ISSN-0169-6246 Report no 70 Wastewater reuse for irrigation in Cali Region, Colombia Communications of the Department of Water Management, Environmental and Sanitary Engineering February 1997 Meike van Ginneken MSc. Cali tertiarycanal flexitube sugarcane offtake ^—\"A rjii nvwwíA Faculty of Civil Engineering Mechanics & Structures TUDelft Structural Mechanics Technische Universiteit Delft TTI I n\ 1X4. Faculty of Civil Engineering ' ^^ ^^ ^ ' ' *• Department of Water Management, university of Technology Environmental and Sanitary Engineeering Wastewater Reuse for the Irrigation of Sugarcane in Cali Region, Colombia Communications Report no. 70 MeiKe van omnenen February 1997 LIBRARY IRC PO Box 93190, 2509 AD THE HAGUE Tel.: +31 70 30 689 80 Fax: +31 70 35 899 64 BARCODE: |l(, S>m LO: T Publication of the Department of Water Management, Environmental and Sanitary Engineering ISSN-0169-6246, report no. 70 Faculty of Civil Engineering Delft University of Technology P.O. box 5048 2600 GA Delft, The Netherlands Copies to be ordered: Ms. E.G. Rothfusz, secretary Room 4.75, Phone 015-2781646, Fax 015-2785559 Preface This report is a revision of my MSc thesis for the faculty of Civil Engineering, department of Water Management, Environmental and Sanitary Engineering of Delft University of Technology. My thesis project took place from November 1995 to August 1996, including a five months field period in Cali, Colombia. The field period was carried out with assistance of CINARA, the Universidad del Valle and the Convenio IHE-DUT-Univalle. I like to thank the following people in Cali for their kind cooperation: Miguel Peña, Hernán Materon, Inés Restrepo, Henri Jimenez, Huub Gijzen, and Rob Lloyd. In Delft I am grateful to Prof.ir. R. Brouwer, prof.dr. M.Donze, prof.ir. J.H.J.M. van der Graaf and ir. P. Ankum for their help and guidance. Meike van Ginneken. February 1997. Summary Wastewater reuse is the process of treating wastewater for beneficial uses, its transportation to the place of use and its actual use. Reuse of wastewater is a way to minimize depletion and contamination of natural water sources, by reintroducing (partly treated) wastewater as an alternative water resource. This project focusses on direct reuse for irrigation of sugarcane. Antecedents and Objective The Valle de Cauca is the basin of the river Cauca, and is located in the South-Western part of Colombia, Latin America. The river Cauca is a highly contaminated river, which is anaerobic for a long stretch. The contamination is for a large part caused by the disposal of untreated municipal wastewater from the city of Cali. Parts of the Valle de Cauca suffer from depletion of water sources. The general objective of this study is to evaluate possibilities for treatment by natural aquatic treatment, transportation, storage and distribution of wastewater effluent from the EMC ALI wastewater treatment plant Cañaveralejo in Cali, Colombia to suit irrigation needs of sugarcane cultivation in the Valle de Cauca. A specific objective is to assess whether treatment by a natural aquatic treatment system for large amounts of domestic wastewater is feasible with regard to use of land area, and socio- economically attractive through the yield of profitable products. The second specific objective is to investigate how the use of wastewater influences sugarcane irrigation, and to integrate wastewater considerations into a distribution system. The Cañaveralejo wastewater treatment plant is the largest to be built in Cali, It will treat 7.6 mVs of domestic and industrial wastewater. The primary effluent of the plant is taken as the influent of the reuse scheme. The quality of the primary effluent of the Cañaveralejo plant is estimated based on the design, data on other plants, measurements, and literature data. The required irrigation water quality is based on literature and local circumstances. The irrigation area of the reuse scheme is located on the right bank of the river Cauca. Design A design for a reuse scheme of the effluent of the Cañaveralejo plant is made. This design includes a duckweed pond system for a flow of 475 1/s, which is 4% of the wastewater of Cali. An alternative irrigation scheme, which uses the duckweed pond effluent is made with a size of 936 ha, which is 0.5% of the agricultural area of the Valle de Cauca. A pond system is selected as the most appropriate treatment system, as it guarantees a high performance and is technically feasible. The pond systems consist of four series of ponds, each of which consist of a 1450 m2 anaerobic pond, a 12,800 m2 facultative pond, and two 11,200 m2 maturation ponds, on which duckweed is grown. Total surface area of the pond system is 20 ha. An alternative subsurface flow wetland design is made. This system turns out to be technically unreliable and more expensive to construct than the duckweed pond system. The effluent of the pond system is more suitable for irrigation than primary effluent. The pond system removes the following harmful substances from the wastewater: BOD, suspended solids, excess nitrogen, helminth eggs, and trace elements (notably cadmium). The designed irrigation system is a furrow irrigation system, flexitubes as quaternary canals, and lined canals. The irrigated area is divided into 10 tertiary units, which get water proportionally. Irrigation and drainage systems are separated. Irrigation is intermittent. Overall efficiency is 49%. The scheme is dual- managed. The canal system has a capacity of 978 1/s. The canal system is an upstream control system with fixed structures (weirs). Water Balance A surface water balance and a groundwater balance of the complete Valle de Cauca are made. These balances show that there is no permanent overexploitation of natural water resources. Groundwater resources are temporarily overexploited in dry periods, especially in areas where farmers use groundwater for irrigation. Economic evaluation The evaluation includes a financial cost-benefit analysis and a qualitative checklist. This checklist judges impacts which are hard to express in financial terms: effectivity, technical feasibility, institutional and regulatory aspects, social impacts, and environmental impacts. An evaluation is made of three alternatives: 1. Reuse with pond system effluent; 2. Reuse with primary effluent; 3. No reuse; activated sludge treatment, and present irrigation scheme; The evaluation shows that alternative 1 and 3 are feasible alternatives. Alternative 1 has a more favorable score than alternative 3. Alternative 2 is inexpensive, but ineffective. Conclusions Reuse of part of the Cañaveralejo effluent for the irrigation of sugarcane of the area between the Rio Cauca and Rio Fraile is an economically feasible and sustainable alternative to decrease effluent disposal problems of Cali. The Cañaveralejo reuse scheme is cheaper to construct, operate and maintain than the combination of an activated sludge treatment and the old irrigation scheme. The quality of the primary effluent of Cañaveralejo plant can serve as a reliable source for irrigation after treatment with a duckweed pond system, without putting at risk public health, crops or soils. Duckweed pond systems are technical feasible for large quantities of domestic wastewater. The use of subsurface flow wetlands for the treatment of large urban wastewater flows is not yet a feasible option, as knowledge about and experience with functioning, design, operation and maintenance under tropical circumstances are limited. The wetland concept is promising for Colombia, where temperature is constant and high yearround. The effluent of a duckweed pond system influences sugarcane irrigation by providing nutrients. The wastewater provides part of the nutrient demand of the sugarcane, so less fertilizer has to be applied. Maintenance of canals and structures increases due to weeds. An improved centralized irrigation scheme is more economical than unimproved individual farm irrigation schemes, with or without wastewater reuse. An improved furrow irrigation system with flexitubes as quaternary canals, larger furrow spacing, and lined canals can halve water demand. The need for reuse of wastewater in the Valle de Cauca will increase in the coming years. Contamination will be increased by population growth and the rise of the standard of living. Depletion of groundwater and surface water is a growing problem, as water demand for agriculture, human use and industry increases. Reuse of municipal wastewater is, however, only a very small factor in solving depletion problems: only 6% of the water use in the Valle de Cauca is used for domestic uses. Reuse projects are more attractive in areas where presently groundwater is used for irrigation. Pumping costs are higher and depletion a serious environmental problem. Resumen Reuso de aguas residuales municipales de cali para el riego de caña de azúcar Antecedentes y objetivo Este proyecto se enfoca en el reuso agrícola directo, considerando el tratamiento, transporte y distribución de aguas residuales para riego. El Rió Cauca es una fuente altamente contaminada, especialmente por las aguas residuales de la ciudad de Cali. El Valle del Cauca sufre de un agotamiento paulatino de sus recursos naturales acuáticos y por lo tanto el reuso agrícola de aguas residuales municipales podría ser una solución atractiva para ayudar a solucionar los problemas de contaminación y agotamiento del recurso. Para determinar la factibilidad económica del reuso se necesitan investigaciones más detalladas. El objetivo general del