This document discusses research into developing a sustainable superabsorbent polymer (SAP) from alginate-like exopolysaccharide (ALE) produced in the NEREDA wastewater treatment process. ALE is a natural hydrogel-type material that is a byproduct of the NEREDA process. Research shows ALE has properties suitable for use in SAPs, including absorbing up to 40 times its weight in water. The NEREDA process produces sludge containing up to 20% ALE, which could potentially be recovered for use in sustainable SAP production. Further research is needed to develop ALE-derived SAPs that meet industry standards for absorption levels and cleanliness for use in hygiene products.
1. Naturally Sourced Sustainable Superabsorbent “Alginate-like Exopolysaccharide” (ALE)
from the NEREDA Waste Water Process – a brief summary
In the contextof developingatrulyrealistic totally naturallysourced totallysustainable
superabsorbentpolymer(SAP),adramaticmove towards thisfully sustainable productcouldcome
fromsome recentworkin the NetherlandsatTU Delftinconnectionwithaerobicgranularsludge in
sewage treatmentbythe NEREDA waste waterprocess. NEREDA isa sustainable andcost-effective
process requiringaquarterof the area of conventional activatedsludgeinstallationsandthisprocess
can reduce up to 50% on energy-costs.Thisaward-winningtechnologywasinventedbythe Delft
Universityof Technologyinthe Netherlandsand developedinaunique public-private partnership
betweenthe University,the DutchFoundationforAppliedWaterResearch(STOWA) andthe Dutch
Water AuthoritiesandRoyal Haskoning DHV.(1) Thissewage treatmentsystem providesa
commodityhighlycost-effectivesource of alginate-likeexopolysaccharide (ALE) materialsfrom
sewage treatment,thesehydrogel type materialsbeinganeconomiccommodity startingpointfor
newtotallysustainable SAPs. ResearchbyYuemei LinfromDelftUniversityof Technology showed
that the substance responsible forthe granulargrowthof the sludge bacteriaisanalginate polymer
(ALE).Consistingprimarilyof sugar,thisalginate polymerbindsextremelystronglywithwater(upto
40 timesitsownweight),canthickenorgel liquidsandformsabasisfor coatings. These properties
wouldbe available atmuchlowerprice levels comparedtoregularseaweedsourcedalginates and
wouldfeature “awaste product”to produce ALE and hence withresearch,atotallynew sustainable
and environmentallyresponsible alginate derivedSAP. The sludge containsupto20 percentof this
ALE polymerwhich,inprinciple,canbe recoveredusingnew technologiesbeingdeveloped. (2) (3)
As alreadydescribedinmyarticlesinconnectionwithSAPsinNonwovensReportInternational, SAPs
are usedextensivelyinbabydiapers,adultincontinence productsandinfemininecare items,the
majorityof existingSAPsbeingbasedonpolyacrylate chemistry. Resultsof awhole hostof testsand
assessmentswithinthe AHPindustryshow thatfromaperformance perspective,anyalginate SAP
2. productshouldideallybe granularandabsorbupto the regionof upto 40x itsweightof 0.9% saline
underload(AUL).The granulesneedtoexhibitgoodgel strength,rapidfluiduptakepropertiesand
retentionof fluidsunderload coupledwithexcellentprocessabilityinconvertingequipment (andbe
amenable tonewAHPrecyclingtechnologies).Formore informationonthe industrystandardtest
methodsforSAPsrefertothe EDANA (EuropeanDisposablesandNonwovensAssociation) website
(4).
Researchhasbeenperformedbyseveral groupsof researchersintoalginatesinconnectionwith
superabsorbents.Examplesinclude apaperbyYoshimuraetal “Alginate-basedsuperabsorbent
hydrogelscomposedof carboxylicacid-amine interaction:preparationandcharacterization”which
describesthat“the highestwaterabsorbencywasobtainedwiththe sample forchitosanfeedratio
to sodiumalginate of 100 mol%,reaching410 g/g inpure water,100 g/g in0.9 % solution,and80
g/g in3.5 % NaCl solution.Hydrogelsinthe presentstudyexhibitedgoodbiodegradability
irrespectiveof amine compound.” (5) A paperby Marandi etal “Synthesisof analginate–
poly(sodiumacrylate-co-acrylamide) superabsorbenthydrogel withlow saltsensitivityandhighpH
sensitivity”describesthe synthesisandswellingbehaviourof asuperabsorbinghydrogel basedon
sodiumalginate (NaAlg) andpolyacrylonitrile (PAN).The effectsof reactionvariableswere
systematicallyoptimizedtoachieve ahydrogel withaswellingcapacityashighas possible.Under
the optimizedconditionsconcluded,the maximumcapacityof swellingindistilledwaterwas610
g/g. The absorbencyof the synthesizedhydrogelswasalsomeasuredinvarioussaltsolutions.The
swellingratiosdecreasedwithanincrease inthe ionicstrengthof the saltsolutions.Inaddition,the
swellingcapacitywasdeterminedinsolutionswithpHsrangingfrom1 to 13. The Alg–poly(NaAA-co-
AAm) hydrogel exhibitedpHresponsiveness,soaswelling–deswellingpulsatilebehaviourwas
recordedat pHs 2 and 8. Althoughnotcited,thispapercouldleadtosome triggeringpropensity
suitable forresponsibleSAPdisposal afteruse andalsoparadoxicallyasa route to ingredients to
yieldtriggereddispersibilityinnonwovenmaterialsallowingfortheirflushabilityinhygiene products
afteruse,the alginate beingconsideredasanonwovenchemical bondingmaterial (6). pHsensitivity
3. isalso reportedby Sadeghi andSoleimaniin “Synthesisof pH-SensitiveHydrogel BasedonStarch-
Polyacrylate Superabsorbent”(7)
Lookingmore generally,BODSAPsare beingresearchedandcompaniesare lookingtoexpand this
activity. (8) (9) (10). Polyacrylate-like SAPabsorbencylevelsare beingaimedforbutthisworkisstill
ongoing.
Importantly, foranypotential SAPapplications, the cleanlinessof NEREDA sourced ALEalginates
needstobe considered andisbeingaddressed –evenif onlytoovercome outsidepublicperceptions
as these alginatescome fromthe NEREDA waste watertreatmentprocess. Some additionalpersonal
thoughtsintothis:
Lowerlevelsof cleanlinesssufficienttocleanthe biopolymers“in line” to bioburdenlevelstowell
belowthe 100 cfu’s/mgleveldemandedforraw materials priortoconversionintononwovenfabrics
by producersinthe US and elsewhere needtobe consideredsoI’ve lookedat“cheaperless
aggressive options”fromionizingradiation –perhapsgoingfor“drydisinfection”(see more onthis
althoughanalbeitprobably expensive wayatthe FraunhoferInstitute –see page 2 “Disinfection
and pathogendestruction”)asopposedtofull sterilizationtogetthe bioburdenlevelstothese levels
(11). I’ve observedsome routesbetweensimplecoronatreatmentsystems(sometimesreferredto
as air plasma) whichhave beenaroundformanyyears – mostapparentlyusedtorenderPEfilms
intoa form where theyacceptadhesivesfordiaperproductionandverysimple/basicEBeam
systemstoyield“disinfection”.Cansucha system worktogive us the low bioburdenlevelsneeded?
Typical corona treatingequipment are available. (12) Anarticle “Bio-decontaminationof plasticand
dental surfaceswithatmosphericpressure airDCdischarges”byZ. Šipoldová,Z.Machala) is
interestinginthisarea. (13)
4. Coldplasmaisreferredtoina paperby Klämpfl etal at “Coldatmosphericairplasmasterilization
againstsporesandother microorganismsof clinical interest”Thisiswell summarizedinthe abstract.
(14)
For the use of SAPsinmedical products,the highestdegreesof cleanlinesscome fromsterilization
by usingeitherbyexposuretoionizingradiationorbygas sterilizationpreferablyemploying
ethylene oxidegas(ETO).Finishedalginateandotherbiopolymerwounddressingsare sterilizedby
these techniques. Referencestothese twoapproaches are atthe Complete Pharmacopoeiafromthe
WorldHealthOrganization(WHO).(15) Assessmentsof sterilizedgoodstakingbioburdensand
packagingintoaccount followBSEN ISO 1117-1:2006+A1:2013 and BS EN ISO 1117-2:2013 for
Gamma and EbeammethodsandBS EN ISO11135-1:2007 forethylene oxide (ETO) sterilization
methods. American(ANSI) standardsare takenfromthese EuropeanproceduresasANSIisa
memberof ISO.Ethylene oxide gassterilizationcancause some viscositychangesinalginate
biopolymers –asobservedby Leoetal in“Effectsof sterilizationtreatmentsonsome propertiesof
alginate solutionsandgels”(16).Also, the use of ionizingradiationcanresultinsome polymer
propertychangesnotablyinmolecularweight –as seenby Wasikiewiczetal “Degradationof
chitosanandsodiumalginate bygammaradiation,sonochemical andultravioletmethods”. (17)
ThisexcitingNEREDA ALEwork isongoingandevolving.SlimyGreenStuff BV (aTU Delftcompany)
has the academiccapabilitytoexpandthisALEapproachto viable SAPsbysuitable industrial
liaisons.(18)
Dr Edmund H Carus (August 2016)
References/Links
1. https://www.royalhaskoningdhv.com/en-gb/nereda/about-nereda
5. 2. “Recoveryandreuse of alginate fromgranularNEREDA sludge”Helle vanderRoest,
Mark vanLoosdrechtet al, Water 21, April 2015
3. “Water InnovationAwardforresearchintorecoveryandreuse of alginate fromgranular
sludge”NEREDA newsDecember17th,2013 at
https://www.royalhaskoningdhv.com/en-gb/nereda/news-events-and-
downloads/20131217a-water-innovation-award/572
4. http://www.edana.org/index.cfm
5. http://www.degruyter.com/view/j/epoly.2009.9.issue-
1/epoly.2009.9.1.968/epoly.2009.9.1.968.xml .
6. http://onlinelibrary.wiley.com/doi/10.1002/app.23373/abstract?deniedAccessCustomis
edMessage=&userIsAuthenticated=false.
7. http://www.scirp.org/journal/PaperInformation.aspx?paperID=18991#.UsBrJvviaSo
8. http://www.adm.com/en-US/products/industrial/superabsorbents/Pages/default.aspx
9. http://skyquestt.com/biodegradable-sap/
10. http://israel21c.org/environment/the-super-israeli-superabsorbent/
11. http://www.fep.fraunhofer.de/content/dam/fep/en/documents/Produktflyer/Sterilisati
on%20und%20Desinfektion_EN_2.0_net.pdf
12. http://www.alibaba.com/countrysearch/CN/corona-treatment-equipment.html
13. http://enviro.fmph.uniba.sk/nato/pdfs/P/p14.pdf
14. http://aem.asm.org/content/early/2012/05/04/AEM.00583-12.full.pdf
15. http://apps.who.int/phint/en/p/docf/
