TY - JOUR
T1 - Layered Double Hydroxides for phosphorus recovery from acidified and non-acidified dewatered sludge
AU - Lundehøj, Laura
AU - Jensen, Henriette Casper
AU - Wybrandt, Lisbeth
AU - Nielsen, Ulla Gro
AU - Christensen, Morten Lykkegaard
AU - Quist-Jensen, Cejna Anna
PY - 2019/4/15
Y1 - 2019/4/15
N2 - Phosphate, which contains the essential element phosphorous (P), is a necessary fertilizer for agriculture, but the current phosphate deposits are running out and alternative sources are needed. Sludge obtained from wastewater treatment plants contains high concentrations of phosphorus and represents an alternative, sustainable source. In this study, sludge obtained from a wastewater treatment plant with biological and chemical phosphorus removal was acidified (pH = 3, 4, 5 and 6) to release orthophosphate followed by sequestration of the orthophosphate by a zinc aluminum layered double hydroxide (Zn
2 Al-LDH). Sulfuric acid (H
2 SO
4 ), nitric acid (HNO
3 ), and hydrochloric acid (HCl) was tested, which showed that only sulfate anions compete with phosphate and results in reduced phosphate recovery (25–35%). The orthophosphate concentration in the liquid phase increased from 20% (raw sludge) to 75% of the total phosphorus concentration at a pH of 3, which enhanced the phosphate uptake by the ZnAl-LDH from 1.7 ± 0.2% to 60.3 ± 0.6%. During acidification, the competing anion carbonate is degassed as CO
2 , which further improved the phosphate uptake. PXRD showed the intercalation of carbonate in the LDH in the raw sludge at pH = 8, whereas orthophosphate was intercalated at lower pH values.
27 Al MAS NMR spectroscopy and powder X-ray diffraction (PXRD) proved preservation of the LDH at all pH values. Furthermore, about a fourth of the Al is present as an amorphous aluminum phosphate (AlPO
4 ) upon exposure to phosphate at low pH (pH = 3 and 5) based on
27 Al MAS NMR spectroscopy. At a pH of 6 about a third of the P is present as brushite (CaHPO
4 ·2H
2 O).
AB - Phosphate, which contains the essential element phosphorous (P), is a necessary fertilizer for agriculture, but the current phosphate deposits are running out and alternative sources are needed. Sludge obtained from wastewater treatment plants contains high concentrations of phosphorus and represents an alternative, sustainable source. In this study, sludge obtained from a wastewater treatment plant with biological and chemical phosphorus removal was acidified (pH = 3, 4, 5 and 6) to release orthophosphate followed by sequestration of the orthophosphate by a zinc aluminum layered double hydroxide (Zn
2 Al-LDH). Sulfuric acid (H
2 SO
4 ), nitric acid (HNO
3 ), and hydrochloric acid (HCl) was tested, which showed that only sulfate anions compete with phosphate and results in reduced phosphate recovery (25–35%). The orthophosphate concentration in the liquid phase increased from 20% (raw sludge) to 75% of the total phosphorus concentration at a pH of 3, which enhanced the phosphate uptake by the ZnAl-LDH from 1.7 ± 0.2% to 60.3 ± 0.6%. During acidification, the competing anion carbonate is degassed as CO
2 , which further improved the phosphate uptake. PXRD showed the intercalation of carbonate in the LDH in the raw sludge at pH = 8, whereas orthophosphate was intercalated at lower pH values.
27 Al MAS NMR spectroscopy and powder X-ray diffraction (PXRD) proved preservation of the LDH at all pH values. Furthermore, about a fourth of the Al is present as an amorphous aluminum phosphate (AlPO
4 ) upon exposure to phosphate at low pH (pH = 3 and 5) based on
27 Al MAS NMR spectroscopy. At a pH of 6 about a third of the P is present as brushite (CaHPO
4 ·2H
2 O).
KW - Ion exchange
KW - Layered double hydroxides (LDH)
KW - Phosphate recovery
KW - Sludge acidification
KW - Solid state NMR spectroscopy
KW - Wastewater
UR - http://www.scopus.com/inward/record.url?scp=85060894669&partnerID=8YFLogxK
U2 - 10.1016/j.watres.2019.01.004
DO - 10.1016/j.watres.2019.01.004
M3 - Journal article
SN - 0043-1354
VL - 153
SP - 208
EP - 216
JO - Water Research
JF - Water Research
M1 - 153
ER -