Smith J A and Carliell-Marquet C M.
Department of Civil Engineering, University of Birmingham
The digestibility of sewage sludge is affected by a number of factors. Activated sludge that has been dosed with iron (Fe) (to remove phosphorus) does not generate as much biogas when it is mesophilically digested as activated sludge that has not been Fe-dosed. The digestibility comparison of non Fe versus Fedosed sludge was carried out in three ways:
(1) Batch tests of sludge from 12 works
(2) Batch tests of sludge dosed with Fe in the laboratory, and
(3) Bench-scale semi-continuous trials comparing an Fe-dosed sludge with Fe and with the Fe removed (using EDTA) or with phosphorus removed (using NaOH).
All results show a similar biogas reduction of ~12%. The mechanism/s responsible for reduced digestibility are not clear but are probably related to the bioavailability of phosphorus within the digester.
KEY WORDS:
Activated sludge, biogas, chemical phosphorus removal, digestibility, iron-dosing, metal fractions.
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