Modeling the inactivation of ascaris eggs as a function of ammonia concentration and temperature

An environmental evaluation of urine-diverting dry toilets in Hiloweyn Camp, Dollo Ado, Ethiopia

Safe and hygienic management of human waste is essential in humanitarian settings. Urine-diverting dry toilets (UDDTs) can enable this management in some humanitarian emergency settings. A seeded, longitudinal environmental study was conducted in Hiloweyn refugee camp, Dollo Ado, Ethiopia, to measure Escherichia coli and Ascaris suum ova inactivation within closed UDDT vaults and to document environmental conditions (temperature, moisture content, and pH) that could influence inactivation. Hiloweyn camp represented an optimal location for a desiccation-based sanitation technology such as the UDDT. E. coli and Ascaris ova inactivation was observed in UDDTs under warm, dry, alkaline conditions at 6, 9, and 12 months of storage; UDDTs with samples containing <1000 E. coli/g total solids increased from 30 % to 95 % over 12 months, and a >2.8-log10 reduction in Ascaris ova viability was observed after 6 months. Additional laboratory-based studies were conducted to provide insights into the field study findings and study the impact of hydrated lime on E. coli and Ascaris ova inactivation. Results suggest that adding hydrated lime to elevate pH > 12 may increase inactivation and decrease storage time. Overall, UDDTs could contribute to the safe and hygienic management of human waste in comparable warm and dry humanitarian settings.

Study of helminth eggs ( Ascaris suum) inactivation by anaerobic digestion and electrochemical treatment

Background

The use of insufficiently treated wastewater or Faecal sludge in agriculture raises concerns because of the pathogen content. Helminth eggs (HE) are one of the most crucial pathogens for ensuring public health and safety. Widely used disinfection treatment methods do not guarantee the complete inactivation of helminth eggs. The current study evaluated the effectiveness of anaerobic digestion and electrochemical process on helminth ( Ascaris suum) egg inactivation.

Methods

Lab-scale biochemical methane potential (BMP) assay was conducted by spiking A. suum eggs in a serum bottle. Total solid (TS), volatile solid (VS), pH, biogas production and its composition, and volatile fatty acids (VFA) were analyzed along with A. suum inactivation every third day for the initial 15 days and fifth day for 45 days. In the second set of experiments, a hypochlorite (4700 ppm) solution was generated by electrolysis of aqueous NaCl solution in a membrane-less electrochemical cell. The hypochlorite was diluted (940, 470, 235, and 156ppm) in wastewater, spiked with A. suum eggs and then examined for inactivation at regular intervals.

Results

The results of the anaerobic digestion treatment documented 98% inactivation of A. suum eggs (0.15 eggs/mL) in 35 days and remained at 0.14 eggs/mL until day 45. Correlation analysis revealed a positive relationship between non-viable eggs and pH and a negative relationship with all the other parameters. Electrochemical treatment achieved 10% inactivation at 940 ppm concentration in 24h.

Conclusions

This study revealed that the inactivation of A. suum eggs by anaerobic digestion or electrochemical treatment is a combined effect of more than one parameter.

Urban sewage sludge stabilization by alkalization-composting-vermicomposting process: Crop-livestock residue use

Waste management practices are vital for human health and the environment in a world where natural resources stress is expected to increase with the growth of population. Our study aimed to evaluate the potential use of crop-livestock residue as a bulking agent associated with the ideal level of hydrated lime for the stabilization and sanitization of urban sewage sludge through the alkalization-composting process. Therefore, we determined the alkalization efficiency on the heavy metal concentration in urban sewage sludge, quantified the viable eggs of helminths in pure and alkalized sludge, and measured the rate of earthworms (Eisenia fetida) surviving in the vermicomposting process using different levels of alkalized urban sewage sludge associated with crop-livestock residue. Four sequential trials were carried out in a completely randomized design with three replicates. The lime alkalization reduced the levels of Ba, As, Pb, Cu, Cr, Mo, Ni, and Zn compared to the pure urban sewage sludge. Using 30% w/w of lime in the urban sewage sludge (SS-30) for composting process reduced the viable helminth eggs by 71, 72, and 69% for sugarcane bagasse (Saccharum officinarum; SB), fresh chopped Napier-grass (Pennisetum purpureum; NG), and bovine ruminal content (BR), respectively. The ideal level of hydrated lime for stabilization and sanitization of urban sewage sludge was found to be 30%, which was able to reduce the heavy metals. The residues have the potential as a bulking agent for the composting of urban sewage sludge when associated with alkalization. The lime alkalization decreases the total number of helminth eggs and the number of viable eggs. The possibility of starting a vermicomposting using the mixtures is promising, evidenced by the earthworm survival in composting urban sewage sludge mixed with crop-livestock residues after 45 days of composting. The earthworm survival is maintained by an association of at least 80% of the crop-livestock residues.

A systematic review and meta-analysis of pathogen reduction in onsite sanitation systems

The safe management of fecal sludge from the 3.4 billion people worldwide that use onsite sanitation systems can greatly reduce the global infectious disease burden. However, there is limited knowledge about the role of design, operational, and environmental factors on pathogen survival in pit latrines, urine diverting desiccation toilets, and other types of onsite toilets. We conducted a systematic literature review and meta-analysis to characterize pathogen reduction rates in fecal sludge, feces, and human excreta with respect to pH, temperature, moisture content, and the use of additives for desiccation, alkalinization, or disinfection. A meta-analysis of 1,382 data points extracted from 243 experiments described in 26 articles revealed significant differences between the decay rates and T99 values of pathogens and indicators from different microbial groups. The overall median T99 values were 4.8 days, 29 days, >341 days, and 429 days for bacteria, viruses, protozoan (oo)cysts, and Ascaris eggs, respectively. As expected, higher pH values, higher temperatures, and the application of lime all significantly predicted greater pathogen reduction rates but the use of lime by itself was more effective for bacteria and viruses than for Ascaris eggs, unless urea was also added. In multiple lab-scale experiments, the application of urea with enough lime or ash to reach a pH of 10 - 12 and a sustained concentration of 2,000 - 6,000 mg/L of non-protonated NH3-N reduced Ascaris eggs more rapidly than without urea. In general, the storage of fecal sludge for 6 months adequately controls hazards from viruses and bacteria, but much longer storage times or alkaline treatment with urea and low moisture or heat is needed to control hazards from protozoa and helminths. More research is needed to demonstrate the efficacy of lime, ash, and urea in the field. More studies of protozoan pathogens are also needed, as very few qualifying experiments were found for this group.

Inactivation and risk control of pathogenic microorganisms in municipal sludge treatment: A review

The rapid global spread of coronavirus disease 2019 (COVID-19) has promoted concern over human pathogens and their significant threats to public health security. The monitoring and control of human pathogens in public sanitation and health facilities are of great importance. Excessive sludge is an inevitable byproduct of sewage that contains human and animal feces in wastewater treatment plants (WWTPs). It is an important sink of different pollutants and pathogens, and the proper treatment and disposal of sludge are important to minimize potential risks to the environment and public health. However, there is a lack of comprehensive analysis of the diversity, exposure risks, assessment methods and inactivation techniques of pathogenic microorganisms in sludge. Based on this consideration, this review summarizes the control performance of pathogenic microorganisms such as enterovirus, Salmonella spp., and Escherichia coli by different sludge treatment technologies, including composting, anaerobic digestion, aerobic digestion, and microwave irradiation, and the mechanisms of pathogenic microorganism inactivation in sludge treatment processes are discussed. Additionally, this study reviews the diversity, detection methods, and exposure risks of pathogenic microorganisms in sludge. This review advances the quantitative assessment of pathogenic microorganism risks involved in sludge reuse and is practically valuable to optimize the treatment and disposal of sludge for pathogenic microorganism control.

Evaluation of the efficiency of some disinfectants on the viability of Hymenolepis nana eggs isolated from wastewater and faecal sludge in Yaounde (Cameroon): importance of some abiotic variables

Hymenolepis nana is responsible for many parasitic infections in tropical areas, with its persistence in aquatic environments as major contributory factor. A study aimed at demonstrating the effectiveness of some disinfectants on the viability of Hymenolepis nana eggs was conducted in microcosm. Sampling consisted of taking wastewater and sewage sludge samples in sterilized containers and then transporting to the laboratory of Hydrobiology and Environmental Sciences for the determination of Hymenolepis nana eggs using standard protocols. The experimental set-up consisted of five replicates, four tests and a control. The test samples were successively treated with four disinfectants (calcium chlorite, hydrogen peroxide, gypsum and sodium hypochlorite). The physico-chemical parameters were measured before and after disinfection. The samples were then observed under an optical microscope after concentration of the sample through sedimentation and McMaster technique. The viability of the eggs was determined using incubation and staining techniques. The analysis revealed that the selected disinfectants significantly reduced the physico-chemical parameters (with an average yield ranging from 79.24 ± 19.43% to 99.24 ± 1.47%). These physico-chemical parameters can significantly influence the treatment of Hymenolepis nana eggs either by absorbing the disinfectant or by constituting a protective barrier for the eggs, and the physico-chemical nature of the disinfectant strongly influences the formation of disinfection by-products. Calcium chlorite showed a greater effectiveness in reducing egg viability with efficiency rates of 93.12 ± 9.12% followed by hydrogen peroxide (89.57 ± 14.55%), sodium hypochlorite (82.51 ± 14.39%) and gypsum (80.85 ± 12.88%). The results obtained with gypsum are almost similar to those obtained with other disinfectants (calcium chlorite, hydrogen peroxide and sodium hypochlorite) and clearly show that this disinfectant can be used in water treatment because, unlike other chemical disinfectants, it has no known toxic effects.

Mechanisms of instantaneous inactivation of SARS-CoV-2 by silicon nitride bioceramic

The hydrolytic processes occurring at the surface of silicon nitride (Si3N4) bioceramic have been indicated as a powerful pathway to instantaneous inactivation of SARS-CoV-2 virus. However, the virus inactivation mechanisms promoted by Si3N4 remain yet to be elucidated. In this study, we provide evidence of the instantaneous damage incurred on the SARS-CoV-2 virus upon contact with Si3N4. We also emphasize the safety characteristics of Si3N4 for mammalian cells. Contact between the virions and micrometric Si3N4 particles immediately targeted a variety of viral molecules by inducing post-translational oxidative modifications of S-containing amino acids, nitration of the tyrosine residue in the spike receptor binding domain, and oxidation of RNA purines to form formamidopyrimidine. This structural damage in turn led to a reshuffling of the protein secondary structure. These clear fingerprints of viral structure modifications were linked to inhibition of viral functionality and infectivity. This study validates the notion that Si3N4 bioceramic is a safe and effective antiviral compound; and a primary antiviral candidate to replace the toxic and allergenic compounds presently used in contact with the human body and in long-term environmental sanitation.

Assessing the microbial risk of faecal sludge use in Ugandan agriculture by comparing field and theoretical model output

Reuse of faecal sludge in agriculture has many potential benefits, but also poses risks to human health. To better understand the potential risks, Quantitative Microbial Risk Assessment (QMRA) was performed for three population groups in Kampala, Uganda: wastewater and faecal sludge treatment plant workers; farmers using faecal sludge; and consumers of faecal sludge-fertilised vegetables. Two models were applied for farmers and consumers, one based on pathogen concentrations from field sampling of sludge, soils and vegetables, and one based on theoretical pathogen contribution from the last sludge application, including decay and soil to crop transfer of pathogens. The risk was evaluated for two pathogens (enterohaemorrhagic E. coli (EHEC) and Ascaris lumbricoides). The field data on sludge, soil and vegetables indicated that the last application of faecal sludge was not the sole pathogen source. Correspondingly, the model using field data resulted in higher risks for farmers and consumers than the theoretical model assuming risk from sludge only, except when negligible for both. For farmers, the yearly risk of illness, based on measured concentrations, was 26% from EHEC and 70% from Ascaris, compared with 1.2% and 1.4%, respectively, considering the theoretically assumed contribution from the sludge. For consumers, the risk of illness based on field samples was higher from consumption of leafy vegetables (100% from EHEC, 99% from Ascaris) than from consumption of cabbages (negligible for EHEC, 26% from Ascaris). With the theoretical model, the risk of illness from EHEC was negligible for both crops, whereas the risk of illness from Ascaris was 64% and 16% for leafy vegetables and cabbage, respectively. For treatment plant workers, yearly risk of illness was 100% from EHEC and 99.4% from Ascaris. Mitigation practices evaluated could reduce the relative risk by 30-70%. These results can help guide treatment and use of faecal sludge in Kampala, to protect plant workers, farmers and consumers.

Hierarchical Bayesian modeling for predictive environmental microbiology toward a safe use of human excreta: Systematic review and meta-analysis

The pathogen concentration in human excreta needs to be managed appropriately, but a predictive approach has yet to be implemented due to a lack of kinetics models for pathogen inactivation that are available under varied environmental conditions. Our goals were to develop inactivation kinetics models of microorganisms applicable under varied environmental conditions of excreta matrices and to identify the appropriate indicators that can be monitored during disinfection processes. We conducted a systematic review targeting previous studies that presented time-course decay of a microorganism and environmental conditions of matrices. Defined as a function of measurable factors including treatment time, pH, temperature, ammonia concentration and moisture content, the kinetic model parameters were statistically estimated using hierarchical Bayesian modeling. The inactivation kinetics models were constructed for Escherichia coli, Salmonella, Enterococcus, Ascaris eggs, bacteriophage MS2, enterobacteria phage phiX174 and adenovirus. The inactivation rates of a microorganism were predicted using the established model. Ascaris eggs were identified as the most tolerant microorganisms, followed by bacteriophage MS2 and Enterococcus. Ammonia concentration, temperature and moisture content were the critical factors for the Ascaris inactivation. Our model predictions coincided with the current WHO guidelines. The developed inactivation kinetics models enable us to predict microbial concentration in excreta matrices under varied environmental conditions, which is essential for microbiological risk management in emerging resource recovery practices from human excreta.

Effectiveness of helminth egg reduction by solar drying and liming of sewage sludge

The present study is aimed at assessing the effectiveness of solar drying process in terms of helminth egg reduction in sewage sludge (SS) generated from an activated sludge wastewater treatment plant (WWTP) in Marrakesh city (Morocco). It is also engaged to highlight a synergic effect of liming (1% CaO) and solar drying on helminth egg reduction. The solar drying process was conducted for 45 days, in summer under a semi-arid climate in a pilot scale polycarbonate-based tunnel (2 m³). Before undergoing solar drying process, data showed an important load of helminth eggs including Ascaris sp., Schistosoma spp., Capillaria spp., Trichuris spp., Ankylostome spp., Toxocara spp., and Taenia spp. in limed sludge (LS) and non-limed sludge (NLS) (15.2 and 17.9 eggs/g, respectively). Ascaris eggs were the most abundant (11.2 and 13.5 eggs/g in LS and NLS, respectively). By the end of the solar drying process, a considerable removal of the total helminth eggs was recorded in LS and NLS (92.8% and 91.6%, respectively). A complete removal of Schistosoma spp., Capillaria spp., Trichuris spp., Toxocara spp. and Taenia spp. was noted in LS and NLS. In the case of Ankylostome spp., data showed a total removal in LS and 81% in NLS; however, the final load is in agreement with the standards (0.4 egg/g). As for Ascaris spp., neither liming nor solar drying process allowed a complete removal (91% and 90% in NLS and LS, respectively) and the final load (1.1 egg/g) does not fulfill the WHO requirements for an agricultural use. Principal component analysis (PCA) demonstrated a negative correlation between dry matter (DM) content (hence temperature) and helminth egg concentration. No significant synergic effect of liming and solar drying process was showed by statistical analysis. This is substantiating that temperature is the key parameter involved in helminth egg removal while undergoing solar drying of SS.

Inactivation of Cryptosporidium parvum oocysts and faecal indicator bacteria in cattle slurry by addition of ammonia

AIMS

To determine inactivation of Cryptosporidium parvum oocysts and reduction of Escherichia coli and enterococci in cattle slurry added aqueous ammonia.

METHODS AND RESULTS

Escherichia coli, enterococci and nonviable C. parvum oocysts (DAPI+PI+) were enumerated every second day for 2 weeks in cattle slurry amended with 60 mmol l^-1 aq. ammonia and compared with untreated slurry at three temperatures. Regardless of temperature, the proportion of nonviable C. parvum oocysts increased significantly faster over time in slurry with added ammonia than raw slurry (P = 0·021) corresponding to 62·0% higher inactivation (P = 0·001) at day 14. Additionally, 91·8% fewer E. coli and 27·3% fewer enterococci were observed in slurry added ammonia at day 14 compared to raw slurry.

CONCLUSION

The addition of aqueous ammonia to raw slurry significantly reduced the viability of C. parvum oocysts and numbers of bacterial indicators. Hence, ammonia is usable at lower pathogen concentrations in slurry before application to agricultural land.

SIGNIFICANCE AND IMPACT OF THE STUDY

Livestock waste is a valuable source of plant nutrients and organic matter, but may contain high concentrations of pathogens like E. coli and Cryptosporidium sp. that can be spread in the environment, and cause disease outbreaks. However, die-off rates of pathogens in organic waste can increase following increasing ammonia concentrations.

Fate of Ascaris at various pH, temperature and moisture levels

Soil-transmitted helminths (STH) are intestinal worms that infect 24% of the world's population. Stopping the spread of STH is difficult, as the eggs are resilient (can withstand high pH) and persistent (can remain viable in soils for several years). To ensure that new sanitation systems can inactivate STH, a better understanding of their resilience is required. This study assessed the inactivation of Ascaris eggs under various conditions, in terms of moisture content (MC) (<20 to >90%), temperature (20-50 °C) and pH (7-12.5). The results highlight that the exposure of Ascaris eggs to elevated pH (10.5-12.5) at temperatures ≤27.5 °C for >70 days had no effect on egg viability. Compounding effects of alkaline pH (≥10.5) or decreasing MC (<20%) was observed at 35 °C, with pH having more of an effect than decreasing MC. To accelerate the inactivation of STH, an increase in the treatment temperature is more effective than pH increase. Alkaline pH alone did not inactivate the eggs but can enhance the effect of ammonia, which is likely to be present in organic wastes.

Current time-temperature relationships for thermal inactivation of Ascaris eggs at mesophilic temperatures are too conservative and may hamper development of simple, but effective sanitation

Ascaris eggs are commonly used as indicators for pathogen inactivation during the treatment of fecal sludge and wastewater due to their highly resistant lipid membrane and ability to survive in the environment for long periods of time. Current guidelines suggest that thermal treatment alone cannot inactivate Ascaris eggs at temperatures below 45 °C, although some evidence in the literature suggests this to be incorrect. Here, we performed a controlled experiment to test the effect of mesophilic temperatures on Ascaris inactivation. We exposed Ascaris suum eggs to a temperature gradient between 34°C and 45 °C under anaerobic and aerobic conditions to observe the required exposure times for a 3-log reduction. Indeed, we found that temperatures lower than 45 °C did inactivate these eggs, and the required exposure times were up to two orders of magnitude shorter than suggested by current guidelines. Results from the anaerobic exposures were used to develop a time-temperature relationship that is appropriate for Ascaris inactivation at mesophilic temperatures. Data from the literature demonstrated that our relationship is conservative, with faster inactivation occurring under environmental conditions when Ascaris eggs were suspended in fecal sludge or manure. A specific aerobic relationship was not developed, but we demonstrated that aerobic conditions cause faster inactivation than anaerobic conditions. Therefore, the anaerobic relationship provides a conservative guideline for both conditions. We demonstrate that relatively low temperatures can considerably impact Ascaris viability and suggest that mesophilic temperatures can be used in waste treatment processes to inactivate pathogens. The development of safe, low-input, mesophilic treatment processes is particularly valuable for ensuring universal access to safe sanitation and excreta management.

Is anaerobic digestion a reliable barrier for deactivation of pathogens in biosludge?

As World Health Organization advocates, the global burden of sanitation related disease and access to safely managed sanitation and safely treated wastewater should be monitored strictly. However, the spread of pathogens through various agricultural applications or direct discharge of sewage sludge generated in municipal wastewater treatment plants poses a serious challenge on the environment and public health. Anaerobic digestion (AD), the principal method of stabilizing biosolids, can efficiently and largely deactivate viable pathogens, including parasite, virus, and the pathogens harboring antibiotic resistance genes. This review aims to provide a critical overview regarding the deactivation of sludge-associated pathogens by AD, through which a serious concern on the effectiveness and rationality of AD towards sludge pathogens control was raised. Meanwhile, the underlying deactivation mechanisms and affecting factors were all discussed, with the focus on pathogen-associated modeling, engineering design and technological aspects of AD. Lastly, a matric method incorporating the operating strategy of AD with the risk assessment was proposed for evaluating the reliability of AD-based pathogen deactivation, while the research agenda forward was also outlined.

Review of global sanitation development

The implementation of the United Nations (UN) Millennium Development Goals (MDGs) and Sustainable Development Goals (SDGs) has resulted in an increased focus on developing innovative, sustainable sanitation techniques to address the demand for adequate and equitable sanitation in low-income areas. We examined the background, current situation, challenges, and perspectives of global sanitation. We used bibliometric analysis and word cluster analysis to evaluate sanitation research from 1992 to 2016 based on the Science Citation Index EXPANDED (SCI-EXPANDED) and Social Sciences Citation Index (SSCI) databases. Our results show that sanitation is a comprehensive field connected with multiple categories, and the increasing number of publications reflects a strong interest in this research area. Most of the research took place in developed countries, especially the USA, although sanitation problems are more serious in developing countries. Innovations in sanitation techniques may keep susceptible populations from contracting diseases caused by various kinds of contaminants and microorganisms. Hence, the hygienization of human excreta, resource recovery, and removal of micro-pollutants from excreta can serve as effective sustainable solutions. Commercialized technologies, like composting, anaerobic digestion, and storage, are reliable but still face challenges in addressing the links between the political, social, institutional, cultural, and educational aspects of sanitation. Innovative technologies, such as Microbial Fuel Cells (MFCs), Microbial Electrolysis Cells (MECs), and struvite precipitation, are at the TRL (Technology readiness levels) 8 level, meaning that they qualify as "actual systems completed and qualified through test and demonstration." Solutions that take into consideration economic feasibility and all the different aspects of sanitation are required. There is an urgent demand for holistic solutions considering government support, social acceptability, as well as technological reliability that can be effectively adapted to local conditions.

Decentralised black water treatment by combined auto-thermal aerobic digestion and ammonia - A pilot study optimising treatment capacity

Partial heating of black water by auto-thermal aerobic digestion was combined with the addition of 1% w/w urea and monitoring of pathogens and indicator organisms over a 21-day period. After initial mixing, the 160 m³ black water (60 m³ heated and 100 m³ non-heated) was left undisturbed. The urea was confirmed to be fully degraded into ammonia (5.1 g N L^-1) first after 14 days, while the pH stabilised at around 9.2 after one week. The initial temperature of 17 °C fell by 6 °C during the study. E. coli and Salmonella spp., which are sensitive to ammonia, were inactivated during the first few days of the study, despite the urea only being partly hydrolysed. At day 14, f-RNA bacteriophages could also no longer be detected. The more persistent somatic coliphages, Enterococcus spp. and Ascaris eggs, showed significant but slow inactivation. The treatment proved to be efficient with regards to salmonella, which is a target pathogen in the Swedish context, but for parasite egg inactivation a higher temperature was required. The treatment would benefit from more frequent stirring to speed up the hydrolysis of urea and thus improve treatment efficiency. The alternative treatment scheme could increase capacity by 2.4 times, albeit with a 40% higher cost per volume due to the increased use of urea.

The time-temperature relationship for the inactivation of Ascaris eggs

A time-temperature plot presenting the inactivation of Ascaris eggs is expanded with additional literature data. The information is of value to designers and operators of sanitation equipment who have Ascaris inactivation as an objective.

Identification of the inactivating factors and mechanisms exerted on MS2 coliphage in concentrated synthetic urine

Volume reduction (condensation) is a key for the practical usage of human urine as a fertilizer because it enables the saving of storage space and the reduction of transportation cost. However, concentrated urine may carry infectious disease risks resulting from human pathogens frequently present in excreta, though the survival of pathogens in concentrated urine is not well understood. In this study, the inactivation of MS2 coliphage, a surrogate for single-stranded RNA human enteric viruses, in concentrated synthetic urine was investigated. The infectious titer reduction of MS2 coliphage in synthetic urine samples was measured by plaque assay, and the reduction of genome copy number was monitored by reverse transcription-quantitative PCR (RTqPCR). Among chemical-physical conditions such as pH and osmotic pressure, uncharged ammonia was shown to be the predominant factor responsible for MS2 inactivation, independently of urine concentration level. The reduction rate of the viral genome number varied among genome regions, but the comprehensive reduction rate of six genome regions was well correlated with that of the infectious titer of MS2 coliphage. This indicates that genome degradation is the main mechanism driving loss of infectivity, and that RT-qPCR targeting the six genome regions can be used as a culture-independent assay for monitoring infectivity loss of the coliphage in urine. MS2 inactivation rate constants were well predicted by a model using ion composition and speciation in synthetic urine samples, which suggests that MS2 infectivity loss can be estimated solely based on the solution composition, temperature and pH, without explicitly accounting for effects of osmotic pressure.

Inactivation of Ascaris Eggs in Human Fecal Material Through In Situ Production of Carboxylic Acids

Discovering new ways to inactivate pathogens in human waste is critical for the improvement of worldwide access to sanitation and for the reduction of the environmental impact of conventional waste treatment processes. Here, we utilized the carboxylate platform and chain elongation to produce n-butyric acid and n-caproic acid via the anaerobic fermentation of human fecal material. Then, we inactivated Ascaris eggs through exposure to these carboxylic acids. Using batch experiments with human fecal material as substrate, we accumulated n-butyric acid and n-caproic acid at total concentrations (uncharged acid plus conjugate base) of 257 and 27.1 mM, respectively. We then showed that carboxylic acids at these concentrations inactivated Ascaris eggs when the pH was below the pK_a for the acids, causing them to exist primarily in the uncharged forms. We observed that uncharged carboxylic acids affected viability rather than the pH itself or conjugate bases. In addition, we modeled the viability of Ascaris eggs as a function of uncharged carboxylic acid concentration for n-butyric acid and n-caproic acid at exposure times of 2, 6, 12, and 20 days. The results presented here indicate that in situ biological production of carboxylic acids in HFM provides a promising method of pathogen inactivation and may lead to new developments in sanitation technology and treatment of fecal sludge.

Achilles heel of environmental risk from recycling of sludge to soil as amendment: A summary in recent ten years (2007-2016)

Recycling sludge as a soil amendment has both positive and negative effects because of its enrichment in both nutrients and contaminants. So far, the negative effect has to be extensively investigated that the severities of different types of contaminants also remain unclear. The environmental behavior and risk of organic contaminant and pharmaceuticals, heavy metal and salt as well as pathogenic microorganisms brought by sludge amendment are summarized and discussed here. Organic contaminants and pharmaceuticals are typically found at low concentrations in sludge, the risks from sludge-amended soil decrease over time owing to its biodegradability. On the other hand, application of sludge generally increases soil salinity, which may cause physiological damage to plants grown in sludge-amended soil. In some extent, this negative effect can be alleviated by means of dilution; however, greater attention should be paid to long term increasing possible risk of eutrophication. Heavy metal (particularly of mobile heavy metals, such as Cd) with high concentrations in sludge and soil receiving considerable sludge can cause its incremental abundance in soil and crop contamination, further posing risks to humans, but most cases showed that there remained not excessive in heavy metal caused by sludge amendment. It is worth noting that increasing soil organic matter content may reduce transfer of heavy metal from soil to crops, but not restrict its uptake by crops at all. Combined literature together, it is summarized that heavy metal becomes a relatively severe bottleneck in recycling of sludge as soil amendment due to its non-biodegradability and potential damage to health by adventuring contamination from agricultural products. Particular attention should therefore be paid to long term monitoring the change of heavy metals concentration in sludge amended soil.

Ammonia as an In Situ Sanitizer: Influence of Virus Genome Type on Inactivation

Treatment of human excreta and animal manure (HEAM) is key in controlling the spread of persistent enteric pathogens, such as viruses. The extent of virus inactivation during HEAM storage and treatment appears to vary with virus genome type, although the reasons for this variability are not clear. Here, we investigated the inactivation of viruses of different genome types under conditions representative of HEAM storage or mesophilic digestion. The goals were to characterize the influence of HEAM solution conditions on inactivation and to determine the potential mechanisms involved. Specifically, eight viruses representing the four viral genome types (single-stranded RNA [ssRNA], double-stranded RNA [dsRNA], single-stranded DNA [ssDNA], and double-stranded DNA [dsDNA]) were exposed to synthetic solutions with well-controlled temperature (20 to 35°C), pH (8 to 9), and ammonia (NH3) concentrations (0 to 40 mmol liter(-1)). DNA and dsRNA viruses were considerably more resistant than ssRNA viruses, resulting in up to 1,000-fold-longer treatment times to reach a 4-log inactivation. The apparently slower inactivation of DNA viruses was rationalized by the higher stability of DNA than that of ssRNA in HEAM. Pushing the system toward harsher pH (>9) and temperature (>35°C) conditions, such as those encountered in thermophilic digestion and alkaline treatments, led to more consistent inactivation kinetics among ssRNA and other viruses. This suggests that the dependence of inactivation on genome type disappeared in favor of protein-mediated inactivation mechanisms common to all viruses. Finally, we recommend the use of MS2 as a conservative indicator to assess the inactivation of ssRNA viruses and the stable ΦX174 or dsDNA phages as indicators for persistent viruses.

IMPORTANCE

Viruses are among the most environmentally persistent pathogens. They can be present in high concentrations in human excreta and animal manure (HEAM). Therefore, appropriate treatment of HEAM is important prior to its reuse or discharge into the environment. Here, we investigated the factors that determine the persistence of viruses in HEAM, and we determined the main mechanisms that lead to their inactivation. Unlike other organisms, viruses can have four different genome types (double- or single-stranded RNA or DNA), and the viruses studied herein represent all four types. Genome type appeared to be the major determinant for persistence. Single-stranded RNA viruses are the most labile, because this genome type is susceptible to degradation in HEAM. In contrast, the other genome types are more stable; therefore, inactivation is slower and mainly driven by the degradation of viral proteins. Overall, this study allows us to better understand the behavior of viruses in HEAM.