Jan Sipma

Microbial CO conversions with applications in synthesis gas purification and bio-desulfurization.

ABSTRACT Recent advances in the field of microbial physiology demonstrate that carbon monoxide is a readily used substrate by a wide variety of anaerobic micro-organisms, and may be employed in novel biotechnological processes for production of bulk and fine chemicals or in biological treatment of waste streams. Synthesis gas produced from fossil fuels or biomass is rich in hydrogen and carbon monoxide. Conversion of carbon monoxide to hydrogen allows use of synthesis gas in existing hydrogen utilizing processes and is interesting in view of a transition from hydrogen production from fossil fuels to sustainable (CO2-neutral) biomass. The conversion of CO with H2O to CO2 and H2 is catalyzed by a rapidly increasing group of micro-organisms. Hydrogen is a preferred electron donor in biotechnological desulfurization of wastewaters and flue gases. Additionally, CO is a good alternative electron donor considering the recent isolation of a CO oxidizing, sulfate reducing bacterium. Here we review CO utilization by various anaerobic micro-organisms and their possible role in biotechnological processes, with a focus on hydrogen production and bio-desulfurization.

Biological nutrient removal in an MBR treating municipal wastewater with special focus on biological phosphorus removal

The performance of an MBR pilot plant for biological nutrient removal was evaluated during 210days of operation. The set point values for the internal recycles were determined in advance with the use of an optimisation spreadsheet based on the ASM2d model to optimise the simultaneous removal of C, N and P. The biological nutrient removal (BNR) efficiencies were high from the start of operation with COD and N removal efficiencies of 92+/-6% and 89+/-7, respectively. During the course of the experiment P removal efficiencies increased and finally a P-removal efficiency of 92% was achieved. The activity of poly-phosphate accumulating organisms (PAOs) and denitrifying poly-phosphate accumulating organisms (DPAOs) increased and the specific phosphate accumulation rates after 150days of operation amounted to 13.6mgPg(-1)VSSh(-1) and 5.6mgPg(-1)VSSh(-1), for PAOs and DPAOs, respectively.

Diversity and ecophysiological features of thermophilic carboxydotrophic anaerobes

Both natural and anthropogenic hot environments contain appreciable levels of carbon monoxide (CO). Anaerobic microbial communities play an important role in CO conversion in such environments. CO is involved in a number of redox reactions. It is biotransformed by thermophilic methanogens, acetogens, hydrogenogens, sulfate reducers, and ferric iron reducers. Most thermophilic CO-oxidizing anaerobes have diverse metabolic capacities, but two hydrogenogenic species are obligate carboxydotrophs. Among known thermophilic carboxydotrophic anaerobes, hydrogenogens are most numerous, and based on available data they are most important in CO biotransformation in hot environments.

Carbon monoxide conversion by anaerobic bioreactor sludges.

Seven different anaerobic sludges from wastewater treatment reactors were screened for their ability to convert carbon monoxide (CO) at 30 and 55 degrees C. At 30 degrees C, CO was converted to methane and/or acetate by all tested sludges. Inhibition experiments, using 2-bromoethanesulfonic acid and vancomycine, showed that CO conversion to methane at 30 degrees C occurred via acetate, but not via H2. At 55 degrees C, four sludges originally cultivated at 30-35 degrees C and one sludge cultivated at 55 degrees C converted CO rapidly into hydrogen or into methane. In the latter case, inhibition experiments showed that methane was formed via hydrogen as the intermediate.

Biotreatment of Industrial Wastewaters under Transient-State Conditions: Process Stability with Fluctuations of Organic Load, Substrates, Toxicants, and Environmental Parameters

Biotreatment of industrial wastewater is often challenged by operation under transient states with respect to organic loads, pollutants, and physical characteristics. Furthermore, the potential presence of inhibitory compounds requires careful monitoring and adequate process design. This review describes difficulties encountered in biological treatment of wastewater with highly variable influent characteristics. Typical design aspects of biological processes are presented and discussed with respect to their success in treating highly fluctuating wastewaters. In general, biomass retention is a key factor for dealing with highly fluctuating and/or inhibitory wastewater, but the how it operates also affects the stability of performance, as it was shown that dynamic operation instead of operation at a constant flow enhances biodegradation onset and more evenly distributed activity. Although ultimately stable effluent quality must be achieved, the microbial population stability is not necessarily high, as it was shown that microbial diversity and flexibility may play a critical role in functional stability.

Thermophilic sulphate reduction in upflow anaerobic sludge bed reactors under acidifying conditions

The feasibility of thermophilic (55°C) anaerobic sulphur removal from partly acidified wastewater was investigated using two 6.5-l upflow anaerobic sludge bed (UASB) reactors (R1 and R2). Both reactors were inoculated with a mixture of mesophilic sulphidogenic sludge and thermophilic methanogenic sludge (ratio 1:1) and were fed with a sucrose:propionate:butyrate mixture in a chemical oxygen demand (COD) ratio of 2:1:1. Initially, reactor R1 was supplied with this feed supplemented with a high sulphate concentration (COD/SO42− ratio of 1.33), while the feed of reactor R2 contained low sulphate levels (COD/SO42 ratio of 6.67). The reactors were operated at a hydraulic retention time of 3.7 h and the imposed volumetric organic loading rates ranged from 4.9 to 19.8, and from 4.9 to 46.5 g COD l−1 day−1 for R1 and R2, respectively. A complete acidification of sucrose occurred in both R1 and R2. The extent of sulphate reduction depended on the imposed COD/SO42− ratios. R1, when operating at an organic loading rate (OLR) and sulphate loading rate (SLR) of 19.8 g l−1 day−1 and 14.8 g l−1 day−1, respectively, achieved a maximum sulphate reduction efficiency of 50%. In the case of a COD/SO42− ratio of 6.67 (R2), sulphate reduction efficiencies exceeding 95% were achieved at an OLR and SLR of 46.5 g l−1 day−1 and 7.0 g l−1 day−1, respectively. In both reactors, the effluent sulphide concentrations were always below 400 mg l−1, of which ∼90% was present as undissociated H2S (under the given conditions — pH 5.8–6.1 and 55°C). The incomplete sulphate reduction in R1 could be attributed to the limited availability of required reducing equivalents. The biogas (including CH4 and CO2) production rates in R1 were very low, i.e. 0.5 l biogas l−1 reactor day−1, resulting in negligible amounts (<10%) of H2S stripped from the reactor liquid. Introduction of N2 as an additional strip-gas (flow rate ∼20 l l−1 day−1) into R1 resulted in an almost complete H2S removal. In R2, the biogas production rates reached ∼3 l l−1 day−1 at an OLR of 38.5 g l−1 day−1. This resulted in a H2S stripping efficiency of ∼50%.

Degradation of Methanethiol in a Continuously Operated Upflow Anaerobic Sludge-Blanket Reactor

The feasibility of anaerobic treatment of wastewater containing volatile organic sulfur compounds was investigated using biomass originating from an anaerobic wastewater treatment facility treating brewery wastewater. Interest focused mainly on the degradation of methanethiol (MT), an extremely volatile and malodorous sulfur compound. Formation of hydrogen sulfide from methanethiol, dimethyl sulfide (DMS), and dimethyl disulfide (DMDS) was observed. Batch experiments showed that methanethiol was predominantly used by methanogenic bacteria as the sole source of energy and carbon. Methane was formed on MT degradation, and in the presence of 2-bromoethanesulfonic acid (BES), a specific inhibitor of methanogens, MT conversion was strongly inhibited. During the MT degradation, DMS and DMDS were the other primary compounds found. Relatively small quantities of DMS were present; whereas the DMDS concentrations could accumulate as a result of the relatively fast rate at which methanethiol autoxidizes in the presence of minor amounts of molecular oxygen. It was shown that DMS and DMDS could be biologically degraded, resulting in the formation of methane and hydrogen sulfide. In a continuous experiment using a laboratory-scale upflow anaerobic sludge-blanket (UASB) reactor with a volume of 2.0 L, the feasibility of anaerobic treatment of methanethiol was tested. The reactor was operated at a hydraulic residence time (HRT) of 6 hours, temperature of 30 degrees C, and pH of 7.3 to 7.6. The maximal MT conversion efficiency in the continuous experiment was reached after approximately 70 days and exceeded 97% at an influent concentration of 6 mM, corresponding to a MT loading rate of 25 mM/d. The specific MT degradation rate, as determined after 40 days of operation in the UASB, measured 1.1 +/- 0.1 mM MT/g volatile suspended solids.d. These results show that anaerobic treatment of MT-containing waste streams is an interesting alternative for currently used physicochemical treatment methods.

Biodegradation of 2-fluorobenzoate and dichloromethane under simultaneous and sequential alternating pollutant feeding

Two up-flow fixed-bed reactors (UFBRs), inoculated with activated sludge and operated for 162 days, were fed 1mmolL(-1)d(-1) with two model halogenated compounds, 2-fluorobenzoate (2-FB) and dichloromethane (DCM). Expanded clay (EC) and granular activated carbon (GAC) were used as biofilm carrier. EC did not have any adsorption capacity for both model compounds tested, whereas GAC could adsorb 1.3mmolg(-1) GAC for 2-FB and 4.5mmolg(-1) GAC for DCM. Both pollutants were degraded in both reactors under simultaneous feeding. However, biodegradation in the EC reactor was more pronounced, and re-inoculation of the GAC reactor was required to initiate 2-FB degradation. Imposing sequential alternating pollutant (SAP) feeding caused starvation periods in the EC reactor, requiring time-consuming recovery of 2-FB biodegradation after resuming its feeding, whereas DCM degradation recovered significantly faster. The SAP feeding did not affect performance in the GAC reactor as biodegradation of both pollutants was continuously observed during SAP feeding, indicating the absence of true starvation.

Hydrogenogenic CO Conversion in a Moderately Thermophilic (55 °C) Sulfate‐Fed Gas Lift Reactor: Competition for CO‐Derived H2

Thermophilic (55 °C) sulfate reduction in a gas lift reactor fed with CO gas as the sole electron donor was investigated. The reactor was inoculated with mesophilic granular sludge with a high activity of CO conversion to hydrogen and carbon dioxide at 55 °C. Strong competition for H2 was observed between methanogens and sulfate reducers, while the homoacetogens present consumed only small amounts of H2. The methanogens appeared to be more sensitive to pH and temperature shocks imposed to the reactor, but could not be completely eliminated. The fast growth rates of the methanogens (generation time of 4.5 h) enabled them to recover fast from shocks, and they rapidly consumed more than 90% of the CO‐derived H2. Nevertheless, steep increases in sulfide production in periods with low methane production suggests that once methanogenesis is eliminated, sulfate reduction with CO‐rich gas as electron donor has great potential for thermophilic biodesulfurization.