No abstract

The use of wastewater to replace other water resources for irrigation is highly dependent on whether the health risk and environmental impacts entailed are acceptable or not. Total count and species of microorganisms found in wastewater vary widely because of climatic conditions, season, population sanitary habits and disease incidence. Salmonella, one of the genera associated with waterborne diseases, lives in the intestine. Thus, it is widely accepted that they have a limited survival period under environmental conditions. Wastewater management practices and the ability of Salmonella to survival under field conditions would determine the health risk associated with its presence in wastewater. Although chlorination is widely used, there are situations in which Salmonella is able to survive the sudden stress imposed by this technique. The aim of this experiment was to contribute to the study of the climatic and soil effects on pathogen survival under agricultural field conditions in order to assess which were the best wastewater management practices from both health and economic points of view. Five pots filled with soil seeded with Medicago sativa and an automatic weather station were used. A secondary effluent was artificially inoculated with Salmonella. In addition, open plates (filled with sterilised soil) and ultraviolet radiation isolated plates (filled with non-sterilised soil) were used. As soil heat emission contributes to the environmental conditions around the bacteria, standardised meteorological temperature data had to be carefully used in the bacterial survival studies under agricultural conditions. Radiation was the main cause of Salmonella mortality as its effect was more important than natural soil bacteria competence. Higher reduction of Salmonella counts could have been associated with longer spring days. Soil was able to effectively remove Salmonella. Subsurface drip irrigation methods could provide an effective tool to prevent health risk associated with wastewater irrigation.

In the Canary Islands the price fluctuation of groundwater (0.3 to 0.7 €/m3), which is a private resource, often limits the recovery of the agricultural investments. Availability of alternative resources (reclaimed water: RW, desalinized seawater: DW and desalinized reclaimed water: DRW) at a foreseeable price will allow people to design the optimal infrastructures adapted to their needs The pumping cost is included in the “public” water price of DW (0.6 €/m3), RW (0.2 €/m3) and DRW (0.42 €/m3), but only if it is under 300 m of altitude. As a subsurface irrigation system (SDI), uses the soil as a natural advanced (but not high cost) water treatment, the in situ reuse of RW produced by lower tech wastewater plants would provide a valuable resource for the small villages. A successful study case is presented here. A 2-year SDI experiment was performed using RW, cultivating alfalfa (Medicago sativa) and Sudan grass hybrid (Sorghum bicolor ssp sudanense). Although a saline (EC: 2.24 dS/m) and sodic (SAR: 6.9) water was used, irrigation with SDI led to high forage yields (between 8.4 and 11.9 kg of fresh matter/m2 obtained by 8 harvests per year). However, sand filter and drip lines have to be cleaned weakly and every 6 months respectively. As a conclusion of this study, adequate plant germination and yields, and feasibility of SDI using a secondary effluent was demonstrated. Besides, water cost represents only 24 to 17 % from the gross income.

Two cases of urinary retention in male dromedaries due to silica uroliths are presented. The animals were urethrostomized and one dromedary was euthanized 7 months later due to urethrostomy obstruction. The estimated daily intake of silica was 84.44 g. Silica, calcium, phosphorus and pH in urine were determined in healthy animals from the same farms, and the following values were obtained: 174.78 2 3.46 mg/l (silica), 41.48 2 4.82 mg/l (calcium), 20.4 2 3.6 mg/l (phosphorus) and pH 8.2, respectively. Possible causes of urolithiasis were the early castration of the animals and the fact that salt was not added to the diet. To our knowledge, this is the first description of silica urolithiasis in the dromedary camel.