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

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.

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

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

Ph. D. / incomplete_metadata

The main objective of the research was to investigate the effect of influent organic compounds on the performance of biological nutrient removal system. To carry out the investigation, a pilot plant system was designed and constructed. The system was operated as a UCT process at an influent flow rate of 0.15 liters/minute and a sludge age of 13 days. The influent wastewater was domestic sewage. Excess biological phosphorus removal and steady-state conditions were established before making experimental measurements, or adding supplemental substrate. The effects of separate addition of formic, acetic, propionic, butyric, isobutyric, valeric, and isovaleric acid, plus glucose, addition on phosphorus release under anaerobic conditions, and phosphorus uptake under aerobic conditions, were studied. The effects of the organic acid additions on the removal of nitrogen and COD, and changes in SOUR, MLVSS, and metals such as iron, magnesium, calcium and potassium, were also studied. In all experiments, the specific substrate was added continuously to the first anaerobic reactor for three days at an influent concentration of 100 mg COD/liter. Samples were collected from each reactor at the end of the addition period and analyzed for orthophosphate, nitrate, nitrite, sulfate, volatile fatty acids, COD, MLVSS, pH and metals. All added substrates, except formic acid and dextrose, caused significant increases in phosphorus release in the anaerobic stage, and phosphorus uptake, in the aerobic stage, and consequently, an increase in phosphorus removal efficiency. The molar ratios of phosphorus release to volatile fatty acid added obtained for propionic acid, acetic acid, butyric acid, and valeric acid were 0.44, 0.77, 0.78, and 1.72 respectively. However, on a COD basis, the greatest ratios of mg phosphorus released to mg COD utilized was produced by the addition of acetic acid (0.37) and valeric acid (0.19). It was also found that the branched organic acids, isobutyric and isovaleric, caused more phosphorus release in the anaerobic stage and better phosphorus removal efficiencies as compared with the nonbranching forms of the same organic acids. The molar ratios of phosphorus release for these two acids were 0.8 and 2.3, respectively, and on a COD basis were 0.16 and 0.25. For engineering applications, it is suggested by this research that at least 20 mg COD equivalent of acetic acid is needed for the removal of I mg phosphorus. The results obtained by this investigation were consistent with the hypothesis proposed by Marais et al., 1983. The most recent biochemical models, proposed by Comeau et al., 1986 and Wentzel et al., 1986, were also tested using the data collected in the present investigation. Both models, in most cases, overestimated the ratios of phosphorus release to volatile fatty acid utilized. A speculative model for anaerobic metabolism by poly-p bacteria of volatile fatty acids which contain both odd and even numbers of carbon atoms was proposed. All added substrates produced no effect on both COD and TKN removals. Metal releases were found to correlate with the amount of phosphorus release. / Ph. D.

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.