|Poster title||Wastewater disinfection for agricultural reuse using solar radiation in a developing county: field observations|
|Poster code||P 1.39|
|Form of presentation||Poster|
Wastewater treatment for agricultural purposes can contribute to decrease discharge of pollutants into water bodies, reduce water uptake from the surface water and groundwater, and recycle nutrients. However, there are environmental risks associated to irrigation with wastewater, mainly due to presence of pathogenic microorganisms. Solar disinfection is a low-cost disinfection method suitable for developing country that can allow safe use of recycled wastewater for irrigation. A pilot study was performed in Botucatu, São Paulo, Brazil, to determine the feasibility of using solar radiation to disinfect reclaimed urban wastewater for agricultural reuse. The effluent from Botucatu City Wastewater Treatment Plant (WWTP) was used as supply; this wastewater passed through biological filters bed (BFB’s) before being directed to solar disinfection. The solar disinfection system (SODIS) used in the experiment has a concrete base and shape of an inverted truncated cone with the following measures: 1.00 meter for larger radius, 0.25 meters for smaller radius and 0.30 meters height. This structural form was adopted to ensure that the walls of the reactor do not produce shadows on the effluent surface for the longest time possible. The experiment was conducted at Faculty of Agronomic Sciences-UNESP, Botucatu-SP, Brazil (22º 51’ 12” S and 48º 25’ 45” W). Fixed depths of wastewater (0.10; 0.15 e 0.20 m) were tested considering different time of exposure to solar radiation from May to July 2018. After passing through the BFB’s, the wastewater presents mean values for chemical oxygen demand (COD), total suspended solids (TSS), turbidity and fecal coliform (Escherichia Coli) of 27.8 mg L-1, 8.6 mg L-1, 1.5 NTU, 2.0 x 104 MPN 100 mL-1, respectively. The three fixed wastewater depths were exposed to solar radiation for a period of 10 hours (from 08:00 a.m. to 6:00 p.m.). The collection of wastewater samples for fecal coliform (E-Coli) analysis was performed every two hours. Results of inactivation assays showed that SODIS can bring down E-coli concentrations of 104 MPN 100 mL-1 in urban wastewater to < 3 MPN 100 ml-1. E-coli was more effectively disinfected by SODIS with 0.10 m wastewater depth, exhibiting logarithms reduction values ranging between 2 log10 (99%) to 4.3 log10 (99.99%) than by the depths of wastewater of 0.15 m (1.2 log10 to 3.8 log10) and 0.20 m (1.0 log10 to 3.9 log10). Although statistical analysis did not show a significant difference (p ≤ 0.05) between the wastewater depths tested. A model was developed to estimate the remaining population of fecal coliforms in wastewater after being exposed to SODIS knowing its initial population, depth of water being treated and solar energy received. SODIS was effective in reducing mean concentration of E. coli in the three wastewater depths tested at the standard recommendation for agricultural reuse proposed by World Health Organization -WHO (≤ 1000 MPN 100 mL-1) after six hours exposures to direct sunlight. Thus, SODIS treated wastewater can successfully be used by rural communities in developing countries.
Keywords: Solar disinfection, wastewater reuse, developing country, E-coli.