Combining submerged membrane technology with anaerobic and ...

Acetic Acid (mg·L -1 )Chapter 2VFA are determined by gas chromatography (HP, 5890A) equipped with a flameionization detector (FID) and an automatic injector (HP, 7673A). The determination isperformed in a glass column (3 m long and 2 mm of internal diameter) filled withchromosorb WAW (mesh 100/120) impregnated with NPGA (25%) and H 3PO 4 (2%). Thecolumn, injector and detector temperatures are 105, 260 and 280°C, respectively. Gas N 2,previously saturated with formic acid before entering into the injector, is used as carriergas with a flow of 24 mL·min -1 . Air and H 2 are used as auxiliary gases with flows of 400and 30 mL·min -1 , respectively. VFA, after being separated in the column according to theirmolecular weights, are burnt in a H 2-air flame and finally measured in the FID at 280°C.The quantification of the sample is made with a 6-8 point calibration curve for each acid inthe range of 0-1 g·L -1 , using pivalic acid as internal standard (figure 2.2). The detectionlimit of the equipment is 20 mg·L -1 .140012001000y = 6043x - 125R² = 0.99980060040020000.00 0.05 0.10 0.15 0.20 0.25Integrated area of the peakFigure 2.2. Example of a calibration curve for the acetic acid.2.1.2. Nitrogen compounds2.1.2.1. AmmoniumThe two major factors that influence the ammonia determination method are theconcentration and the presence of interferences, such as chlorine. For the determination oflow ammonia concentration without the presence of interferents, a colorimetric method(Wheatherburn, 1967) is used. This method base on the reaction of NH 3 with HClO andphenol, forming a strong-blue compound (indophenol) which can be colorimetricallydetermined using a spectrophotometer (Cecil CE 7200) at 635 nm.66