Design of Value Chains for Microalgal Biorefinery at Industrial Scale: Process Integration and Techno-Economic Analysis.

The objective of this work was to identify industrial scenarios for the most promising microalgal biorefinery value chains on the basis of product selection, yields, and techno-economic performance, using biological characteristics of algae species. The development, value creation, and validation of several new processing routes with applications in food, aquafeeds and non-food products were particularly considered in this work. The techno-economic performance of various single product value chains (SP) and multiproduct value chains (MP) was evaluated for four industrial microalgal strains. Cost-revenue optimization was done for a 10 kton microalgal dry weight y-1 simulated biorefinery plant, using flow sheeting software for equipment sizing, mass and energy flow modeling, and subsequent techno-economic evaluation. Data on yield, material and energy consumption were based on pre- and pilot size production plants (TRL 5-6). Revenue optimization was accomplished by first analyzing the performance of single product value chains of the microalgal strains. Subsequently, a strategy was developed to exploit almost all biomass based on the most promising microalgal strains. The cultivation costs are most of the time the major costs of the value chains. For the single product value chains common process bottlenecks are low product yields, especially for soluble proteins where only a small fraction of the biomass is leading to economic value. The biorefinery costs (excluding cultivation) vary significantly for various species, due to the species-specific operating conditions as well as differences in product yields. For the evaluated single product value chain scenarios the costs for utilities and other inputs were in general the highest contributing expenses. A biorefinery approach significantly increases the biomass utilization potential to marketable products from 7-28% to more than 97%. Although the cascading approach increases the total production costs of the multiproduct value chains significantly, this is more than compensated by the increased overall biomass revenue. For all selected multiproduct chains there is a significant potential to become profitable at a relevant industrial scale of 10 kton per year. Additional insights in the product functionality, quality, and their market size are needed to narrow down the wide range of foreseen product revenues and resulting profits.

Ethanol-based organosolv fractionation of wheat straw for the production of lignin and enzymatically digestible cellulose.

Wheat straw fractionation by ethanol organosolv was studied as pretreatment for enzymatic cellulose hydrolysis. A parametric study focusing on temperature, reaction time, acid catalyst dose, solvent concentration, and particle size was performed to determine their influence on delignification, xylan hydrolysis, and enzymatic cellulose digestibility. Major process parameters were found to be temperature, ethanol concentration, and acid dose. Optimisation of the process towards enzymatic digestibility resulted in a maximum glucose yield of 86% without the use of a catalyst (lignin yield 84%, organosolv at 210 °C, 50% w/w aqueous EtOH). Using 30 mM H2SO4 as catalyst resulted in similar glucose and lignin yields at a lower temperature (190 °C, 60% w/w aqueous EtOH). Lowering the pretreatment temperature by using an acid catalyst substantially improved the yield of the hemicellulose derivatives xylose and furfural. A systematic approach in pretreatment optimisation is vital for development of efficient lignocellulosic biorefineries.

Prediction of volumetric productivity of an outdoor photobioreactor.

Volumetric productivity of Monodus subterraneus cultivated in an outdoor pilot-plant bubble column was predicted with a mathematical model. Two border cases to model the photobioreactor were chosen. Firstly, a model with no light integration in which it is assumed that microalgae can adapt immediately to local light conditions. Secondly, full light integration implicating that microalga can convert all absorbed light with a photosynthetic yield based on average light intensity. Because temperature and light conditions in our photobioreactor changed during the day, photosynthetic yields at any combination of temperature and light intensity were needed. These were determined in repeated-batch lab-scale experiments with an experimental design. The model was evaluated in an outdoor bubble column at different natural light conditions and different temperatures. Volumetric productivities in the bubble column were predicted and compared with experimental volumetric productivities. The light integration model over-estimated productivity, while the model in which we assumed no light integration under-estimated productivity. Light integration occurred partly (47%) during the period investigated. The average observed biomass yield on light was 0.60 g.mol(-1). The model of partly light integration predicted an average biomass yield on light of 0.57 g.mol(-1) and predicted that productivity could have been increased by 19% if culture temperature would have been maintained at 24 degrees C.