Risk Is More Than Just a Number

Summarizes efforts by the Health Council of the Netherlands to develop a national risk management approach

The emergence and spreading of an improved traditional soil and water conservation practice in Burkina Faso:

"This paper describes the emergence of improved traditional planting pits (zaï) in Burkina Faso in the early 1980s as well as their advantages, disadvantages and impact. The zaï emerged in a context of recurrent droughts and frequent harvest failures, which triggered farmers to start improving this local practice. Despair triggered experimentation and innovation by farmers. These processes were supported and complemented by external intervention. Between 1985 and 2000 substantial public investment has taken place in soil and water conservation (SWC). The socio-economic and environmental situation on the northern part of the Central Plateau is still precarious for many farming families, but the predicted environmental collapse has not occurred and in many villages indications can be found of both environmental recovery and poverty reduction." Authors' Abstract

Agroenvironmental transformation in the Sahel: Another kind of “Green Revolution"

millions fed, food security, Sahel, Zai, Stone bunds, Agroforestry, Soil management,

Comparing nonsynergy gamma models and interaction models to predict growth of emetic Bacillus cereus for combinations of pH and water activity values

This research aims to test the absence (gamma hypothesis) or occurrence of synergy between two growth-limiting factors, i.e., pH and water activity (aw), using a systematic approach for model selection. In this approach, preset criteria were used to evaluate the performance of models. Such a systematic approach is required to be confident in the correctness of the individual components of the combined (synergy) models. With Bacillus cereus F4810/72 as the test organism, estimated growth boundaries for the aw-lowering solutes NaCl, KCl, and glucose were 1.13 M, 1.13 M, and 1.68 M, respectively. The accompanying aw values were 0.954, 0.956, and 0.961, respectively, indicating that equal aw values result in similar effects on growth. Out of the 12 models evaluated using the preset criteria, the model of J. H. T. Luong (Biotechnol. Bioeng. 27:280–285, 1985) was the best model to describe the effect of aw on growth. This aw model and the previously selected pH model were combined into a gamma model and into two synergy models. None of the three models was able to describe the combined pH and aw conditions sufficiently well to satisfy the preset criteria. The best matches between predicted and experimental data were obtained with the gamma model, followed by the synergy model of Y. Le Marc et al. (Int. J. Food Microbiol. 73:219–237, 2002). No combination of models that was able to predict the impact of both individual and combined hurdles correctly could be found. Consequently, in this case we could not prove the existence of synergy nor falsify the gamma hypothesis

Factors influencing the accuracy of the plating method used to enumerate low numbers of viable micro-organisms in food

This study aims to assess several factors that influence the accuracy of the plate count technique to estimate low numbers of micro-organisms in liquid and solid food. Concentrations around 10 CFU/mL or 100 CFU/g in the original sample, which can still be enumerated with the plate count technique, are considered as low numbers. The impact of low plate counts, technical errors, heterogeneity of contamination and singular versus duplicate plating were studied. Batches of liquid and powdered milk were artificially contaminated with various amounts of Cronobacter sakazakii strain ATCC 29544 to create batches with accurately known levels of contamination. After thoroughly mixing, these batches were extensively sampled and plated in duplicate. The coefficient of variation (CV) was calculated for samples from both batches of liquid and powdered product as a measure of the dispersion within the samples. The impact of technical errors and low plate counts were determined theoretically, experimentally, as well as with Monte Carlo simulations. CV-values for samples of liquid milk batches were found to be similar to their theoretical CV-values established by assuming Poisson distribution of the plate counts. However, CV-values of samples of powdered milk batches were approximately five times higher than their theoretical CV-values. In particular, powdered milk samples with low numbers of Cronobacter spp. showed much more dispersion than expected which was likely due to heterogeneity. The impact of technical errors was found to be less prominent than that of low plate counts or of heterogeneity. Considering the impact of low plate counts on accuracy, it would be advisable to keep to a lower limit for plate counts of 25 colonies/plate rather than to the currently advocated 10 colonies/plate. For a powdered product with a heterogeneous contamination, it is more accurate to use 10 plates for 10 individual samples than to use the same 10 plates for 5 samples plated in duplicat

Strategies for sustainable natural resource management

This brief describes two case studies as follows: "Sub-Saharan Africa, with the highest fertility rate in the world, faces increasing demographic pressure on its natural resource base.... Old strategies for coping with these new pressures on the natural resource base are becoming increasingly infeasible... Consequently, Africa's farmers require new solutions to address the increasing pressure on the continent's soil and water resources. Among hundreds of innovative efforts across the continent, two promising sets of responses have emerged in different locations.... First is the use of planting basins, an approach that has emerged in recent decades in both the Sahel and Zambia.... The second strategy involves the use of improved fallows, introduced over the past decade in eastern Zambia and western Kenya." [from Text]. The authors look at the impact and the drivers of change and conclude with key lessons learned for buidling future successes.

The resilience of indigenous knowledge in small-scale African agriculture: key drivers

The successful use of indigenous knowledge (IK) in development practice in rural Africa over the last couple of decades has proved to be elusive and disappointing. Using empirical field data from northern Malawi, this study suggests that the two key drivers for farmers in this area are household food security and the maintenance of soil fertility. Indigenous ways of knowing underpin the agricultural system which has been developed, rather than the adoption of more modern, ‘scientific’ ways, to deliver against these drivers. Such IKs, however, are deeply embedded in the economic, social and cultural environments in which they operate

Membrane bioreactor for waste gas treatment

SummaryThis thesis describes the design and testing of a membrane bioreactor (MBR) for removal of organic pollutants from air. In such a bioreactor for biological gas treatment pollutants are degraded by micro-organisms. The membrane bioreactor is an alternative to other types of bioreactors for waste gas treatment, such as compost biofilters and bioscrubbers. Propene was used as a model pollutant to study the membrane bioreactor.A membrane bioreactor for waste gas treatment consists of a gas and a liquid compartment, separated by a membrane. Gaseous pollutants diffuse through the membrane and are consumed by microorganisms present in the liquid phase. The organisms are supplied with water and inorganic nutrients via this liquid phase. Various membrane bioreactors described in the literature are reviewed in Chapter 2. In the work presented in this thesis, microporous hydrophobic material was selected because of its low mass transfer resistance and the availability of both sheets and fibres. For the removal of propene from air the mass transfer resistance of this type of membrane was found to be negligible (Chapter 3).The propene-degrading bacterium Xanthobacter Py2 was shown to form biofilms in membrane bioreactors. Continuous propene removal by biofilms of Xanthobacter Py2 was demonstrated in both flat sheet reactors and hollow-fibre reactors. In both configurations the biofilms are situated on the membrane in the liquid phase. Propene consumption rates could be described quite accurately with the computer programme BIOSIM, that describes simultaneous diffusion and reaction in a biolayer (Chapter 3).During continuous operation of hollow-fibre reactors at inlet concentrations of 0.5 to 6 gram propene per m 3, the propene conversion decreased after several weeks (Chapter 4). Clogging of the fibres by excess biomass formation and acidification due to ammonium oxidation, were identified as possible causes. However, when both clogging and ammonium oxidation were prevented, the propene conversion still decreased in time.Apparently other factors than clogging and nitrification affect the long-term performance of biofilms of Xanthobacter Py2, growing In an MBR. These factors might be Identified with new methods for biofilm analysis, which allow the localization of activity within the biofilm.According to the Dutch emission standards, hydrocarbons such as propene, in offgas have to be reduced to less than 150 mg m -3. In Chapter 5, two propenedegrading strains were compared for their ability to degrade such low concentrations of propene and the faster growing strain, Xanthobacter Py2, was selected. At a concentration of 300 to 600 mg m -3in the gas phase, a 20 days startup period was required for biofilm formation. Once the biofilm had been established, the amount of active biomass adapted to the amount of propene available Within several days. Propene could be removed continuously from air at a concentration of 15 to 50 mg m -3in the gas phase without supplying other organic nutrients to the microbial population (Chapter 5).Besides the removal of poorly water soluble pollutants like propene, the membrane bioreactor is also suitable for the removal of pollutants that result in acidification, such as chlorinated hydrocarbons. Therefore, in Chapter 6 the biodegradation of trichloroethene (TCE) by Xanthobacter Py2 was tested during growth on propene in a stirred vessel. The aerobic biodegradation of TCE is difficult because of toxic intermediates that are formed. With Xanthobacter Py2 continuous cometabolic degradation of TCE was shown to be feasible with concentrations up to 206 μM in the liquid phase. The amount of TCE that could be degraded, depended on the TCE concentration and ranged from 0.03 to 0.34 grams of TCE per gram of biomass.Membrane bioreactors for gas-liquid contact have several potential applications. They are suitable for the removal of poorly soluble pollutants from air because of their large gas-liquid interface and small mass transfer resistance. Especially if biodegradation of a poorly soluble pollutant results in acidification, the membrane bioreactor might be a unique tool, since the acidic product can be removed via the liquid phase. Other applications might be the removal of highly chlorinated hydrocarbons from air by an aerobic or a combined anaerobic/aerobic: process, as was recently suggested in literature. Membrane bioreactors may also be useful tools in biofilm research, because of easy handling and processing of biofilm samples, excellent oxygen transfer properties and the possibility to apply counter gradients