Stillage Stream Research Articles

Dynamic and equilibrium precipitation of struvite from the concentrated cellulosic ethanol stillage.

The phosphate rock mineral is the main source of P-fertilizer production. It is estimated to become depleted in next century. Thus, the recovery of phosphorus from waste streams has attracted great interest. The cellulosic ethanol production is seen as more and more important in future. During the production of cellulosic ethanol, the phosphorus element is released from lignocellulosic biomasses and ends up dissolved as phosphate ions in the stillage stream. In this study, the struvite (MgNH4PO4 · 6 H2O) recovery from the concentrated cellulosic ethanol stillage (ES) was conducted under room conditions with an initial pH at 7-9. The effect of Mg2+, PO43-, NH4+ and Ca2+ during struvite precipitation tests was investigated. The optimized pH value for struvite recovery is estimated at 8.5, by which 85% of PO43- and 46% of Mg2+ are removed from the liquid stream. The mass fraction of struvite in recovered crystal sample reaches 82 wt.%. The economic evaluation of struvite recovery from ES was also investigated. This work proves that the struvite is potentially to be recovered with high purity from the concentrated cellulosic ethanol stillage.

Extractive Fermentation of Ethanol from Sweet Sorghum Using Vacuum Fractionation Technique: Optimization and Techno-Economic Assessment

Abstract Direct extraction of high purity ethanol from fermentation broth was investigated using a vacuum fractionation technique. Batch and repeated-batch extractive fermentation of ethanol were carried out using concentrated sweet sorghum as a carbon source. The effect of product inhibition was reduced by continuous removing ethanol from the fermented broth. About 60 % relative viability was observed in fermented broth with a higher productivity value. Due to the high value of living cells presented in the medium, repeated-batch extractive fermentation was subsequently performed. The ethanol was continuously fractionated out from the system at the average rate of 10.2 g/h with the concentration of approximately 80 wt%. There were 8 cycles of fermentation using only 1 time inoculation. Nevertheless, the calculated ethanol productivity and relative viability for each fermentation cycle were decreased gradually due to the accumulation of toxic substances in fermented broth. The simulation of 200 liters continuous extractive fermentation system using ASPEN PLUS was studied including process optimization and economical consideration. 18.5 liters of ethanol solutions 82 wt% with insignificant amounts of by-product was produced from a 200 liters extractive fermentation system per day. Production cost including raw material and utilities cost was approximately 0.71 €/liter. The economic and systemic performance process were subsequently analyzed, and including that ethanol loss was recovered using a gas scrubber connected to the vapor exiting the venturi tank as well as in the stillage stream. The calculated utility costs after process modification were 0.5 €/liter of ethanol, approximately 30 % of production cost was reduced.

Converting Chemical Oxygen Demand (COD) of Cellulosic Ethanol Fermentation Wastewater into Microbial Lipid by Oleaginous Yeast Trichosporon cutaneum.

Cellulosic ethanol fermentation wastewater is the stillage stream of distillation column of cellulosic ethanol fermentation broth with high chemical oxygen demand (COD). The COD is required to reduce before the wastewater is released or recycled. Without any pretreatment nor external nutrients, the cellulosic ethanol fermentation wastewater bioconversion by Trichosporon cutaneum ACCC 20271 was carried out for the first time. The major components of the wastewater including glucose, xylose, acetic acid, ethanol, and partial of phenolic compounds could be utilized by T. cutaneum ACCC 20271. In a 3-L bioreactor, 2.16g/L of microbial lipid accumulated with 55.05% of COD reduced after a 5-day culture of T. cutaneum ACCC 20271 in the wastewater. The fatty acid composition of the derived microbial lipid was similar with vegetable oil, in which it could be used as biodiesel production feedstock. This study will both solve the environmental problem and offer low-cost lipid feedstock for biodiesel production.

Simultaneous saccharification and fermentation process for ethanol production from steam-pretreated softwood: Recirculation of condensate streams

Wastewater from fuel ethanol production plant represents a considerable potential pollutant. Treatment is an essential operation in the overall conversion of lignocellulosic to ethanol. This significantly reduces the effluent volume, and reduces the need of fresh water. Present work concerns a simultaneous saccharification and fermentation (SSF) process for ethanol production from steam-pretreated softwood. Within this process, the effect of recirculation of the condensate from the evaporation of the stillage stream was investigated. The condensate employed in this study represents the condensate of four evaporators connected in series, with each evaporator producing a condensate corresponding to 14% of the process stream after distillation of the SSF broth. The investigation demonstrated that it was possible to replace 100% of the fresh water used in the process (except for the steam used in the pretreatment), by recirculation of all the condensate fractions together, without affecting the ethanol yield and the productivity in SSF. A significant factor was the absence of lactic acid production, which is sometimes observed when the pretreated material is diluted with fresh water. The prospect of using condensate to replace fresh water offers an attractive means of reducing the cost of wastewater management and thereby improving the overall economic feasibility of the process.

Nutrient recovery from the dry grind process using sequential micro and ultrafiltration of thin stillage

The effectiveness of microfiltration (MF) and ultrafiltration (UF) for nutrient recovery from a thin stillage stream was determined. When a stainless steel MF membrane (0.1 μm pore size) was used, the content of solids increased from 7.0% to 22.8% with a mean permeate flux rate of 45 L/m 2/h (LMH), fat increased and ash content decreased. UF experiments were conducted in batch mode under constant temperature and flow rate conditions. Permeate flux profiles were evaluated for regenerated cellulose membranes (YM1, YM10 and YM100) with molecular weight cut offs of 1, 10 and 100 kDa. UF increased total solids, protein and fat and decreased ash in retentate stream. When permeate streams from MF were subjected to UF, retentate total solids concentrations similar to those of commercial syrup (23–28.8%) were obtained. YM100 had the highest percent permeate flux decline (70% of initial flux) followed by YM10 and YM1 membranes. Sequential filtration improved permeate flux rates of the YM100 membrane (32.6–73.4 LMH) but the percent decline was also highest in a sequential MF + YM100 system. Protein recovery was the highest in YM1 retentate. Removal of solids, protein and fat from thin stillage may generate a permeate stream that may improve water removal efficiency and increase water recycling.

Polyelectrolyte flocculation of grain stillage for improved clarification and water recovery within bioethanol production facilities

Polyelectrolytes were investigated for flocculation of a corn whole stillage stream to improve solid–liquid clarification operations and reduce downstream utility requirements for evaporation and drying within a bioethanol process. Despite a negative zeta potential for the stillage solids, an anionic polyelectrolyte was found to provide the best flocculation. At the optimal dosage of 1.1 mg polymer/g dry suspended solids, an anionic flocculant provided a clarified stream with only 0.15% w/w suspended solids (equivalent to a total dissolved solid to total suspended solid ratio greater than 40, and a viscosity reduction of 39% compared to an unflocculated “clarified” stream). The resulting solids cake had greater than 40% w/w solids, and more than 80% water recovery was found in the clarified stream. Addition of flocculant improved filtration flux by six fold and/or would allow for up to a 4-times higher flow rate if using a decanting centrifuge for clarification of corn stillage.

Cellulase Production from Spent Lignocellulose Hydrolysates by Recombinant Aspergillus niger

A recombinant Aspergillus niger strain expressing the Hypocrea jecorina endoglucanase Cel7B was grown on spent hydrolysates (stillage) from sugarcane bagasse and spruce wood. The spent hydrolysates served as excellent growth media for the Cel7B-producing strain, A. niger D15[egI], which displayed higher endoglucanase activities in the spent hydrolysates than in standard medium with a comparable monosaccharide content (e.g., 2,100 nkat/ml in spent bagasse hydrolysate compared to 480 nkat/ml in standard glucose-based medium). In addition, A. niger D15[egI] was also able to consume or convert other lignocellulose-derived compounds, such as acetic acid, furan aldehydes, and phenolic compounds, which are recognized as inhibitors of yeast during ethanolic fermentation. The results indicate that enzymes can be produced from the stillage stream as a high-value coproduct in second-generation bioethanol plants in a way that also facilitates recirculation of process water.

Recirculation of process streams in fuel ethanol production from softwood based on simultaneous saccharification and fermentation.

The effect of process stream recirculation on ethanol production from steam- pretreated softwood based on simultaneous saccharification and fermentation (SSF) was investigated for two process configurations. In the first configuration, a part of the stillage stream after distillation was recycled and, in the second configuration, the liquid after SSF was recycled. The aim was to minimize the energy consumption in the distillation of the fermentation broth and in the evaporation of the stillage, as well as the use of fresh water. However, recirculation leads to an increased concentration of nonvolatiles in the first configuration, and of both volatiles and nonvolatiles in the second configuration. These substances might be inhibitory to the enzymes and the yeast in SSF. When 60% of the fresh water was replaced by stillage, the ethanol yield and the productivity were the same as for the configuration without recirculation. The ethanol production cost was reduced by 17%. In the second configuration, up to 40% of the fresh water could be replaced without affecting the final ethanol yield, although the initial ethanol productivity decreased. The ethanol production cost was reduced by 12%. At higher degrees of recirculation, fermentation was clearly inhibited, resulting in a decrease in ethanol yield while hydrolysis seemed unaffected.

Recycling of process streams in ethanol production from softwoods based on enzymatic hydrolysis

In ethanol production from lignocellulose by enzymatic hydrolysis and fermentation, it is desirable to minimize addition of fresh-water and waste-water streams, which leads to an accumulation of substances in the process. This study shows that the amount of fresh water used and the amount of waste water thereby produced in the production of fuel ethanol from softwood, can be reduced to a large extent by recycling of either the stillage stream or part of the liquid stream from the fermenter. A reduction in fresh-water demand of more than 50%, from 3 kg/kg dry raw material to 1.5 kg/kg dry raw material was obtained without any negative effects on either hydrolysis or fermentation. A further decrease in the amount of fresh water, to one-fourth of what was used without recycling of process streams, resulted in a considerable decrease in the ethanol productivity and a slight decrease in the ethanol yield.

Recirculation of process water in the production of ethanol from softwood

In the production of ethanol from lignocellulosics, large quantities of water are needed in various process steps. In industrial processes, recycling of process streams is necessary to minimise fresh water requirements and decrease the amount of wastewater produced. This leads to increases in various substances, both volatile and non-volatile, which inhibit fermentation. In the present study ethanol was produced from softwood in a bench-scale process development unit. The stillage stream from the distillation step was fractionated by evaporation and various evaporation fractions characterised and their inhibitory effect on fermentation investigated. It was found that the volatile fractions have no negative effect on the fermentation, while the non-volatile fraction inhibited fermentation and resulted in a decreased yield. Simulation of a six-effect evaporation unit based on the experimental data shows that the intermediate evaporation condensate fractions are most suited for disposal. The chemical and biological oxygen demands are only about 10% of the value in the stillage stream. Evaporation has been shown to be an effective way to drastically diminish the build-up of inhibitory compounds when process streams are recirculated, but the energy demand is high. Various process configurations to reduce the energy demand are suggested.