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

A novel approach for stabilizing fresh urine by calcium hydroxide addition

In this study, we investigated the prevention of enzymatic urea hydrolysis in fresh urine by increasing the pH with calcium hydroxide (Ca(OH)2) powder. The amount of Ca(OH)2 dissolving in fresh urine depends significantly on the composition of the urine. The different urine compositions used in our simulations showed that between 4.3 and 5.8 g Ca(OH)2 dissolved in 1 L of urine at 25 °C. At this temperature, the pH at saturation is 12.5 and is far above the pH of 11, which we identified as the upper limit for enzymatic urea hydrolysis. However, temperature has a strong effect on the saturation pH, with higher values being achieved at lower temperatures. Based on our results, we recommend a dosage of 10 g Ca(OH)2 L(-1) of fresh urine to ensure solid Ca(OH)2 always remains in the urine reactor which ensures sufficiently high pH values. Besides providing sufficient Ca(OH)2, the temperature has to be kept in a certain range to prevent chemical urea hydrolysis. At temperatures below 14 °C, the saturation pH is higher than 13, which favors chemical urea hydrolysis. We chose a precautionary upper temperature of 40 °C because the rate of chemical urea hydrolysis increases at higher temperatures but this should be confirmed with kinetic studies. By considering the boundaries for pH and temperature developed in this study, urine can be stabilized effectively with Ca(OH)2 thereby simplifying later treatment processes or making direct use easier.

Transport of Human Adenoviruses in Water Saturated Laboratory Columns

Groundwater may be contaminated with infective human enteric viruses from various wastewater discharges, sanitary landfills, septic tanks, agricultural practices, and artificial groundwater recharge. Coliphages have been widely used as surrogates of enteric viruses, because they share many fundamental properties and features. Although a large number of studies focusing on various factors (i.e. pore water solution chemistry, fluid velocity, moisture content, temperature, and grain size) that affect biocolloid (bacteria, viruses) transport have been published over the past two decades, little attention has been given toward human adenoviruses (hAdVs). The main objective of this study was to evaluate the effect of pore water velocity on hAdV transport in water saturated laboratory-scale columns packed with glass beads. The effects of pore water velocity on virus transport and retention in porous media was examined at three pore water velocities (0.39, 0.75, and 1.22 cm/min). The results indicated that all estimated average mass recovery values for hAdV were lower than those of coliphages, which were previously reported in the literature by others for experiments conducted under similar experimental conditions. However, no obvious relationship between hAdV mass recovery and water velocity could be established from the experimental results. The collision efficiencies were quantified using the classical colloid filtration theory. Average collision efficiency, α, values decreased with decreasing flow rate, Q, and pore water velocity, U, but no significant effect of U on α was observed. Furthermore, the surface properties of viruses and glass beads were used to construct classical DLVO potential energy profiles. The results revealed that the experimental conditions of this study were unfavorable to deposition and that no aggregation between virus particles is expected to occur. A thorough understanding of the key processes governing virus transport is pivotal for public health protection.

Persistence of viruses in desert soils amended with anaerobically digested sewage sludge

Pima County, Ariz., is currently investigating the potential benefits of land application of sewage sludge. To assess risks associated with the presence of pathogenic enteric viruses present in the sludge, laboratory studies were conducted to measure the inactivation rate (k = log(10) reduction per day) of poliovirus type 1 and bacteriophages MS2 and PRD-1 in two sludge-amended desert agricultural soils (Brazito Sandy Loam and Pima Clay Loam). Under constant moisture (approximately -0.05 x 10 Pa for both soils) and temperatures of 15, 27, and 40 degrees C, the main factors controlling the inactivation of these viruses were soil temperature and texture. As the temperature increased from 15 to 40 degrees C, the inactivation rate increased significantly for poliovirus and MS2, whereas, for PRD-1, a significant increase in the inactivation rate was observed only at 40 degrees C. Clay loam soils afforded more protection to all three viruses than sandy soils. At 15 degrees C, the inactivation rate for MS2 ranged from 0.366 to 0.394 log(10) reduction per day in clay loam and sandy loam soils, respectively. At 27 degrees C, this rate increased to 0.629 log(10) reduction per day in clay loam soil and to 0.652 in sandy loam soil. A similar trend was observed for poliovirus at 15 degrees C (k = 0.064 log(10) reduction per day, clay loam; k = 0.095 log(10) reduction per day, sandy loam) and 27 degrees C (k = 0.133 log(10) reduction per day, clay loam; k = 0.154 log(10) reduction per day, sandy loam). Neither MS2 nor poliovirus was recovered after 24 h at 40 degrees C. No reduction of PRD-1 was observed after 28 days at 15 degrees C and after 16 days at 27 degrees C. At 40 degrees C, the inactivation rates were 0.208 log(10) reduction per day in amended clay loam soil and 0.282 log(10) reduction per day in sandy loam soil. Evaporation to less than 5% soil moisture completely inactivated all three viruses within 7 days at 15 degrees C, within 3 days at 27 degrees C, and within 2 days at 40 degrees C regardless of soil type. This suggests that a combination of high soil temperature and rapid loss of soil moisture will significantly reduce risks caused by viruses in sludge.

Comparison of PCR and cell culture for detection of enteroviruses in sludge-amended field soils and determination of their transport

PCR and cell culture assays for enteroviruses were conducted on soil samples collected from an experimental farm that had received mesophilic anaerobically digested sludge for the past 7 years. Of 24 samples assayed, 21 samples were positive by PCR, implying that at least some viral nucleic acid sequences remained intact. However, these viral particles were unable to infect the Buffalo Green Monkey cell line used in subsequent cell culture assays. It is significant that positive PCR detection of nucleic acid sequences occurred even though the most recent sludge application was 3 months prior to soil sampling. Viral nucleic acid sequences were detected by PCR at points vertically and laterally displaced from sludge injections, illustrating significant transport of viruses. Rainfall and irrigation events may have contributed to viral transport.

Hazards from pathogenic microorganisms in land-disposed sewage sludge

Sewage sludge is a complex mixture of organic and inorganic compounds of biological and mineral origin that are precipitated from wastewater and sewage during primary, secondary, and tertiary sewage treatment. Present in these sludges are significant numbers of microorganisms that include viral, bacterial, protozoan, fungal, and helminth pathogens. The treatment of sludge to reduce biochemical oxygen demand, solids content, and odor is not always effective in reducing numbers of pathogens. This becomes a public health concern because the infectious dose for some of these pathogens may be as low as 1 particle (virus) to 50 organisms (Giardia). When sludge is applied to land for agricultural use and landfill compost, these pathogens can survive from days (bacteria) to months (viruses) to years (helminth eggs), depending on environmental conditions. Shallow aquifers can become contaminated with pathogens from sludge and, depending on groundwater flow, these organisms may travel significant distances from the disposal site. Communities that rely on groundwater for domestic use can become exposed to these pathogens, leading to a potential disease outbreak. Currently, methods to determine the risk of disease from pathogens in land-disposed sludge are inadequate because the sensitivity of pathogen detection is poor. The application of recombinant DNA technology (gene probes and polymerase chain reaction) to environmental samples may provide increased sensitivity for detecting specific pathogens in land-disposed sludge and greatly improved risk assessment models for our exposure to these sources of pathogens.