To the far left can be seen a 1.8 meter high x 2.5 cm i.d. Pyrex column packed with 1.25 cm berl saddles and filled with desugared Spent Sulfite Liquor (SSL), making it appear as a dark brown column. In this view Ozone is being injected into the bottom of the column while raw (untreated SSL) is being continuously introduced at the top and removed at the base thus establishing a countercurrent system. There is also a recycle "side loop" to a small 500 ml stirred flask with a pH probe and automatic titrator adding aqueous 10% NaOH for pH control. Operating temperature was ambient 24 oC with no appreciable heat of reaction. See Fig. 1, the process flow diagram.
An operator is leaning on a large gray box, a Welshbach Ozone Generator that is producing a stream of oxygen containing an ozone concentration of 2% wt from a pure oxygen feed. This ozone rich stream is fed continuously from this generator into the ozonation column. Ozone concentration of both influent and effluent gases is monitored by bubbling samples through gas absorbers containing a 2% aqueous solution of KI and titrating the free I2 produced with a standard sodium thiosulfate solution (32, 38, 77, 137, 195).
Preliminary experiments with SSL ozonated at varying conditions, such as reaction time and pH, indicated a pH of 3.0 and ozonation time of 3 hours proved most promising for CH4 production through anaerobic fermentation. Ozone consumption was 15 g/liter of SSL under these conditions.
It was found that SSL must be diluted prior to fermentations to 75% with water (75:25 SSL to distilled water). Consequently, all fermentation experiments were carried out using this 75:25 feed.
This view of two containers demonstrates the color change between the untreated SSL in the beaker on the left and ozonated SSL in the flask on the right. The reduction in color probably results from partial destruction of the aromatic ring system together with the chromophores of lignin responsible for its dark brown color. In addition to change of color, volatile and nonvolatile organic acids in the effluent were determined qualitatively and quantitatively by gas chromatography. The organic acids formic, acetic and oxalic were identified as being produced. Some of the organic components in the SSL were competely oxidized to CO2, the presence of which was detected in the column reactor exhaust gas stream by gas chromatography during the entire period of ozonation. Infrared spectral scans taken for raw SSL and ozonated SSL suggested that significant transformation of aromatics to carboxylic acids had occurred during ozonation.
Biological Oxygen Demand (BOD) indicated an appreciable increase of metabolizable organics when ozonation was conducted at pH 3.0, while there was very little increase on BOD when ozonation occurred at alkaline pH. The Chemical Oxygen Demand (COD) of the ozonated SSL was reduced by 18% from untreated SSL when ozonation was carried out at either acid or alkaline pH. Tests indicated a 7% decrease in the sulfur content of the ozonated SSL due to precipitation of sodium sulfate and calcium oxalate during pH control with NaOH. An approximate 5% decrease in total organic carbon was observed due to loss of carbon as CO2 and production of calcium oxalate.
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