RECOMENDACIONES Y RUTAS DE REFLEXIÓN. 1 RECOMENDACIONES

The two sets of prehydrolysate solutions used in the experiments were generated in a pilot digester. The first solution was prepared with steam at 700 kPa, 170 ºC for 110 minutes followed by hot water treatment for 15 minutes [10]. A mixture of aspen (60%) and maple (40%) wood chips was used for the prehydrolysate solution. The second solution was prepared by using hot water only. Water was added to the digester and it was heated indirectly with steam to 170 °C in 50 minutes. The digester was maintained at 170 °C for an additional 65 minutes. The compositions of the generated prehydrolysate solutions are given in Table 6.1.

Table 6.1: Composition of prehydrolysate used for the experiments Concentration (g/L) Component Solution 1 Solution 2

Total sugars 21,8 39.0 Total phenols 4.7 4.6 Acetic Acid 3.8 6.3 Sugar monomers 3.1 6.5 Total solids 3.4 4.5 Furfural 0.7 0.7 Hydroxymethylfurfural 0.1 0.1 K 0.04 - Na 0.02 0.01 Ca 0.15 0.16 Fe 0.00 0.00

Solution 1 was used in the preliminary experiments while solution 2 was used to validate the efficiency of the strategy with a different solution.

Activated carbon was purchased from Jacobi Carbons Ltd, alum powder from Bulk Barn Ltd, Canada and ferric sulfate from Mallinckrodt analytical reagents. The Folin & Ciocalteu’s phenol reagent and 3,5-Dinitrosalicylic acid were purchased from Sigma Aldrich. Potassium sodium tartrate (Rochelle salt) came from MP Biomedicals and sodium hydroxide from Laboratoire

MAT. Sulfuric acid was purchased from Caledon Laboratories Ltd and Chitin originated from ABK-Gaspésie Inc. All materials were used as received without further purification.

6.2.2 Membranes and filtration procedure

The SEPA CF II, cross-flow flat-sheet membrane from GE OSmonics that was used in this study has been described in a previous publication [11]. The membrane test unit can accommodate various flat sheet membranes. A fresh membrane sheet was used in each experiments. As illustrated in Figure 6–2 A), the prehydrolysate in the tank was fed to the membrane unit at a predetermined volumetric flow rate and pressure. Samples of the permeate and concentrate streams were taken for analysis at regular intervals after the flows reached steady state. The same procedure was repeated in all the membranes screening experiment.

Feed Permeate Pressure Indicator & Valve Variable Speed Pump Concentrate Temperature Indicator Feed Tank Feed Permeate cylinder Pressure Indicator & Valve Variable Speed Pump Concentrate Temperature Indicator Feed Tank A) B)

Figure 6–2: Schematic of membrane system for A) membrane selection B) prehydrolysate concentration

The observed retention (rejection) of the main components was used as a measure of detoxification efficiency and was determined using equation (1), where Cf represents the

concentration of the component in the feed and Cp the concentration in the permeate.

R = 100 * (Cf - Cp)/Cf ( 24 )

Concentration trials with the selected membranes were performed by discharging the permeate stream to a reservoir as shown in Figure 2B). The volumetric concentration factor (VCF) obtained can be calculated by equation (2).

In this equation, Vi is the initial feed volume and Vf the final feed volume. The VCF is 1 during

the membrane selection run when no concentration is performed. The characteristics of seven commercial organic membranes were evaluated. The retention and flux characteristics for six of the membranes with molecular weight cut off (MWCO) between 100 and 500 have been previously reported [10]. The seventh membrane, an ultrafiltration membrane with a MWCO of 3500 was compared in order to broaden the experimental range.

6.2.3 Activated Carbon (AC) adsorption

Two types of adsorption tests were carried using activated carbon. The first was a batch series of experiments in which 5g, 10g and 15 g of activated carbon was mixed with 150 mL of prehydrolysate at room temperature in a magnetically stirred flask. A treated sample (1 mL) was taken for analysis after 45 minutes and the stirring was continued for another 45 minutes before the final sample was taken. The treated prehydrolysate was collected and filtered through a 0.45 µm membrane. The second test was a continuous experiment run in which activated carbon was introduced into a 4 cm diameter burette. Prehydrolysate was then fed into the burette and allowed to pass through the activated carbon layer. Treated prehydrolysate was collected in a graduated cylinder and passed through a 0.45 µm filter before analysis.

6.2.4 Flocculation

Preliminary flocculation tests were carried out in beakers. Calculated doses of the flocculants (chitin, ferric sulfate - Fe2(SO4)3.6H2O, and Alum - KAl(SO4)2.12H20) were added to 500 mL of

the prehydrolysate solution, this was followed by the addition of sodium hydroxide to bring the pH to 6. The beakers were stirred using a magnetic stirrer for 30 minutes and left to settle. Treated prehydrolysate were analyzed with and without passing the samples through a 0.45 µm filter. After a flocculant had been selected, optimization experiments for the coagulant dosage, pH, and choice of alkali for pH adjustment were carried out with a jar test apparatus. The jar was agitated for 15 minutes upon addition of the flocculant at a speed of 150 rpm. The speed was then reduced to 50 rpm after adjustment of the pH for another 30 minutes.

6.3 Analyses

6.3.1 Sugars analysis

Sugar monomers composition in the prehydrolysate was measured using a Dionex DX600 ion chromatograph equipped with a pulsed amperometric detector and Carbopac PA1 column [12]. The oligomeric sugars content was determined by hydrolysis using 2.5 % wt/vol of sulphuric acid for 120 minutes in an autoclave prior to analysis. The dinitrosalycilic acid (DNS) colorimetric method [13] was adapted for determining the total reducing sugars before and after filtration and flocculation experiments.

6.3.2 Furans analysis

Furfural and hydroxymethylfurfural composition were measured by HPLC (Agilent Technologies, Germany) using a 280 nm diode array detector (DAD) and a Nucleosil C18 column. The eluent used was a mixture of acetonitrile, water and acetic acid [11].

6.3.3 Phenols analysis

The total phenols composition was measured by a UV-Visible colorimetric method using a Folin–Ciocalteau reagent method adapted from Singleton and Rossi [9]. A volume of 500 µL of diluted samples, a blank sample and standard solution were pipetted in separate tubes, 3800 µL of water and 200 µL of Folin-Ciocalteu reagent were added. After 3 minutes, 500µL of NaOH 6% (wt/vol) was added, the tubes were vortexed and the samples were placed in the dark to stabilize. The absorbance was measured at 725 nm and the total phenol content was calculated as gallic acid equivalents. A HPLC analysis method that is capable of measuring gallic acid, catechol, vanillin and syringaldehyde was developed. The previously described HPLC was equipped with a 280 nm DAD for gallic acid and catechol detection and a 313nm DAD detector for vanillin and syringaldehyde. In both cases, a Nucleosil C18 column (150 x 4.6 mm) was used. The eluent used was a mixture of acetonitrile and 0.1% wt/wt of phosphoric acid solution (CH3CN 15%,

phosphoric acid solution 85%) and it was fed to the column at 17000 kPa and 25ºC at a flow rate of 0.8 mL/min.

6.3.4 Organic acids analysis

Organic acids concentrations were measured using the same HPLC. It was however equipped with A 210 nm diode array detector (DAD) and an Inertsil ODS-3 (150 X 4.6 mm) column. The method was adapted to determine the concentrations of acetic, lactic, propanoic and butyric acids.

6.3.5 Physico-chemical characteristics

The metal ions were measured with an Optima 4300 DV Inductively coupled plasma atomic emission spectroscope (PerkinElmer Inc., USA). An Accumet AB250 pH/ISE Meter (Fisher Scientific, USA) and an Orion 3-Star Benchtop Conductivity Meter (Thermo Scientific, Canada) were used to measure the pH and conductivity respectively.

6.4 Results and discussion