Elimination of human enteric viruses during conventional waste water treatment by activated sludge

The present study was undertaken to determine if viruses were selectively eliminated during waste water treatment. Human enteric viruses were detected at all steps of treatment in a conventional activated sludge waste water treatment plant. Liquid overlays and large volume sampling with multiple passages on BGM cells permitted the detection of poliovirus (serotypes 1, 2, and 3), coxsackievirus B (serotypes 1, 2, 3, 4, and 5), and echovirus (serotypes 3, 14, and 22), as well as reoviruses. The mean virus concentration was 95.1 most probable number of infectious units per litre (mpniu/L) in raw sewage, 23.3 in settled water, 1.4 in effluent after activated sludge treatment, and 40.3 mpniu/L in sludge samples. All samples of raw sewage and settled water, 79% of effluent water, and 94% of sludge samples contained viruses. The mean reduction was 75% after settling and 98% after activated sludge treatment. Poliovirus type 3 was rarely isolated after the activated sludge treatment, but was still detected in about one-third of the sludge samples. Reoviruses and coxsackieviruses were detected at similar rates from all samples and appear to be more resistant to the activated sludge treatment than poliovirus type 3. Poliovirus types 1 and 2 were present in almost every sample of raw sewage and settled water and still found in about half of the effluent and sludge samples, indicating a level of resistance similar to that of reoviruses and coxsackieviruses.     

Sporicidal Action of Auto-oxidized Ascorbic Acid for Clostridium

Neutralized ascorbic acid (AA), buffered or unbuffered and autoclaved or filter-sterilized, was sporicidal for Clostridium. A 0.2% concentration of AA was generally employed, and spore counts were made in a soft-agar modification of Wynne's medium in Prickett tubes. Spores of Clostridium botulinum 115B were less susceptible than those of C. sporogenes PA 3679, whereas C. bifermentans spores were by far the most sensitive. At 75 C, spores of PA 3679 were killed at a rate of about 9% at 0 min (warm-up) to 99+% at 100 min. The lower the temperature, the longer the time needed for a given lethality. The percentage of killing increased with increasing concentrations of AA, and the rate of killing was lower at a higher concentration of spores. At least two mechanisms were operative: a major mechanism involving a product(s) of AA auto-oxidation, and a minor mechanism involving copper-ascorbate toxicity. AA reduced in natural gas was not sporicidal after 18.5 hr at 25 C, whereas 92% of the spores were killed by oxidized AA. Although H(2)O(2) per se was sporicidal, catalase did not reverse lethality of fresh or oxidized AA. Dehydroascorbate was as sporicidal as any AA preparation. Added copper (0.00001%) increased the rate of lethality of freshly prepared AA from 66 to 83% but was not effective with thoroughly oxidized AA. Ethylenediaminetetraacetic acid, NH(4) (+), and phosphate partially reversed AA toxicity, deionized water had no effect, and complex media, as well as thioglycolate, eliminated AA lethality. Since the percentage of killing was affected by spore concentration, AA did not seem to stimulate "lethal germination."     

Development of toxicity tolerant water hyacinth (Eichhornea crassipes) for effective treatment of raw sewage

Pioneering research efforts in the handling of municipal sewage in developing countries have involved the use of water hyacinth (Eichhornea crassipes) to purify sewage for possible re-use of the effluent water for domestic purposes. The ability of water hyacinth to remove pollution from raw sewage has been found to be impaired by sewage toxicity. Trials were therefore carried out to adapt water hyacinth to toxicity and thereby increase its ability to remove pollutants from raw sewage. The plants were adapted using an active bio-degrader consisting of Pseudomonas aeruginosa, Escherichia coli, Klebsiella ozaenae, Klebsiella edwardsiella and Baccillus subtilis. The adaptation progressed through 20, 40, 60 and 80% sewage dilution until plants capable of growth in 100% raw sewage were obtained. Plants were observed for morphological growth and at four weeks, samples were collected for tissue analysis. The plants progressively absorbed nutrients from sewage up to the fourth week, when signs of toxicity were obsereved through wilting, loss of turgidity and reduction in leaf number. However, plants that survived through a series of adaptations under various sewage dilutions exhibited luxuriant growth on raw sewage. In synergy with the active bio-degrader, the efficiency of the adapted water hyacinth to remove pollutants (nutrients) from raw sewage was enhanced by 93%.     

Settling rates and density of spores of Henneguya doori (Myxosporea) in water.

Using Henneguya doori from Perca flavescens (yellow perch), the current study provides a method for examining settling rates, attitudes, and densities of myxosporean spores. Fresh and fixed spores settled similarly at 8.34 x 10(-6) m/sec and 8.53 x 10(-6) m/sec, respectively. The spores settled in the anterior end first, did not rotate, and had a specific gravity of 1.062. Comparison of settling rates proved more effective for determining spore density than direct chemical estimation. The slow rate of settling permits effective dispersal in open water.     

THE EFFECT OF CERTAIN SOIL TREATMENTS ON DIDYMELLA STEM-ROT OF TOMATOES

About 93% of Didymella lycopersici spores were destroyed after 4 weeks incubation in unsterilized soil. A survey of the microflora of glasshouse soil receiving different treatments and inoculated with D. lycopersici showed no clear relation between numbers of any group of organisms and the incidence of stem rot. Sterilized soil was not made toxic to D. lycopersici by the growth of a number of soil microorganisms even after 9 months incubation, but addition of unsterilized soil or of a suspension of unsterilized soil quickly restored toxicity. Direct observations of spores in soil on slides showed that their fate varied with the treatment of the soil before inoculation. With fresh soil or air-dry soil moistened 2 or more days before inoculation, lysis of spores occurred. With air-dry soil moistened and inoculated simultaneously, some spores germinated but growth of germ tubes soon ceased. No direct connexion could be seen between the fate of the spores and soil microorganisms. Addition of glucose to unsterilized soil reduced its toxicity to D. lycopersici. Soils steamed for 1 min. or longer were not toxic to D. lycopersici , but soils steamed for very short periods were as toxic as unsterilized soils although the soil microflora was much reduced.     

水体中病毒浓缩方法及其条件优化

本研究探讨了在自来水和污水两种不同的水体环境中, 三氯化铝沉淀法和正电荷滤膜法浓缩回收病毒的效率, 并比较应用不同的浓缩条件、洗脱物质时的病毒回收率, 从而建立有效的环境样本中病毒的浓缩方法。结果表明, 三氯化铝沉淀法在两种水体中的回收率均较高, 最高回收率分别达到96.0%和92.0%, 但正电荷滤膜法在两种水体中的回收率差别较大。在自来水中, 正电荷滤膜法的最高回收率为93.9%, 在污水中的最高回收率仅为69.9%, 这说明正电荷滤膜法适用于病毒含量较高且悬浮物等杂质较少的样本。在应用于自来水样时, 两种方法均可起到有效的病毒浓缩作用, 但在悬浮物等杂质较多的污水中, 三氯化铝法具有较好的回收效率。     

Virus movement in soil columns flooded with secondary sewage effluent.

Secondary sewage effluent containing about 3 X 10(4) plaque-forming units of polio virus type 1 (LSc) per ml was passed through columns 250 cm in length packed with calcareous sand from an area in the Salt River bed used for ground-water recharge of secondary sewage effluent. Viruses were not detected in 1-ml samples extracted from the columns below the 160-cm level. However, viruses were detected in 5 of 43 100-ml samples of the column drainage water. Most of the viruses were adsorbed in the top 5 cm of soil. Virus removal was not affected by the infiltration rate, which varied between 15 and 55 cm/day. Flooding a column continuosly for 27 days with the sewage water virus mixture did not saturate the top few centimeters of soil with viruses and did not seem to affect virus movement. Flooding with deionized water caused virus desorption from the soil and increased their movement through the columns. Adding CaCl2 to the deionized water prevented most of the virus desorption. Adding a pulse of deionized water followed by sewage water started a virus front moving through the columns, but the viruses were readsorbed and none was detected in outflow samples. Drying the soil for 1 day between applying the virus and flooding with deionized water greatly reduced desorption, and drying for 5 days prevented desorption. Large reductions (99.99% or more) of virus would be expected after passage of secondary sewage effluent through 250 cm of the calcareous sand similar to that used in our laboratory columns unless heavy rains fell within 1 day after the application of sewage stopped. Such virus movement could be minimized by the proper management of flooding and drying cycles.     

Virus movement in soil columns flooded with secondary sewage effluent.

Secondary sewage effluent containing about 3 X 10(4) plaque-forming units of polio virus type 1 (LSc) per ml was passed through columns 250 cm in length packed with calcareous sand from an area in the Salt River bed used for ground-water recharge of secondary sewage effluent. Viruses were not detected in 1-ml samples extracted from the columns below the 160-cm level. However, viruses were detected in 5 of 43 100-ml samples of the column drainage water. Most of the viruses were adsorbed in the top 5 cm of soil. Virus removal was not affected by the infiltration rate, which varied between 15 and 55 cm/day. Flooding a column continuosly for 27 days with the sewage water virus mixture did not saturate the top few centimeters of soil with viruses and did not seem to affect virus movement. Flooding with deionized water caused virus desorption from the soil and increased their movement through the columns. Adding CaCl2 to the deionized water prevented most of the virus desorption. Adding a pulse of deionized water followed by sewage water started a virus front moving through the columns, but the viruses were readsorbed and none was detected in outflow samples. Drying the soil for 1 day between applying the virus and flooding with deionized water greatly reduced desorption, and drying for 5 days prevented desorption. Large reductions (99.99% or more) of virus would be expected after passage of secondary sewage effluent through 250 cm of the calcareous sand similar to that used in our laboratory columns unless heavy rains fell within 1 day after the application of sewage stopped. Such virus movement could be minimized by the proper management of flooding and drying cycles.     

Growth of moulds inoculated into commercial mineral water

The growth of mould spores of Penicillium sp. and Cladosporium sp. inoculated in a commercial mineral water product was studied. The strains had been isolated as fungal foreign bodies in commercial mineral waters. In product A, which was not originally sterilized and was contaminated with psychrophilic bacteria, the inoculated mould spores of the strains did not grow; no increases in viable colony counts or beta-glucans concentration in the samples were observed during storage. In a sterilized product A, inoculated spores of the strains grew into visible foreign bodies. The viable colony counts and the beta-glucans concentration in the samples increased during storage. These results showed that in a sterilized mineral water product, mould spores could grow into visible foreign bodies.     

Genetoxicity of water samples from the scenic Lijang river in the Guilin area, China, evaluated by Tradescantia bioassays.

The Lijang river which passes through the Guilin mountains, and Guilin city is a world renowned scenic spot on the southwest border of China. The river and its tributaries receive water from the mountain tops and springs underground. The river water was clean two decades ago before the development of industrial establishments and extra heavy tourism. Deforestation over the mountain tops on the upper stream and its tributaries in the last decades has created serious erosion and increased sedimentation in the river. In the present study, the Tradescantia micronucleus (Trad-MCN) and Tradescantia stamen hair mutation (Trad-SHM) assays were used to evaluate the genetoxicity of water samples collected from 60 different sites along the river. Results indicate that most of the water samples from the tributaries were highly mutagenic, and that pollutants had accumulated in the main river in the Guilin city area from the industrial effluent and city sewage. Both the Trad-MCN and Trad-SHM assays were highly effective for the detection of mutagens in the water samples.     

Importance of convection to the enhancement of erythrocyte sedimentation rates in inclined tubes

Erythrocytes were settled from whole blood in standard 200 x 2.5 mm erythrocyte settling rate tubes placed vertically and at various angles from 85 degrees to 15 degrees from the horizontal. In all cases sedimentation rates measured along the slope increased with decreasing angle from the horizontal. Vertical settled distances rapidly increased down to an angle of 70 degrees and then changed very little even down to angles as shallow as 30 degrees. Evidence is presented that convection plays a significant role in the inclined settling of erythrocytes, as has already been demonstrated with clay, or glass bead suspensions in water. Inclined settling enhancements obtained are quite similar to those observed under similar conditions with yeast cells in aqueous glucose.     

Microbial transformation of nitroaromatic compounds in sewage effluent

The transformation of mono- and dinitroaromatic compounds was measured in sewage effluent maintained under aerobic or anaerobic conditions. Most of the nitrobenzene, 3- and 4-nitrobenzoic acids, and 3- and 4-nitrotoluenes and much of the 1,2- and 1,3-dinitrobenzenes disappeared both in the presence and absence of oxygen. Under anaerobiosis, 2,6-dinitrotoluene and 3,5-dinitrobenzoic acid disappeared slowly, but no loss was evident in 28 days in aerated sewage. Aromatic amines did not accumulate during the aerobic decomposition of the mononitro compounds. They did appear in nonsterile, but not in sterile, sewage incubated aerobically with the dinitro compounds and anaerobically with all the chemicals. Analysis by gas chromatography and combined gas chromatography-mass spectrometry showed that aniline was formed from nitrobenzene, toluidine was formed from 3- and 4-nitrotoluenes, and aminobenzoic acid was formed from 3- and 4-nitrobenzoic acids under anaerobiosis, and that nitroaniline was formed from 1,2- and 1,3-dinitrobenzenes, aminonitrotoluene resulted from 2,6-dinitrotoluene, and aminonitrobenzoic acid was a product of 3,5-dinitrobenzoic acid under both conditions. The isomeric forms of the metabolites were not established. Aniline, 4-toluidine, and 4-aminobenzoic acid added to sewage disappeared from aerated nonsterile, but not from sterile, sewage or sewage in the absence of oxygen. 2-Nitroaniline, 2-amino-3-nitrotoluene, and 2-amino-5-nitrobenzoic acid added to sewage persisted for at least 60 days in aerobic or anaerobic conditions. Gas chromatographic and gas chromatographic-mass spectrometric analyses demonstrated that acetanilide and 2-methylquinoline were formed from aniline, 4-methylformanilide and 4-methylacetanilide were formed from 4-toluidine, 2-methylbenzimidazole was a product of 2-nitroaniline, and unidentified benzimidazoles were formed from 2-amino-3-nitrotoluene in the absence of oxygen, and that 2-nitroacetanilide and 2-methyl-6-nitroacetanilide were formed from 2-nitroaniline and 2-amino-3-nitrotoluene, respectively, in the presence or absence of oxygen. It is suggested that the transformations of widely used nitroaromatic compounds should be further studied because of the persistence and possible toxicity of products of their metabolism.     

Microbial Transformation of Nitroaromatic Compounds in Sewage Effluent

The transformation of mono- and dinitroaromatic compounds was measured in sewage effluent maintained under aerobic or anaerobic conditions. Most of the nitrobenzene, 3- and 4-nitrobenzoic acids, and 3- and 4-nitrotoluenes and much of the 1,2- and 1,3-dinitrobenzenes disappeared both in the presence and absence of oxygen. Under anaerobiosis, 2,6-dinitrotoluene and 3,5-dinitrobenzoic acid disappeared slowly, but no loss was evident in 28 days in aerated sewage. Aromatic amines did not accumulate during the aerobic decomposition of the mononitro compounds. They did appear in nonsterile, but not in sterile, sewage incubated aerobically with the dinitro compounds and anaerobically with all the chemicals. Analysis by gas chromatography and combined gas chromatography-mass spectrometry showed that aniline was formed from nitrobenzene, toluidine was formed from 3- and 4-nitrotoluenes, and aminobenzoic acid was formed from 3- and 4-nitrobenzoic acids under anaerobiosis, and that nitroaniline was formed from 1,2- and 1,3-dinitrobenzenes, aminonitrotoluene resulted from 2,6-dinitrotoluene, and aminonitrobenzoic acid was a product of 3,5-dinitrobenzoic acid under both conditions. The isomeric forms of the metabolites were not established. Aniline, 4-toluidine, and 4-aminobenzoic acid added to sewage disappeared from aerated nonsterile, but not from sterile, sewage or sewage in the absence of oxygen. 2-Nitroaniline, 2-amino-3-nitrotoluene, and 2-amino-5-nitrobenzoic acid added to sewage persisted for at least 60 days in aerobic or anaerobic conditions. Gas chromatographic and gas chromatographic-mass spectrometric analyses demonstrated that acetanilide and 2-methylquinoline were formed from aniline, 4-methylformanilide and 4-methylacetanilide were formed from 4-toluidine, 2-methylbenzimidazole was a product of 2-nitroaniline, and unidentified benzimidazoles were formed from 2-amino-3-nitrotoluene in the absence of oxygen, and that 2-nitroacetanilide and 2-methyl-6-nitroacetanilide were formed from 2-nitroaniline and 2-amino-3-nitrotoluene, respectively, in the presence or absence of oxygen. It is suggested that the transformations of widely used nitroaromatic compounds should be further studied because of the persistence and possible toxicity of products of their metabolism.     

大沽排污河生态修复河道水质综合评价及生物毒性影响

为了改善城市河道水质,实现排污河污染控制与修复,在天津市大沽排污河的上游代表性河段开展了河道原位生态修复工程示范。对植物修复后河道的污染状况进行了监测和分析,与清洁河道做了比较,并对水质修复效果和生物毒性影响状况进行综合分析和评价,研究生态修复示范工程对排污河水质的修复效果和生态效应。结果表明:经种植水葱等水生植物进行生态修复后,河道污染一定程度上降低,水质得到改善。大沽河主要污染是营养元素N、P污染和有机物污染,重金属污染不严重。植物修复对电导率、溶解性总固体(TDS)、盐度、氯化物有一定影响,但影响不显著;对COD等有机污染的修复效果较好,最高去除效率可达54%,但相比清洁水域值依然较高,有机污染依然较严重;对营养元素N、P没有修复效果,反而修复区有升高的趋势,相对清洁水域污染严重。主成分分析表明水质参数主要是氨氮、总氮、总磷代表的营养元素及pH值、DO、电导率、TDS、盐度和氯化物,综合评定结果显示修复区域芦苇根部水质最好;聚类分析将17个水质指标分成5类,并与主成分分析结果显示出一致性。植物根际周边的微生物数量多,群落多样性高。植物修复对水样植物毒性影响明显,能降低其毒性;水样对发光菌均具有毒性作用,存在潜在的急性生物毒性;修复区水样对水生动物大型蚤不存在急性生物毒性。     

Vacuum Probe: New Approach to the Microbiological Sampling of Surfaces

The need for a device to sample large areas that are lightly contaminated with microorganisms motivated the development of the vacuum probe. The intended use of the instrument is to sample clean surfaces in laminar flow clean rooms, but the device could be used for sampling surfaces in other clean environments. Such a device was designed, fabricated, and tested at Sandia Laboratories, Albuquerque, N.M. In these tests, the vacuum probe removed a mean of 89% and assayed a mean of 67% of bacterial spores, approximately 1 mum in length, settled on smooth surfaces which were free from viscous films.     

Leaching of boron through sewage sludge amended soil: the role of clinoptilolite

A laboratory experiment was conducted to determine the release of boron from soil-sewage sludge mixtures by leaching using a clinoptilolite type natural zeolite, before land application of the sewage sludge. Soil columns were filled up with the clinoptilolite soil after mixing with sewage sludge at a rate of 30 tons ha(-1) and with two different particle sizes (0.1-0.25 and 1.0-2.0 mm) of clinoptilolite each at the concentrations of 1% and 2%. The particle size and the application rate of clinoptilolite affected both boron leaching from soil compared to the control treatment (soil and sewage sludge mixture). The total soluble boron leached from a soil column varied from 66-92% depending on the applications of clinoptilolite and reached 96% for the control treatment, following application of 80 cm depth of water in all treatments. In the cases of the 1% application rate of 0.1-0.25 and 1-2 mm sized clinoptilolite 78% and 92% of the total boron leached, respectively. While at 2% application rate of 0.1-0.25 and 1-2 mm zeolite, 66% and 87% of total soluble boron leached, respectively. Boron concentrations in the soil layers increased as application rate increased and particle size of clinoptilolite decreased because of its high adsorption capacity. Adsorption isotherms indicated that clinoptilolite had a high adsorption capacity for boron compared to the sewage sludge and soil.     

Interactions and Survival of Enteric Viruses in Soil Materials

There were marked differences in the abilities of eight different soil materials to remove and retain viruses from settled sewage, but for each soil material the behavior of two different viruses, poliovirus type 1 and reovirus type 3, was often similar. Virus adsorption to soil materials was rapid, the majority occurring within 15 min. Clayey materials efficiently adsorbed both viruses from wastewater over a range of pH and total dissolved solids levels. Sands and organic soil materials were comparatively poor adsorbents, but in some cases their ability to adsorb viruses increased at low pH and with the addition of total dissolved solids or divalent cations. Viruses in suspensions of soil material in settled sewage survived for considerable time periods, despite microbial activity. In some cases virus survival was prolonged in suspensions of soil materials compared to soil-free controls. Although sandy and organic soil materials were poor virus adsorbents when suspended in wastewater, they gave ≥95% virus removal from intermittently applied wastewater as unsaturated, 10-cm-deep columns. However, considerable quantities of the retained viruses were washed from the columns by simulated rainfall. Under the same conditions, clayey soil material removed ≥99.9995% of the viruses from applied wastewater, and none were washed from the columns by simulated rainfall.     

Survival of Filamentous Fungi in Hypersaline Dead Sea Water

A variety of filamentous fungi have recently been isolated from the Dead Sea (340 g/L total dissolved salts). To assess the extent to which such fungi can survive for prolonged periods in Dead Sea water, we examined the survival of both spores and mycelia in undiluted Dead Sea water and in Dead Sea water diluted to different degrees with distilled water. Mycelia of Aspergillus versicolor and Chaetomium globosum strains isolated from the Dead Sea remained viable for up to 8 weeks in undiluted Dead Sea water. Four Dead Sea isolates (A. versicolor, Eurotium herbariorum, Gymnascella marismortui, and C. globosum) retained their viability in Dead Sea water diluted to 80% during the 12 weeks of the experiment. Mycelia of all species survived for the full term of the experiment in Dead Sea water diluted to 50% and 10% of its original salinity. Comparison of the survival of Dead Sea species and closely related isolates obtained from other locations showed prolonged viability of the strains obtained from the Dead Sea. Spores of isolates obtained from the terrestrial shore of the Dead Sea generally proved less tolerant to suspension in undiluted Dead Sea water than spores of species isolated from the water column. Spores of the species isolated from the control sites had lost their viability in undiluted Dead Sea water within 12 weeks. However, with the exception of Emericella spores, which showed poor survival, a substantial fraction of the spores of Dead Sea fungal isolates remained viable for that period. The difference in survival rate between spores and mycelia of isolates of the same species points to the existence of adapted halotolerant and/or halophilic fungi in the Dead Sea.     

The sensitivity and reproducibility of the zebrafish (Danio rerio) embryo test for the screening of waste water quality and for testing the toxicity of chemicals

The sensitivity of the zebrafish embryo test, a test proposed for routine waste water control, was compared with the acute fish toxicity test, in the determination of six types of waste water and ten different chemicals. The waste water was sampled from the following industrial processes: paper and cardboard production, hide tanning, metal galvanisation, carcass treatment and utilisation, and sewage treatment. The chemicals tested were: dimethylacetamide, dimethylsulphoxide, cadmium chloride, cyclohexane, hydroquinone, mercuric chloride, nickel chloride, nonylphenol, resmethrin and sodium nitrite. For many of the test substances, the zebrafish embryo test and the acute fish toxicity test results showed high correlations. However, there were certain environmentally-relevant substances for which the results of the zebrafish embryo test and the acute fish toxicity test differed significantly, up to 10,000-fold (Hg(2+) > 150-fold difference; NO(2)(-) > 300-fold; Cd(2+) > 200-fold; resmethrin > 10,000-fold). For the investigated waste water samples and chemicals, the survival rate of the zebrafish embryos showed high variations between different egg samples, within the range of the EC50 concentration. Subsequently, 5-6 parallel assays were deemed to be the appropriate number necessary for the precise evaluation of the toxicity of the test substances. Also, it was found that the sensitivities of different ontogenetic stages to chemical exposure differed greatly. During the first 12 hours after fertilisation (4-cell stage to the 5-somite stage), the embryos reacted most sensitively to test substance exposure, whereas the later ontogenetic stages showed only slight or no response, indicating that the test is most sensitive during the first 24 hours post-fertilisation.     

Interactions and survival of enteric viruses in soil materials

There were marked differences in the abilities of eight different soil materials to remove and retain viruses from settled sewage, but for each soil material the behavior of two different viruses, poliovirus type 1 and reovirus type 3, was often similar. Virus adsorption to soil materials was rapid, the majority occurring within 15 min. Clayey materials efficiently adsorbed both viruses from wastewater over a range of pH and total dissolved solids levels. Sands and organic soil materials were comparatively poor adsorbents, but in some cases their ability to adsorb viruses increased at low pH and with the addition of total dissolved solids or divalent cations. Viruses in suspensions of soil material in settled sewage survived for considerable time periods, despite microbial activity. In some cases virus survival was prolonged in suspensions of soil materials compared to soil-free controls. Although sandy and organic soil materials were poor virus adsorbents when suspended in wastewater, they gave >/=95% virus removal from intermittently applied wastewater as unsaturated, 10-cm-deep columns. However, considerable quantities of the retained viruses were washed from the columns by simulated rainfall. Under the same conditions, clayey soil material removed >/=99.9995% of the viruses from applied wastewater, and none were washed from the columns by simulated rainfall.