Thesis (M. Phil.)--University of Hong Kong, 1989.

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

Prolific growth of Ulva lactuca L. in some marine environments into which sewage is discharged causes many problems. An understanding of the reasons for this growth is required so that it can be controlled or prevented. The thesis is concerned with tackling this problem and also investigating whether Ulva lactuca can be used as an indicator organism for pollution. Prior to studies on growth of Ulva in polluted conditions, its pattern of life-history and mode of growth had to be elucidated. These findings led to the development of suitable laboratory culture facilities and development of a technique for studying growth by use of excised discs of thallus tissue. Laboratory culture was based upon the use of Erdschreiber medium and growth measured by percentage increase in area after two weeks in culture. Laboratory nutrient bioassays using growth rate measurements were used to determine the effects of likely growth rate stimulating substances found in sewage, including three nitrogen forms, (nitrate-N, nitrite-N and ammonium-N), orthophosphate, acetate, adenine and kinetin, and sewage-contaminated mud itself. Only ammonium-nitrogen within the range 0.4 to 7.8 mg dm -3, and sewage-contaminated mud, were found to significantly stimulate the growth rate of Ulva above that of Erdschreiber control medium. Further growth rate assessments were made with samples of field seawater collected at points throughout two sewage-polluted harbours, Poole in Dorset with an Ulva problem, and Langstone in Hampshire at present without a problem. The results obtained were correlated with the concentrations of nutrients in the water samples, and with results of the earlier artificially enriched seawater experiments. Ammoniumnitrogen was confirmed to be the only compound in field water which significantly stimulated growth of Ulva over that obtained with the control medium. The regions where prolific growth of Ulva occurred in Poole Harbour were the only areas which had field water with ammonium-nitrogen levels elevated to the range &aown in laboratory studies to cause significantly higher growth rates of Ulva discs. Water from Langstone Harbour although sewage-polluted did not stimulate growth of Ulva discs and water analysis revealed. ammonium- nitrogen levels below those determined as growth stimulatory. The ability of Ulva to act as a test organism for a range of toxic substances including industrial/domestic sewage sludge, detergent, copper, zinc, lead, cadmium and mercury was studied. Graded growth responses were obtained for these components, and toxic levels of them were found to be similar to those for other macro-algae. Ammonium-nitrogen was thus found to be the factor responsible for prolific growth of Ulva in the field. In order to prevent or minimise nuisance caused by enhanced Ulva growth it is recommended that the level of ammonium-nitrogen is kept below 0.3 mg dm -3 in seawater at all times. Because of specificity of response to a siaagle compound it is concluded that Ulva cannot be used as a general pollution indicator species, but its prolific growth in the field certainly indicates elevated ammonium-nitrogen levels.

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Graduation date: 1973

Thesis (M.S. - Civil Engineering and Engineering Mechanics)--University of Arizona. / Includes bibliographical references.

Thesis (Ph. D. - Civil Engineering and Engineering Mechanics)--University of Arizona. / Includes bibliographical references.