Seeking the reuse of effluents and sludge from conventional wastewater treatment plants: Analysis of the presence of intestinal protozoa and nematode eggs

Parasites in Sewage: Legal Requirements and Diagnostic Tools

Despite the vast amount of water on Earth, only a small percent is suitable for consumption, and these resources are diminishing. Moreover, water resources are unevenly distributed, leading to significant disparities in access to drinking water between countries and populations. Increasing consumption and the expanding human population necessitate the development of novel wastewater treatment technologies and the use of water treatment byproducts in other areas, such as fertilisers. However, water treatment sludge often cannot be used to enhance crop production due to the presence of parasite eggs, particularly from roundworms (Ascaridae family), which are resistant to environmental factors and can pose a threat for several years. Legislation prohibits the use of sludge containing parasite eggs as fertiliser. In some cases, water may not contain parasite eggs but larvae, which require different detection methods. Additionally, the presence of eggs does not necessarily indicate danger since they may lose infectivity due to prolonged storage or exposure to chemical compounds in the sewage. This paper reviews European Union regulations on wastewater treatment, the selected parasitic diseases related to the presence of parasites in wastewater, the spectrum of detection methods, and highlights differences in viability and invasiveness, which is intended to draw attention to the need to determine both biological properties of parasites.

Discharges of Wastewater Treatment Plants Needed Further Monitoring to Minimize Potential Risk of Entamoeba and Blastocystis for Public Health

The protozoan parasites Entamoeba histolytica and Blastocystis hominis are responsible for causing human amebiasis and hominis infections, respectively. These infections are highly prevalent and are often linked to waterborne diseases. Due to the absence of regulations for monitoring these protozoa at the discharge points of wastewater treatment plants (WWTPs), the effluents reaching surface waters contribute to waterborne transmission. This underscores the significance of the removal capacities of WWTPs in reducing the spread of these infectious parasites. Therefore, this study examined five different types of WWTPs in Ankara, Turkey, over a year to assess their capacities to remove E. histolytica and B. hominis. The seasonal abundances of genes specific to these protozoa in both the influents and effluents of each WWTP were measured using a quantitative polymerase chain reaction. The reduction in the number of protozoan rDNA copies between the influent and effluent samples was evaluated as the removal capacity, expressed in log10 reduction (LRV) values. The results elucidated that the removal of E. histolytica and B. hominis was highly affected by the process used. Membrane bioreactor systems displayed the highest removal capacity with LRV > 3. Therefore, discharges of WWTPs with other processes could need further monitoring to minimize the potential risk for public health.

Wastewater treatment plants discharges disseminated more Giardia than Cryptosporidium

Parasitic protozoa Giardia intestinalis and Cryptosporidium parvum are causative agents for giardiasis and cryptosporidiosis, respectively. These infections are mostly associated with waterborne diseases. The discharges from wastewater treatment plants (WWTPs) that reach surface waters cause waterborne transmission because there are no regulations for monitoring these protozoa. This emphasizes how crucial the removal capacities of WWTPs to prevent the spread of infectious parasitic pathogens. For this reason, in this study, five different types of WWTPs including conventional activated sludge (CAS), biological nutrient removal (BNR), sequencing batch reactor (SBR), membrane bioreactor (MBR), and WWTP with coagulation-flocculation and UV disinfection (CoFlUV) units were investigated over a year, seasonally in terms of their G. intestinalis and C. parvum removal capacities. The seasonal abundances of these protozoa-specific genes in both the influents and effluents of each WWTP were determined by qPCR. The reduction of protozoan rDNA copies in the effluent wastewater samples compared with the influent wastewater samples was assessed as log₁₀ reduction values (LRVs). LRVs >3 were reachable for C. parvum in all types of WWTPs tested. However, only LRVs 1-2 were reachable for G. intestinalis in CAS, SBR, CoFlUV, and MBR. Significant seasonal variations were just observed in SBR and CAS for G. intestinalis and C. parvum (p < 0.05), respectively. The findings depicted that WWTPs tested disseminated more giardiasis causative agents than cryptosporidiosis. Therefore, G. intestinalis needs to be monitored in WWTPs' discharges to reduce any potential damage of this parasite to public health. PRACTITIONER POINTS: Removal of G. intestinalis and C. parvum in WWTPs was affected by the process. LRV 2.92 was the highest LRV achieved for G. intestinalis. LRV >3 was reachable for C. parvum. WWTPs discharges disseminated more G. intestinalis than C. parvum. WWTPs effluents should be monitored in terms of G. intestinalis.

Performance of sewage treatment technologies for the removal of Cryptosporidium sp. and Giardia sp.: Toward water circularity

Cryptosporidium sp. and Giardia sp. are parasites that cause diseases in the population. Most of parasite diseases regarding the consumption of drinking water polluted with sewage are caused by Cryptosporidium sp. or Giardia sp. it is because of the incomplete disinfection of the wastewater treatment. Therefore, in this work the removal or inactivation efficiency of different treatment technologies presented by around 40 scientific studies was evaluated, with a view to water circularity. For Cryptosporidium sp., we conclude that the most efficient secondary technologies are aerobic technologies, which remove between 0.00 and 2.17 log units (Ulog), with activated sludge presenting the greatest efficiency, and that the tertiary technologies with the greatest removal are those that use ultrasound, which reach removal values of 3.17 Ulog. In the case of Giardia sp., the secondary technologies with the greatest removal are anaerobic technologies, with values between 0.00 and 3.80 Ulog, and the tertiary technologies with the greatest removal are those that combine filtration with UV or a chemical disinfection agent. Despite the removal values obtained, the greatest concern remains detecting and quantifying the infectious forms of both parasites in effluents; therefore, although the technologies perform adequately, discharge effluents must be monitored with more sensitive techniques, above all aiming for circularity of the treated water in a context of the water scarcity that affects some parts of the world.

Quantitative microbial risk assessment of enteroviruses in raw-eatable vegetables irrigated by wastewater: examining different scenarios of washing

Due to the increasing water crisis, the reuse of wastewater deserves attention as a method to reduce the pressure of the water crisis, especially in developing countries. The application of health risk assessment models is a way to estimate disease burdens associated with crop irrigation by wastewater effluents. In this study, a quantitative microbial risk assessment (QMRA) with probabilistic Monte-Carlo simulation was used to estimate the annual risk of enteroviruses (EVs) infection and disease burden for consumers of effluent-irrigated raw vegetables in Tehran, the capital of Iran. Wastewater effluent samples were collected over two seasons: summer and winter. EVs were analyzed in three stages, concentration and separation, cell culture, and real-time PCR (RT-PCR). A questionnaire was used to determine the dominant patterns of vegetable washing by consumers. There were 4 vegetable washing steps: wiping away mud (A), rinsing (B), using detergents (C), using disinfectants (D). 5 patterns of washing were examined in the laboratory and the concentration of enteroviruses was measured in every pattern. pattern 1: just wiping away mud (A), pattern 2: wiping away mud and rinsing (AB), pattern 3: wiping away mud by using detergents and rinsing (ABCB), pattern 4: wiping away mud by using disinfectants and rinsing (ABDB), and pattern 5: wiping away mud by using detergents and disinfectants and rinsing (ABCBDB). For washing pattern 1, pattern 2, and pattern 3, the estimated annual infection risk of EVs was estimated to be 5.6 × 10^-1, 3.6 × 10^-1, 1.7 × 10^-1 (risk/per.day), and burden of disease was calculated as 3 × 10^-2, 2 × 10^-2, and 9 × 10^-3 (burden/year), respectively. The results showed that if vegetables are washed according to method 5, the microbial risk will be minimized and the excess prevalence of viral infections will be eliminated.

Can quarantine plant-parasitic nematodes within wastes be managed by useful tools in a circular economy approach?

Seen as an integral part of sustainable development, circular economy represents a model of production and consumption notably based on the limitation of both resource wastage and environmental impact. Laboratories and commercial companies working on plant pathogens, in particular quarantine species, must effectively disinfect their waste to avoid disseminating these organisms. The methods used for waste disinfection can however incur high energy costs or pose environmental and human health hazards. Here, we tested the effectiveness of five disinfection methods - chlorination, heat treatment, composting, mesophilic methanation and waste stabilization ponds - on plant-parasitic nematodes belonging to the genera Globodera and Meloidogyne. For the widely used chlorination and heat treatment methods, we showed that they can be very effective in inactivating nematodes at relatively low chlorine doses and temperatures (60 °C-3 min and 50 °C-30 min), respectively. For the three other disinfection methods tested, initially designed for waste recycling, we obtained different levels of efficiency. Composting and mesophilic methanation (based on cattle or pig slurry) both led to the complete elimination of nematodes, even for short treatment durations. However, waste stabilization ponds showed contrasting results, ranging from virtually no effect to high levels of inactivation of nematodes. Our study demonstrates that it is possible to use more environmentally friendly disinfection methods to control plant-parasitic nematodes. In particular, this finding paves the way towards the treatment of infected plant materials using composting or methanation, providing that disinfection is still reached under other (real-life) treatment conditions, especially with other kinds of waste. Both composting and methanation recycle and thus valorize infected waste; they are viable alternatives to landfilling or incineration, thereby demonstrating the usefulness of a circular economy approach.

Detection of Cryptosporidium spp. and Giardia spp. in Environmental Water Samples: A Journey into the Past and New Perspectives

Among the major issues linked with producing safe water for consumption is the presence of the parasitic protozoa Cryptosporidium spp. and Giardia spp. Since they are both responsible for gastrointestinal illnesses that can be waterborne, their monitoring is crucial, especially in water sources feeding treatment plants. Although their discovery was made in the early 1900s and even before, it was only in 1999 that the U.S. Environmental Protection Agency (EPA) published a standardized protocol for the detection of these parasites, modified and named today the U.S. EPA 1623.1 Method. It involves the flow-through filtration of a large volume of the water of interest, the elution of the biological material retained on the filter, the purification of the (oo)cysts, and the detection by immunofluorescence of the target parasites. Since the 1990s, several molecular-biology-based techniques were also developed to detect Cryptosporidium and Giardia cells from environmental or clinical samples. The application of U.S. EPA 1623.1 as well as numerous biomolecular methods are reviewed in this article, and their advantages and disadvantages are discussed guiding the readers, such as graduate students, researchers, drinking water managers, epidemiologists, and public health specialists, through the ever-expanding number of techniques available in the literature for the detection of Cryptosporidium spp. and Giardia spp. in water.

Detection and removal of Giardia spp. cysts and Cryptosporidium spp. oocysts by anaerobic reactors in Brazil

The discharge of raw wastewater into the environment can be a contamination source of Giardia spp. cysts and Cryptosporidium spp. oocysts. The UASB (Upflow Anaerobic Sludge Blanket) reactor is the most popular technology applied for wastewater treatment in Brazil, nevertheless there is little information concerning its capacity for (oo)cyst removal. In this context, this study investigated the occurrence and removal of Giardia spp. cysts and Cryptosporidium spp. oocysts by three different UASB reactors (i.e. Reactor A, B, and C) treating different wastewater types. In the wastewater influent, the concentration varied from 493.3 to 14,000 cysts·L^-1 for Giardia spp. and from 'not detected' to 53.3 oocysts·L^-1 for Cryptosporidium spp.. The (oo)cyst concentration increased after the anaerobic treatment in Reactors A and B, while Giardia spp. log-removal of 0.5 ± 0.2 was found in Reactor C. The increment in (oo)cyst concentration may happened due to the inefficacy for (oo)cyst removal by the specific UASB reactor and/or due to the reduction of matrix interference for reactor effluent samples in the detection method. The results suggest that hydraulic retention time (HRT) may be the key parameter for Giardia spp. removal by the UASB reactor. Furthermore, no parameter analysed (physical-chemical and indicator microorganisms) showed a common correlation with the (oo)cyst concentration in the three UASB reactors. Considering that official data of cryptosporidiosis and giardiasis cases are rarely reported in Brazil, monitoring Giardia spp. cysts and Cryptosporidium spp. oocysts in wastewater could be an alternative to estimate the occurrence of diseases in the served population.

Wastewater fertigation in agriculture: Issues and opportunities for improved water management and circular economy

Water shortages are an issue of growing worldwide concern. Irrigated agriculture accounts for about 70% of total freshwater withdrawals globally, therefore alternatives to use of conventional sources need to be investigated. This paper critically reviews the application of treated wastewater for agricultural fertigation (i.e., water and nutrient recovery) considering different perspectives: legislation, agronomic characteristics, social acceptability, sustainability of treatment technologies. Critical issues that still need further investigation for a wider application of fertigation practices include accumulation of emerging contaminants in soils, microbiological and public health implications, and stakeholders' acceptance. A techno-economic methodological approach for assessing the sustainability of treated wastewater reuse in agriculture is subsequently proposed herein, which considers different possible local conditions (cultivated crops and effluent characteristics). The results showed that tailoring effluent characteristics to the desired nutrient composition could enhance the process economic sustainability; however, water savings have a major economic impact than fertilizers' savings, partly due to limited P reuse efficiency. The developed methodology is based on a practical approach and may be generalized to most agricultural conditions, to evaluate and encourage safe and efficient agricultural wastewater reuse practices.

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.

Using system dynamics to assess the complexity of rural toilet retrofitting: Case study in eastern China

Rural toilet retrofitting (RTR) is a complex, dynamic system that is affected by many factors and the positive/negative feedback relationships between subsystems and variables. Traditional technologies and management methods face challenges in fundamentally describing and solving problems in RTR. To bridge this gap, this study utilizes system dynamics and causal loop diagrams to explain such problems based on data collected from the stakeholders of the RTR in Jiaozhou from 2018 to 2019. Specifically, this study examines the RTR system from the perspectives of household users, wastewater treatment plants, local governments, grassroots promoters, operation and maintenance personnel, toilet supplier and construction teams, and fecal sludge end users. The factors and processes involved in RTR are identified, and the feedback and relationships among its major stakeholders are established. Results show that the motivation of farmers to engage in RTR is a key variable that affects their final decisions regarding retrofitting and maintaining toilet functions. Meanwhile, the important variables related to the feedback and relationships among the major stakeholders of RTR are mostly focused on policies, subsidies, technology, satisfaction, and cooperation. A scientific analysis method and the updated RTR plan for toilet revolution are then formulated to promote the implementation of RTR in developing countries.