Leaching and accumulation of trace elements in sulfate reducing granular sludge under concomitant thermophilic and low pH conditions
Gonzalez-Gil, G. ; Lopes, S.I.C. ; Saikaly, P.E. ; Lens, P.N.L. - \ 2012
Bioresource Technology 126 (2012). - ISSN 0960-8524 - p. 238 - 246.
anaerobic-digestion - uasb reactors - heavy-metals - bed reactor - bacteria - degradation - reduction - removal - media - water
The leaching and/or accumulation of trace elements in sulfate reducing granular sludge systems was investigated. Two thermophilic up-flow anaerobic sludge bed (UASB) reactors operated at pH 5 were fed with sucrose (4 g COD l(reactor)(-1) d(-1)) and sulfate at different COD/SO42- ratios. During the start-up of such acidogenic systems, an initial leaching of trace elements from the inoculum sludge occurred regardless of trace elements supplementation in the reactor influent. The granular sludge maintained the physical structure despite high Fe leaching. After start-up and nonetheless the acidic conditions, Co, Ni, Cu, Zn, Mo and Se were retained or accumulated by the sludge when added. Particularly, Ni and Co accumulated in the carbonates and exchangeable fractions ensuring potential bioavailability. Otherwise, the initial stock in the inoculum sludge sufficed to operate the process for nearly I year without supplementation of trace elements and no significant sludge wash-out occurred.
The impact of Co and Ni speciation on methanogenesis in sulfidic media - Biouptake versus Metal dissolution
Jansen, S. ; Gonzalez-Gil, G. ; Leeuwen, H.P. van - \ 2007
Enzyme and Microbial Technology 40 (2007)4. - ISSN 0141-0229 - p. 823 - 830.
sulfate-reducing bacteria - anoxic aqueous systems - anaerobic-digestion - iron sulfides - methanobacterium-thermoautotrophicum - methanosarcina-barkeri - methanol degradation - stability-constants - granular sludge - nickel
The speciation of the trace nutrients Co(II) and Ni(II) in sulfide containing media can control the methanogenic activity of Methanosarcina sp., which is of importance for the optimisation of anaerobic treatment of wastewater containing methanol. To obtain more insight in the mechanistic backgrounds, dissolved metal concentrations and methane production rates were measured for a highly enriched culture, obtained from anaerobic sludge, at various total metal and sulfide concentrations. The methanogenic activity increased with increasing total metal and decreased with increasing total sulfide. Dissolution kinetics and the influence of soluble metal sulfide species explain the trends in the concentrations of the dissolved metal species. The results suggest that the stimulation of the methanogenic activity is related to the free metal ion concentration. Flux calculations and measurements of uptake by a pure culture of Methanosarcina barkeri show that limitation by slow dissolution of the solid metal sulfides is unlikely. Growth therefore seems to be primarily controlled by the biouptake characteristics of the microorganism
Effect of yeast extract on speciation and bioavailability of nickel and cobalt in anaerobic bioreactors
Gonzalez-Gil, G. ; Jansen, S. ; Zandvoort, M.H. ; Leeuwen, H.P. van - \ 2003
Biotechnology and Bioengineering 82 (2003)2. - ISSN 0006-3592 - p. 134 - 142.
cathodic stripping voltammetry - chemical speciation - dissolved copper - metal speciation - natural-waters - methanosarcina - complexation - kinetics - bacteria - growth
The speciation of metals plays an important role in their bioavailability. In the case of anaerobic reactors for the treatment of wastewaters, the ubiquitous presence of sulfide leads to extensive precipitation of metals like nickel and cobalt, which are essential for the metabolism of the anaerobic microorganisms that carry out the mineralization of the pollutants present in the wastewater. In practice, nickel, cobalt, and iron are added in excessive amounts to full-scale installations. This study is concerned with the complexation of nickel and cobalt with yeast extract and its effect on the biogas production by methanogenic biomass. Adsorptive stripping voltammetry (AdSV) was used to get information about the stability and complexing capacity of the metal-yeast extract complexes formed. Nickel and cobalt form relatively strong organic complexes with yeast extract. The bioavailability of these essential metals in anaerobic batch reactors was dramatically increased by the addition of yeast extract. This is due to the formation of dissolved bioavailable complexes, which favors the dissolution of metals from their sulfides. Trace doses of yeast extract may be effective in keeping additions of essential metals to anaerobic reactors at a minimum.
Conversion and toxicity characteristics of formaldehyde in acetoclastic methanogenic sludge
Gonzalez-Gil, G. ; Kleerebezem, R. ; Lettinga, G. - \ 2002
Biotechnology and Bioengineering 79 (2002)3. - ISSN 0006-3592 - p. 314 - 322.
biodegradation - reactor
An unadapted mixed methanogenic sludge transformed formaldehyde into methanol and formate. The methanol to formate ratio obtained was 1:1. Formaldehyde conversion proceeded without any lag phase, suggesting the constitutive character of the formaldehyde conversion enzymes involved. Because the rate of formaldehyde conversion declined at increased formaldehyde additions, we hypothesized that some enzymes and/or cofactors might become denatured as a result of the excess of formaldehyde. Furthermore, formaldehyde was found to be toxic to acetoclastic methanogenesis in a dual character. Formaldehyde toxicity was partly reversible because once the formaldehyde concentration was extremely low or virtually removed from the system, the methane production rate was partially recovered. Because the degree of this recovery was not complete, we conclude that formaldehyde toxicity was partly irreversible as well. The irreversible toxicity likely can be attributed to biomass formaldehyde-related decay. Independent of the mode of formaldehyde addition (i.e., slug or continuous), the irreversible toxicity was dependent on the total amount of formaldehyde added to the system. This finding suggests that to treat formaldehyde-containing waste streams, a balance between formaldehyde-related decay and biomass growth should be attained