Journal
ENVIRONMENTAL TECHNOLOGY
Volume 42, Issue 12, Pages 1836-1845Publisher
TAYLOR & FRANCIS LTD
DOI: 10.1080/09593330.2019.1681522
Keywords
Anaerobic digestion; thermophilic; mesophilic; uncontrolled phosphorus precipitation
Categories
Funding
- CDTI (Centre for Industrial Technological Development)
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This study compared the operation of mesophilic and thermophilic anaerobic digestion of sewage sludge and their effects on uncontrolled phosphorus precipitation. The results showed that struvite formation may occur under mesophilic conditions, while iron phosphates formation or adsorption processes on solid surfaces may account for phosphorus fixation at shorter hydraulic retention times.
This study compares the operation of mesophilic and thermophilic anaerobic digestion of sewage sludge and their effects in uncontrolled phosphorus precipitation. The research has been carried out using a pilot plant consisting of two digesters of 1.6 m(3) working volume, treating the mixed sludge of Alzira WWTP (Valencia, Spain). The digesters were operated in parallel, at different conditions: mesophilic (38 +/- 2.0 degrees C) and thermophilic (55 +/- 2.5 degrees C) temperatures and organic loading rates (OLR) ranging from 1.1 to 1.7 kg volatile solids (VS) m(-3) d(-1) and different hydraulic retention times (HRT) 20, 15 and 12 days. Uncontrolled precipitation was evaluated through P, Mg and Ca mass balances in both digesters. The results revealed that up to 82% of the available P and 81% of the available Mg precipitated in the mesophilic digester at HRT = 20 days which suggests the possible formation of struvite in both digesters. At lower HRT (HRT = 12 days) Mg and Ca precipitation was negligible and P fixation has been attributed to the possible formation of iron phosphates or adsorption processes on solid surfaces.
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