Use and performance of BioSand filters in Posoltega, Nicaragua

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An evaluation of BioSand Filters, a method of Household Water Treatment, was conducted in Posoltega, Nicaragua, with objectives of determining the long-term filtration efficiency and the rate of sustained use. Field methods included microbial and turbidity water quality testing and interviews with filter users regarding the operation, maintenance and perceptions towards the filters. Of the 234 BioSand Filters installed in 1999 and 2004, only 24 were found to still be in operation. The average filtration efficiency was found to be 98% for total coliforms, 96% for E. coli and 88% for turbidity. Statistically significant effects on filtration efficiency were detected for the source contamination, the inverse of the flow rate, and the standing depth of water over the sand. A follow-up laboratory QA/QC procedure was undertaken to validate the field methods, which consisted of membrane filtration (MF) with m coliBlue24 growth media, and SolarCult dipslides. It was found that MF with m coliBlue24 produced useful reproducible results, and is an appropriate method for conducting field water quality testing. The dipslides were found to be an appropriate tool for testing source water quality and assessing the applicability of BioSand Filters, and may be an appropriate tool for local health representatives to promote safe water practices within the community. However, the dipslides should not be used as a presence / absence test for drinking water due to the high limit of detection. The low rate of sustained use (10%) is mostly a result of the structural failure of the concrete walls of the filter, in particular for those filters from 2004. Anecdotal evidence suggests insufficient quality control during the construction. The filtered water and the stored post-filtered water did not meet the WHO guidelines for safe drinking water on account of the presence of E. coli. Also identified were improper maintenance practices and unsafe storage of post-filtered water. These problems could have been addressed through the development of a holistic water system approach, such as the World Health Organization Water Safety Plan.

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... Concerning the quantity of the water treated (20 L/h), this volume gives satisfaction to the communities because it covers a lot. This level of population opinion about the BSF was higher than that obtained in Nepal (89%) by Paynter (2001), but slightly lower than that obtained in Haïti (99%) and in Nicaragua (100%) (Vanderzwaag, 2008). Concerning the utilization of the water produced by the BSF, communities used them for drinking, bathing, cooking and housework. ...
... The variation of the results between these two works could be explained by the raw water quality and the manner that experiments have been conducted by the authors. Furthermore, the treatment efficiency achieved in this work with the BSF is within the same order of results in literature (50 to 90%) (Vanderzwaag, 2008). Comparing the NH 4 + , NO 2 and NO 3 concentrations of the BSF effluents, one could find that they are lower than WHO drinking water standards (WHO, 2008). ...
... After their filtration on the BSF, the entire microorganism colonies were removed (100%). The mechanisms implicated in bacteria removal by the BSF could be: adsorption, physical straining and natural die-off of the microbial because of lack of carbon source (Elliott et al., 2006 2007; Vanderzwaag, 2008;Fiore et al., 2010). ...
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A concrete biosand filter (BSF) was designed, and its performance was evaluated on three different water used in the rural communities. The field study was conducted by using tap, well and pump waters, and a questionnaire was administered to apprehend the community’s attitudes in the BSF utilisation. BSF performance was characterised by analysing the filtrates concentration in NH4+, NO3- , NO2-, COD, Escherichia coli, and Clostridium perfringens. The BSF was approved by 94% of the population for water quality, ease of use and quantity of clean water produced. The main results are effective removal of microorganisms (C. perfringens, E. coli), chemical transformation and removal of NH4+, NO3- and COD at concentrations below WHO drinking water standards. BSF technology could be a solution in the provision of portable water to rural areas and might represent an alternative for the use of expensive bottled water.
... This confusion and maintenance problems have been shown to negatively impact sustained use of BSFs by families. For example, biosand filters installed near Posoltega, Nicaragua, had a sustained use rate of only 10% (Vanderzwaag 2008). Specifically, 10 of 34 BSFs from 1999 and 14 of 200 BSFs distributed in 2004 were still in use in early 2007. ...
... Recontamination of the water in storage vessels is sometimes a problem. A field study in Nicaragua found that the average total coliforms in the source water were 10 4 CFU/100 mL, 250 CFU/100 mL in filtered water, but 3000 CFU/100 mL in stored water (Vanderzwaag 2008). Similar results were found with E. coli: 120, 6, and 60 CFU/100 mL in source water, filtered water, and stored water, respectively. ...
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Safe drinking water is a critical need in developing communities around the globe. A variety of disinfection methods can be used at a community scale or as household water treatment. It is important that such methods are appropriate and sustainable for the environmental, economic, and societal constraints of each setting. This chapter highlights some of the methods commonly used in developing communities and compares their documented disinfection effectiveness in laboratory tests and field use. The strengths and weaknesses of each approach in regards to the removal and/or inactivation of bacteria, viruses, and protozoans are compared. Community scale methods reviewed include slow sand filtration, riverbank filtration, and solar-based approaches. Commonly used household treatment methods, also called point-of-use (POU) treatment, that are reviewed include chemical treatment, biosand, ceramic water filters, and solar disinfection. Global application of POU methods is increasing, but their long-term use and effectiveness is generally poorly documented. Many of these methods are undergoing increasing levels of research, but performance differences between the lab and field studies are a concern. A few studies have also documented health benefits associated with the use of these treatment methods; however, more research of this type is also needed.
... BSF technology had been favourably accepted by users, on a number of counts: † Considerable improvement in taste, odour and appearance of the water was evident (Vanderzwaag 2007). † Like other filtration technologies, BSF does not introduce chemicals into the water. ...
... Chemicals such as chlorine may affect its acceptability due to objections about taste and odour (Clasen 2008). † The health of the family was perceived to have improved after using the filter (Vanderzwaag 2007). † BSF is able to operate well under a wide range of conditions, such as temperature, pH and turbidity. ...
A biosand filtration (BSF) unit is an intermittently operated slow sand filter designed for household use. This paper reviews the practical application of BSF, identifies the important design considerations and proposes a systematic design procedure. The media properties, water requirements, filter cycle time and water temperature are identified as the most important design input parameters. The resultant specifications are the water dosage volume, water production rate and media bed dimensions. We propose two parameters for characterising the filtration rate, namely the initial and average clean bed filtration rate. Mathematical expressions for these two parameters and the filtration time are derived. Guideline values for the filtration rate and the ratio of the pore volume to the water dosage volume are established and used as design checks. It is noted that the filtration rate is determined solely by the properties of the water temperature and the media-customary constraints posed by the bed area and the bed depth had been eliminated. Therefore the heart of BSF design lies in the careful and appropriate selection of the filter media. The design procedure proposed is illustrated with an example for a typical rural household in Venda, South Africa.
... [4][5][6]9,10 However, although BSFs use simple technology that has been proven appropriate for many developing countries, few field studies have evaluated how effective and sustainable they are beyond six years. [11][12][13] As a result, there is currently little empirical evidence that BSF technology is effective and sustainable in the long term. ...
... These results are consistent with those of similar BSF field studies worldwide. 4,6,7,9,[11][12][13][22][23][24][25][26] Although flow rates were lower than those recorded in 2005, many users did not seem to mind and continued to clean and use their filters regularly, even though clogging was reported as leading to disuse in some filters. 20 That filtered water was found with higher E. coli concentrations than source water in three instances was not surprising and shows that in reality, filters may not always be properly functioning. ...
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A field study assessing the sustainability and efficacy of 55 biosand filters installed during 1999-2010 was conducted in the Artibonite Valley, Haiti during 2011. Twenty-nine filters were still in use. Duration of filter use ranged from < 1 to 12 years. Water quality, microbial analysis, and flow rate were evaluated for each functioning filter. Kaplan-Meier analysis of filter lifespans showed that filter use remained high (> 85%) up to seven years after installation. Several filters were still in use after 12 years, which is longer than documented in any previous study. Filtered water from 25 filters (86%) contained Escherichia coli concentrations of < 10 most probable number of coliforms/100 mL. Recontamination of stored filtered water was negligible. Bacterial removal efficiency was 1.1 log(10). Comparable results from previous studies in the same region and elsewhere show that biosand filter technology continues to be an effective and sustainable water treatment method in developing countries worldwide.
... An evaluation of BSFs to determine the long-term filtration efficiency and the rate of sustained use was conducted in Posoltega, Nicaragua. Although in this earlier study was reported that the average filtration efficiency was found to be 98% for total coliforms, 96% for E. coli and 88% for turbidity (Vanderzwaag 2008), the mathematical models to calculate the design's parameters are still not fully understood . Important considerations in the development of models are the availability and use of equations to calculate the depth of sand filter and water velocity. ...
... An evaluation of BSFs to determine the long-term filtration efficiency and the rate of sustained use was conducted in Posoltega, Nicaragua. Although in this earlier study was reported that the average filtration efficiency was found to be 98% for total coliforms, 96% for E. coli and 88% for turbidity (Vanderzwaag 2008), the mathematical models to calculate the design's parameters are still not fully understood . Important considerations in the development of models are the availability and use of equations to calculate the depth of sand filter and water velocity. ...
... Water can then be safely consumed almost immediately, and the health improvements are large (Clasen & Bastable, 2003;Clasen, Roberts, Rabie, Schmidt, & Cairncross, 2006;Fewtrell et al., 2005). Vanderzwaag (2008) reports high breakage rates for filters in Nicaragua, but this does not appear to be a common problem. ...
... An evaluation of BSFs to determine the long-term filtration efficiency and the rate of sustained use was conducted in Posoltega, Nicaragua. Although in this earlier study was reported that the average filtration efficiency was found to be 98% for total coliforms, 96% for E. coli and 88% for turbidity (Vanderzwaag 2008), the mathematical models to calculate the design's parameters are still not fully understood . Important considerations in the development of models are the availability and use of equations to calculate the depth of sand filter and water velocity. ...
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The performance of bio-sand filters (BSF) should be monitored periodically to ensure the quality of water produced for the safety of consumers. An engineering design of BSF is proposed to achieve the desired efficacy of the treatment system. Accurate designs to achieve bio-sand filtration are not available in detail for most BSFs since present physical models were not originally able to calculate design's parameters. This paper develops the mathematical models to calculate the depth of sand filter and water velocity in operating the proposed BSF especially to remove organic and suspended matter simultaneously. Parameters in the equations are all physically meaningful, experimental data validation shows the equations remained accurate. The baseline design's parameters are analyzed to contribute to bio-sand filtration process technology. The filtration rates and depths of sand filter proposed in designing of the BSF system are justified.
An evaluation was conducted in 2007 on biosand filters that were installed in Posoltega, Nicaragua in 1999 and 2004. The objectives were to characterize the condition and use of filters eight and three years after installation, determine filter performance of those filters still in use, and identify determinants of successful long-term use and performance. Methods consisted of household identification, user questionnaires, and water quality testing. Of the 234 filters installed, only 24 were found to still be in use. Average log reductions were 1.73 (98%) for total coliforms, 1.36 (96%) for Escherichia Coli, and 0.91 (88%) for turbidity. Statistically significant effects were detected for the magnitude of the contamination of source water, the peak hydraulic loading rate, and the standing depth of water over the filter media. Questionnaire results indicated user training on filter maintenance could improve the peak hydraulic loading rate and hence filter performance. The low rate of sustained use (10%) is an indication of failed implementation, and is attributable to structural failure, particularly cracking of the concrete filters from 2004. Nonetheless, this evaluation demonstrated the biosand filter technology to be robust since those filters still in use were performing as expected three and eight years postimplementation.
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Efficiency of a household plastic biosand filter (BSF) for the removal of turbidity and fecal contamination was evaluated. Water of river Ravi was used as influent. Water filtered through BSF was further treated using Solar Disinfection (SODIS). The study was conducted for raw water with low pollution level (total coliforms <500 MPN/100 ml) and high pollution level (total coliforms between 500-20,000 MPN/100 ml). The average value of turbidity removal by BSF was 94.5 % with 0.9 NTU as average turbidity of effluent. For raw water with low pollution level, the BSF was able to achieve a maximum of 2.2 log10 unit reduction (99.4 %) for total coliforms (39 MPN/100 mL in effluent) and 1.95 log10 unit reduction (98.5 %) for fecal coliforms (9 MPN/100 mL in effluent). While for raw water with high pollution level, the maximum removal of 1.5 log10 unit (97.5 %) for total coliforms (1430 MPN/100 mL in effluent) and 1.8 log10 units (98.4 %) for fecal coliforms (387 MPN/100 mL in effluent) was achieved in BSF. To make the effluent fit for drinking it was further treated using SODIS, which rendered the BSF effluent fit for drinking with zero fecal coliforms count (for full sunny and partially cloudy conditions). Newly proposed plastic BSF could be a good replacement of already used concrete household BSF (used in more than 63 countries) being cheaper in cost and lighter in weight by 85% and 80%, respectively than the concrete BSF.
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A non-randomized assessment of long-term biosand filter (BSF) use and sustainability in the Artibonite Valley near Deschapelles, Haiti was conducted during March, 2011. Of the 55 BSFs visited, 47% were no longer in use. Filter lifespan ranged from <1 year to systems still in use after 12 years. Interviews with BSF owners revealed problems related to intermittent filter use due to travel for employment or personal matters; broken or missing filter parts; and fears that the filter would not be effective against cholera. In addition, 17 BSF field studies were reviewed to identify common issues impacting usage. Culturally appropriate technologies and education materials explaining proper maintenance and operation are essential for improved filter performance and sustainability. For Haiti, education materials should be provided in Creole and French and should include, (1) diagrams and descriptions of how the BSF works, (2) how to troubleshoot common problems, (3) how to properly maintain filters, and (4) a contact in case of questions. Operational problems can be minimized by providing long-term technical support, periodic water quality monitoring, and maintenance assistance for filter users.
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This document is not issued to the general public and all rights are reserved by the World Health Organization. The document may not be reviewed, abstracted, quoted, reproduced or translated, in part or in whole, without the prior written permission of WHO. No part of this document may be stored in a retrieval system or transmitted in any form or by any means -electronic, mechanical or other without the prior written permission of WHO. The views expressed in documents by named authors are solely the responsibility of those authors. Foreword Around 2.2 million die of basic hygiene related diseases, like diarrhoea, every year. The great majority are children in developing countries. Interventions in hygiene, sanitation and water supply make proven contributors to controlling this disease burden. For decades, universal access to safe water and sanitation has been promoted as an essential step in reducing this preventable disease burden. Nevertheless the target of "universal access" to improved water sources and basic sanitation remains elusive. The "Millenium Declaration" established the lesser but still ambitious goal of halving the proportion of people without access to safe water by 2015. Achieving "universal access" is an important long-term goal. How to accelerate health gains against this long-term backdrop and especially amongst the most affected populations is an important challenge.
Conference Paper
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Nicaragua's León-Chinandega aquifer is extensively contaminated by organochlorine pesticides applied over decades of agricultural activity. Models of flow and transport of a 330 km 2 area of the aquifer are developed with the aim of testing conceptual models of contaminant transport. It is concluded that the pesticides found in groundwater and are transported to the water table through preferential flow, through shortcutting around wells, or through wind-blown particles delivered to poorly-protected wells. La couche aquifère de León-Chinandega du Nicaragua est intensivement souillée par les pesticides à base d'organochlore apliques des décennies finies d'activité agricole. Des modèles de l'écoulement et du transport d'un area de 330 km2 de la couche aquifère sont développés dans le but d'examiner les modèles conceptuels du transport de contaminant. On le conclut que les pesticides ont trouvé en eaux souterraines sont transportés à la table de l'eau par l'écoulement préférentiel, par le raccourcissement autour des puits, ou par les particules vent-soufflées fournies aux puits pauvre-protégés.
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Groundwater flow in the Leon-Chinandega aquifer was simulated using transient and steady-state numerical models. This unconfined aquifer is located in an agricultural plain in northwest Nicaragua. Previous studies were restricted to determining groundwater availability for irrigation, overlooking the impacts of groundwater development. A sub-basin was selected to study the groundwater flow system and the effects of groundwater development using a numerical groundwater flow model (Visual MODFLOW). Hydrological parameters obtained from pumping tests were related to each hydrostratigraphic unit to assign the distribution of parameter values within each model layer. River discharge measurements were crucial for constraining recharge estimates and reducing the non-uniqueness of the model calibration. Steady-state models have limited usefulness because of the major variation of recharge and agricultural pumping during the wet and dry seasons. Model results indicate that pumping induces a decrease in base flow, depleting river discharge. This becomes critical during dry periods, when irrigation is highest. Transient modeling indicates that the response time of the aquifer is about one hydrologic year, which allows the development of management strategies within short time horizons. Considering further development of irrigated agriculture in the area, the numerical model can be a powerful tool for water resources management.
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Approximately one billion people world-wide lack access to adequate amounts of safe water. Most are in developing countries, especially in rapidly expanding urban fringes, poor rural areas, and indigenous communities. In February and March 2005, a field study of 107 households was conducted to evaluate the use and performance of the Manz BioSand filter in the Artibonite Valley of Haiti. Approximately 2000 filters had been installed in this area over the preceding 5 years by the staff in Community Development at Hospital Albert Schweitzer, Deschappelle, Haiti. Interviews, observations, and water samplings were carried-out by two teams of Haitian enumerators, each consisting of a nurse and a filter technician. Water analyses were performed by Haitian lab technicians using the membrane filtration method to determine Escherichia coli counts. The enumerators and the lab technicians completed a 2 week training program before beginning the study; they worked under the direct supervision of the primary investigator. Laboratory quality was monitored by running 10% blank and 10% duplicate samples. The households contained an average of 5.4 persons. Filters had been in use for an average of 2.5 years, and participants were generally satisfied with their filter's performance. Shallow, hand-dug wells provided the only source of water for 61% of the households, with 26% using water piped from springs or deep wells, and 13% having access to both. Only 3% had plumbing in their homes. Source water from shallow wells contained an average of 234 E. coli cfu/100 mL. Piped sources averaged 195 E. coli cfu/100 mL. Of the source water samples 26% contained 0-10 E. coli cfu/100 mL. Of the filtered water samples 97% contained 0-10 E. coli cfu/100 mL (80% with 0 cfu/100 mL, and 17% with 1-10 cfu/100 mL). Overall bacterial removal efficiency for the filters was calculated to be 98.5%. Turbidity decreased from an average of 6.2 NTU in source water samples to 0.9 NTU in the filtered water. None of the households treated the water after filtering; 91% used the filtered water only for drinking. No problems related to filter construction were observed; 13% were found to have significantly decreased flow rates (all restored by cleaning the filter). Recontamination was found to occur, with only 3% of the samples from the filters' spouts containing >10 E. coli cfu/100 mL and 22% of the stored filtered water samples at point-of-use containing >10 cfu/100 mL. The Manz BioSand filters are an attractive option for supplying water treatment to family units in rural areas of poorly developed countries.
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More than a billion people in the developing world lack access to safe and reliable sources of drinking water. Point of use (POU) household water treatment technology allows people to improve the quality of their water by treating it in the home. One emerging POU technology is the biosand filter (BSF), a household-scale, intermittently operated slow sand filter. Laboratory and field studies examined Escherichia coli reductions achieved by the BSF. During two laboratory studies, mean E. coli reductions were 94% and they improved over the period of filter use, reaching a maximum of 99%. Field analysis conducted on 55 household filters near Bonao, Dominican Republic averaged E. coli reductions of 93%. E. coli reductions by the BSF in laboratory and field studies were less than those typically observed for traditional slow sand filters (SSFs), although as for SSFs microbial reductions improved over the period of filter use. Further study is needed to determine the factors contributing to microbial reductions in BSFs and why reductions are lower than those of conventional SSFs.
Simple and low cost interventions at the household level can improve household drinking water quality with a corresponding impact on the global burden of diarrhoeal disease and death. There is a need to devise the effective deployment strategies that will achieve high level coverage with high rates of uptake and sustained use. WHO is developing guidelines for technology performance evaluation that will help countries in developing policies and standards. UNICEF, the World Bank's Water and Sanitation Programme (WSP) and the regional office of WHO have urged caution and identified the need for further expansion to be preceded by an independent performance and sustainability assessment. The central challenge is to scale up, requiring the support of major funding agencies working through national governments.
Safe potable water is a luxury that is generally unavailable to the majority of rural and suburban populations of developing, underdeveloped, and often developed countries. Important consid- erations in the development and maintenance of safe water supplies is the availability and use of efficient, inexpensive, and appropriate technology for removing microbial hazards, parasites, and toxicants. The Manz intermittent slow sand filter was known to be user friendly, small enough to fit into the smallest kitchen, and could remove up to 97% of the fecal coliforms present in the raw water before treatment by the Manz filter. This filter was evaluated for its ability to remove parasitic cysts and toxicants as well as bacteria. Using two different filters and two different water supplies our results indicated that the intermittent slow sand filter could remove 83+% total heterotrophic bacterial populations, 100% of Giardia cysts, 99.98% of Cryptosporidium oocysts, and 50 -90% of organic and inorganic toxicants when administered in concentrations varying from 10 - )100 = environmental pollution levels. Methodology details are provided in the paper. Q 1999 by John Wiley & Sons, Inc. Environ Toxicol 14: 217)225, 1999
Despite numerous constraints, community participation remains a central element in most water projects. In fact, the concept is so fundamental that hardly any donor will consider funding a project if no active involvement of an organized group of community members is evident. This article describes the success of a project that actively avoided working with groups, but specifically targeted individuals with the introduction of a simple but effective form of household-level sand filtration.
Thesis (M. Eng.)--University of Calgary, 1995. Includes bibliographical references.
In many parts of the developing world, drinking water is collected from unsafe surface sources outside the home and is then held in household storage vessels. Drinking water may be contaminated at the source or during storage; strategies to reduce waterborne disease transmission must safeguard against both events. We describe a two-component prevention strategy, which allows an individual to disinfect drinking water immediately after collection (point-of-use disinfection) and then to store the water in narrow-mouthed, closed vessels designed to prevent recontamination (safe storage). New disinfectant generators and better storage vessel designs make this strategy practical and inexpensive. This approach empowers households and communities that lack potable water to protect themselves against a variety of waterborne pathogens and has the potential to decrease the incidence of waterborne diarrheal disease.
Recovery of total coliforms and Escherichia coli on a new membrane filtration (MF) medium was evaluated with 25 water samples from seven states. Testing of the new medium, m-ColiBlue24 broth, was conducted according to a U.S. Environmental Protection Agency protocol. For comparison, this same protocol was used to measure recovery of total coliforms and E. coli with two standard MF media, m-Endo broth and mTEC broth. E. coli recovery on the new medium was also compared to recovery on nutrient agar supplemented with 4-methylumbelliferyl-beta-D-glucuronide. Comparison of specificity, sensitivity, false positive error, undetected target error, and overall agreement indicated E. coli recovery on m-ColiBlue24 was superior to recovery on mTEC for all five parameters. Recovery of total coliforms on the new medium was comparable to recovery on m-Endo.
Since 1990, the number of people without access to safe water sources has remained constant at approximately 1.1 billion, of whom approximately 2.2 million die of waterborne disease each year. In developing countries, population growth and migrations strain existing water and sanitary infrastructure and complicate planning and construction of new infrastructure. Providing safe water for all is a long-term goal; however, relying only on time- and resource-intensive centralized solutions such as piped, treated water will leave hundreds of millions of people without safe water far into the future. Self-sustaining, decentralized approaches to making drinking water safe, including point-of-use chemical and solar disinfection, safe water storage, and behavioral change, have been widely field-tested. These options target the most affected, enhance health, contribute to development and productivity, and merit far greater priority for rapid implementation.
A novel technique has been developed to monitor Escherichia coli contamination on carcasses using membrane filtration and m-ColiBlue24 (mCB). mCB is a membrane filtration medium that simultaneously detects total coliforms and E. coli (EC) in a period of 24 +/- 4 h. A study was conducted, using a sponge method to obtain samples from pork carcasses and the excision technique to remove samples from beef carcasses, that compared mCB to standard methods. On pork carcasses (n = 77), the mean values for mCB and violet red bile agar were 7.4 CFU/15 cm2 and 6.1 CFU/15 cm2, respectively. The paired t test (P > 0.05) indicated no significant difference between the two methods (t = 0.5; P = 0.6). Samples from beef carcasses (n = 57) were used to compare mCB to both coliform count and EC Petrifilm. Of these samples, 27 were artificially inoculated with cattle manure. The mean total coliform count was 4.2 log CFU/cm2 and 4.0 log CFU/cm2 on mCB and coliform count Petrifilm, respectively. The mean EC count on mCB was 4.0 log CFU/cm2 and 3.5 log CFU/cm2 on EC Petrifilm. When comparing mCB to both coliform count (t = 2.4; P = 0.02) and EC (t = 3.5; P < 0.01) Petrifilm, paired t tests (P < or = 0.05) indicated significant differences.
Many states are replacing microbiological water quality standards based on "fecal" or thermotolerant coliforms (ThCs) with new standards that employ Escherichia coli as the indicator organism. Implicit in these new standards are assumptions about the equivalence of E. coli enumeration tests and the E. coli levels that will provide protection equivalent to former ThC standards. To investigate these assumptions, E. coli levels in split samples (tests conducted on portions of the same grab sample) collected from small urban streams were determined using enzyme-specific media (Colilert, m-ColiBlue24, and nutrient agar with MUG) and compared to levels determined with conventional culture media (m-FC and m-TEC). Although levels observed with all tests were highly correlated, significantly fewer E. coli were enumerated with m-TEC than with enzyme-specific media (paired Student's t-test, alpha>99%). In addition, E. coli were found to comprise a larger fraction (84-104%, depending on the test) of the total presumptive ThC concentration than that suggested by the United States Environmental Protection Agency (63%). Both of these observations (1) the improvement in E. coli yields observed with enzyme-specific media, and (2) the greater proportion of ThC organisms that are E. coli, indicate that more water quality violations will occur when enzyme-specific media are used for testing than if conventional culture media are used.
The current AOAC Method 966.24 for enumeration of Escherichia coli in foods uses a most probable number (MPN) procedure with extensive confirmation steps. Two new methods based on membrane filtration (MF) were compared to the MPN reference method for detection of high levels of E. coli in 5 food types, some of which represent categories for which the U.S. Food and Drug Administration (FDA) mandates additional testing if an action level of 10(4)/g E. coli is exceeded. Ground beef, which is not FDA regulated, was also tested. The 5 food types were all inoculated at 3 levels: 10(2)/g, > or = 10(4)/g, and > or = 10(5)/g E. coli. An MF protocol using either m-ColiBlue24 (CB) or lauryl sulfate tryptose plus BCIG (LST/BCIG) was an effective potential alternative to the reference method. Sensitivity and specificity for both CB and LST/BCIG were 98 and 100%, respectively. Agreement between MPN and both CB and LST/BCIG was 98%. The 2 proposed methods allow completion of both presumptive and confirmatory steps in 1-3 days, whereas the reference method requires as many as 11 days. Exclusivity testing with 50 non-E. coli strains indicated 100% were correctly ruled out by the proposed protocols. Inclusivity testing was used to determine whether typical results were obtained after incubation of E. coli cultures on CB or LST/BCIG for 24 h. Of 50 E. coli strains tested, 100% yielded typical results after incubation on CB, and 98% yielded typical results after incubation on LST/BCIG.
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