The effects of applying different types of treated wastewater on citrus trees were studied in Murcia, in the south-east of Spain. Two treatments with wastewater effluents of different quality were applied for three consecutive years. In the first case, the wastewater received a secondary treatment (conventional activated sludge). In the second case, the irrigation water was a mix of well water and wastewater from a tertiary treatment plant (conventional activated sludge with ultraviolet tertiary treatment). The characteristics of the tertiary treated wastewater make it better for irrigation than the secondary treated wastewater. It was considered that high salinity, Cl and B concentration could be the main restrictions associated with treated wastewater irrigation in both cases, although leaf toxicity levels were not observed. The soil nitrate concentration increased over the experimental time period in both water irrigation treatments. The production was affected by the wastewater quality and the total crop yield was lower in the plots irrigated with secondary treated wastewater. However, in these plots, the fruit-quality indexes such as external colour, weight, peel thickness, firmness, soluble solids, pH, total acidity and maturity index were significantly better than those observed in the plots irrigated with tertiary treatment. The soil microbiological analysis revealed an absence of faecal coliforms, Escherichia coli and helminth eggs in the experimental plots irrigated with tertiary treated wastewater, but with secondary treated wastewater the soil accumulation of faecal coliforms exceeded health standards. In both cases, there was an absence of microbiological contamination on fruits.
