UBC Theses and Dissertations
Possible methods of decreasing cell yields in waste treatment systems Nix, Peter G.
It has previously been shown that low p0₂ stimulated the respiration of facultative bacteria suggesting that precise control of dissolved oxygen in waste treatment systems might be an effective method of increasing carbon dioxide production at the expense of cell yield. In continuous cultures of glucose limited Escherichia coli B, controlled at less than 8mmHg, we have demonstrated a 57% increase in carbon dioxide production at the expense of both cell yield and supernatant carbon. Batch cultures of Pseudomonas aeruginosa 9027 showed an even greater loss of efficiency at low oxygen tensions. Studies with mixed populations (batch culture) showed some evidence of yield reduction (in spite of inherent difficulties with floculation and natural selection). However, the reduction was considered to be too small to warrant the practical application of dissolved oxygen control in waste treatment systems. While completely anaerobic E. coli B cells appear to be uncoupled by aeration, alternating a continuous culture between anaerobic and aerobic growth did not similarily affect the cells - evidently E. coli B requires a substantial amount of time (over 4 hours) to fully adapt to anaerobic conditions. In any case, unlike E. coli B, the growth of stable anaerobic mixed populations did not become "uncoupled" when aerated - indicating that this technique would not be suitable in waste systems. Studies with an ultra-violet irradiated continuous culture of E. coli B showed considerable increases in carbon dioxide production at the expense of cell yield. In addition, the process of floculation was greatly enhanced. The practical possibilities of implementation in waste treatment systems, warrent further investigation of the effects of u.v. irradiation on bacterial growth.
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