Solar Water Disinfection (SODIS)destined for worldwide use?by Martin Wegelin and Bernhard SommerLast year's publication of Rob Reed's article'Sunshine and fresh air: a practical approach tocombating water disease' provoked sustainedreader interest in what seems such a simplesolution to a major problem. Here we can publishthe results of extensive field and lab tests.

(EAWAG/SANDEC) embarked onextensive laboratory and field tests toboth assess the potential of SODIS, andto develop an effective, sustainable andlow-cost water-treatment method.

Sanitary engineers, photochemists,bacteriologists, and virologists con-ducted comprehensive laboratory tests.Complementary field tests were carried

Questions Acceptance of SODIS Integration of SODIS Alfordability of SODIS

Actions Changing Water Changing Water Paying for WuterTreatment Habits Handling Habits Quality Improvement

- simple method - provision of special containers • low investment and(wJler boiling is cumbersomt:. (e,g. Imlf-blnckcncd p/;:L'itic bOllles operatinlt cost.,sunlight exposure is easy) or plastic bngs) (lower costs Ih3n for other methods.

c.g. waler boiling, chlorin:nion)

Criteria 'lIld . cost-saving method - con\'cllicm'c of containers • sustainability of SODISIncentives (water boiling requires energy. (e,g. direci cOIl,",umptiun uftreatcd (containers cnn he supplied and

Enhancing e.g. firewood or kerosene, water from container is ~illlplt·) replaced from locnlly available

Changes sunlight cxposure is free) resources und material)

• convenient method • special attention given to - consumers recognise(waler boiling demands careful drinking watcr health bcnefitshandling of hoi pots. plastic bottles (e.g. drinking water is treated and (paying for good W<llcrL]ualilY

are praclical and easy to handle) stored differently from water used is less cx.pcnsi\'c than paying

for other purposes) for medical treatment}

RESEARCH ON SOLAR water disin-fection - applying the solar radiationmethod - was initiated by ProfessorAftim Acra at the American Universityof Beirut. Acra's work motivated theIntegrated Rural Energy Systems Asso-ciation (INRESA), an associated pro-gramme of the United Nations' Univer-sity, to launch a network projectin 19l-l5. The Brace Research Institutein Montreal organized a workshopin 19l-ll-l to review the results ofthis field research; and in 1991,the Swiss Federal Institute forEnvironmental Science and Technol-ogy/Department of Water and Sanita-tion in Developing Countries Table J. Implementing aspects of SOD IS.

(Source: Acra et. al., UNICEF, 1984)

out in co-operation with CINARA inCali, Colombia.

In the past, two different water-treat-ment processes using solar energy weredeveloped to improve the microbiolog-ical water quality. The first, using pre-dominantly UV-A radiation, is knownto have a bactericidal effect. The sec-ond, utilizing infrared radiation to raisethe water temperature to over 70°C, isknown as pasteurization. Simultaneoususe of both solar energy sources -UV-A light and infrared radiation -seems a good idea. The two processeswere assumed to complement eachother, therefore, EAWAG focused onthese combined effects and discoveredsynergies between radiation and heateffects. This constitutes a breakthroughin the development of the technologyand significantly enhances the potentialof SODIS application.

Figure 2 illustrates the synergies pro-duced by the combined used of radia-tion and thermal treatment on the inac-tivation of faecal coliforms. Two differ-ent faecal-coliform inactivation testswere carried out at constant water tem-peratures of 30°C and 50°C, respec-tively. The combined effect of solarradiation and water temperature isshown by the two curves. A series ofparameter tests at water temperaturesbetween 20 and 55°C revealed that the

What's the idea?i ro-organi m are vuln r-

abl to light and heat. olarenergy fr e and uni ersallyn ailable, is barnes ed in Ule\ ater-treatment proce~known as olar water di in-fection ( 001). Fibour 1show, tran 'parent contain-er' filled with water ande po cd to full sunlight for

veral hou on titule theb' ic cone pL om rna beU'ed as a batch proce atbou hold level to treat mallquantilie' of drinking-waterin bottles or plastic bags.ince the daily capacit of the

batch proc is limited, how-eve~ b the volume of watertared in the un-exposed

bottles, OD can also beu d in continuou -flowtern , comprising alar colJec-tors and heat exchangers, toincrease the daily drinking-wat r output ignificantly.H nc. om continuou-Dow r actors can be used todi infect the water upply ofin titutioll U h ~ h pitalsand hoals.

SANDEC 8197

continuous-flow system(reactors with heat

exchangers)

The Idea

The Possibilities

batch system(tranparent bottles

or plastic bags)

Figure J. Application of solar waterdisinfection.

30 WATERLiNES VOL. 16 NO.3 JANUARY 1998

Figure 2 shows the effect of solar radiation and lrater tell/perature 011

inactivation of faecal coliforms; (right), a Togo I'illager takes a 11lI(f~blackell('dbottle and plastic bag to disinfect water using SOD/So

oOl{2

ctLUa:()

thermore, the ratio between exposedsurface area and stored water volumegreatly influences temperature devel-opment. Flat plastic bags 2-6 cm-fullyield a far better area-to-volume ratiothan normal round bottles, and reachhigher water temperatures. Finally, thetype and shape of support materialused to carry the plastic bottles or bagsdirectly intluence water-temperaturedevelopment. Half-blackened plasticbottles placed on a corrugated-iron roofoffer the best configuration for SODISbatch process application. The water isheated by the infrared light which isabsorbed by the black paint. The con-vective heat is absorbed and conveyedto the bottle by the metal sheet.

The batch process has a limitedcapacity, however, and its daily outputgenerally corresponds to the water vol-ume stored in the plastic bottles orbags. This capacity can be significantlyincreased in a continuous-now system.Such installations - illustrated in Fig-ure 4 - consist of a raw water tank, anexposure vessel called a reactor. athermovalve, a heat exchanger to pre-heat the raw water with the energyyielded by the treated water, to becooled and stored in a treated-watertank. As these systems can be operatedby gravity, an electrical pump is unnec-essary. The tlow is regulated by a ther-movalve that opens and closes at thethreshold temperature of 50"C. Toreduce construction costs, EAWAG andSwisscontact have designed a new

10080

,,temperature

300 Ceffect of

30° b.} temperature50°..... (dark control)

500 Ceffect of

40 60fluence UV-A [Wh/m2]

20

EquipmentSODIS requires sunlight, exposure timeand adequate containers. Plastic min-erai-water and soft-drinks bottles aregradually replacing glass. Plastic bottlesare made of either PET (polyethyleneterephtalate), or PVC (polyvinyl chlo-ride), the latter perhaps containingsome additives to increase its elasticity,which, in high concentrations, coulddiffuse into the water and pose a healthrisk. PET bottles are inert and, there-fore, far preferable for SODIS.

Once the polluted water is bottled andexposed to sunlight, solar radiation hasto travel through the wall of the bottleinto the water. UV-A light (with a wave-length of between 320 and 400 nm), themost bactericidal sunlight spectrum,should have a high light transmittancethrough the material of the bottle.

Water temperature is the second mostimportant process parameter. Tempera-ture increase is dependent on containertype and support material used. Toimprove water heating, transparent-plastic bottles should be half-blackenedto enhance infrared light absorption asillustrated in Figure 3 on page 32. Fur-

water treatment if they believe they willbenefit directly - as health benefits areoften indirect, they may be perceivedonly in the long-term. Table I summa-rizes the implementing aspects ofSODIS, and lists criteria and incentiveswhich enhance its acceptance and use.

30° D } temperature50°. and sunlight

water temperatureinactivation

1o

10

100

10000

100000

'"E~(5(J

Eo 1000o

inactivation rate offaecal coliforms remainsconstant within a 20to 40°C temperaturerange. But, at a thresh-old water temperatureof 50°C, the requiredtluence (dose of solarradiation itegrated inthe 350 to 450nm wave-length range) of UV-Alight is about four timessmaller that at 30°e. Asthe graph indicates,inactivation of bacteriaat 50°C can be attrib-uted to three differentfactors: heat effect, sun-light exposure and syn-ergies caused by thecombined application oftemperature and radia-tion. Furthermore, sincethe oxygen concentra-tion enhances the inacti-vation of bacteria,SODIS should alwaysbe applied under aero-bic conditions.

The second phase of the SODIS pro-ject developed and field-tested suitablecontainers and reactors for the water-treatment process. The small diameterquartz tubes used in Phase 1 werereplaced by locally available glass andplastic bottles, as well as plastic bags.

The field tests confirmed the labora-tory results. As soon as the water temper-ature reaches 50°C, the inactivationprocess is accelerated and usually leadsto complete disinfection. Figures 3 and 4,on page 32, show the inactivation curvesof faecal coliforms and Vibrio choleraein plastic bottles and SOOTS bags.

EAWAG's SODIS project is cur-rently in its third phase - the mostdecisive yet. Socio-cultural acceptance,applicability and financial viability arebeing studied in demonstration projectsconducted by local partners in Colom-bia, Bolivia, Burkina Faso, Togo,Indonesia, Thailand, and China; thesites cover a range of different social,climatic, and living conditions.

But people's health will not improvejust because they have new equipmentor facilities - they have to use them.Minor improvements to existing water-supply practices are more likely to beaccepted than major and suddenchanges. SODIS will only be used andapplied if the target population is con-vinced of its advantages over the tradi-tional ways of treating and handlingdrinking-water. Consumers need to befully aware of the bacteriological trans-mission routes of water-borne diseasesand how to reduce or avoid them.Finally, private users will only invest tn

WATERLINES VOL. ]6 NO.3 JANUARY 1998 31

o

40 ~:Jiii

30 ~EQ)

20 ':Q)

iii10 S:

60

60

20 40 60 80 100

UV-A Dose [Wh/m2]

,,,----;-- 50

, ~: -- - - -,. - - 40 2:!

, :J

: ~----~-- 30 ~

EQ)

, f-----~--20 Q)

, -: ~

- - - -. - - 10,,,, 0

20 40 60 80 100

Fluence UV-A [Wh/m2)

10

Eoo~-::::>u.o

1o

1o

100000

100000

= 10000Eoo~~g(5 100o(ij

"Q)ltlU.

SODIS plant with a modified, flat-plateECOSOL collector which combines thesolar collector and reactor in one unit. I

ResultsThe SODIS demonstration projects arebeing carried out in conditions differ-ent from previous experiments. Theprocess is not applied under strictlycontrolled conditions; the material andmethods used are often not ideal; theraw-water pollution is generally muchlower; and the handling of the treatedwater is, frequently, inadequate. Never-theless, SODIS does work. Mondomoin Colombia is supplied with untreatedwater drawn from a small river con-taining an average faecal-coliform con-centration of about 600 CFU/I 00 ml.The 91 treated-water samples analysedreveal that 69.2 per cent of the SODISbags and 61.5 per cent of the plasticbottles reduced the level of coliformsto 3 or less CFU/I 00 ml (a 99.5 percent removal efficiency).

The SODIS

CD

Figure 3. (top) Inactivation of colifonns and vitroclzolerae in half-blackened plastic bottlesand SODIS plastic bags. Figure 4. (bottom) Layout and peiformance of SODIS reactor.

@)®@

CD,

10 11 12 13 14 15 16 17Hour

EAWAG has produced two videos onSODlS; they are available in English,Spanish, French, and German. The firstvideo presents the water-treatmentmethod as well as the laboratory andfield tests carried out in Switzerland,Colombia and Costa Rica; the secondintroduces SODIS and shows how ithas been implemented in the demon-stration projects.2ReferencesI. A comprehensive field demonstrationprogramme in Costa Rica will test this newSODIS plant in 1998.2. Video cassettes can be ordered for $40/videofrom EAWAG.

AcknowledgementsThe SODIS project has received considerablefinancial support from the Swiss Agency forDevelopment and Cooperation (SOC). TheEAWAG/SANDEC's co-operation partners:CINARA in Cali. Colombia; Programa de Aguasin Cochambamba, Bolivia: NATURAMA inOuagadougou, Burkina Faso: CREPA in Lome,Togo: Royal Scientitic Society in Amman,Jordan; Yayasan Dian Desa in Yogyakarta,Indonesia; Khon Kaen University and EC in HonKaen, Thailand; NSAS in Yinchuan, China;Swisscontact and AyA in San Jose, Costa Rica,have greatly contributed to developing theSODIS technology.

Faecal Coliforms [1100 mil

raw water T T Ttreated water ~ ~

- - --- •••••••••••••• --- ••••••• >, •••• _~70

~ 60

i!! 50~1ii~ 40a.E"•... 30

20

DisseminationNational workshops are being orga-nized in the seven developing countriesparticipating in the SODIS project.Each workshop will include a generalintroduction to the water-treatmentmethod, participants will hear resultsand first-hand experiences, and canjoin in discussions on disseminationstrategies at the regional or nationallevel. Hopefully, these workshopswill lead to follow-up programmeslaunching SODIS on a large scale.

7 6 9

around 55 per cent will continue to useit when the project ends. Acceptanceis also high elsewhere: the neighboursof communities involved in the projectin Thailand and Indonesia have started10 use SODlS, and Melikan has estab-lished a plastic-bottle supply scheme;the bottles are sold for $O.20lbottleto old and new consumers, a clearindication of the project's sustainability.

water-treatmentmethod is simple toapply. Neverthe-less, people willhave to be intro-duced to the tech-nique carefully,and get guidanceabout day-to-dayapplication if theyare to benefit fully.Experience inIndonesia illus-trates the impor-tance of proper and continuous training.In the rural community of Mclikan, 40per cent of the villagers have started toplace their containers on chairs or con-crete floors which, compared to expo-sure on black rocks, corrugated zinc ortile roofs, are not ideal locations - thedisinfection efficiency is lower, andonly SO per cent of the exposed watersamples were free of faecal coliforms.After people received training, and suit-able, corrugated zinc sheets, the num-ber of inadequate applications wasreduced to 3 per cent. A better educatedpopulace in the semi-urban communityof Dobalan meant correct SODIS appli-cation was easier to implement, but stillallowed for improvement.

To find out whether people acceptedthe SODIS method, project workerscarried out interviews and surveys. InChina, around half of the people inter-viewed said they still drink untreatedwater even though they are aware thatthe quality is poor; while untreatedwater consumption rises to 100 per centin other countries. The Chinese regardSODIS application as convenient, and

32 WATERLINES VOL. 16 NO.3 JANUARY 1998