Microbiological and chemical assessment of wastewater discharged by infiltration trenches in fractured and karstified limestone (Sca.re.s. project 2019–2020)

This study investigated the environmental contamination of groundwater as a consequence of the discharge of treated wastewater into the soil. The investigation focused on a wastewater treatment plant located in an area fractured by karst in the Salento peninsula (Apulia, Italy). Water samples were collected at four sites (raw wastewater, treated wastewater, infiltration trench, and monitoring well), monthly from May to December 2019 (with the exception of August), and were tested for (1) panel of bacteria; (2) enteric viruses; and (3) chemical substances. A gradual reduction in the concentration of bacteria, viruses and contaminants of emerging concern was observed across the profile of soil fissured by karst. All monitored bacteria were absent from the monitoring well, except for Pseudomonas aeruginosa. Pepper mild mottle virus and adenovirus were detected at all sampling sites. Personal care products and X-ray contrast media showed the greatest decrease in concentration from infiltration trench to the monitoring well, while the highest residual concentrations in the monitoring well were found for anticonvulsants (78.5%), antimicrobials (41.3%), and antipsychotic drugs (38.6%). Our results show that parameters provided by current law may not always be sufficient to evaluate the sanitary risk relating to the discharge of treated wastewater to the soil

Multiobjective Optimization of an Electroxidation Process of Biologically Pre-Treated Landifill Leachate by Response Surface Methodology and Desirability Function Approach

The optimization of the electrochemical step in a combined (biological and electro-oxidative) landfill leachate treatment was performed using a two stages approach, response surface methodology coupled with the desirability function. Four constraints were imposed, namely the discharge limit for COD (i.e. 160 mg / L), the maximization of color removal, the minimization of both residual chlorine and specific energy consumption. Each variable was modeled employing a second-order regression model. Analysis of variance (ANOVA) showed coefficient of determination (R2) values greater than 0.96, ensuring satisfactory fitting of the model output with the experimental data. After optimization at current density of 133 mA/cm2, stirring speed of 566 rpm and reaction time 46.2 min, the constrained COD removal percentage of 78.2% (corresponding to the aforementioned discharge limit) and a color removal maximization of 99.3% were observed. In addition, the minimization of residual chlorine and specific energy consumption reached the values of 1213 mg/L and 42.4 kWh/m3, respectively. The proposed methodology proved to be effective for saving time and experimental effort guaranteeing the achievement of optimal combination factors to reach specific target response. It is also noticeably that the overall operating treatment cost was lower than that presently found for sanitary landfill leachates. However, the high residual chlorine production leading to final effluent AOX concentration up to 35 mgCl-/L, represents an intrinsic treatment drawback. Keywords: Landfill leachate, electrooxidation, response surface methodology, desirability optimization methodology, COD removal, colour remova

Multiobjective Optimization of an Electroxidation Process of Biologically Pre-Treated Landifill Leachate by Response Surface Methodology and Desirability Function Approach

The optimization of the electrochemical step in a combined (biological and electro-oxidative) landfill leachate treatment was performed using a two stages approach, response surface methodology coupled with the desirability function. Four constraints were imposed, namely the discharge limit for COD (i.e. 160 mg / L), the maximization of color removal, the minimization of both residual chlorine and specific energy consumption. Each variable was modeled employing a second-order regression model. Analysis of variance (ANOVA) showed coefficient of determination (R2) values greater than 0.96, ensuring satisfactory fitting of the model output with the experimental data. After optimization at current density of 133 mA/cm2, stirring speed of 566 rpm and reaction time 46.2 min, the constrained COD removal percentage of 78.2% (corresponding to the aforementioned discharge limit) and a color removal maximization of 99.3% were observed. In addition, the minimization of residual chlorine and specific energy consumption reached the values of 1213 mg/L and 42.4 kWh/m3, respectively. The proposed methodology proved to be effective for saving time and experimental effort guaranteeing the achievement of optimal combination factors to reach specific target response. It is also noticeably that the overall operating treatment cost was lower than that presently found for sanitary landfill leachates. However, the high residual chlorine production leading to final effluent AOX concentration up to 35 mgCl-/L, represents an intrinsic treatment drawback. Keywords: Landfill leachate, electrooxidation, response surface methodology, desirability optimization methodology, COD removal, colour remova