Wastewater tertiary treatment options to match reuse standards in agriculture

In Italy, the restrictive approach for reclaimed water (RW) use in agriculture has led to some difficulties in spreading this practice. In particular, matching microbiological standards, evaluated in terms of Escherichia coli, is quite prohibitive and highly intensive disinfection systems are the sole option to adequately treat municipal wastewater. A different view of the same concern is offered by the World Health Organization (WHO) that proposed a pragmatic approach, based on microbial risk assessment, to evaluate case by case the pathogen reduction in case of RW use in agriculture and how to achieve this. In the study two different tertiary treatment options for RW use in agriculture were examined. The first option named “extensive tertiary treatment system – ETTS” included in series: horizontal sub-surface constructed wetland system, biological pond, storage reservoir, sand and disk filters. The second option named “hybrid tertiary treatment system – HTTS” included in series: horizontal sub-surface constructed wetland system, sand and disk filters, ultraviolet (UV) system. Moreover, the microbial contamination on crop irrigated by RW from both examined systems was evaluated. An economic analysis was carried out for a life cycle of 20 years of the treatment systems. Economic benefits and total cost of RW for agricultural irrigation using both the tertiary treatment options were evaluated. Results evidenced that total costs of RW were similar for both options, anyway other benefits can support the choice of ETTS to treat RW for vegetable crop irrigation, especially for rural areas in developing countries.