- Email: [email protected]
Membrane bioreactors in wastewater treatment
Membrane bioreactors are increasitiqlv provinB their worth as a viable water purification and wastewater treatment option. Thomas A . Peters} , Ralph Giinther2, and Klaus Vossenka ul 3 describe a ne w membrane bioreactor system that is findinB use in the treatment wastewater on ships and in sewaBe treatment.
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rowing co nce r n in recen t years around the world regarding environmental pollution, th e anticipation of tighten ed glohal waste discharge regulations , and the need for reuse of water are the main driving for ces for th e development of techn olo gie s for improved wastewater purificati on . Th e membrane hioreactor (MBR ) is on e suc h technology that is findin g its way from th e laboratory to full-scale appli cation. Only a few years ago, membrane bior eactors wer e virtually unh eard o f, now a few co mme rc ially viable syste ms ar e findin g uses in wastewater tr eatment and look set to take the indu stry by sto r m in th e fut ure . Th e MBR uses ultrafiltrat ion o r mi crofiltrati on membranes for th e co m plete ret ention of a biom ass. T his leads to a high biom ass co nce nt ration in th e react or and a highly efficient biol og ical reacti on process wi th redu ced sludge p rodu cti on , insen sitivity to high load s o f co ntam inants and chang ing peak load s, as well as co nt ro lled safe se paratio n of bact eria, viruses and parasit es wh ere ultrafiltrati on membranes are used . Further ad vantages are sma ll foo t -pri nt and eco no m ic ope ra tio n th at allo ws for high filtrate flux es with low ene rgy demand even for sm all decen tr aliz ed plants. In thi s article an examp le is pr esented of th e development of thi s kind o f pl ant for wast ew at er tr eatm ent on ships and for an ap plication in se\\;age tre atme nt.
Wastewater purification on ships Rising cos ts for wast e handling o n ships and in por ts is a majo r driving force fo r th e development of so lutio ns th at co uld co ntr ibute to a "gree n ship" co ncept o r an "en vironmentall y so und" ship . T he high am ount of g rey water discharged overbo ard du e to incr eased numbers of
permeate dralna.e tube permeate flow channel
Figure 1: FM (flat membrane) module. Source: ROCHEM UF-Systeme GmbH
18
JanuaryIFebruary 2000
passen gers ran gin g from 1000 to 30 00 on cr uise ships and o n fer ries or th e e ffiue nt fro m differ ent so urces o n ships in th e fisher y and cargo bu sin ess causes severe damage to th e enviro nme nt. In mo st cases, th e efll ue nt is st ill not tr eat ed o r th er e is usu ally a large rate of chlor ine used to di sinfect the e fflue nt before passing it overboard. In ports and in ar eas with low eco logi cal tol erance th e wastewater has to be sto re d o n board . That requires a lot of
Filtration + Separation
VENT LINE PROCESS AIR
space and wcight that cannot be ignored . If thi s accumulated amount of wast ewater is to be purified immediately on board for discharge purposes it is necessary to have a scwage plant co nta ining a sm all plant volume . Th e MBR, with its co mbinat io n of bioreact or and ultrafilt ration system , is a viable o ption for thi s type of appli cation enabling th e o pe rato r to m eet th e required
FILTRATE
discharge limits and to reu se th e purified water again for techni cal appli cati on s. Thi s also allows for a co ntrolled safe separation of bact eri a, viru ses and parasit es. As a useful co m par ison, Table I lists th e di fferen t co ntam inants and th e ability of th e main pro cesses used in wat er treatm ent to redu ce th em .
SLUDGE
Rochem UF- yste me GmbH , Germany, toge ther with a number of ren owned institutions, have develop ed a purifi cation
Figure 2: Flow schematic membrane bioreactor Bio-Filt 4D •
plant for th is purpose based on th e co mbination of a bioreactor adapte d to th e o per-
FM-mod u le for ult r afiltrati on w ith a
cle anability and high availability, as well
ating co nd itio ns o n a ship with a flat m em -
high den sit y bio m ass r eact o r. Thi s
brane ultrafiltration syste m (FM-mo d ule Figure 1). Th e same module has also been used in tr ials on a sewage tr eatm ent plant in
mo d ule has been devel op ed speci fically for th e separation of bact eri a, viru ses
as, high filtrat e flux es with low ene rgy demand .
order to op timize ene rgy demand .
Th e pat ented co ncept of a m embrane
and part icles in th e sub -micro n range
cushio n stac k with a co m p letely o pe n feed channel (no spacers o r suppo r t plat es) in co m binat io n with str aight -
fro m wa te r w ith high fou ling pot ential and is well sui te d for use in MBR applicatio ns. T he co m bination of o pe n
The FM-module System
through feed flow co m bines th e
The M BR syste m (Bio-Fi lt®) devel op ed at Roch em co m bine its flat m em bran e
channe l co nst r uct ion and narrow ga p
adv an tages of both th e co m mo n tubular
techno logy allo ws for exceptio na l
and di sc-tube m odule syste ms . Th e
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destruc io of contaminan 5 = concentration or selective separa 'on of can aminants
()l MAP p,.dpll Icr , 01 101
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W
Table 1: Suitability of water treatment processes for the reduction of different contaminants.
Filtration + Separation
JanuaryIFebruary 2000
19
Figure 3: Membrane bioreactor Bio-Filt~ . Source: ROCHEM UF Systeme GmbH
vertical plac em ent o f th e modul es in co mbination with a feedside air lwater flushing allows m embrane cleaning and a stable op eration for long periods without frequent use of chemical cleaning agents. In addition th e wid e spectrum of co m merc ially available flat she et m embranes means that optimal sel ection of a membrane for each individual application is possible. Th e pri nciple eleme nts of this m odule syste m are the membrane cushions. Eac h cushio n consists of two rectangular m embranes, two int ernal permeat e spacers , and an incorporated carrier plat e , that are welded ultrasonicly on th e outer edges. Each membrane element consists of a se ries of th ese membrane cushions stacked one on top of the other with a space that is supported by two pins. These cushions are enclosed in two halves of a shell . In addi tion to fixing the membrane stacks, the guide pi ns, in combination w ith co rresponding bore holes in the half-shell elements, carry off the perm eat e . Ten of these membrane cushio n elements are co nnected in se ries and installed in a pr essure tub e to produce the
20
JanuarylFebruary 2000
FM-module. By connecting the mem bran e cushion elements in series, performancelower ing flow deflections can be eliminated . This also brings about a reduction in en ergy demand du e to th e fact that th e walls of th e flat channels between th e individual membrane cushions are form ed only by smoo th membranes and co nseque ntly (since separati ng knobs or space rs ar e avoid ed ) losses in Ilow pr essure are reduced to a minimum. Th e Roch em FMmodule technology has been pr oven over se veral years in many different are as o f wastewat er
purificati on , wh ereb y th e easy m odifi cati on o f th e free path feed side (d istance between m embran e cushions) mak es possibl e th e applicatio n of thi s module in a wide ran ge o f suspe nde d solid co nce ntrations . Thi s includes high solid -m atter conte nt or high biomass co nce nt rations suc h as th ose found in biol ogical wastewater treatment.
Pilot Plant for Wastewater Purification on Ships Th e design cr ite r ia for a syste m to purify wastewater on board a ship was to minimize space requirem ents, maximize
feed to syste m recycle stre am to biorcactor recycle stream to UF modules purifie d water feed pressure transmembrane pressure temperature in th e rea ct or MWCO membrane surface ret ention tim e
throughput, and mechanically blo ck the discharge of organic matter and mic roorganisms. The pilot plant utilizes a high density biomass reactor and a nonfouling ultrafiltration system to me et the criteria. In th e actual plant th e wastewater is fed into the rea ctor chambe r, designed as a modular system, togeth er with th e process air and transported through th e modules in a cro ss-flow operation mode (Figure 2) . The biomass retained by th e membranes is fed back to th e reactor tog ether with th e partial stream circulating on th e feed wat er side of th e membranes. Th e filtrat e Ilowing through th e membranes is pure and can be discharged. Co ntro l variabl es for the co nce ntration o f th e biomass in th e reactor are th e filtrat e Ilux of th e ultrafiltration membranes and th e amount o f co nce ntrated slud ge disch arged fro m th e react or. Th e ope rating paramet ers - like hydrauli c ret ention tim e, oxyge n d em and , recir culation volume, o pe rati ng pressure , sludge discharge and ene rgy demand - ar e co ntro lled and adapted to th e techn olo gical needs. Table 2 indi cat es so me dat a fro m th e pilot plant for a defin ed ope rating situation. Th e biot echn olog ical details refer to an am ount of total solids (1'5) of 18 gI l.
Exper iments At first it was necessar y to co ntro l th e pilot plant to a co ntinuo us ope ration and to obse rve th e most important paramet er s. In orde r to m ake su re that at any tim e th er e was eno ugh oxyge n for microbiological decompositi on th e 1'5 in th e feed strea m was kept co nsta nt at 7 gI l for 40 days and th en at 7 .5 gl I for another 20 davs, In a stainless ste el reactor with an incr eased air supply during th e seco nd phase of th e trial, th e micr oorganism s
.
250ll h 4 m ' /h
40 m'/h 225 .5 IIh 3 bar 2.7 bar 30° C 50 kDalton 10.71 m? 4.98 h
Table 2: Operating data of pilot plant
Filtration + Separation
grew to a value of about 28 gIl in 10 days and were kept constant at this level for 30 days. Afterwards the plant has been working in a continuous op erati on in the range of 15 to 20 gIlTS .
Results Th e g ro wt h in th e microorganism s star te d imm ediately after th e star t up of th e plant in Augu st 1998, reachin g th e level of 7 gI l after 10 days. Th e T O C in th e bioreact or g re w at the same tim e to a value of 4000 mgll. During th e o perat ion o n a level of 7 and 7.5 gI l th e T O C came down to values between 2500 and 3000 mgll. With a co nsta nt amount of to ta l so lids the TOC also rem ained co nsta nt with th e same type of sewage after an init ial g row th and no adjustment. After insta llation of th e second bioreactor the values for the TO C followed the values for th e TS with th e growth in the microo rganisms, reachin g values in the range of 8000 mgll at a T S of
28 gIl. Afte r the whole plant worked continuo usly the TO C values of the permeate came almos t to a consta nt point. In general it is normal to achieve values of 20 to 40 mgl l TO C in the perm eate. Th at shows that the wastew ater can be purified adeq uately also wh en th e density of the microorganisms, ex presse d by th e TS, was much highe r (28 gI l) than in the first 8 weeks of ope ration (7 to 7 .5 gI l). In sum me r 1999 , the navy of a European co untry placed an order for five MBR Bio-Filt units highlighting th e increasing uptake of th ese syste ms around the world .
Pilot Plant on Sewage Treatment Plant A pilot plant based on the design , conce pt and operating procedure of the membrane bioreactor Bio -Filt has been in operation since October 1998 on a sewage treatm ent plant in Ge r many.T he main emphasis of this long te r m tri al is o n th e o ptim izatio n of the plant ope ration in term s of decreasi ng the energy dem and and increasing th e filtr ate flux und er real on site co nd itions. Th e plant is equipped with tw o indep end ent modul e blocks, one with 5 FM-mo dulcs with a total of 40 m? install ed membrane area. Th e other with one modul e w ith a transpar ent pr essure vessel and half shells for th e in-situ visual obser vation and contro l of th e changes in
Filtration + Separation
filtrate flux total solids transmembrane pressur e differ en ce air co nsumption total ene rgy consum ption (sum of energy co nsum ption for PLC, feed cross -flow and air injecti on )
40 I m 2 / h
16 gIl 0 .2 - 0 .4 bar 0 .3 - 0 .5 m 3N/m 2 m <"lJlh ran r
1.0 - 1.5kWh /m 3
Table 3: Operating data of the pilot plant OIMBS
th e membrane elem ents and on the membrane surface for the alteration of process par amet er s. T he plant is o pe rated in th e advan ced scm i-cross flow mod e with a significantl y low specific ene rgy dem and . Some o pe rat ing data are show n in Table 3. Average values for the biol ogi cal degradat ion are th e re duc tion of CO D fro m 365 to 10 mg 0/ 1, BOD fro m 115 to 2 mg 0/1and NH4 from 22 to
< I. O ne of the reason s for the high degradation ratio is the improved efficiency of the use of oxyge n need ed for the biod egradation . Th is result s fro m air force d th rou gh the flat channels between th e membrane cushions. As no channe ling or air losses can occ ur, the air injected int o the syste m is in ver y int en sive contact with th e water and the highest possible yield for th e transfer of oxyge n from the air int o th e water is achieved.
References Geissler S., Vossenkaul K., MelinTh. , Ohle P., Brand s E., Dohmann M. ( 1999) Erfahrungsberi cht aus dem Betrieb ein er Versuchsanlage zum Th ema "O ptim ier te Int egration der Membrantechnik in di e biologische Stufe kommunal er Klaranlagcn" . DECHEMAJahr estagungen •99, Wi esbad en, 27. -2 9. 04 . 1999 Guttau S., Gunther R. ( 1999) Abwasseraulbercitung mit Bioreaktor und Ultrafiltration. SPEKTRUM, Techni sche Llnivcrsitat HamburgHarburg, Sommer sem ent er 1999 Pet er s Th. ( 1998) Impro ved Water and Waste Water Purifi cation with th e DTUF Modul e System. UTA T ECH NOLOGY & E V1RO ME T, International Ed ition , 4 ( 1.998)
Conclusions The membrane bioreac to r Bio-Filt® based on the FM-mod ule for ult rafiltration and a bioreactor of modul ar design manufact ured as mu lti-ta nk co nstruction (Figure 3) was develop ed for the imp roved purification of wastewater that can be easily adap ted to differe nt applications. Th e ope n channel const r uctio n and nar row gap technology realized in the FM-mod ule and the ver y efficie nt rin sing and clean ing me tho d develop ed for this modul e are the basis for th e reliable function of the waste water purifi cation pr ocess and the ope rating safety of thi s combination of membrane filtration and bior eactor techn ology. High filtrat e fluxes, low energy demand and high availabilit y of thi s techn ological approach lead to an eco no mic waste water purifi cation pro cess with small installati on space that can help to reduce the negative impa ct to the enviro nme nt of waste water discharged from ships .
Acknowledgements Part of this paper was presented at th e MBR 2 co nfere nce , Cranfield University, 2nd Jun e 1999 . MBR2 proceedin gs (priced £.50 per set incl. p&p) may be obtained from Lesley Roff on tel: + 44 (0) 1234 754176 or E-mail : a.l.roff@ cranfield .ac.uk
Contact I Dr.-Ing. Th oma s Pet er s, Con sulting for Membrane Technology and Enviro nme ntal Enginee ring, Broichstrasse 91 , 41462 euss, Germany. tel: + 49 2 1 3 1 22 896 3; fax: + 49 21 31 54 5040.
2 Arh eitsb erei ch Apparatebau, Techni sche Llnivcrsitat Hamburg-Harburg, Germany.
l lnstitut fur Vcrfahrcnstcchnik, Rheinisch -Westfalisch e Technische Hochs chule Aachen, Germany.
JanuarylFebruary 2000
21
if
r
• I
rowing co nce r n in recen t years around the world regarding environmental pollution, th e anticipation of tighten ed glohal waste discharge regulations , and the need for reuse of water are the main driving for ces for th e development of techn olo gie s for improved wastewater purificati on . Th e membrane hioreactor (MBR ) is on e suc h technology that is findin g its way from th e laboratory to full-scale appli cation. Only a few years ago, membrane bior eactors wer e virtually unh eard o f, now a few co mme rc ially viable syste ms ar e findin g uses in wastewater tr eatment and look set to take the indu stry by sto r m in th e fut ure . Th e MBR uses ultrafiltrat ion o r mi crofiltrati on membranes for th e co m plete ret ention of a biom ass. T his leads to a high biom ass co nce nt ration in th e react or and a highly efficient biol og ical reacti on process wi th redu ced sludge p rodu cti on , insen sitivity to high load s o f co ntam inants and chang ing peak load s, as well as co nt ro lled safe se paratio n of bact eria, viruses and parasit es wh ere ultrafiltrati on membranes are used . Further ad vantages are sma ll foo t -pri nt and eco no m ic ope ra tio n th at allo ws for high filtrate flux es with low ene rgy demand even for sm all decen tr aliz ed plants. In thi s article an examp le is pr esented of th e development of thi s kind o f pl ant for wast ew at er tr eatm ent on ships and for an ap plication in se\\;age tre atme nt.
Wastewater purification on ships Rising cos ts for wast e handling o n ships and in por ts is a majo r driving force fo r th e development of so lutio ns th at co uld co ntr ibute to a "gree n ship" co ncept o r an "en vironmentall y so und" ship . T he high am ount of g rey water discharged overbo ard du e to incr eased numbers of
permeate dralna.e tube permeate flow channel
Figure 1: FM (flat membrane) module. Source: ROCHEM UF-Systeme GmbH
18
JanuaryIFebruary 2000
passen gers ran gin g from 1000 to 30 00 on cr uise ships and o n fer ries or th e e ffiue nt fro m differ ent so urces o n ships in th e fisher y and cargo bu sin ess causes severe damage to th e enviro nme nt. In mo st cases, th e efll ue nt is st ill not tr eat ed o r th er e is usu ally a large rate of chlor ine used to di sinfect the e fflue nt before passing it overboard. In ports and in ar eas with low eco logi cal tol erance th e wastewater has to be sto re d o n board . That requires a lot of
Filtration + Separation
VENT LINE PROCESS AIR
space and wcight that cannot be ignored . If thi s accumulated amount of wast ewater is to be purified immediately on board for discharge purposes it is necessary to have a scwage plant co nta ining a sm all plant volume . Th e MBR, with its co mbinat io n of bioreact or and ultrafilt ration system , is a viable o ption for thi s type of appli cation enabling th e o pe rato r to m eet th e required
FILTRATE
discharge limits and to reu se th e purified water again for techni cal appli cati on s. Thi s also allows for a co ntrolled safe separation of bact eri a, viru ses and parasit es. As a useful co m par ison, Table I lists th e di fferen t co ntam inants and th e ability of th e main pro cesses used in wat er treatm ent to redu ce th em .
SLUDGE
Rochem UF- yste me GmbH , Germany, toge ther with a number of ren owned institutions, have develop ed a purifi cation
Figure 2: Flow schematic membrane bioreactor Bio-Filt 4D •
plant for th is purpose based on th e co mbination of a bioreactor adapte d to th e o per-
FM-mod u le for ult r afiltrati on w ith a
cle anability and high availability, as well
ating co nd itio ns o n a ship with a flat m em -
high den sit y bio m ass r eact o r. Thi s
brane ultrafiltration syste m (FM-mo d ule Figure 1). Th e same module has also been used in tr ials on a sewage tr eatm ent plant in
mo d ule has been devel op ed speci fically for th e separation of bact eri a, viru ses
as, high filtrat e flux es with low ene rgy demand .
order to op timize ene rgy demand .
Th e pat ented co ncept of a m embrane
and part icles in th e sub -micro n range
cushio n stac k with a co m p letely o pe n feed channel (no spacers o r suppo r t plat es) in co m binat io n with str aight -
fro m wa te r w ith high fou ling pot ential and is well sui te d for use in MBR applicatio ns. T he co m bination of o pe n
The FM-module System
through feed flow co m bines th e
The M BR syste m (Bio-Fi lt®) devel op ed at Roch em co m bine its flat m em bran e
channe l co nst r uct ion and narrow ga p
adv an tages of both th e co m mo n tubular
techno logy allo ws for exceptio na l
and di sc-tube m odule syste ms . Th e
I:S::·~~·
ht
COD
p. oc.eu
:..:. blolosl al
inraor.·. .. ladsabltll O'ltAC b d h Ol:-
.......... ilcr.
tUb
. .
S
S
hal
eo polytydi<
• hvdIC.·
· ·
.
·
0
+
+
+
+
+
+
+
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-
· · ·
· ·
I, . . . . .
+
0
cho lui oxidation
.
+
0
+
adso,pll
0
0
.
+
0
.
-
+
+
+
+ hI
0
+
+
+
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-
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+
+
+
2.4
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+
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I
2.6
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..
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:1.1 . redlo·
:1.7
...halll·
• Illatien (....ltd)
:1.8
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...-10
0'
. -
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+ = suitable not suitable o
= partially suitable
1.1' 1.2 2.1- 2.11
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-
PO' 1100
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hIop.' Ir II 10" P (21 cper ir al t1 hpit
destruc io of contaminan 5 = concentration or selective separa 'on of can aminants
()l MAP p,.dpll Icr , 01 101
,,,Is.-.'
W
Table 1: Suitability of water treatment processes for the reduction of different contaminants.
Filtration + Separation
JanuaryIFebruary 2000
19
Figure 3: Membrane bioreactor Bio-Filt~ . Source: ROCHEM UF Systeme GmbH
vertical plac em ent o f th e modul es in co mbination with a feedside air lwater flushing allows m embrane cleaning and a stable op eration for long periods without frequent use of chemical cleaning agents. In addition th e wid e spectrum of co m merc ially available flat she et m embranes means that optimal sel ection of a membrane for each individual application is possible. Th e pri nciple eleme nts of this m odule syste m are the membrane cushions. Eac h cushio n consists of two rectangular m embranes, two int ernal permeat e spacers , and an incorporated carrier plat e , that are welded ultrasonicly on th e outer edges. Each membrane element consists of a se ries of th ese membrane cushions stacked one on top of the other with a space that is supported by two pins. These cushions are enclosed in two halves of a shell . In addi tion to fixing the membrane stacks, the guide pi ns, in combination w ith co rresponding bore holes in the half-shell elements, carry off the perm eat e . Ten of these membrane cushio n elements are co nnected in se ries and installed in a pr essure tub e to produce the
20
JanuarylFebruary 2000
FM-module. By connecting the mem bran e cushion elements in series, performancelower ing flow deflections can be eliminated . This also brings about a reduction in en ergy demand du e to th e fact that th e walls of th e flat channels between th e individual membrane cushions are form ed only by smoo th membranes and co nseque ntly (since separati ng knobs or space rs ar e avoid ed ) losses in Ilow pr essure are reduced to a minimum. Th e Roch em FMmodule technology has been pr oven over se veral years in many different are as o f wastewat er
purificati on , wh ereb y th e easy m odifi cati on o f th e free path feed side (d istance between m embran e cushions) mak es possibl e th e applicatio n of thi s module in a wide ran ge o f suspe nde d solid co nce ntrations . Thi s includes high solid -m atter conte nt or high biomass co nce nt rations suc h as th ose found in biol ogical wastewater treatment.
Pilot Plant for Wastewater Purification on Ships Th e design cr ite r ia for a syste m to purify wastewater on board a ship was to minimize space requirem ents, maximize
feed to syste m recycle stre am to biorcactor recycle stream to UF modules purifie d water feed pressure transmembrane pressure temperature in th e rea ct or MWCO membrane surface ret ention tim e
throughput, and mechanically blo ck the discharge of organic matter and mic roorganisms. The pilot plant utilizes a high density biomass reactor and a nonfouling ultrafiltration system to me et the criteria. In th e actual plant th e wastewater is fed into the rea ctor chambe r, designed as a modular system, togeth er with th e process air and transported through th e modules in a cro ss-flow operation mode (Figure 2) . The biomass retained by th e membranes is fed back to th e reactor tog ether with th e partial stream circulating on th e feed wat er side of th e membranes. Th e filtrat e Ilowing through th e membranes is pure and can be discharged. Co ntro l variabl es for the co nce ntration o f th e biomass in th e reactor are th e filtrat e Ilux of th e ultrafiltration membranes and th e amount o f co nce ntrated slud ge disch arged fro m th e react or. Th e ope rating paramet ers - like hydrauli c ret ention tim e, oxyge n d em and , recir culation volume, o pe rati ng pressure , sludge discharge and ene rgy demand - ar e co ntro lled and adapted to th e techn olo gical needs. Table 2 indi cat es so me dat a fro m th e pilot plant for a defin ed ope rating situation. Th e biot echn olog ical details refer to an am ount of total solids (1'5) of 18 gI l.
Exper iments At first it was necessar y to co ntro l th e pilot plant to a co ntinuo us ope ration and to obse rve th e most important paramet er s. In orde r to m ake su re that at any tim e th er e was eno ugh oxyge n for microbiological decompositi on th e 1'5 in th e feed strea m was kept co nsta nt at 7 gI l for 40 days and th en at 7 .5 gl I for another 20 davs, In a stainless ste el reactor with an incr eased air supply during th e seco nd phase of th e trial, th e micr oorganism s
.
250ll h 4 m ' /h
40 m'/h 225 .5 IIh 3 bar 2.7 bar 30° C 50 kDalton 10.71 m? 4.98 h
Table 2: Operating data of pilot plant
Filtration + Separation
grew to a value of about 28 gIl in 10 days and were kept constant at this level for 30 days. Afterwards the plant has been working in a continuous op erati on in the range of 15 to 20 gIlTS .
Results Th e g ro wt h in th e microorganism s star te d imm ediately after th e star t up of th e plant in Augu st 1998, reachin g th e level of 7 gI l after 10 days. Th e T O C in th e bioreact or g re w at the same tim e to a value of 4000 mgll. During th e o perat ion o n a level of 7 and 7.5 gI l th e T O C came down to values between 2500 and 3000 mgll. With a co nsta nt amount of to ta l so lids the TOC also rem ained co nsta nt with th e same type of sewage after an init ial g row th and no adjustment. After insta llation of th e second bioreactor the values for the TO C followed the values for th e TS with th e growth in the microo rganisms, reachin g values in the range of 8000 mgll at a T S of
28 gIl. Afte r the whole plant worked continuo usly the TO C values of the permeate came almos t to a consta nt point. In general it is normal to achieve values of 20 to 40 mgl l TO C in the perm eate. Th at shows that the wastew ater can be purified adeq uately also wh en th e density of the microorganisms, ex presse d by th e TS, was much highe r (28 gI l) than in the first 8 weeks of ope ration (7 to 7 .5 gI l). In sum me r 1999 , the navy of a European co untry placed an order for five MBR Bio-Filt units highlighting th e increasing uptake of th ese syste ms around the world .
Pilot Plant on Sewage Treatment Plant A pilot plant based on the design , conce pt and operating procedure of the membrane bioreactor Bio -Filt has been in operation since October 1998 on a sewage treatm ent plant in Ge r many.T he main emphasis of this long te r m tri al is o n th e o ptim izatio n of the plant ope ration in term s of decreasi ng the energy dem and and increasing th e filtr ate flux und er real on site co nd itions. Th e plant is equipped with tw o indep end ent modul e blocks, one with 5 FM-mo dulcs with a total of 40 m? install ed membrane area. Th e other with one modul e w ith a transpar ent pr essure vessel and half shells for th e in-situ visual obser vation and contro l of th e changes in
Filtration + Separation
filtrate flux total solids transmembrane pressur e differ en ce air co nsumption total ene rgy consum ption (sum of energy co nsum ption for PLC, feed cross -flow and air injecti on )
40 I m 2 / h
16 gIl 0 .2 - 0 .4 bar 0 .3 - 0 .5 m 3N/m 2 m <"lJlh ran r
1.0 - 1.5kWh /m 3
Table 3: Operating data of the pilot plant OIMBS
th e membrane elem ents and on the membrane surface for the alteration of process par amet er s. T he plant is o pe rated in th e advan ced scm i-cross flow mod e with a significantl y low specific ene rgy dem and . Some o pe rat ing data are show n in Table 3. Average values for the biol ogi cal degradat ion are th e re duc tion of CO D fro m 365 to 10 mg 0/ 1, BOD fro m 115 to 2 mg 0/1and NH4 from 22 to
< I. O ne of the reason s for the high degradation ratio is the improved efficiency of the use of oxyge n need ed for the biod egradation . Th is result s fro m air force d th rou gh the flat channels between th e membrane cushions. As no channe ling or air losses can occ ur, the air injected int o the syste m is in ver y int en sive contact with th e water and the highest possible yield for th e transfer of oxyge n from the air int o th e water is achieved.
References Geissler S., Vossenkaul K., MelinTh. , Ohle P., Brand s E., Dohmann M. ( 1999) Erfahrungsberi cht aus dem Betrieb ein er Versuchsanlage zum Th ema "O ptim ier te Int egration der Membrantechnik in di e biologische Stufe kommunal er Klaranlagcn" . DECHEMAJahr estagungen •99, Wi esbad en, 27. -2 9. 04 . 1999 Guttau S., Gunther R. ( 1999) Abwasseraulbercitung mit Bioreaktor und Ultrafiltration. SPEKTRUM, Techni sche Llnivcrsitat HamburgHarburg, Sommer sem ent er 1999 Pet er s Th. ( 1998) Impro ved Water and Waste Water Purifi cation with th e DTUF Modul e System. UTA T ECH NOLOGY & E V1RO ME T, International Ed ition , 4 ( 1.998)
Conclusions The membrane bioreac to r Bio-Filt® based on the FM-mod ule for ult rafiltration and a bioreactor of modul ar design manufact ured as mu lti-ta nk co nstruction (Figure 3) was develop ed for the imp roved purification of wastewater that can be easily adap ted to differe nt applications. Th e ope n channel const r uctio n and nar row gap technology realized in the FM-mod ule and the ver y efficie nt rin sing and clean ing me tho d develop ed for this modul e are the basis for th e reliable function of the waste water purifi cation pr ocess and the ope rating safety of thi s combination of membrane filtration and bior eactor techn ology. High filtrat e fluxes, low energy demand and high availabilit y of thi s techn ological approach lead to an eco no mic waste water purifi cation pro cess with small installati on space that can help to reduce the negative impa ct to the enviro nme nt of waste water discharged from ships .
Acknowledgements Part of this paper was presented at th e MBR 2 co nfere nce , Cranfield University, 2nd Jun e 1999 . MBR2 proceedin gs (priced £.50 per set incl. p&p) may be obtained from Lesley Roff on tel: + 44 (0) 1234 754176 or E-mail : a.l.roff@ cranfield .ac.uk
Contact I Dr.-Ing. Th oma s Pet er s, Con sulting for Membrane Technology and Enviro nme ntal Enginee ring, Broichstrasse 91 , 41462 euss, Germany. tel: + 49 2 1 3 1 22 896 3; fax: + 49 21 31 54 5040.
2 Arh eitsb erei ch Apparatebau, Techni sche Llnivcrsitat Hamburg-Harburg, Germany.
l lnstitut fur Vcrfahrcnstcchnik, Rheinisch -Westfalisch e Technische Hochs chule Aachen, Germany.
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