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Frontiers of Environmental Science & Engineering

Front. Environ. Sci. Eng.    2018, Vol. 12 Issue (4) : 3
Acidogenic sludge fermentation to recover soluble organics as the carbon source for denitrification in wastewater treatment: Comparison of sludge types
Lin Lin1, Ying-yu Li1, Xiao-yan Li1,2()
1. Environmental Engineering Research Centre, Department of Civil Engineering, The University of Hong Kong, Pokfulam, Hong Kong, China
2. Shenzhen Engineering Research Laboratory for Sludge and Food Waste Treatment and Resource Recovery, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China
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CEPS sludge was compared with conventional primary and secondary sludge for the VFAs yield.

Fe-based CEPS sludge exhibited the highest efficiency of organic recovery.

Fermented CEPS sludge liquor provided a sufficient carbon source for denitrification.

99% of nitrate removal was achieved based on the Fe-CEPS and sludge fermentation.

For biological nitrogen (N) removal from wastewater, a sufficient organic carbon source is requested for denitrification. However, the organic carbon/nitrogen ratio in municipal wastewater is becoming lower in recent years, which increases the demand for the addition of external organic carbon, e.g. methanol, in wastewater treatment. The volatile fatty acids (VFAs) produced by acidogenic fermentation of sewage sludge can be an attractive alternative for methanol. Chemically enhanced primary sedimentation (CEPS) is an effective process that applies chemical coagulants to enhance the removal of organic pollutants and phosphorus from wastewater by sedimentation. In terms of the chemical and biological characteristics, the CEPS sludge is considerably different from the conventional primary and secondary sludge. In the present study, FeCl3 and PACl (polyaluminum chloride) were used as the coagulants for CEPS treatment of raw sewage. The derived CEPS sludge (Fe-sludge and Al-sludge) was then processed with mesophilic acidogenic fermentation to hydrolyse the solid organics and produce VFAs for organic carbon recovery, and the sludge acidogenesis efficiency was compared with that of the conventional primary sludge and secondary sludge. The results showed that the Fe-sludge exhibited the highest hydrolysis and acidogenesis efficiency, while the Al-sludge and secondary sludge had lower hydrolysis efficiency than that of primary sludge. Utilizing the Fe-sludge fermentation liquid as the carbon source for denitrification, more than 99% of nitrate removal was achieved in the main-stream wastewater treatment without any external carbon addition, instead of 35% obtained from the conventional process of primary sedimentation followed by the oxic/anoxic (O/A) treatment.

Keywords Sewage sludge      Chemically enhanced primary sedimentation (CEPS)      Acidogenic fermentation      Organic carbon recovery      Nitrogen removal     
This article is part of themed collection: Bio-based Technologies for Resource Recovery (Responsible Editors: Aijie Wang & David Stuckey)
Corresponding Author(s): Xiao-yan Li   
Issue Date: 27 June 2018
 Cite this article:   
Lin Lin,Ying-yu Li,Xiao-yan Li. Acidogenic sludge fermentation to recover soluble organics as the carbon source for denitrification in wastewater treatment: Comparison of sludge types[J]. Front. Environ. Sci. Eng., 2018, 12(4): 3.
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Lin Lin
Ying-yu Li
Xiao-yan Li
Fig.1  Schematics of the wastewater treatment by primary sedimentation or CEPS, side-stream sludge fermentation, and the O/A process
Fig.2  The pollutant concentrations in the wastewater influent and the effluent after simple and chemically enhanced primary sedimentation
Primary sludge 4700±120 4680±100 3284±231 9154±120 3576±115 0.39±0.01 167.6±12.1 26.1±2.1
Fe-sludge 6040±230 4640±180 3256±289 9360±200 4076±220 0.44±0.03 203.7±9.5 129.3±5.0
Al-sludge 6280±150 4540±150 3167±156 8904±282 2717±185 0.31±0.02 206.2±10.2 132.6±7.2
Secondary sludge 4567±200 4619±140 3174±117 7785±155 2046±125 0.26±0.02 248.0±15.7 109.8±5.0
Tab.1  Characteristics of the primary sludge, CEPS sludge (Fe-sludge and Al-sludge) and secondary sludge after the concentration adjustment (unit: mg/L, expect BOD/COD)
Fig.3  The particle size distributions of different sludge samples before and after acidogenic fermentation
Fig.4  Performance in (a) hydrolysis and (b) acidogenesis of the different sludge during fermentation
Fig.5  Release of nutrients from the different sludge after acidogenic fermentation.
Fig.6  The nitrate removal efficiency in wastewater treatment without (control) and with (mixed) the addition of the fermented sludge supernatant
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