COAGULANT DOSE IN RELATION TO BACTERIAL AND TURBIDITY REMOVAL IN WATER FLOCCULATION

Abstract

Tho efficiency of bacterial removal is a major factor in decidirg the adequacy of water treatment unite, Pbr bacterial removal, flocculation is most important pro.requieite to filtration, The removal of bacteria in flocculation of water anti its relationship with turbidity removal has been studied* Coogulatnt dosages which gave both turbidity and bacterial removals to a considerable extent mere found with jar teat fcr raw watcir hair different tarbiditiess '31:ventage bacterial an turbidity removals both varied parabolically with alum dose. tip to 97 per cent bacterial removal was observed. A definite correlation exists between the perceztage turbidity (Y) and bacterial (x) removal, the coefficient of correlation boirg 0.74 A common linear re lationship between the t70 reatovale can be expressed as Y ra 2.98 X .170. DITRODUCTION Treatment of waters hap been a subject matter of investigation from the very dawn of civilisation, The tech. ague of clarification of turbid water, with almond paste, riaa lazy= to tts ancient Pgyptians(i). la olden time, tha use of flarmalit(2) a plant seed, as a coagulant, was pre, . valont in pia; and in Chim. Coca(3) and probably alum also wsre used for the clarif ication of water, Filtration is the last urn of defence against paSsing of colloidal particles and viruses or bacteria in rater while flocculation to of link in the chain of methodo to rPmove these, Ittr removal of =ater..borre bacteria, flocculation and filtration are considervd to be the standard methods, :Besides other things the bacterial removal ef ft. cioncor will therefore decide the adequacy of those treat. rent units, Tiy filtration, it is usually meant that it will not only loner down The turbidlly to permissible limits, but also strain out microscope organisms* The removal of bacteria is usually 'insufficiently effective to place dependence on the filter alone for the production of a hygienically safe water( ) With the recent advances in treatment of water, it has been postAble to reeace fterbidity leas thin 3 ppm by coeguiation lob To (5) • Worn scopie organiame aleo get removed in coagulation. Obvicus question there fibre le if filtration be at all nemseary. Studieo by Chang(6) ot. al. on the removal of virusoo by flocculation Imply that with a better dose of coagulant bacteria can also be removed to a consi.. derablo extent. They obeerved that bacterial removal at 15 ppm alum dose roe 75 per cent and at 25 ppm alum dose 99 per cent when the turbidity was quite low at both dosage 3evel(6) This reveale that coalzulant doses adequate for turbidily removal are not neceesarily eo for bacterial. A compranise dose can be struck with advantage. It would thus be useful to know 4 (1) Optimum doss required for turtidily removal be applicable to bacterial removal also (ii) The information obtained with artificially prepared water in the lab oratory be appliclble to the treatrrint o raw natural waters. There is no justification for over doeing and mat. ing of chemicals but also there in a strong use for controlled coagulation. For 4thio the dosage selected abould be the one that at the a conomic costa, feasible to coagulate 4 (2) pR on the removal of Coxsackie aril Pat: Aerial VirWog from water by llocculation. They found that flocculation by Aluminium ThAlphate when used properly can remove a high percentage of viruses from the supernatant treated water up to 99,99 per cent with 100 ppm dose of aluminium sulphate. Ferric) chloride hoe also been tried by them and it has been found to be more efficient and safer than alum in the flocculation of Tatar because of higher percentage of virus removal an3 lesser tendency of virus...floc disassocia-tion.. A log.log linear relationship existed for both virusos botz--o, n the ratio of a percent ige removal of VIZIA9 to alum amen and the percentage of virue remaining in the settled water. It shows an increase in percentage removal of both viruses with the ircroase in alum doses-. They obtaired removal as high as 99.1 per cent in acme cases. Khanna in the laboratory study on rater floccu. lation has found bacterial removal, in general, higher than 95 per cent!0) Correlation between Turbidity and acc terial Removal A direct correlation batmen removal of turbiditr and bacteria s teen found out by various works 5 Streeter(' ) hale expressed the relation betomen the bacterial Quality of raw TTater we the effluent resultizt from coagulation and nedimentation ap Ea gl Am11..11.1.111.1110001•0, eRn a levig '11 in which R mt bacterial colltant of raw water baciorial coniont of effluent from the C3 ttl Ina baoin detention tire wten T wan exprenseditourn„ the value of e and n for the experimental plant wan faind to be 0,57 and 0.88 reEpeodvely, The •S Public Res/ fr7e, ?vice ) has expre need the relationship be tte hector/al content of influ3nt an effluent water in purification proceesen an I can in which It y denote respectively, the bacterial content of the influent ant of tle effluent water. Ohoeh(il) while working at Calcutta Water Perks aloe fbund a direct relationohip between removal of turbidity' are conform concentration, at all atogen of purification, There 1s! ht veryno cortelation bet=sen the initial tarb14. dity of water and its bactorial count. nathur(") has fano reported at Obardrawal Water Mirka, Delhi that the bacterial efficiency of preimaatment to the OM= as th efficiency in removim turbidi, iy • The prPfzeat study to directed more torztrcle the practice problems involved in the use of coagulants* attempt has been made to discuss the Chemietry of coagulation or hydraulics of flocculation. It is confired to select out a alum dose which given max immt value of the ratio of bacterial aul turbidity removal equal to one if any. Ob 33 ctive s of tb present study care to see; 0) The remove of bacteria and turbidity in water flocculation under varying doacga° of coagulant on either aide of their optimum values (2) The interrelationship batmen bacterial ani turbidity removal 9 (3) The variation of the optimum alum dose with Initial raw' cuter cactarial count and tarblditr ) The variation of the optimum removal with initial condition of tacterial count and tyrbi. dity in raw rater