Showing papers by "Frederik Hammes published in 2011"

Bacterial colonization of pellet softening reactors used during drinking water treatment.

Abstract: Pellet softening reactors are used in centralized and decentralized drinking water treatment plants for the removal of calcium (hardness) through chemically induced precipitation of calcite. This is accomplished in fluidized pellet reactors, where a strong base is added to the influent to increase the pH and facilitate the process of precipitation on an added seeding material. Here we describe for the first time the opportunistic bacterial colonization of the calcite pellets in a full-scale pellet softening reactor and the functional contribution of these colonizing bacteria to the overall drinking water treatment process. ATP analysis, advanced microscopy, and community fingerprinting with denaturing gradient gel electrophoretic (DGGE) analysis were used to characterize the biomass on the pellets, while assimilable organic carbon (AOC), dissolved organic carbon, and flow cytometric analysis were used to characterize the impact of the biological processes on drinking water quality. The data revealed pellet colonization at concentrations in excess of 500 ng of ATP/g of pellet and reactor biomass concentrations as high as 220 mg of ATP/m3 of reactor, comprising a wide variety of different microorganisms. These organisms removed as much as 60% of AOC from the water during treatment, thus contributing toward the biological stabilization of the drinking water. Notably, only a small fraction (about 60,000 cells/ml) of the bacteria in the reactors was released into the effluent under normal conditions, while the majority of the bacteria colonizing the pellets were captured in the calcite structures of the pellets and were removed as a reusable product.

Biotreatment of Drinking Water

Abstract: Conventional biofiltration refers to filtration processes where the filter comprises porous material that is colonized by indigenous microbial communities and where these microorganisms perform at least one of the essential functions of the filtration process. Biofilters such as granular active carbon (GAC) filters, rapid sand filters (RSFs), and slow sand filters (SSFs) are key processes in the biotreatment of drinking water in both industrialized and developing countries. The main purpose of biofiltration is the removal of biodegradable organic carbon, but a wide variety of possible filter configurations, together with a broad range of different water types and pretreatment methods, contribute to extremely diverse biofiltration performance results reported in literature. The biological component of all biofilters comprises indigenous bacteria that proliferate in biofilms at low nutrient concentrations. This article specifically focuses on the state of the art of engineered biofiltration systems (e.g., GAC, RSF, SSF) and investigates the key differences between these filter types from a microbiological perspective. Different methodologies for the analysis of organic carbon, particularly the bioavailable fractions, as well as for the analysis of biomass on granulated materials are discussed and compared. The final section highlights open questions and future research opportunities of this field.

Household drinking water in rural Ethiopia - impact of defluoridation filters on microbial drinking water quality in the Rift Valley

Abstract: In the Ethiopian Rift Valley, there are two main concerns about drinking water: fluoride and fecal contamination. OSHO (an Ethiopian NGO) works on a defluoridation project with household and community filters to remove fluoride from drinking water. The project area includes seven villages, with more than 300 household filters in use and one community filter. This is the first study on the impact of household defluoridation filters in rural Ethiopian microbial water quality. The visited villages use different water sources, such as surface water, boreholes, windmills or dug wells. Microbial contamination is present at the sources, and in much higher extent in the households. Compact Dry plates (Nissui Ltd, Japan) were uses to detect E.coli, total coliforms and Enterococci as fecal indicator organisms. The method is valid for detection and enumeration of microbial water contamination even under the challenging conditions of rural Ethiopia. The bacterial growth in dependence of incubation temperature showed similar counts above 30°C, which leads to representative results even if the power supply is interrupted. It was compared to standard methods (Colilert, IDEXX, and Petrifilm, 3M) and did not show significant differences. The household filters have an overall positive impact on fecal indicator organisms in all studied villages; nevertheless the contamination level is very high. The main contamination was taking place between the source and the inlet, respectively the jerrycan. There were no differences in drinking water quality found in a glass from household filter or community filter. The microbial inactivation of copper was tested in the lab and in the field, but no general improvement of the water quality found. Microbial contamination levels are alarmingly high in all studied households, and measures have to be taken enhance water quality. Hygiene and sanitation are very poor or absent in the area, and diarrheal diseases widespread. Technical possibilities to improve the situation are chlorination of the filters and source water, replacement of sand filter with candle filter, installation of sanitation facilities. They will not be sustainable without awareness creation and education of the interrelation between water, sanitation, hygiene and health.