No description available.

by Po-keung Wong. / Thesis (M.Phil.)--Chinese University of Hongkong. / Bibliography: leaves 265-298.

An alum coagulation treatment facility employing mixing, flocculating, and settling units, designed by criteria commonly used in the design of water treatment facilities, was operated to determine whether or not it could effectively remove algae and other suspended matter from raw sewage stabilization lagoon effluent. Algal sludge produced by the treatment facility was investigated: (1) to evaluate its potential as a soil conditioner; (2) to determine whether a stabilization lagoon could be used for algal sludge disposal; and (3) to determine whether or not sludge recirculation would reflect a chemical savings. The experimental lagoons and treatment facility, owned by Sanitary District No. 1 of Pima County, Arizona, were located near Tucson, Arizona. It was found, in a field study, that mixing, flocculating, and settling units commonly used for water treatment were efficient in clarifying lagoon effluent and produced a water with the appearance of tap water. Active photosynthesizing algae, producing high oxygen concentrations in lagoon effluent, caused flotation of alum coagulated algal sludge; however, by selecting lagoon effluent low in dissolved oxygen content, algal sludge flotation in the treatment facility was prevented. Algal sludge with Less than one percent total solids was readily dewatered in three days by sand bed drying. Resuspension of air dried algal sludge resulted in a maximum moisture uptake of 50 percent of the final wet weight. Dry algal sludge contained 47 to 61 percent volatile solids, 1.6 to 5.2 percent total phosphorus, and 3.6 to 4.9 percent organic nitrogen. No significant amount of ammonia nitrogen or nitrite-nitrate nitrogen was present in the sludge. The composition and characteristics of dry algal sludge indicate applicability as an aid to soil conditioning. For three months the characteristics of a lagoon used for algal sludge disposal were compared with a control lagoon operated in parallel; it was found that the returned algal sludge was not detrimental to the stabilization process. Acid treated and non-acid treated algal sludge produced from completely treated lagoon effluent had a clarifying value when reused with alum to coagulate effluent, but neither acid treated nor nonacid treated sludge produced from partly treated effluent caused additional clarification when returned with the same coagulant dose that initially produced the sludge. None of the different types of return sludge investigated had a clarifying value when returned under operating conditions necessary to obtain a coagulant savings.

The application of high rate algal ponds (HRAP) in the treatment of brewery effluent that met the South African Department of Water Affairs and Forestry's (DWAF) general limits for discharge into a natural water resource of 1998 were tested during a lO-month baseline phase, followed by an 11-month optimization phase. The objective of the baseline phase was to monitor the seasonal performance of HRAPs. The hydraulic retention time (HRT) fluctuated between 11.16 d and 12.00 d in HRAPs. The chemical oxygen demand (COD) increased from 130.12 ± 6.94 mg/L (post-AD), to 171.21 ± 7.99 mg/L (post-HRAP) . The presence of algal cells and evaporation contributed towards an increase in post-HRAP COD. The ammonia (NH₄-N) concentration decreased from 46.59 ± 2.47 mg/L (post-AD), to 1.08 ± 0.12 mg/L (post-HRAP). The nitrite (NO₂- N) concentration remained below 1.00 mg/L in post-pilot plant AD, post-PFP and post-HRAP effluent. The phosphate (PO₄-P) concentration decreased from 29.81 ± 1.39 mg/L (post-AD) to 17.30 ± 1.16 mg/L PO₄-P. The objective of the optimization phase was to manipulate the HRT to achieve the maximum treatment rate that met the DWAF general limits for discharge into a natural water resource of 1998. Nitrogen (as NH₄-N, NO₃-N, NO₂-N) removal efficiency was used as an indicator of nutrient removal success. HRT was influenced by season. The optimal HRT for autumn was 4.30 d at a temperature of 20.53ºC in HRAP A2 (heated) and 18.96ºC in HRAP B2 (ambient). The optimal HRT for summer was 2.74 d at 29.90ºC in HRAP A2 (heated) and 26.36ºC in HRAP B2 (ambient). The COD decreased from 152.33 ± 4.85 mg/L (post-AD) to 95 .00 ± 3.75 mg/L (post-HRAP A2), and to 100.82 ± 5.93 mg/L (post-HRAP B2). The incoming NH₄-N concentration decreased from 42.53 ± 1.38 mg/ L (post-AD), to 1.70 ± 0.81 mg/ L (post-HRAP) . The nitrate (NO₃-N) concentration post-HRAP was 12 - 14 mg/L. The main methods for NH₄-N removal were probably NH₄-N volatilization through algal uptake. HRAPs were able to lower nitrogen and phosphorous concentrations to within the DWAF limits under normal operating conditions. It is recommended that HRAP treated brewery wastewater be used for irrigation after salt removal, or alternatively, for groundwater recharge . Regulatory exemptions would be required for higher than permitted COD and EC concentrations to enable these actions.