Abstract
Anaerobic digestion of a mixture of manure and sewage sludge by combination of the biological predigestion at 73°C with methanization at 55°C was studied with regard to the biogas process efficiency,energy balance and sanitation effect. Performance of the two-stage digestion was compared with theconventional, one-stage moderate thermophilic digestion at 55°C and mesophilic digestion at 37°C,respectively. The best performance was achieved by the two-stage treatment both in terms of VolatileSolids (VS) removal and biogas yield. Up to 60% of VS was removed and a specific methane yield of 300ml CH4 gVS-1 was achieved. Sanitation effect was measured as inactivation of the indicators of bacterialpathogens - the faecal enterococci and spores of Clostridium perfringens. Elimination of faecal enterococcito non-detectable level occurred only during treatments at 73°C and 55°C. Numbers of Clostridiumperfringens spores were reduced solely by the combined 73°C/55°C treatment.
Highlights
The advantages of anaerobic digestion (AD) systems include: (i) increased specific activity of methanogens leading in a higher methane product (ii) more stability with better pH control; (ii) more reduction of Volatile Solids (VS) and (iv) high potential for removing pathogens [6, 7, 8, 9]
It is well known that the sewage sludge and animal manure are the main sources of organic waste in Iraq
The energy produced by anaerobic digestion (AD) of these two types of wastes could be increased significantly, if the waste available in the country was treated by anaerobic digestion [1]
Summary
The advantages of AD systems include: (i) increased specific activity of methanogens leading in a higher methane product (ii) more stability with better pH control; (ii) more reduction of VS and (iv) high potential for removing pathogens [6, 7, 8, 9]. In a recently published study [9] we already characterized a two-stage reactor system showing improved digestion efficiency when operated at 68°/58°/55°C [4, 9].
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