Yu-Ling Cheng

Smoldering combustion as a treatment technology for feces: sensitivity to key parameters

ABSTRACT Poor sanitation results in increased spread of diseases and environmental pollution. In many parts of the globe, treatment of feces needs an urgent solution that ensures elimination of pathogens using minimal resources. Self-sustaining smoldering combustion of feces mixed with sand has been has been recently studied as a potential technology. A combination of different experimental parameters is essential to ensure robust operation, where oxidation coexists with pyrolysis and water evaporation. This work presents the results of a series of thirty-two experiments conducted in order to study the sensitivity of the process to the following experimental parameters: moisture content, sand-to-feces ratio, airflow, sand grain size and ignition temperature. It was found that smoldering temperature and velocity are independent on the moisture content and ignition temperature; while are strongly dependent on other parameters, specially the airflow. The information presented is crucial to control the process, allowing its implementation to a real scenario.

Global divergence in critical income for adult and childhood survival: analyses of mortality using Michaelis–Menten

Life expectancy has risen sharply in the last 50 years. We applied the classic Michaelis–Menten enzyme kinetics to demonstrate a novel mathematical relationship of income to childhood (aged 0–5 years) and adult (aged 15–60 years) survival. We treat income as a substrate that is catalyzed to increase survival (from technologies that income buys) for 180 countries from 1970 and 2007. Michaelis–Menten kinetics permit estimates of maximal survival and, uniquely, the critical income needed to achieve half of the period-specific maximum. Maximum child and adult survival rose by about 1% per year. Critical incomes fell by half for children, but doubled for men. HIV infection and smoking account for some, but not all, of the rising critical incomes for adult survival. Altering the future cost curve for adult survival will require more widespread use of current interventions, most notably tobacco control, but also research to identify practicable low-cost drugs, diagnostics, and strategies. DOI: http://dx.doi.org/10.7554/eLife.00051.001

Effects of neighbourhood and household sanitation conditions on diarrhea morbidity: Systematic review and meta-analysis

Sanitation in neighbourhood and household domains can provide primary protection against diarrhea morbidity, yet their distinct health benefits have not been succinctly distinguished and reviewed. We present here the first systematic review and meta-analysis of the distinct effect of neighbourhood and household sanitation conditions on diarrhea morbidity. We identified studies reporting the effect of neighbourhood-level exposure to wastewater or household sanitation facilities on diarrhea, by performing comprehensive search on five databases, namely the Cochrane library, PubMed, Embase, Scopus and Web of Science, from the earliest date available to February 2015. Twenty-one non-randomized studies and one randomized controlled trial met the pre-determined inclusion criteria, consisting of six datasets on neighbourhood sanitation conditions (total 8271 subjects) and 20 datasets on household sanitation (total 20021 subjects). We calculated the pooled effect estimates of neighbourhood and household sanitation conditions on diarrhea morbidity using the inverse variance random-effects model. The pooled effect estimates showed that both neighbourhood sanitation conditions (odds ratio = 0.56, 95%CI: 0.40–0.79) and household sanitation (odds ratio = 0.64, 95%CI: 0.55–0.75) are associated with reduced diarrheal illness, and that the magnitudes of the associations are comparable. Evidence of risk of bias and heterogeneity were found in the included studies. Our findings confirm that both neighbourhood sanitation conditions and household sanitation are associated with considerable reduction in diarrhea morbidity, in spite of a number of methodological shortcomings in the included studies. Furthermore, we find evidence that neighbourhood sanitation conditions is associated with similar magnitude of reduction in diarrhea morbidity as household sanitation. The findings suggest that, in addition to household sanitation provision, dual emphasis on neighbourhood sanitation through public sanitation infrastructure provision and community-wide sanitation adoption is advisable for effective reduction of diarrheal disease burden.

Estimating Oxygen Needs for Childhood Pneumonia in Developing Country Health Systems: A New Model for Expecting the Unexpected

Background Planning for the reliable and cost-effective supply of a health service commodity such as medical oxygen requires an understanding of the dynamic need or ‘demand’ for the commodity over time. In developing country health systems, however, collecting longitudinal clinical data for forecasting purposes is very difficult. Furthermore, approaches to estimating demand for supplies based on annual averages can underestimate demand some of the time by missing temporal variability. Methods A discrete event simulation model was developed to estimate variable demand for a health service commodity using the important example of medical oxygen for childhood pneumonia. The model is based on five key factors affecting oxygen demand: annual pneumonia admission rate, hypoxaemia prevalence, degree of seasonality, treatment duration, and oxygen flow rate. These parameters were varied over a wide range of values to generate simulation results for different settings. Total oxygen volume, peak patient load, and hours spent above average-based demand estimates were computed for both low and high seasons. Findings Oxygen demand estimates based on annual average values of demand factors can often severely underestimate actual demand. For scenarios with high hypoxaemia prevalence and degree of seasonality, demand can exceed average levels up to 68% of the time. Even for typical scenarios, demand may exceed three times the average level for several hours per day. Peak patient load is sensitive to hypoxaemia prevalence, whereas time spent at such peak loads is strongly influenced by degree of seasonality. Conclusion A theoretical study is presented whereby a simulation approach to estimating oxygen demand is used to better capture temporal variability compared to standard average-based approaches. This approach provides better grounds for health service planning, including decision-making around technologies for oxygen delivery. Beyond oxygen, this approach is widely applicable to other areas of resource and technology planning in developing country health systems.

Cost comparison of centralized and decentralized wastewater management systems using optimization model

There is a growing interest in decentralized wastewater management (DWWM) as a potential alternative to centralized wastewater management (CWWM) in developing countries. However, the comparative cost of CWWM and DWWM is not well understood. In this study, the cost of cluster-type DWWM is simulated and compared to the cost of CWWM in Alibag, India. A three-step model is built to simulate a broad range of potential DWWM configurations with varying number and layout of cluster subsystems. The considered DWWM scheme consists of cluster subsystems, that each uses simplified sewer and DEWATS (Decentralized Wastewater Treatment Systems). We consider CWWM that uses conventional sewer and an activated sludge plant. The results show that the cost of DWWM can vary significantly with the number and layout of the comprising cluster subsystems. The cost of DWWM increased nonlinearly with increasing number of comprising clusters, mainly due to the loss in the economies of scale for DEWATS. For configurations with the same number of comprising cluster subsystems, the cost of DWWM varied by ±5% around the mean, depending on the layout of the cluster subsystems. In comparison to CWWM, DWWM was of lower cost than CWWM when configured with fewer than 16 clusters in Alibag, with significantly less operation and maintenance requirement, but with higher capital and land requirement for construction. The study demonstrates that cluster-type DWWM using simplified sewer and DEWATS may be a cost-competitive alternative to CWWM, when carefully configured to lower the cost.

Exposure–response relationship of neighbourhood sanitation and children's diarrhoea

To assess the association of neighbourhood sanitation coverage with under‐five childrens diarrhoeal morbidity and to evaluate its exposure–response relationship.

Options for Medical Oxygen Technology Systems in Low-Resource Settings: A Framework for Comparison

Four different medical oxygen system configurations are presented and compared across a wide range of criteria relevant to low-resource settings. Two systems make use of power when available to generate and store oxygen for later use; the others use a backup battery bank (grid- or solar-charged) during power interruptions. Some system designs have been realized as prototypes with some field experience, and others are still conceptual. The results of this review and analysis have implications for future work involving the evaluation, development, and prototyping of alternative oxygen supply systems for settings with poor grid power and limited financial and technological resources.

Assessment of Power Availability and Development of a Low-Cost Battery-Powered Medical Oxygen Delivery System: For Use in Low-Resource Health Facilities in Developing Countries

The use of oxygen concentrators for the supply of medical oxygen in developing countries is increasingly becoming an alternative to conventional compressed gas cylinders, which are expensive to refill and logistically challenging to transport. Oxygen is important for obstetric, surgical, and an aesthesia care, as well as for the effective management of many diseases including severe sepsis, malaria, and pneumonia. One major obstacle to the effective use of oxygen concentrators in resource poor settings is the need for a constant power supply. An assessment of power availability in three health centres in The Gambia is presented, which highlights the issue of intermittent electricity supply for real health centre settings in a developing country. A battery-powered oxygen delivery system is also presented, which is charged from an intermittent grid power supply. This oxygen system will be beneficial in areas with little or intermittent electricity supply, such as The Gambia, where oxygen is in short supply.

Operations research in global health: a scoping review with a focus on the themes of health equity and impact

BackgroundOperations research (OR) is a discipline that uses advanced analytical methods (e.g. simulation, optimisation, decision analysis) to better understand complex systems and aid in decision-making.SummaryHerein, we present a scoping review of the use of OR to analyse issues in global health, with an emphasis on health equity and research impact. A systematic search of five databases was designed to identify relevant published literature. A global overview of 1099 studies highlights the geographic distribution of OR and common OR methods used. From this collection of literature, a narrative description of the use of OR across four main application areas of global health – health systems and operations, clinical medicine, public health and health innovation – is also presented. The theme of health equity is then explored in detail through a subset of 44 studies. Health equity is a critical element of global health that cuts across all four application areas, and is an issue particularly amenable to analysis through OR. Finally, we present seven select cases of OR analyses that have been implemented or have influenced decision-making in global health policy or practice. Based on these cases, we identify three key drivers for success in bridging the gap between OR and global health policy, namely international collaboration with stakeholders, use of contextually appropriate data, and varied communication outlets for research findings. Such cases, however, represent a very small proportion of the literature found.ConclusionPoor availability of representative and quality data, and a lack of collaboration between those who develop OR models and stakeholders in the contexts where OR analyses are intended to serve, were found to be common challenges for effective OR modelling in global health.