Note: Descriptions are shown in the official language in which they were submitted.
--2--
Tne invelltioll relates to a m e; hod for the biological con\~ersion of sub-
strates in ~hich substrate and microbial material are mLYed, it^ neces~ary
aifter preliminary purification of the substrate, and the thus obtained ,nicrobial
syste m is kept under reaction conilitions.
In the following bacteria, yeasts and the li'i;e, mixed with a corresponding
substrate, are understood by microbial systems. Such ;nicrobial s)stems are
often designated as biomass which effects a biological reaction as a self-
contained system. In particular, microbial systems are acti~,ated or cligested
sludge. Equally, tile microbial biocoenoses as are present in the acetic or
lO alcoholic fermentation shaIL be classed under the concept of microbial systems.
Such microbial systems take in the s~lbstance usuall~ by absorption to the
cell membrane. ~Yithin the ran8e oE the ceLl membralle first degradation reac--
tions take place. The absorption rate of the substrate -~s determirled among
other ti~ings by tlle concelltration of the primclry metabolites in the c~ll plasm.
15 Depending on the t~,pe of the employed microorgal~isms such a microbial system
is able to effect a certa n biological reaction or to convert certain substancescontained in the sul~strate.
For im provirlg the charging of the microorganisms ~:ith the subs~rate
to be converted polyelectrolytes are added ~ ich ob~iously e:cert an in1uence
20 upon ttle transport processes througil the cell m e m l-rane. The additioll or`
greater amounts of polyelectrolytes StlOWS oEten negative inEluences upon
the activ-ity of Lil(' microbes w;~ich can be e~pLIined b~ the fact that the
transport proce~-se.s througrl the ceL1 m e m brane are blocl~ed~ nu m ber of
microbial systems are e:cceedingly dit'~icult to float and tne separatior, of
~5 the substrates to be convertecl i5 succe~sslil orLl.y to an unsatisfdctory e:~terlt.
The additiorl of greater arnounts oE polyelectrol)tea has lisadvantaca~eous efL'ects
on the se~.!age load. Furtller m ore, a nu m ber of bio1O~,ical reactions in such
microbial systems go on very s1OI~1ly becal;se a fast abs~rp~ioll of t'-ne substrdte
to be degrcl~late~l by the microbes is not pos~ible.
The invention aims .at increasing the chargillg rat~ of micro'ui,l1 ma;eri.~l
a~
--3--
by the substrate, at ~liminishing dramaticaLly the amoun~: oE polyelectrolytes
to be adcied, and at irnpro~,ing the floatability of the charged biomass. In
order to solve this proble m the invention con ~ists essentially in applying an
electric field in the miYing space and/or :in a ~otation de~ice after mi.~ing
5 the substrate ~ith the microbial m aterial using pulsating direct current, and
in effecting a biolog:ical reaction subsequently without appl~ing an electric
field. Ilerein it turned out to be essential that puL~ating direct current is
used for build-up of the electric field. Such a pulsating direct current can
a]so be a swe:lling current which starting ~rom a minimum value has hr-llf-
lO waves of only one single polarity. By using such an electric field after mi.~ingthe substrate with the microbial m aterial it has been surprisingly found that
the substrate is absorbed to an increasLng extent by the microbes, wherein
the concentrations of the prim ary m etabol:ites to be e~;pected ob~iously clo
not exert an influer-ce wort:ll rnentioning upon tile substIate resorption rate.
15 It is alrea(ly l~no~r-l to subject sewage ~aters to elect~-olysis bec'ore biological
purificatioll. Until now, ho~lever, there was a prej~lcLice of the eYperts agaiJlst
subjecting the bio m ass to the influence of an electrLc f-ield. The surpri~iing
etfects oE the inf1uence ot an elecLric ielrl built up with p~lsatulg d:irect
current upon the t-iorna~ss can be pos-~ibly eY~pk~ ed by the fact that the charge
20 dist~ibution :in the ce~l m e m brane is changed by the il~1uerlce of the electric
~ie:ld, by ~hich the transport processes throuc,h the ce11 men.lbrane are e.ssell-
tially acceLerrlted. 'L`he superiority of using p~Llsating d~rect currellt in corn-
par-Lsorl ~ ith smoc)th direct currellt could be proved b~ e.~;pe!imen~, althuu~h
an e:~act e~;plallation coukl not be found. 'I`he super~orit.y .owar-ds the use
_5 of alterllatillO curr-erlt s~ith posLtive and negative halL-.~avc?s r~ be indicated
by the fact that inver-sioll of pol~rit y of such half~ ves in zero crossover
d:isturbs a~ain Lhe activation of the cell rn e n~ b~-alles. ~ pplying such an
electric l~iekl an a~l~iitiona1 absorption of subs;rate by Lhe mic.robes coul~l
be observe(l an(l in isolated cases it could e~ t?n be i. bsr r ~ ed that the alicrobes
30 absorb substclnces t hey usuaLl-. do not co~ erL. 'I`hl s~ .'or e~:a m ple în : he
t71
--4---
species Saccharom~!ces cere~ iae (b~ewer's yeast) it was observed that apart
~ro m the he.~;oses usuaUy converted by tl~is species it absorbs also pentoses
in the electric l~ieLd uncler anaerobic conditions. Subsequently, it was obser-
ved that under the influence oE the electric field ~ylose is fermented to
5 aLcohol by this species. In the case of other microbes it couLd be obser~ ed
that not only greater a m ounts of substrate could be absorbed by the microbes
in shorter time, but also that the separability of the biomass was essentially
improved. M-icrobiaL systems dificuLt to float and unfLoatable srlbstances
could be easiLy separated in presence of an electric field and the remaining
concentration in the resid~laL water after separation of the biomass following
the absorption o~ substrate showed essentiaLly lower ~alues of sewage water
than in the known methods. The relatively 'nigher supply of substrate in the
ceU obiously forces the celL to accelerated reaction and as a consequence
an essentially faster reaction to ~he requ~l-ed end products w as observed.
Above aIL the need of polyelectrolytes in ilotation could be essentiaLly re-
duced. For e~cample it was observed that a ilotation which ~ith convention~l
m ethods without using an electric ield needed three quarters of an hour
to an hour, could be inished in 4 to 5 minrltes, wherein a lower concentration
of substrate remc~ined in the sewage water.
A fLotation is particuLarly favourable in the scope of waste water puri-
ication plants, as the puriication plant is designed corresponding to the
average require m ents. 13y flotation peak values in the occurrence of waste
water to be pur;fied can be coped with very sim ply by the fact that the
fLoated sludge which cannot be supplied any m(lre ul the normally dimensioned
l~iological puri'Liccltioll stage is aiscll.3rge(l all(l burnt or is intermediatell
stored in concerltrated form in orcler to be subjected after iards correspon-
dillgly dil~lted to the convelltionc~l biologic~ purillicati(m. The ~lotation stage
hereill mal;es above all short-term regr:lating intervent ions posssible becauseof the low need of time, as for instance the sepa;atioll of sludge whictl
after repeated ventilation can be recycled to the mi~ing ve~s~sel. Also in this
- s -
~.~a~ it is pos~ible to take the difEerent occurr~rlce c~E ~ ater to be puri~ied
into account ancl to ensure a reg~LLar through-put thro~lgh the biological puri-
fication stage. The partial feedbacl; of floated sludge to repeated n~liYing
a:Llo~s the addition o:E smaILer amo~lnts oE nutritious substances especiaILy
5 in domestic se~iage.
In the scope of the process according to the in~entioi3 it has proved
favourable to use a terminaL voltage of 2 - 30 V preferably 4 - 12 V for
the buiLd-up of the electric fieLd.
I~]SO if the adclition of polyelectrolytes can be (liminished, it is ad\an-
10 tageous though particuLar1y in order to achieve im proved' conductivity ofthe solution to add polyelectrolytes to the m.iYture of subsrrate and micro-
bi~l m aterial before applying the electric field . Surpr~ingly aLso the addition
of ion exchangers invol~ ed an il!l provemellt of substrate absorption and
f] otatio n .
Preferably the electr;.c ~i.e.kl .is app~ied :iutermittillgl.y. ~her~in the electric
field is appliecl at :least in a f.-rst temporal stage of ~he reilction in ~ihiCIl
the substrate is al)solbed by the m:icrobia:l !nateria~ !i.thin this fi~-s; Lempor~l
stage a sigri.E:i.cant :improveillerlt of changing Or th~ microbes ~iith s~im~LL-
taneous clim~ isllillg of the need of time an~l .sin~l~Ltalleous impro-~ement
20 oE EloatabiLity h.lS ShO~
In b:iocoenoses which do not ten(l to violen~ prodll ~tion of g~lS i;n mediate-
ly after chargirlg :it is ad~ ancagec3lls to support flotat iorl b- e:lectrolyt ic d~
composition. In this case proceeding is s~itab:ly such as to app:L~ a teriil:ina:l
~o:Ltage at30ve tile decoinpo~iLion voltage oi the soLuti.ll o~ s.:bst.rate-biorn3ss
25 in the first tempor~-LI stage :in order to pronlot.e ilot..ltion o~ the biomass
chclrge(~ ith substrate. In b:iocoenoses ;rich Libera~e &reater a:nounts of
fernlen~atioll gases the terminal. ~olcage can be chosen to be lower.
Tn every case it it i'a~o~lrable t.o ~all~i nutr:iti~ ~i..i sub.~.t~3il. es alrea~'i .
bei'c)re ap~ r~iilg the clectric f-.-i.el(l ~Yhei ein it n~Ce~?~` Iry the pi3 is 5rol~gi~t
:3(.1 to tl~e most Ea~our lble \.aL:.Ie i~or biologic 1L re.l~tic3il. ~ta.ldar(L;~ th;.' pti
3~
--6--
to the v~Llue most favourable Eor the subsec1uent bio1Ogical reaction alLo~.s
further diminishing of the amount of polyeLectrolyte to be added.
Preferably, an electric field with essentially horizontaL iines of flux
is used. In such an electric fieLd the eLectrodes are usucilly arranged verticaILy
5 and the production of gas setting in at the surface supports the fLotation
of the bio m ass.
Since the bio m ass shaIL not be subjected to an electric fieLd du.-ing
the actual biological reaction ~hich can be carried out as an anaerobic or
aerobic reaction, and above all in order to use an optional method of pro-
lO ceed-ing for the subsequent reaction, as fer m entation, putrefaction, respiration
or a usual sLudge vessel, the proces~s accorcLing to the invention is effected
so that charging of the bio m ass with substrate and biologicaL reaction of the
biomass charged ~ith substrate is carried out in separate r,esse~s, wherein
tt1e m aterial charged :~ith substrate is separate(! ancl supplied to ~he reaction
15 space and the biomass i~ recycle~1 to the mi~ir1g space after reac ion in the
reaction space. By proceeding thus the most different biomasses can be ta',~en
into account. While for instance yeast liberates carbon dio.~ide ~ery fas-
and thereEore does not re(~r1ire special s~1pport by electlolytic decomposition
for fast an(1 co~1 plete ELotation in the f:irst stage oE charging of the micro-
20 bial materiaL ~ith the substrate, it is preterable to apply higher voltagesto activated .sludge ~ ich is bac31y Loatable in the ~irst st~ges of the reaction
in wlLic11 charging oE the biomass takes place in order to promote ~lotat,ion.
The electric tielcl can be app:Lied most preferE1b1y ~ithin the scope oE
the methoc1 accorc1in~ to the invention by arrar~ g eLectro~les i~1 a disLE~nce
25 fro m each other in the mi:cing space and/or f~lo-ation spacP, ~;hich ~listance
is 0,5 - 2 m m/V, pre'.e1aL1ly 1 in m~V in the ra11~,e o~ 2 - 30 ~ 3epen~1ing
on the voltage choser1. Coniplyil1g ~;ith these concLirior1s an optimum in re-
lation to the charging o~ the microhes ;;ith substrate a11d 3J~. relation to the
.`iol~aion 0~ ~lle C'lal`'e(~ )nla~; co~ be o1-se1ve~1. E~rei`er;~1~1y the p^ 1cC~iS
30 is effecier1 so that the ~listE1nce of e1ectrodes in t.1e 11Oi~aLion s?ace as com-
~2~
,
pared ~iLh th~ d;stance cE the el clrodes in the m~ lg space and/or thetermina1 voltage in the mL~;ing space as coml)ared with the termilaL voltagle
in the Elotation space are chosen greater
l~ithin the scope of this process degradable anodes i. e. of zLu m-irLiu m
5 or iron as ~eIL as anodes resistant to the electrolitic decomposition can
be usecl. Separation of the charged bio .n ass can be sustained by using Loccu-
lating agents. The stim ulating effect of the eLectric rieLd for the absorption
of substrate couLd be found both for anaerobic and for aerobic reactions.
Favourably the process according to the invenhon can be effected con
10 ~inuously wher~irl after mixing the substrate with microbial mateIial this
miYture is continuously suppLied to a irst space in ;hich charging of the nLi-
crobial materiaL ~ith the substrate occurs uslder the infLuence of the elect~ic
field In t;Lis first space also the ~:lotation is effected an l the biomas~s is
separated . The thus separated and charged bio m a~ss can be bio1Ogically con-
15 verted in a subsequent reacti.on space.
~ fter the b:iolog:ic1~. reac~ion the b:iomass can be recjcled after de-
gradation of the substrate witiLin the scope of the process according to the
inventiorl wherefrom a partic-Llally economicaL proceeding results.
In the folLowing the inventiol is made clear by ev~amples of embodiment~
r:xa m ple
Do nestic sewage with a biologiczl need oE o:~.gen BSB5 of 550 mgtl
was m:i.xed with acti.vated sLudge in the ratio l:l. The content of dlied matter
in the activated sl.l.ldge~ (returll sLu(i~ e ) ~ as S.0 g/l. ;~ i ter a sL;.n-ing and~or
25 mi.~ing time of appro:~O 2.5 min tile biomass was subjected to an eLec~r.ic
fieLd. The distance of the electrodes herein ~as 15 m m and a secondary
ter ninaL voltage of 16 V alld a current den~it~ of 0.5 .~/dm~ ;ere chosell.
The time of tloLd :in the electric field was ~) miil Subs~- ~uentl~ a concentraiioll
of 25 g dried mattel/kg of the f.loated sLu(ige and loading of t he res~duaL
30 ~ater BSB5 oE ~0 mg/1 ere found.
. ~.
~22¢3~3~`7
For the purposs-~ of co m parison the sa m S? test w as repeated t;ithout using
an eLectric fieLd. Starting fro m a miYture of sewage water and activated
sL~Idge in the ratio of l:l Witil a starting volume of 1 1 a sedimentation rate
of 0.24 m/h was found, corresponding to a time of hold ot 2 h. The sludge
5 volume was 330 .nl, ~herein the resid~aL load in the decanted liqtLid was
2lO mg/l, expressed in BSB5. From this comparison the esseni~lly lower load
of the residual ~ater and the essenti~lLy faster chargingof the biomass under
the infLuence of the electric field emerge clearly.
10 Example 2:
A sugar solution of the concentration 200 gtl ~ as m~Yed with a yeast
sLurry. The content of dried matter was 100 g~L .^~fter a time of stil~-ing
and/or miYing of 10 min an electric ield was app~is-~d, whers~in the slistance
of the electrodes was 5 m ~n and the term:Ln~l Yolt tge was chosen to be
15 bet~,een 4 and 5 V. l`he c~lrrent density .~as chosen between C).~ and ~ .~Jcdm2,
wherein the time of ilold in the electric fiekl :~tclS lû n~rt. B~ proceeding
thus, a s~lgar concentration of 163 g~l in tlle floated sLndge and a sugar
concentration of 37 g/l in the flotation water collld be lound.
For tne purpose of comparison the sar,~.e process w as repeated without
20 appLying an els-~ctric field, but witil addition o a considerable a mount of a
polyelectroLyte. Starting fro m ths-~ abo~ e slescribed m i~YtUl e of the sugar solution
witll tl~e yeast slul-ry, afts~r a(lsliLion of l )O g/~ oi polyelectrol~ te and a
tinte oE stisrirlg ansi/or mi:~ing o IQ rilin, a fLotatio~ th tne c~rbon c~ioY-ide
Cormed in tlle fcrmelltation ~as effscted for 13 Illin. Ln spits~ of the longer
25 llotal:ion time compars~s'i with the flotation in tne s~le~ ;liC fi~_ld a sugar cc,n-
centratiorl of only 13~3 g/l itl the floate~ l3-t~ s sugi!r conru~ntr;srion
oL only 62 g/L in the s'`locatioll w.3t~r :.~ers~ fourl~l.
A plllsatitl~ direct: rlllrellt with a p~lL~ ion Lre lus~llc; o,~ al pro:~. 100
llz has pIol~ed pastic Ll~arl~ slLitable~
DUI:iS~C~, thc~ tlot~ltioil l.c~ll sepIIr^sbl~ iloc.c~ r~ for l)fS;I 'lear~in :~ILtLt~s
a~
_c~_
very shor~ tim e. These aoccules h.-lve an exceILent charging. The structure
of the floccules is not necessarily convenient, though, for further biological
reaction in an activatecl sludge vessel and it can be advantageous to destroy
the structure of the floccules before the biological reaction by ventilation.
5 Such a ventilation of sludge can also be used to recycle a portion of the
sludge to the mixing vessel and thus to subject a sludge constant in relation
to biological dried matter to biological conversion. The residual waste water
from the Qotation process can usually be directly supplied to the main canal.
The separation of mixture, flotation and biological reaction allows a nu m ber
10 of recircuLations, wherein particularly the iu~terposecl sludge ventilation is
of great advantage for recycling a part of the sludge to the mixing vessel
or for destroying the structure of floccules to im prove subsequent conversion.
Parts of the ventilated sludge can also be subjected to a further sludge
treatment together with the sludge taken Erom the preliminary or a secondary
15 sedimentatioll tank by which a sim ple adaptation to the e:cisting plant capacity
is m ade possible.
