San Andres Island is located in the Caribbean northwest of the Colombian Coast. The northern part of the island is the center of the urban population and tourism, whereas the southern part of the island has a lower density, more rural population. The existing total water demand for the entire island is estimated around 5.14 mgd; however, the existing infrastructure for water supply only has an installed capacity of 2.65 mgd. This water supply infrastructure includes a water softening plant with a rated capacity of 1.5 mgd, located in the center of the island, plus a seawater reverse osmosis (RO) plant serving the northern part of San Andres with a capacity of 1.14 mgd. This plant was built in 2005 and is currently operated under a private concession agreement. Groundwater levels have declined and deteriorated to the point that only 0.34 mgd can currently be produced in the softening plant. The water supply problem is compounded by the fact that unaccounted water losses have been determined to be as high as 70%. To address these serious near term problems and to develop a long term reliable and sustainable water supply for the island, the Colombian government has undertaken a three phase approach which includes a Short Term Emergency Supply desalination plant with a capacity of 0.57 mgd (25 lps), a Medium Term Desalination system with a capacity of 1.14 mgd (50 lps), and the development of comprehensive Water Resources Master plan (WRMP). The WRMP was the first phase to be initiated and started with an analysis of all aspects of the water cycle, including water sources, water treatment, wastewater collection and disposal, rainwater management and the social and environmental aspects in the island. Water treatment technologies being evaluated include water softening, retrofitting and optimization of the existing facilities, brackish water reverse osmosis, wastewater reuse, rain water collection, and seawater RO. Preliminary results from this study have indicated that while other water supply and treatment options may help to supplement the longer term water supply solution, seawater reverse osmosis is the best water supply option to address the current water supply shortfall. As a result, the Short Term Emergency Supply and the Medium Term Supply Desalination Plant were initiated. This paper will present the design concept and considerations for the Medium Term Desalination Plant, which is being developed as a fast track desalination solution on a Design/Build contract basis. The approach for integration of the Medium Term Desalination plant into the existing seawater desalination plant site will also be presented. The paper will also present opinions of cost for the capital and operation and maintenance costs for the Medium Term Desalination Plant. While the existing seawater RO plant has been successful and generally provided a reliable supply of potable water, this paper will examine a number of improvements that are proposed for incorporation in the new facility including deeper supply wells for more consistent feed water supply and quality, greater spacing distance between the wells to reduce interaction between the wells, more redundancy of the pretreatment equipment for higher reliability, higher efficiency barometric energy recovery devices, membrane elements with reduced pressure loss, standby emergency diesel generator, improved product passivation, and better accessibility for equipment operation and maintenance.
This presentation is available to AMTA Members only.
- Kurt Kiefer, PE, BCEE / Pedro Antonio Rojas Pena
- CDM Smith Inc.
- AMTA/AWWA Membrane Technology Conference, Long Beach, CA
- AMTA/AWWA Membrane Technology Conference
- Seawater, Desalination, Reverse Osmosis