CA2067380A1 - Causing liquid/solid interaction - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

In order to remove e.g. nitrate from water with a short contact time, the water is mixed with small particles of ion-exchange resin in a tank (1), to form a suspension of a concentration of 1.25 to 5% w/w. m e particle mesh size is e.g. from 5µm to 0.5 mm. The suspension is passed from the tank (1) and in the pipework, the nitrate content of the water is significantly reduced. The ion-exchange resin is returned to the tank (1) and can be recirculated on average about four times. A bleed of the suspension is taken from the tank (1), is regenerated, and is recycled to the tank (1).

Description

06 f~PR '92 15:37 MRRKS & CLERKS LONDON P.10 j 2067380 PC~/GB 9 0 1 0 11 5 1 4 ~8 10 i~l 1 2~ OcSober 1 CAUSI NG LI QUI D ~ SOL~ D I N~ERACT~ ON

aak~round of the rn~entl~o-n T~e invontlo~ relat~s generally to causing a liguid ~o interact with a solld Nor~ally, mas~ t~anRfQr will occur between the liquid and the ~olld, but thl4 i~ not n-ce~sarily 80. The mas~ transfer can b~ to or fro~ the liguia Th~ inventlon may be appliod for instance to leachiAg, ion~exchsng~, cryst~llisatlon, drylng, Qpecific solution, ~o~ption, ro~sting, 601id-partlcle-catalysed liqyid-phase reactlons, and li~uld-solld reaetions, and the appllcatlon of th-s- ¦
proce~ses to che~lcal rcactions ln general Durlng contac~, ion or othor xchan~e ~ay take pl4ce, or one or !
mo~e compouna~ ~ay be adsorbod, ~b~or~e~ or che~iisorbod, or relea~6,d; th- co~pouAds will u~ually b- in the, form of lon~ or ~olQcule~, but th~y could be colloid31 or other agglome~at~ons, or mixtures or in ,~o~e oth~r ~or~ Any nu~b-r o~ c~o~ical speaies may b~ involved, d-p-nd~ ng o~ th- r-qulro~Qnt$ of th- particular proce~8 I~ tho ~nventioA i~ applled to ion exchang-, lt can b~ u~-d ~or the contact ~tep and/or for the r--g--DOr--tL OD 0~ ~1 utl o n C tUp.

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. PCT ~ `dl ~;I,pilc~,t;on 06 RPR '92 15:38 MRRKS & CLERKS LONDON P.11 20B7380 P~i~ g O l ~ 1 ' 2 ~ OCt~b~t 1091 Speclflcally, the lnvention ha~ b-en dev-loped ln the course of ion exchange procedures for removlng nl~ra~e ~rom wat~r, but can ~e partlcularly useful in r-ducing the hardness of water, selectively removing or rega~nlng !
materials such as pollutants or metals from waeer, a~d ad~orbing colour The nor~al procedure i3 to bring the liquid into contact i with tho solid, separate the llquia from the solia, regenerate the solid, and bring further li~uld in~o contaet with the solid The solld, eg th-so~bing/reloasing substrate, would usually be insolubl-, i eg r~in, clay, mineral or ~las~
,' 1.
To date, tho standard procedure for operating a 801id~aqueous liquid system was to support the solid ~n i a colu~n and to operate a batch procedure, pa~sing the proce~- liguid, clo~ing off the process liguid, passing r-g-n-rating olution, and then pa--ing the proc~s~
llquid Thl~ procedure wa~ relatively complicatod I -Furth-r~or-, t~- soild particl- sizes could not be low-rl th~n round 0 4 to 0 5 m~, otherwi~e ~he sur~ace tenslon¦
o~ water prevented sufficien~ly rapid draining undor gravlty, and g~n~r~l pr~ctic~ was to use E~articlu 91Z~

of 0 ~ mm upward~ Th- ~olid wa~ usualiy ~ ~h- ~orm of¦
.
baad- (on~ tan~rd bead size was 1 1 mm), which may " , ,, , . . . _ ~1 SUBSTI~UT St~FE T

'136 flPR '92 15:56 MRRKS ~ CLERKS LONDON P. 1 ~ "09"04~9~ ' 2n~738~ 1 PCT~GB90~0151 ;~a~e had a coatln~ o~ tho reac~ ve mater~al, but no~mally were completely made of che reaCtlve mAt~rlal.
~he na~ural swel:ing and contractLon of t~e sol~d causes cracklng and spa.l~n~, and the small part:cles so formed can c!og ~he bed of solid , ' , As an ~lternatlve eO thls procedure, contlnuous grav:t~
~cttling ~rocedures have been propos~d. In th~s cas~e, t~.e solid must be of such a slze that the rate of ~esce~t (or different~dl rate in :an up-flowin~ u~d) Q reason~bly rap~d. The g~neral view is that the be~d diamcter~ must be at leagt 0.5 mm, for sufficiently rapld ~cttling. ~hesc procedures are eomplicated b~c~use b~ads may ~tlck in valv-s or the valving us~d may crush the ~ds, leading to unwanted clogg~ng and in uffici~ntly rapid sedimentation. A spoci'lc proposal has ~-~n made in GB-A-I 070 Z51, provlding a co~nter current proce~ where the ~olid~ are ln effect in J ~ o ~ r- is no discussion of tbe ~iz-- of e~
8 ~ ~-ttcles but, ln prietice, it is found that a ~5~ r o ~e l-ast O.S mm is rcguired for successul oper~tion. As another instance, in EP-A-0 010 969 ~ouling and xc~s~iv~ b~ck pz-ssure c~n occur.

~hc ~ep~rat~on o' ~in- solid par~icles can be dificult, i~ bcing ~mpr~ct~cal to u~e f~lter columns. Thus it ha~

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06 ~PR '92 15: 38 M~RKS & CLERKS LONDON P lZ
206738~ PC~/G~ 9 ~ / ~1 51 4 2 ~ 10 ~1 ~P, ~ctober'!10~l' beon ~uggested that the part~cle~ can be coagul~t~d or' aggiomerated~ for instance when u~ing magnetlc par,~cl-~

It is de~irable to provide a contlnuousl,y operatlng~yste~n ~,rhere tlle concentr~tiorls re~ain fai~ly constant aAd where the a~ount of solid required is k-pt a~ low as poss$ble.

The I nvention . ' The in~ntion provides a method of cau~ing a llqu~d ~0 interact with a ~olid, comprlslng forming a suspen~ion of p~rticle~ of the solid in the liquid and ~oving the' olid pa~ticl-J and th- liquld ln tho sam~ direction whilo th- liquld lnteracts wi~h ~he solid p~rtlcl~s, romoving liquid fro~ ~he suspensiion, recycling solid partlcles f,~o~ the suspen3ion aftcr liquid has been re~oved, a~d regenerating solid particles, some of ehe ~oiid particles being recycled without regeneration .

Tho $~-ntlon, p~rticularly ~h-n u~lng a combi~atlon o ~ho aoCu~rent ~o~-~ont of the li~uid and dlscrete p~rtlcl~s o~ tho solld and crosg~low 11~ra~10n (or a .
rolatod barr$er f~ltration method~, can take advaneage of th- nhano-d k$n-tics of g microre8ins without drawbaoXs of ~xcessLve pre~sure drop a~d dang-r of _ . ....... . . I
~Uni: d '~in~.~!,.n P~ n~ Off'ca I PCT in!e-n~lorlal A~ ication _ SUBSTITUTE SHEET

~;V~. & CLERKS LONDON 2 0 6 7 3 8 ~
V~0 91~1W791 PC'r~G890/~

'oullnc or elogg:n~ '~hlC~. LS Q~per:enced ~ coi~n arrange~e~es, or ;ne at:r t' on ard _elated ~echan:ca bloc~sng and losses commoniy assoc~a~ed w~ cont;nuo~s Sy~ltem5.

The ~ethod of th~ ~nv-ntson is s~mple and e~ic~en~
Plant s~zes can be reduc~d and qu~pment costs lowered ~he ~thod can be conCin~oUs or nearLy continuous I

Sbe inven~1co c~n b- v--o tor con~ac:~n} se-}~ nd ~o: I
~ reg~neration st~ge, or used only ~n a r-generat~on s~age or only ;n a con~actsng s~age Normal val~in~ can be incorporatod if de~ir~d becau--spl~tt:~g or COmmLnut~On of tho part~cles is no Longer o~ grea~ ~ign~f~cance a~ th- op~ratsng particle Si2~ can , ~e very s~ll Thus t~e snvention l;ows u-~ of 'in~
m~t-rial, wh~ther it ss origi~ally ~l~e or, bre~ks down t ~ ~t s~a~ a~ a r-~ult o~ att,ri~ion ~n ~he prqc~ss ¦

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~' ~h~ particl~s can hav~ ~ny form whlch :s su_tablo, g 'l~ros or platel~ts or the more cra~eson-l ~ph-r~s an~
sph-roids For sphorscal or ~pherosdal particls~ sh- !
s1ze~ can be conssdered as sLeve pass sszeS (g~e~ng :he ' .

06 fPR '9Z 15:39 M~RKS & CLERKS LONDON ~ 2~6738~ P.13 1 PCT/GB 9 0 / a 1 5 1 4 28 lQI 91 6 ~ 8 O¢to~)el 1901 s~o~inal diamete~), and in ge~-ral the siz~ h-rein ar- ¦
si-ve or ~e~h pass siz-s .'.,. I
Constraints on the maximum size of the pa~ticle- aro related to the economic and operatlng condltlonJ o f lndl~dual proce~es by a number of alfferent paramete~s, such as ~olume, surface aro~, mlni~u~ or maximu~ presented a~ea, ~axi~um ~re en~ed ar~ ni~u~
dim-n~ion and maximum dlmen~lon Though a st~ndard slze of about 1 m~ ~or peoiflcally 1 1 mm) can b- u~ed, partlcularly in larg- plants, the partlcl-s ~r- i p~ef-rably sm~ll compared to those used in standard procedures, 80 that the effectlve specific surfac~
14rge~ and the exchange/sorption/solution/reactlon klnetics ~re more rapid R latlve reduction ln sizc can lncrea~e th- app~r-nt nu~ber of sites available ~or ~ction but, mor import~ntly, can enhanc~ the react~on klnQtics ~here is better r~ndom con~act, partlcularly ~t low ¢onc-ntr~t~on~ The partlcle size can b-o~tial~ed to ~uit th- p~rtlcular proc-Js requ~r-m-ntJ, but ~olids ¢an b- w ed a~ ~upplied, e ~ with no preliminary slevlng ~o re~ove fines In g-n-ral, ehe partlcle slze ls pr-ferably ~aller than that selected for u--, for ~n~t~nce, in packe~ col~mns or fl~t-r b-d~ The p~rtlcl- ~iz- ~s preferably le~8 than a~out 0 5, 0 4 or 0 3 am, or le~s than 0 25 or 0 2 mm.

~ ol~l P~o~ Oiflce SU~STITUTE S~EET l l ?cr~ u~ofial Appli~a~ion 06 PPR ~15:58 ~I~RKS & CLERKS LONDON
.- 206738~
~91J1~791 PCTrGB90/OlSI~ I ¦

Generall~, althouqr. ~e par:;c:es n~ed mot be ~o-med ~y a Comm~nut~on rechr.~cue, the part;c' e slze can be ~..at a powdered sollc. Qulte o~een, ~he upper . limlt on par.,:cle 5~ ze lS that ~mpo~ed :~y seac~ on kinet:~s and aiso pumpsnc and the energy needed ~o mainta~n 1 ~rg~ ¦
par~zcle ~n suspens~o~. ~here ls not usuaily.a~y advan~age :~ us:r.g larqe par~:cles, out there is no reason why they should not be used. ~onethele~s, an ad~sntage of thc lnv-ntion is that one can u~e p~r:iclo~ ¦
o~ a slze sm~ han nor~al.

There is no theoretlcal low-r limit to ehe p~rt cl~ 51Z-t~at can be u~-d, though in prict~c~l terms particles o~
;ess ~an about 0. ~ or O. ~ microns ~111 not ~e us-d. .
Th- ~ze of 0.1 m~crons s de~crm~ned ~y ~h~ cut off 5~ze O~ a microfilter, b~t thss size could ~e r-duced fus'th~r ~ n ul~rafilter were used. A m~.nimum ~rac~ c~l s~Z- of 0.~ or 0.~ mlcrons ~s mor- rc~l~se:c.
H~ ~araclc~ of le~s th~n 50 mscro~ t~nd to torm a ~n~vaeer ~nd be difficult to dew~t~r.
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~o g~ve a Sp-c f:c example, for the ion-exch~ngQ r~sln used in th~ Exam~le~ below there is no real ~dv~n~ag-e~n ln haa~ng part~cle sizes le~s ~h~n lOO micron.

Par~cl~ s~i- range~ m~y ~e 50 ~o 120 microns or 100 to ' 200 ~lc~on~, or ~or acr~vated carbon lO0 to 600 ~icrons.~

- 06 PPR'9Z 15:58 M~RKS & CLERKS LONDON 2 o 6 7 3 8 ~ P.6 PCT/G890to~ r Rat~o of Solid to L;~ULd .he concentratlon or w/w rat:o o solid to l;qu d can ~e ¦
chose~ as approprlate ~or :nstance, some adsor~en~
solids have rela~eiy low capacl;; and nee~ to be us~
in high co~centratlon Some suspensLons ox slu-r~es can remain fluid at up to 60~ soli~s whilst othors are sol~d at 2~; the concentratson must be such as to perms~
suspension and pump~n~ Within the need for the susp-ns~on to re~ain pumpable, the propertles, and act~al sol,ids conten~, of the ~uspens~on will vary deoending on the application For instance, the proport~on of solids may be as low as 0 2% or even lower, or the propor~lon may be over 20% or ovor 30%.
~n a plant, there can bn different concentrat~ons ;n different parts, fo: instance in the treatmen~ s;age and!
in the regene~ation stage ~n gener~l, the concentr~tion of the solid ~n the liquid can b~
relatively low dur~ng the cocurrent movem-nt and ceton, e g ~elow about 10~ ~/w, preferably fro~ !
S~ down to about 1~ ¦
;~ ~' , i Contact 5t~e Any form of turbule~t or other suspension can b- us-d wh~ ch ehe solid par~ cles and the lLquid are m~xed 06 PPR '92 15:59 MRRKS & CLERKS LONDOI`I ~06738~ P 7 ,, ~'OY1/~79t PCT~GB9~/0151~ ¦
!

:nt~matel~ ~nd randoml~J - ~or Lns~ance, ~ho ~nt~a~
.~lX` n~ ,an be ach~eved eg by ~avlng a tanX ~zh a ', y opeLler ~n it or provldlng a 'l~ldlsed bed Th- ¦
suspens~on n~ed not ~'e a sta~le suspension, le the solid particles may slnk or rlse ~ there is no flow or no a~tation, 'he tec~niqu~ ~e~ng ~ type of flu~dzsa~Lon'¦
tech m gue In general terms, :he partlcl-s will be d~screte; ie not aggr~gated ~he sol~d and `~qu~,d'~ay be put zo~ether prLor co int-oduction to a chamber where the ~ntim-te and rando~ ' mix:ng occurs However, ln one procedure, after for~na ¦
ehc ~uspenslon, th~ suspension lS p~ssed along a long supply lin~ with subseantial re~idence ti~e to the 'llt~r in wh~ch the ~ep~rati,on LS effected; the sup~y line can bo 3~y 1 to 2 5 m lonq In qoner-l, contact _lm-s ar~ prcfcra~ly gr~ater,than aoout l or 2 mlnuee~
~n~ l-ra than bout 20 m~nuees, say ~bout 4 or 5 ~nut~! Tho tim is chos-~ ~s approp~at- to th~
aiz-~, th- d-gre- of agitation, ~nd the o~ kin-ti cs. . . I .
~

Seoara~ion Sta~c . . . ! .
ThQ ~cpar~t~on or llquz~ r~oval se~ge can ~ car-led ou~ ~n any s~:abl- ~ay I: lS not necesSary t~a~ eh~ ' s-para~:on stag- should occu: ~n' a cAamb~r diff-rcn_ I

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92 15 59 MRRK5 8~ CLERKS LONDON PCr~G89~/o~ r from that ~n which the conea~ se~ge s carrled ou;
However, ~he m~xture lS pre'erably passed to a filte , wh~cl- can be anv suleabie fi!ter ~u. ~s preferably a crossfLow filter, whlch may be usèd ln a dead-end ~ode The advantage of using a dead-end mode is that a ~uch -h~g~er flux can sometlmes ~e'obtaine~,' possibly twen~y ~imes as ~rea~ ' Th~ filter can for instance be as descri~ed in 5B-A-2'185 906 or US 4 765 906 ~he sepa~ation s~age can lnvolve thQ s~ep~ of buiid~ ng up a membrane,'bullding up a cake of .~e contac~ n~ ~a~erLal, possib1y -egenerat~ng the contactlng m~ter~al and washing ~t while on the filter, breaking up the cake, e~
with rollers as describe~ ~ GB-A-2 i85 906 or ~5-A-4 765 906, opening up the closed end if Lt is a de~d--nd ', fil;er and flushinq out; alternatlvely, if ehere lS a ~ag fil~e~, turn~ng the ilter ~nsid~ out wlth an i~erted me~4e~ such ag a p~ston A flexible filter :s pre~err-d, neve~thele~s, the f~lter n~ed noe b~ xsbLe ch-ot filter could be used, and the cake nely scraped off the filter In some cases, :he atag~ can occur on or in t~e filter itself, ~' a~prop~iate to the par~cylar p~ocess; ;n suc~ a case, the filter c~n be pre-coated, and then coated with thc solld whiCh is th-n l~mobilised on the filtcr in so~-way; req n-rat~on can t~en take place on the fileer 'I .
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06 ~R '9Z 15:44 ll~RKS ~ CLERKS LONDON 2 ~ 6 7 3 8 ~ PC~ g ~ 1 4 1 9 1~ 91 11 19 Dec~- 1991 ~he u8e of a fllter reduces attr$tlon of ths contact m~terial, and al~o reduces th- ~f-ct of such attr~ t~ on ln that llquld cAn be s-moved even with sub micron p~rtlcles pr-sent The uee of a crossflow filte~ ¦
~nable~ a constant conce~tratlon o th- solid in the liquid to be m~intained, at least for long p-r~od~ ¦
b-tween ~iltor cleaning o~ratlon-Yreferably, ~uf~lclent llqu$~ ls lQ~t after the ~eparation for the olid partlcl~- to remain in the for~
of a su-p-n~ion, ~-y a~ a slurry, whloh ~a~ tat-~recycl$ng '''' .

At the end of the ~eparation phase, the liquid may pASS
'nto a furth-r cont~ct stAge with the same batch of ia (but regenerat-d) or a diferent batch o~ solid R~en-~atLon st~e .
,ho olid ~ay b- regen rAsed b-for~ r-cyoling, and t~'s ~ay bo ~on at th- s-paratton slte, o~ elsewhQr-Typic~l reg-n ration will be done by im~er~ion in a sultabl- fluid, g i~ rsion of ion oxehing- r-sin in br~n-, but any suieabl- proce-s can bo us-d, ~uch as caustic or acld washing, leaching, ~a~ elution, he-t~ng,¦

xposur- to light or ot~er electromagnottc r~dla~on, pA~ge of 06 ~PR '92 16: 00 ~I~RKS & CLERKS LONDON 2 O 6 7 3 8 ~ P. 10 ~0 91/04791 PC r/GB90JO 15 .1 .

el~ct~ic current or physLcal shock Further ~a~hlrg o~
f'ushing ~ay be requlred after regeneratlon, to returr the solid to a su~table ~onditio~ for re-use or d~sposa For rege~e~ation, a procedure can be used whlc~ ls ~nvent;ve per se The procedure ~5 a ~e~hod of concacti~g a li~u~d ~ith a solid, co~prising formlng a ¦
suspen ion of tho solid ln a liquid, passing tbe suspension to a filte~ so that the 11ter holds the sol~d back, and ~hen passing a liquid through th- f leo~
~n the opposiée dlreccion to remove the solld rom the ¦
filter and for~ a suspensioA ~he filter is preferably¦
_n th- for~ of a bag filtor so that it has a large retention capacity The method o operation keeps the filter clean, without requiring any special clean~nq step as such For regeneration, the solid can ~e suspended in a ~eak regeneratLng aqent, and then removed¦
fro~ the f$1te~ wlth a StrOAg regenerating ~-nt; for th~ Jolid can be suspended in ~ f$rst washlng ~n~tAen r-~oved ~ro~ the filter with a socond ~ ~iquia Normally, both procedure~ will be adopt-d consecutively, in different fi7ters Reg-n-~ation is p~eferably carried out ~y feed~ng the solid particl-s ~ro~ the mean~ for remo~ng liquid from the suspenslon back to a cha~ber ~n which said 06 ~qPR '92 15:~9 M~RKS & CLERKS LONDON 28 1~ s ~, 13 .
suspe w lon ~s m~intaine~, and drawlng su~pen~lon ~so~
saia cha~b~r for ~egeneration; ln otho~ words, t~- ~oll~'¦
par~icles ar- r~cycled withou~ regenerat~on, a s~par~t-regeneration loop ~eing maintained An alternatlve is to provide a bleed-off for removing a proportlon of the ¦
so}id p~ticl~ ~s they ar~ recycled to the ~u8p-n-10~ , c~amber ¦ ' !
eturn Sta~e ~he last stage 1~ the r-tur~ stago, when the regenerat-d¦
or unregenerated solid may be returned to the ~tart ~ !
the proc-du~o o~ reintroduction at a controlle~ or measu~e~ r to, if the solid doe~ not remain ln ~$tu throughout rn a continuo~s proc~dure, there may be a slo~ bl--d-off !
of the ~olid partlcles for dischargs or regeneration, 1, which $s replac-d by a slow feed o~ solid parelcle~
wSllst the ~a~or portion of the solid particle~
r--clrculate~ The Jolid particl-~ ca~ be r~cycl-d on avor~g- at l-a~t about twice before r~generatiOn or disch~rge, g a~out three or ~our times La~ge recirculatlon ~mp~ove~ the ut~l~sation of th- so~id by u~lng lts full capacity, enabl~s hlgher'conc-nt~ations of ~olid to b~ u~ed, ~nd makes the quality of th-p~oduct more conslstent I

ad ~ oJ,~m Pete:~t Offlce SUBStlT~JtE SHEE~ I
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06 PPR ~9Z 1~:01 MRRKS & CLERKS LONDON 21D67380P-lZ ¦
wO 91/0.~191 PCT/GB90/0151~ ~
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SD C fic Uses oS the ~ r.ven~Lon ~he liquid is not necessarily water, but Lt Wlll be SO
:- many cases ~he ~nven~lon can be parti~ularly usefu~ ¦
wnen remov~g unwante~ materlals Crom water whsch are ~n i low concentration, for in~tance reducing concentra~ons of nitrate, ~oron, strontiu~ or caesiu~ An advaneage of the invention is that low prescur- diff-rentials can ¦
~e use~ for the ~ilter ng, say less than about 350, 2S0 or 200 kPa and down to abou~ 150, 100 or 50 kPa, allowln~ large volumes to be ereated; say more than a4Ou~ 10 or 20 m3/hour; ;h~s can be par:scularly useful in the water industry Oth-r uses envisaged include ¦

using or rogenerating powdered activated ca~bon employed for purifying liqusds, e g eo remove pesticides or other trace or~anic poll~tants such as tsihalomethanes, n u~ing powdered activat-d carbon to re~ove e~u~s~ons such a- paint from WatQr, or to removo organics suc~
as oil and butan- gas from a water/oLl/g~s e~uls~on - nor~ally the car~on would noe be regen-r~ted !

06 ~PR '9Z 16:02 M~RKS 8~ CLERKS LONDOI~ ~0673~ P.13 ~1) 91/lW791 PCT/GB9h/nl!~
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us~n~ or regenerat~a ~agne;~e or oeher -eaenerable, c_ :lon-rege~erable, coagu' a~ der.:s;
~, . ' i using ~iolog~cally and o~her na~urally derlved abQosbents in treat:ng process flui~s suc~ as ra~ioacti~e wastes (here speclal f~lters such 8s woven carbon or qlass fi~re, or sta~nless steel or phosphor bronze, may De used);

con~rnuous lon e~change, :~ general - nor~ai:y ~he ~on exchPnged uould be r-generated .' ' ~ ' ' '~
Tbc ~nvention w~ll be further de~cribed, by way of ~xample, with r~ferenc~ eo the acco~p~ny nq drau~nqs, ;~ ¦
~h~ch - i I t~ ~ re schematic diagrams oS thr-~ di~f-r-ne¦
r c~r~ying out the meehod of th- ~nvent~on;

Figures 5a and 5b is a diagram of a pilo~ plant; and Figure 6 i5 a vlew, par~ly n vert~cal sec~:on, of a sock 'i~t~r ~n the ~lan~ Oc Fiqures 5a and Sb.
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0~i92 16:02 M~RKS & CLERKS LONDON ~ P. l4 ;
. W0 91/0~791 2 0 6 7 3 8 PC~ `.BW)tl~ r .

~hroughoue~ the ~ame refo -nce~ are us~d ~or compon-n~s ¦
c~rrying out s1mllar funceions .. .. , . l Fi~ure ;
.,,, ''', ,' ,,' .
~he contactin~ solid and the process 1:quld are ~xed :
~ tank ' ~nd ~re o~mpe~ out throu~h a ;arge d~meeer, long fLexible hose 2 wound around a dr~m, g~ving sub~t~ntial cont~ct time, the hose 2 acting a~ a contac~
.. cha~ber. The length of the hose ~ may be 1. 7S ~, g~v~n~
an ~pproxi~ee re~idence time of one m-nute at a flow rate of ~O l/m Adequate ~ixinq ~s requ~ed so th~t sufficient ~ontact occurs, and if desired, a stirr-r cao be included in the mix~ng tank l, though the pu~p~ng ac- ion will norm~lly giv~ good contact ~n the hose 2;
~oth i~ th- stirred mlxing eank I and in th~ hose 2 -h~
solid and the liqu~d are mo~ng ~n cocurrene The subst~ntiaL residence t~me ~n the hose 2 ena~les the t~nk 1 tO bo smaller and/or tho ~esidenc- e~o ~n :hc r~l eo bo horter. Th- ~ixture then pas~-- to a ~ro~flow f~ltrat~on un~t 3 fro~ which the cle~n procel~ !
flu~a i~ uieh~rawn ae ~ I

At l--st two m thods of r-gener~eion ~re po-s~ bl~. :ni a first method, th- reg-neran~ (regenerating agent~ ~ f~d fro~ a fito~ago eank (no~ shown) onto the sol~d on ~h- l .

06 f~PR '92 15: 44 MFIRKS ~ CLERKS LONDON 2 0 ~ 7 3 8 U PC~/~B 9 ~ I d 1 ~ 1 1 9 li I 9 17 19 Deco~u ~ 1991 filter ~o that the ~olid is regeneratea on th- filter Ater regenoration, the ~olid i~ re~ov-d fro~ th-filter, to pas6 along a recycle line S back to th-mixing tank 1 In a second method, the solid is re~ov-d fro~ th- filter and pa~ed to a conta¢t t8n~, the olid then being regenerated, filtered, washea and rot~rned to the mixlng tank 1 Th- ~ethod used dop-nds upon the a-- of regeneration, though ~asically the ~lr~t method ¦
i8 faster ana easier than the ~econd .' .
An ~lternativ~ proce~ure can b- used, particularly ~h-n it i~ eh-aper to discharg~ the 60lid for lat-r regenera~ion (wblch may be the cas- with e g powdor-d activa~ed carbon) Wlthout rog-neration on the fllt-r j, the solia i~ recircula~e~ along the lin~ S a- a concentrat-d slurry or suspen~lon In this way, the solid ¢an ~e re-clrculated for in6tance a m an 20 t~ m-J
~efo~e ~elng r-g-n-rat-d or discharged Th~
rec~rcu~atlon can occur during the normal c~os~flow ~lltratlon, or a cycl- of re~o~ing th- solid Pro~ th-filt-r can b- incorporated so that the ~olia so removod is l~m-diately r-clrculated Standard componants ar- shown in a conventlon~l ~anner, ~ncluding lev-l gaug-s, one-way valve~, stop valv-~ an~
proc~ur- gaugo~ ~h~re i~ a flow ~eter 6 and an ._ . ~

01i P~PR '92 15:45 M~:lRKS ~ CLERKS LONDON 2 0 6 7 3 8 O P.25, PCT/G~ 9 0 1 O 11 5 1 4 ! 9 ~2 ¦ ~1 19 ~ ~ ;~z 1 elsctronic oon~rol 7 for a main ~ump 8 The filt-r 3 can be a~ di~olosed in US 4 765 gO6 Fiqure 2 A dead-ended crossflow filtration ~nit ~1 i9 u~ed, 1-. a ., cro~flow filt~ation unit w~th a closed out~et valve A
contact cha~ber 18 not shown, but may be included if aeqired Howovor, sufffcien~ contact ~ay occur in t~e tank l and ln the plpework A recycle line 12 18 shown, up~tream of the filter 6 The regeneration can be a~ !
above , The plant of ~igure 3 i5 simllar to that of ~i~ure 1 ~ ¦
ve~sQl 13 ls shown for the collect~on of treated water withdrawn at 4, and a resin feed tank 14 ~ shown for Qedin~ the ~ixing tank 1 There i5 a line lS for r--d~ng unt~eatQd water However, a further c~o~Jflow f~ter 16 i~ ~hown in a second recycle line 17 which al~o includ-- eguip~ent 18 for regene~atlng the resin and wa~hlng lt The filter 16, which aan be used ln tho ¦
croi-flow or d-ad-end ~ode, removes urther f~ult from tho ~e~in be~ore Lt is passed to the e~u~p~-nt 18 ThQ
bul~c of the rcst n can ~e recyolea th2~ough the lin- S, 1 .

06 ~PR '92 15:40 M~RKS & CLERKS LONDON i P. 15 2067380 PC~/GB 9 0 l ~ li 5 1 4 28 lq 91 2 a Octo~er~
~u~ficlent being recycled through the line 17 to koep a suita~le ~gencratlon level Fiaure 4 ~he con~acting ~tage of the plant of Figure 4 is ~ lar ~o that de-crib~d in relation to the alter~ativ-proc-dure of F~gur~ 1 A prooe~s liquid i8 fed at 21 and a re~in suspenslon or slurry is fed ~t 22 into A
~eed tank 1 ~he su~penQiOn iA the feed tan~ 1 18 drawn of~ at 2~ by ~ans of a fee~ ~ump 8 and pas-e~ through a~
cro~sflow filt-r 3 In the filter 3, the liquid i~
removed and a suspension or slurry of the solid with reduced liquid content i~ returned at 5 to the feed tank !
1 whilst thc re~ove~ liquid exits ~t 4 .. . !
Tho r gen-ration procedure is count-rcurren~ I
re~ener~tion in a number o~ cocurrent steps Th-r- is a~
bl--d 24 whlch i~ pump-d by a variable-~trokc di~placem-nt pump 25 into a thickening dovico 26 of any ~uitabl- type, illustrated a~ a ro~ary vacuum filt!r ~h- pu~p 2~ controls the ~olid concentration ana hence the solid d-teAtLon ti~e in ths ~ystem The filtr~t~ i9 1 withdrawn at 27 and i~ returned to ~he feed tan~ 1 ~he thickenod solid p~sses into a t~nk 28 cont~inin~ w-ak -og-n-rant, wh-r- i~ form~ a quspens~on in the . . . ~ SIJBSTITU~E SHE~T
i ~ al APS~i~cat~on , I

-- .--06 f~PR '9Z 16:04 ~1~RKS ~ CLERKS LONDON 206738~ P.18 ~'o 91~n.1191 p~/~ tl~l~ r ' ' I 1 regenerant. The suspeAslor. ~s pump~ b~; a 2u~p -5 through a reverslble 50C~ f:~ ter '0 and the f~ a~e :3 returned to the t~nk 28 the solld be1ng held ~ac:~ :n the fi~ter '0. After a suf~icient number of cy~l~s, ¦
valves 31 32 are closed and val~es 33 ~4 are opened.
There s a fu~ther tank 35 contAlnlng strong regenerant which is then pumped by a pump 36 ln the reverse !
direction ~hrough the filter 30 backwashing the fllter 30 and picking up ~h~ solid reta~ned ~n he filee~ ' and formlng it lnto a ~uspenslon whLch 1S carr~ed .o d he~d tank 37 (if requl-ed). The su~pension of sol~d ln ¦
srrong regene~ane is drawn off the head tank 37 at 38 ~nd passed to a ~econd thickening device 39 o~ any ~ui~able ~ype ill~st~ated as a rotary vacuum filter.
T~e filtrate fro~ the device 39 ~s drawn off ~y a pump 40 ar.d is returned to the strong regenerant tank 'S.
optionally by way o' the head tank ~1. j For rtnsin~ the thickened res~n from ehe ~h~cken~nq ¦ j dov~co 39 is passed to a rinse tank ~2 to wh~c~ rln~n l~qu~.is a~d-d; here it is mi~ed w~th a rlnsing 1~quld to for~ a Suspens~on ~nd t~e su~pen~ion is pumped by al pump 43 t~rough a sacond sock filter 44 and r~turned to¦
the rin~ t~nk 42. Aft~ a su~ta~le nu~ber of cyc`es. j ~alves 45 46 are closed and valves 4~ 48 are opened.
~here Ls a res~n so~ul~on ~ank 49 to which mak--up - 0Ei I~IPR '9Z 1~:05 M~IRKS & CLERKS LONDON 2 o 6 7 3 8 ~ P. 19 I
~ ~ ,~0 ~I/n~ PC~r/~

: ~
Lqu~d ;s a~lded, and :~ILS ;_qu~.d :s pumoed by ~ pus~;: c,~, ~ e reverse d:--c' ~ on rhroug~ ;he sock ~'l.er ~
c~r-. a~a~ the sol:d heid back ln ;he sock ~ er ~ ' and ~orm a suspenslon ~n the ~ank 49 Fro~ the tank ~, a ~OSltlve d~splacemen~ pump Sl pumps the regenerae~d i 30i~d :n suspenslon ~ack ;o the ~eed tank : Surplus ¦ -:nse llqu~d lS _e~oved '-om the eank 42 and spen;
¦ regenerant ~s removed f:om the tank 28.

~;.e S~er.~ soiu:~ o . :s ru~ o'~ cont:n~ousl{ and :n a s~al' stream, and _oncentratlons around ehe system ~re ~u~scant ally constant. Thus ehere lS no re~ulrement ~or large ~alanclng tanks and blending.

Piaures Sa and 9~ ¦

~:,u~es ~a and -b shou'd be ,o_ned alon~ ~:nes:
-espect:vo r:sht and le~t marglns.

T~ ~ilo~ plan~ of r:gu~e- 5a and 5b L5 based _n ~he plant of Figure ~.

~n e~e cont~ct stage ~FLgure Sa), a numbor of 'il:ers ' ¦
ar~ ~ed, divided ~n~o ;~re- banks sach se~Lced bv -s owr. ~ump 3 - ~ho banks of f~leers 7 can be operaeed ~. 06 ~PR '9~16:05 MQRKS ~ CLERKS LONDON 2067380 P.Z0 1 '0 91/U.~791 " 1'C'I /(~B9/~ r 1 . 1 lndependently or ~o~e~he~ to ach eve the deslr~d capac ty. The ~ er ~ are eursaLn ~od~ as ~ sc os~
~ gares '; 2 ~ aa and `8b o' us ~ 65 9G~ 5~c- ¦
w ~h a bacK-pressure 4aii valve 60 ~he f~ltes~ c-a: i into a ~ray 61 whlc~ ln turn hos flap v~lved ou~7e~s so .hat t can dra1n a; ~ ;nto a treated ~a~er tank 52 o-.. ' ! .
can dr~r at 63 :nto ;he feed tank 1 ~ F the qual~ s unacceptable These ls a cleanlng devlce for cleam ng the filters 3 generally as described in US 4 ~65 906;
there is an arrangement for drawlng treae-d waeer from the treated water tank 62 and pu~pinq it with a pu~p 64 through a hose r--l 65 to mov-able spray nozzles 66 ~or cleaning the fi~ters 3 ehe spray nozzles 66 belng car-~ed by ~ e-ansportin~ dev~ce 67 The fe-d ~nX ~5 equ ~ped wlth a ~et mlx pump 68 to ensure that ehe so ;~ i and liquld form a good suspension There ~s a helicai ~-ter 69 n ~he .eed l:ne il ~ho treated wate~ ra~k 62 co~ains a V-notch ~e~r 70 form~ng a sep~rit- ¦
co~jart~ent 71 from wh~ch treate~ water LS pumped ~y a puq~ 72 (contsolled by a level swltch 73) eo a serv~c- ¦
u~t-~ t~nk 74 of s~y 2 m3 capac~ty In th- regenera~on stage (Figure 5b) each thickener 26 39 is assoc~ated ~lth a _~p-ceive suc~ion au~ ary un~t 7S 76 T~e f 'trae- Crom the ~hickener 26 can ~e pass~d alorg a l~ne '1a and pumped ~y a pump 77 :o ~~e , PR '9Z 16. 06 ~1~RKS & CLERKS LONDON 2 0 6 7 3 8 ~ P. 21 .l I/(~79! P(~/~;B9~
. . . a~ I
~eed ~arX !, ~ ?~ss ~ o~g a ; ne '~ and ~- ?'~P~ !
bv a pum~ 78 tO the _e~ed ~-a~er tan~ 62, accord~ng :-~uall~y The fi`~-~ee ~:om ~he th~ckener 39 c~n ~-passed a_onc a l:ne 40a and retu-ned ;o the s~rong -e~enera-~ cark '~ ~y a pu~p ~9, or ~an be passe~ alona a l:ne 40b and pumped by a pump 80 to the feed ~ank 1 o-vla a l;ae 81 to àny of the ~anks 2a, 35, 42 or 49 A
regenerant ~aturator 82 ~5 shown for feeding regeneran~
to :he strong re~enerant tank 3S There ~5 ~n o~erflow feed 83 ~ro~ the stronq r~generane tank '5 to t~e ue~k :eaenerars ~ank 28 ~he weak ~eaenerant ~ank 28 ~s pro~ ed Ul_~ a s~ e_ 84 ~~e:e ~s an o~er~`ow i:ne 85 f so~ the weak regene:ant ~ank 28 to a wasee tank 86 wh~c~ overflows ln~o a bas~n ~7 pu~ped to w~ste by a pu~p ~8 In th~ r~nsing stage, the rlnse tank 42 has a~ overflow !:ne a9 ~e-ding to ehe uaste eank 86, and the eank 49 ~as a safety overflow 90 leadinq ~o ehe wast- ~ank a6.
} Th~ t~nk 49 h~s ~ st~~rer I for form~ng ~ suspens~on o~
; th~ solid 1.
~ervlce uater l:n- 92 as prov~ded for stars up - !

~n any o~ ~he Fiqures, tuO or more ~xing t~nks 1 c-n ~-used :- parallel rn F:g~res ' to 4, two or more ~ srs or 'i or j -~n ~- used ~n parailel :~

, ' '' ' I .

06 ~PR '9Z 15: 41~ M~i~KS ~ CLERKS LOI`IDON 2 0 6 7 3 g J P. 16 P~16B ~ ~ / 01 $14 28 1~ 19~
2 4 2 8 ctobe4 1 ~ead-end mode 1~ employed for the flltratlo~ unlts, thl~
enable~ A sem~-continuous proceduro to be oy-rat-d ~Y
sw~tchlng from flltsr 3, 11 or 16 to ~he other F~aur- 6 F~gure 6 lllu~trates the sock filter 30 or 44 ~e filter 30, 44 compsis-Y two cylindrlcal casing~ 101 bolted together at flange~ 102 The flanges 102 sandwieh between them suitab,le gaskets, flang-J 103 on two stainles8 4teel conical cages 104 whlc~ are wlthin the ca~ings, and the flange of a fllter cloth 10~ ~he filter cloth 105 iS stltched to for~ a cone of the samo slze aS the conical cages 104 wlth a flang~ on the open ¦
Qnd of the con- Tho çag~s 104 prevent the fllt-r cloth¦
lOS o~er-extending and bursting, ie 'they su~end and re-train th- ~ilter cloth 105 ~he f~ltor cloth lOS can¦
be for~sd of poIyester and can ~e of a s~ngl- ply of t~-~ame s~e¢i~cation as de~cribsd with reference to F~gure~ 17 to 18a of US 4 765 906.

~ .

On a laboratory ~cale, the plant o Figu~o 1 was u~-d to r-duce nit~to concentsatlon in wa~or from 93 to 1QSJ

than 13 mg-N0 .

U"~ ~.;o^.: O~f~ce c~ l ~ e TITI ITC C LI C C
P~ r~ A~ tion ~~ ccT

06 RPR '92 15: 45 Mf~RKS & CLERKS LONDON 2 0 ~ 7 3 8 ~) P. 26 PC~/G~ 9 0 /1 1151 . 25 1 ~ Dec~r: 0~3r 1091 U~ing "Duolite M~croi.onex AOH" lon-exchange re81n (a8 upplled by Roh~ & ~aa~) a~ a powde~ havlng partlcl-s 1~ ¦
th- range of 5 to 90 ~m, the contact tl~o was one minute. Although a specific ion-exchange re~in ls mentloned, a~y suitable powdered anionlc re-ln may be used. Th~ concontration was.prererably gr~ter than 0.05%, 0.1% being effectlve and about 0.2% bo~ng proferred - the~e seems to be no great advantage in haYi~g concentratlons greater than 0.2~ at thls ~asticular i~it$al nitrate concentrat~on.

The ~llter 3 waQ a~ de~cribed with re~erence to Plgures 5 to 10 and 17 to 18b o~ US ~ 765 906. US 4 165 906 explains how the held-bacX solid can be r-moved fro~ the I
fllter 3. The ~ressure differential was lS0 kPa acros- i the fllter 3, a #uitable range belng 100 to 200 kPa.
.1 Ex~ e 2 on ~ l-bor~tosy ~cale, th- plant of Figure 3 wa~ u~-d ~r ~e~ucing nitrate concentratlon ln water fro~ 100 to ~ NO3/1. Th- resln as ln Example l was ted i~ a~
a lur~y ln wster at O.1% w/w concen~sation, and wa~
~ilt-re~ by the f~lter 3 in cros~flow.~ode wlth.past of the sl~rry r~cyeling via tho line S to ~he ~xing tan~
1. A bleed ~tsen~ wa~ ~-pasat-d by valvo~ to ~low lnto --- 0~ RPR '92 16:07 11~RKS & CLERKS LONDOIY 2067380 P.24 ~0 91/~ 91 " rC~ vl~

the f1lter ;6 whic~ waS oper~ced :- de~d-cnd mode. ~b.Q
p-od~c: wa~er thuS obca:ned was com~lncd wlth ~4a~ '-o~
~ne r- ~ ter 3 and col ' ec~ed ~. n ;.'1~ tank 13. Once suf~ clenc ~esln had been col;ected :n the fi_.er 'i, a alve was opened aliow~ng ~rlne solut~on (regen~ran~ J :O I
wash the resln into the ~onk l8 ~or regenerat:on. ~.e ~rine solution waS fol'owed by a small amount oC p:oduce water to clean the filter 15 befo~e ~t was re-~ntroCuce~ ¦
~nto service as a dead-end ~ileer.
i Other details were as 1 n ~xample l. I

' .
Ex~ol~ 3 On a p~lot plant scaLe, :he plar.e o~ ure 5 wa~ used for reducing nitrate concentrat~or. .n ground water 'r~m ¦
~bou~ 60 to l9 mg-~O3~.. The t~.~oughpur was 11.9 m3,hour. She ground water contalned no detec~ble ~oli~J. Nin- filter~ 3 were used. each 8 ~ long.

.

; A ~Pusollt-~ AS20E ~on-oxchanqe res~n was used, ~s a owder having p3rticles ~n a range of 50 eo ~00 ~
~h! re~ln ~-r dosed by the pump 51 ~nto ~he ~eed tank : j ~c such a r~te t~at ;he ~esln waS O. 2% w/w o~ ~.e .aw water, thoug~ ~he dynamlcs of the sysce~ caused the osLn conc-ntra~on :n :;~e ~eed eank 1 to be '.
... ' I' .,. - i 06 RPR '9Z 15:46 MRRKS & CLERKS LONDON 2 0 6 7 3 8 a PCT/G8 9PliZ7! ~ 1 5 1 27 19 ~ec~ ~ J~ 1~91 slgn~flcantly higher, namely about 1 25~ At ~teady state, the tot~l load o re~in in the ~y-t-m wa~ a~out 11 kg The bloed pump 25 was pumplng at ~bout 1000 l~h, ¦
a~ountlng to 16% o~ the f~ed The pressure in the filte~ 3 was about 175 kPa, or possibly up to 200 kPa (higher pre~ure~ than thls could be used lf the raw wator contalned ~olld m~tter whlch ~oul~d tho filters 3) T~e flltor~ 3 removed a~out 96~ o~ the water Y~om the ~ucpenslon flowlng lnto t~e f~lter~ 3 T~- rosln on average recycled about four ti~es ~o the feed tank before belng r~generated I

The thickener~ 26, 39 wero op~rated to discharge the 801id6 at 50% w~w concentration The f~lter 30 wa~
rever~e flow backwa8hed on each regeneration cycle aft-r , three minut-~ 10% w/w ~odiu~ chloride solution wa- i u$ed a~ tne strong regeneran~ and 5% w/w sodiu~ chloride !
~olut~or a~ tbo we~k rogen-rant 1, The desir-d nitrate concentra~ion was obtain~d ~n t'~e tr-at-d wat-r, and chlorides were below 200 mg/l wator !
!
recovory wa~ about 84~ ' I

The ave,rag- r-tentlon t~me in the ~ced tank 1, p~p-work ¦
and f~lter~ 3 wa~ about 4 or 5 minutes , ' ' I .

~06 RPR '9Z 16:08 MRRKS 8. CLERK5 LONDOl`i 2 0 6 7 3 8 ~ P.26 ' '' PC~/~,8~ 1CI~
~)91~0 ~a Th- ~ilters 3 were as dLsclosed ln Fig~res 11, 1^, li, '8a and 18b of US ~ 7~5 ~06. However, as ~he~e were no solfds ~resent Ln ~he raw waeer, r.o cle~nlng cycl~ waS
_e~ ed. Some of the res~-. set~led on ;he weave o' ~be ~ e~ support to form a membrane, bu~ ~h~ remainder o' -h- re-ln did not ~u~ld ~p a s~gnifican~ layer.
',' ' . Il ~ 1 1 Example 3 was _~peaeed ~t~ a dif 'erent _aw wa~er.

ate conc~ntra~:on was reduced f~om 4~.3 ~o 16.5-18 mg-~03/1.
' i Exam~le 5 Ex~mple 5 is as ~xample 3, w~th t~e follow~n~ para~e~ers¦ .
d,~f ferent: ¦
' Resin dose: 0.8~ w~w of t~e raw water, ; Concen~ration ~n the 'eed tank: 5~ w/w;
'rotal load of resLn: ~4 kg;
Water secov-ry: 96~
.' 1,, !

~e p~esenS in~en~on has been descr~ed a~o~- purel-; by way ~ exa~ple, and modl-~ca~ons can be ~ad- w~ch~n ;~.e 5p~ 0~ th~ ven ion.

Claims (20)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of causing a liquid to interact with a solid, comprising:
forming a suspension of particles of the solid in the liquid and moving the solid particles and the liquid in the same direction while the liquid interacts with the solid particles;
removing liquid from the suspension;
recycling solid particles from the suspension after liquid has been removed; and regenerating solid particles;
some of the solid particles being recycled without regeneration.

2. The method of Claim 1, wherein liquid is removed from the suspension by crossflow filtration.

3. The method of Claim 1 or 2, wherein solid particles are continuously recycled.

4. The method of any of the preceding Claims, wherein after removing liquid from the suspension, sufficient liquid is left for the solid particles from the suspension to remain suspended, the solid particles being then recycled.

5. The method of the preceding Claims, wherein a proportion of the solid particles is continuously removed either for discharge or for regeneration and recycling.

6. The method of any of the preceding Claims, further comprising continuously regenerating solid particles.

7. The method of Claim 6, wherein a proportion of the solid particles are regenerated after liquid has been removed from the suspension.

8. The method of Claim 6, wherein solid particles are regenerated by continuously passing them around a regeneration loop.

9. The method of Claim 8, wherein the regeneration loop is separate from the loop for recycling solid particles after liquid has been removed.

10. The method of Claim 8 or 9, wherein there is a chamber in which suspension is maintained, suspension being drawn from said chamber for regeneration.

11. The method of Claim 6, 7, 8, 9, 10, wherein a suspension is formed of the solid in a weak regenerating agent, the suspension is passed to a filter so that the filter holds the solid back, and a stronger regenerating agent is passed through the filter in the opposite direction to remove the solid from the filter and form a suspension of the solid in the stronger regenerating agent.

12. The method of Claim 6, 7, 8, 9 or 10, wherein the solid is regenerated by treatment with a regenerating agent, and is then washed by forming a suspension of the solid in a first wash liquid, passing the suspension to a filter so that the filter holds the solid back, and passing a second wash liquid through the filter in the opposite direction to remove the solid from the filter and form a suspension of the solid in the second wash liquid.

13. The method of any of preceding Claims, wherein the particle size is about 1 mm or less.

14. The method of any of the preceding Claims, wherein the liquid is water and said solid is in the water in low concentration.

15. The method of Claim 14, wherein the water comprises nitrate ions which are removed by the solid particles.

16. The method of any of the preceding Claims, wherein the solid is ion exchange resin.

17. The method of any of the preceding Claims, wherein, as the solid particles and liquid are moved and interact, the concentration of the solid in the liquid is not greater than about 10%.

18. The method of any of the preceding Claims, wherein the solid particles are recycled on average at least about twice before regeneration or discharge.

19. Plant for causing a liquid to interact with a solid comprising:
a chamber comprising means for maintaining therein a suspension of solid particles in a liquid, whereby the solid and the liquid can act on one another;
means for feeding the solid and the liquid to the chamber;
means for removing liquid from the suspension;
means for regenerating solid particles; and means for recycling some the solid particles from the liquid removing means to said chamber without regeneration.

20. The plant of Claim 19, wherein the means for removing liquid from the suspension is a crossflow filter.