Short-term and long-term effects of increasing temperatures on the stability and the production of volatile sulfur compounds in full-scale thermophilic anaerobic digesters

This study compares the effect of a rapid increase of the digester temperature (from 54 degrees C to 58 degrees C in 2 weeks) with a slow increase (from 53.9 degrees C to 57.2 degrees C at a rate of 0.55 degrees C per month) on full-scale thermophilic anaerobic digestion at Hyperion Treatment Plant. The short-term test demonstrated that rapidly increasing the digester temperature caused elevated production of volatile sulfur compounds, most notably methyl mercaptan, but volatile solids destruction and methane production were not significantly affected. The increase of the volatile fatty acid to alkalinity ratio from 0.1 to over 0.3 indicated a transient change in digester biochemistry, which was reversed by lowering the temperature. In the long term-test, a slow increase of digester temperature, the production of hydrogen sulfide increased above temperatures of 56.1 degrees C, but was controlled by increased injection of ferrous chloride. Methyl mercaptan was detected in trace amounts at the highest temperature tested (57.2 degrees C). This test showed insignificant effects on other digestion parameters, although some temperature-independent changes were observed that could have been seasonal effects over the year that the long-term test lasted. Thus a slow temperature increase was preferable. This observation contrasts with previous results showing the desirability of a rapid temperature rise to first establish a thermophilic culture when converting from mesophilic operation. Further research is warranted on temperature limits and process changes to optimize thermophilic anaerobic digestion.     

Modeling product formation in anaerobic mixed culture fermentations

The anaerobic conversion of organic matter to fermentation products is an important biotechnological process. The prediction of the fermentation products is until now a complicated issue for mixed cultures. A modeling approach is presented here as an effort to develop a methodology for modeling fermentative mixed culture systems. To illustrate this methodology, a steady-state metabolic model was developed for prediction of product formation in mixed culture fermentations as a function of the environmental conditions. The model predicts product formation from glucose as a function of the hydrogen partial pressure (P(H2)), reactor pH, and substrate concentration. The model treats the mixed culture as a single virtual microorganism catalyzing the most common fermentative pathways, producing ethanol, acetate, propionate, butyrate, lactate, hydrogen, carbon dioxide, and biomass. The product spectrum is obtained by maximizing the biomass growth yield which is limited by catabolic energy production. The optimization is constrained by mass balances and thermodynamics of the bioreactions involved. Energetic implications of concentration gradients across the cytoplasmic membrane are considered and transport processes are associated with metabolic energy exchange to model the pH effect. Preliminary results confirmed qualitatively the anticipated behavior of the system at variable pH and P(H2) values. A shift from acetate to butyrate as main product when either P(H2) increases and/or pH decreases is predicted as well as ethanol formation at lower pH values. Future work aims at extension of the model and structural validation with experimental data.     

Treatment of acid mine drainage by sulphate-reducing bacteria using permeable reactive barriers: A review from laboratory to full-scale experiments

Acid mine drainage in-situbioremediation has in the last decades drawnthe attention in the field of environmentalbiotechnology. The most recent treatmenttechnique are the permeable reactive barriersusing sulphate-reducing bacteria. This viewdescribes the basis of many of the currentapproaches to use sulphate-reducing bacteria inacid mine drainage treatment, from laboratoryto full-scale realisations, and the limitationsencountered when applied to full scaleapplications.     

On-line near infrared monitoring of glycerol-boosted anaerobic digestion processes: evaluation of process analytical technologies

A study of NIR as a tool for process monitoring of thermophilic anaerobic digestion boosted by glycerol has been carried out, aiming at developing simple and robust Process Analytical Technology modalities for on-line surveillance in full scale biogas plants. Three 5 L laboratory fermenters equipped with on-line NIR sensor and special sampling stations were used as a basis for chemometric multivariate calibration. NIR characterisation using Transflexive Embedded Near Infra-Red Sensor (TENIRS) equipment integrated into an external recurrent loop on the fermentation reactors, allows for representative sampling, of the highly heterogeneous fermentation bio slurries. Glycerol is an important by-product from the increasing European bio-diesel production. Glycerol addition can boost biogas yields, if not exceeding a limiting 5-7 g L(-1) concentration inside the fermenter-further increase can cause strong imbalance in the anaerobic digestion process. A secondary objective was to evaluate the effect of addition of glycerol, in a spiking experiment which introduced increasing organic overloading as monitored by volatile fatty acids (VFA) levels. High correlation between on-line NIR determinations of glycerol and VFA contents has been documented. Chemometric regression models (PLS) between glycerol and NIR spectra needed no outlier removals and only one PLS-component was required. Test set validation resulted in excellent measures of prediction performance, precision: r(2) = 0.96 and accuracy = 1.04, slope of predicted versus reference fitting. Similar prediction statistics for acetic acid, iso-butanoic acid and total VFA proves that process NIR spectroscopy is able to quantify all pertinent levels of both volatile fatty acids and glycerol.     

New pathways for ammonia conversion in soil and aquatic systems

Ammonia conversion processes are essential for most soil and aquatic systems. Under natural conditions, the many possible reactions are difficult to analyze. For example, nitrification and denitrification have long been regarded as separate phenomena performed by different groups of bacteria in segregated areas of soils, sediments or aquatic systems sequentially in time. It has now been established that strict segregation in place and time of the two processes is not necessary and that both denitrifiers and nitrifiers have versatile metabolisms. However, the rates described for aerobic denitrifiers are very low compared to the rates observed under anoxic conditions. Also the rates of nitrifier denitrification are quite low, indicating that these conversions may not play an important role under natural conditions. In addition, these processes often result in the emission of quite large amounts of undesirable products, NO and N₂O. Heterotrophic nitrification might be of relevance for systems, that contain a high carbon to nitrogen ratio. Recently, a novel process (Anammox) has been discovered in which ammonium serves as the electron donor for denitrification of nitrite into dinitrogen gas. ¹⁵N labeling studies showed that hydrazine and hydroxylamine were important intermediates in this process. Enrichment cultures on ammonium, nitrite and bicarbonate resulted in the dominance of one morphotypical microorganism. The growth rate of the cultures is extremely low (doubling time 11 days), but the affinity for ammonium and nitrite and the conversion rates (9.2 10^–4 mol kg^–1 s^–1) are quite high. Some of the reported high nitrogen losses in soil and aquatic systems might be attributed to anaerobic ammonium oxidation. In addition, this conversion offers new opportunities for nitrogen removal, when it is combined with recently developed processes for partial nitrification.     

Detection and Decontamination of Residual Energetics from Ordnance and Explosives Scrap

Extensive manufacturing of explosives in the last century has resulted in widespread contamination of soils and waters. Decommissioning and cleanup of these materials has also led to concerns about the explosive hazards associated with residual energetics still present on the surfaces of ordnance and explosives scrap. Typically, open burning or detonation is used to decontaminate ordinance and explosive scrap. Here the use of an anaerobic microbiological system applied as a bioslurry to decontaminate energetics from the surfaces of metal scrap is described. Decontamination of model metal scrap artificially contaminated with 2,4,6-trinitrotoluene and of decommissioned mortar rounds still containing explosives residue was examined. A portable ion mobility spectrometer was employed for the detection of residual explosives residues on the surfaces of the scrap. The mixed microbial populations of the bioslurries effectively decontaminated both the scrap and the mortar rounds. Use of the ion mobility spectrometer was an extremely sensitive field screening method for assessing decontamination and is a method by which minimally trained personnel can declare scrap clean with a high level of certainty.     

氨基酸对白念珠菌形态学影响的研究

目的初步探讨单个氨基酸对白念珠菌形态学的影响。方法用0．67％的酵母氮源基础培养基和2％葡萄糖配制成SD合成培养基,37％恒温摇床培养,研究单个天然氨基酸对白念珠菌形态学的影响,并分别通过不添加碳源和厌氧条件下培养观察对精氨酸诱导的菌丝的影响。结果在含10mmol／L的L－精氨酸的SD液体培养基中,可见大量的菌丝。在含10mmol／L的L一半胱氨酸、L．苏氨酸、L－缬氨酸和L－色氨酸的sD液体培养基中,可见典型的酵母细胞,未见菌丝。在含10mmol／L的其他单个氨基酸的SD液体培养基中可见混合的酵母和菌丝结构。在不含氨基酸或含各种天然氨基酸的SD固体培养基上,白念珠菌的菌落均光滑。但在含10mmol／L的L-精氨酸固体培养基上,光滑的菌落周围可见小的突起,镜下可见菌丝。无氧条件下,无论有无碳源,含精氨酸的SD培养液中白念珠菌只能形成酵母细胞,生长部分受到抑制。结论精氨酸可以诱导白念珠菌菌丝形成,厌氧条件下精氨酸不能诱导白念珠菌菌丝形成。