Viable Ascaris Research Articles

Mesophilic anaerobic digestion of waste activated sludge in an intermittent mixing reactor: Effect of hydraulic retention time and organic loading rate

An anaerobic digester was operated at mesophilic temperature and with intermittent mixing conditions to treat waste activated sludge. The organic loading rate (OLR) was increased by decreasing the hydraulic retention time (HRT), and the effect on process performance, digestate characteristics and inactivation of pathogens was investigated. The removal efficiency of total volatile solids (TVS) was also measured by biogas formation. The HRT varied from 50 to 7 days, corresponding to OLR from 0.38 to 2.31 kgTVS.m−3.d−1. The acidity/alkalinity ratio remained within stable limits (lower than 0.6) at 50-, 25- and 17-day HRT; due to an imbalance between the production and consumption of volatile fatty acids, the ratio increased to 0.7 ± 0.2 at HRT of 9 days and 7 days. The highest TVS removal efficiencies were 16, 12 and 9%, which were obtained at 50-, 25- and 17 day-HRT, respectively. Intermittent mixing provided solids sedimentation greater than 30% for almost all HRT tested. The highest methane yields (0.10–0.05 m3.kgTVSfed−1.d−1) were obtained when the reactor was operated at a higher HRT (50-17 days). At lower HRT, methanogenic reactions were likely limited. Zinc and copper were the main heavy metals found in the digestate, while the most probable number (MPN) of coliform bacteria remained below 106 MPN.g TVS−1. Neither Salmonella nor viable Ascaris eggs were found in the digestate. In general, increasing the OLR by decreasing the HRT to 17 days under intermittent mixing conditions provided an attractive alternative to treat sewage sludge despite some limitations due to biogas and methane yields.

Persistent Ascaris Transmission Is Possible in Urban Areas Even Where Sanitation Coverage Is High.

In low-income, urban, informal communities lacking sewerage and solid waste services, onsite sanitation (sludges, aqueous effluent) and child feces are potential sources of human fecal contamination in living environments. Working in informal communities of urban Maputo, Mozambique, we developed a quantitative, stochastic, mass-balance approach to evaluate plausible scenarios of localized contamination that could explain why the soil-transmitted helminth Ascaris remains endemic despite nearly universal coverage of latrines that sequester most fecal wastes. We used microscopy to enumerate presumptively viable Ascaris ova in feces, fecal sludges, and soils from compounds (i.e., household clusters) and then constructed a steady-state mass-balance model to evaluate possible contamination scenarios capable of explaining observed ova counts in soils. Observed Ascaris counts (mean = -0.01 log10 ova per wet gram of soil, sd = 0.71 log10) could be explained by deposits of 1.9 grams per day (10th percentile 0.04 grams, 90th percentile 84 grams) of child feces on average, rare fecal sludge contamination events that transport 17 kg every three years (10th percentile 1.0 kg, 90th percentile 260 kg), or a daily discharge of 2.7 kg aqueous effluent from an onsite system (10th percentile 0.09 kg, 90th percentile 82 kg). Results suggest that even limited intermittent flows of fecal wastes in this setting can result in a steady-state density of Ascaris ova in soils capable of sustaining transmission, given the high prevalence of Ascaris shedding by children (prevalence = 25%; mean = 3.7 log10 per wet gram, sd = 1.1 log10), the high Ascaris ova counts in fecal sludges (prevalence = 88%; mean = 1.8 log10 per wet gram, sd = 0.95 log10), and the extended persistence and viability of Ascaris ova in soils. Even near-universal coverage of onsite sanitation may allow for sustained transmission of Ascaris under these conditions.

Viability determination of Ascaris ova in raw wastewater: a comparative evaluation of culture-based, BacLight Live/Dead staining and PMA-qPCR methods.

Accurate evaluation of viable Ascaris ova in wastewater is the key to mitigating Ascaris reinfections in endemic regions. In this study, the viability of Ascaris ova in raw wastewater was determined using three different detection methods: culture-based, BacLight Live/Dead staining and propidium monoazide-quantitative polymerase chain reaction (PMA-qPCR). Furthermore, comparative assessment of viability utilising the aforementioned detection methods was performed using seeded experiments in wastewater. The percentage of viability was: culture-based (82%), BacLight Live/Dead staining (87%) and PMA-qPCR (85%) respectively. Despite the fact that no statistical difference was shown in the viability determination among the three methods, PMA-qPCR-based viability determination would be preferable over the other two methods for evaluating potential public health risks with A. suum ova due to its accuracy, being least subjective and its rapid reaction time.

Inactivation of viable Ascaris eggs during faecal sludge co-composting with chicken feathers and market waste

Author(s): Manga, M; Camargo-Valero, MA; Evans, BE | Abstract: Faecal Sludge (FS) contains high concentrations of pathogenic microorganisms that are 10-100 times higher than those in domestic wastewater. Proper and sustainable treatment is required to inactivate these pathogens if FS is to be recycled in agriculture, so as to minimise public health and environmental risks. Composting is one of the common low-cost technologies of sanitising FS in Urban Africa; however, it is associated with longer pathogen inactivation periods that make it commercially uneconomical. This study investigated the effect of different organic wastes types and their mixing ratios with FS on the inactivation efficiency of viable Ascaris eggs (suum and lumbricoides) during composting. Dewatered FS was mixed with market waste (MW), chicken feathers (CF) and sawdust (SD) in different ratios. Compost piles of FS:MW:SD and FS:CF:SD both in volumetric ratios of 1:2:1 and 1:3:1 were set-up in duplicate (3 m3 each), composted and monitored weekly for viable Ascaris eggs presence for a period of 15 weeks. The results suggest that the organic waste types have a significant effect on the temperature evolution and pathogen inactivation efficiency while their mixing ratios do not. Piles containing CF achieved the shortest pathogen survival period of 4 weeks compared with 6-8 weeks for those with MW. The temperature-time factor was found to be the most important variable responsible for viable Ascaris eggs inactivation. However, other mechanisms such as microbial antagonism or antibiotic action induced by indigenous microorganisms and toxic by-products such as free ammonia were found to have also played an important role in Ascaris eggs inactivation. All piles attained 100% Ascaris eggs inactivation from FS, and therefore, the compost was safe for use in agriculture. The study findings suggest that composting of FS with CF can reduce Ascaris eggs inactivation periods by 42%, which may thus reduce the operational costs of FS treatment facilities.

‘LaDePa’ process for the drying and pasteurization of faecal sludge from VIP latrines using infrared radiation

This paper studies a faecal sludge treatment process, LaDePa (Latrine Dehydration and Pasteurization), which includes: (i) the characterization of the rheological and plastic behaviour of faecal sludge in the feeding section; (ii) the study of the drying and pasteurization performance of the process using a laboratory-scale prototype; and (iii) an evaluation of the processed faecal sludge for reuse in agriculture or as a biofuel.Experiments conducted using a rheometer show that the faecal sludge exhibits shear thinning behaviour, i.e. viscosity decrease with shear rate increase. Plasticity tests in a cone penetrometer showed that the faecal sludge has a more liquid than plastic behaviour, which may affect extrusion quality, unless a plasticizer is added, as sawdust in this study.The extent of drying and pasteurization of the samples was determined based on moisture content and the presence of viable Ascaris eggs respectively. As the intensity of infrared radiation was increased, drying was faster and more efficient in terms of energy consumption. However, the pellets were thermally degraded at temperatures above 200 °C. After processing in the LaDePa, Ascaris eggs were deactivated or severely damaged so that they would be not able to develop.The last part of the study was conducted by determining the content of nutrients (C, N, P, K) and calorific value. The results showed that the processed pellets have suitable characteristics for reuse in agriculture and as a biofuel: similar nutrient content to manure and compost, and similar calorific value to wood. Drying did not affect the nutrient content and calorific value of the dry bone of faecal sludge.

Influence of Long-Term Storage Operating Conditions on the Reduction of Viable Ascaris Eggs in Sewage Sludge for Agricultural Reuse

The National Environment Council (CONAMA Resolution 375/06) defined to achieve sanitation quality parameters, for the use of sewage sludge in agriculture, the adoption of additional pathogen reduction processes is necessary. Sludge that is stored for longer periods generally shows higher levels of sanitation, particularly on the helminth egg inactivations which are among the most resistant pathogens. The objective of this study was to monitor the Ascaris egg removal and inactivation efficiency of long-term storage of sludge from septic tanks and up-flow anaerobic sludge blanket (UASB) reactors, besides evaluating the influence of covering and manually revolving or stirring the sludge over a 2-year period. The study was undertaken in the cities of Fazenda Rio Grande and Apucarana, Southern Brazil. In total, 18 experimental treatments were installed and nine samples were assessed at weeks 0, 4, 9, 13, 17, 30, 47, 61, and 104. The standard defined in the CONAMA for class A sludge (one viable egg per 4 g TS) was reached for all treatments at 9 weeks of storage. Two years of storage were necessary in order for the covered, UASB-centrifuge sludge to reach CONAMA standards. Of the six treatments using septic sludge, only one achieved the established standard. This treatment was realized in Apucarana and involved a revolving/stirring process. The period of 104 weeks of storage of the septic sludge was not sufficient to completely inactivate Ascaris eggs for the other treatments. Between study locations, Apucarana performed better than Curitiba which is likely due to greater levels of insolation and temperature.

Removal and Deactivation of Intestinal Parasites in Aerobic Mesophilic Composting Reactor for Urine Diverting Composting Toilet

ABSTRACT.Urine diverting composting toilets are becoming increasingly popular and are promoted to sanitize human excreta for recycling them into fertilizer. This study aimed to assess the removal and deactivation of intestinal parasites during the composting process. Batch experiments were conducted by composting human feces in an aerobic composting reactor using shea nut shells as bulky matrix. During 60 composting days, the removal of helminthes eggs and protozoa cysts was assessed and compared with the removal of indicator bacteria and pathogenic bacteria. The bacteria were analyzed by the single layer method on selective media and parasites were counted directly by microscope after compost preparation. The viability of helminthes eggs and protozoan cysts was assessed by a staining exclusion dyeing method. At low temperature, desiccation and alkaline pH obtained during the composting process could not completely destroy indicator bacteria while Salmonella sp. was eliminated after 30 composting days. Entamoeba hystolitica cysts were present in feces at a higher concentration (854/g mean) than Ascaris lumbricoides eggs (204/g mean). The composting process had reduced the total number of Ascaris eggs after 35 days while Entamoeba cysts were still present (beyond 54/g cysts) after 60 composting days. There were no viable Ascaris eggs after 30 days while the viability of Entamoeba cysts was still up 31%. In high concentration, Entamoeba cysts had survived stronger than Ascaris eggs during the composting process. Because of the persistence of some pathogens in compost both Ascaris eggs and Entamoeba cysts are good indicators for parasite removal.

Real scale environmental monitoring of zoonotic protozoa and helminth eggs in biosolid samples in Brazil.

Biosolid is the product of the activated sludge treatment system and its final disposition is subject of ongoing discussion as this residue can therefore harbor a great number and variety of pathogens. This study was aimed to (1) monitor the presence of Giardia and Cryptosporidium in biosolid samples from a treatment plant in Campinas, SP, Brazil, (2) observe Giardia cyst wall morphological integrity in treated samples using scanning electron microscopy (SEM) and (3) verify the presence and viability of helminth eggs. Cysts were present in 33.3% of the samples, whereas oocysts were detected in 8.3%. Viable Ascaris sp. Toxocara sp. and similar to Trichuris sp. eggs were found through the use of Mexican Official Norm. Results demonstrate the difficulties inherent in working with biosolid as factors such as temperature, ionic strength and pH influenced the recovery of cysts and oocysts. Pores and ruptures were not observed in cyst wall visualized by SEM following 45days of exposure to sunlight, only minimal morphological changes. These observations emphasize both the importance of adequate treatment of sewage sludge and the need to develop appropriate techniques for the detection of Giardia and Cryptosporidium in this type of sample. This is the first time that a study was done in a real scale for biosolid samples in determining the presence of pathogenic protozoa as Giardia and Cryptosporidium in Brazil, and also observed minimal cyst wall damage after sunlight treatment.

Characterization of biosolids and evaluating the effectiveness of plastic-covered sun drying beds as a biosolids stabilization method in Lusaka, Zambia

Introduction The Lusaka Water and Sewerage Company (LWSC) produces *800–1,000 kg of treated sewage sludge per day at its Manchinchi wastewater treatment plant (WWTP). The biosolids are used for land application purposes although the contaminant and pathogen composition and quality of the biosolids have been unknown until this study. Zambia does not have legal standards and guidelines for biosolids management or application. The Manchinchi plant in Lusaka suffers from constant breakdowns such that the effectiveness of the plant to produce quality grade biosolids for land application use is questionable. In peri-urban areas, the problem of poor sanitation is being addressed using different technologies including urine diversion ecosan toilets. The effectiveness of ecosan toilets to stabilize faecal sludge has not been assessed in Zambia. The purpose of this study was to stabilize and characterize the biosolids from Manchinchi plant and ecosan toilets. Stabilization was done by use of drying beds and irradiation. The parametres that were used for characterization were microbiological, parasitological and heavy metals. Results Biosolids from the Manchinchi WWTP sun drying bed, ecosan toilets and from an experimental plasticcovered drying bed were found to contain different pathogenic microorganisms and contaminant levels. A radiation dose and time-related declining trend in pathogens loads in biosolids were observed. By the third week, no viable Ascaris eggs were detected. Based on controlled conditions, the biosolids quality was found to be within the internationally acceptable standards for restricted use. Conclusions Both the untreated LWSC biosolids and ecosan sludge contained pathogen levels with the potential to cause environmental and public health hazards if used for agriculture purposes. Under plastic-covered drying beds, viable Ascaris eggs were not detected by the fourth week of treatment and the biosolids were stabilized to levels equivalent to Class C of the Australian standards for restricted land application. Covered drying beds can be considered as cost effective stabilization treatment technology for biosolids in developing countries. The technology has potential benefits for improving public health and reducing environmental pollution in Zambia, especially during the rainy season when biosolids are directly discharged into the environment.

Pathogen and indicator inactivation in source-separated human urine heated by the sun

Source-separation of urine enables energy-efficient recycling of large quantities of high quality plant nutrients from the wastewater system to food production. To manage the risk of diseases transmission the urine should be sanitised, which is commonly done by storage. The sanitisation of urine at three ambient exposures, resulting in fluctuating storage temperatures, was studied in 10 L plastic jerry cans in Kampala, Uganda. Follow-up studies using similar temperature cycles were performed under laboratory conditions. Daily mean mid-point temperature in jerry cans in full sun, adjacent to a wall and indoors was 24, 24 and 22 °C (amplitude 7.5, 4.7 and 1.2 °C), respectively. In urine stored at full sun (total ammonia nitrogen 4 ± 1.5 g L−1, pH 9) Escherichia coli, Salmonella and Enterococcus spp. (initially 105–106cfu mL−1) were not detected (<101cfu mL−1) after 11 h, 14 h and 50 d, respectively. No viable Ascaris suum eggs were found after 40 d. The t90 for enterobacteria phage MS2, coliphage Φx 174 and Salmonella typhimurium phage 28B in sun-exposed cans was 8.2, 37 and 55 d respectively. Fluctuating temperatures in combination with ammonia gave faster inactivation of bacteria and Ascaris suum eggs than the same constant mean temperature.

Pathogenic parasites and enteroviruses in wastewater: support for a regulation on water reuse

Brazilian regulations for nonpotable reuse are being established using World Health Organization guidelines, however, they should be developed based on local monitoring studies. This study intended to analyze enteroviruses, protozoa and viable Ascaris sp. eggs in raw (24) and treated (24) effluents from four Wastewater Treatment Plants of São Paulo State, Brazil. The protozoa were detected with the US Environmental Protection Agency (USEPA) Method 1623 in the treated effluents and by centrifugation/Immunomagnetic Separation in the raw influent samples. Viable Ascaris sp. eggs were analyzed according to a modified USEPA method. Enteroviruses were quantified by using human rhabdomyosarcoma cells after adequate concentration procedures. All wastewater influents were positive for Giardia sp. whereas Cryptosporidium sp. was detected in 58.3% of the samples. Giardia sp. and Cryptosporidium sp. were present in 79.2 and 25.0% respectively, of the treated wastewater samples. Viable Ascaris sp. eggs were detected in 50.0 and 12.5% of influent and treated wastewater samples. Enteroviruses were isolated in the 24 raw influent samples and in 46% of the treated samples. Taking into account the densities of Giardia sp. in some treated wastewaters intended to be used as reclaimed water, Quantitative Microbial Risk Assessment studies should be conducted to establish pathogen quantitative criteria for a future Brazilian regulation for water reuse.

The Effectiveness and Safety of Vermi- Versus Conventional Composting of Human Feces with Ascaris suum Ova as Model Helminthic Parasites

Composting toilets have been promoted for management of human waste at remote sites in parks and alpine areas of recreation, but they may not be effective for producing a stable and safe end product. Vermicomposting has been shown to result in a more degraded final product but its effectiveness for pathogen destruction was unclear due to conflicting information in the literature. This study sought to resolve the debate on whether or not vermicomposting could produce a hygenic end product that would be safe for disposal locally. Vermicomposting was tested for destruction of the model pathogens, helminthic parasites, in an experiment with highly concentrated and viable Ascaris suum (2626±1306 ova/g, 61.6±8.7% viable) inoculated into fecal matter and coir (30:70 ratio) with and without Eisenia fetida worms. After 90 days at 19±3 oC six, eight, and 12 worms were found alive with no significant difference between treatments or through time found in TS% (12-15%), ova concentration and ova viability. A 100 times reduction in the concentration of Escherichia coli resulted from the worm treatment versus the control. Significantly higher nitrate (22 735±4 741 mg/kg NO3 - ) and lower pH (pH 4.60±0.01) were found in the treatment as compared to the control (5 078±2 167 mg/kg NO3 - ) (pH 6.56±0.30). Despite these improvements in fecal matter processing, vermicomposting was found ineffective at reducing Ascaris suum ova concentration and viability. Decentralized vermicomposting can efficiently stabilize and mature fecal matter; however prior to unrestricted end product use, an additional sanitation step is necessary.

Detection and quantification of viable Ascaris sp. and other helminth eggs in sewage sludge

Some epidemiologic studies conducted in developing countries demonstrated a high incidence of enteroparasites, Ascaris sp. being the most prevalent. Therefore, the use of sewage sludge in agriculture may pose risks to human health. In order to protect public health, a Brazilian regulation has established standards regarding its use in rural areas. The objective of this study was to quantify Ascaris sp. and other helminth eggs in sewage sludge from five wastewater treatment plants from a dense metropolitan region, and also to check compliance with the law. The analysis was carried according to USEPA 2003. A rich parasitological fauna was found, with a prevalence of the eggs of Ascaris sp. (9.55%). The samples analyzed presented a large variety of helminth eggs, and Ascaris sp. proved to be the most prevalent which put in evidence that its application poses public health concerns.

Enumeration of viable and non-viable larvated Ascaris eggs with quantitative PCR

The goal of this study was to further develop an incubation-quantitative polymerase chain reaction (qPCR) method for quantifying viable Ascaris eggs by characterizing the detection limit and number of template copies per egg, determining the specificity of the method, and testing the method with viable and inactivated larvated eggs. The number of template copies per cell was determined by amplifying DNA from known numbers of eggs at different development stages; the value was estimated to be 32 copies. The specificity of the method was tested against a panel of bacteria, fungi, protozoa and helminths, and no amplification was found with non-target DNA. Finally, fully larvated eggs were inactivated by four different treatments: 254 nm ultraviolet light, 2,000 ppm NH(3)-N at pH 9, moderate heat (48 °C) and high heat (70 °C). Concentrations of treated eggs were measured by direct microscopy and incubation-qPCR. The qPCR signal decreased following all four treatments, and was in general agreement with the decrease in viable eggs determined by microscopy. The incubation-qPCR method for enumerating viable Ascaris eggs is a promising approach that can produce results faster than direct microscopy, and may have benefits for applications such as assessing biosolids.

Impact of climate and bulking materials on characteristics of compost from ecological toilets

Urine-diversion dehydration toilets (UDDT) are common throughout the developing world, and the toilet product is widely used as compost. There is no comprehensive research to date that characterizes the compost to determine its quality, extent of pathogen inactivation, and the effects of climate and bulking materials on the compost. Compost was collected from 45 UDDT in Bolivia and analyzed for physical, chemical, and biological parameters. Eighty percent and 56% of samples did not meet acceptable compost guidelines for moisture content and pH, respectively, indicating desiccation was the dominant process in UDDT. Bulking materials significantly impacted compost characteristics in terms of pH, carbon, carbon-to-nitrogen ratio, and carbon stability (P < 0.05). Composts with ash exhibited, on average, low carbon concentrations (4.9%) and high pH values (9.7), which can be harmful to plants and composting microorganisms. Composts with sawdust exhibited, on average, high carbon concentrations (40.0%) and carbon-to-nitrogen ratios (31.0). Climate had no significant impact on chemical characteristics, however composts from humid regions had significantly higher moisture contents (34.4%) than those from arid climates (24.8%) (P < 0.05). Viable Ascaris lumbricoides ova were identified in 31% of samples, including samples with high pH, low moisture contents, and long storage times.

Fate of the pathogen indicators phage ΦX174 and Ascaris suum eggs during the production of struvite fertilizer from source-separated urine

Human urine has the potential to be a sustainable, locally and continuously available source of nutrients for agriculture. Phosphate can be efficiently recovered from human urine in the form of the mineral struvite (MgNH 4PO 4·6H 2O). However, struvite formation may be coupled with the precipitation of other constituents present in urine including pathogens, pharmaceuticals, and heavy metals. To determine if struvite fertilizer presents a microbiological health risk to producers and end users, we characterized the fate of a human virus surrogate (phage ΦX174) and the eggs of the helminth Ascaris suum during a low-cost struvite recovery process. While the concentration of phages was similar in both the struvite and the urine, Ascaris eggs accumulated within the solid during the precipitation and filtration process. Subsequent air-drying of the struvite filter cake partially inactivated both microorganisms; however, viable Ascaris eggs and infective phages were still detected after several days of drying. The infectivity of both viruses and eggs was affected by the specific struvite drying conditions: higher inactivation generally occurred with increased air temperature and decreased relative humidity. On a log–log scale, phage inactivation increased linearly with decreasing moisture content of the struvite, while Ascaris inactivation occurred only after achieving a minimum moisture threshold. Sunlight exposure did not directly affect the infectivity of phages or Ascaris eggs in struvite cakes, though the resultant rise in temperature accelerated the drying of the struvite cake, which contributed to inactivation.

Pathogen reduction effects of solar drying and soil application in sewage sludge

The responses of sludge faecal coliforms, Salmonella, and Ascaris lumbricoides to heat drying, solar dehydration, and inactivation in soil are examined in this study. The presence of Salmonella in raw sludge cake after treatment was low, and absent for most of the cases. Likewise, the viable Ascaris eggs were not determined because of absent or low prevalence. Faecal coliforms, on the other hand, drastically decreased from 4.2 × 10^7 MPN g^{-1} Dry Solid (DS) to absence by heat drying. Faecal coliform numbers in solar and non-solar drying treatments were not declined below 1.0 × 10^3 MPN g^{-1} after drying to 90% DS and also during the storage of 12 weeks. After 6 weeks, faecal coliform and Salmonella levels in the soil surface application fell below undetectable limits. The coliform numbers below soil surface fell gradually over 12 weeks and numbers were below undetectable limits at end of the experiment. These results showed that although the solar drying has significant effects on removing pathogenic microorganisms during hot and dry periods, the soil treatment was still necessary for the final complete inactivation. Solar exposure on the soil surface was found to be effective on the elimination of pathogens.

Safety Aspects of Handling and Using Fecal Material from Urine‐Diversion Toilets—A Field Investigation

The most advantageous approach to pathogen destruction in a urine-diversion toilet vault is to maximize the effects of various environmental factors (i.e., pH, temperature, moisture content, type of bulking agent, and storage time). To quantify these effects, a field experiment was set up, consisting of 6 urine-diversion toilet vaults, each with a different combination of feces and bulking agent (soil, ash, wood shavings, sodium hydroxide, or straw) and ventilation (ventpipe/no ventpipe). The pH of the mixes varied from 6.37 to 10.09. Temperature probes, which were connected to a data logger, were inserted to the heaps, and the logger monitored over a period of nearly 10 months. Mean heap temperatures ranged from 16.8 degrees C in winter to 27.6 degrees C in summer. In addition, samples were taken at intervals from the various heaps in the vaults and also from an open heap exposed to the elements. The samples were subjected to microbiological testing to quantify the pathogen dieoff over time. In the vaults, there was a 3log10 (99.9%) reduction of total coliform between 130 and 250 days, fecal coliform between 100 and 250 days, and fecal streptococci from 125 days and longer. In the open heap, these times varied, from 115 days for both total and fecal coliform, to 140 days for fecal streptococci. Viable Ascaris ova were reduced to zero between 44 and 174 days in the vaults and by 44 days in the open heap. The results of this research showed that ventilation of the vault by means of a ventpipe does not result in any meaningful difference in the vault temperature or the rate of pathogen dieoff. While the type of bulking agent used does not significantly affect the temperature of the heap, it does have an effect on the rate of pathogen dieoff. The ordinary soil mix was seen to give the best results, and this was ascribed to the effect of competing microorganisms in the soil itself. It is concluded that, for safety, vaults of urine-diversion toilets should be sized for a storage period of 9 to 12 months from the last use.

Association between intestinal parasitic infections and type of sanitation system in rural El Salvador

To identify demographic, behavioural and environmental determinants of intestinal parasitic infection, evaluate the impact of a variety of dry sanitation systems on intestinal parasitic infection, and evaluate the safety of using stored biosolids in agriculture in order to guide future sanitation interventions in rural areas of El Salvador. Interviews were conducted with 109 households in eight communities where double-vaulted and solar urine-diverting desiccating latrines, pit latrines or no latrines were used. Faecal samples from 499 individuals were tested for enteric helminths and protozoa. Users of solar desiccating latrines had the lowest prevalence of enteric parasite infection. Double-vault, urine-diverting desiccating latrines effectively reduced the transmission of some pathogens, but may not achieve the conditions sufficient for the complete destruction of the more environmentally persistent pathogens, Ascaris lumbricoides and Trichuris trichiura. Contact with inadequately treated latrine biosolids was associated with an increased risk of Ascaris infection. Solar latrines were associated with the overall lowest prevalence of enteric parasitic infections. Members of households where latrine biosolids were used in agriculture had a higher prevalence of infection than those where biosolids were buried. We therefore recommend the promotion of solar latrines in rural areas of El Salvador over other dry sanitation systems, and recommend that stored biosolids not be used in agriculture.

Laboratory Evaluation of Thermophilic‐Anaerobic Digestion to Produce Class A Biosolids. 2. Inactivation of Pathogens and Indicator Organisms in a Continuous‐Flow Reactor Followed by Batch Treatment

Thermophilic-anaerobic digestion in a single-stage, mixed, continuous-flow reactor is not approved in the United States as a process capable of producing Class A biosolids for land application. This study was designed to evaluate the inactivation of pathogens and indicator organisms in such a reactor followed by batch treatment in a smaller reactor. The combined process was evaluated at 53 degrees C with sludges from three different sources and at 51 and 55 degrees C with sludge from one of the sources. Feed sludge to the continuous-flow reactor was spiked with the pathogen surrogates Ascaris suum and vaccine-strain poliovirus. Feed and effluent were analyzed for these organisms and for indigenous Salmonella spp., fecal coliforms, Clostridium perfringens spores, and somatic and male-specific coliphages. No viable Ascaris eggs were observed in the effluent from the continuous reactor at 53 or 55 degrees C, with greater than 2-log removals across the digester in all cases. Approximately 2-log removal was observed at 51 degrees C, but all samples of effluent biosolids contained at least one viable Ascaris egg at 51 degrees C. No viable poliovirus was found in the digester effluent at any of the operating conditions, and viable Salmonella spp. were measured in the digester effluent in only one sample throughout the study. The ability of the continuous reactor to remove fecal coliforms to below the Class A monitoring limit depended on the concentration in the feed sludge. There was no significant removal of Clostridium perfringens across the continuous reactor under any condition, and there also was limited removal of somatic coliphages. The removal of male-specific coliphages across the continuous reactor appeared to be related to temperature. Overall, at least one of the Class A pathogen criteria or the fecal coliform limit was exceeded in at least one sample in the continuous-reactor effluent at each temperature. Over the range of temperatures evaluated, the maximum time required to meet the Class A criteria by batch treatment of the continuous-reactor effluent was 1 hour for Ascaris suum and Salmonella spp. and 2 hours for fecal coliforms.