Wastewater use in agriculture: irrigation of sugar cane with effluents from the Cañaveralejo wastewater treatment plant in Cali, Colombia.

In Valle del Cauca, south-west Colombia, surface and ground waters are used for sugar cane irrigation at a rate of 100 m3 of water per tonne of sugar produced. In addition large quantities of artificial fertilizers and pesticides are used to grow the crop. Preliminary experiments were undertaken to determine the feasibility of using effluents from the Cañaveralejo primary wastewater treatment plant in Cali. Sugar cane variety CC 8592 was planted in 18 box plots, each 0.5 m2. Six were irrigated with conventional primary effluent, six with chemically enhanced primary effluent and six with groundwater. For each set of six box plots, three contained local soil and three a 50:50 mixture of sand and rice husks. The three irrigation waters were monitored for 12 months, and immediately after harvest the sugar content of the sugar cane juice determined. All physico-chemical quality parameters for the three irrigation waters were lower than the FAO guideline values for irrigation water quality; on the basis of their sodium absorption ratios and electrical conductivity values, both wastewater effluents were in the USDA low-to-medium risk category C2S1. There was no difference in the sugar content of the cane juice irrigated with the three waters. However, the microbiological quality (E. coli and helminth numbers) of the two effluents did not meet the WHO guidelines and therefore additional human exposure control measures are required in order to minimize any resulting adverse health risks to those working in the wastewater-irrigated fields.

Feasibility of waste stabilization pond technology for small municipalities in Colombia.

The selection of any wastewater treatment technology should take into consideration both "software" and "hardware" aspects. There are contrasting opinions regarding the feasibility of waste stabilisation ponds (WSP): some emphasise their advantages while others are concerned with their high land area requirements. As with any technology, WSP are feasible under specific circumstances related to the context where they are to be implemented. In this study data were collected from three regions in Colombia (Nariño, Tolima and Valle del Cauca) in order to assess the feasibility of WSP under real conditions in a tropical country. A feasibility matrix was developed in order to organise and synthesise the information gathered. The results obtained showed that WSP are highly feasible in Tolima and Valle del Cauca due to the fact that these regions have geographical, socio-economic and technical characteristics that enhance the advantages of WSP technology. Nariño has a very mountainous topography along with other local limitations that hinder the application of WSP technology. The cost of land was not found to be a real limitation for the technology, whereas the availability of land is. Finally, the feasibility matrix may be a good planning tool at regional or national levels in order to help decision-making regarding cost-effective wastewater treatment alternatives on the basis of local conditions.

Microbiological quality of a waste stabilization pond effluent used for restricted irrigation in Valle Del Cauca, Colombia.

This paper discusses the applicability of effluent reuse in agriculture after treatment in a series of anaerobic, facultative and maturation ponds. The WSP system is located in Ginebra municipality, a small town in southwest Colombia. The total HRT is 12 days. Several samples of the final effluent were taken over a 55 day period and were analysed for E. coli, Streptococcus spp. and helminth eggs. Some additional grab samples were taken to determine the presence of pathogenic bacteria such as Salmonella spp. and Shigella spp. The results showed that the system was able to remove 4 log units of E. coli, 1 log unit of Streptococcus spp. and 100% of helminth eggs. Meanwhile, Salmonella spp. were detected in the effluent of the facultative pond whilst Shigella spp. were not detected in any sample. The main species of helminth eggs encountered were Taenia spp., Ascaris spp., Trichuris spp., Hymenolepis nana, H. diminuta and Enterobius vermicularis. Removal efficiencies were satisfactory despite the relatively short HRT. Nevertheless, WHO guidelines were slightly surpassed in the case of E. coli for unrestricted irrigation. The helminth egg value was always below the maximum WHO limit. Hence, this effluent can be safely used for restricted irrigation provided that field workers are protected from direct contact with wastewater given the presence of Salmonella spp. in the facultative pond effluent.