Km Foxon

Challenges with up-scaling dry sanitation technologies

The acceleration of sanitation delivery towards meeting the South African Governments target of completely eradicating the existing backlogs by 2010, has led to a surge of activities. As part of its strategy for ensuring that basic sanitation is provided, the policy has recommended that a ventilated improved pit latrine (VIP) is considered as the basic minimum requirement in the form of a sanitation technology. The up-scaling and delivering of sanitation in many cases in the form of VIPs and its derivatives, as well as urine diversion technology are beginning to pose many technical challenges. The principles on which they have been designed are not always being observed in practice. As a result, some systems are filling up much faster than expected. Research has found that the breakdown in the faeces is not happening as would be expected in an anaerobic reactor, and that the drying of faeces in humid conditions, even with the use of drying agents, is not optimum. These problems, which are being experienced in the field, will have long term repercussions on the sustainability of sanitation provision. This paper aims to share these experiences and findings of research, and the impact it may have on the Sanitation MDG goals.

A critical review of experimental and predicted methane generation from anaerobic codigestion

Anaerobic digestion is increasingly being considered as a treatment option for an extensive range of waste biomass, due to the potential for energy recovery, in the form of methane production, and lower sludge volumes relative to aerobic treatment processes. Furthermore, when two substrates are codigested (i.e. digested together), added benefits are foreseeable, such as increased methane production and detoxification of toxic compounds via cometabolic degradation pathways. The objectives of this study were to compare experimental and predicted methane production from codigestion literature studies in order to objectively evaluate digester performance. Two predictive methods were used, both assuming methane yields are additive: literature values for digestion of single substrates and a stoichiometric method using model substrates to represent different substrates. Waste sources included in the analysis were primary sewage sludge, waste activated sludge, cow manure, waste paper, grease trap sludge, fat oil and grease and algal sludge. It was found that methane production could approximately be predicted using both methods, with literature methane yields from the same study being the most accurate predictor. One important finding from this study was that the assumption that methane yields are additive is a reasonable one. Furthermore, both predictive methods may be usefully employed as a screening tool to compare methane yields between different types and blends of substrates.

Ancient water and sanitation systems - applicability for the contemporary urban developing world.

The idea of implementing ancient water and wastewater technologies in the developing world is a persuasive one, since ancient systems had many features which would constitute sustainable and decentralised water and sanitation (WATSAN) provision in contemporary terminology. Latest figures indicate 2.6 billion people do not use improved sanitation and 1.1 billion practise open defecation, thus there is a huge need for sustainable and cost-effective WATSAN facilities, particularly in cities of the developing world. The objective of this study was to discuss and evaluate the applicability of selected ancient WATSAN systems for the contemporary developing world. Selected WATSAN systems in ancient Mesopotamia, the Indus Valley, Egypt, Greece, Rome and the Yucatan peninsula are briefly introduced and then discussed in the context of the developing world. One relevant aspect is that public latrines and baths were not only a part of daily life in ancient Rome but also a focal point for socialising. As such they would appear to represent a model of how to promote use and acceptance of modern community toilets and ablution blocks. Although public or community toilets are not classified as improved sanitation by WHO/UNICEF, this is a debatable premise since examples such as Durban, South Africa, illustrate how community toilets continue to represent a WATSAN solution for urban areas with high population density. Meanwhile, given the need for dry sanitation technologies, toilets based on the production of enriched Terra Preta soil have potential applications in urban and rural agriculture and warrant further investigation.

Modelling of ionic interactions with wastewater treatment biomass

Titration data for samples of mixed salts with glycine, bakers yeast cell mass and anaerobic digester sludge were obtained and compared to a speciation model of weak acid-base interaction in aqueous solutions. The effect of glycine on the buffer intensity of the solution could be precisely described by the speciation model but did not represent the proton exchange characteristics of either bakers yeast or anaerobic sludge well. A model component, UKZiNe, consisting of carboxylic acids, phosphate and amine groups described the bakers yeast well, and a combination of UKZiNe and carbonate-yielding inorganic solids described anaerobic digester sludge. The effect of biomass on buffer intensity in the pH range 6.5 to 8 was small for the concentration ranges tested.

The effect of moisture content and alkalinity on the anaerobic biodegradation of pit latrine sludge.

This study investigated the effect of additional moisture and/or alkalinity on the rate of anaerobic digestion in samples of material obtained from pit latrines. In modified serum bottle tests it was shown that poor gas production rates were observed from all experiments with material collected at the lower part of one pit. Using material from the top layer of a second pit it was shown that experimental bottles produced significant amounts of gas for all treatments. Analysis of data indicated that treatment with additional alkalinity had no discernible effect on anaerobic gas production rates, but that there was some correlation between moisture content and gas production rate. These results did not support the hypothesis that low pH buffering capacity was a limiting factor in the rate of digestion of pit latrine sludge, but confirmed that low moisture content could reduce the rate of stabilisation. This implies that increasing the moisture content in a pit latrine has the potential to increase biological stabilisation rates in the pit when the material is not already well-stabilised.

The effect of moisture content and alkalinity on the anaerobic biodegradation of VIP contents

This study investigated the effect of additional moisture and/or alkalinity on the rate of anaerobic digestion in samples of material obtained from pit latrines. In modified serum bottle tests it was shown that poor gas production rates were observed from all experiments with material collected at the lower part of one pit. Using material from the top layer of a second pit it was shown that experimental bottles produced significant amounts of gas with both the addition of water and the addition of alkalinity. The results supports the motivating hypotheses that moisture content and pH buffering capacity obtained in VIP material are low and may be limiting factors in the rate of stabilisation that may occur in these pits. This implies that increasing the moisture content and alkalinity in the pit has the potential to increase stabilisation rate in the pit when the material is not already well-stabilised.