When referring to anaerobic treatment, I am talking about the process where archea organisms produce methane as a part of waste stabilization. The chemistry of the anaerobic process on the surface appears much more complex than the aerobic system, but it is very similar except we are not using elemental oxygen as a terminal electron acceptor. (I'll get back to this biochemistry section in a future post). When considering an anaerobic digester unit you should first know the advantages and disadvantages of anaerobic waste treatment:
Advantages
Advantages
- Low biological solids yield which means less wasting than seen in aerobic treatment
- Tolerant of heavy loadings, actually heavy loadings of 5 - 10 kg COD/m3 of reactor volume is almost a necessity compared to 1 kg COD/m3 for aerobic system loading
- With the low cell yield it is often not necessary to add nitrogen or phosphorus macronutrients
- Methane can yield energy for use
Disadvantages
- Methanogenic archea are slow growing microbes
- Can produce odors if influent is high in sulfur and/or methanogens are not healthy resulting in exhaust containing volatile organic acids
- pH must be controlled along with monitoring of volatile fatty acids
- Does not do well with dilute wastes and some materials that are better treated via aerobic pathways (insoluble fats, oils, grease)
- Does not remove ammonia-nitrogen
- Temperature must be maintained year round in target zone - for most mesophilic digesters it is 35 - 40oC.
- Methane producing microbes require some micronutrients that may be lacking this includes Fe, Co, Ni, Mo. For a journal article on micronutrients and bacillus fermentation product improving methane production study - http://www.ncbi.nlm.nih.gov/pubmed/16180439
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