ANAEROBIC DIGESTORS- OPENING UP PANDORA'S BOX

The use of anaerobic digestion process in biological wastewater treatment has often been hailed as the ultimate answer in the treatment of various types of wastewaters. There are many advantages cited in using this fermentation technology such as wastewater stability, sludge reduction, dewaterability, energy and fertilizers. Yet such attractive technology that is in the dreams of environmental engineers are often the 'nightmare' of wastewater operations,

The sad truth is the anaerobic digestion process is very sensitive and instable process and easily prone to failure..

The failure of control of the anaerobic digestion is often attributed to the failure of understanding the microbiology and biochemistry of the process

ANAEROBIC DIGESTION AS COMPLEX FERMENTATION
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The anaerobic digestion is a very complex fermentation process because:

1 It is a mix culture microbial populations all involving in the process
2 It is made up of two basic groups of microorganisms; acidogens and methanogens with their own physiological attributes requiring their own specific growth requirements but still dependent on each other in the anaerobic digestion process
3 Methanogens are obligate anaerobic bacteria very fragile, slow growers and easily killed by exposure to oxygen and other extreme conditions
4 Complex substrate loading to the anaerobic digestors
5 Very high solid content and complex rheology of the substrate
6 Poor mixing conditions pf most anaerobic digestors
7 Washouts and slug dosings or shock loadings affecting the bacteria
8 Effect of temperature and ph upon the two groups of microorganisms

OPERATION OF ANAEROBIC DIGESTOR AND CLOSE MONITORRING
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Since one of the hall,arks of anaerobic digestion process is its sensitivity and stability, the success of its operation depend on close monitoring of the anaerobic digestion process. The optimu operating characteristics of an optimally run anaerobic digestor are marked by:

1 High volume of gas production
2 High percentage of CH4 to CO2 ratio
3 Neutral pH
4 Very low concentration of TVFA of less than 200mg/litre
5 Presence of short chain fatty acids such as acetic and propionic acids with little or no trace of butyric and valeric acids

The optimal range occurs in a very narrow range thus close monitoring are required to detect any changes and to take detection before the impending disaster

It should be noted that the TVFA profile is not the cause of a digestor failure but symptoms of the inefficient and uncoupling of the anaerobic digestion process between the acidogens and methanogens