Chemically enhanced primary treatment of wastewater in Honduran Imhoff tanks

Abstract

Imhoff tanks represent approximately 40% of the wastewater treatment infrastructure in Honduras. This thesis evaluates the usage of solid aluminum sulfate as a means to achieving national effluent regulations in Imhoff tanks in the municipality of Las Vegas, Santa Barbara. The report contains a brief background on both Imhoff tanks and chemically enhanced primary treatment and a discussion of the governing technical considerations. The residents of Las Vegas produce a very high amount of relatively dilute domestic wastewater (approximately 1,000 liters/person/day). Bench scale testing and pilot testing during January 2008 in the Las Vegas Imhoff tanks found that a dosage of approximately 150 mg/l alum (17% Al2O3) was necessary to treat Las Vegas? domestic wastewater. However, solution preparation and chemical injection were found to be difficult to achieve under current conditions and the cost of alum in this quantity is prohibitively expensive. The final recommendations to the municipality of Las Vegas include encouragement to conserve water and a comprehensive plan to better maintain the Imhoff tanks in order to achieve higher levels of treatment. This thesis also documents the author's efforts to ascertain the status of Imhoff tanks in the rest of Honduras in terms of their size, design, and maintenance. During January 2008 three other Imhoff tanks in the department of Santa Barbara and one in the department of La Paz were visited and all were found to be in varied states of disrepair. However, several hold the potential to be rehabilitated after the removal of sludge.