Degradation of BTEX by anaerobic bacteria: physiology and application

Pollution of the environment with aromatic hydrocarbons, such as benzene, toluene, ethylbenzene and xylene (so-called BTEX) is often observed. The cleanup of these toxic compounds has gained much attention in the last decades. In situ bioremediation of aromatic hydrocarbons contaminated soils and groundwater by naturally occurring microorganisms or microorganisms that are introduced is possible. Anaerobic bioremediation is an attractive technology as these compounds are often present in the anoxic zones of the environment. The bottleneck in the application of anaerobic techniques is the lack of knowledge about the anaerobic biodegradation of benzene and the bacteria involved in anaerobic benzene degradation. Here, we review the existing knowledge on the degradation of benzene and other aromatic hydrocarbons by anaerobic bacteria, in particular the physiology and application, including results on the (per)chlorate stimulated degradation of these compounds, which is an interesting new alternative option for bioremediatio

Transformation of chlorinated compounds by methanogenic granular sludge

Chlorinated compounds are an important group of contaminants often found in sediments, groundwater, soils, wastewaters, and off-gasses. Many of these pollutants are found on the EPA list of Priority Pollutants indicating their potential hazard for the environment. Initial degradation can occur via dechlorination reactions which are carried out by specific halorespiring bacteria or by acetogenic and/or methanogenic bacteria which dechlorinate via aspecific reactions. The dechlorination rates of halorespiring bacteria are generally high, due to the high degree of substrate specificity. However, these bacteria are limited in the number of chlorinated compounds they can degrade. This may be a disadvantage when they are put in to use for the remediation of environments with a mixture of chlorinated compounds. In those cases, a better strategy is the application of acetogenic and methanogenic bacteria which have a broad substrate specificity.This research has evaluated the aspecific dechlorinating ability of unadapted acetogenic and methanogenic bacteria in methanogenic granular sludge. The long-term goal of the research is the evaluation of the applicability of unadapted methanogenic consortia in the bioremediation of wastestreams contaminated with mixtures of pollutants.Chlorinated alkanes and cycloalkanes were completely or substantially degraded to lower- or non-chlorinated compounds by methanogenic (granular) sludge without prior adaptation. Different dechlorination reactions were observed. Chlorinated methanes were degraded mainly via oxidative and substitutive reactions to non-halogenated compounds like CO 2 , while chloroethanes were dechlorinated via dichloroelimination and reductive hydrogenolysis to lower chlorinated ethenes and ethanes. The cycloalkanes,α- andβ-HCH, were degraded via different reactions to a mixture of benzene and chlorobenzene. The degradation of chlorinated alkenes (tetrachloroethene and lower chlorinated ethenes) and aromatic compounds (hexachlorobenzene, and pentachlorophenol) by unadapted consortia takes place at low rates. This dechlorination of chloroethenes and pentachlorophenol is much slower compared to (cyclo)alkanes. Sometimes a long lag phase is required (lower chlorinated benzenes). PCBs were not degraded. All the degradation products, lower chlorinated alkanes and alkenes, and (chloro)benzene in case of HCH, are biodegradable under aerobic conditions.Contaminated soils often contain many bacteria, which are able to perform remediation provided that the environmental conditions are favorable. In that case, the addition of granular sludge does not seem to be necessary for the degradation the chlorinated compounds. However, the presence of a methanogenic bacterial consortium can lead to e.g., a decrease of the redox-potential, thus favoring the environmental conditions for other, more specialized dechlorinating bacteria. Another application of granular sludge may be the use of the facultative anaerobic or microaerophilic bacteria in the sludge. These bacteria can degrade the persistent dechlorination products under higher redox-conditions. Altogether, the broad spectrum applicability of the unadapted methanogenic granular sludge may make it a useful first "tool" in the (in situ) bioremediation of contaminated environments.</p

Mestvergisting bij korte verblijftijden

In four CSTR laboratory reactors research has been conducted into the effect of reduction of the retention time on the biogas production from pig and cattle slurry and the volatile fatty acid content in the digester. Further, the effect of adding a small amount of glycerine on the retention time and the volatile fatty acid content in the digester has been researched

Grondsmaak in kweekvis deel 2

Grondsmaak is wereldwijd een van de belangrijkste beperkende factoren voor de afzet van kweekvis afkomstig uit vijvers en recirculatiesystemen. Dit wordt vooral veroorzaakt door de lage waardering van consumenten voor kweekvis met grondsmaak. Marktprijs en marktvolume komen daardoor onder druk te staan. Daarnaast brengt de bestrijding van grondsmaak extra kosten met zich mee voor de producent. Ook in Nederlandse kweekvis komt grondsmaak voor. In Nederland wordt op verschillende fronten gewerkt aan het voorkomen en bestrijden van grondsmaak. In het eerste deel van deze serie over grondsmaak (Aquacultuur 2011, nr. 2) werd vooral ingegaan op de achtergronden en gevolgen van grondsmaak. In dit tweede deel wordt dieper ingegaan op de diverse aspecten van het bestrijden van grondsmaak in kweekvis

Explorative research on innovative nitrogen recovery

This report comprises the results of an explorative study on innovative nitrogen recovery from side streams of wastewater treatment plants (WWTPs) in the Netherlands. The main objective of the study was to identify promising new technologies for recovery of nitrogen which can be subsequently used as an artificial fertilizer. This shortcircuits the global nitrogen cycle and thereby reduces the environmental impact of the nitrogen cycle that has been distorted by human influence (eutrophication, greenhouse gases)

Sanitation Challenge 2008: voorbij de heilige huisjes?

Momenteel leven ongeveer 2,4 miljard mensen zonder adequate sanitataire voorzieningen. Eén van de Millenium Development Goals richt zich dan ook op de halvering van dit aantal voor 2015. Mede daarom is 2008 door de Verenigde Naties uitgeroepen tot het Internationale jaar van de Sanitatie. Dit vormde de aanleiding voor de leerstoelgroepen Milieubeleid en Milieutechnologie van Wageningen Universiteit, LeAF en TTIW Wetsus om onder auspiciën van IWA de 'Sanitation Challenge: an International Conference on new Sanitation Concepts and Models of Governance' te organiseren. Het congres vond eind vorige maand plaats in Wageningen met als voornaamste doel de verschillende groepen die betrokken zijn bij onderzoek, ontwikkeling en implementatie van (nieuwe) sanitatie in een wetenschappelijke omgeving bij elkaar te brengen en discussie over potentiële oplossingen, zowel op technisch als sociaal niveau, mogelijk te make

Verslag van de 'Sanitation Challenge: An international conference on new sanitation concepts and models of governance'.

Van 19 tot en met 21 mei vond in Wageningen de `Sanitation Challenge: an international conference on new sanitation concepts and models of governance¿ plaats. Het voornaamste doel was om de verschillende groepen die betrokken zijn bij onderzoek, ontwikkeling en implementatie van (nieuwe) sanitatie in een wetenschappelijke omgeving bij elkaar te brengen en discussie over potentiële oplossingen, zowel op technisch als sociaal niveau, mogelijk te make