A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 1987

Attached-growth waste stabilization ponds (AGWSP) are a modification of waste stabilization ponds (WSP), having inert media installed inside the pond water for attached-biomass growth. Stability of AGWSP and WSP when subjected to organic and toxic (cadmium chloride) shock loadings was investigated using laboratory-scale units fed with synthetic waste water and operated at a hydraulic retention time (8) of 5 days. AGWSP showed better performance during transient periods when subjected to shock and increased loadings such as from 100 to 300, 100 to 500 and 50 to 300 kg COD/ (ha. d) . Shock loading of 50 to 300 kg COD/(ha .d) caused a maximum COD (filtered) of 167.4 mg/Lin the effluent, which was higher than a maximum COD (filtered) of 116.9 mg/L in the effluent when a lower magnitude of such as from 100 to 300 kg COD/(ha.d) was applied. A tank-in-series model was applied to predict the pond responses due to shock loadings. A shock loading of 300 kg COD/(ha.d) for one day duration was found to have little effect on the AGWSP performance when being operated initially at 50 kg COD/(ha .d). Cadmium shock loadings at 5, 10, 20 mg / L, applied for one day, was found to have little effects on the COD removal of both AGWSP and WSP. Physical and chemical characteristics of the pond environment were considered to be responsible for cadmium removal. AGWSP was more effective in cadmium removal at 5 and 10 mg/L cadmium shock loads, but at the 20 mg/L cadmium shock load , both ponds behaved similarly. Peak effluent cadmium concentrations did not exceed 1.6 mg/L at all shock loadings.