Investigation of the diversity of homoacetogenic bacteria in mesophilic and thermophilic anaerobic sludges using the formyltetrahydrofolate synthetase gene.

Homoacetogenic bacteria are strict anaerobes capable of autotrophic growth on H(2)/CO(2) or CO, and of heterotrophic growth on a wide range of sugars, alcohols, methoxylated aromatic compounds and one carbon compounds, yielding acetate as their sole metabolic end-product. Batch activity tests on anaerobic granular sludge, using H(2)/CO(2) as a substrate and 2-bromoethanesulfonate (BES) as a specific methanogenic inhibitor revealed that H(2)/CO(2) conversion and concomitant acetate production commenced only after a lag period of 60-100 h. This finding suggests that the homoacetogenic population of digester sludge could be maintained by heterotrophic growth on sugars or other organic compounds, rather than by autotrophic growth on H(2)/CO(2). In the present study, two upflow anaerobic sludge bed (UASB) reactors were operated at 37 degrees C and 55 degrees C for two distinct trial periods, each characterised by the application of influents designed to enrich for homoacetogenic bacteria. Specific primers designed for the amplification of the functional gene encoding formyltetrahydrofolate synthetase (FTHFS), a key enzyme in the acetyl-CoA pathway of acetogenesis, were used as a specific probe for acetogenic bacteria. The diversity of acetogens in the granular sludge cultivated in each reactor was revealed by application of FTHFS targeted PCR. Results show that biomass acetogenic composition was dependent upon the operational temperature of the reactor and the substrate supplied as influent.     

Silage effluent digestion by an upflow anaerobic filter

Silage effluent is generally regarded as one of the major agricultural pollutants of water courses. Efficient anaerobic digestion of silage effluent was achieved by a 3-day hydraulic retention in an upflow anaerobic filter. The filter was a laboratory scale unit containing a limestone chip support matrix. At loading rates ranging from 7.8 to 14.2 kg COD m⁻³ active volume day⁻¹, the average COD removal obtained ranged from 86 to 89% with a TOA removal of 82–88%. The methane content of the biogas produced ranged from 81 to 88%. The rate of COD conversion to CH₄ was independent of the loading rate under the conditions tested and the observed efficiency averaged 0.357 m¹ CH₄(STP) kg⁻¹ COD introduced to the reactor.The reactor tolerated considerable variation in influent pH without any apparent decrease in digestion efficiency. It is apparent from the results obtained that a reactor which is in routine use for slurry digestion may also be utilised for silage effluent digestion on a seasonal basis.     

Large‐scale anaerobic degradation of betaine

Betaine, also known as N,N,N‐trimethyl glycine, is a soluble nitrogenous compound present at significant concentrations in sugar‐beet molasses. Molasses is used as substrate in a wide range of industrial fermentations, for example, alcohol, acid and yeast cell production. Betaine is not consumed to any significant extent during these fermentations and appears to largely pass through the subsequent processing stages, becoming an important constituent of the wastewater produced by these industries. The present study confirmed that betaine is present in large amounts in sugar‐beet molasses (up to 6% w/w) and in the effluent of processes using sugar‐beet molasses as substrate (up to 4.5 g dm⁻³). Betaine appeared to be almost completely degraded in the two full‐scale anaerobic treatment plants sampled. This was confirmed by anaerobic activity tests performed with both acclimated and unacclimated anaerobic sludge. The results obtained suggest the possible involvement of a multistep degradation process, with the likelihood of a nitrogen‐containing intermediate. Finally, although not totally discountable, betaine degradation does not appear to be coupled to sulfate reduction during treatment of high‐sulfate wastewaters. © 1999 Society of Chemical Industry     

Microbial sulphate reduction during anaerobic digestion: EGSB process performance and potential for nitrite suppression of SRB activity.

The present study investigated mesophilic anaerobic treatment of sulphate-containing wastewater in EGSB reactors and assessed the inclusion of nitrite in the reactor influent as a method for control of biological sulphate reduction. Two EGSB reactors, R1 and R2, were operated for a period of 581 days at varying volumetric loading rates, COD/SO4(2-) ratios and influent nitrite concentrations (R2 only). COD removal efficiencies of > 93% were achieved in both reactors at influent sulphate concentrations of up to 3,000 mg l(-1). A two-fold increase in the influent sulphate concentration, giving an influent COD/SO4(2-) ratio of 2, resulted in a reduction in reactor COD removal efficiency to 84% and 89%, in R1 and R2, respectively. Despite inclusion of nitrite in the R2 influent at concentrations up to 500 mg NO2-N l(-1), sulphate reduction proceeded similarly in R2 and R1, suggesting the ineffectiveness of nitrite as a potential inhibitor of SRB     

Controlled Starting of AC Induction Motors

As the demand for electrical energy continues to increase, increasing restrictions will be placed on full-voltage starting of ac induction motors. Inrush is the problem. The utilities are tending to enforce more rigorously the historical limits on the amount of inrush allowed. Reduced-voltage starters have traditionally been used to reduce the impact of motor starting inrush. All traditional starters have reduced the amount of inrush, but none have eliminated it. The type of driven load must be taken into consideration in order to provide motor torque sufficient to start the load while eliminating the starting current inrush. The Ultra Torq is a motor plus solid-state starter combination which provides a solution to the problem. The Ultra Torq controls the rate-of-change of kVA with respect to time, thereby eliminating the problem of inrush. A successful start is assured by matching the motor, starter, and controller to the torque requirements of the load and to the kVA limits of the system. The match makes the difference.     

Use of anaerobic hybrid reactors for treatment of synthetic pharmaceutical wastewaters containing organic solvents

The performance of anaerobic hybrid reactors treating an organic solvent-containing synthetic pharmaceutical wastewater was evaluated under various wastewater volumetric loading rates and influent compositional changes. The biodegradation, toxicity and treatability of the target C₃ and C₄ solvents, tert-butanol, isopropanol, isobutanol, sec-butanol and ethyl acetate, were examined. At a hydraulic retention time (HRT) of 2 days and volumetric loading rates ranging from 3·5 to 4·5 kg COD m⁻³ day⁻¹, the reactors achieved total and soluble COD removal efficiencies of 97–99% in less than five times the HRT. These removal rates were achieved following the introduction of target solvents not previously supplied to the reactors. However, inadequate removal of tert-butanol resulted in a decrease in the soluble COD removal efficiency to 58%. Bacterial enrichments from the reactor biomass using tert-butanol as the sole substrate proved unsuccessful, confirming that tert-butanol is poorly degradable anaerobically. Inclusion of a trace metal cocktail in the feed did not affect steady-state reactor performance, but was beneficial during changes in the influent composition. After 405 days of operation, the matrix-associated biomass contributed only a minor fraction (2–4%) of the total biomass present in both reactors. On takedown, the retained biomass present in the matrix-free section of both reactors was found to be granular in nature, despite the omission of trace elements from the influent to one of the AHRs. The specific methanogenic activity profile of the granular sludge from the trace element limited AHR was, however, significantly lower (α = 0·05) than that of the reference AHR.     

Identification of mesophilic and thermophilic fermentative species in anaerobic granular sludge.

Large quantities of biodegradable food waste in the form of fruit and vegetables are still being deposited in landfill sites in Ireland. The development of an anaerobic digestion process using fermentative species which degrade the carbohydrate-rich waste could divert the food waste from landfills. We identified fermentative species grown on glucose and sucrose at mesophilic and thermophilic temperatures using molecular biology techniques. The dominating fermentative bacteria of the mesophilic sludge were of the Bacteroidetes and Spirochaetes classes. Although both groups of bacteria are typically fermentative their substrate range appears to be limited. The dominating fermentative bacteria in the thermophilic sludge was Thermoanaerobacterium aotearoense of the Clostridia class. The indications are that Thermoanaerobacterium aotearoense may be highly suitable to biodegrade a carbohydrate-rich influent feed due to its possibly very rapid growth rate and also an extensive substrate range.     

A 3.2 GHz 26 dB wide-band monolithic matched GaAs MESFET feedbackamplifier using cascodes

Feedback around cascode stages is demonstrated to be a useful means of making matched direct coupled amplifiers with higher bandwidths than afforded by conventional common-source topologies. Design techniques are described for an amplifier which is capable of operation to DC and which exhibits a measured gain of 26 dB, a 3.2 GHz bandwidth, and a 2.5:1 VSWR in a 1-μm GaAs MESFET process. A novel adjustment scheme is introduced whereby the amplifier's frequency response can be modified using a DC bias voltage to ensure stable circuit operation in spite of MESFET modeling inaccuracies and GaAs processing variations     

Enrichment of acetogenic bacteria in high rate anaerobic reactors under mesophilic and thermophilic conditions

The objective of the current study was to expand the knowledge of the role of acetogenic Bacteria in high rate anaerobic digesters. To this end, acetogens were enriched by supplying a variety of acetogenic growth supportive substrates to two laboratory scale high rate upflow anaerobic sludge bed (UASB) reactors operated at 37 °C (R1) and 55 °C (R2). The reactors were initially fed a glucose/acetate influent. Having achieved high operational performance and granular sludge development and activity, both reactors were changed to homoacetogenic bacterial substrates on day 373 of the trial. The reactors were initially fed with sodium vanillate as a sole substrate. Although % COD removal indicated that the 55 °C reactor out performed the 37 °C reactor, effluent acetate levels from R2 were generally higher than from R1, reaching values as high as 5023 mg l⁻¹. Homoacetogenic activity in both reactors was confirmed on day 419 by specific acetogenic activity (SAA) measurement, with higher values obtained for R2 than R1.Sodium formate was introduced as sole substrate to both reactors on day 464. It was found that formate supported acetogenic activity at both temperatures. By the end of the trial, no specific methanogenic activity (SMA) was observed against acetate and propionate indicating that the methane produced was solely by hydrogenotrophic Archaea. Higher SMA and SAA values against H₂/CO₂ suggested development of a formate utilising acetogenic population growing in syntrophy with hydrogenotrophic methanogens. Throughout the formate trial, the mesophilic reactor performed better overall than the thermophilic reactor.     

A 10-b, 75-MHz two-stage pipelined bipolar A/D converter

A 4-b flash first quantizer is cascaded with an efficient 7-b second quantizer to attain 10-b resolution after error correction. As the second quantizer itself embodies analog subranging through folding and interpolation, its complexity is comparable with that of the first quantizer. An input track and hold preceding the first quantizer acquires dynamic signals with low distortion, and a second track and hold delays the analog residue signal to pipeline the operation of the two quantizers. This collection of components, accompanied by all necessary digital circuits for encoding and error correction is fabricated on an all-NPN 4-GHz f_T bipolar IC measuring 4×4 mm, which dissipates 800 mW from ±5-V supplies. At a 75-MEPi conversion rate, the untrimmed ADC exhibits 59 db S/(N+D) with a 6-MHz full-scale input, which diminishes by only 3 dB when the input frequency rises to 50 MHz