Rune Bakke

Biofilm thickness measurements by light microscopy

Abstract Light microscopy has been used to measure biofilm thickness. The vertical displacement of the sample required to focus from the biofilm-liquid interface to the biofilm-substratum interface is measured by the stage micrometer. Biofilm thickness is proportional, but not equal, to the measured vertical displacement. An expression for the proportionality constant, kf, in terms of refractive indices is determined from a geometric analysis of the light path. kf can be estimated as the ratio of the refractive index of the film to the refractive index of the media interfacing the film between the objective lens and the sample. The thickness of any transparent film may be determined by light microscopy when the refractive index of the film is known.

Oxygen Effects in Anaerobic Digestion – A Review

This article reviews the experimental and theoretical studies conducted on the possible effects of oxygen in biogas generating anaerobic digesters. The interactions of oxygen with various biochemical processes associated with anaerobic digestion are discussed together with other relevant aspects. The conventional perception of oxygen being merely toxic in anaerobic digestion (AD) is refuted. Digesters can withstand significant levels of oxygenation without drastic negative impacts. Limited quantities of oxygen can even lead to improved AD reactor performance under certain operating conditions. Co-existence of anaerobic and aerobic cultures in a single bioreactor environment has been demonstrated. It is shown that the partial aeration assisted AD can serve as a beneficial treatment strategy for simultaneous waste treatment and energy generation, for a multitude of organic waste categories.

Quantification of biofilm accumulation by an optical approach

Methods for non-invasive, in situ, measurements of biofilm optical density and biofilm optical thickness were evaluated based on Pseudomonas aeruginosa experiments. Biofilm optical density, measured as intensity reduction of a light beam transmitted through the biofilm, correlates with biofilm mass, measured as total carbon and as cell mass. The method is more sensitive and less labor intensive than other commonly used methods for determining extent of biofilm mass accumulation. Biofilm optical thickness, measured by light microscopy, is translated into physical thickness based on biofilm refraction measurements. Biofilm refractive index was found to be close to the refractive index of water. The P. aeruginosa biofilms studied reached a pseudo steady state in less than a week, with stable liquid phase substrate, cell and TOC concentrations and average biofilm thickness. True steady state was, however, not reached as both biofilm density and roughness were still increasing after 3 weeks.

Biofilm removal by low concentrations of hydrogen peroxide.

A micro‐annular reactor (MAR) was developed for studying biofilm processes. It is simple to operate under pure culture conditions and allows easy, non‐invasive monitoring of biofilm accumulation. Two marine bacteria were investigated which formed biofilms under conditions of continuous flow and during batch growth in rich media. Exposure of biofilms to low levels of hydrogen peroxide (1–5 mM) and ferric ions (0·03–0·1 mM) led to their detachment and removal, even though the growth of free cells was not totally inhibited under these conditions, and new biofilms formed readily upon introducing fresh medium. Repeated treatments of the same biofilm with hydrogen peroxide resulted however, in progressively less biofilm removal. The results show that biofilm removal can be accomplished with hydrogen peroxide at levels well below those required for total disinfection and point to a mechanism where the extracellular biopolymer matrix is degraded rather than intracellular components.

Oil reservoir biofouling control

The potential tocontrol biological activity in reservoirs through removal of sulphate from the injection water is evaluated theoretically and experimentally in this study. A sandstone core and a transparent glass cell with an etched pore pattern (2‐D cell) were used as porous media, and these were continuously flooded with lactate‐containing sea water. Biological activity was studied by microscopy of the glass cell and through lactate and sulphide analyses of the effluent from the sandstone core. Reduction in permeability was registered as pressure across the cells. The results indicate that limitation of sulphate in the injection water may lead to increase in permeability in porous media. The souring problem may also be reduced through reduction of sulphate load on porous formations. Sulphate can be efficiently removed from sea water through nano‐filtration (membrane technology), thereby reducing the potential for hydrogen sulphide generation from more than 500 ppm to less than 19 ppm. The potential for ...

Anaerobic degradation of carbon capture reclaimer MEA waste

The anaerobic biodegradation of reclaimer MEA (monoethanolamine) waste (MEAw) with easily degradable co-substrates was investigated in a laboratory-scale bioreactor at room temperature during a 160 d experimental run. The reactor that was constructed with three phases to facilitate attached biofilm and suspended biomass retention for degradation of the complex and challenging MEAw performed well. A feed strategy of step-wise increasing organic loading rate (OLR) by either increasing feed MEAw concentration or the hydraulic loading rate was applied. The system performance was evaluated by chemical oxygen demand (COD) removal efficiency, methane yield, MEA removal, and the accumulation of ammonia and volatile fatty acid (VFA). The total COD removal efficiency initially was 93% when the feed was mainly easily degradable co-substrate. The total removal dropped to 75% at the end when MEAw constituted 60% of the feed COD. Ion chromatography results show that the MEA and some unidentified feed chemicals were almost completely consumed. The main products of MEAw degradation were ammonia, VFAs and biogas. The ammonia nitrogen concentration reached about 2.0 g/L, which may explain the observed inhibition of acetoclastic methanogenesis leading to acetate accumulation. Methane accounted for up to 80% of the biogas generated. The highest methane yield was 0.34 L/g-COD while the yield was 0.16 L/g-COD at the highest load. This study shows that more than 80% reclaimer MEAw COD degradation with a co-substrate can be maintained in a hybrid anaerobic bioreactor operated in a wide loading range.

A new method for polyhydroxyalkanoate (PHA) accumulating bacteria selection under physical selective pressure.

An aerobic dynamic discharge (ADD) process involving physical selective pressure to favor the accumulation of polyhydroxyalkanoates (PHAs) accumulating bacteria in microbial mixed cultures (MMCs) is proposed and evaluated in this study. Sequencing batch reactor PHA production in the ADD mode was compared to the conventional aerobic dynamic feeding (ADF) mode. Results showed that the cultures selected under the ADD mode showed a better PHA producing potential than ADF mode cultures in terms of both maximum PHA content and selection time, explained by altered physical selective pressure. The maximum PHA content of 74.16 (± 0.03)% and PHA yield of 0.72 (± 0.07) C mol PHA/C mol Ac were achieved after 30 days of the ADD operation, which were much higher than those obtained under the same organic loading rate in the ADF operation. The ADD mode is a promising method for quick selection of a strong-PHA accumulating culture.

State estimation and model-based control of a pilot anaerobic digestion reactor

A state estimator and various model-based control systems have been designed for a real anaerobic digestion (AD) pilot reactor fed with dairy manure. The model used is a modified Hill model which is a relatively simple dynamical AD process model. The state estimator is an Unscented Kalman Filter (UKF) which uses only methane gas flow measurement to update its states. The model and the state estimates are used in different control systems. One of the control systems aims at controlling the methane gas flow to a setpoint. Simulations indicate that the setpoint tracking performance of a predictive control system is considerably better comparing with PI control, while disturbance compensation is not much better. Consequently, assuming the setpoint is constant, the PI controller competes well with the predictive controller. A successful application of predictive control of the real reactor is presented. Also, three different control systems aiming at retaining the reactor at an operating point where the volatile fatty acids (VFA) concentration has a maximum, safe value are designed. A simulation study indicates that the best control solution among the three alternatives is PI control based on feedback from estimated VFA.

Metabolic divergence in simultaneous biological removal of nitrate and sulfide for elemental sulfur production under temperature stress

The simultaneous removal of NO3- and HS- at temperature stress (25-10°C) is evaluated here. An expanded granular sludge bed (EGSB) reactor was run over 120days at N/S molar ratio of 0.35 (for S0 production) under constant sulfur loading rate of 0.4kgS/m3d. The simultaneous removal of NO3- and HS-, was achieved at applied conditions. Average HS--S removal varied from 98 (25°C) to 89.2% at 10°C, with almost complete NO3- removal. Average S0 yield ranged from 83.7 at 25°C to 67% at 10°C. The temperature drop caused a decrease in granular sludge accumulated S0 fraction by nearly 2.5 times. Decreased temperature caused metabolic pathway change observed as higher SO42- production, apparently allowing the biomass to obtain more energy per HS- consumed. It is hypothesized that the metabolic shift is a natural response to compensate for temperature-induced changes in energy requirements.

Biogasification of Waste Monoethanolamine Generated in Post Combustion CO2 Capture

Publisher Summary This chapter intends to investigate the suitable operating conditions for converting waste Monoethanolamine (MEA) into a CH4 rich biogas through anaerobic biogasification. MEA contaminated liquid waste generated in post combustion CO2 captures poses a disposal issue. Anaerobic biogasification potential of waste MEA is evaluated in a series of laboratory experiments conducted under different operating conditions. Provision of a limited amount of oxygen may enhance the methane potential of waste MEA. Codigestion of MEA together with a readily biodegradable substrate is found to be a solution to overcome ammonia and pH inhibition caused by low C/N ratio and high alkalinity. Substrate inhibition caused by waste MEA can be overcome by acclimatization. MEA degradation pathways via acetic and ammonium, with and without oxygen, are included in an anaerobic digestion model (ADM 1-Ox). MEA degradation to methane by anaerobic digestion with no or small quantities of free oxygen is adequately predicted by model simulations. Micro-aeration has a favorable effect on the methane generation potential. A cosubstrate approach is required to obtain stable biogasification of waste MEA in a continuous flow reactor, in order to increase the low C/N ratios typical for amine wastes and hence to avoid the ammonia and pH inhibition.