CA1130020A

CA1130020A - Method and a device for biologically purifying liquids

Info

Publication number: CA1130020A
Application number: CA333,067A
Authority: CA
Inventors: Jacob Pielkenrood
Original assignee: Pielkenrood Vinitex BV
Current assignee: Pielkenrood Vinitex BV
Priority date: 1978-08-02
Filing date: 1979-08-02
Publication date: 1982-08-17
Also published as: GB2034296B; BR7904942A; GB2034296A; AU4938479A; SG53583G; FR2432486A1; ES483011A1; DE2930489A1; MY8500020A; AU536288B2; NL7904891A

Abstract

A B S T R A C T O F T H E D I S C L O S U R E

A method and a device for biologically purifying a liquid by means of a mainly aerobic process in which the liquid to be treated is contacted in a treatment space with micro-organisms and at least during a part of this contacting period oxygen is supplied and thereafter the mass of micro-organismes and reaction products is allowed to settle from the liquid. According to the invention the whole treatment takes place in the same treatment space to which the liquid to be treated is supplied batch-wise, and the treated liquid is removed from this space at the end of the treatment, and so much of the settled active mass is kept in said space as is required for treating a next batch. Several of such treatment spaces can be connected in parallel, and also a parallel connection with a continuously operating device is possible for taking up peak loads of the latter.

Description

~3~20 ~.

- ~ The i~flnt~on relato~ to a method and a de~ice for bio-log~call~ purffying aqueous liquide.
Purifying ~asto Yator ~y o-an~ of ~icro-orga~is~s at a ;sio~lta~eous s~ppl~ of o~ygon, ~o that th ~e oi¢ro-orga~io~o will ~foed thomselvoo on the dige~tibl- oo-ponsnt~ prosent in tho Yater, a~d convort theso s~bstan¢os i~to cell matter, rinoral sub~tanoes ~and m-tabolic products auch as C02 and wator, io a go~orall~ kno~n ~nd uGh uood ~othot ~or ~ainly aorob~o p~rification o~ water Of oouroe caro ~hould bo taken thon that tho nu~bor and kind of tho ~icro-organi~s in th- tr-atinR do~ico aro suffi¢i-~t $or digostint tho ~utricial ¢ooponent~ offor-~ to tho~ ~ithin tho ~v~ilablo ti~o poriod. ~onorally this ~ill r-quiro r-tain~n6 tho ~a¢ti~- oicro-oræa~is~o in tho troat~ont to-ico, or o-par-ting th ~icro-organiaos pt-sent in the treat-d e~d diocharged liquld and returni~g tho~ toY~rds tho treat~ont ~pac-. Slnco icro-oreania~a ~ultiply the~s-l~ ~, ~nd thoir ~ount in th troat~ent spac- ~ill tradu~ creao- toYard6 ~nad~issibl- ~alu 8~ ro~o~al of OSC008 ooll ~att~r and ~inoral oub~tano~ al~aJs rsquirod.
It i~ g-n-r:allJ d-~rod that th ~icro-or~anl~ hich ,are ablo to di~-st the offcred nutriont~ ~ill aocumulato tho~aol~o--$~ th s~to in a surficio~t d~groe. Thia ia, ~oYo~er, not al~ay-su~f$~ 1y the oa~0 in praotic-. In particular micro-or~anio~
ma~ d-~olop ~hich aro abl- to digost th~ oS~erad nutriaata l~deed, ~but oannot bo auffiGi-ntl~ s-p~r~ted rro~ the suppliod Y~t-rl oo tbat~ on tho ono ha~d~ a~ unsllo~ablo loao of oicro-orgAnis~s ~a~
occur, a~d, on tho other hand, the discharged purifiod ~ater ~111 be pollut-d in an ~allo~abl~ de8res by ouch non-soparablo ~icro-organi~a. Ih ord-r to obtain, ne~-rtholoo~, a ~atisfactory opo-~ratio~ ~n fi~oh C~B-8~ tho ooparation part is often overdi~-nsionod ~h-n dosignlns A purification 6ystom. Tho badl~ soparablo ~attor ill~ then, be ~uf~ioiently soparated fro~ the ~ator, but the con-,~' ' , ' , ~ ', ' ` ' 1~3`~PZ~) contratio~ o~ th ioro-organi~oa ~n the liquid to bo roturnot ~ill, th-n, oft~n b- ~-ry ~all, ao that tho a~ount of liquid to bo ro-turnod ~ill bo largo in rolation to the umount of wator to be puri-fied Th~refor- not only tho treat~ent doYicc, but al~o tho eopara-tion portion ~ill bo ~oro hos~ily loaded accordi~sly, and th~ co~-B-qUo~co th-roof ~sy bo an inaufficient purification effcct Sinco it ia difficult or hardl~ poasible to pro~oto tho growth of the do-sirot kinda oS d cro-organi~s a~d to suppross the groYth of other ~inds ~ithout r~co~-tructi~g or unlar6ing tho dovico, tho purifica-tion off-ct of siating do-ico- ia ofto~ far ~ro~ opti~al Th biolo6ical purification of aq~oua liquids coapri~ing ~a uist~rc of ~ariouA digostiblo co~pononta ~ill ofton t~k- plaoe for th- ariOUa co~pon-nt~ under diSferent optioal condltiona und, ~or each cooponont, b~ ~oans of di$ferent ~icro-organis~s Alao ~Y$th a siugl- digoatiblo aubatanco the biologiGal pur~fication ~ill ao~otiros ta~ placo in partial Htep4, and for o~ch tep th-ro ~ t difforent opti~al conditioua.
In ord r to obtain tho doairod degroo of purity, either ~- co~pro-~a- ahoult be fo~nd ao as to obtaiu avora6oly acceptabl-couditione for tho arioua icro-organia~a, or a nuebor of biologi-cal ata~-~ sho~ld bo arra~B-diu aori-a, i~ ach of Yhich the con-ditio~ can b- at- aa favourabl- ao poa~ible for opti~ally r-ali-i~t a 8i--n biolo~ical offoct. 80~-ti-ea it ia tried to croate difr-r-nt conditions in dif~oront pointa of tho Ba O treatmont de-ico, o that in on- do-ieo th- ario~a biolog~cal acti-ities tako place ai~ul-~tan-ouely but ~or- or loaa spatiall~ aoparatod I~ th roquirod purification cannot be realisod co~plot-l~
ln th biologioal ~annor, tho biological treatmont can be follovod b~ a ph~sico-~hoaical treat~ont, 6 a dopho~phatiaing treat~ent, gonorall~ callod tho third ntato In ortor to roduoo tho loat of tho biologioal stago in a ai-plo annor, a pr-aoti~ontatlon will bo appliod in m~ny inatancoa, in order to r-novo non--olublo ~ubatancos, ~hich ~ill onl~ be di-6eatod b~ tho ~icro-orga~iema H~tor a long period Moreover an aorobic biological puri~ication ¢an bo pro-ced-t by a phyaico-cho~ical purification ~hich roliov-s the biolo-3 ~L~3~ ,2,i~
gical pusification to a large extent. Finally an aerobic purifica-tion, irrospect~v~ Or the character of a po~sibly preceding ope-ration, can bs followed by an anaerobic purification.
The devices for performing such a biological purification can be realised in many ~ays. The oxygen 6upply nearly always takes placo by introducing an oxygen containing gas such as air. When, in the followin~ description, oxygen or oxygen 6upply are ~entioned, thi6 vill mean the o~ygen present in the oxygen contain~g ga6 as required for the biological proce66. This oxygen 6npply, for in-6tance, can take place by means of surface aerator~, by ~ean6 of nozzles positioned in the liquid, to which oxygen containing gas iB ~upplied under pressur~, or b~ means of liquid circulated by a pump in which an oxygen containing gas i8 introduced by ~e~ns of a mixing venturi or tho liko. Furthermore a distinction can be made in the 6ize of the introduced gas bubbles, and the o2y~en s~pply can take place in a locally reutricted or in a spatially distributed manner. The biological~aYcti~e material can, for instance, be su~-pended in the treatment 6paco in the liquid to be treated (so-called active sl~ge), and can also be adhered to a carrier su6pended in the liquid~ It i8 al~o possible to bind the acti~e material to a solid carrier, thus formlng a 60-called biological filter, ~hich carrier can al60 be mo~able. In the devices of the fir~t kind, the surplus sludge, i.e. the increaseLn the-sludge ~mount by multiplication of the ~icro-organisms and by production of mineral 6ubstance~, will, after as ~eparation of the activé sludge from the purified water, be divided from the am~unt of sludge to be returned, and, when using bound micro-or~ni6~, the surplus sludge will be repelled and taken along Yith the purified liquid~ and 6hould be ~eparatGd Dru~ the l~e~.
Such sy~tems have~ from the be8inn~ng of their develop-~ent (1914)~ ~9manufacturod aB oontinuouBly operatin8 6yBtems YhiCh will take in the liquid varying in amount and composition as it i8 ~upplied, and the purified liquid wlll be removed fro~ the device by displacement. The liquid content in the complete 6y~tem iB~ then, sub6tantially constant. Even if the liquid to be treated i6 pro-duced b~tch-wi6e, the operatiûn of the system i8 ~enerally as des-cribed. In that case often buffer ves~els are u6ed 60 as to ~aintain ~3 ' an uninterrupted a~erago flow rate towardo the biologlcal de~ic~.
It is truo that, ln tho laboratory, experimenta for in~estigating the possibilitios for biologioal purificAtion are porfor~ed by operating batch-wiso, but, as ~oon as the de~i8n parameters of a biological sy~to~ are to bo detormined, a continuou~ly operating model will be w od al~o on laboratory ~cale.
The invontbn i8 basod on tho insight that al80 on a practi-csl scale a batch-wiso operation is poasiblo, and the inv~lon pro-~ide~ a Qothod in ~hish a biological purification de~ico i8 opora-ted in an interrupted ~anner. Tho o$fect thereof i~ that in a ~i~plede~ice a biological purification will bo obtainod, ~hich is equiva-lont to or o~en b-ttor than what is po~dblo in tho ourr~nt con-tinuousl~ oporating device~. Without ostension or ~odification o~
the batch-wi~e opcrating do~ices of the in~ention it appears that th~ ~ost coJplcx biological purification process can be perfor~-d thoroin, for which, in the current oontinuou~ly operatinR do~icos, additiou~ aro required which ~ako the de~ico co~plicated and/or req~ir- oodifications ~hich are diffioultly to operate or to control, and~ at any rate, gi~e riso to ~ub~tuntial increases in the co~t.
Tho batch-wi~- operation according to tho in~ention iB ~uitable for any typo o~ biological purification, i.o. either with ~uspendod or bound ~icro-organio-~ and for any type of oxygen supply.
~ he ~ethod according to th- in~ontion for biologically purifying an aqueou~ liquid, in vhich thi~ liquid, if necoo~ary aftor bein6 freed in ~o~e ~unner fron s-parable irpurities, i8 b-in6 contactet in a treatront space~ under suppl~ of an oxygon containing tas~ ~ith aioro-organis~ pre~ont in that space, aftor Yhich the aicro-or6ani~ms pre~ont in tho liquid aro o-p~ratod tharofro- b~
eodi ontation, io oharaotorioed in that a batch of tho liquid to bo troatod is ~uppliod to thc troatmont ~pac- in vhlch ~pacc the micro-or~anio~ of tho provious treatmont have b-on left, in that durin~
or after ~uppl~ing the liquid batch, tho ~upply o~ oxygon containing ga~ toward~ tho treat~ent cpaco i8 switched on, and is only s~itchad off, oventually, as soon as the de~ired purification dogreo has ~een reachod, aftor ~hich tho liqu~d i5 allowod to co-o to rest ~o that tho sub~tance~ suspond-d in the liquld can sedi~ontato in the sa~e treat~ent space~ in that the purified liquid presont above the sedi~ent i8 drained off, and in that, finally, tho miero-organisms re~aining in the treatment space aro kept thsro under such conditions that their activity is sufficiently ~aintainod until the next liquid batch is supplied.
Thus all the ~teps requirod for the biological treatment tako place in the 6ame spac- but, now, ~ucceeding one another in ti~e. Wh~n the biological purification takRs placo in different partial step~, these will 6ucceod one another, po6sibly with 60me oYerlapping, and tho conditions can, then, be adapted optimally to tho or6ani~ms which ars most effecti~o on that mo~ent, or to desirod rfocts. Thls can often take placo automatically, sinoe, for in~tanco, at first cortain micro-organism~ will di8est sub-6tance~ suitable a6 nutr~ent6 at a high speed from tho supplied liquid, ~o that tho o~gon consumption vill be high and tho concon-tration of dissol~od oxygon will be low, after which, as ooon ac tho~o substancos will hav- disappoared for the groater part, tho o~ygen consu~ption will decrease, and tha oxygon concontration will increas~ accordingly, 80 that~ then~othor or~ani~ms prosent in tho liquid will auto~aticall~ ~oet with moro faYourablo condition~, for instacco for o%ydizing nitrogen pr~ent a~ a~monia, which au~onia ~ay, for in~tanco, ha~o originatod from organic nitrogon. Such ~ub-~equent oporationo may, how-~er, aloo bo promoted, if no¢o~sar~, by an artificial chango in tho condition~, and the momento at whioh this ha~ to tako placo can be doterminad, if noces~ary~by mean- o~
~ea~uro-ents. This artificial chan~e in conditions can ~o~etimos b-- brought about by addinB additional sub~tanc-s, and ofton it can bo ~u~ficient to 4tor~ a 6mall part of tho untreated liquid ~oparatol~, and to roturn it towards tho troatm-nt spaco after deplotion o~ th-nutriont~ ~or th- micro-organism~, in order to ~tart or oupport theroin an othor sp-cific a~foct. Thls ~ay, for in~tanoo, bo th-ca-e with tho anaeroblc troatmont which ~ill be discu~sod bolow.
If aftor th~ b~ological treatment an additional physico-chonical treatment i~ requirod, this can take placo again in th-sa e ~pace, and eithcr before or aftor ~odimentation of tho ~icro-orta~isms. Tho producto producod by this phy~ico-chemical proco~

aro takon up by tho ~a88 0~ oicro-organis~o, and ofte~ ha~o, thoro, an additional u~eful $unction aB A weight~ng mass, 80 tbat the sed~-~snt~tion vill b- i~pro~od and will tako pla¢e in a shorter time It is also possiblo to add spocial substancos ~ust before th0 sedi~en-tation which nhanco the flocculation o~ the micro-organismo and/or the ~edi~entation of ~ineral sub~tancos.
If~ $or obtainin~ a completo puriiication, the aerobic to bo biological troat~-nt isf~ollowod by ~ anaerobic troat~ent, this too c~n b- dono in tho sa~e space, and the ~icro-orga~is~s in ouo-ponsion can bo kopt in suspension thon by ~-ans of Yery short gao supply poriods or by replacing tho oxygen containing gas b~ an in~rt gas, or al80 by u6ing a ~uitablo agitator. I$ the o~ygen 6upply takos placo by ~eans of a circulation pu~p ~ith osygon boinK
introduced into tho circulat-d liquid, the do~irod stirring action c~n also b- obtainod by shutting ofi the oxy6on s~pply tovard~ tho liquid bnt kooping tho pu~p in operation The surp~u~ of ~icro-organi~ms obtainod b~ ~ultiplication and th- ~inoral components $orm-d can be ro~o~od fro~ the treatmont spac- in difforont ~ay8, O-g- by re~oving a part of tho sedi~ent poriodicall~ ai'tor odinontation, or by drawing of~ a part Or tho batch and tho ~att-r ~u~pond-d thorein during at l-ast a part o$
tho osyg-n suppl~ period or during a part ot tho sodirentation poriod. It i~, thon, po6sible to koop, at choico, hea~y ~atorial $or in~tanco in tho troat~ont spaco by allowing it to o-dine~tato, ~a~d to r-~o~o only thon the liquid with tho lighter compononto.
This may, for instanco, be fa~ourabl- when tho mi¢ro-organio~ aro adharod to biggor and/or hea~ior particlos, or when tho ~icro-orga-~is 8 coalosc- to lar6or aggro6atos which ~odi~entato ~ore oasily, and whioh~ preforably, ~hould bo stored for tho next operation. I~
a proolarifier i~ us-d, at loast a part of th- ro~o~ed surplu~ oan be r-turnod towards this pr-olarifier Tho t-~ic- aocording to the in~ontion co~prises a containor which io adaptod to porfor- thoroin all tho roquirod etops of the ~othod Or tbe in~-ntion suoco~oi~oly.
~5 Tho in~entio~ will now be olucidated boloY by roforonco to a dra~ing, ~howing in:

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' ' 7 ~ 3~

Fig. 1 A ~ehomati¢al representation o$ a first ~mbodiment of tho do~c- according to tha inv0ntion;
Fig. 2 A oimplified sche~atical repreoentation of a com-pound de~ice co~prising a plurality of devices of FiB. 1; and Fi~. 3 a schematical representation of anothor embodi~ent Or the de~ico according to tho in~ention.
The de~ice accordint to the invention sche~atically shown in Fi8. 1 i8 intended for biological purifloation without a pro-ceding preclarification, and the liquid to bc purified is supplied batch-vise. Thi~ liquid ~ay, for in~tanco, originate fro~ a factor~
which produces wa~te water only during a part or specific parts of the day. Thi~ is~ for instance, tho ca~e with slaughter-housos and tha like.
The liguid to be treated i8 supplied by a duct 1 uhich csn be pro~id-d with a valva 2, and which leads to a basin 3, which constitute~ the ~ost i~portant part of tho deYice according to tho i~ ontion.
Noar th~ botto~ of tho basin 3 outflo~ oponings 4 pro~ided in a t~bo 5 ar- ahown, which tube iB connocted to an air pu~p 6 80 a8 to allo~ air to be introducod into tho liquid prosont in tho ba~in 3. Thls t~bo i~ ahown only by way of example, and can be ro-pl~c~d by any othor aerator which ie able to introduce air into tho liquid at a ~ore or less ~ariable liquid le~el.
In th- basin 3 d cro-organis~s ara present which are left fro~ the precoding batch-wi~- treatment, and which are required for tho purification of the liquid to b- treated.
In or near tho lateral ~all of the baoin a tapping point ? iC pro~id~d ~hich iB~ by tho intor~sdiary of a val-o 8, conneoted to a diochargo duct 9. Abov- the opening 7 a second tapping point 7~ is indicated with interrupted lines~ whioh, by ~ans of A ~al~o 8~, is connoctod to tho duot 9 too. ~he nw~bor of ~uoh suporpo~ed tapping pointo i~ not restricted to two. I~ ~ore than ona oponinR
7 is present, one can tap at differont le~ols a~ da~ired. Other tapping ~eans can be used instead, e.B. o~erflow duct~ which c~n follow th- changlng liquid levol in the basin ~, or other suitablo tapping ~eans.

, ' ~3~(3 2~
In the ba~in 3 an opening 10 for surplus sludge c~n be pro-~ided, which communicate~ wit'n a duct 11 pro~ided wit~ a Yalve 12, and leAds towards a batch-wise operating sludge treatment ~tage 13 in which a separation i8 brought about into concentrated surplus sludge, on the one hand, which i6 discharged at 14, and ~ quantity of clarified water, on the other hand, which i6 di6charged at 15, and ths di6charge duct can communicate with the duct 9.
The sludge treatment gtage 1~ i6 6ho~n, in Fig. 1, at a lower level than the basin 3, but *hi~ i8 not nece6sarily the case, and thi6 treatment stage can also be positioned at the ~ame level as the ba6in ~, and can, for instance, be separated from the latter bg means of partition~. In particular thi~ may be the caRe ~f the sludge discharge takes place at times that the basin 3 iB completely or nearly completel~ filled, 60 ~h~ the sludge discharge towards the stage 13 can be offected by the pre6sure of the overlying water.
The clarified water separated in the stage 13 can flow off by its own l~vel differenco toward6 the discharge duct 9.
The operation of this device takes place in 6ubstantiall~
four ~teps:
(1) At the boginning of the filling, the active sludge left back reaches~ for in6tance, the level 16 in the basin 3. ~he liquid to be treated will then more or le~s gradually fill the basi~
3. Already during filling the aeration can be started, b~t it . iB alBo possible to wait until the ba~in 3 iscompletely ~illed.

(2) A~ter switching on the aeration~ the biological purification begins, and is continued until the liquid i8 sufficiently purified.
(~) A~ BOOn a~ the de6ired purity is reached, the aeration is inter-rupted, and the sludge mass which wa_ ~.ept i- o~qps~a~on by th~
aeration, i8 then allo~ed to settle. During a part of the ~eco~d step or al60 during a part o$ the third one, surplus sludge ~an be drawn o~f through the opening 10 or the higher opening 10' indicated in Fig. 1 with interrupted lines, so as to en6ure that not too mu~h sludge will be present during the treatment of

3~ the next batch.

(4) After completin~ the ~edimentation, the clarified liquid can be ~.3~P2~
,.~

discharged through the opening 7. If higher discharge openings are present, discharge can begin already during sedimentation at that level where no longer micro-organisms are present. This can also take place if use is made of a discharge which is always situated near the liquid surface. After removing the clarified liquid, a quiescent time can follow if necessary, during which the activity of the remaining sludge can be maintained by periodic aeration.
The basin 3 operates therefore, on the one hand, as a biological purification vessel, and, on the other hand, as a sedimentation vessel. Since, during a substantial part of the biological treatment (step 2), the concentration of nutrients is large in respect of that in comparable continuously operating devices, the velocity of the biological conversion will be particularly high, so that this device can be made particularly small as compared to the known devices. Moreover the device of the invention is particularly simple.
The present device can be controlled in a very simple manner, and the control lends itself also to automatisation. This can, for instance, be done by means of time switches, but it is preferred to design the control means in such a manner that one proceeds to the next step only after completion of the preceding one. The end point of step (2), for instance, can-be determine by establishing the increase of the dissolved oxygen concentration at the end of the ::
clarification. In some cases, when the liquid contains ammonia or ammonia is produced therein, the concentration thereof can be deter-mined. For as soon as the nutrients for the micro-organisms present in the liquid have been digested, oxygen will become available for oxidising ammonia by means of other micro-organisms, so that a decrease of the ammonia content is an indication for the fact that the digestible substances have been digested. Also the discharge of clarified X

.:, 3L~ 3~
9a liquid can be controlled by means of measurements, in particular in the case of discharge openings situated at different heights or of an adjustable discharge with a controllable immersion depth. The control can, for instance, be performed in conformity with a turbidity measure-ment near the dis-, .
~ : 20 ~ ~ .

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.. .: . , :.: .: : ; ,: .:.: ::: - :: .:: : . :: . . . :
:, :- . . . ., .:: .

~1 3~
charge, 80 that liquid will be drawn of~ at a lower level only a~
the turbidity in that point will have decrea~ed below a certain threshold value.
The sludge treatmellt stage 13 oi th~s device i6 very small in co~paricon with the settler~ used in the current de~ices, as 6edimentation takes already place in the basin 3, and in the stage 13 only surplus sludge will be thickened.
Th~ hi8her discharge opening ~0' 6chematically indicated in Fig. 1 with the as60ciated duct 11' and valve 12' may be u~ed, for instance, if one wishe~ to obtain, at first, the 6edi~entation of a sludge layer and to remove the surplus sludge in a higher point.
The hea~ier nediment will, then, not be removed. This can, for in-~tance, be Yavourable when the micro-organism~ are adhered to hea-vier carrier partioles, and the adhered micro-org~isms 6hould be kept in the basin 3, ~hereas repelled organi6ms together with mine-ral sub~tances should be remo~ed as surpaus~sludg~. ~oreover it has 6urpri~ingly appeared that al80 without U6ing heavier carrier sub-stances and with systematically removing lighter sl~dge particles as surplus sludge,automatically a quickly settling active mass will be formed which has more favourable settling properties than the smal-ler sludge particles. The amount of surplus sludge to be removed depends, of course, on the amo~t of active slu~ required for treating a 6ubsequent liquid batch, further on the growth Or the micro-orga-ni6m population~ and finally on the a~ount o~ produced mineral sub-6tance6.
It iB po~sible to add, at a suitable momeut, additionalRubstances from a contai~er ~ to the liquid to be treated, 60 as to bring abo~t an additional effect. An example thereof i5 the ad-dition of agents pro~oting the sedimentation or flocculation of the micro-organisms and the produced or present mineral substanc~s ~o as to accelerate 6ettlin~. Moreo~er the particles of ~ineral sub-stances settled in this manner may serve as adhesion ~uclei for micro-organi6ms so as to enhance sedimentation thereof, or, when reu6ed, to improve the effect of the mlcro-organi6ms. It i~, of ~5 cour6e, al60 possible, a6 mentioned abo~e, to adhere the micro-organism6 to hea~ier particles already from the outset, or to obtain ~.B

3~

larger particles by a certain coalescenco of the mioro-organisms themsel~e6. Moreover the operating condition6 can be mo~ified also in other ways, for instance by varying the temperature or the acidity.
Beside3 micro-organisms suspended in the liquid, adhered or not to heavier particles, use can also be made of organisms ad-hered to fixed carrier surfaces in a known manner not further des-cribed. ~hese surfaces may have the shape of plates or disc~ im-mersed into the liquid, which can be remo~ed from the liquid at the end of the operation. This can, for instance, al~o be done by con-6tructing these plates as rotatable discs which only partly extend into the liquid. By rotation thereof these micro-organi6ms will be periodically introduced into the liquid, and are subsequently ex-po6ed to the air. As the micro-organism6 on such plAtes multiply, a part thereof will be repelled from the carrier surface together with the produced mineral products, and will land in the liquid.
After the interr~ption of ths biological purification process, the~e 6ubstances l~nded in tho liquid can settle, and can be romo~ed at lea6t partly from the liquid. Of course sedi~entation will, then, be fa6ter than in the caso that all the micro-organism~ are SU6-pendod in the liquid.
It i8 sometimes fa~ourable to add, at a later moment, a 6uitable nutrient for the micro-organism6, e.g. a part of the liquid to be treated, to the liquid in the ve~6el ~, which i8 indicatod in Fi~. 1 by the auxiliary container 18, in which a part of the supplied liquid can be ~tored. This ma~ havn a fa~ourable effect on the puri-fication, for in6tance by startin6 and promoting an additional acti-~ity by other micro-organi6m~, or by maintaining the a¢ti~ity of micro-organisms during the time that other micro-or~anis~ aro bringing about another offect.
~his iB particularly rele~ant in the oase that, after tho aerobic bioloKical troatment, an anaerobio biologioal treatment should take place in the basin 3, e.g. for denitrifying aerobically produced nitrate. Of course the micro-or6anisms suspended in the liquid which aro suitable for thi~ anaerobic treatment should be kept in su6pension to that end. ~his can be obtained by 6tirring by ~eans of an additional agitator. It is also possible to bring ~2 about the roquired liquid mo~ement by means of short air blast~
from the no~zles 4 which are insufficient for substantially in-creasiu~ the oxygen conte~t of the liquid. ~lso an inert gas can be introduced into the liquid instead of air through the nozzles 4-If the oxygen 6upply takes place by introducing water mixed withair by means o a liquid pump, it i9 ~ufficient to 6hut off the air 6upply, BO that only water i8 introduced which will keep the liquid mass in the basin 3 in motion.
In the sludge treatment ~tage 13 a level sensor may be pro-qided, by ~eans of wbich the valve 12 or 12' will be clo6ed a~ soon as a given le~el has been reached. In this ma~ner th~ am~unt of sludge can be automatically controlled. If this level 6ensor i~ made ad-justable, an adaptation to any prevailing condition can be obtained.
If a plurali~y of tapping openiug6 % or a tapping means ~5 to be kept uear the liquid surface is used, discharging the clari-fied water car. already begin before 6ettling has been fully completed.
The complete 6ettling of the sludge asfar as the level 16 may some-times last rather lon~ in proportion to the time avai~able until the supply of the next batch, so thatt accordinely, little time i8 left for remo~ing the clarified liquid. This ca~ be unfaqourable i~
it is not po6sible to discharee the clarified liquid fastly, for in~ta~ce in view of the capacity of the drain, in particular in the case o~ draini~g the clarified water into a sewer or waterway. It i8 advisible, then, to begin with removire clarified liquid as soon a~ possible after the beginning of the sedi~entation, and to that end the abo~e-mentioned discharge means can be u~ed which allow to begin the discharge near the liquid surface where 6ettling i8 com-pletely terminated 600n. In particular use can be made, as mentioned ~bo~e, of a turbidity meter which alls~ '^ determ~n~ when the ~edi-~0 mentation ha~ proceeded ~ufficiently far.
In the device described abo~e for a batch-wise treatment of batch-wi~e 6upplied amount~ of water to be purified (e.g. once n day), the ~olume of the basin 3 can easily be calculated fro~ the ~ize of the batch and the required amount of remaining active sludge, the ~olume of this sludge mass being relatively ~mall, and being, geDerally, ]ess than Z0 ~ of the liquid ma66. ~ith a basin 3 ha~ing .~ .

13 1~ 31~?~ ~ ~

a ~olume which iB only 20 ~ more than the batche6 to be treated, a purification effeat can be obtained which can only be obtained in a current continuously operating de~ice if its liquid ~olume iB
Ge~eral times lar~er.
The advantages of this batch-wise operation are 80 ~reat that, even when the l~quid to be cleaned i~ 6upplied in a 6ubstantial-ly uninterrupted manner, a division into 6eparate batch-~i6e opera-tin~ parts will offer great advantages.
Fig. 2 shovs a 6chematical representation of a device suitable for that purpose~ which can, for the re6t, al60 be used when the device of F'g. 1 requires extension, and the plurai devics 6hown in Fig~ 2 can al~o be used for takin~ in rarely occurring impact loads~
The plural device shown comprises a plurality of basins 3 according to Fi~. 1, which are shown in a highly 6impli~ied fashio~.
A}l reference numerals corre~pond to tho6e of Fig. 1. Although only two ba~in6 3 have been ~hown, their number can be cho6en arbitrarily large.
The 6upply ~alves 2 of the various basins 3 are connected in parallel to the 6ingle ~upply duct 1. Also the discharge valves 8 of the6e ba6ins are connected in common to one 6in~1e di6charge duct 9. The aeration tubes 5 of the various basin6are, now, provided with a Yalve 19, which valves are connected in parallel to the pump 6. Also the sludge discharge Yalves 12 are connected in common with one single sludge treatment ~essel 13, and the water discharge 15 is returned towards the di6charge duct 9.
By ~lternately opening the supply valves 2, the basins 3 _an be fillod with liquid charges. After fillin~ a baein ~ the as~ociated ~alve 19 i8 opened 80 a6 to brin~ about the aeration oi the contents of this basin. At the end of the purification period, the valYe 8 in qUestiOn is opened, and, if sludge is to be drawn of~, the associated valYe 12 is opened.
The ~arious ~alves may be actuated by means of a pro~r~mme 6~itch in the correct 6uCce6sion~ and~ if ~ecessary, le~el 6ensors in the YariOUs basi~ may be used for closing the associated supply valve 2 as 600n as the desired level in the basin 3 has been reached~

.

"~
.

1~3~2`~

As n ~atter of fact each basin 3 can be provided ~ith an associated air pump 6, and, ir desired, s~eral sludge treatment staBes ~3 ~ay be used. Tha number of stages 13 is not necessarily equal to th~
nu~ber of basins 3, if only ~uitably operated 6witches are used.
Fig. 3 shows another embodi~ent of the device of ~ig. 1, in which, again, corresponding part~ ha~e been indicated by the 6ame reference numerals, ~h~ch parts are represented in a highly ~impli-fied ~a~ner.
The supply duct 1 is, a~ain, pro~ided ~ith a val~e 2, ~0 which, however, doe~ not lead direotly towards the basin 3, but to-wards a preclarifier 20. In this preclarifier a part of the inpuri-ties i6 removed from the 6upplied liquid in a non-aerobic-biological m~nner. Example~ thereof are sedimentation, if necessary by mea~s of auxiliary substanoes and/or air bubbles, physico-che~ical treat-me~t, anaerobic treatment and the like. ~or the purpose~ of the description of the in~ention the character of the preclarifying stage is not important, so that it~ structure need not to be dis-cussed in detail.
~atter separated in the preclarifier 20 i8 dischar8ed through a duct 21. The preclarified liquid iB led through a duct 22 towards a basin 3 according to Fig. 1. ~hc branching 2Z' indicated 6chematically in Fig. 3 i~d~cates in which manner, in a co~pound devico according to Fig. Z, the preclarifier 20 can be coupled to a plurality of basin~ 3.
~ The basin 3 iB~ for the re6t, constructed in the manner of ~i6. 1, with as the only differenco that the sludge discharge ~uct ,~ wi'h a ~al~c 12 does not lead toward8 a sludge treabment 6ta~e 13, but conmunicate6 with a re~rs duct 2~. At ~3' a br~n~hi~b iB 6hown again, indicatin~ how in the case of a plural de~ice ac-~0 cording to Fig. 2 a nu~ber of basins 3 can be connected to a single retur~ duct 23. This duct leads back towards the entry ~ide of the preclarifier 20, but can also open into the duct 1 beyond the val~e 2. The ba~i~ 3 i~, moreover, connected to an aeratin~ pu~p 6, if necessary together with other basin~ 3, and the discharge for clari-fied water 7, if nece6sary by the inter~ediary of a valve 8, con-nects again with a discharge 9 which, a~ indicated at 9', can also i~ .

~ 3~2~

connect to the discharge ~ides of other basins 3.
The surplus sludge iB~ in this device, not thickened in a 6eparate stage, but is returned towards the preclarifier 20, which often hardly means an additional load for the preclarifier. The biological surplus sludge is, then, removed together with the sub-stances separated by the preclarification process.
If neces6ary a pump can be included in the duct 23, and this duct may also open in any other suitable point in the pre-clarifier, for instance when a certain ~ucces6ion of treatment steps takes place therei~, and the introduction of sludge can better be done in a more remote step.
Also in this modified embodiment the ba6in 3 i8 u6ed for a plurality of succe6sive process step6.
It will be clear that within the scope of the invention many modifications are possible. The e6sence of the invention, how-ever, iB that all the process step6 to which the liquid to be puri-fied i8 to be sub~itted, with the exception of the not always re-quir~d pre6eparation, take place in the sa~e space, viz~ in the basin 3, 80 that the device according to the invention requires ~uch less 6pace than the known devices~ and is much 6impler. In particular, in contrast to the known devices, the number of vessels need not to be equal to the number of process 6tep~, since these 6teps can now be performed con6ecutively in the 6ame ba6in. ~160 ~hen using 6everal basins 3 in parallel for treating batches which succeed one another faster, and, i~ particular, for treating a 6ub-6tantially continuou6 supply, the total volume of the device will be 6maller than in a device of the known type de6igned for the 6ame capacity, ~ince, in the known device~, in contrast to the device according to the invention, only small level fluctuations will occur.
~0- It i8, further~ore, pos~ible to convert a known de~ice with several ba6in~5r vessels into, for instance, a plural device according to Fig. 2, in which, then,the relatively large after-~edimentators can be provided with aeratin6 means and, then, can be used as basins 3 for biological pu~ification. In this manner an exi~ting device can be adapted to treating substantially larger amounts, which, if an existing device has become insufficient because of the increasing liquid supply, will lead to ~ubstahtial cest and space savin~s.

.. , . . . . . . . ..... . . ... . . ... . _ . , . . .. . .. ~ ... . .. .

16 ~3~

~ In the preceding de~cription it has already been said that ~le active sludge to he used for a next batch can be kept alive in the basin 3 by aeration. At longer interruption6 of the supply it may be advisible to fitabilise the sludge. Ihis is done by a strong aeration which, since nutrient6 are absent, ha6 the effect that a part of the micro-organi6msis digested by others, non-digestable mineral substances then being produced, and no organic substances subject to putrefaction will remai~. Thi6 leads to an aerobic 6tabilisation and extensive mineralization of the sludge to ~o be 6tored.
The existing continuously operating biological treatment devices are often capable of satisfactorily treating waste water or the like to be treated, if the 6upply ratc and/or impurity con-centration are sub~tantially constant, but in practice the ~upply 1~ rat~ andJor concentration will ~how peakR, ~o that, at intervals, the purification will be les3 than optimal, although the average polution degree remains below the maximally allovable level. Such a device i6, then, to be extended~ if BUCh a less 6atisfactory purification during load peak6 ~hould be avoided, which means that the de~ice will be underloaded during a very considerable time.
Accordi~ to the invention a current continuously operat~ng device can be made 6uitable for sbsorbing such load peaks, in that a batch-wise operating device of the kind de6cribed above i~ con-nected in paralle} thereto. Thi~ additional device needs only to absorb a peak load a few times a day, and, as described already above, the structure and éontrol of such a device are ~ery si~ple.
The continuously operating original device is then relieved of the6e peak load6, and can operate in the most optimal manner. Since the additional batch-wi6e operating device of the invention needs only relatively little fipace, 6uch an extension is generally reali6able without any difficultly, and, moreover, the cost will be sub6tantial-ly lower than those of a second continuously operating de~ice which, moreover, will operate in the average uneconomically.
It will be clear that 6uch an extension i8 not restricted ~5 to one single additional device. After some exten8ion8th9 ~ituation . .

, -- , . . . . .......................... , . _ . . .
B

1 7 1~l.3~2 El of a compound de~ice of Fig. 2 will be reached to which a continuou~-ly operating device is connected i~ parallel which absorb~ the con-stant and, in relation to the total load~ possibly small basic load.
Inversely, if a a certain constant basic flow iB developing, a de~iee of the invention ean be extended by mean~ of a relatively small continuously operating device. In a new device to be constructed one may alsoc~o-se this structure from the outset.
In auch a eompound de~iee which operates partly continuou~-ly a~d partly batch-wi~e, one will 6witch over from the first to-wards the second kind of operation when tho supply rate exeeeds agi~en ~alue or if, by mean~ of the current mea~uring and control apparatus, it is~està~lish that the oxygen demand in the aeration staBes of the continuously operating part of the deviee inereases beyond a eertain limit. In thi~ manner the operation of the eou-tinuously operating part can bo stabilised in a very eon6iderablede~ree, wherea6 the impact or peak loads will be absorbed in a ~ery effecti~e manner by the batch-wise operating part.

Claims

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

1. A method for biologically purifying a liquid, in which the liquid is contacted in a treatment space with micro-organisms present in that space under supply of an oxygen containing gas, after which the micro-organisms and reaction products present in the liquid are separated from the liquid by sedimentation, characterised in that a batch of the liquid to be treated is supplied to the treatment space, in which space the micro-organisms of a preceding treatment have been left, in that during or after supplying the liquid batch, the oxygen supply towards the treatment space is switched on, and is, eventually, switched off again as soon as the desired purification degree of the liquid has been reached, after which the liquid comes to rest and the substances suspended in the liquid can sedimentate, in that the clarified liquid present above the sediment is drawn off, and in that, finally, the micro-organisms remaining in the treatment space are stored therein under such conditions that their activity remains conserved in a sufficient degree until the supply of the next liquid batch, the amount of the stored sediment being adapted to what is needed for treating the next batch, and the surplus sediment is removed.

2. The method of claim 1, characterised in that the working conditions in successive steps or partial steps, as the case may be, are adapted in the most favourable manner to the operation taking place in each step or partial step, and in accordance with measurements of the state of the liquid being treated, the adjustment of the working conditions being obtained, for instance, by adding additional substance.

3. The method of claim 2 wherein the measurements of the state of the liquid being treated are of the oxygen concentration and/or demand.

- Page 1 of Claims -

4. The method of claim 2 or 3 characterised in that a part of the liquid to be treated is stored, and is added to the liquid in the treatment space at a suitable moment.

5. The method of claim 1, characterised in that before or after the aerobic treatment a treatment without substantial oxygen supply is performed, the liquid during said anaerobic treatment being kept in motion by stirring or by introducing into the liquid an oxygen depleted or oxygen-free gas or liquid.

6. The method of claim 5, in which the oxygen supply during the aerobic treatment takes place by injecting an oxygen containing liquid, characterised in that during the anaerobic treatment, the oxygen supply towards the injected liquid is interrupted.

7. The method of claim 1, characterised in that during or after the biological treatment a physico-chemical treatment is performed in the same treatment space, comprising adding during or after the oxygen supply additional substances enhancing the sedimentation of the micro-organisms and of mineral components present in the liquid or produced therein.

8. The method of claim 1, characterised in that the surplus sediment produced by multiplication of micro-organisms and/or production of mineral components is removed from the treatment space during an arbitrary period of the treatment as needed by drawing off liquid with sediment suspended therein from the treatment space.

9. The method of claim 8, characterised in that the discharge of surplus sediment takes place above an already settled sediment layer, in order to remove lighter sediment with preference over heavier sediment.

10. The method of claim 1, in which the liquid to be treated is treated first in a preseparator, characterised in - Page 2 of Claims -that at least a part of the removed surplus sediment is returned to the preseparator.

11. The method of claim 1, characterised in that the treated liquid is discharged from the liquid portion present above the sedimentating material already before termination of the sedimentation.

12. The method of claim 1, characterised in that a substantially constant part of the supplied liquid is submitted to a continuous biological purification treatment, and the remaining variable part is treated batch-wise.

13. A device, intended for executing the method of claim 1, comprising a container adapted to be used as a treat-ment space for treating a liquid supplied thereto with micro-organisms, and provided with a liquid supply, means for intro-ducing an oxygen containing gas into the liquid, and means for discharging the treated liquid, characterised in that the con-tainer is adapted for admitting liquid batches supplied at intervals, in that this container is, furthermore, provided with means for collecting and discharging sediment, and in that the container is, finally, provided with means for controlling the supply of liquid and oxygen containing gas and for discharging liquid in such a manner that the gas supply can be interrupted for allowing the liquid to come to rest and the sedimentatable material to sedimentate therefrom, before the next liquid batch is supplied.

14. The device of claim 13, characterised by an auxiliary container connected to the liquid container, in which a part of the supplied liquid can be temporarily stored.

15. The device of claim 13, characterised by means for keeping the liquid present in the container in motion with-out a substantial oxygen supply, in order to allow an anaerobic process to take place.

- Page 3 of Claims -

16. The device of claim 15, characterised in that the means for keeping the liquid in motion are adapted to introduce an oxygen depleted or oxygen-less gas or liquid into the liquid.

17. The device of claim 13, characterised by one or more sludge discharge ducts connected in the container and provided with a valve.

18. The device of claim 17, provided with a pre-clarifier included in the supply duct, characterised in that one or more sludge discharge ducts are connected to the preclarifier.

19. The device of claim 13, characterised in that the liquid discharge comprises a plurality of discharge ducts opening at different heights in the container, each duct being provided with a valve.

20. The device of claim 13, characterised in that the liquid discharge is adapted to discharge the treated liquid from near the liquid surface.

21. The device of any one of claims 19 or 20, characterised by a sensor for determining the turbidity degree of the liquid near the liquid discharge, which sensor is adapted for controlling the discharge in correspondence to the turbidity degree thus determined.

22. The device of claim 13, characterised by a plurality of treatment containers connected in parallel to a supply and a discharge duct, the supply and discharge connections thereof being provided with valves which are adapted to be alternately actuated, so as to supply to these containers alternately a liquid batch and to discharge therefrom treated liquid respectively.

23. The device of claim 13, characterised in that the device is connected in parallel to a device for executing a continuous biological purification, and is provided with valves which are adapted for branching off, as needed, a part of the supplied liquid flow.

24. The device of claim 23, characterised by means for measuring the flow rate and/or the impurity concentra-tion or the oxygen demand in the continuous flow, and for controlling the branching valves in conformity therewith.

25. The device of claim 13, wherein the oxygen containing gas is air.