Tools for Risk Analysis: Updating the 2006 WHO guidelines

This chapter reviews developments since the WHO Guidelines for the safe use of wastewater in agriculture were published in 2006. The six main developments are: the recognition that the tolerable additional disease burden may be too stringent for many developing countries; the benefits of focusing on single-event infection risks as a measure of outbreak potential when evaluating risk acceptability; a more rigorous method for estimating annual risks; the availability of dose-response data for norovirus; the use of QMRA to estimate Ascaris infection risks; and a detailed evaluation of pathogen reductions achieved by produce-washing and disinfection. Application of the developments results in more realistic estimates of the pathogen reductions required for the safe use of wastewater in agriculture and consequently permits the use of simpler wastewater treatment processes

Ammonia volatilisation in waste stabilisation ponds: a cascade of misinterpretations?

Ammonia volatilisation has generally been reported as, or assumed to be, the main nitrogen removal mechanism in waste stabilisation ponds (WSP). Nitrogen removal via ammonia volatilisation is based on two observations: (a) in-pond pH values can reach high values (>9, even >10), so increasing the proportion of the total ammonia present as the un-ionized form or free ammonia (NH(3)); and (b) in-pond temperatures can also be high, so improving the mass transfer rate of free ammonia to the atmosphere. Consequently, one of the most widely accepted models for ammonia removal in WSP is that reported by Pano & Middlebrooks in 1982, which was developed to reflect the occurrence of these two observations. This work reports how simple mathematical models for ammonia volatilisation in WSP, in spite of the possibility of their giving good predictions, may not accurately describe the main pathways and mechanisms involved in ammonia removal in WSP

Nitrogen removal in maturation waste stabilisation ponds via biological uptake and sedimentation of dead biomass.

In this work a set of experiments was undertaken in a pilot-scale WSP system to determine the importance of organic nitrogen sedimentation on ammonium and total nitrogen removals in maturation ponds and its seasonal variation under British weather conditions, from September 2004 to May 2007. The nitrogen content in collected sediment samples varied from 4.17% to 6.78% (dry weight) and calculated nitrogen sedimentation rates ranged from 273 to 2868 g N/ha d. High ammonium removals were observed together with high concentrations of chlorophyll-a in the pond effluent. Moreover, chlorophyll-a had a very good correlation with the corresponding increment of VSS (algal biomass) and suspended organic nitrogen (biological nitrogen uptake) in the maturation pond effluents. Therefore, when ammonium removal reached its maximum, total nitrogen removal was very poor as most of the ammonia taken up by algae was washed out in the pond effluent in the form of suspended solids. After sedimentation of the dead algal biomass, it was clear that algal-cell nitrogen was recycled from the sludge layer into the pond water column. Recycled nitrogen can either be taken up by algae or washed out in the pond effluent. Biological (mainly algal) uptake of inorganic nitrogen species and further sedimentation of dead biomass (together with its subsequent mineralization) is one of the major mechanisms controlling in-pond nitrogen recycling in maturation WSP, particularly when environmental and operational conditions are favourable for algal growth

Diabetes status and post-load plasma glucose concentration in relation to site-specific cancer mortality: findings from the original Whitehall study

ObjectiveWhile several studies have reported on the relation of diabetes status with pancreatic cancer risk, the predictive value of this disorder for other malignancies is unclear. Methods: The Whitehall study, a 25year follow-up for mortality experience of 18,006 men with data on post-challenge blood glucose and self-reported diabetes, allowed us to address these issues. Results: There were 2158 cancer deaths at follow-up. Of the 15 cancer outcomes, diabetes status was positively associated with mortality from carcinoma of the pancreas and liver, while the relationship with lung cancer was inverse, after controlling for a range of potential covariates and mediators which included obesity and socioeconomic position. After excluding deaths occurring in the first 10years of follow-up to examine the effect of reverse causality, the magnitude of the relationships for carcinoma of the pancreas and lung was little altered, while for liver cancer it was markedly attenuated. Conclusions: In the present study, diabetes status was related to pancreatic, liver, and lung cancer risk. Cohorts with serially collected data on blood glucose and covariates are required to further examine this area

Network modelling for road-based Faecal Sludge Management

Improvements in the collection and treatment of sewage are critical to reduce health and environmental hazards in rapidly-urbanising informal settlements. Where sewerage infrastructure is not available, road-based Fecal Sludge Management options are often the only alternative. However, the costs of fecal sludge transportation are often a barrier to their implementation and operation and thus it is desirable to optimise travel time from source to treatment to reduce costs. This paper presents a novel technique, employing spatial network analysis, to optimise the spatio-topological configuration of a road-based fecal sludge transportation network on the basis of travel time. Using crowd-sourced spatial data for the Kibera settlement and the surrounding city, Nairobi, a proof-of-concept network model was created simulating the transport of waste from the 158 public toilets within Kibera. The toilets are serviced by vacuum pump trucks which move fecal sludge to a transfer station from where a tanker transports waste to a treatment plant. The model was used to evaluate the efficiency of different network configurations, based on transportation time. The results show that the location of the transfer station is a critical factor in network optimisation, demonstrating the utility of network analysis as part of the sanitation planning process

Hygiene, Sanitation, and Water: Forgotten Foundations of Health

As the first article in a four-part PLoS Medicine series on water and sanitation, Jamie Bartram and Sandy Cairncross argue that the massive burden of ill health associated with poor hygiene, sanitation, and water supply demands more attention from health professionals and policymakers

Surgery for fistula-in-ano in a specialist colorectal unit: a critical appraisal

ABSTRACT

Global Distribution of Outbreaks of Water-Associated Infectious Diseases

Water is essential for maintaining life on Earth but can also serve as a media for many pathogenic organisms, causing a high disease burden globally. However, how the global distribution of water-associated infectious pathogens/diseases looks like and how such distribution is related to possible social and environmental factors remain largely unknown. In this study, we compiled a database on distribution, biology, and epidemiology of water-associated infectious diseases and collected data on population density, annual accumulated temperature, surface water areas, average annual precipitation, and per capita GDP at the global scale. From the database we extracted reported outbreak events from 1991 to 2008 and developed models to explore the association between the distribution of these outbreaks and social and environmental factors. A total of1,428 outbreaks had been reported and this number only reflected ‘the tip of the iceberg’ of the much bigger problem. We found that the outbreaks of water-associated infectious diseases are significantly correlated with social and environmental factors and that all regions are affected disproportionately by different categories of diseases. Relative risk maps are generated to show ‘hotspots’ of risks for different diseases. Despite certain limitations, the findings may be instrumental for future studies and prioritizing health resources