Integrated Wastewater Management in the Lake Atitlán Basin: an Ecological Engineering Challenge
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Integrated Wastewater Management in the Lake Atitlán Basin: An Ecological Engineering Challenge GREGORY HINDS1, KELLY VANNOY1, ELIZABETH JACHENS2, STEWART OAKLEY2* 1University of South Florida, Tampa, Florida, USA 2California State University, Chico, California, USA *Corresponding author: email: [email protected], Tel: 1-530-898-4976 Initial Study Conducted: 2012 Report Prepared: 2013 Revised: 2014 Completed: 2015 ABSTRACT Lake Atitlán, Department of Sololá, Guatemala, is undergoing rapid water quality degradation as a result of the ongoing discharge of wastewater from the basin’s population (>250,000) into the lake. This is a direct threat to the ecology of the lake, to public health, and to the future economic stability of the region. The purpose of this paper is to establish and evaluate wastewater management alternatives for the mitigation of this threat. It is imperative that wastewater management within the basin prevents the anthropogenic loading of nutrients into the lake. Thus, treatment processes for nutrient removal before discharge to the lake and wastewater export were identified as the only practical options. Accordingly, the following two alternatives were evaluated and compared: (1) decentralized wastewater treatment within each municipality through the use of secondary and tertiary treatment systems for nutrient removal; and (2) export of wastewater from each municipality via an integrated pipeline network to a centralized wastewater stabilization pond system outside of the basin designed to enable effluent reuse in agriculture and the recovery of energy through anaerobic pretreatment. A life cycle cost analysis (LCCA) approach was taken in comparing the alternatives. Capital costs, projected operation and maintenance costs, and wastewater valorization potential over the 20 year design life, ranging from 2016 to 2036, were included in the LCCA. The results of the analysis indicate that the export/reuse alternative is the economically and environmentally superior option and is therefore the most appropriate solution for integrated wastewater management within the Lake Atitlán basin. i TABLE OF CONTENTS 1. Introduction ............................................................................................................................. 1 2. History- Lake Studies ............................................................................................................. 2 2.1 Lake Washington.............................................................................................................. 2 2.2 Lake Tahoe ....................................................................................................................... 2 2.3 Lake Amatitlán ................................................................................................................. 3 3. Lake Atitlán ............................................................................................................................ 4 4. Wastewater Management Alternatives ................................................................................... 6 4.1 Assessment of Initially Considered Wastewater Management Alternatives ................... 7 4.2 Activated Sludge Treatment with Tertiary Processes for Nutrient Removal ................... 7 4.2.1 Life Cycle Cost Analysis .......................................................................................... 7 4.3 Wastewater Export to a Centralized Wastewater Stabilization Pond System ................ 10 4.3.1 Sewer Pipeline ........................................................................................................ 11 4.3.2 Hydroelectric Power Potential ................................................................................ 16 4.3.3 Wastewater Stabilization Pond System and Methane Production .......................... 18 4.3.4 Effluent Reuse ......................................................................................................... 22 4.3.5 Sludge Management................................................................................................ 24 4.3.6 Life-cycle Analysis ................................................................................................. 25 5. Conclusions and Recommendations ..................................................................................... 27 Acknowledgements ....................................................................................................................... 32 References ..................................................................................................................................... 32 ii 1. INTRODUCTION Lake Atitlán is located in the southwestern highlands of Guatemala. An ancient volcanic explosion formed the enormous caldera that now harbors the lake. It is the deepest lake in Central America with a depth of over 340 meters. Lake Atitlán has been described by many as one of the most beautiful lakes in the world (Huxley, 1934) and is listed as one of the 500 most sacred places on Earth by National Geographic. Lake Atitlán is a site of great ecological, economic, and cultural significance, it is a prevailing tourist destination, recreational site, and fishery, and it is also the primary source of water for human consumption in the watershed. Figure 1-1 shows a picture of Lake Atitlán taken in 2012 from the east side of the lake. Figure 1-1: Lake Atitlán, Volcano Toliman (left), and Volcano San Pedro (right) The Lake Atitlán watershed is a large endorheic basin which contains 18 municipalities. The total population of the basin is estimated to be in excess of 250,000 people (INFOM, 2013). The majority of the municipalities in the basin do not have wastewater treatment facilities. The wastewater from the shoreline municipalities is discharged directly to the lake and the wastewater from the elevated municipalities is discharged to rivers and streams that flow to the lake. Other wastewater that percolates into the groundwater further contributes to the contamination of the lake. The ongoing deposition of wastewater into Lake Atitlán has significantly increased the concentration of nutrients and pathogens in the lake water which has dramatically altered the aquatic ecosystem and imperiled human utility. The once oligotrophic Lake Atitlán is now noticeably undergoing eutrophication. Algae blooms in 2008 and 2009 brought worldwide attention to the severity of the situation. The welfare of the lake, the lake basin, and all of its inhabitants are dependent upon the development and implementation of a sustainable wastewater management plan within the watershed which inhibits the influx of nutrients and pathogens to the lake. The purpose of this study is to: (i) establish potential alternatives for the integrated management of wastewater within the Lake Atitlán basin, (ii) assess the feasibility of the alternatives based on economic and environmental sustainability using a life cycle cost analysis approach, and (iii) develop conclusions, recommendations, and preliminary designs pertaining to the proposed alternative. 1 2. HISTORY- LAKE STUDIES Water quality degradation and cultural eutrophication is a common threat to freshwater lakes within populated watersheds worldwide. Raw wastewater and effluent waters from wastewater treatment plants represent the large majority of the contamination responsible for this threat. Some heavily contaminated lakes, such as Lake Amatitlán near Guatemala City, have become toxic, hypereutrophic bodies of water that are hazardous to their surrounding environment and the local residents. Many other lakes have been saved from this tragic fate through the completion of well-designed contamination control projects in the field of wastewater management. For example, Lake Washington and Lake Tahoe in the western United States began showing signs of eutrophication early on in the 20th century but subsequent wastewater effluent diversion projects were completed and the lakes were restored to their initial oligotrophic conditions. There are now dozens of documented examples demonstrating that eutrophication is detrimental to aquatic ecosystems and that eutrophication indicators, including both total algal biomass and algal/cyanobacterial bloom occurrences, decrease after nutrient input from wastewater is reduced. The cases of Lake Washington, Lake Tahoe, and Lake Amatitlán are discussed in greater detail herein. 2.1 Lake Washington By the early-1920’s, the water quality of Lake Washington within metropolitan Seattle, Washington was declining, and what was previously an oligotrophic lake had begun its descent to a eutrophic system. Despite prevalent use of wastewater treatment facilities, the lake sustained noxious cyanobacteria blooms from the 1920’s through the 1960’s because of sewage effluent inputs. Actions to prevent the sewage effluent from entering Lake Washington started in the 1960’s. An elimination of sewage and treatment discharges to Lake Washington was imposed in 1968, and a diversion project was completed soon after. The cyanobacterial blooms immediately began to decline as a result (Chandra et al., 2013; Restoration, 1992). 2.2 Lake Tahoe Lake Tahoe is roughly twice the size of Lake Atitlán. It is known throughout North America for its stunningly clear and deep blue waters with Secchi disk readings between 23 and 33 meters. This pristine oligotrophic lake, nestled high in the Sierra Nevada Mountains of California, set precedence for large scale sewage effluent exportation to a reservoir outside of the