Microwaving human faecal sludge as a viable sanitation technology option for treatment and value recovery - A critical review

Fecal sludge characterization, treatment, and resource recovery options: a state-of-the-art review on fecal sludge management

A rise in population and urbanization demanded that a robust fecal sludge management (FSM) value chain be used to restructure the sanitation system throughout the world securely. A significant global need exists to adopt efficient and sustainable FSM. On-site sanitation systems (OSS) produce fecal sludge (FS). FS is produced when excreta and blackwater are combined and stored or treated, either alone or in combination with greywater. FS can be semisolid or slurry and raw or partially digested. Critical examination of FS characteristics, i.e., biochemical oxygen demand (BOD), chemical oxygen demand (COD), total solids (TS), and pathogen count, varies from 600-56,836 mg/l, 6656 to 201,200 mg/l, 830-123,000 mg/l, and 105 to 109 E. coli/l of FS respectively. Helminth eggs range from 2500-25,000/l of FS. Public health and the environment are negatively impacted by septic tank overflows and the careless discharge of FS into open spaces affecting groundwater quality, water bodies, irrigation fields, open drains, places outside villages, etc. Thus, deciding on a proper treatment technology for FS before discharging it into open land or reusing FS is essential to create a pollution-free environment. This paper highlights the practices adopted for FSM under its different processes, such as collecting, characterization, treating, and reusing of on-site FS and bibliometric analysis on documents on fecal sludge. A thorough analysis has been carried out by reviewing all important literature available globally.

Health effects and externalities of the popularization of sanitary toilets: evidence from Rural China

BACKGROUND

This study aimed to assess the impact of the increased prevalence of sanitary toilets in rural areas on the health of rural residents, and whether the popularity thereof has a positive externality. This study investigates whether the broader use of sanitary toilets has had a positive effect on the health of people who do not have access to them.

METHODS

Data from the China Family Panel Studies from 2012 to 2014 and a two-way fixed effect model were used to investigate the relationship between the prevalence of village sanitary toilets and the health of rural residents of all ages.

RESULTS

The results showed that: (1) the increase in the prevalence of sanitary toilets in villages is conducive to improving the health level of rural residents; (2) the widespread adoption of sanitary toilets in rural areas has improved the health of not only residents with access to these toilets but also residents without access; (3) the health of children is more sensitive to improvements in sanitary conditions of toilets; and (4) there are significant regional differences in the impact of the popularity of sanitary toilets on the health of rural residents.

CONCLUSIONS

This study found that the popularity of sanitary toilets has externalities, improving not only the health of residents who use them but also the health of other residents. This study enriches the literature in the field of health effects of sanitation improvement, while providing a reference for developing countries to further enhance the living environment in rural areas. In the future, the popularization of sanitary toilets should be vigorously promoted to reduce the incidence of diseases.

Potential barriers in implementing the rural toilet retrofitting project: A qualitative study in Jiaozuo, China

Background

China has launched a large "toilet revolution" in rural areas, but the results show that sanitation has not always been markedly improved. Few scholars have paid attention to this issue, and the list of the reasons is scattered and incomplete.

Method

Using the qualitative research method, this study interviewed seven village cadres and 39 villagers in three villages of Jiaozuo City to examine the implementation barriers to rural toilet retrofitting (RTR) projects in China.

Results

Using the Van Meter and Van Horn policy implementation approach, the research has found that: (a) unreasonable standards and objectives fail to incorporate local conditions and improve the actual quality; (b) lack of capital and human resources cannot renovate new toilets; (c) uncoordinated inter-organizational communication and enforcement activities by top-down mechanism lead to policy implementers and target groups' dissatisfaction with the policy; (d) weak and unenthusiastic, inadequate implementing agencies, reduce their working ability; (e) inappropriate economic, social and political conditions impede the villagers' acceptance; and (f) an attitude of passive acceptance by the implementers reduce the working motivation.

Conclusion

To improve sanitation in rural China, it is necessary to solve the six barriers. The findings of this study can provide recommendations and guidance for implementing the RTR and related public health policies.

Cesspits as Onsite Sanitation Facilities in the Non-Sewered Palestinian Rural Areas: Users’ Satisfaction, Needs and Perception

The main aim of this research was to assess the problems of using cesspits in the non-sewered areas in the West Bank of Palestine by the means of a questionnaire, with a sample size of 485 households, targeting the cesspits’ owners. People who use cesspits for house onsite wastewater management are not satisfied with them, and most of them complain about high disturbance during discharge of the cesspits (75.5%). Emptying cesspits represents a financial burden, costing 6% of the households’ monthly income. The frequency of cesspits’ emptying decreases substantially when there are onsite GWTPs. People accept that constructing a house with an onsite GWTPs when supported by external funding, and to a much lesser extent when they need to fund them themselves. The majority of people prefer sewerage networks for wastewater management(74.8%), followed by onsite GWTPs (15.5%), and cesspits are the least preferable (9.5%). Therefore, a more technically sound individual home onsite wastewater management system should be applied to replace cesspits so as to solve their negative implications on the socio-economic, environmental, and health aspects in the Palestinian rural communities.

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.

Microwave treatment of municipal sewage sludge: Evaluation of the drying performance and energy demand of a pilot-scale microwave drying system

Sewage sludge management and treatment can represent up to approximately 30% of the overall operational costs of a wastewater treatment plant. Microwave (MW) drying has been recognized as a feasible technology for sludge treatment. However, MW drying systems exhibit high energy expenditures due to: (i) unnecessary heating of the cavity and other components of the system, (ii) ineffective extraction of the condensate from the irradiation cavity, and (iii) an inefficient use of the microwave energy, among others issues. This study investigated the performance of a novel pilot-scale MW system for sludge drying, specifically designed addressing the shortcomings previously described. The performance of the system was assessed drying municipal centrifuged wasted activated sludge at MW output powers from 1 to 6 kW and evaluating the system's drying rates and exposure times, specific energy outputs, MW generation efficiencies, overall energy efficiencies, and specific energy consumption. The results indicated that MW drying significantly extends the duration of the constant rate drying period associated with the evaporation of the unbound sludge water, a phase associated with low energy input requirement for evaporating water. Moreover, the higher the MW output power, the higher the sludge power absorption density, and the MW generation efficiency. MW generation efficiencies of up to 70% were reported. The higher the power absorption density, the lower the chances for energy losses in the form of reflected power and/or energy dissipated into the MW system. Specific energy consumptions as low as 2.6 MJ L^-1 (0.74 kWh L^-1) could be achieved, well in the range of conventional thermal dryers. The results obtained in this research provide sufficient evidence to conclude that the modifications introduced to the novel pilot-scale MW system mitigated the shortcomings of existing MW systems, and that the technology has great potential to effectively and efficiently drying municipal sewage sludge.

A Review of Microwave Synthesis of Zinc Oxide Nanomaterials: Reactants, Process Parameters and Morphoslogies

Zinc oxide (ZnO) is a multifunctional material due to its exceptional physicochemical properties and broad usefulness. The special properties resulting from the reduction of the material size from the macro scale to the nano scale has made the application of ZnO nanomaterials (ZnO NMs) more popular in numerous consumer products. In recent years, particular attention has been drawn to the development of various methods of ZnO NMs synthesis, which above all meet the requirements of the green chemistry approach. The application of the microwave heating technology when obtaining ZnO NMs enables the development of new methods of syntheses, which are characterised by, among others, the possibility to control the properties, repeatability, reproducibility, short synthesis duration, low price, purity, and fulfilment of the eco-friendly approach criterion. The dynamic development of materials engineering is the reason why it is necessary to obtain ZnO NMs with strictly defined properties. The present review aims to discuss the state of the art regarding the microwave synthesis of undoped and doped ZnO NMs. The first part of the review presents the properties of ZnO and new applications of ZnO NMs. Subsequently, the properties of microwave heating are discussed and compared with conventional heating and areas of application are presented. The final part of the paper presents reactants, parameters of processes, and the morphology of products, with a division of the microwave synthesis of ZnO NMs into three primary groups, namely hydrothermal, solvothermal, and hybrid methods.

The kinetics of typical medical waste pyrolysis based on gaseous evolution behaviour in a micro-fluidised bed reactor

In order to obtain the kinetic parameters during typical medical waste pyrolysis, the typical medical waste is pyrolysed in a micro-fluidised bed reactor. The gases evolved from the typical medical waste pyrolysis are analysed by a mass spectrometer, and only H₂, CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆, C₃H₈ and C₄H₄ are observed. According to the gaseous product concentration profiles, the activation energies of gaseous formation are calculated based on the Friedman approach, and the average activation energies of H₂, CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆, C₃H₈ and C₄H₄ formation during typical medical waste pyrolysis are in sequence as 65.10, 39.98, 35.17, 38.71, 40.75, 41.79, 58.57 and 63.95 kJ mol^-1. Moreover, the activation energy with respect to the gases mixture formation is 52.70 kJ mol^-1. Hence, it is concluded that the activation energy of typical medical waste pyrolysis is 52.70 kJ mol^-1. The model-fitting method is used to determine the mechanism model of medical waste pyrolysis. The results indicate that the chemical reaction ( n = 1) model (G(x) = -ln(1-x)) is the optimum.

Microwave Technologies: An Emerging Tool for Inactivation of Biohazardous Material in Developing Countries

Inappropriate treatment and disposal of waste containing biohazardous materials occurs especially in developing countries and can lead to adverse effects on public and occupational health and safety, as well as on the environment. For the treatment of biohazardous waste, microwave irradiation is an emerging tool. It is a misbelief that microwave devices cannot be used for inactivation of solid biohazardous waste; however, the inactivation process, and especially the moisture content, has to be strictly controlled, particularly if water is required to be added to the process. Appropriate control allows also inactivation of waste containing inhomogeneous compositions of material with low fluid/moisture content. Where appropriate, especially where control of transport of waste cannot be guaranteed, the waste should be inactivated directly at the place of generation, preferably with a closed waste collection system. In waste containing sufficient moisture, there are direct useful applications, for example the treatment of sewage sludge or human feces. A number of examples of microwave applications with impacts for developing countries are presented in this review. In respect to energy costs and environmental aspects, microwave devices have clear advantages in comparison to autoclaves.

Application of dielectric constant measurement in microwave sludge disintegration and wastewater purification processes

It has been numerously verified that microwave radiation could be advantageous as a pre-treatment for enhanced disintegration of sludge. Very few data related to the dielectric parameters of wastewater of different origins are available; therefore, the objective of our work was to measure the dielectric constant of municipal and meat industrial wastewater during a continuous flow operating microwave process. Determination of the dielectric constant and its change during wastewater and sludge processing make it possible to decide on the applicability of dielectric measurements for detecting the organic matter removal efficiency of wastewater purification process or disintegration degree of sludge. With the measurement of dielectric constant as a function of temperature, total solids (TS) content and microwave specific process parameters regression models were developed. Our results verified that in the case of municipal wastewater sludge, the TS content has a significant effect on the dielectric constant and disintegration degree (DD), as does the temperature. The dielectric constant has a decreasing tendency with increasing temperature for wastewater sludge of low TS content, but an adverse effect was found for samples with high TS and organic matter contents. DD of meat processing wastewater sludge was influenced significantly by the volumetric flow rate and power level, as process parameters of continuously flow microwave pre-treatments. It can be concluded that the disintegration process of food industry sludge can be detected by dielectric constant measurements. From technical purposes the applicability of dielectric measurements was tested in the purification process of municipal wastewater, as well. Determination of dielectric behaviour was a sensitive method to detect the purification degree of municipal wastewater.

Fecal sludge management in developing urban centers: a review on the collection, treatment, and composting

The problems posed by fecal sludge (FS) are multidimensional because most cities rapidly urbanize, which results in the increase in population, urban settlement, and waste generation. Issues concerning health and waste treatment have continued to create alarming situations. These issues had indeed interfered with the proper steps in managing FS, which contaminates the environment. FS can be used in agriculture as fertilizer because it is an excellent source of nutrients. The recent decline in crop production due to loss of soil organic component, erosion, and nutrient runoff has generated interest in the recycling of FS into soil nutrients through stabilization and composting. However, human feces are considerably liable to spread microorganisms to other persons. Thus, sanitation, stabilization, and composting should be the main objectives of FS treatment to minimize the risk to public and environmental health. This review presents an improved FS management (FSM) and technology option for soil amendment that is grouped into three headings, namely, (1) collection, (2) treatment, and (3) composting. On the basis of the literature review, the main problems associated with the collection and treatment of FS, such as inadequate tools and improper treatment processes, are summarized, and the trends and challenges that concern the applicability of each of the technologies in developing urban centers are critically reviewed. Stabilization during pretreatment before composting is suggested as the best method to reduce pathogens in FS. Results are precisely intended to be used as a support for decisions on policies and strategies for FSM and investments for improved treatment facilities.