Development of thermochromic strips as a water pasteurization indicator

Jurud of Eninonenal Seienes Vol. l5.No6.pp.863- -864.2003IS 1001 10742CNI-2629XArtidle ID: 1074200-0863-020CLC number: X830.2Document code: ADevelopment of thermochromic strips as a water pasteurizationindicatorIshtiaq A. Qazil ，M. Ali Awan2 , M. Anwar Baig(1.Pakistan Council of Renewble Enesy Trhnogioe(PCRET), Islamahad, Palistun. E-mal: ihiag-qazaia @ yaoo vom; 2. Iatitnte ofEnvinometal Sciencer and Enincenge IESE), Natioal Univenily of Sienes & Technodug (xUSr). Realpindi, Palisea)Abstract: Biling of waler, for pufraion. cnmoly pertired in lbe wold, has meny poblems asociated wih it like danger of sealding.scealing in the vesspls. renoval of useful minerals and blandness ol taste elc. Water can be made safr for drinking simply by heating at 65T for6 minutes. A colour indicahing stip was dereloped which changes colour from red lo puple at 67r. Use of this strip cean help in peteunizingwater withnut the above problems and with considenable energy saring.balatn'Keywords: thermochromic srip; pasteurization indicator; PakistanIntroductionAccording to the United Nations Children' s Fund( UNICEF) about 60% of rural farmilies and 23% ofurban fanmilies in developing countries are withoul safe drinking waler and in some areas the waler suppliesmay be heavily contaminated with pathogenie organisms. Outbreaks of water bormne of infectious diseasesike hepatis are thus common in many parts of the world( Hanmer. 1996).Diarrhea, a common disease of children in the developing countries, is caused by the use ofmicrobialy contaminated waler . Dehydration, resulting from diarrhea， is the leading cause of death inchildren, under the age of five, klling an estimated five million children annually( Andreatla, 1994).Microbially contaminated water is usually boiled to make it free of microbials and safe for drinking.Boiling of waler. comnonly practiced, has many drawbacks associated with it, like danger of scalding,scaling of the boiling vessels, removal of useful minerals and blandness of taste( caused by the removal ofminerals and dissolved oxygen).It is generally known that heating water at 65C for six minutes will kill most of the nmicroorganisms(Andrealta，1994). The process is known as pasteurization a term is usually associated with milk.Pasteurization of water, performned al a lower temperalure than biling, can result in considerable savings infuel costs with associaled economic benefits.In order to do this, however, we need to have a convenient method of knowing, if and when, thewater being heated has atlained the cnitical lower temperature of 65 C. The present work describes thdevelopment and use of an indicator strip for this purpose that has been found to be very ronvenient andeffective in use.1 Methods.1 Thermochronic indicator stripsPaste of a thermochromic compound was prepared by following the method of Hughes( Hughes, 1998)by using sodium metabisulfite as the reducing agent. The thermochromic paste was then applied to anordinary filter paper and dried. The dried paper was cut inta strips, which were subsequently laminatedwith plastic. The resul was a low cost, plastic coated stip, which would change colour from“ red" to"purple" at 67C. The change is very sharp, easily noticeable and totally reversible . These characleristicsmake the strip an ideal indicator that can be conveniently used in monitoring the pasteurization lemperature(659C) of water.1.2 Pasteurization of water500 ml of tap water was heated on a Bunsen bumer . The temperalure was frequently monilored bydipping the above mentioned strip in the water. When the strip exhibited a colour change from red topurple the flame intensity under the water was reduced . This temperature monitoring was cuntinued for 6-7 minutes，in order to get pasteurized water. The procedure was applied to a number of waiter samples forreplication purposes .1.3 Standard coliform testThe standard total coliform test was performed on all the中国煤化工d" walersamples, using the Standard Menbrane Filtration Method( Eaton,TYHCNMHG864Ishtiaq A. Qazi et al.Vol.IS1.4 Dissolved oxygen delerminationDissolved oxygen contents of both the “ pasteurized”and “unpasteurized" water sanples weredelermined by“Oximeter 0xi538 WTW" . Before D0 detemination pasteurized water was given sufcienttime for cooling( approximately one and a half hour) .2 Results and discussionAn average of twenty nine coliform colonies( in the incubated petri dish) ulong with other non-coliformcolonies were observed for“unpasteurized" water samples，whereas, no such colonies were present in thedish prepared by' pasteurized" water samples . This shows the electiveness of the process .In general, heat kills microorganisms by denaturing their proteins. Above 509 most of the proteinmolecules become denatured. The denaturation of essential proteins， such as enzymes ，hormones,antibodies, transport and structural proteins by heat are well known ( Levinson，1996). Heat disnupts“hydrogen bonds”which hold protein chains together in their secondary and tertiary structures. Loss oftertiany struclure of a native protein results in loss of biological activity of the microorganisms and theirdeath( Sleigh, 1994) .The pasteurization process. which is used primarily for milk, is equally elective in klling germspresent in contaminated water. Pasteurization of water consists of heating a water sample: to 65C for 6minutes, or to a higher temperature for shorter time. This much heat is sufficient to kill the vegetative cellsof most of the microorganisms including pathogens .The solubility of oxygen in water reduces considerably with the rise in temperature and is almost nil inboiling waler. If the dissolved oxygen( D0) and minerals in water are removed, the taste of water becomesundesirable. As expected，our investigations show that loss of DO in“pasteurized" water sarmples, heatedonly to 65C, is far less than that of boiled waler samples, where almost all the D0 is removed .Ohviously, if the pasteurized water is given sufficient time for cooling it re-dissolves oxygen from air morequickly than the boiled water. In our sludy 500 ml of pasteurized water achieved the value of DOequivalent to normal tap water(7 .8 mg/L) in approximately one and half hours. This period is almost 2.5times less than that required by the same volume of boiled water to achieve the same D0 level. Hence,pasteurized water is not spoiled in taste or appearance .3 ConclusionsThe plastic coaled colour-indicating strip developed by he authors is very eficient in idenifying thewater pasteurization temperature. Use of, these strips could help in providing good quality，palatable waterto the user with considerable energy saving . The strips could also find application in efective disinfectionof water through solar heating, replacing the Soya been fat flled tube plastic tube, generally recommendedfor this purpose( Andreatta，1994). As such, these could be of immense value to the relief workens intimes of crises resulting in overcrowded situations following floods, earthquakes or infux of refugees and soon.Acknowledgements: Mr. Muhammad Basharat and Mr. Idrees Ahmed， IESE members of the laboratorystaff are to be thanked for their assistance.References :Andrealta D, 1994. A sunmnary of water pasteurization techmiques[ EB]. USA: htp://ilacocokio org/ solarwet . htmlEalonAD eal..1995. Standard methods for the exanination of waler and wastewalr[S]. 19th edition. USA: American Public HealthAspocistion.Hanmer M J, 1996. Wwater and wasteraler tetnolog[ M].3nd edition. USA: Prentice Hall Iteraioan, lneHuyghes J C.1998. Thermochromic solids[ EB]. Australia: htp://ichened . chem. wise. edu/ JoumlIsue/1998/Jsn/abs57 . htmdLevinson w. Juwetx E, 1996. Medical micrbiology & inmunodlagyl M}.4th edirtion. USA: Prentice Hall Intermational, Ine.Sleigh J D, Tinbury M C, 1994. Medical bectriology[ M].4bh editio. UK: Churchil Iiring Slone.(Reeivrd for reriew Augut 5, 2002. Acepted Septemher 8.2002)中国煤化工MYHCNMHG