Virus movement in soil during saturated and unsaturated flow.

Virus movement in soil during saturated and unsaturated flow was compared by adding poliovirus to sewage water and applying the water at different rates to a 250-cm-long soil column equipped with ceramic samplers at different depths. Movement of viruses during unsaturated flow of sewage through soil columns was much less than during saturated flow. Viruses did not move below the 40-cm level when sewage water was applied at less than the maximum infiltration rate; virus penetration in columns flooded with sewage was at least 160 cm. Therefore, virus movement in soils irrigated with sewage should be less than in flooded groundwater recharge basins or in saturated soil columns. Management of land treatment systems to provide unsaturated flow through the soil should minimize the depth of virus penetration. Differences in virus movement during saturated and unsaturated flow must be considered in the development of any model used to simulate virus movement in soils.     

Effect of soil permeability on virus removal through soil columns.

Laboratory experiments were performed on four different soils, using 100 cm long columns, to determine the extent of virus movement when wastewater percolated through the soils at various hydraulic flow rates. Unchlorinated secondary sewage effluent seeded with either poliovirus type 1 (strain LSc) or echovirus type 1 (isolate V239) was continuously applied to soil columns for 3 to 4 days at constant flow rates. Water samples were extracted daily from ceramic samplers at various depths of the column for the virus assay. The effectiveness of virus removal from wastewater varied greatly among the different soil types but appeared to be largely related to hydraulic flow rates. At a flow rate of 33 cm/day, Anthony sandy loam removed 99% of seeded poliovirus within the first 7 cm of the column. At flow rates of 300 cm/day and above, Rubicon sand gave the poorest removal of viruses; less than 90% of the seeded viruses were removed by passage of effluent through the entire length of the soil column. By linear regression analyses, the rate of virus removal in soil columns was found to be negatively correlated with the flow of the percolating sewage effluent. There was no significant difference in rate of removal between poliovirus and echovirus in soil columns 87 cm long. The rate of virus removal in the upper 17 cm of the soil column was found to be significantly greater than in the lower depths of the soil column. This study suggests that the flow rate of water through the soil may be the most important factor in predicting the potential of virus movement into the groundwater. Furthermore, the length of the soil column is critical in obtaining useful data to predict virus movement into groundwater.     

Effect of soil permeability on virus removal through soil columns

Laboratory experiments were performed on four different soils, using 100 cm long columns, to determine the extent of virus movement when wastewater percolated through the soils at various hydraulic flow rates. Unchlorinated secondary sewage effluent seeded with either poliovirus type 1 (strain LSc) or echovirus type 1 (isolate V239) was continuously applied to soil columns for 3 to 4 days at constant flow rates. Water samples were extracted daily from ceramic samplers at various depths of the column for the virus assay. The effectiveness of virus removal from wastewater varied greatly among the different soil types but appeared to be largely related to hydraulic flow rates. At a flow rate of 33 cm/day, Anthony sandy loam removed 99% of seeded poliovirus within the first 7 cm of the column. At flow rates of 300 cm/day and above, Rubicon sand gave the poorest removal of viruses; less than 90% of the seeded viruses were removed by passage of effluent through the entire length of the soil column. By linear regression analyses, the rate of virus removal in soil columns was found to be negatively correlated with the flow of the percolating sewage effluent. There was no significant difference in rate of removal between poliovirus and echovirus in soil columns 87 cm long. The rate of virus removal in the upper 17 cm of the soil column was found to be significantly greater than in the lower depths of the soil column. This study suggests that the flow rate of water through the soil may be the most important factor in predicting the potential of virus movement into the groundwater. Furthermore, the length of the soil column is critical in obtaining useful data to predict virus movement into groundwater.     

Poliovirus removal from primary and secondary sewage effluent by soil filtration.

Adsorption of poliovirus from primary sewage effluent was similar to that from secondary sewage effluent in both batch soil studies and experiments with soil columns 240 cm long. Virus desorption by distilled water was also similar in a soil column that had been flooded with either primary or secondary effluent seeded with virus. These results indicated that absorption of poliovirus from primary effluent and virus movement through the soil were not affected by the higher organic content of primary sewage effluent.     

Poliovirus removal from primary and secondary sewage effluent by soil filtration.

Adsorption of poliovirus from primary sewage effluent was similar to that from secondary sewage effluent in both batch soil studies and experiments with soil columns 240 cm long. Virus desorption by distilled water was also similar in a soil column that had been flooded with either primary or secondary effluent seeded with virus. These results indicated that absorption of poliovirus from primary effluent and virus movement through the soil were not affected by the higher organic content of primary sewage effluent.     

Effect of Ionic Composition of Suspending Solution on Virus Adsorption by a Soil Column

The effect of various electrolytes on the adsorption of poliovirus was measured in 250-cm-long soil columns with ceramic samplers at different depths. Viruses suspended in deionized water moved much farther through the soil than those suspended in tap water, whereas movement in sewage water was intermediate. The salt content of the tap water and sewage water promoted virus adsorption, but evidently the organic compounds in sewage retarded adsorption. When viruses were suspended in chloride solutions of K⁺, Na⁺, Ca⁺, and Mg²⁺, virus adsorption increased as the cation concentration and valence increased. The depth of virus penetration was related to the ionic strength of the solutions. Virus penetration data for NO₃⁻, SO₄²⁻, and H₂PO₄⁻ salts of K⁺, Na⁺, and Ca²⁺ indicated that other anions were more effective than Cl⁻ in promoting virus adsorption. Also, NH₄⁺ was more effective than other cations in limiting the penetration depth of viruses. It seems that ions composed of radicals are more effective than ions composed of single atoms in promoting virus adsorption. Al³⁺ was the most effective ion in limiting virus penetration, probably owing to flocculation of the viruses. Adding AlCl₃ concentrations to secondary sewage effluent to provide an Al³⁺ concentration of 0.1 mM reduced the virus penetration depth to 40 cm. These studies show that the ionic composition of the suspending solutions must be considered in predicting virus penetration depths, and it may be practical to add low concentrations of a flocculating agent such as AlCl₃ to sewage water to limit virus movement through very porous soils.     

Effects of organic matter on virus transport in unsaturated flow.

The effects of natural humic material and sewage sludge organic matter (SSOM) derived from primary treated sewage sludge on virus transport by unsaturated flow through soil columns were evaluated. Bacteriophage MS-2 was applied to loamy fine sand columns 0.052 m in diameter and 1.05 m long. Virus concentrations in the influent and effluent were measured daily for 7 to 9 days. In the first experiment, virus transport through two fresh soil columns was compared with that through a column previously leached with more than four pore volumes (T) of well water. The soil water organic matter concentrations in the leachate of the fresh soil declined with time. Relative virus concentrations (C/Co) from one fresh soil column reached 0.82 in 0.9 T and then declined to 0.51 by 2.1 T. The other fresh soil column reached and maintained a steady-state relative virus concentration [(C/Co)s] of 0.47 from 1.5 to 2.5 T. The leached column reached and maintained a (C/Co)s of 0.05. Concentrations measured at 0.2-, 0.4-, 0.8-, and 1.05-m depths indicated that most virus particles were removed in the surface 0.2 m. In the second experiment, one leached column was pretreated with SSOM derived from primary treated sewage sludge and the other leached column was untreated. SSOM concentrations declined with depth. A suspension of virus and SSOM in well water was applied to both columns. Although the (C/Co)s values were similar (0.41 for the pretreated column and 0.47 for the untreated column), breakthrough was delayed for the untreated column. Both natural humic material and sewage sludge-derived SSOM increased the unsaturated-flow transport of MS-2.     

Effects of organic matter on virus transport in unsaturated flow.

The effects of natural humic material and sewage sludge organic matter (SSOM) derived from primary treated sewage sludge on virus transport by unsaturated flow through soil columns were evaluated. Bacteriophage MS-2 was applied to loamy fine sand columns 0.052 m in diameter and 1.05 m long. Virus concentrations in the influent and effluent were measured daily for 7 to 9 days. In the first experiment, virus transport through two fresh soil columns was compared with that through a column previously leached with more than four pore volumes (T) of well water. The soil water organic matter concentrations in the leachate of the fresh soil declined with time. Relative virus concentrations (C/Co) from one fresh soil column reached 0.82 in 0.9 T and then declined to 0.51 by 2.1 T. The other fresh soil column reached and maintained a steady-state relative virus concentration [(C/Co)s] of 0.47 from 1.5 to 2.5 T. The leached column reached and maintained a (C/Co)s of 0.05. Concentrations measured at 0.2-, 0.4-, 0.8-, and 1.05-m depths indicated that most virus particles were removed in the surface 0.2 m. In the second experiment, one leached column was pretreated with SSOM derived from primary treated sewage sludge and the other leached column was untreated. SSOM concentrations declined with depth. A suspension of virus and SSOM in well water was applied to both columns. Although the (C/Co)s values were similar (0.41 for the pretreated column and 0.47 for the untreated column), breakthrough was delayed for the untreated column. Both natural humic material and sewage sludge-derived SSOM increased the unsaturated-flow transport of MS-2.     

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.     

Effects of compost produced from town wastes and sewage sludge on the physical properties of a loamy and a clay soil

Organic fertilizer produced by composting 62% town wastes, 21% sewage sludge and 17% sawdust by volume, was applied at the rates of 0 (control), 75, 150 and 300 m³ ha⁻¹ to loamy and clay soils, in order to investigate its potential for soil improvement. The experiments were conducted in areas characterised by a semi-arid climate. The chemical properties of the soils were affected directly by the amendment compost. The physical properties of the amended soils were improved in all cases as far as the saturated and unsaturated hydraulic conductivity, water retention capacity, bulk density, total porosity, pore size distribution, soil resistance to penetration, aggregation and aggregate stability, were concerned. In most of the cases the improvements were proportional to the application rates of the compost and they were greater in the loamy soil than in the clay soil.     

Evaluation of various soil water samplers for virological sampling.

Two commercially available soil water samplers and a ceramic sampler constructed in our laboratories were evaluated for their ability to recover viruses from both tap water and secondary sewage effluent. The ceramic sampler consistently gave the best recoveries of viruses from water samples. Soil columns containing ceramic samplers at various depths provide a simple method for studying virus transport through sewage-contaminated soils.     

Evaluation of various soil water samplers for virological sampling

Two commercially available soil water samplers and a ceramic sampler constructed in our laboratories were evaluated for their ability to recover viruses from both tap water and secondary sewage effluent. The ceramic sampler consistently gave the best recoveries of viruses from water samples. Soil columns containing ceramic samplers at various depths provide a simple method for studying virus transport through sewage-contaminated soils.     

Survival of enteroviruses in rapid-infiltration basins during the land application of wastewater.

The downward migration through soil of seeded poliovirus type 1 and echovirus type 1 and of naturally occurring enteroviruses during infiltration of sewage effluent through rapid-infiltration basins was investigated. After 5 days of flooding, the amount of seeded poliovirus type 1 that had migrated 5 to 10 cm downward through the soil profile was found to be 11% of that remaining at the initial burial depth. The amount of echovirus type 1 determined to have moved an equal distance was at least 100-fold less. Migration of naturally occurring enteroviruses during infiltration of sewage effluent through soil could not be measured with accuracy because of the possibility of virus survival from previous applications of effluent. The rate of inactivation for seeded poliovirus 1 and echovirus 1 buried in the infiltration basins ranged between 0.04 and 0.15 log10 units per day during the time when the basins were flooded. Inactivation of these same seeded virus types and of indigenous enterovirus populations in the infiltration basins during the drying portion of the sewage application cycle ranged between 0.11 and 0.52 log10 units per day. The rate of virus inactivation was dependent upon the rate of soil moisture loss. These results indicate that drying cycles during the land application of wastewater enhance virus inactivation in the soil.     

Survival of enteroviruses in rapid-infiltration basins during the land application of wastewater

The downward migration through soil of seeded poliovirus type 1 and echovirus type 1 and of naturally occurring enteroviruses during infiltration of sewage effluent through rapid-infiltration basins was investigated. After 5 days of flooding, the amount of seeded poliovirus type 1 that had migrated 5 to 10 cm downward through the soil profile was found to be 11% of that remaining at the initial burial depth. The amount of echovirus type 1 determined to have moved an equal distance was at least 100-fold less. Migration of naturally occurring enteroviruses during infiltration of sewage effluent through soil could not be measured with accuracy because of the possibility of virus survival from previous applications of effluent. The rate of inactivation for seeded poliovirus 1 and echovirus 1 buried in the infiltration basins ranged between 0.04 and 0.15 log10 units per day during the time when the basins were flooded. Inactivation of these same seeded virus types and of indigenous enterovirus populations in the infiltration basins during the drying portion of the sewage application cycle ranged between 0.11 and 0.52 log10 units per day. The rate of virus inactivation was dependent upon the rate of soil moisture loss. These results indicate that drying cycles during the land application of wastewater enhance virus inactivation in the soil.     

Poliovirus retention in soil columns after application of chemical- and polyelectrolyte-conditioned dewatered sludges

The transport of poliovirus type 1 (strain LSc) was studied in Red Bay sandy loam columns that were treated with chemical- or polyelectrolyte-conditioned dewatered sludges and then leached with natural rainwater under saturated flow conditions. Poliovirus was concentrated in the alum and ferric chloride sludges that were produced following the flocculation of virus-seeded raw sewage. Virtually complete inactivation of the virus was observed following the flocculation of raw sewage or the stabilization of alum and ferric chloride sludges with lime at pH 11.5. Poliovirus was also concentrated in polyelectrolyte-conditioned dewatered sludge that was produced from virus-seeded, anaerobically digested sludge. Despite the saturated flow conditions for a sustained period, no viruses were detected in the leachates of the soil columns that were treated with these chemical and chemically treated sludges. Since the viruses were mostly associated with the solids in these sludge samples, it is believed that they were immobilized along with the sludge solids in the top portion of the soil columns.     

Poliovirus retention in soil columns after application of chemical- and polyelectrolyte-conditioned dewatered sludges.

The transport of poliovirus type 1 (strain LSc) was studied in Red Bay sandy loam columns that were treated with chemical- or polyelectrolyte-conditioned dewatered sludges and then leached with natural rainwater under saturated flow conditions. Poliovirus was concentrated in the alum and ferric chloride sludges that were produced following the flocculation of virus-seeded raw sewage. Virtually complete inactivation of the virus was observed following the flocculation of raw sewage or the stabilization of alum and ferric chloride sludges with lime at pH 11.5. Poliovirus was also concentrated in polyelectrolyte-conditioned dewatered sludge that was produced from virus-seeded, anaerobically digested sludge. Despite the saturated flow conditions for a sustained period, no viruses were detected in the leachates of the soil columns that were treated with these chemical and chemically treated sludges. Since the viruses were mostly associated with the solids in these sludge samples, it is believed that they were immobilized along with the sludge solids in the top portion of the soil columns.     

Sorption and desorption of arsenic from sandy soils: Column studies

Rate‐limited sorption/desorption can have a profound effect upon the transport of sorbing contaminants. Numerical and analytical models used to predict chemical movement through the subsurface rarely incorporate the effects of nonlinear sorption and desorption kinetics, resulting in potentially large overestimates of mass extractability. Mass transfer characteristics of arsenic‐contaminated soils at the site of a former arsenical herbicide manufacturer in Houston, Texas, were examined in the laboratory using soil columns. Unaffected soils comprised of silty sands to coarse sands were collected from the uppermost aquifer. Two soil columns were loaded with a known mass of mixed organic and inorganic forms of arsenic resident in site ground water. A third control column was prepared with dry 20 × 30 mesh ASTM silica sand. Leachate samples were collected from each void volume until arsenic breakthrough was achieved. The dynamic test applied a continuing head of water, operating in an upflow mode through 4‐in. diameter by 12‐in. long soil columns repacked to in situ density. A flow‐through velocity of one void volume per day was chosen for arsenic loading to the columns and 0.08 void volume per day during the desorption phase of the test. Uncontaminated ground water was then passed through the columns, and the tests were restarted in the desorption mode. Analysis of the leachate and resulting arsenic concentrations in the test columns allowed for the calculation of distribution coefficients that describe arsenic behavior. Measured distribution coefficients during desorption ranged from 0.26 after one void volume to 3.3 after six void volumes had been passed through the column.     

Ponded infiltration into soil with biopores — field experiment and modeling

Preferential movement of water in macropores plays an important role when the process of ponded infiltration in natural porous systems is studied. For example, the detailed knowledge of water flow through macropores is of a major importance when predicting runoff responses to rainfall events. The main objectives of this study are to detect preferential movement of water in Chernozem soil and to employ numerical modeling to describe the variably saturated flow during a field ponded infiltration experiment. The infiltration experiment was performed at the Macov experimental station (Calcari-Haplic Chernozem in Danubian Lowland, Slovakia). The experiment involved single ring ponded infiltration. At the quasi steady state phase of the experiment dye tracer was added to the infiltrating water. Then the soil profile was excavated and the penetration pattern of the applied tracer was recorded. The abundance of biopores as a product of fauna and flora was found. To quantify the preferential flow effects during the infiltration experiment, three-dimensional axisymmetric simulations were carried out by a two-dimensional dual-continuum numerical model. The water flow simulations based on measured hydraulic characteristics without consideration of preferential flow effects failed to describe the infiltration experiment adequately. The 3D axisymmetric simulation based on dual-permeability approach provided relatively realistic space-time distribution of soil water pressure below the infiltration ring.     

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.