Phytoremédiation d'eaux usées industrielles

Le projet de recherche porte sur le traitement et la valorisation de rejets aqueux industriels provenant de la production de biocarburants. L'objectif de ce projet est de proposer une solution innovatrice à la gestion de ces déchets. Par conséquent, l’utilisation de microalgues a été proposée et étudiée comme approche pour le traitement biologique d’effluents industriels et la production de biomasse algale. La phytoremédiation représente l’ensemble des techniques de traitement nécessitant des plantes afin de traiter divers polluants liquides, gazeux ou solides. Dans ce contexte, les microalgues font déjà l'objet de multiples études démontrant leur capacité à traiter des eaux usées municipales et industrielles. De plus, ces micro-organismes représentent une solution durable puisqu'ils sont naturellement aptes à assimiler plusieurs types de polluants, tout en accumulant des molécules d’intérêts. À cause de la complexité des effluents industriels, des études approfondies doivent être réalisées pour évaluer la faisabilité de cette approche ainsi que sa transposition vers des échelles supérieures. Contrairement aux procédés de traitements d’eaux usées conventionnels, la phytoremédiation est considérée comme étant une technologie d’épuration écologique, puisqu’elle requiert généralement moins de ressources énergétiques et de produits chimiques. En plus de contribuer au traitement d’effluents aqueux, les microalgues peuvent participer à la réduction des gaz à effet de serre lors du processus de photosynthèse, séquestrant ainsi le gaz carbonique anthropogénique tout en produisant de l’oxygène. Les travaux de recherche visent à déterminer les conditions de culture optimales (souches de microalgues, prétraitement des effluents, cycle de lumière, etc.) nécessaires au développement des microalgues et à la dépollution des différents substrats contaminés. La caractérisation de la biomasse algale permet ensuite de déterminer les diverses options de valorisation disponibles pour la production d’énergie ou de biocommodités. La première partie de l’étude se concentre sur le traitement d’eaux usées toxiques provenant d’une unité de gazéification (Westbury, QC) de déchets municipaux par la compagnie Enerkem. L’étude permet une meilleure compréhension sur le couplage d’un procédé d’oxydation avancée avec un procédé biologique par les microalgues. La deuxième partie porte sur la valorisation ii d’un effluent industriel généré lors de la production de bioéthanol de première génération à partir de maïs par la compagnie Greenfield Global (Varennes, QC). À l’aide d’un plan d’optimisation statistique en deux étapes, le traitement de l’effluent et la production de microalgues ont pu être maximisés. La troisième partie se consacre sur le traitement de jus de fermentation issus de la production de bioéthanol de seconde génération à partir d’écorce de bois. Dans cette étude, des consortiums de différents types d’algues ont été évalués pour dépolluer les effluents de fermentation et générer des produits à valeur ajoutée. L’ensemble de ces travaux contribuent à améliorer les connaissances à propos de la culture des microalgues appliquées à la dépollution d’effluents industriels. Ces travaux s’intègrent dans un contexte de bio-économie circulaire où les déchets sont considérés comme étant une matière première pour la production d’énergie et de produits d’intérêts tels que des antioxydants ou des pigmentes naturels

Thin stillage treatment and co-production of bio-commodities through finely tuned Chlorella vulgaris cultivation

Recent years marked the revitalization of microalgal phytoremediation efforts due to the promise of converting organic-rich effluents into various biofuels and biocommodities, including potential CO 2 uptake. In this work, the phytoremediation potential and subsequent production of Chlorella vulgaris biomass containing high added-value metabolites were investigated using thin stillage effluent generated by a starch-based ethanol production plant. A fractional-factorial strategy was developed in order to reveal and understand the variables influencing the investigated process, followed by central composite and response surface methodologies for maximizing the desired outputs. Among process variables such as antibiotic addition, substrate sterilization, pH, light regimes and agitation speed, the latter three manifested the strongest effects on the microalgal proliferation and their phytoremediation efficiency. Further insights on desired process conditions were obtained targeting both maximal effluent treatment and microalgal commodities potentials with minimum operating costs. 85% of total carbon and all of the glycerol, organic acids and carbohydrates were consumed by the microalgae under reduced illumination, pH 6 and 290 rpm after 7 d of cultivation. The Chlorella vulgaris biomass was produced at a rate of 0.9 g/L/d manifesting a high protein content of 32% (w/w) together with 14% (w/w) of carbohydrates and 7% (w/w) of lipids. In addition, natural photosynthetic pigments were generated at a rate of 0.98 mg/L/d (total chlorophylls) and 0.19 mg/L/d (carotenoids). This work highlights the potential of a novel microalgae-based thin stillage phytoremediation process with simultaneous co-generation of high added-value metabolites

Treatment and valorization of municipal solid waste gasification effluent through a combined advanced oxidation – microalgal phytoremediation approach

Liquid effluents generated during the gasification process of municipal solid wastes (MSW) represent highly heterogenous and recalcitrant substrates, and thus require energy-intensive treatments prior to their discharge into the environment. However, these streams represent untapped carbon sources which can be converted, under the right conditions, to platform molecules, decreasing thus the elevated costs of current mitigation approaches. Thus, the present study describes a novel two-step chemical and biological effluent treatment process which co-generates microalgal biomass containing valuable functionalcomponents. The detoxification potential of ozone, ultrasonication and a combination of both of these advanced oxidation processes (AOPs) were initially evaluated using wastewater generated from scrubbing primary syngas produced from the gasification of MSW. The pretreated effluents were subsequentlyused to cultivate Chlorella vulgaris microalgae under various illumination (light/dark cycles of 24h/0h, 12h/12h and 0h/24h) and nutrient (supplementation of yeast extract) regimes, in order to assess theirpotential to further convert the remaining carbon into value-added functional biomolecules, such as photosynthetic pigments. The use of ozone, either individually or combined with ultrasounds, showed the best performances for the substrate detoxification prior to the biological treatment step. It was determined that 20 min of oxidative reaction using ozone coupled with ultrasounds was sufficient to degrade up to 70% of the total phenol compounds, 64% of the COD, and 75% of the color initially present in the gasification wastewater. The further microalgal phytoremediation and conversion experiments showed that 12 h of illumination per day, together with 0.5 g/L of yeast extract, generated the highestmicroalgae growth rate (0.29 d 1), biomass productivity (244 mg/L/d), photosynthetic pigment accumulation (12.0 and 4.5 mg/L of total chlorophyll and carotenoids, respectively) as well as total carbonremoval (57 %). Therefore, the combination of AOPs with mixotrophic cultivation of C. vulgaris demonstrates for the first time an alternative to current treatment strategies of highly-recalcitrant industrial wastewaters, which includes the further valorization of the carbon available in these streams

A two-step optimization strategy for 2nd generation ethanol production using softwood hemicellulosic hydrolysate as fermentation substrate

Ethanol production using waste biomass represents a very attractive approach. However, there are considerable challenges preventing a wide distribution of these novel technologies. Thus, a fractional-factorial screening of process variables and Saccharomyces cerevisiae yeast inoculum conditions was performed using a synthetic fermentation media. Subsequently, a response-surface methodology was developed for maximizing ethanol yields using a hemicellulosic solution generated through the chemical hydrolysis of steam treatment broth obtained from residual softwood biomass. In addition, nutrient supplementation using starch-based ethanol production by-products was investigated. An ethanol yield of 74.27% of the theoretical maximum was observed for an initial concentration of 65.17 g/L total monomeric sugars. The two-step experimental strategy used in this work represents the first successful attempt to developed and use a model to make predictions regarding the optimal ethanol production using both softwood feedstock residues as well as 1st generation ethanol production by-products

High-efficiency second generation ethanol from the hemicellulosic fraction of softwood chips mixed with construction and demolition residues

Using lignocellulosic residues for bioethanol production could provide an alternative solution to current approaches at competitive costs once challenges related to substrate recalcitrance, process complexity and limited knowledge are overcome. Thus, the impact of different process variables on the ethanol production by Saccharomyces cerevisiae using the hemicellulosic fraction extracted through the steam-treatment of softwood chips mixed with construction and demolition residues was assessed. A statistical design of experiments approach was developed and implemented in order to identify the influencing factors (various nutrient addition sources as well as yeast inoculum growth conditions and inoculation strategies) relevant for enhancing the ethanol production potential and substrate uptake. Ethanol yields of 74.12% and monomeric sugar uptakes of 82.12 g/L were predicted and experimentally confirmed in bench and bioreactor systems. This innovative approach revealed the factors impacting the ethanol yields and carbohydrate consumption allowing powerful behavioral predictions spanning different process inputs and outputs

Transitioning Towards a Circular Economy in Québec : An Integrated Process for First-, Second- and Third-Generation Ethanol from Sweet Sorghum and Chlorella vulgaris Biomass

Full feedstock potential needs to be tapped to make lignocellulosic ethanol an economically viable reality. This work focuses on the Saccharomyces cerevisiae ethanol fermentation of fresh sorghum carbohydrates extracted through a mild steam-treatment process, and the subsequent Chlorella vulgaris cultivation using the generated liquid and gaseous fermentation effluents. The first section of the manuscript focuses on the effect of nutrient addition (fermentation effluent, yeast extract and urea) on the conversion efficiency of the sorghum carbohydrates to ethanol. Overall, the fermentation time was reduced to half when yeast extract and urea were supplemented to the free and hemicellulosic carbohydrate stream, accelerating the total sugar consumption time from 24 h to under 12 h. However, regarding the cellulosic carbohydrate hydrolysate, the sole addition of urea resulted in a slight improvement of the fermentation kinetics. The second half of the manuscript presents the impact of these different fermentation effluents and various process parameters (addition of yeast extract, antibiotic and CO2) on the microalgal cultivation and composition. The cellulosic hydrolysate yielded the highest concentrations of microalgal carbohydrates (507 mg/L) under a CO2-rich environment. Further cultivation scale-up assays confirmed these observations in the presence of 10% CO2 using the mixed fermentation effluents of the free and constitutive sorghum carbohydrates. Thus, an integrated sorghum-based first- (free carbohydrates), second- (constitutive carbohydrates) and third-generation (microalgal carbohydrates) ethanol production process was thoroughly investigated. This work could represent a step towards bridging the gap leading to full-scale commercialization of these advanced-biofuel technologies

Phytoremediation of bark-hydrolysate fermentation effluents and bioaccumulation of added-value molecules by designed microalgal consortia

Recent years marked an increased focus towards the valorization of biorefinery side-streams for the production of various high added-value molecules and platform chemicals. The present study tackles the opportunity of using liquid ethanol fermentation effluents of bark hydrolysates for microalgal conversion to various marketable molecules. Initially, 12 green microalgae strains were screened for their ability to thrive on these substrates and uptake some of the available organic compounds. Once the most suitable strains were identified, three mixed microalgal consortia were formulated and investigated in order to maximize, either individually or both simultaneously, their biomass production and phytoremediation performances. For instance, the consortium α containing Scenedesmus obliquus, Acutodesmus obliquus, Chlorella sorokiniana and Chlorella vulgaris strains was able to consume up to 70% of C5 sugars (xylose and arabinose) and 60% of C6 sugars (fucose and hexose). The uptake of these organic compounds initially present in the fermentation effluent accounted for the removal of 27% of the total organic carbon. In addition, the microalgal community produced 55 mg/L/d, 41 mg/L/d and 26 mg/L/d of carbohydrates, lipids and proteins respectively. The photosynthetic pigments accumulated in the harvested biomass comprised of 25.8 mg/L of total chlorophyll and 5.9 mg/L of carotenoids. Finally, the pyrolysis characteristics of the algal biomass were evaluated trough thermogravimetric analysis and the elemental composition was compared with conventional lignocellulosic feedstocks. Thus, this work proves the dual opportunity of both reducing the toxicity of lignocellulosic ethanol fermentation effluents as well as generating high-value biomass by employing specifically-designed microalgal populations

High-Gravity Fermentation for Bioethanol Production from Industrial Spent Black Cherry Brine Supplemented with Whey

By-products from different industries could represent an available source of carbon and nitrogen which could be used for bioethanol production using conventional Saccharomyces cerevisiae yeast. Spent cherry brine and whey are acid food by-products which have a high organic matter content and toxic compounds, and their discharges represent significant environmental and economic challenges. In this study, different combinations of urea, yeast concentrations, and whey as a nutrient source were tested for bioethanol production scale-up using 96-well microplates as well as 7.5 L to 100 L bioreactors. For bioethanol production in vials, the addition of urea allowed increasing the bioethanol yield by about 10%. Bioethanol production in the 7.5 L and 100 L bioreactors was 73.2 g·L−1 and 103.5 g·L−1 with a sugar consumption of 81.5% and 94.8%, respectively, using spent cherry brine diluted into whey (200 g·L−1 of total sugars) supplemented with 0.5 g·L−1 urea and 0.5 g·L−1 yeast at 30 °C and a pH of 5.0 after 96 h of fermentation for both systems. The results allow these by-products to be considered low-economic-value alternatives for fuel- or food-grade bioethanol production

Single-stage extraction of whole sorghum extractives and hemicelluloses followed by their conversion to ethanol

Maximizing the extracted carbohydrates from lignocellulosic biomass represents one critical step towards a wide implementation of industrial-scale second-generation ethanol production. To this purpose, a novel steam-based treatment strategy targeting the whole sweet sorghum biomass was developed. This extraction was followed by a non-enzymatic hydrolysis of the hemicellulose fraction and ethanol fermentation. By doing so, both the free carbohydrates present in the plant stems as well as the hemicelluloses trapped inside the various structural components were recovered and converted. A statistical design of experiments (DoE) approach was developed to investigate the most suitable steam-treatment severity to maximize the recovery of these carbohydrates while simultaneously minimizing the production of fermentation inhibitors. The severity of the treatment was estimated from the combined effects of temperature (150 °C – 210 °C) and cooking time (1–7 min). The optimal treatment conditions identified in this work (3 min retention time at 180 °C) successfully allowed recovering 30% of monomeric carbohydrates (based on sorghum dry weight). Three of the most efficient steam-explosion severities were investigated further in order to evaluate their impact on the subsequent ethanol fermentation using Saccharomyces cerevisiae yeast. A maximum ethanol yield of above 95% was achieved using the mixed carbohydrate streams recovered using the optimal steam-based extraction conditions. Thus, the present work thoroughly describes for the first time and to the best of our knowledge, a single-stage recovery of sorghum extractives and hemicelluloses, followed by their efficient fermentation to ethanol

Treatment and Valorization of Agro-Industrial Anaerobic Digestate Using Activated Carbon Followed by Spirulina platensis Cultivation

International audienceThe increased production of biogas through the anaerobic digestion (AD) process has raised several concerns regarding the management of liquid digestate, which can present some environmental risks if not properly handled. Among the different techniques to treat AD digestate, microalgae and cyanobacteria cultivation has emerged as a sustainable approach to valorizing digestate while producing valuable biomass for production of biofuels and high value bioproducts. However, the intrinsic parameters of the liquid digestate can strongly limit the microalgae or cyanobacteria growth as well as limit the uptake of residual nutrients. In this study, the detoxification potential of activated carbon (AC) was evaluated on agro-industrial liquid digestate prior to Spirulina platensis cultivation. Different doses of AC, ranging from 5 to 100 g/L, were tested during adsorption experiments in order to determine the adsorption capacity as well as the removal efficiency of several compounds. Experimental results showed the high reactivity of AC, especially towards phosphate (PO4-P), total phenol (TP) and chemical oxygen demand (COD). At a dosage of 50 g/L, the AC pretreatment successfully achieved 54.7%, 84.7% and 50.0% COD, TP and PO4-P removal, corresponding to adsorption capacity of 94.7 mgDCO/g, 17.9 mgTP/g and 8.7 mgPO4-P/g, respectively. Even if the AC pretreatment did not show significant effects on Spirulina platensis growth during toxicity assays, the AC adsorption step strongly participated in the digestate detoxification by removing hardly biodegradable molecules such as phenolic compounds