Is there a need for alkalization in methane fermentation processes?
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The studies on the methane fermentation process in technical installations mention the need to use a sodium hydroxide solution in order to stabilize the pH in the fermenter at an optimal level. This applies in particular to the treatment of industrial wastewater.
Under optimal operating conditions, there may be a temporary overload of the anaerobic sludge with a load of pollutants, resulting from the high variability of the composition of wastewater flowing from the plant. In such situations, if this results in a tendency to lower the pH in the fermenter, NaOH solution should be used in the appropriate dose, but generally these are emergency situations, significantly deviating from the accepted normal operating conditions.
On the other hand, assuming continuous alkalizing of the fermenting mixture in the operational assumptions is simply a misunderstanding. This is due to the fact that by artificially regulating the pH in the fermenter, we will never achieve very high purification effects, because some of the organic acids formed are bound in sodium salts, which in turn are marked as COD/BOD5 in digested wastewater.
What causes the problem of unstable pH in the fermenter? The main reason is the inadequate biological quality of the anaerobic sludge, which at the start-up stage was inadequately adapted to the treatment of specific industrial wastewater. Even wastewater, e.g. from the production of fruit juices, with a pH of about 5, can be fermented without additional alkalization, which is also a significant operating cost. The proper biological quality of anaerobic sludge concerns in particular the issue of quantitative relationships between groups of anaerobic bacteria that carry out individual phases of methane fermentation, which has a direct impact on the efficiency of wastewater treatment and obtaining a high concentration of methane in biogas, up to 80%. An important advantage of such sludge is a very high resistance to periodic overloading with a load of organic pollutants.