Methanol as electron donor for thermophilic biological sulfate and sulfite reduction

Sulfur oxyanions (e.g. sulfate, sulfite) can be removed from aqueous waste- and process streams by biological reduction with a suitable electron donor to sulfide, followed by partial chemical or biological oxidation of sulfide to elemental sulfur. The aim of the research described in this thesis was to make this biological process more broadly applicable for desulfurization of flue-gases and ground- and wastewaters by using the cheap chemical methanol as electron donor for the reduction step. Besides determining the selectivity and rate of reduction of sulfur oxyanions with methanol in bioreactors, also insight was acquired into the microbiology of the process. At pH 7.5 and thermophilic (65 °C) conditions (applicable for flue-gas desulfurization), sulfate-reducing microorganisms ultimately outcompete methanogenic consortia for methanol in anaerobic high-rate bioreactors. Methane formation from methanol was quickly inhibited by imposing slightly acidic pH-values (6.7 instead of 7.5). Acetate represented a side-product from methanol at 65 °C, accounting for up to 13 % of the methanol degraded. The rate of acetate formation was linearly correlated to the rate of sulfate and sulfite reduction with methanol. At a hydraulic retention time (HRT) of 10 h, maximum reduction rates of 6 g SO 32- .L -1 .day -1 (100% elimination) and 4-7 g SO 42- .L -1 .day -1 (40-70% elimination) were attained simultaneously in the reactors, equivalent to a sulfidogenic methanol-conversion rate of 6-8 g COD.L -1 .day -1 (COD:Chemical Oxygen Demand). The resulting sulfide concentration of about 1800 mg S.L -1 (or the H 2 S concentration of 200 mg S.L -1 at pH 7.5) limited the rate of sulfate reduction at HRT=10 h.At a hydraulic retention time of 3-4 h, maximum reduction rates of 18 g SO 32- .L -1 .day -1 (100% elimination) and about 12 gS O 42- .L -1 .day -1 (50% elimination) were attained, equivalent to a sulfidogenic methanol-conversion rate of 19 g COD.L -1 .day -1 . At this HRT, the sulfate reduction rate was limited by the biomass concentration of 9 to 10 g VSS.L -1 that maximally was retained in the reactor. The time needed to reach maximum process performance amounted to 40-60 days. From one of the reactors a thermophilic sulfate reducing bacterium, Desulfotomaculum strain WW1 was isolated, that probably represented the most abundant sulfate reducer. In the reactor, strain WW1 is not confined to the use of methanol, as it also grows on methanol degradation products like acetate, formate and H 2 /CO 2 . The presence of high numbers of methanol-oxidizing, hydrogen-producing bacteria in the sludge indicated that hydrogen may represent an important electron donor for sulfate reduction in the sludge. In the cultures in which the presence of these species was demonstrated, the formation of acetate (about 15% of the methanol degraded) seemed to be strictly coupled to growth of the methanol-oxidizing species. This might explain the coupling of sulfide and acetate formation from methanol in the reactors. Methanol was not a suitable electron donor for mesophilic (30 °C) sulfate reduction, relevant for bio-desulfurization of cold or slightly heated ground- or wastewater. Under mesophilic conditions, methanol was primarily degraded to methane.</p

Energie uit rioolwater en keukenafval bij hoge druk

Decentrale sanitatie als invulling van een duurzame waterketen is bedacht in Wageningen en tussen 2002 en 2005 door een aantal partijen in het noorden van Nederland ontwikkeld tot een bruikbaar concept. Het demonstratieproject DeSaH in Sneek heeft laten zien dat het toepassen van decentrale sanitatie en hergebruik veel mogelijkheden biedt en zeker ook een aantal aanknopingspunten voor verdere ontwikkelingen. De resultaten van het innovatieve concept kunnen echter nog aanzienlijk worden verbeterd. Ondergetekenden zijn na het ontwerp voor het project in Sneek het laboratorium ingedoken, om met nieuwe partijen te werken aan de verbetering van de efficiency, de energieprestatie en de marktpotentie van het concept. Het resultaat is een nieuwe zuiveringstechnologie: hogedrukgistin

Bioscorodite crystallization for arsenic removal

In the bio-scorodite process, arsenic is precipitated as crystalline iron arsenate, i.e. scorodite (FeAsO4·2H2O). This is a more economic and more environmentally friendly method for arsenic immobilization than the chemical production of iron- or calcium arsenate, as fewer chemicals are needed. Moreover, scorodite is an attractive medium for arsenic control and immobilization because it is stable, compact and has a very low solubility. Therefore it is regarded as the most ideal form for long-term arsenic storage. We have demonstrated that bio-crystallization of arsenic into scorodite crystals is possible with the aid of microorganisms. The operational conditions of the bio-scorodite process allow for a fast growth of the microorganisms and facilitate the crystallization of scorodite, avoiding the precipitation of other iron oxides or amorphous iron arsenates. The bio-scorodite process brings several advantages compared to chemical crystallization such as the lower required temperature (70°C), the control of supersaturation by biological oxidation and no need for crystal parents or seeds to begin the crystallization. Arsenic concentrations are removed to ppm level with starting concentrations ranging from 1000 to 2000 mg L-1. The produced bioscorodite crystals are very similar to the scorodite mineral found in nature. By control of the iron feed and the pH, the production of other iron precipitates is avoided. The latter facilitates easy separation of the solid product. Based on their highly crystalline nature, the biogenic scorodite crystals seem very suitable for safe disposal. At present the research has started with the continuous production of scorodite in bioreactors. The follow-up challenges are focused on the selection of a suitable reactor configuration

Kinetics of ferrous iron oxidation by batch and continuous cultures of thermoacidophilic Archaea at extremely low pH of 1.1–1.3

The extreme acid conditions required for scorodite (FeAsO4·2H2O) biomineralization (pH below 1.3) are suboptimal for growth of most thermoacidophilic Archaea. With the objective to develop a continuous process suitable for biomineral production, this research focuses on growth kinetics of thermoacidophilic Archaea at low pH conditions. Ferrous iron oxidation rates were determined in batch-cultures at pH 1.3 and a temperature of 75°C for Acidianus sulfidivorans, Metallosphaera prunea and a mixed Sulfolobus culture. Ferrous iron and CO2 in air were added as sole energy and carbon source. The highest growth rate (0.066 h-1) was found with the mixed Sulfolobus culture. Therefore, this culture was selected for further experiments. Growth was not stimulated by increase of the CO2 concentration or by addition of sulphur as an additional energy source. In a CSTR operated at the suboptimal pH of 1.1, the maximum specific growth rate of the mixed culture was 0.022 h-1, with ferrous iron oxidation rates of 1.5 g L-1 d-1. Compared to pH 1.3, growth rates were strongly reduced but the ferrous iron oxidation rate remained unaffected. Influent ferrous iron concentrations above 6 g L-1 caused instability of Fe2+ oxidation, probably due to product (Fe3+) inhibition. Ferric-containing, nano-sized precipitates of K-jarosite were found on the cell surface. Continuous cultivation stimulated the formation of an exopolysaccharide-like substance. This indicates that biofilm formation may provide a means of biomass retention. Our findings showed that stable continuous cultivation of a mixed iron-oxidizing culture is feasible at the extreme conditions required for continuous biomineral formation

Citric acid wastewater as electron donor for biological sulfate reduction

Citrate-containing wastewater is used as electron donor for sulfate reduction in a biological treatment plant for the removal of sulfate. The pathway of citrate conversion coupled to sulfate reduction and the microorganisms involved were investigated. Citrate was not a direct electron donor for the sulfate-reducing bacteria. Instead, citrate was fermented to mainly acetate and formate. These fermentation products served as electron donors for the sulfate-reducing bacteria. Sulfate reduction activities of the reactor biomass with acetate and formate were sufficiently high to explain the sulfate reduction rates that are required for the process. Two citrate-fermenting bacteria were isolated. Strain R210 was closest related to Trichococcus pasteurii (99.5% ribosomal RNA (rRNA) gene sequence similarity). The closest relative of strain S101 was Veillonella montepellierensis with an rRNA gene sequence similarity of 96.7%. Both strains had a complementary substrate range

Handelingsperspectief circulaire economie Amsterdam - Gezamenlijke oplossingen en kansen voor betere kringloopsluiting in Metropoolregio Amsterdam (MRA) - Factsheets bij het visiedocument

Als resultaat van de samenwerking met de Metropoolregio Amsterdam benoemt Wageningen UR in dit document voor vier kringlopen actuele mogelijkheden en bijbehorende maatregelen om de kringlopen zo goed mogelijk te sluiten. In de vorm van factsheets wordt voor elke maatregel uitgewerkt wat deze oplevert voor de dimensies people, planet, profit en proces en wat de kosten, de risico’s en de randvoorwaarden daarbij zijn. De vier kringlopen zijn fosfaat, water, afval en voedsel

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)

Recycling Food System Nutrients in a Circular Economy

Planet Earth already exists for over 5 billion years, while humans have been around for only a million years.The impact of human activity on the natural ecosystem has increased dramatically over the last few hundred years, mainly through agriculture, industry, and urbanisation, resulting in the consumption of natural resources at high rate. Modern agriculture, with the use of fertilizers and agrochemicals, has increased productivity drastically and has loosened the connection between location of food production and location of food consumption. As a result local/regional accumulation of nutrients occurs in terms of waste streams with negative impact on the environment, in combination with regional depletion elsewhere.The circular economy has been generally accepted now by most scientists, policy makers and entrepreneurs, as concept and new paradigm for organizing the food production –consumption cycle. As a consequence any stream of material within that cycle should be considered as an input elsewhere in the cycle. The main question addressed in this paper is ‘how to organize the recycling of food system nutrients effectively and efficiently’?As socio-economic, environmental and cultural conditions differ from one place to the other on the planet there is not one single solution that fits all food systems for organizing a circular economy. Therefore, a mix of several solutions may occur side by side. This diversity will contribute positively to the robustness of the system towards fluctuations due to impacts generated either by nature or by mankind. An important constraints to modifications to food systems is that the modifications and recycling are acceptable by the stakeholders involved. Therefore, initiatives have to be taken to bring together different stakeholders in order to exchange ideas and to explore common grounds for future cooperation. Position papers are written to stimulate partners to move away from their own comfort zone and think about new types of solutions. As the world changes, new techniques become available and new generations prefer to make different choices. What was good in the past might no longer be good enough for the future. Here the first results from this forward-looking and integrated approach are reported