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postgraduate thesis: An iron-facilitated chemical and biological process for phosphorus removal and recovery during wastewater treatment
Title | An iron-facilitated chemical and biological process for phosphorus removal and recovery during wastewater treatment |
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Authors | |
Advisors | |
Issue Date | 2013 |
Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
Citation | Zhao, K. [趙鈧]. (2013). An iron-facilitated chemical and biological process for phosphorus removal and recovery during wastewater treatment. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b5153745 |
Abstract | Phosphorus (P) is an important pollutant of concern in wastewater that causes eutrophication and algal blooms in water body. On the other hand, P is a valuable natural resource for agricultural and industrial use. With the rapid depletion of mineral phosphorus on earth, there is a need to recover phosphorus from wastewater. In this study, a new chemical and biological process facilitated with iron dosing has been developed for P removal and recovery during wastewater treatment. The system consists of a main stream identical to the conventional activated sludge process in an aerobic sequencing batch reactor (SBR) for P removal and a side stream of sludge recirculation through an anaerobic SBR (AnSBR) for P release and recovery from the P-rich sludge.
In the aerobic SBR treating a synthetic domestic wastewater, Fe(III) (FeCl3) was dosed to remove P by precipitation and adsorption. Fe(III) dosing at a Fe/P molar ratio of 1.5:1 could reduce the P concentration from more than 10 mg/L to below 1 mg/L in the final effluent. Compared to other dosing periods, dosing Fe(III) right before the SBR settling could achieve the best result in sludge flocculation and P removal. Meanwhile, organic removal was well maintained as 90% of the chemical oxygen demand (COD) was degraded in the aerobic SBR. In the AnSBR, phosphate precipitated with ferric iron in the sludge was released owing to microbial Fe(III) reduction, and a positive correlation was found between the phosphate and ferrous iron concentrations in the sludge suspension. Chemical tests showed that significant P release from Fe(III)-P occurred only if the acidic condition and the reducing condition were combined. For the AnSBR sludge, a higher organic loading, lower pH and higher biomass concentration resulted in a higher level of Fe(III) reduction and P release. Organic acidogenesis prevailed in the reactor and lowered the pH to ~4.5, which facilitated the P release from the solid phase into the liquid phase. With a solids retention time (SRT) of 10 days, the anaerobic supernatant contained a phosphate concentration of up to 70 mg/L, while the settled sludge was returned to the aerobic SBR. The phosphate could be readily recovered from the supernatant with Fe-induced precipitation by aeration and pH adjustment, and the overall P recovery could be achieved at about 70%. In addition to the treatment performance, the speciation of P in the aerobic sludge and the anaerobic sludge also was investigated. A significant change in the immediately available P and the redox-sensitive P was found in the sludge through the aerobic-anaerobic cycle. Such chemical transformation is believed to be crucial to the P removal and recovery during the wastewater treatment process. |
Degree | Master of Philosophy |
Subject | Sewage - Purification |
Dept/Program | Civil Engineering |
Persistent Identifier | http://hdl.handle.net/10722/196027 |
HKU Library Item ID | b5153745 |
DC Field | Value | Language |
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dc.contributor.advisor | Zhang, T | - |
dc.contributor.advisor | Li, XY | - |
dc.contributor.author | Zhao, Kang | - |
dc.contributor.author | 趙鈧 | - |
dc.date.accessioned | 2014-03-21T03:50:06Z | - |
dc.date.available | 2014-03-21T03:50:06Z | - |
dc.date.issued | 2013 | - |
dc.identifier.citation | Zhao, K. [趙鈧]. (2013). An iron-facilitated chemical and biological process for phosphorus removal and recovery during wastewater treatment. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b5153745 | - |
dc.identifier.uri | http://hdl.handle.net/10722/196027 | - |
dc.description.abstract | Phosphorus (P) is an important pollutant of concern in wastewater that causes eutrophication and algal blooms in water body. On the other hand, P is a valuable natural resource for agricultural and industrial use. With the rapid depletion of mineral phosphorus on earth, there is a need to recover phosphorus from wastewater. In this study, a new chemical and biological process facilitated with iron dosing has been developed for P removal and recovery during wastewater treatment. The system consists of a main stream identical to the conventional activated sludge process in an aerobic sequencing batch reactor (SBR) for P removal and a side stream of sludge recirculation through an anaerobic SBR (AnSBR) for P release and recovery from the P-rich sludge. In the aerobic SBR treating a synthetic domestic wastewater, Fe(III) (FeCl3) was dosed to remove P by precipitation and adsorption. Fe(III) dosing at a Fe/P molar ratio of 1.5:1 could reduce the P concentration from more than 10 mg/L to below 1 mg/L in the final effluent. Compared to other dosing periods, dosing Fe(III) right before the SBR settling could achieve the best result in sludge flocculation and P removal. Meanwhile, organic removal was well maintained as 90% of the chemical oxygen demand (COD) was degraded in the aerobic SBR. In the AnSBR, phosphate precipitated with ferric iron in the sludge was released owing to microbial Fe(III) reduction, and a positive correlation was found between the phosphate and ferrous iron concentrations in the sludge suspension. Chemical tests showed that significant P release from Fe(III)-P occurred only if the acidic condition and the reducing condition were combined. For the AnSBR sludge, a higher organic loading, lower pH and higher biomass concentration resulted in a higher level of Fe(III) reduction and P release. Organic acidogenesis prevailed in the reactor and lowered the pH to ~4.5, which facilitated the P release from the solid phase into the liquid phase. With a solids retention time (SRT) of 10 days, the anaerobic supernatant contained a phosphate concentration of up to 70 mg/L, while the settled sludge was returned to the aerobic SBR. The phosphate could be readily recovered from the supernatant with Fe-induced precipitation by aeration and pH adjustment, and the overall P recovery could be achieved at about 70%. In addition to the treatment performance, the speciation of P in the aerobic sludge and the anaerobic sludge also was investigated. A significant change in the immediately available P and the redox-sensitive P was found in the sludge through the aerobic-anaerobic cycle. Such chemical transformation is believed to be crucial to the P removal and recovery during the wastewater treatment process. | - |
dc.language | eng | - |
dc.publisher | The University of Hong Kong (Pokfulam, Hong Kong) | - |
dc.relation.ispartof | HKU Theses Online (HKUTO) | - |
dc.rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works. | - |
dc.rights | This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. | - |
dc.subject.lcsh | Sewage - Purification | - |
dc.title | An iron-facilitated chemical and biological process for phosphorus removal and recovery during wastewater treatment | - |
dc.type | PG_Thesis | - |
dc.identifier.hkul | b5153745 | - |
dc.description.thesisname | Master of Philosophy | - |
dc.description.thesislevel | Master | - |
dc.description.thesisdiscipline | Civil Engineering | - |
dc.description.nature | published_or_final_version | - |
dc.identifier.doi | 10.5353/th_b5153745 | - |
dc.identifier.mmsid | 991036118049703414 | - |