Moyasar T. Yahya

MS-2 AND POLIOVIRUS TRANSPORT IN POROUS MEDIA : HYDROPHOBIC EFFECTS AND CHEMICAL PERTURBATIONS

In a series of pH 7 continuous-flow column experiments, removal of the bacteriophage MS-2 by attachment to silica beads had a strong, systematic dependence on the amount of hydrophobic surface present on the beads. With no hydrophobic surface, removal of phage at pH 5 was much greater than at pH 7. Release of attached phage at both pH values did occur, but was slow; breakthrough curves exhibited tailing. Poliovirus attached to silica beads at pH 5.5 much more than at pH 7.0, and attachment was also slowly reversible. Time scales for phage and poliovinis attachment were of the order of hours. The sticking efficiency factor (α), reflecting microscaie physicochemical influences on virus attachment, was in the range of 0.0007–0.02. Phage release was small but measurable under steady state conditions. Release was enhanced by lowering ionic strength and by introducing beef extract, a high-ionic-strength protein solution. Results show that viruses experience reversible attachment/detachment (sometimes termed sorption), that large chemical perturbations are needed to induce rapid virus detachment, and that viruses should be quite mobile in sandy porous media. Even small amounts of hydrophobic organic material in the porous media (≥0.001%) can retard virus transport.

Virus transport and removal in wastewater during aquifer recharge

Abstract To assess soil-aquifer treatment of sewage effluent for removal of viruses, studies were conducted at a recharge/recovery site near Tucson, Ariz. Two 13 m2 basins were constructed in coarse sand alluvium, one for secondary- and one for tertiary-treated effluent. Bacterial viruses, MS2 and PRDI, and a chemical tracer, potassium bromide (KBr), were added to effluent applied to these basins. Infiltration rates ranged from 0.2 to 16.8 m/d. Samples of unsaturated flow from depths of 0.30–6.08 m below the basin were taken through porous stainless steel suction-samplers. Bromide and virus results indicated the presence of preferential flow conditions that produced irregular concentration profiles with depth. Virus transport was retarded (R = 1.9) at the beginning of a flooding cycle, but viruses were transported faster than the average water velocity (R = 0.47) when applied after the infiltration rate had declined following 4 days of flooding. Virus specific removal rates (b) during percolation through soil were 2.3–120 times greater than in bottles of effluent or ground water. PRDI was removed more rapidly during percolation (b = 0.65 h−1) than MS2 (b = 0.23 h−1). Effluent type did not significantly affect b for MS2, but the PRDI rate was nearly 3 times greater with secondary effluent (1.0 h−1) compared to tertiary effluent (0.35 h−1). Virus removals at the 4.3 m depth ranged from 37 to 99.7%.

Bacteria transport in a porous medium: Retention of bacillus and pseudomonas on silica surfaces

Abstract Pseudomonas fluorescens and Bacillus subtilis transport was studied in water flowing through laboratory columns packed with 0.5-mm silica beads. The rate of bacterial attachment to the silica was shown to reach steady state after about one pore volume of bacteria-containing solution had passed through the column. Column-outlet concentrations were 6–80% of inlet concentrations. There was less P. fluorescens retardation at pH 5.5 versus 7.0; since the pH iep s (isoelectric point) for both bacteria are at lower pHs, this difference indicates that the change in electrostatic repulsion over this pH range was relatively unimportant in determining bacteria retention in the porous medium. Transport of both species was highly retarded, suggesting that neither could be quickly transported over long distances in sandy soils. Results were adequately described using a steady-state transport model with bacterial attachment to soil as a pseudo-first-order process. Sticking efficiency (α), calculated using the steady-state colloid-filtration model, was near one. The continued appearance of bacteria in the column effluent for several pore volumes after switching to a bacteria-free inlet solution shows attachment to be reversible, though slowly reversible.

Efficacy of a combined system of copper and silver and free chlorine for inactivation of Naegleria fowleri amoebas in water

Electrolytically generated copper and silver ions (400:40 and 800:80 μg/l) were evaluated, separately and combined with 1.0 mg/l free chlorine, for their efficacy in reducing the viable numbers of Naegleria fowleri amoebas in water (pH 7.3 and 23-25°C). Inactivation rates (k = log 10 reduction/min) and T 99 values (exposure time required to achieve a 99% or a 2 log 10 reduction) of the disinfectants were determined. Copper and silver alone, at ratio of 400:40 to 800:80 μg/l caused no significant inactivation of N. fowleri even after 72 hours of exposure (k = 0.00017 and 0.00013, respectively). Addition of 1.0 mg/l free chlorine to water which contained 400:40 or 800:80 μg/l copper and silver resulted in enhanced inactivation rates (k = 0.458 and 0.515, respectively) compared to either chlorine alone (k = 0.33) or the metals alone. Water containing 800:80 μg/l copper and silver with 1.0 mg/l chlorine showed a T 99 value of 3.9 minutes, while chlorine alone showed a T 99 of 6.1 minutes. Enhanced inactivation of N. fowleri by a combined system of free chlorine and copper and silver may be attributed to the different mechanism that each disinfectant utilizes in inactivating the amoebas, and may suggest a synergistic effect.

Synergistic inactivation of Escherichia coli and MS-2 coliphage by chloramine and cupric chloride

Reaction of free chlorine with organic compounds in water during drinking water treatment may lead to the formation of potentially carcinogenic compounds known as trihalomethanes (THMs). Monochloramine and metals have been investigated as alternative disinfectants. However, the action of either disinfectant alone requires greater concentrations and longer contact times compared to free chlorine. This experiment evaluated the efficacy of combining monochloramine (1–2.5 mg/l) and copper in the form of cupric chloride (0.1–0.8 mg/l) to determine if inactivation of MS-2 coliphage and Escherichia coli was synergistic and thereby decreasing the concentration and contact time for adequate inactivation of these organisms. Combination of 5 mg/l monochloramine and 0.1–0.4 mg/l cupric chloride was sufficient to produce a 3 log10 inactivation of MS-2 coliphage after 10 min. Nearly 120 min was required for the same log10 inactivation of MS-2 using 5 mg/l monochloramine alone and less than a 0.5 log10 reduction was observed after 120 min using 0.4 mg/l cupric chloride alone. A 6 log10 reduction of E. coli was observed after 10- and 20-min exposures to 2.5 mg/l monochloramine and 0.8 or 0.4 mg/l cupric chloride, respectively. To achieve the same inactivation of E. coli using monochloramine alone, a concentration and contact time of 5 mg/l for 60 min was required. No inactivation of E. coli was observed after exposure to 0.4 or 0.8 mg/l cupric chloride after 60 min. Synergism was demonstrated in the inactivation of both organisms using the combined chloramine copper system.

Oligotrophic bacteria in ultra-pure water systems: Media selection and process component evaluations

SummaryPresently, tryptic soy agar (TSA) medium is used in the semiconductor industry to determine the concentration of viable oligotrophic bacteria in ultra-pure water systems. Deionized water from an ultra-pure water pilot plant was evaluated for bacterial growth at specific locations, using a non-selective medium (R2A) designed to detect injured heterotrophic as well as oligotrophic bacteria. Results were compared to those obtained using Tryptic Soy Agar. Statistically greater numbers of bacteria were observed when R2A was used as the growth medium. Total viable bacterial numbers were compared both before and after each treatment step of the recirculating loop to determine their effectiveness in removing bacteria. The reduction in bacterial numbers for the reverse osmosis unit, the ion exchange bed, and the ultraviolet sterilizer were 97.4%, 31.3%, and 72.8%, respectively, using TSA medium, and 98.4%, 78.4%, and 35.8% using R2A medium. The number of viable bacteria increased by 60.7% based on TSA medium and 15.7% based on R2A medium after passage of the water through an in-line 0.2-μm pore size nylon filter, probably because of the growth of bacteria on the filter. Our results suggest that R2A medium may give a better representation of the microbial water quality in ultra-pure water systems and therefore a better idea of the effectiveness of the various treatment processes in the control of bacteria.

Inactivation of Legionella pneumophila by potassium permanganate.

Abstract Potassium permanganate (KMnO4) was investigated for its ability to inactivate cultures of agar‐grown Legionella pneumophila in a phosphate buffer (pH 6.0 and pH 8.0) at 7°C At pH 6.0, significantly higher inactivation rates, k values, (0.300 log10 reduction min−1 of L. pneumophila were observed compared to those at pH 8.0 (0.032 log10 reduction min−1). By exposure to 5.0 mg L−1 KMnO4 more than 99% (2 log10 cfu mL−1) reduction in the bacterial numbers was achieved within 10 minutes at pH 6.0; however, at pH 8.0, at least 60 min was required for 99% reduction. KMnO4 was significantly more effective at 5.0 mg L−1 compared to 2.5 and 1.0 mg L−1. Water systems with KMnO4 may gain disinfection credits as proposed by the U.S. Environmental Protection Agency.

Inactivation of Bacteriophage MS‐2 and poliovirus in copper, galvanized and plastic domestic water pipes

Survival of bacteriophage MS‐2 and poliovirus was evaluated in new and aged copper, galvanized and plastic polymer (polybutylene, cross‐linked polyethylene, polyvinylchloride) pipes. Inactivation rates (k = — [log10Ct — log10C0]/t) were calculated as a log10 reduction h‐1. Levels of copper leached from copper pipes, over a period of 24 h, ranged from 400–800 μg 1‐1. Numbers of viable MS‐2 were reduced significantly in copper pipes (k = 0.32) compared to plastic polymer pipes (k: = 0.03). New galvanized pipes showed greater inactivation of MS‐2 (k = 2.57) when compared to new copper pipes, and similar rates were also observed in the aged pipes. Poliovirus showed more resistance (k = 0.015 and 0.009 for copper and galvanized pipes, respectively) to the action of copper and galvanized pipes than MS‐2. Addition of 0.20 (μg 1‐1 free chlorine to water containing 400 (μg 1‐1 leached copper significantly enhanced the inactivation of both viruses (k = 4.74 for MS‐2 and 0.04 for poliovirus, respectively) when compa...

Evaluation of potassium permanganate for inactivation of bacteriophage MS‐2 in water systems

Abstract Potassium permanganate (KMnO4) has been as an oxidant for decades to remove and control iron and manganese in surface water supplies. This oxidant was investigated for its ability to inactivate bacteriophage MS‐2 and thereby reduce the amount of chlorine required for a 99.99% reduction of virus during drinking water treatment as required by the U.S. Environmental Protection Agencys Surface Treatment Rule (U.S. EPA 1989). Experiments were conducted in potassium monophosphate buffer (pH 6.0 and pH 8.0) at 7°C. At time intervals from 0 to 30 min, samples were taken and mixed immediately with a solution of sodium thiosulfate:sodium thioglycolate to neutralize residual KMnO4. At 0.5 and 5.0 mg/L KMnO4, results showed no significant differences (p<:0.05) in the inactivation of MS‐2 between experiments done at pH 6.0 and those at pH 8.0. Ninety‐nine percent of the virus was inactivated after 50, 35, and 5 min of exposure time to 0.5, 1.5, and 5.0 mg/L potassium permanganate at pH 8.0, respectively. It ...