Exploring toilet plume bioaerosol exposure dynamics in public toilets using a Design of Experiments approach.

Bioaerosols generated during toilet flushing can contribute to the spread of airborne pathogens and cross-contamination in indoor environments. This presents an increased risk of fomite-mediated or aerosol disease transmission. This study systematically investigated the factors contributing to increased bioaerosol exposure following toilet flushing and developed an empirical model for predicting the exposure-relevant bioaerosol concentration. Air in a toilet cubicle was sampled by impaction after seeding with Clostridium difficile spores. Design of Experiments (DoE) main effects screening and full factorial design approaches were then employed to investigate the significant factors that heighten the risk of exposure to bioaerosols post-flush. Our findings reveal that the inoculated bacterial concentration (C), time elapsed after flushing (t), lateral distance (d), and mechanical ventilation (v) are significant predictors of bioaerosol concentration, with p-values < 0.05. The interaction term, C × d showed a marked increase in bioaerosol concentration up to 232 CFU/m3 at the closest proximity and highest pathogen load. The interplay of C and t (C × t) demonstrated a time-dependent attenuation of bioaerosol viability, with concentrations peaking at 241 CFU/m3 immediately post-flush and notably diminishing over time. The lateral distance and time post-flush (d × t) interaction also revealed a gradual decrease in bioaerosol concentration, highlighting the effectiveness of spatial and temporal dilution in mitigating bioaerosol exposure risks. Furthermore, there is an immediate rise in relative humidity levels post-flush, impacting the air quality in the toilet environment. This study not only advances our understanding of exposure pathways in determining bioaerosol exposure, but also offers pivotal insights for designing targeted interventions to reduce bioaerosol exposure. Recommendations include designing public toilets with antimicrobial surfaces, optimizing ventilation, and initiating timely disinfection protocols to prioritise surfaces closest to the toilet bowl during peak exposure periods, thereby promoting healthier indoor environments and safeguarding public health in high-traffic toilet settings.

Toilet plume bioaerosols in health care and hospitality settings: A systematic review.

BACKGROUND: The spread of some respiratory and gastro-intestinal infections has been linked to the exposure to infectious bioaerosols released after toilet flushing. This represents a health hazard and infection risk for immunocompromised patients, health workers and the public, particularly within the health care and hospitality settings. This systematic review provides current knowledge and identifies gaps in the evidence regarding toilet plume bioaerosols and the potential contributory role in spreading infections in health care and hospitality settings. METHODS: The PRISMA guidelines were used. Searches were run in PubMed, Scopus, and Google Scholar from 1950 to 30th June 2021. Searches of global and regional reports and updates from relevant international and governmental organizations were also conducted. RESULTS AND CONCLUSION: The search yielded 712 results, and 37 studies were finally selected for this review. There is a lack of national and international bioaerosol sampling and exposure standards for health care and hospitality settings. Toilet plume bioaerosols are complex in nature, thus, measured bioaerosol concentrations in these settings depend on many variables and may differ for every pathogen responsible for a particular infectious disease. The contact and airborne transmission risks posed by toilet plume bioaerosols also remain unquantified. They are an important pathway that can increase the exposure to enteric and airborne pathogens. Hence, quantitative risk assessment and related research are needed to investigate these transmission risks.

Exploiting constructed wetlands for industrial effluent phytodesalination in Jing-Jin-Ji urban agglomeration, China.

The unsustainable exploitation of water resources and growing salinization impacting China's Beijing-Tianjin-Hebei (Jing-Jin-Ji) agglomeration threatens the region's economic growth and drives the exploration of alternative resources. The region's industries face a financial burden due to increasing constraints on water exploitation and discharge regulations. These have resulted in increased industrial salt concentration rejections/discharges, meanwhile, constructed wetlands (CWs), deployed as a perfunctory receptacle for industrial effluents in the region, are underexploited for treating/removing salts. Also, halophytic plants local to the region have promising chloride uptake (60.6 g/kg and 256.0 g/kg of plant dry weight) and can reduce water conductivity by 40%. Exploitation of CWs, using local halophytes has not been explored for phytodesalination purposes in the region. Hence, this study analyses the water resource and salinization crisis in the agglomeration and further evaluates workable potential and critical technical considerations for using local halophytes in CWs to treat industrial salt-laden effluents. While acknowledging this intervention for removing industrial effluent salt may not meet compliance in the region, effluent post-phytodesalination presents opportunities for industries to meet regulatory stipulations on water reuse rates. Furthermore, such effluent may be used for irrigation and can ameliorate the salinization and groundwater exploitation crisis as a cleaner recharge source.

The exploitation of phytoremediation via local halophytes for treating salt-laden industrial water discharges, with specific reference to the Beijing-Tianjin-Hebei (Jing-Jin-Ji) urban agglomeration, has not been explored nor reported in the literature. This study addresses these critical knowledge gaps, providing new insights and technical considerations for workable large-scale phytodesalination applications for deploying and implementing constructed wetlands using locally available halophytes suited to Jing-Jin-Ji agglomeration. This distinguishes this pertinent study intended to engage researchers, industrials, and other stakeholders in the focus area and beyond. HighlightsThe Jing-Jin-Ji urban agglomeration is facing a salinization crisis.All indexes indicate a decline in groundwater resources and quality.Untapped local halophytes have immense phytodesalination potential: up to 256 g/kg (dry weight) Cl⁻ uptake.Drivers and technical parameters for exploiting constructed wetlands for phytodesalination in the region are discussed.

Country-level assessment of agrifood waste and enabling environment for sustainable utilisation for bioenergy in Nigeria.

It is essential to plug inefficiencies due to agrifood losses and wastes, which pose a significant threat to the sustainable supply of nutritional agrifood commodities/products. Country-specific evaluations of the extent of agrifood losses/wastes, including the pathways and impacts on net agrifood production, are crucial to inform interventions, research, policies and investments. This kind of knowledge is scarce in sub-Saharan Africa (SSA) countries, many of which are food insecure. This paper presents an estimation of and the bioenergy potential for agrifood loss and waste (AFW) - the edible and inedible residual biogenic fractions of crops and animal commodities/products - in Nigeria. Our findings reveal that Nigeria generates 183.3 ± 8.9MT of AFW per annum. About 27% of the average annual total domestic supply of edible agrifood commodities/products is lost before reaching markets/consumers. The intrinsic bioenergy potential of the inedible AFW fraction generated annually in Nigeria is estimated to be 1,816.8 ± 117.3PJ; this is sufficient to meet 2030's bioenergy targets and replace a third of its total (grid, off-grid and self-generation) supply targets. However, Nigeria lacks regulatory, policy and institutional frameworks specific to AFW management. This study recommends a sustainable approach to managing AFW, addressing the interlinked challenges of bioenergy production, public health and environmental sustainability. Besides addressing knowledge gaps in the Nigerian agrifood sector, the information generated in this study is well-timed to inform decision-making and policy formulation on decentralised AFW-based bioenergy interventions to achieve energy supply targets in the country by 2030 and beyond. This study is also strategic to guide future research/interventions that align with AFW utilisation/clean energy generation in SSA.

Comparative evaluation of conventional and microwave hydrothermal carbonization of human biowaste for value recovery.

This paper compares conventional and microwave hydrothermal carbonization (HTC) of human biowaste (HBW) at 160 °C, 180 °C and 200 °C as a potential technology to recover valuable carbonaceous solid fuel char and organic-rich liquor. Also discussed are the influence of HTC heating methods and temperature on HBW processing conversion into solid fuel char, i.e. yield and post-HTC management, dewaterability rates, particle size distribution and the carbon and energy properties of solid fuel char. While HTC temperatures influenced all parameters investigated, especially yield and properties of end products recovered, heating source effects were noticeable on dewatering rates, char particle sizes and HBW processing/end product recovery rate and, by extension, energy consumed. The microwave process was found to be more efficient for dewatering processed HBW and for char recovery, consuming half the energy used by the conventional HTC method despite the similarity in yields, carbon and energy properties of the recovered char. However, both processes reliably overcame the heterogeneity of HBW, converting them into non-foul end products, which were easily dewatered at <3 seconds/g total solids (TS) (c.f. 50.3 seconds/g TS for a raw sample) to recover energy-densified chars of ≈17 MJ/kg calorific value and up to 1.4 g/l of ammonia concentration in recovered liquor.

Characterization of Solid Fuel Chars recovered from Microwave Hydrothermal Carbonization of Human Biowaste.

Microwave hydrothermal carbonization (M-HTC) is reported in this study as a viable sanitation technology that can reliably overcome the heterogeneous nature of human faecal biowaste (HBW) and realize its intrinsic energy value. Solid chars produced from the M-HTC process at 180°C and 200°C were characterized to further the understanding of the conversion pathways and their physicochemical, structural and energetic properties. The study revealed solid chars recovered were predominantly via a solid-solid conversion pathway. In terms of yield, more than 50% of solid chars (dry basis) can be recovered using 180°C as a benchmark. Additionally, the carbonized solid chars demonstrated enhanced carbon and energy properties following the M-HTC process: when compared to unprocessed HBW, the carbon content in the solid chars increased by up to 52%, while the carbon densification factor was greater than 1 in all recovered chars. The calorific values of the chars increased by up to 41.5%, yielding heating values that averaged 25MJ.kg-1. Thermogravimetric studies further revealed the solid fuel chars exhibited greater reactivity when compared with unprocessed HBW, due to improved porosity. This work strengthens the potential of the M-HTC sanitation technology for mitigating poor sanitation impacts while also recovering energy, which can complement domestic energy demands.

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

The prolonged challenges and terrible consequences of poor sanitation, especially in developing economies, call for the exploration of new sustainable sanitation technologies. Such technologies must be: capable of effectively treating human faecal wastes without any health or environmental impacts; scalable to address rapid increases in population and urbanization; capable of meeting environmental regulations and standards for faecal management; and competitive with existing strategies. Further and importantly, despite its noxiousness and pathogenic load, the chemical composition of human faecal sludge indicates that it could be considered a potentially valuable, nutrient-rich renewable resource, rather than a problematic waste product. New approaches to faecal sludge management must consequently seek to incorporate a 'valuable resource recovery' approach, compatible with stringent treatment requirements. This review intends to advance the understanding of human faecal sludge as a sustainable organic-rich resource that is typically high in moisture (up to 97 per cent), making it a suitable candidate for dielectric heating, i.e. microwave irradiation, to promote faecal treatment, while also recovering value-added products such as ammonia liquor concentrate (suitable for fertilizers) and chars (suitable for fuel) - which can provide an economic base to sustain the technology. Additionally, microwaving human faecal sludge represents a thermally effective approach that can destroy pathogens, eradicate the foul odour associated human faecal sludge, while also preventing hazardous product formations and/or emissions, aside from other benefits such as improved dewaterability and heavy metals recovery. Key technological parameters crucial for scaling the technology as a complementary solution to the challenges of onsite sanitation are also discussed.