Optimization of wastewater stabilization ponds in Honduras

Abstract

During the academic year of 2008-2009, three Master of Engineering students from the Department of Civil and Environmental Engineering at the Massachusetts Institute of Technology (MIT) conducted a study of wastewater treatment systems in Honduras. Building upon previous research, this study assessed the state of centralized wastewater treatment facilities. The project included travel to Honduras in January 2009 for a field survey of these facilities. In addition, the students undertook more focused individual work on various facets of sustainable wastewater treatment. Robert McLean examined options for enhancing performance of an existing Imhoff tank. Mahua Bhattacharya investigated sludge handling practices and alternatives including a study of sludge resource value and potential reuse. Lisa Kullen studied flow behavior in waste stabilization ponds focusing on benefits to effluent quality attainable through operational modifications. This thesis presents a summary of this investigation including a Honduran national and water sector background, and trends based upon site visits and observations. With the context of the sanitation sector thus defined, a detailed investigation of wastewater stabilization ponds follows. This study explores hydrodynamic changes and water quality improvements attainable through various modifications in maintenance and operation of these facilities. Extensive use of flow modeling is employed to demonstrate the quantifiable impact of the modifications discussed.

(cont.) Analytical calculations of ideal pond performance are compared to computer numerical flow modeling results, computed using the INTROGLLVHT modeling software. This comparison examines the sensitivity of pond performance to a number of variable factors including sludge accumulation and distribution, pond outlet geometry, and inlet flow symmetry. The largest effect and greatest sensitivity was found for unbalanced, asymmetric flows, yielding greatly reduced pond efficiency. Sludge accumulation had a significant effect on final effluent quality due to reduced pond volume and residence time. However, the distribution of a given volume of sludge and the spacing of pond outlets both had minimal effect on effluent quality. Recommendations for pond maintenance developed from this analysis include a careful balance of pond flow and strict adherence to a scheduled desludging routine.