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. / published_or_final_version / Civil Engineering / Master / Master of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/196027 |
| Date | January 2013 |
| Creators | Zhao, Kang, 趙鈧 |
| Contributors | Zhang, T, Li, XY |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License |
| Relation | HKU Theses Online (HKUTO) |
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