Serge R. Guiot

Integration of microalgae cultivation with industrial waste remediation for biofuel and bioenergy production: opportunities and limitations

There is currently a renewed interest in developing microalgae as a source of renewable energy and fuel. Microalgae hold great potential as a source of biomass for the production of energy and fungible liquid transportation fuels. However, the technologies required for large-scale cultivation, processing, and conversion of microalgal biomass to energy products are underdeveloped. Microalgae offer several advantages over traditional ‘first-generation’ biofuels crops like corn: these include superior biomass productivity, the ability to grow on poor-quality land unsuitable for agriculture, and the potential for sustainable growth by extracting macro- and micronutrients from wastewater and industrial flue-stack emissions. Integrating microalgal cultivation with municipal wastewater treatment and industrial CO2 emissions from coal-fired power plants is a potential strategy to produce large quantities of biomass, and represents an opportunity to develop, test, and optimize the necessary technologies to make microalgal biofuels more cost-effective and efficient. However, many constraints on the eventual deployment of this technology must be taken into consideration and mitigating strategies developed before large scale microalgal cultivation can become a reality. As a strategy for CO2 biomitigation from industrial point source emitters, microalgal cultivation can be limited by the availability of land, light, and other nutrients like N and P. Effective removal of N and P from municipal wastewater is limited by the processing capacity of available microalgal cultivation systems. Strategies to mitigate against the constraints are discussed.

Genomic Analysis of Carbon Monoxide Utilization and Butanol Production by Clostridium carboxidivorans Strain P7T

Increasing demand for the production of renewable fuels has recently generated a particular interest in microbial production of butanol. Anaerobic bacteria, such as Clostridium spp., can naturally convert carbohydrates into a variety of primary products, including alcohols like butanol. The genetics of microorganisms like Clostridium acetobutylicum have been well studied and their solvent-producing metabolic pathways characterized. In contrast, less is known about the genetics of Clostridium spp. capable of converting syngas or its individual components into solvents. In this study, the type of strain of a new solventogenic Clostridium species, C. carboxidivorans, was genetically characterized by genome sequencing. C. carboxidivorans strain P7(T) possessed a complete Wood-Ljungdahl pathway gene cluster, involving CO and CO(2) fixation and conversion to acetyl-CoA. Moreover, with the exception of an acetone production pathway, all the genetic determinants of canonical ABE metabolic pathways for acetate, butyrate, ethanol and butanol production were present in the P7(T) chromosome. The functionality of these pathways was also confirmed by growth of P7(T) on CO and production of CO(2) as well as volatile fatty acids (acetate and butyrate) and solvents (ethanol and butanol). P7(T) was also found to harbour a 19 Kbp plasmid, which did not include essential or butanol production related genes. This study has generated in depth knowledge of the P7(T) genome, which will be helpful in developing metabolic engineering strategies to improve C. carboxidivoranss natural capacity to produce potential biofuels from syngas.

Long-term impact of dissolved O2 on the activity of anaerobic granules

The impact of influent dissolved O2 on the characteristics of anaerobic granular sludge was investigated at various dissolved O2 concentrations (0.5–8.1 ppm) in 1‐ and 5‐L laboratory‐scale upflow anaerobic sludge bed (UASB)‐like anaerobic/aerobic coupled reactors with a synthetic wastewater (carbon sources containing 75% sucrose and 25% acetate). The rate of dissolved O2 supplied to the coupled reactor was as high as 0.40 g O2/Lrx·d, and the anaerobic/aerobic coupled reactors maintained excellent methanogenic performances at a COD loading rate of 3 g COD/Lrx·d even after the reactors had been operated with dissolved O2 for 3 months. The activities of granular sludge on various substrates (glucose, propionate, and hydrogen) were not impaired, and acetate activity was even improved over a short term. However, after 3 months of operation, slight declines on the acetoclastic activities of granules were observed in the coupled reactor receiving the recirculated fluid containing 8.1 ppm dissolved O2.

Enhanced Biodegradation of Petroleum Hydrocarbons in Contaminated Soil

Soil samples taken from a contaminated site in Northern Quebec, Canada, exhibited a low capacity for biodegradation of total petroleum hydrocarbons (TPH), despite a high capacity for the mineralization of aromatic hydrocarbons and a low toxicity of soil leachates as measured by Microtox assay. Toxicity assays directly performed on surface soil, including earthworm mortality and barley seedling emergence, indicated moderate to high levels of toxicity. Soil biostimulation did not improve the removal of petroleum hydrocarbons, while bioaugmentation of soil with a developed enrichment culture increased the efficiency of hydrocarbon removal from 20.4% to 49.2%. A considerable increase in the removal of TPH was obtained in a bioslurry process, enhancing the mass transfer of hydrocarbons from soil to the aqueous phase and increasing the efficiency of hydrocarbon removal to over 70% after 45 days of incubation. The addition of ionic or nonionic surfactants did not have a significant impact on biodegradation of hydrocarbons. The extent of hydrocarbon mineralization during the bioslurry process after 45 days of incubation ranged from 41.3% to 58.9%, indicating that 62.7% to 83.1% of the eliminated TPH were transformed into CO2 and water.

Solubility of pentachlorophenol in aqueous solutions : the pH effect

Abstract As indicated in most literature reports, the solubility of pentachlorophenol (PCP) in water ranges between 10 and 20 mg l−1. Since PCP is a weak acid (pKa 4.35), its solubility increases drastically with increasing pH. When PCP dissolves in water two forms are normally present: undissociated PCP (PCP°) and a dissociated anionic form, i.e. pentachlorophenolate (PCP−). Both forms differ in their physico-chemical properties and in their microbial response and toxicity. It is therefore important to know the solubility behaviour of PCP at specific pHs when working with site remediation and toxicity assessment. While anionic PCP is very soluble, experimental data have shown that undissociated PCP has a solubility limited to 10 μM (3 mg l−1). Theoretical calculations have confirmed this value to be independent of the solutions pH. A non-empirical model was developed for estimating the “total” PCP aqueous solubility at different pHs using the standard solubility value and PCPs dissociation constant. The method may be extended to other chlorophenols and to most wastewaters.

The effect of real-time external resistance optimization on microbial fuel cell performance

This work evaluates the impact of the external resistance (electrical load) on the long-term performance of a microbial fuel cell (MFC) and demonstrates the real-time optimization of the external resistance. For this purpose, acetate-fed MFCs were operated at external resistances, which were above, below, or equal to the internal resistance of a corresponding MFC. A perturbation/observation algorithm was used for the real-time optimal selection of the external resistance. MFC operation at the optimal external resistance resulted in increased power output, improved Coulombic efficiency, and low methane production. Furthermore, the efficiency of the perturbation/observation algorithm for maximizing long-term MFC performance was confirmed by operating an MFC fed with synthetic wastewater for over 40 days. In this test an average Coulombic efficiency of 29% was achieved.

Potential of wastewater-treating anaerobic granules for biomethanation of synthesis gas.

Gasification of biomass produces a mixture of gas (mainly carbon monoxide (CO), carbon dioxide (CO(2)), and hydrogen (H(2))) called synthesis gas, or syngas, by thermal degradation without combustion. Syngas can be used for heat or electricity production by thermochemical processes. This project aims at developing an alternative way to bioupgrade syngas into biogas (mainly methane), via anaerobic fermentation. Nonacclimated industrial granular sludge to be used as reactor inoculum was initially evaluated for mesophilic carboxydotrophic methanogenesis potential in batch tests at 4 and 8 mmol CO/g VSS.d, in the absence and presence of H(2) and CO(2), respectively. Granular sludge was then introduced into a 30 L gas-lift reactor and supplied with CO, to study the production of methane and other metabolites, at different gas dilutions as well as feeding and recirculation rates. A maximal CO conversion efficiency of 75%, which was gas-liquid mass transfer limited, occurred at a CO partial pressure of 0.6 atm combined with a gas recirculation ratio of 20:1. The anaerobic granule potential for methanogenesis from CO was likely hydrogenotrophic, combined with CO-dependent H(2) formation, either under mesophilic or thermophilic conditions. Thermophilic conditions provide the anaerobic granules with a CO-bioconversion potential significantly larger (5-fold) than under mesophilic conditions, so long as the gas-liquid transfer is alleviated.

Electrolysis-enhanced anaerobic digestion of wastewater.

This study demonstrates enhanced methane production from wastewater in laboratory-scale anaerobic reactors equipped with electrodes for water electrolysis. The electrodes were installed in the reactor sludge bed and a voltage of 2.8-3.5 V was applied resulting in a continuous supply of oxygen and hydrogen. The oxygen created micro-aerobic conditions, which facilitated hydrolysis of synthetic wastewater and reduced the release of hydrogen sulfide to the biogas. A portion of the hydrogen produced electrolytically escaped to the biogas improving its combustion properties, while another part was converted to methane by hydrogenotrophic methanogens, increasing the net methane production. The presence of oxygen in the biogas was minimized by limiting the applied voltage. At a volumetric energy consumption of 0.2-0.3 Wh/L(R), successful treatment of both low and high strength synthetic wastewaters was demonstrated. Methane production was increased by 10-25% and reactor stability was improved in comparison to a conventional anaerobic reactor.

Enhancing solubilisation and methane production kinetic of switchgrass by microwave pretreatment

This study investigated the effects of microwave pretreatment of switchgrass in order to enhance its anaerobic digestibility. Response surface analysis was applied to screen the effects of temperature and time of microwave pretreatment on matter solubilisation. The composite design showed that only temperature had a significant effect on solubilisation level. Then the effects of the microwave pretreatment were correlated to the pretreatment temperature. The sCOD/tCOD ratio was equal to 9.4% at 90°C and increased until 13.8% at 180°C. The BMP assays of 42 days showed that microwave pretreatment induced no change on the ultimate volume of methane but had an interesting effect on the reaction kinetic. Indeed, the time required to reach 80% of ultimate volume CH(4) is reduced by 4.5 days at 150°C using the microwave pretreatment.

Impact of the reactor hydrodynamics and organic loading on the size and activity of anaerobic granules

Abstract Wastewater treatment processes based on the upflow anaerobic sludge bed design are strongly dependent on the aggregation of biomass into macroscopic granules (1–3 mm) which settle well. The reactor hydrodynamics is of importance in the granulation process. The effect of the liquid upflow velocity υ UP associated with the operating time on the mean granule size and on the hydrogen, formate, acetate, propionate and glucose specific activities was studied, at various specific loading rates, in upflow sludge bed and filter reactors of 13 l fed with sugar wastewater. Reactors which were operated at 0.9 m h −1 behaved as fixed beds while those run at 2.2, 4.4 and 6.6 m h −1 were fluidized, because an immediate spatial gradient of the sludge particle sizes was induced. The υ UP had a significant positive effect on mean granule size. A specific loading rate increase from 0.5 to 1.5 g chemical oxygen demand per gram of volatile suspended solids per day raised proportionally the biomass growth rate, but had no positive effect on the granule development in size. Moreover, the υ UP had little effect on the specific wash-out rate of the smaller particles. Henceforth the resulting final size of granules is essentially a function of the hydrodynamic regime. Major impact on granule net steady size is attributed to several mechanisms related to fluidization: improved penetration of substrates into biofilm; insignificance of liquid shear relative to the shear of gas; reduction of particle friction and attrition with the bed voidage. Acidogenic (glucotrophic) activity decreased with υ UP increased yielding minimum values at intermediate υ UP , between 2 and 5 m h −1 . Postacidogenic activities (propionate, acetate, formate, H 2 ) were positively influenced by υ UP to a slight extent. Glucose activity gradient within the granule bed was highly and inversely correlated to the granule size, while for acetate activity gradients, the correlation was direct, although less strong. These observations are discussed in detail with regard to an ordered distribution of the consortium populations within the granule spatial structure.