8. CAPITULO VIII ANEXOS
8.2. Anexo: Plan de Gestión Integral de Residuos Peligrosos:
A disposable plunging jet bag was constructed by Hyclone Europe for use as the disposable microbial bioreactor which was compared with the stirred tank bioreactor in chapter 6. The design is detailed in chapter 6 and shown in figures 14 to 16. In addition to the microbial fermantions, the disposable plunging jet bag was used for kLa and mixing studies.
4.1.3.1 Description of disposable plunging Jet bag
The disposable plunging jet bag, which is shown in figures 14 to 16, consisted o f a square, bottomed plastic bag, which was inserted into a cylindrical perspex support. The
plastic bag was 0 66 m in height with a square based bottom of width 0 25 m and was constructed by Hyclone Europe (Newcastle, UK) for our personal use. The sides of the bag were constructed from four panels, which were welded along the sides. The bottom and top o f the bag was a pyramid base of four equal triangles. Both the base and the top could be pulled out to form a flat square bottom and top. The bag was stretched into a cylindrical support of 0 29 m in diameter and 0*66 m in height. Due to the bags
flexibility it stretched into the support so that it fitted the support tightly. In the top of the bag holes were mounted for the addition o f the nozzle and for feed streams such as the alkali, acid, inoculum and fermentation feeds. At a distance o f 0 05 m from the top at either side of the bag, two holes allowed attachment of an air inlet and outlet. The outlet to the pump was located at a distance o f 0 05m from the bottom on one side of the bag. The DOT probe and pH probes were positioned on the opposite side at a distance o f 0 05 m from the bottom. The outlet was connected in series to the mono pump and the process side o f a heat exchanger (Alfa laval type POI-VL, Manufacturing no. 30100-14060, Alfa laval. Sharpies, Camberley, UK) before being connected to the inlet of the plunging jet, which consisted o f a nozzle. The cooling side of the heat exchanger was connected to a water bath, (F6, haarke, Germany) which was set at 20°C. The temperature of the liquid inside the plunging jet bag was measured with a temperature logger, (Squirrel, SQl 600 Grant instrument, Cambridge, UK). Four nozzles were constructed with diameters o f 2 4 mm, 2*8 mm, 3-2 mm and 4-0 mm, where the length o f the nozzle was 15 times the nozzle diameter. The nozzles were lengthened by 35 times the nozzle diameter with a length o f pipe o f 4-0 mm in diameter, which proceeded the narrower diameter o f between 2-4 mm to 4-0 mm. A fifth nozzle of 2-4 mm and 15 times the diameter in length was lengthened by 0-45 m with a pipe of 4-0 mm in diameter. This fifth nozzle was used for experiments investigating the height o f fall.
4.1.3.2 Measurement of kta
The kta was measured in the disposable plunging jet by the same method as the disposable plunging jet mimic with several exceptions. The dissolved oxygen tension
was reduced to 0 % by putting nitrogen gas across the headspace and operating the mono pump so that the plunging jet entrained the nitrogen gas. When the DOT reached 0% the pump was switched off and air was blown across the headspace for a fixed time so that the nitrogen gas in the headspace was replaced by air. With the liquid at 0 % and the headspace full o f air, the k ta was measured by simultaneously switching on the mono pump and chart recorder. As before changes in the dissolved oxygen tension, (DOT) were measured with an Ingold probe (Mettler Toledo Ltd., Leicester, UK.) which was connected to a chart recorder. Although the temperature o f the water was maintained at 20 °C by the heat exchanger and water bath, it was recorded for each run.
4.1.3.3 Measurement of mixing
The disposable plunging jet bag was relatively opaque so the mixing time could not be measured by colour changes associated with a sodium sulphite solution mixing with a potassium triioxide solution. The mixing time was measured as the time taken for a pulse of sodium hydroxide to raise the pH to an equilibrium value. For each run the pH o f the water in the plunging jet was adjusted to 6 0 units with concentrated alkali and acid. With the mono pump running 10 mL o f 6 M NaOH was added and the time was measured for the pH to increase from 6 0 to 110 units. After each run liquid was removed via the sample line so that the liquid volume was fixed. The pH was measured with an Ingold probe (Mettler Toledo Ltd., Leicester, UK.) connected to a chart recorder. The pH probe had a probe response time, which unlike with the oxygen probe could not be describe by a simple mathematical function. Thus the probe response time was included in the final mixing time