Jean-Claude Frigon

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.

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.

The treatment of cheese whey wastewater by sequential anaerobic and aerobic steps in a single digester at pilot scale

The treatment of reconstituted whey wastewater was performed in a 400 L digester at 20 degrees C, with an anaerobic digestion step, followed by a step of aerobic treatment at low oxygen concentration in the same digester. In a first set of 48 cycles, total cycle time (T(C)) of 2, 3 and 4 days were tested at varying organic loading rates (OLR). The COD removal reached 89+/-4, 97+/-3 and 98+/-2% at T(C) of 2, 3 and 4 days and OLR of 0.56, 1.04 and 0.78 g COD L(-1) d(-1), respectively. The activity of the biomass decreased for the methanogenic population, while increasing by 400% for the acidogens, demonstrating a displacement in the predominant trophic group in the biomass bed. A second set of 16 cycles was performed with higher soluble oxygen concentration in the bulk liquid (0.5 mg L(-1)) during the aerobic treatment at a T(C) of 2 days and an OLR of 1.55 g COD L(-1) d(-1), with a soluble COD removal of 88+/-3%. The biomass specific activities showed a compartmentalization of the trophic group with methanogenic activity maintained in the biomass bed and a high acidogenic activity in the suspended flocs.

Impact of liquid-to-gas hydrogen mass transfer on substrate conversion efficiency of an upflow anaerobic sludge bed and filter reactor.

Abstract Efficient anaerobic degradation may be completed only under low levels of dissolved hydrogen in the liquid surrounding the microorganisms. This restraint can be intensified by the limitations of liquid-to-gas H 2 mass transfer, which results in H 2 accumulation in the bulk liquid of the reactor. Dissolved hydrogen proved to be an interesting parameter for reactor monitoring by showing a good correlation with short-chain volatile fatty acid concentration, namely propionate, which was not the case for the H 2 partial pressure. Biogas recycle was performed in a upflow anaerobic sludge bed and filter reactor. The effects of varying the ratio of recycled-to-produced gas from 2:1 (9 l/l reactor per day) to 8:1 (85 l/l reactor per day) were studied. By increasing the liquid—gas interface with biogas recycling, the dissolved hydrogen concentration could be lowered from 1.1 to 0.4 μ m . Accordingly, the H 2 sursaturation factor was also reduced, leading to an important improvement of the H 2 mass transfer rate, which reached 20.86 h −1 (±9.79) at a 8:1 gas recycling ratio, compared to 0.72 h −1 (±0.24) for the control experiment. Gas recycling also lowered the propionate concentration from 655 to 288 mg l −1 and improved the soluble chemical oxygen demand removal by 10–15%. The main problem encountered was the shorter solid retention time, which could lead to undesirable biomass washout at high gas recycling ratio. This could be circumvented by improving the reactor design to reduce the turbulence within the biomass bed.

Combining photolysis and bioprocesses for mineralization of high molecular weight polyacrylamides.

The influence of ultraviolet photolysis as a pretreatment to the aerobic and anaerobic biological mineralization of a 14C-polyacrylamide was assessed using a series of radiorespirometry bioassays. The polyacrylamide studied was non-ionic with molecular weights ranging between 100,000 and 1 million. Aerobic and anaerobic biomineralization of the unphotolysed (raw) polyacrylamide was found to be only 0.60% and 0.70%, respectively, after 6 weeks of incubation, and hence indicative of the natural recalcitrance of polyacrylamide to microbial degradation. The effectiveness of UV irradiation in the physical breakdown of the polyacrylamide chain into oligomers was demonstrated by the shift in the molecular weight distribution and the positive correlation between the time of irradiation and the degree of its biological mineralization. The molecular weight fraction below 3 kD, which represents only 2% of the raw polyacrylamide, was increased to 41, 60 and 80% after 12, 24 and 48 hours of photolysis, respectively. This in turn, yielded, after 6 weeks of incubation, an aerobic mineralization of 5, 17 and 29% of 150 mg/L polyacrylamide, respectively, and an anaerobic mineralization of 3, 5 and 17%, respectively. Biomass acclimation substantially improved the specific initial rate of biomineralization of the photolysed polyacrylamides, but not the overall percentage of polyacrylamides mineralized.

Harmonization of the quantitative determination of volatile fatty acids profile in aqueous matrix samples by direct injection using gas chromatography and high-performance liquid chromatography techniques: Multi-laboratory validation study

The performance parameters of volatile fatty acids (VFAs) measurements were assessed for the first time by a multi-laboratory validation study among 13 laboratories. Two chromatographic techniques (GC and HPLC) and two quantification methods such as external and internal standard (ESTD/ISTD) were combined in three different methodologies GC/ESTD, HPLC/ESTD and GC/ISTD. Linearity evaluation of the calibration functions in a wide concentration range (10-1000mg/L) was carried out using different statistical parameters for the goodness of fit. Both chromatographic techniques were considered similarly accurate. The use of GC/ISTD, despite showing similar analytical performance to the other methodologies, can be considered useful for the harmonization of VFAs analytical methodology taking into account the normalization of slope values used for the calculation of VFAs concentrations. Acceptance criteria for VFAs performance parameters of the multi-laboratory validation study should be established as follows: (1) instrument precision (RSDINST≤1.5%); (2) linearity (R(2)≥0.998; RSDSENSITIVITY≤4%; REMAX≤8%; REAVER≤ 3%); (3) precision (RSD≤1.5%); (4) trueness (recovery of 97-103%); (5) LOD (≤3mg/L); and (6) LOQ (10mg/L).

Anaerobic Digestion as an Effective Biofuel Production Technology

The methane produced from the anaerobic digestion of organic wastes and energy crops represents an elegant and economical mean of generating renewable biofuel. Anaerobic digestion is a mature technology and is already used for the conversion of the organic fraction of municipal solid wastes and primary and secondary sludge from wastewater treatment plant. High methane yield up to 0.45 Nm3 CH4/kg volatile solids (VS) or 12,390 Nm3 CH4/ha can be achieved with sugar and starch crops, although these cultures are competing for high quality land with food and feed crops. The cultivation of lignocellulosic crops on marginal and set-aside lands is a more environmentally sound and sustainable option for renewable energy production. The methane yield obtained from these crops is lower, 0.17–0.39 Nm3 CH4/kg VS or 5,400 Nm3 CH4/ha, as its conversion into methane is facing the same initial barrier as for the production of ethanol, e.g., hydrolysis of the crops. Intensive research and development on efficient pretreatments is ongoing to optimize the net energy production, which is potentially greater than for liquid biofuels, since the whole substrate excepted lignin is convertible into methane. Algal biomass is another alternative to food and feed crops. Their relatively high methane potential (up to 0.45 Nm3 CH4/kg VS fed) combined with their higher areal biomass productivity make them particularly attractive as a feedstock for an anaerobic digestion-based biorefinery concept.

Acidogenic fermentation of Scenedesmus sp.-AMDD: Comparison of volatile fatty acids yields between mesophilic and thermophilic conditions

This study compared the acidogenic fermentation of Scenedesmus sp.-AMDD at laboratory-scale, under mesophilic (35°C) and thermophilic conditions (55°C). Preliminary batch tests were performed to evaluate best conditions for volatile fatty acid (VFA) production from microalgal biomass, with respect to the inoculum, pH and nutrients. The use of bovine manure as inoculum, the operating pH of 4.5 and the addition of a nutrient mix, resulted in a high VFA production of up to 222mgg(-1) total volatile solid (TVS), with a butyrate share of 27%. Both digesters displayed similar hydrolytic activity with 0.38±0.02 and 0.42±0.03 g soluble chemical oxygen demand (COD)g(-1) TVS for the digesters operated at 35 and 55°C, respectively. Mesophilic conditions were more favorable for VFA production, which reached 171±5, compared to 88±12 mg soluble CODg(-1) TVS added under thermophilic conditions (94% more). It was shown that in both digesters, butyrate was the predominant VFA.