TITLE:
Recovery and Upgrading of Phosphorus from Digested Sewage Sludge as MAP by Physical Separation Techniques
AUTHORS:
Tsuyoshi Hirajima, Takao Hagino, Mia Kose, Mohsen Farahat, Keiko Sasaki
KEYWORDS:
Phosphorus Recovery, Sewage Sludge, MAP, Physical Separation, Removal of Heavy Metals
JOURNAL NAME:
Journal of Environmental Protection,
Vol.7 No.6,
May
12,
2016
ABSTRACT: Physical separation apparatuses; a vibrating screen, a 4-inch
hydrocyclone and a Multi-Gravity Separator (MGS) were used to recover
phosphorus as MAP (magnesium ammonium phosphate, MgNH4PO4.6H2O) from anaerobic
digested sludge of two sewage-treatment plants A and B. For plant A, the MAP
grade increased from 0.08% to 88.9% with 90.4% recovery and for plant B, the
grade increased from 0.11% to 73.8 with 93.2% recovery. The collected MAP
products containing impurities such as organic materials and heavy metals were
further upgraded through dry and wet magnetic separation tests at different
magnetic flux densities. A dry magnetic separator was tested on both MAP
products (MAP-A and MAP-B), while the wet magnetic separation process was
exclusively experimented for the removal of impurities from MAP-B. Feed
samples, as well as magnetic and nonmagnetic products were analyzed by
absorption spectroscopy, XRD, ICP-AES, polarizing microscope observation, and
SEM-EDX. The grade of MAP products could be improved by about 4% - 9% after
magnetic separation (the most appropriate magnetic force being 15,000 Gauss).
During both dry and wet magnetic separation processes, not only heavy metals
have been removed, but also nonmagnetic constituents like Al, Ba, and Ca. This
may be attributed to the attachment of fine magnetic particles on the
nonmagnetic surfaces, rendering them magnetic properties.