~4ater R,,s~'ur~i~ Vo[ q. pp "1)7 to 7[2. Pergamon Press 19"5 Printed in Great Britain. REMOVAL OF VIRUSES FROM WATER BY SORPTION ON COAL P. P. OZA* and MALAYCFL4.UDHURI Department of Civil Engineering. Indian Institute of Technology. Kanpur. Uttar Pradesh. India {Received 13 October 1973) Abstract--The objective of this research was to investigate the potential of bituminous coal as sorbent for removing viruses from water and to delineate the sorption mechanism(s)• This study was undertaken in view of the increasing use of coal in water and wastewater treatment. Bacteriophage T4 against Escheri- chia coil BB was used as a model virus and coal samples from Neyveli and Giridih were used as sorbents. A sampling method for rapid separation of unsorbed viruses from the sorbent was standardized which consisted of filtering the sample containing coal and viruses through a Whatman filter paper soaked in beef extract. Effects of the following parameters on virus sorption were investigated: pH. ionic strength. temperature, and presence of proteinaceous matter. Maximum virus sorption (about 70°,i;)was observed at pH 8"0 with input virus concentration 1.44 x 10 "~ PFU ml- ~. coal size 350 t~m and ionic strength 0.02. Optimum ionic strength for virus sorption was found to be 0-015. Higher temperatures increased the sorption capacity and the activation energy was found to be 30-3 kcal/mole. This and low desorption values (6-107/o) suggested irreversible chemisorption. Effect of carbon content ofcoal on sorption-desorption was studied using pure graphite which showed negligible desorption. Effect of proteinaceous matter was investigated using 5?J; domestic wastewater and the culture broth• Proteinaceous matter appeared to compete with virus for sorption sites on coal and reduced sorp- tion by about 1 ,"°/~,,. Kinetics and equilibria of sorption on Neyveli coal at pH values 5.5. 7.1 and 8.0 were studied in a non- flow agitated system. Eqt, ilibrium sorption was attained in 90 min. the bulk of it being over in 45 min. Sorption data followed Langmuir type isotherm plots and suggested L2 type plot according to Gile's classification (J. Chem. Soc. Part 3, p. 3973, 1960). Isotherm plot with 5?/0 domestic wastewater gave an S curve, suggesting moderate to large intermolecular attraction and implying strong competition • o/ for substrate sites from molecules of the solvent• Monomolecular coverage to the extent of only 0 1/o of total surface area agreed with the assumptions of isotherm plot and penetration into micropores and macropores of coal was ruled out. INTRODUCTION Viruses representative of different enteric groups have been isolated from raw and treated domestic waste- water and their presence has been demonstrated in receiving waters. Transmission of viruses by the water route has been recognized [,1-3]• Viruses could be a serious problem in the practice of water reuse and it appears that improved means of removing or inacti- vating them will be required to achieve virus free effluents from advanced wastewater treatment [4]. Active carbon is a commonly used sorbent for removing organic contaminants from water both in water purification and advanced wastewater treat- ment. However, laboratory and field studies indicated that active carbon was not very efficient in removing viruses from water I-%7]. Viruses are probably excluded from the micropores ofactive carbon because of their size [5]. The micropores are fissures of ap- proximately 10-30 ',~ dia [8], whereas the average size of picornaviruses (enteroviruses of man and other ani- mals) is 200-400 A [9]. Recently several investigations * Present address: Department of Civil Engineering, L.D. College of Engineering, Ahmedabad 380015, India. This paper was received for the Paris Conference. but together with several more was accepted for Water Research as there was no place for it on the Conference Programme. on the use of coal for removing organic contaminants from domestic and industrial wastewaters [ 10-13] and sorption of selected pesticides and phosphorous con- taining compounds have been conducted [,14]. Our preliminary investigations on the use of coals for removing viruses from water have demonstrated their potential as sorbents for viruses [15]. Use of coals has advantages over use of other sorbents because of their availability, lower cost and recovery of fuel value after exhaustion. The present study was designed to examine the sorp- tion of viruses on coals in greater detail using con- trolled laboratory conditions. Effects of various para- meters on sorption were also studied so as to be able to delineate the sorption mechanism. MATERIALS AND .METHODS Viruses and preparation Bacteriophage T4 against Escherichia coli was selected as the model virus for this study because of its stability in agi- tated systems and its greater ease of culturing and enume- ration [5]. Bacterial and animal viruses have many similar physical, chemical and biological properties, i.e. size. net electric charge, protein coat, etc. [16]. Thus it may be assumed that their differences in behaviour when subjected to sorption may not be much greater than the differences in these p.roperties among animal viruses alone. Furthermore. more ts known about the composition and properties of 707