Abstract
This study was undertaken to evaluate the efficiency of a liquid-solids separation process and microwave pretreatment, as well as anaerobic biodegradability of microwave pretreated dairy manure. Liquid-solids separation of raw dairy manure resulted in solid and liquid fractions having different properties, with the solid fractions richer in total and volatile solids content and liquid fractions richer in nutrients and metal ions. Substantial amounts of soluble chemical oxygen demand and nutrients were released into the solution after the microwave treatment. The microwave pretreated dairy manure was also subjected to anaerobic digestion. The kinetic parameters of methane production potential, maximum methane production rate and lag time were determined using the modified Gompertz equation. Anaerobic digestion of liquid manure, without microwave treatment, outperformed the sets with microwave treatment. The microwave-treated liquid dairy manure, without acid addition had better results in terms of methane potential and methane production, than with acid addition. Thermophilic digestion exhibited a higher maximum methane production rate than that of mesophilic digestion, but lower methane yields. The microwave pretreatment of dairy manure resulted in high soluble chemical oxygen demand; however, methane yield was not increased.
Highlights
Anaerobic digestion is a technology widely used for treatment of organic waste for methane production
Liquid–solids separation of raw dairy manure resulted in solid and liquid fractions that had different properties; the solid fractions were richer in total solids (TS) and volatile solids (VS) content, while the liquid fractions were richer in nutrients and metal ions
Rico et al reported that the higher the percentage of water used for dilution, the higher SCOD/TS ratio was obtained in the liquid fraction
Summary
Anaerobic digestion is a technology widely used for treatment of organic waste for methane production. A mechanical liquid-solids separation process, resulting in a separated liquid fraction with much less suspended solids, can remove most of fibrous solids in dairy manure. This will allow the anaerobic digester to be operated at a shorter hydraulic retention time (HRT) or a higher loading rate [1]. Lo et al [2] conducted mesophilic anaerobic digestion of unscreened and screened manure, after liquid-solid separation, for the same organic loading rates at 16 days hydraulic retention time; liquid-solids separation had a minimal effect on the rate of methane production. The screened dairy manure was used as feed material for a fixedfilm reactor; a very high methane volumetric production rate was produced when the digester was operated at very short HRTs, as low as 3 h [3]
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