CURRENT RESEARCH Adsorption of Poliovirus onto Activated Carbon in Wastewater Charles P. Gerba,* Mark D. Sobsey,’ Craig Wallis, and Joseph
L. Melnick
Department of Virology and Epidemiology, Baylor College of Medicine, Houston, Tex. 77025
The effect of pH and soluble organic matter on virus adsorption to activated carbon in treated sewage was determined. Poliovirus removal from wastewater effluent was greatly improved by lowering the pH to 3.5-4.5 or by reducing the amount of organics by lime coagulation. Batch studies indicated that virus adsorption to activated carbon in wastewater could be described by Freundlich isotherms. In column experiments virus removal was found to be dependent on column length as well as hydraulic loading. Virus and soluble organics adsorbed a t low pH could become deadsorbed by a rise in pH.
The use of physicochemical and other advanced waste treatment methods will probably predominate in future years (I, 2). A group headed by Middlebrooks (cited in ref. 1 ) has recently reviewed the capabilities and costs of a number of advanced treatment processes and concluded that processes offering the most promise include activated carbon. In addition, several tertiary treatment plants are now in operation in the United States utilizing granular activated carbon to treat domestic wastes ( 3 ) . Research has also been recently directed toward the development of powdered activated carbon for the treatment of wastewater ( 4 ) . Activated carbon has been found capable of adsorbing a great variety of organic materials including viruses (2,s). Cookson has extensively studied the mechanism of bacteriophage T4 adsorption by activated carbon in buffered distilled water (5-8). He has postulated that the adsorption sites on the activated carbon are carboxyl or lactone groups, since adsorption can be completely blocked by esterifying these groups. He has also proposed that amino groups on the virus become associated with the negatively charged carboxyl groups on the carbon by electrostatic attraction. Adsorption was influenced by both pH and the ionic strength of the solution, with optimum adsorption a t a pH of 7 and an ionic strength of 0.08. Sproul et al. (9) have used bacteriophage T2 to evaluate virus removal by several different types of activated carbon in secondary effluent. Significant variation among individual activated carbons was found. They also demonstrated removal efficiencies of between 18 and 40% for poliovirus by sewage-fed columns of granular activated carbon operated on a continuous flow-through basis. Elution of the viruses was observed when the column runs were continued beyond the virus exhaustion point. In comparative studies with synthetic river water and domestic sewage carried out by Watson and Drewry (IO), bacteriophage f2 removals by columns of activated carbon were considerably less in those fed with wastewater. They concluded that competition for adsorption sites with the Present address; Department of Environmental Sciences and Engineering, School of Public Health, University of North Carolina, Chapel Hill, N.C. 27514.
virus by other organic matter was a major factor in the lower efficiency of activated carbon for virus removal from wastewater. These results were also confirmed by Cliver ( I 1 ) using poliovirus. This investigation was undertaken to gain additional information on virus removal from sewage effluents by activated carbon and methods by which this process could be optimized. Materials and Methods
All virus assays were performed on BSC-1 cells which were passaged, grown, and maintained by previously described methods (12). Virus was propagated in baboon kidney cells. Kidneys obtained from immature baboons were trypsinized and grown as described (12). A plaque-purified line of type 1 poliovirus (strain LSc) was used. Stock virus was grown in baboon kidney cells, concentrated tenfold, and partially purified by membrane chromatography ( I 3 ) ,and stored at -7OOC. Virus samples were diluted in tris(hydroxymethy1)aminomethane-buffered saline containing 2% fetal calf serum, penicillin (100 U/ml) and streptomycin (100 pg/ml). Before assay, all samples were frozen a t -3OOC overnight to reduce the problem of bacterial contamination in cell cultures. Virus assays were performed by the plaque-forming unit (PFU) method as used in this laboratory (14). Chlorinated secondary effluent from a local trickling filter plant servicing a residential area of Houston, Tex., was used in this study. Samples brought to the laboratory were immediately dechlorinated by addition of sodium thiosulfate and either filtered through a series of honeycomb textile filters (Commercial Filters Division, Carborundum Co., Lebanon, Ind.) (15) with a smallest nominal porosity of 1 p, or clarified by lime coagulation. Clarification by lime was achieved by adding calcium hydroxide until a pH of 11.5 was reached. The sewage was then mixed on a mechanical stirrer for 20 min, allowed to settle for 20 min, and the supernatant fluid was collected by decanting. The pH of lime-treated sewage was adjusted to low pH by the addition of 1N HC1. In batch studies, sewage was buffered in some experiments by addition of either sodium acetate or glycine using concentrations of O.O5M, and pH adjustments were made by the addition of 1N HC1 or 1N NaOH, before addition of the virus. The relative removal of soluble organic matter was determined by measuring ultraviolet (uv) absorbance at 254 nm. The correlation between total organic carbon (TOC) and uv absorbance in sewage (16) and the usefulness of uv absorbance as an indicator of activated carbon performance has been previously demonstrated ( 17 ) . The activated carbon used in this study was Pittsburgh type OL (Pittsburgh Activated Carbon Division, Calgon Corp.). This granular charcoal is made from bituminous coal with a large portion of the total surface area in pores 2-50 nm in diameter. In column studies, 20 X 50 mesh was used, while in batch studies the granular charcoal was pulVolume 9, Number 8, August 1975
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