Philippe Vandevivere

Environmental Impact and Mechanisms of the Biological Clogging of Saturated Soils and Aquifer Materials

The biological clogging of natural porous media, often in conjunction with physical or chemical clogging, is encountered under a wide range of conditions. Wastewater disposal, artificial groundwater recharge, in situ bioremediation of contaminated aquifers, construction of water reservoirs, or secondary oil recovery are all affected by this process. The present review provides an overview of the techniques that are used to study clogging in the laboratory, or to monitor it in field applications. After a brief survey of the clogging patterns most commonly observed in practice, and of a number of physical and chemical causes of clogging, the various mechanisms by which microorganisms clog soils and other natural porous media are analyzed in detail. A critical assessment is also provided of the few mathematical models that have been developed in the last few years to describe the biological clogging process. The overall conclusion of the review is that although information is available on several aspects of the biological clogging of natural porous media, further research is required to predict its extent quantitatively in a given situation. This is particularly true in cases that involve complicating factors such as predation or competition among organisms.

New and Broader Applications of Anaerobic Digestion

The general performance of anaerobic digesters and the diversity of wastes that these can treat have been increasing steadily during the last decade as a result of new reactor designs, operating conditions, or the use of specialized microbial consortia. This article illustrates a few examples of new or broader applications of anaerobic digestion to the treatment of sewage, slurries, industrial wastewater, and solid wastes. In the case of domestic sewage, the sustainability of the overall process is much improved by the adoption of an anaerobic pretreatment step, for example, an upflow sludge blanket (USB) reactor. New methods for nutrient removal need to be coupled with anaerobic digestion. These may include, for example, anaerobic ammonium oxidation (anammox) and chemical P precipitation. In terms of industrial wastewaters, new additives are being developed that help the anaerobic sludge deal with unbalanced or toxic wastewaters. Engineering of anaerobic sludge granules is a new area of research that ser...

Decrease of the hydraulic conductivity of sand columns by Methanosarcina barkeri

The extent to which a methanogen can clog sand columns was examined: two permeameters packed with clean quartz sand were sterilized, saturated with water, inoculated with Methanosarcina barkeri and percolated under upward flow conditions. After approx. 5 months, the hydraulic conductivity of the sand had decreased to 3% and 25% of the highest values measured earlier. At that point, gas-filled regions in the sand were clearly visible through the transparent walls of the permeameters, and methane bubbles were continuously released from the columns into the effluent. Scanning electron microscopy observations and biomass assays indicated that cell mass accumulation did not contribute significantly to the observed decrease of the hydraulic conductivity. This decrease was therefore attributed to pore blocking due to the entrapment of methane bubbles.

GAC-Amended UASB Reactor for the Stable Treatment of Toxic Textile Wastewater

A feasibility study was carried out in the laboratory for the sequential anaerobic/aerobic treatment of textile wastewater. The process units consisted of an anaerobic UASB (upflow anaerobic sludge blanket) reactor and a SCAS (semi-continuous activated sludge) reactor. A contact-sorption layer with GAC (granular activated carbon) was provided at the bottom of the conventional UASB reactor. The raw textile wastewater first passed through the GAC bed and then through the sludge bed. By means of the GAC bed, the top-layer granular sludge was protected from toxicants. Biological regeneration of GAC, which was enhanced via a recycle flow, was demonstrated. The combined GAC-UASB and SCAS treatments allowed a stable performance and a COD (chemical oxygen demand) and colour removal of 98 and 95 %, respectively.

Sampling Method For The Observation Of Microorganisms In Unconsolidated Porous Media Via Scanning Electron Microscopy

A sampling and mounting procedure is proposed that minimizes macroscopic rearrangements of solid particles when preparing unconsolidated samples for scanning electron microscopy.