Martijn P. J. Smit

Biological Alkylation and Colloid Formation of Selenium in Methanogenic UASB Reactors

Bioalkylation and colloid formation of selenium during selenate removal in upflow anaerobic sludge bed (UASB) bioreactors was investigated. The mesophilic (30 degrees C) UASB reactor (pH = 7.0) was operated for 175 d with lactate as electron donor at an organic loading rate of 2 g COD L(-1) d(-1) and a selenium loading rate of 3.16 mg Se L(-1) d(-1). Combining sequential filtration with ion chromatographic analysis for selenium oxyanions and solid phase micro extraction gas chromatography mass spectrometry (SPME-GC-MS) for alkylated selenium compounds allowed to entirely close the selenium mass balance in the liquid phase for most of the UASB operational runtime. Although selenate was removed to more than 98.6% from the liquid phase, a less efficient removal of dissolved selenium was observed due to the presence of dissolved alkylated selenium species (dimethylselenide and dimethyldiselenide) and colloidal selenium particles in the effluent. The alkylated and the colloidal fractions contributed up to 15 and 31%, respectively, to the dissolved selenium concentration. The size fractions of the colloidal dispersion were: 4 to 0.45 mum: up to 21%, 0.45 to 0.2 mum: up to 11%, and particles smaller than 0.2 mum: up to 8%. Particles of 4 to 0.45 mum were formed in the external settler, but did not settle. SEM-EDX analysis showed that microorganisms form these selenium containing colloidal particles extracellularly on their surface. Lowering the temperature by 10 degrees C for 6 h resulted in drastically reduced selenate removal efficiencies (after a delay of 1.5 d), accompanied by the temporary formation of an unknown, soluble, organic selenium species. This study shows that a careful process control is a prerequisite for selenium treatment in UASB bioreactors, as disturbances in the operational conditions induce elevated selenium effluent concentrations by alkylation and colloid formation.

Chemical dispersants : Oil biodegradation friend or foe?

Chemical dispersants were used in response to the Deepwater Horizon oil spill in the Gulf of Mexico, both at the sea surface and the wellhead. Their effect on oil biodegradation is unclear, as studies showed both inhibition and enhancement. This study addresses the effect of Corexit on oil biodegradation by alkane and/or aromatic degrading bacterial culture in artificial seawater at different dispersant to oil ratios (DORs). Our results show that dispersant addition did not enhance oil biodegradation. At DOR 1:20, biodegradation was inhibited, especially when only the alkane degrading culture was present. With a combination of cultures, this inhibition was overcome after 10days. This indicates that initial inhibition of oil biodegradation can be overcome when different bacteria are present in the environment. We conclude that the observed inhibition is related to the enhanced dissolution of aromatic compounds into the water, inhibiting the alkane degrading bacteria.

Biological Production of Selenium Nanoparticles from Waste Waters

Due to the photoelectric, semi-conducting and X-ray-sensing properties, selenium is an element of great economic potential. Since nanomaterials display special properties compared to bulk particles, the production of selenium nanostructures (wires, rods or spherical particles) has attracted much attention. In this study, alternative approaches to classical synthesis were investigated, producing selenium nanospheres biologically during treatment of contaminated water.

Biodegradation of cis-1,2-Dichloroethene in Simulated Underground Thermal Energy Storage Systems.

Underground thermal energy storage (UTES) use has showed a sharp rise in numbers in the last decades, with aquifer thermal energy storage (ATES) and borehole thermal energy storage (BTES) most widely used. In many urban areas with contaminated aquifers, there exists a desire for sustainable heating and cooling with UTES and a need for remediation. We investigated the potential synergy between UTES and bioremediation with batch experiments to simulate the effects of changing temperature and liquid exchange that occur in ATES systems, and of only temperature change occurring in BTES systems on cis-DCE reductive dechlorination. Compared to the natural situation (NS) at a constant temperature of 10 °C, both UTES systems with 25/5 °C for warm and cold well performed significantly better in cis-DCE (cis-1,2-dichloroethene) removal. The overall removal efficiency under mimicked ATES and BTES conditions were respectively 13 and 8.6 times higher than in NS. Inoculation with Dehalococcoides revealed that their initial presence is a determining factor for the dechlorination process. Temperature was the dominating factor when Dehalococcoides abundance was sufficient. Stimulated biodegradation was shown to be most effective in the mimicked ATES warm well because of the combined effect of suitable temperature, sustaining biomass growth, and regular cis-DCE supply.

Effectiveness of stimulating PCE reductive dechlorination: A step-wise approach

Reductive dechlorination of tetrachloroethene (PCE) and its daughter products in aquifers is often hampered by Fe(III) reducing conditions. Rigorous treatment to adjust the redox potential and stimulate dechlorination may be costly and potentially have negative effects on other aquifer functions. A step-wise experimental strategy was applied to investigate the effectiveness of various adjustment scenarios. Batch experiments with ascorbic acid (AA) and sodium lactate (SL) showed that 75μmol electron equivalents per gram dry mass of aquifer material was required to reach a sufficiently low redox potential for the onset of PCE dechlorination. Similar effects of either AA or SL on the measured redox potential suggest electron donors are not specific. However, the relative rates of Fe(III) and sulphate reduction appeared to be specific to the electron donor applied. While redox potential stabilised around -450mV after titration and sulphate was reduced to zero in both treatments, in the AA treatment a faster production of Fe(2+) was observed with a final concentration of 0.46mM compared to only 0.07mM in the SL treatment. In subsequent batch experiments with aquifer material that was pre-treated with AA or SL, PCE reductive dechlorination occurred within 30days. Further stimulation tests with extra electron donor or inoculum revealed that adding electron donor can accelerate the initiation of PCE biodegradation. However, bioaugmentation with dechlorinating bacteria is required to achieve complete reductive dechlorination to ethene. The findings from step-wise approaches are relevant for improving the cost-effectiveness of the design and operation of in-situ bioremediation at initially unfavourable environmental conditions.

Oil biodegradation: Interactions of artificial marine snow, clay particles, oil and Corexit

During the Deepwater Horizon (DwH) oil spill, interactions between oil, clay particles and marine snow lead to the formation of aggregates. Interactions between these components play an important, but yet not well understood, role in biodegradation of oil in the ocean water. The aim of this study is to explore the effect of these interactions on biodegradation of oil in the water. Laboratory experiments were performed, analyzing respiration and n-alkane and BTEX biodegradation in multiple conditions containing Corexit, alginate particles as marine snow, and kaolin clay. Two oil degrading bacterial pure cultures were added, Pseudomonas putida F1 and Rhodococcus qingshengii TUHH-12. Results show that the presence of alginate particles enhances oil biodegradation. The presence of Corexit alone or in combination with alginate particles and/or kaolin clay, hampers oil biodegradation. Kaolin clay and Corexit have a synergistic effect in increasing BTEX concentrations in the water and cause delay in oil biodegradation.

Impact of compost and manure on the ripening of dredged sediments

PurposeIn low lying areas with dense networks of canals for land drainage, sediments accumulate in the waterways and have to be periodically dredged. These adjacent areas are mainly used for farming and agriculture and suffer from high rates of subsidence. The recycling of organic amendments, such as sediments, compost and manure, in agricultural soils can improve plant growth and yield, soil carbon content, and microbial biomass and activity, and have the potential to reverse the process of land subsidence.Materials and methodsThe effect of mixing bio-waste compost and the solid fraction of swine manure with dredged sediments before dewatering and biochemical ripening was investigated in terms of type and quantity of organic matter, CO2 production and O2 consumption, and N, P and S content. The water released during dewatering, the aggregate stability, and the undrained shear strength after ripening were also assessed since these areas have to be assessable by trucks and cattle.Results and discussionFor the sediment with compost and manure the transformations in the type of organic matter, CO2 production and O2 consumption were larger compared to the individual fractions, indicating a positive priming effect. Most volume lost during ripening can be attributed to the loss of water and not to the loss of organic matter. In addition, the mixtures result in very stable aggregates and showed an undrained shear strength three times higher than measured for the sediments.ConclusionsSediments, compost and manure can be used and applied as beneficial use to reverse the process of land subsidence in low lying areas.

The initial risk assessment and emission control from contaminated sediments

Abstract Discharged persistent organic pollutants and heavy metals into the rivers are often assumed to adsorb on sediments without re-suspension, thus sediments may function as a sink for contaminants. Sediments, however, may also function as a (secondary) source of contaminants, depending on the hydrodynamic characteristics of a river. To assess whether the sediments function as a sink or a source of contaminants, a preliminary risk assessment using the so-called SEDINA tool (SEDiment INitial Assessment) is recommended. By comparison of the total concentrations of pollutants in sediments upstream, at, and downstream of the site area, the role of sediments can be determined. When the sediments functions as a sink, no specific sediments-related measures are required, although monitoring of the surface water and sediments quality is recommended. If the output of the SEDINA tool reflects that the sediments may function or function as a source of contaminants, the risk-reduction measures are necessary that may include emission control at the source(s), pathway(s) and/or receptor(s).