Wastewater treatment focused on the reuse and provision of agricultural supplies: Combination of phosphate adsorption and microbial reduction

Abstract

The efficiency of wastewater treatment systems is measured in terms of physicochemical and biological parameters. In this study two-stages of treatment were evaluated for the phosphate and microbial removal from wastewater for agricultural purposes. Iron (oxy)hydroxide was incorporated into a natural clay for phosphate removal and essential oils (Eucalyptus globulus and Citrus limon) were used for microbial reduction from wastewater. An overall experimental evaluation was performed from synthetic wastewater and further validated in real wastewater in batch mode. Phosphate adsorption capacity of iron (oxy)hydroxide clay (PMFe5) was three times higher than parent clay (PMFe1). Phosphate removal by PMFe5 was effective at neutral pH, which is attributed to physical and chemical adsorption mechanisms by means of hydrogen bonding adsorption and chemical complexation reactions, respectively. PMFe5 removed phosphate and ammonium at 65.8% and 72.3%, respectively from real wastewater. On the other hand, the use of emulsions of Eucalyptus globulus and Citrus limon essential oils allowed the decrease of bacterial load from wastewater. The microbial reduction was more effective using Eucalyptus globulus than Citrus limon essential oil. The fecal and total coliforms were reduced to a maximum extent of 100% using Eucalyptus globulus at 100 mg L−1. Microbial content was reduced to 100% using Citrus limon at 1000 mg L−1. Thus, reusability of wastewater for irrigation purposes is possible using an iron clay and essential oils. The use of PMFe5 as tertiary treatment stage could be crucial to recover phosphate–phosphorous from wastewater treatment plants reaching the regulatory levels. The content of total and fecal coliforms was also efficiently reduced using essential oils. On one hand, wastewater can be reused in irrigation activities according to the water quality standards. On the other hand, a nutrient enriched material can be provided as phosphate source for soil amendment application. The combination of both treatment technologies provides important agricultural supplies.