Optimization of Anaerobic Co-Digestion of Sewege Sludge and Brewery Yeast Waste
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Date
2009-06
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Addis Ababa University
Abstract
A batch anaerobic digestion experiment was carried out to determine the optimum methane
produced from digestion of sewage sludge and brewery yeast waste in different mix, and the
fertilizer potential of the sludge after digestion.
The maximum methane production from anaerobic digestion of sewage sludge and brewery yeast
waste was assessed in batch tests using armfield glass made anaerobic digester in chemical
engineering laboratory. The volume of biogas produced and methane composition of different
mix of the feed stock were determined by water displacement and geotechnical land fill gas
analyzer model GA 45, respectively. It was observed that the independent variable – mix ratio
significantly affect (p-value 0.0027) the dependent variable – amount of methane produced since
the p-value is less than the chosen α-level usually 0.05. The calculated volume of methane in the
biogas produced per gram COD removed were 0.218L, 0.103L, and 0.075L and per gram volatile
solid removed were 0.271L, 0.172L and 0.136L for sewage sludge alone, 80:20% mix, and
60:40% mix of sewage sludge to brewery yeast waste respectively. In general From the digestion
of sewage sludge alone: 0.44 m3/d/m3 biogas with 57.75% methane was produced; 0.74 m3/d/m3,
and 0.91 m3/d/m3 biogas with 19.84% and 19.34% methane produced from 80:20% mix and
60:40% mix of sewage sludge to brewery yeast waste, respectively. The mix ratio significantly
affects the biogas production (p-value 1.65*10-9). Totally 83,850 m3 CH4/year can be captured
and hence same amount of methane emission into the atmosphere is prevented from the sewage
sludge currently managed in Addis Ababa waste water treatment plant if anaerobic digester is
used.
With regard to the fertilizer potential of the digestate; heavy metal content is not a limiting factor
in the use of sewage sludge managed in Addis Ababa waste water treatment as a soil conditioner
and fertilizer. Moreover, the nitrogen, phosphorus and potassium content of the sludge satisfy
specific plant uptake requirements in many land application systems. Sun drying on drying beds
after anaerobically digested sludge is helpful in the viability of land application of treated sludge
by completely inactivating the pathogen and reducing the potential risk.
Key words: Biogas, Methane, Organic fertilizer, Anaerobic digestion, Digester, Sewage sludge,
Brewery yeast waste
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Keywords
Biogas; Methane;Organic fertilizer; Anaerobic digestion; Digester; Sewage sludge; Brewery yeast waste