by Lydia Chang. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1989. / Bibliography: leaves 154-165.

The primary objective of this research was to determine if efficient biological phosphorus removal could be established under low sludge retention time of 2 days and a nominal hydraulic retention time of 4 to 6 hours. The two-stage Phoredox process was selected because of the practical application of retrofitting high rate treatment plants to achieve bio-P removal without the additional tankage required for an anoxic section and the additional expense of a recycle system. It has been shown that nitrate recycled into the anaerobic reactor impacts on bio-P removal and the two-stage Phoredox process provides no control over nitrates entering the anaerobic reactor. Therefore a secondary objective of this research was to determine if a low sludge retention time mode of operation could be used as an effective way to prevent nitrification in the activated sludge treatment process. Another objective was to observe mixed liquor settling characteristics of the two-stage Phoredox process operated under high rate conditions. A pilot scale two-stage Phoredox activated sludge treatment process operating under high rate conditions was used to meet these objectives. The desired bio-P removal biomass was not observed under SRT operating conditions of 2, 3 and 5 days. Partway into the research a sludge bulking condition developed which was identified as filamentous growth. On two occasions this severe filamentous growth resulted in the process failing and the system being restarted. On one occasion after the system was restarted using a seed sludge from a three-stage Phoredox pilot plant, a bio-P removal biomass was present. This condition only lasted for a short period and ended as filamentous growth began to become dominant. The process failed because of this phenomenon. The system was restarted using a seed sludge and again filamentous growth dominated. Chlorine addition was found to be the only method to control this phenomenon and was continued to the end of the research. The desired bio-P removal biomass was not observed even during the last period of the research when the SRT was increased to 8 days. During this research a stable bio-P removal biomass was not established. For a short period a bio-P removal biomass was present but failed to persist. Nitrification never became established at any time. Sludge settleability was poor due to filamentous growth which developed partway into the research and was present throughout the remainder of the study. Chlorine addition was the only method found that remedied this settling problem. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

A study of the anaerobically digested sludge form a full-scale biological phosphorus removal (BPR) plant (York River Wastewater Treatment Plant, York River, Va.) was conducted to determine the effects of BPR on sludge characteristics and conditioning requirements. Data collected from the plant indicated that both the total and soluble phosphorus (P) concentrations in the anaerobically digested sludge increased dramatically with the initiation of BPR. Accompanying this increase in total P was an increase in the total concentrations of magnesium and potassium content of the sludge, supporting the observations that these ions are co-transported with P during the accumulation and release of P by P accumulating organisms. The majority of the phosphate present in the pre- and post- BPR anaerobically digested sludges was bound by calcium, magnesium, and iron phosphorus precipitates including hydroxyapatite, struvite, and vivianite. Calcium phosphorus precipitates were the most prevalent in both sludges, but the percentage of magnesium phosphorus precipitates increased with the onset of BPR. Cationic organic polymer conditioning dosages needed to achieve acceptable sludge dewatering rates for the post-BPR sludge were similar to those required by the pre-BPR sludge. The cationic organic polymer used to condition these sludges was ineffective in removing excess phosphate; therefore, the addition of either one or both of the inorganic chemicals ferric chloride and calcium hydroxide was required to remove soluble phosphorus. Conditioning with either ferric chloride or calcium hydroxide alone was not effective in achieving acceptable dewatering rates; however, when used together the chemicals produced acceptable dewatering rates and soluble P removal from the post-BPR sludge. / Master of Science

The role of metal cations in enhanced biological phosphorus removal (EBPR) from wastewater by activated sludge was investigated. Potassium and magnesium were simultaneously required for efficient EBPR. Neither potassium nor magnesium could induce enhanced phosphorus uptake on its own. Cations were co-transported with phosphorus during anaerobic release and aerobic uptake. With every mole of phosphorus, between 0.23 and 0.43 moles of potassium and between 0.25 and 0.36 moles of magnesium were co-transported. Calcium appeared to be involved in EBPR to a limited extent, and did not seem to chemically co-precipitate with phosphorus. For every gram of chemical oxygen demand (COD) consumed by the sludge in the anaerobic zone of the experimental systems, 0.22 grams of phosphorus were released at a 15 d mean cell residence time and 20°C. Approximately 20 mgCOD/L were taken up by the sludge before any phosphorus was released. Phosphorus release could be described by first order kinetics. Phosphorus uptake under aerobic conditions could also be described by first order kinetics. The total phosphorus uptake in the anoxic and aerobic zones of the experimental systems was proportional to the total phosphorus release in the anaerobic zone. For every gram of phosphorus released, between 1.1 and 1.2 grams of phosphorus were taken up by the sludge regardless of the operating conditions. Phosphorus uptake by the sludge in the aerobic phase was hindered by the presence of acetate in solution. Uptake commenced only after all of the available acetate was first consumed by the sludge. Distilled water, 0.85 percent sodium chloride, and 5 mM and 50 mM ethylene diamine tetra-acetic acid were used to extract chemically precipitated phosphorus from EBPR sludge. Each of the washing media seemed to cause some cell lysis, suggested by the extraction of non-reactive phosphorus. The duration of wash seemed to affect the extent of cell lysis. Phosphorus fractionation extracts were assayed for deoxyribonucleic acid to determine whether cell lysis occurred. The assay was apparently not affected by the contents of the sludge supernatant. / Ph. D.

Constructed wetlands are considered an inefficient technology for long-term phosphorus (P) removal. The P retention effectiveness of subsurface wetlands can be improved by using appropriate substrates. The objectives of this study were to: (i) use sorption isotherms to estimate the P sorption capacity of the two materials, masonry sand and light weight expanded shale; (ii) describe dissolved P removal in small (2.7 m3) subsurface flow wetlands; (iii) quantify the forms of P retained by the substrates in the pilot cells; and (iv) use resulting data to assess the technical and economic feasibility of the most promising system to remove P. The P sorption capacity of masonry sand and expanded shale, as determined with Langmuir isotherms, was 60 mg/kg and 971 mg/kg respectively. In the pilot cells receiving secondarily treated wastewater, cells containing expanded shale retained a greater proportion of the incoming P (50.8 percent) than cells containing masonry sand (14.5 percent). After a year of operation, samples were analyzed for total P (TP) and total inorganic P (TIP). Subsamples were fractionated into labile-P, Fe+Al-bound P, humic-P, Ca+Mg-bound P, and residual-P. Means and standard deviations of TP retained by the expanded shale and masonry sand were 349 + 169 and 11.9 + 18.6 mg/kg respectively. The largest forms of P retained by the expanded shale pilot cells were Fe+Al- bound P (108 mg/kg), followed by labile-P (46.7 mg/kg) and humic-P (39.8). Increases in the P forms of masonry sand were greatest in labile-P (7.5 mg/kg). The cost of an expanded shale wetland is within the range of costs conventional technologies for P removal. Accurate cost comparisons are dependent upon expansion capacity of the system under consideration. Materials with a high P sorption capacity also have potential for enhancing P removal in other constructed wetland applications such as stormwater wetlands and wetlands for treating agricultural runoff.

abstract / Civil Engineering / Doctoral / Doctor of Philosophy

Ph.D. (Biochemistry) / Please refer to full text to view abstract

The study of nitrate utilization as the final electron acceptor in biological phosphorus removal systems was investigated. The objectives of the study were (1) to determine whether polyphosphate (polyP) microorganisms can use nitrate as the final electron acceptor, and (2) to evaluate and compare polyP accumulation in the biomass of the system using nitrate as the terminal electron acceptor to the system using oxygen as the terminal electron acceptor. Two lab-scale biological phosphorus removal systems were operated as the A/O Process under the same conditions except for the terminal electron acceptor involved. The first system, System I, was operated as an Anaerobic/Anoxic process and the other, System II, was operated as an Anaerobic/Anoxic process. Both systems were operated at a 5-day sludge age and the same nominal hydraulic retention time of 9.1 hours (2.9 hours anaerobic, 6.2 hours anoxic or aerobic). The sludge recycle flow rate was equal to the influent flow rate. The two systems were fed with the same domestic wastewater spiked with sodium acetate and potassium phosphate to give the wastewater a COD concentration of 300-400 mg/L and a phosphorus concentration of 13-14 mg/L as P. Nitrate was fed to the second reactor of System I, while the second reactor of System II was aerated. The results showed that polyP microorganisms can use nitrate as the final electron acceptor. In this research, the Anaerobic/Anoxic system removed more phosphorus (74 mg P/day) from solution than the Anaerobic/Aerobic system (64 mg P/day). The phosphorus content of the sludge in the Anaerobic/Anoxic system was greater than that of the Anaerobic/Aerobic system, i.e. 6.5% as compared to 5.6%. The above evidence strongly confirms that polyP microorganisms can use nitrate as the final electron acceptor and that excess biological phosphorus uptake occurs under anoxic condition. The implication is that COD stored in the anaerobic reactor can be used to simultaneously remove nitrogen and phosphorus, which can substantially reduce the amount of COD required for combined nutrient removal. / Master of Science

The objective of this study was to examine excess biological phosphorus removing bacterial populations and their substrate utilization mechanisms. This study was a smaller part of a overall study of temperature effects upon excess biological phosphorus removal. Bacterial populations in both a continuous flow UCT (University of Cape Town) system and batch reactors were examined by direct counting using a well known staining procedure (Neisser staining), and a microscopic counting method developed by Cech and Hartman (1993). Substrate utilization was examined using PHB (Poly-β -Hydroxybutyrate - an internal substrate storage product) analysis by gas chromatography to supplement COD and acetate measurements. The results showed that Poly-P bacterial counts were significantly greater at a 5 day sludge age compared to a 10 day sludge age. It was noted from microscopic observations that the size of the poly-phosphate granules in the bacteria seemed to be a better indicator of system performance than the actual counts. It also was observed that the 'G' bacteria first described by Cech and Hartman (1993) were abundant at the 10 day sludge age but completely absent at the 5 day sludge age. PHB storage occurred in both the anaerobic zone and the first aerobic tank, and PHB utilization was seen in the subsequent aerobic tanks of the UCT system. The formation of PHB in the first aerobic reactor when no substrate was available supports the Mino (1987) model for excess biological phosphorus removal. In batch studies, substrate storage release were demonstrated in the aerobic zone. This explained why when acetate was present in the aerobic zone net phosphorus uptake didn't occur until all the acetate was utilized. When the temperature was lowered in the UCT system nitrification ceased. This resulted in soluble COD breakthrough into the aerobic zone, which stimulated filamentous growth, and eventually caused a lack of PHB formation. All of these factors contributed to a loss of excess biological phosphorus removal at the low temperature. / Master of Science

Due to the unpredictable nature of sludges, it is imperative to test a sludge from every new process in order to design the sludge handling equipment properly. In this study, sludge from the Virginia Initiative Plant, a pilot scale unit employing the UCT biological nitrogen and phosphorus removal process, operating at Lambert's Point Primary Treatment Plant in Norfolk, Virginia, was tested against sludge from a conventional activated sludge process. A bench scale waste activated sludge unit was employed for the purpose. Tests were conducted to compare batch thickening, vacuum dewatering and centrifugal dewatering characteristics of both sludges. The results obtained indicated both sludges to be highly comparable in all the areas of testing. The results obtained have also been explained in terms of AVI, a measure of sludge floc water content, a fundamental sludge property. Due to the similar nature of the sludges, previously established design criteria can be used for designing the sludge handling equipment for BPR sludges. / M.S.