. The piezometric fall to thedownstream is obtained by implementing a well for the col-
of the output in which the discharge is obtained through ans [2,3]. On the other hand, the use of GAC was encour-nomics and by the possibility of removing a wide rangeants, such as chlorinated solvents, hydrocarbons and
However, GAC presents several disadvantages due tolchemical characteristics of its surface: pore plugging,
with humic substances and inorganic ions, alwaysroundwater, adverse effect of pH on the adsorption of. Additionally, GAC has been shown to be slightly effec-ment of water containing very soluble compounds, suched organics, or low molecular weight compounds, suchoride (VC) .l of MTBE is challenging because this compound is par-calcitrant and different processing systems based onhysicalchemical and biological features proved to beective, particularly when considering the restrictiveired for this contaminant, such as 350 g/L in water,ated as a hydrocarbon, or still worse, the 2040 g/L
tory threshold.nt modied zeolites (SMZs) have been described asctive for the treatment of hydrocarbon-containing, although evidencing progressive surfactant releaseive impact both on economics and environmental pro-].
ging results have been reported also for siliceousic) zeolites .er illustrates the design of the industrial demo-scalein and gate conguration, according to the prescrip-
environmental plan of safety of the industrial site. Ther drained from an existing trench, or part of it, instead ofved by pump and treat processes outside the ground,ate formed by specic reactive zeolites, thus creatingd gate PRB conguration. The system was placed justround level, but higher than the groundwater table, sodue to a siphon structure whose operation is ensuredive hydraulic upstream downstream gradient. Dur-ign phase the sources of pressure losses have beena minimum and devices have been used to minimizee formation of gas that could put at risk the continu-for passive hydraulic operation. As drain of the PRB
trench was employed, while the gate (reactive ele-performed using two pairs of lters, each containingt material selected according to its specicity towardssses of contaminants present: a rst zeolite suited forion of aliphatic and light aromatic components and alite useful towards larger hydrocarbons and MTBE. Thecan be operated in series or in parallel and are sized toe of 4 to 8 m3/day (depending on conguration). The
of zeolite application concern with the organic con-lectivity, the rapid kinetics, the lack of interferencesd humic substances (also at tens g/L) and, mainly, thepacity in the removal of almost all the organic com-sent in groundwater of petrochemical and petrol sites.uch prerogatives were demonstrated only in labora-
where the experimental conditions and especially thee limited and under constant control [2,8,9]. The effec-the zeolites is ensured by their regular channels able toadsorb organic molecules with dimension and polarity
with those of the contaminants to be removed .lites were identied for efcient removal of MTBE, 1,2-C. Particularly, ZSM-5 zeolite turned out suitable foralogen-aliphatic and mono-aromatic molecules, suchd halogenbenzene derivatives, while mordenite was
found rings, as MTBfor thereactivfunctiobut in
Filtmordeconstitabatemterms tions idemonter, locthe duwith dformanthe tesmaterience overify nence
In bfor theent binmorde
Figsin planthe sysdrain. Aoperatsiphonsystemthe gater, wiand dolene shThe sipin watphenodrain tand thwater lectionmol/mol] 2100 230< 0.01 < 0.05
] Clay (20) Alumina (20)iameter length) [mm] 1.5 3 1.5 3
appropriate for molecules with two or more aromatictually halogen- and alkyl-substituted, and ethers suchrthermore, these microporous adsorbents are proposedntamination of groundwater with the use of permeableriers. To assure the high permeability necessary for the
of the PRB, zeolites were not used in form of powder, of extrudates.ontaining the two hydrophobic zeolites, ZSM-5 andwith high SiO2/Al2O3 molar ratio, placed in succession,
an innovative adsorption system suitable for the in situof contaminants in groundwater. Its effectiveness (inoval of the contaminants below the target concentra-
sed by the Italian legislation or local authorities) wased during the whole period of treatment of groundwa-
close to a coastal renery. The eld treatment, withn of one year, was divided into two operational phasesnt water ow: the rst one to verify the material per-nd the second one to verify the system limits. Afterdetailed physico-chemical characterization of the usedas carried out in order to determine the effective pres-taminant molecules within the zeolite pores and toodications, if any, induced by the prolonged perma-
e zeolites in groundwater .
were supplied by Tosoh Corp. as extruded cylinders; thetics are reported in Table 1.ases zeolites with high silica content, properly selectedgh hydrophobicity, were used. Note the use of differ-
for the two zeolites: clay for ZSM-5 and alumina for In both cases, the binder is set at 20 wt%.amples to be characterized have been collected afterm top and bottom of each lter.
f drain and gate
d 2 show the schematic representations (in section andectively) of the experimental drain and gate PRB withof reactors (gate) fed by groundwater received from thetlined in Fig. 1, the ow of water is ensured by the siphonather than falling piezometrically. The presence of thes not change the passive behaviour of the hydraulichon operation allows building the room that housesar the surface, rather than submerged in groundwa-vious advantages for both construction and operationot affect the integrity of the high density polyethy-
which ensures the tightness of the drainage trench. arrangement results in the liberation of gases dissolvedithin the reactors, which are placed in depression. This
206 R. Vignola et al. / Chemical Engineering Journal 178 (2011) 204 209
Fig. 1. Schematic of the experimental PRB, operating sip
suction pipe and the hydraulic level remains lower than that of thetrench, thanof the renethat of the come the pand drives designed toneously, to downstreammonths of o
Two opeto better eused. The pQ = 4 m3/da
Contamicentrationsof 5 mg/L foThe proximcentration, Cl: 10,700NO3: 10 mcarbons, 35respectively
Phase A:lter (M) in
Fig. 2. Represgate.
Phase B:ere assion
m3/datile is accter sater aZ an
connputeing aC, wi
amowas stabi0 C lysisraphP-685 mmlent-ks to a pump which raises water to treatment systemry. The difference between water level of the well and
trench, as low as few centimeters, is sufcient to over-ressure loss due to several meters of reactive material,the water ow through the siphon. This solution was
maintain the passive properties of PRB and, simulta-meet the prescription to prevent the dispersion in the
aquifer. The reactive system has been sized for sixperation at ow rate of 8.4 m3/day.
rational phases, six months long each, were conductedvaluate the effective performance of the materialshases were characterized by different water ow (Q);y in the rst one and Q = 8.4 m3/day in the second phase.nation during the six months of treatment, the con-
of inlet organic contaminants were almost constantlyr total petroleum hydrocarbons and 5 mg/L for MTBE.ity of the sea was well evidenced by a constant con-always very high, of inorganic ions: Na+: 8537 mg/L;
mg/L; Ca2+: 630 mg/L; SO42: 26 mg/L; Mg 2+: 36 mg/L;g/L; Fe3+: 2.6 mg/L. Output target levels: total hydro-0 g/L; MTBE, 10 g/L; BTEX, 1, 15, 50 and 10 g/L,.on system the dimensions of treatment lters werer the two phases.
120 kg ZSM-5 lter (Z) followed by 150 kg mordenite a Z + M succession.
(M) wa succebottom
EstiQ = 8.4
Waof Z llters
Air stage: from 3
Anamatoga GC HID = 0.2tor Agientation of a spatial arrangement of the elements of the drain and
for 1 min, h5 min. The vfor 30 min apparatus. were lled detector wo