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Frontiers of Environmental Science & Engineering

Front. Environ. Sci. Eng.    2016, Vol. 10 Issue (3) : 578-584
Recovering humic substances from the dewatering effluent of thermally treated sludge and its performance as an organic fertilizer
Yuning YANG,Huan LI()
Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China
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The biologic treatment of the dewatering effluent from thermally treated sludge is difficult due to the high concentration of refractory humic substances. On the other hand, humic substances are an important source of organic fertilizer. In this study, a novel process using ferric coagulant was developed to recover humic substances from dewatering effluent for use as an organic fertilizer. When ferric coagulant was applied to raw dewatering effluent, up to 70% of humic substances were enmeshed by hydrolyzed ferric ions at an optimum pH of 4.5. The proper mass ratio of iron ions to humic substances was 0.6. In the recovered material, humic substances accounted for 24.2% of the total dry solids, and the amount of phosphorus (equivalent phosphorus pentoxide) was 6.2%. Heavy metals and other components all met the legal requirements for organic fertilizer. When the recovered material was applied to soybeans, the germination and growth of the seeds was significantly improved.

Keywords sewage sludge      humic substances      recovery      phosphorus      fertilizer     
Corresponding Authors: Huan LI   
Online First Date: 16 December 2015    Issue Date: 05 April 2016
 Cite this article:   
Yuning YANG,Huan LI. Recovering humic substances from the dewatering effluent of thermally treated sludge and its performance as an organic fertilizer[J]. Front. Environ. Sci. Eng., 2016, 10(3): 578-584.
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Yuning YANG
Huan LI
components concentration /(mg·L-1)
organic matter total organic carbon 5186.2±148.0
HAs 2180±42
FAs 1317±96
proteins 430.9±15.8
lipids 400.0±20.0
saccharides 57.8±2.0
nucleic acids 199.5±16.8
inorganic matter pH 7.3±0.2
P 160.0±3.0
Si 122.4±12.1
Mg 40.9±5.2
Fe 16.2±2.2
Ca 12.2±2.7
heavy metals Cu 0.420±0.000
Mn 0.304±0.024
Ni 0.222±0.032
Sr 0.208±0.035
Zn 0.062±0.009
As 0.033±0.043
Co 0.026±0.013
Mo 0.009±0.003
Sn 0.008±0.001
Cd 0.003±0.004
Pb 0.002±0.001
Cr Nd
Hg Nd
Tab.1  ?Characteristics of the raw wastewater
Fig.1  Recovery rate of humic substances from raw wastewater at different pHs and doses of FeCl3 (Fe/HS indicates the mass ratio of iron ions to humic substances)
Fig.2  ?Recovery rate of humic acids (HAs), fulvic acids (FAs) and total humic substances by FeCl3 at different pHs and doses of FeCl3 (Fe/HS indicates the mass ratio of iron ions to humic substances): (a) Fe/HS=0.55; (b) Fe/HS=0.90
components content limits
organic /(wt.%) 55.1±6.3 ≥45
humic substances /(wt.%) 24.2±1.5
pH 6.0?6.5 5.5–8.5
P2O5 /(wt.%) 6.2±0.1 ≥5
Fe /(wt.%) 18.9±1.2
Si /(wt.%) 3.0±0.0
Mg /(wt.%) 1.2±0.0
Ca /(wt.%) 0.2±0.0
As /(mg·kg-1) 11.4±0.0 15
Pb /(mg·kg-1) 3.9±0.0 50
Cd /(mg·kg-1) 1.1±0.0 3
Cr /(mg·kg-1) Nd 150
Hg /(mg·kg-1) Nd 2
Mn /(mg·kg-1) 428.2±72.5
B /(mg·kg-1) 404.9±29.6
Cu /(mg·kg-1) 129.2±32.7
Sr /(mg·kg-1) 49.5±10.8
Co /(mg·kg-1) 7.9±3.8
Mo /(mg·kg-1) 2.8±2.6
Sn /(mg·kg-1) 2.5±0.3
Ni /(mg·kg-1) 1.7±0.4
Tab.2  Components of the recovered material and the standard of organic fertilizer
Fig.3  ?FTIR of the precipitate at different pH values
Fig.4  ?Precipitation rate of iron ions in raw wastewater when the mass ratio of iron ions to humic substances was 1.00
Fig.5  Effect of the FeCl3 dose on the humic recovery rate from raw wastewater and the humic content in the precipitate at pH 4.5 (Fe/HS indicates the mass ratio of iron ions to humic substances)
Fig.6  Effect of the recovered material for an application of 87.5 kg·hm-2 on the germination of soybeans
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