Honduras Wastewater Treatment: Chemically Enhanced Primary Treatment and Sustainable Secondary Treatment Technologies for Use with Imhoff Tanks by Robert C. McLean B.S. Civil Engineering Environmental Engineering Concentration California State Polytechnic University – Pomona, 2008 SUBMITTED TO THE DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTERS OF ENGINEERING IN CIVIL AND ENVIRONMENTAL ENGINEERING AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY JUNE 2009 © 2009 Massachusetts Institute of Technology All rights reserved Signature of Author………………………………………………………………………………… Robert C McLean Department of Civil and Environmental Engineering May 8, 2009 Certified by………………………………………………………………………………………… E. Eric Adams Senior Research Engineer and Lecturer of Civil and Environmental Engineering Thesis Supervisor Accepted by………………………………………………………………………………………... Daniele Veneziano Chairman, Departmental Committee for Graduate Students Honduras Wastewater Treatment: Chemically Enhanced Primary Treatment and Sustainable Secondary Treatment Technologies for Use with Imhoff Tanks by Robert C. McLean Submitted to the Department of Civil and Environmental Engineering on May 8, 2009 in partial fulfillment of the requirements for the Degree of Masters of Engineering in Civil and Environmental Engineering ABSTRACT Wastewater treatment within Honduras is indicative of the state of water and sanitation services throughout the developing portions of Central America. One technology which comprises approximately 40 percent of all treatment facilities within Honduras is the Imhoff tank. First patented in 1906 the Imhoff tank has long been out of favor within the developed world as newer technologies and large centralized processing of wastewater have developed. Nevertheless, Imhoff tanks remain appropriate primary treatment technology for decentralized facilities like those found throughout Honduras. A large number of Honduras’ systems have fallen into various states of disrepair due to neglect through lack of proper maintenance. One system within the municipality of Las Vegas, Honduras was examined extensively to determine the appropriateness of rehabilitating these systems utilizing various enhancement technologies. Water quality measurements were obtained for the Las Vegas system, which was found to be providing only negligible removals of wastewater constituents. Two large factors figuring into this are: measured flow rates were approximately 50 percent higher than originally anticipated in design and routine maintenance on the system has been neglected. Utilizing chemically enhanced primary treatment with ferric chloride as a coagulant, it was possible to increase removal efficiencies and achieve regulatory effluent standards for chemical oxygen demand, turbidity, and pH, despite the high flows. However, it is doubtful the costs associated with dosages required to achieve these removals are sustainable for communities such as Las Vegas. To address these deficiencies further sustainable practices for optimizing the Imhoff tanks as well as designs for both pre-treatment and secondary treatment options appropriate for use in Honduras were developed. The recommended system allows achievement of regulatory effluent levels while maintaining low annual operating costs for the system. Thesis Supervisor: E. Eric Adams Title: Senior Research Engineer and Lecturer of Civil and Environmental Engineering Acknowledgements: Many hands can move mountains – Similarly many people have contributed to the creation of this work. The help and encouragement of these people have set in place the stones that make up the path that I have travelled in arriving at this point. Some of whom I have had the opportunity to know for only a brief period. Others have provided inspiration, insight, and a light to find my way in the years that have led up to this point. First, I would like to thank the efforts of my teammates Mahua Bhattacharya and Lisa Kullen who provided assistance, humor, and familiar faces while on our journey in Honduras. Most importantly they provided the reminder that I was not going this alone. Thanks also go out to Aridaí Herrera who provided invaluable insight, coordination, and resources for efforts both here at MIT and in Honduras. Ari was instrumental in coordinating numerous events and meetings, transporting us within Honduras, and acting as a translator. Without Ari’s assistance far more difficulties would have been encountered in trying to perform this work while in Honduras. I would also like that thank my thesis advisor, Dr. E. Eric Adams; were it not for Eric’s insights and experience in leading students through the fast paced Masters of Engineering program at MIT far more difficulty would have been encountered along the way. Thanks are owed to Eric for selecting me for the opportunity of researching and working within the fascinating country and culture of Honduras. Eric’s insights, experience, and encouragement have been instrumental in arriving at this completed work. I would also like to thank the community of Las Vegas, Luis and Carolina Evelyn, and Victor Cuevas for your gracious hospitality and assistance while I was in Honduras. Similarly I would like to thank Charlie Tyler of the Massachusetts Water Resource Authority for assisting me in obtaining samples for research and sharing his experience. Many people provided inspiration and encouragement prior to me starting my journey here at MIT, people who without the help of, I would not ever have arrived here. The Department of Civil Engineering at California State Polytechnic University-Pomona provided the foundation upon which to build my engineering career, I would like to thank the entire faculty within that department for passing along the torch of knowledge. To my Mother, Sister Jennifer, and Brother Pete, thank you immensely for the familial support and encouragement that was needed to hone me into the person I have become. Similarly I would like to thank the person who I will soon be striking off on familial endeavors of my own with, Brittany Salter. Without Brittany’s encouragement and shared experience I would not have been able to complete a large portion of my academic journey. She continues to be an inspiration in so many facets of my life. I have had the opportunity to enjoy her company along many of the steps taken upon this path. Were it not for her compassion, understanding, knowledge, and friendship this journey would have been far more difficult. Thanks, Robert C McLean Table of Contents CHAPTER 1: INTRODUCTION .............................................................................................................................. 8 1.1 BACKGROUND OF RECENT STUDIES PERFORMED WITHIN THE LAS VEGAS REGION ............................................ 9 1.2 SCOPE OF THIS WORK ........................................................................................................................................ 10 CHAPTER 2: SURVEY OF WATER AND SANITATION WITHIN HONDURAS ......................................... 11 2.1 HONDURAS GENERAL – INTRODUCTION ............................................................................................................ 11 2.2 WATER AND SANITATION WITHIN HONDURAS .................................................................................................. 12 2.3 REGULATORY FRAMEWORK OF WASTEWATER SECTOR WITHIN HONDURAS .................................................... 13 2.4 IDENTIFIED TRENDS .......................................................................................................................................... 15 2.4.1 Design Trends ........................................................................................................................................... 16 2.4.2 Operation and Maintenance Trends ......................................................................................................... 16 2.4.2.1 General Maintenance .......................................................................................................................................... 16 2.4.2.2 Water Quality and Monitoring ............................................................................................................................ 16 2.4.2.3 Sludge Management ............................................................................................................................................ 17 2.4.3 Trends in Community Issues ..................................................................................................................... 17 2.5 RECOMMENDATIONS FROM SURVEY REPORT .................................................................................................... 18 CHAPTER 3: EXAMINATION OF IMHOFF TANK SYSTEMS ...................................................................... 19 3.1 INTRODUCTION TO IMHOFF TANKS:................................................................................................................... 19 3.2 DESIGN GUIDELINES FOR AN IMHOFF TANK : ..................................................................................................... 19 3.3 MAINTENANCE REQUIREMENTS FOR IMHOFF TANKS : ....................................................................................... 22 3.4 ADVANTAGES AND LIMITATIONS OF IMHOFF SYSTEMS : .................................................................................... 23 3.5 SUMMARY : .......................................................................................................................................................