A.J.H. Janssen

Biotechnological Treatment of Sulfate-Rich Wastewaters

Sulfate-rich wastewaters are generated by many industrial processes that use sulfuric acid or sulfate-rich feed stocks (e.g., fermentation or sea food processing industry). Also, the use of reduced sulfur compounds in industry, that is, sulfide (tanneries, kraft pulping), sulfite (sulfite pulping), or thiosulfate (pulp bleaching, fixing of photographs), contaminates wastewaters with sulfate. A major problem for the biological treatment of sulfate-rich wastewaters is the production of H2S. Gaseous and dissolved sulfides cause physical (corrosion, odor, increased effluent COD) or biological (toxicity) constraints that may lead to process failure. H2S is generated by sulfate-reducing bacteria, in both anaerobic and aerobic (anoxic microenvironments) wastewater treatment systems. No practical methods exist to prevent sulfate reduction. Selective inhibition of SRB by molybdate, transition elements, or antibiotics is unsuccessful at full scale. Selection of a treatment strategy for a sulfate-rich wastewater dep...

Application of bacteria involved in the biological sulfur cycle for paper mill effluent purification

In anaerobic wastewater treatment, the occurrence of biological sulfate reduction results in the formation of unwanted hydrogen sulfide, which is odorous, corrosive and toxic. In this paper, the role and application of bacteria in anaerobic and aerobic sulfur transformations are described and exemplified for the treatment of a paper mill wastewater. The sulfate containing wastewater first passes an anaerobic UASB reactor for bulk COD removal which is accompanied by the formation of biogas and hydrogen sulfide. In an aeration pond, the residual CODorganic and the formed dissolved hydrogen sulfide are removed. The biogas, consisting of CH4 (80-90 vol.%), CO2 (10-20 vol.%) and H2S (0.8-1.2 vol.%), is desulfurised prior to its combustion in a power generator thereby using a new biological process for H2S removal. This process will be described in more detail in this paper. Biomass from the anaerobic bioreactor has a compact granular structure and contains a diverse microbial community. Therefore, other anaerobic bioreactors throughout the world are inoculated with biomass from this UASB reactor. The sludge was also successfully used in investigation on sulfate reduction with carbon monoxide as the electron donor and the conversion of methanethiol. This shows the biotechnological potential of this complex reactor biomass.

Kinetics of chemical and biological sulphide oxidation in aqueous solutions

Abstract A new equation for the non-catalysed sulphide chemical oxidation rate in a phosphate buffered system at pH 8.0 and 25°C is found. Our experiments show that the reaction order with respect to the oxygen concentration, n, depends on the sulphide concentration. The following equation is proposed: i= k[S]m[O]n log[S] (mg/1 h). The values for the constants m, n, k were found to be 0.41, 0.39 and 0.57 respectively. The biological oxidation rate in cell suspensions from a bioreactor, also measured in a phosphate buffered system at pH 8.0 and 25°C, was found to be a factor 75 faster than the chemical non-catalysed oxidation rate at sulphide concentrations around 10 mg/l. At higher sulphide concentrations this difference becomes less, e.g. at 100 mg/l the biological oxidation rate is only 7 times faster than the chemical oxidation rate. The two cell suspensions used in the experiments behave quite differently towards the sulphide concentration. Cell suspension 1 (taken from a reactor operated at a sulphide concentration of 7 mg/1) exerts its maximal oxidation rate (230 mg/l h) at a sulphide concentration of 10 mg/l. Cell suspension 2 (taken from a reactor operated at a sulphide concentration of 95 mg/1) exerts its maximal biological oxidation capacity (120 mg/1 h) at a sulphide concentration of 150 mg/1. The total oxidation rate (chemical and biological) of cell suspension 2 at 150 mg/1 is 210 mg/l h (of which only 5% is chemical). Cell suspension 1 shows severe substrate inhibition at sulphide concentrations exceeding 10 mg/l, while cell suspension 2 shows no sulphide inhibition up to a sulphide concentration of 600 mg/1.

Degradation of Methanethiol by Methylotrophic Methanogenic Archaea in a Lab-Scale Upflow Anaerobic Sludge Blanket Reactor

ABSTRACT In a lab-scale upflow anaerobic sludge blanket reactor inoculated with granular sludge from a full-scale wastewater treatment plant treating paper mill wastewater, methanethiol (MT) was degraded at 30°C to H2S, CO2, and CH4. At a hydraulic retention time of 9 h, a maximum influent concentration of 6 mM MT was applied, corresponding to a volumetric loading rate of 16.5 mmol liter−1 day−1. The archaeal community within the reactor was characterized by anaerobic culturing and denaturing gradient gel electrophoresis analysis, cloning, and sequencing of 16S rRNA genes and quantitative PCR. Initially, MT-fermenting methanogenic archaea related to members of the genus Methanolobus were enriched in the reactor. Later, they were outcompeted by Methanomethylovorans hollandica, which was detected in aggregates but not inside the granules that originated from the inoculum, the microbial composition of which remained fairly unchanged. Possibly other species within the Methanosarcinacaea also contributed to the fermentation of MT, but they were not enriched by serial dilution in liquid media. The archaeal community within the granules, which was dominated by Methanobacterium beijingense, did not change substantially during the reactor operation. Some of the species related to Methanomethylovorans hollandica were enriched by serial dilutions, but their growth rates were very low. Interestingly, the enrichments could be sustained only in the presence of MT and did not utilize any of the other typical substrates for methylotrophic methanogens, such as methanol, methyl amine, or dimethylsulfide.

Biological treatment of refinery spent caustics under halo-alkaline conditions

The present research demonstrates the biological treatment of refinery sulfidic spent caustics in a continuously fed system under halo-alkaline conditions (i.e. pH 9.5; Na(+)= 0.8M). Experiments were performed in identical gas-lift bioreactors operated under aerobic conditions (80-90% saturation) at 35°C. Sulfide loading rates up to 27 mmol L(-1)day(-1) were successfully applied at a HRT of 3.5 days. Sulfide was completely converted into sulfate by the haloalkaliphilic sulfide-oxidizing bacteria belonging to the genus Thioalkalivibrio. Influent benzene concentrations ranged from 100 to 600 μM. At steady state, benzene was removed by 93% due to high stripping efficiencies and biodegradation. Microbial community analysis revealed the presence of haloalkaliphilic heterotrophic bacteria belonging to the genera Marinobacter, Halomonas and Idiomarina which might have been involved in the observed benzene removal. The work shows the potential of halo-alkaliphilic bacteria in mitigating environmental problems caused by alkaline waste.

Volatile organic sulfur compounds in anaerobic sludge and sediments: biodegradation and toxicity.

A variety of environmental samples was screened for anaerobic degradation of methanethiol, ethanethiol, propanethiol, dimethylsulfide, and dimethyldisulfide. All sludge and sediment samples degraded methanethiol, dimethylsulfide, and dimethyldisulfide anaerobically. In contrast, ethanethiol and propanethiol were not degraded by the samples investigated under any of the conditions tested. Methanethiol, dimethylsulfide, and dimethyldisulfide were mainly degraded by methanogenic archaea. In the presence of sulfate and the methanogenic inhibitor bromoethane sulfonate, degradation of these compounds coupled to sulfate reduction occurred as well, but at much lower rates. Besides their biodegradability, also the toxicity of methanethiol, ethanethiol, and propanethiol to methanogenesis with methanol, acetate, and H2/CO2 as the substrates was assessed. The 50% inhibition concentration of methanethiol on the methane production from these substrates ranged between 7 and 10 mM. The 50% inhibition concentration values of ethanethiol and propanethiol for the degradation of methanol and acetate were between 6 and 8 mM, whereas hydrogen consumers were less affected by ethanethiol and propanethiol, as indicated by their higher 50% inhibition concentration (14 mM). Sulfide inhibited methanethiol degradation already at relatively low concentrations: methanethiol degradation was almost completely inhibited at an initial sulfide concentration of 8 mM. These results define the operational limits of anaerobic technologies for the treatment of volatile organic sulfur compounds in sulfide-containing wastewater streams.

Pathways of sulfide oxidation by haloalkaliphilic bacteria in limited-oxygen gas lift bioreactors

Physicochemical processes, such as the Lo-cat and Amine-Claus process, are commonly used to remove hydrogen sulfide from hydrocarbon gas streams such as landfill gas, natural gas, and synthesis gas. Biodesulfurization offers environmental advantages, but still requires optimization and more insight in the reaction pathways and kinetics. We carried out experiments with gas lift bioreactors inoculated with haloalkaliphilic sulfide-oxidizing bacteria. At oxygen-limiting levels, that is, below an O(2)/H(2)S mole ratio of 1, sulfide was oxidized to elemental sulfur and sulfate. We propose that the bacteria reduce NAD(+) without direct transfer of electrons to oxygen and that this is most likely the main route for oxidizing sulfide to elemental sulfur which is subsequently oxidized to sulfate in oxygen-limited bioreactors. We call this pathway the limited oxygen route (LOR). Biomass growth under these conditions is significantly lower than at higher oxygen levels. These findings emphasize the importance of accurate process control. This work also identifies a need for studies exploring similar pathways in other sulfide oxidizers such as Thiobacillus bacteria.

SURFACE CHARACTERISTICS AND AGGREGATION OF MICROBIOLOGICALLY PRODUCED SULPHUR PARTICLES IN RELATION TO THE PROCESS CONDITIONS

Abstract The effect of surface properties and the effects of several process conditions, e.g. loading rate, ionic strength and the presence of polymers, on the degree of aggregation of sulphur particles were studied. Sulphur is formed under oxygen-limiting circumstances during the partial oxidation of sulphide by a mixed culture of thiobacillus -like bacteria. Since the freshly excreted particles are in a colloidal state, with a diameter of approximately 100 nm, their aggregation is a prerequisite in order to obtain a satisfactory sedimentation. Titration experiments revealed that the negative sulphur surface charge is determined by the presence of multiple functional groups. Attention was also paid to the effect of the chain length, hydrophilicity and charge of a number of dissolved polymers on the degree of sulphur aggregation. The degree of polymer adsorption on the sulphur surface mainly depends on the hydrophobicity and charge of the polymer. Since the charge of biologically produced sulphur is negative at pH 8.0, a highly charged cationic polymer like Q N -HEC inhibits the sulphur aggregation. For Perfectamyl and carboxymethylcellulose no clear effect was measured. Particularly for long-chain polymers, a distinct negative effect on the aggregation was found. Steric hindrance, apparently, is an important factor in the aggregation process. Upon increasing the sulphide loading rate, larger sulphur aggregates were formed while the opposite trend was observed for increasing salt concentrations. In practice, therefore, a sulphide-oxidizing bioreactor should be operated at high loading rates to enhance the settleability of the sulphur sludge.

Reactions between methanethiol and biologically produced sulfur particles.

Recently, new biotechnological processes have been developed to enable the sustainable removal of organic and inorganic sulfur compounds from liquid and gaseous hydrocarbon streams. In comparison to existing technologies (e.g., caustic scrubbing or iron based redox technologies) far less chemicals are consumed, while reusable elemental sulfur is formed as the main end-product. This research shows that in these processes a number of consecutive reactions occur between methanethiol (MT) from the hydrocarbon stream and the formed biosulfur particles, leading to the formation of (dimethyl) polysulfides. This is an important feature of this family of new bioprocesses as it improves the MT removal efficiency. The reaction kinetics depend on the MT and biosulfur concentration, temperature, and the nature of the biosulfur particles. The first reaction step involves a S8 ring-opening by nucleophilic attack of MT molecules to form CH3S9(-). This work shows that CH3S9(-) reacts to polysulfides (S3(2-), S4(2-), S5(2-)), dimethyl polysulfides [(CH3)2S2, (CH3)2S3], and dissociated H2S, while also some longer-chain dimethyl polysulfides [(CH3)2S4-7] are formed at μM levels. Control experiments using orthorhombic sulfur flower (S8) did not reveal these reactions.

Biodegradation Potential of Halo(alkali)philic Prokaryotes

Oil and gas exploitation and downstream processing may generate large volumes of contaminated aqueous wastewaters. Without treatment, the discharge of these streams into the environment would lead to considerable environmental problems. A combination of physicochemical and biological treatment processes are applied to treat such polluted streams (e.g., in conventional water purification plants). However, the application of microorganisms in these streams is rather limited streams to salt levels well below those of seawater. The potential of microorganisms to degrade various organic and inorganic pollutants at higher salinities was surveyed in the open literature. The advantage of biological treatment processes that operate at elevated salinities is that no dilution water is needed, which is particularly relevant for arid regions. The available literature is scarce, especially concerning truly halophilic bacteria that thrive at salt concentrations significantly higher than in seawater. The obvious trend of most of the publications indicates a significant inhibition of the biodegradation activity at salt concentrations above 10 wt.%. However, a specialized group of extremophilic microorganisms, called halo(alkali)philes, could replace freshwater or marine organisms in the biodegradation processes at salinities above 1.5 M and pH values above 9. They are present in natural hypersaline habitats and can be activated either directly in situ by addition of micronutrients and aeration, or introduced into engineered water treatment systems. In a number of studies, the possibility of microbial HC degradation up to 5 M NaCl has been mentioned. Relatively little is known about the removal of toxic inorganic compounds, such as H2S, CO, and CN−, at halo(alkaline) conditions. These compounds are clearly associated with the processing of oil, coal, and gas. An exception is the application of sulfur-cycling bacteria, as these organisms have been intensively studied during the last decade. Sulfur-oxidizing and sulfidogenic bacteria can function efficiently at extremely saline and alkaline conditions. The general conclusion from this survey is that many biodegradation routs are, in principal, possible at high salt/pH but more research is needed to make a real progress in the development of engineered processes that can be applied to protect the environment.