Andrea Turolla

Influence of Aqueous Inorganic Anions on the Reactivity of Nanoparticles in TiO2 Photocatalysis

The influence of inorganic anions on the photoreactivity and aggregation of titanium dioxide nanoparticles (NPs) was assessed by dosing carbonate, chloride, nitrate, phosphate, and sulfate as potassium salts at multiple concentrations. NP stability was monitored in terms of aggregate morphology and electrophoretic mobility (EPM). Aggregate size and fractal dimension were measured over time by laser diffraction, and the isoelectric point (IEP) as a function of anion and concentration was obtained by measuring EPM versus pH. Phosphate, carbonate, and to a lesser extent, sulfate decreased the IEP of TiO2 and stabilized NP suspensions owing to specific surface interactions, whereas this was not observed for nitrate and chloride. TiO2 NPs were exposed to UV-A radiation, and the photoreactivity was assessed by monitoring the production of reactive species over time both at the NP surface (photogenerated holes) and in the bulk solution (hydroxyl radicals) by observing their reactions with the selective probe compounds iodide and terephthalic acid, respectively. The generation of photogenerated holes and hydroxyl radicals was influenced by each inorganic anion to varying degrees. Carbonate and phosphate inhibited the oxidation of iodide, and this interaction was successfully described by a Langmuir-Hinshelwood mechanism and related to the characteristics of TiO2 aggregates. Chloride and nitrate do not specifically interact with TiO2, and sulfate creates relatively weak interactions with the TiO2 surface such that no decrease in photogenerated hole reactivity was observed. A decrease in hydroxyl radical generation was observed for all inorganic anions. Quenching rate constants for the reaction of hydroxyl radicals with each inorganic anion do not provide a comprehensive explanation for the magnitude of this decrease, which arises from the interplay of several physicochemical phenomena. This work shows that the reactivity of NPs will be strongly influenced by the makeup of the waters they are released into. The impact of anion species on hydroxyl radical inhibition was as follows: carbonate > chloride > phosphate > nitrate > sulfate.

Peracetic acid for secondary effluent disinfection: a comprehensive performance assessment.

The paper is a review of previous research on secondary effluent disinfection by peracetic acid (PAA) integrated with new data about the effect of a preliminary flash-mixing step. The process was studied at bench and pilot scale to assess its performance for discharge in surface water and agricultural reuse (target microorganisms: Escherichia coli and faecal coliform bacteria). The purposes of the research were: (1) determining PAA decay and disinfection kinetics as a function of operating parameters, (2) evaluating PAA suitability as a disinfectant, (3) assessing long-term disinfection efficiency, (4) investigating disinfected effluent biological toxicity on some aquatic indicator organisms (Vibrio fischeri, Daphnia magna and Selenastrum capricornutum), (5) comparing PAA with conventional disinfectants (sodium hypochlorite, UV irradiation). PAA disinfection was capable of complying with Italian regulations on reuse (10 CFU/100 mL for E. coli) and was competitive with benchmarks. No regrowth phenomena were observed, as long as needed for agricultural reuse (29 h after disinfection), even at negligible concentrations of residual disinfectant. The toxic effect of PAA on the aquatic environment was due to the residual disinfectant in the water, rather than to chemical modification of the effluent.

Performance of electro-osmotic dewatering on different types of sewage sludge

Abstract The feasibility of pressure‐driven electro‐dewatering (EDW) on sludge samples taken after different biological processes, stabilisation methods or mechanical dewatering techniques was assessed. First, the influence of potential values on EDW of anaerobically and aerobically stabilised, mechanically dewatered, sludge samples was investigated. Preliminary tests carried out by applying a constant potential (10, 15 and 20 V) in a lab‐scale device confirmed the possibility to reach a dry solid (DS) content of up to 42.9%, which corresponds to an increase of 15% of the dry content in dewatered sludge without the application of the electrical field. Dewatering increased with the applied potential but at the expense of a higher energy consumption. A potential equal to 15 V was chosen as the best compromise for EDW performance, in terms of DS content and energy consumption. Then, the influence of the mechanical dewatering was studied on aerobically stabilised sludge samples with a lower initial DS content: the higher initial water content led to a lower final DS content but with a considerable reduction of energy consumption. Finally, the biological process, studied by comparing sludge samples from conventional activated sludge and membrane bioreactor processes, didn’t evidence any influence on EDW. Experimental results shown that DS obtained after mechanical dewatering, volatile solids and conductivity are the main factors influencing EDW. Anaerobically digested sludge reached the highest DS content, thanks to lower organic fraction. HighlightsEDW has allowed achieving sludge dry solids up to 42.9%.EDW was more effective on anaerobically digested sludge, consuming less energy.Electric potential of 10–20 V allowed achieving high dry solids in sludge.Initial dry solids, volatile solids and conductivity of sludge control EDW efficiency.

Assessment of a colorimetric method for the measurement of low concentrations of peracetic acid and hydrogen peroxide in water

The recent growing interest in peracetic acid (PAA) as disinfectant for wastewater treatment demands reliable and readily-available methods for its measurement. In detail, the monitoring of PAA in wastewater treatment plants requires a simple, accurate, rapid and inexpensive measurement procedure. In the present work, a method for analyzing low concentrations of PAA, adapted from the US EPA colorimetric method for total chlorine, is assessed. This method employs N,N-diethyl-p-phenylelnediamine (DPD) in the presence of an excess of iodide in a phosphate buffer system. Pink colored species are produced proportionally to the concentration of PAA in the sample. Considering that PAA is available commercially as an equilibrium solution of PAA and hydrogen peroxide (H2O2), a measurement method for H2O2 is also investigated. This method, as the one for the determination of PAA, is also based on the oxidation of iodide to iodine, with the difference that ammonium molybdate Mo(VI) is added to catalyze the oxidation reaction between H2O2 and iodide, quantifying the total peroxides (PAA+ H2O2). The two methods are suitable for concentration ranges from about 0.1-1.65 mg L-1 and from about 0.3-3.3 mg L-1, respectively for PAA and H2O2. Moreover, the work elucidates some relevant aspects related to the operational conditions, kinetics and the possible interference of H2O2 on PAA measurement.

Effect of suspended solids on peracetic acid decay and bacterial inactivation kinetics: Experimental assessment and definition of predictive models

The work addresses the effect of total suspended solids (TSS) on disinfection by peracetic acid (PAA) concerning both PAA decay and bacterial inactivation kinetics. The effect of TSS on PAA decay was evaluated at five TSS concentrations (5, 40, 80, 120 and 160 mg/L), obtained from stock TSS solutions prepared from activated sludge samples. The influence of the soluble matter associated to the suspended solids on PAA decay was evaluated separately, using the same stock TSS solution after the removal of solids by filtration. The contributions of suspended and soluble fractions were found to be independent, and a predictive model formed by two additive sub-models was proposed to describe the overall PAA decay kinetics. Moreover, an uncertainty analysis was performed by a series of Monte Carlo simulations to propagate the uncertainties associated to the coefficients of the model. Then, the disinfectant dose (mg/L min) was highlighted as the main parameter determining disinfection efficiency on a pure culture of E. coli and an inactivation kinetic model was developed based on the response of E. coli to various PAA doses. Finally, the effect of TSS (40 and 160 mg/L) on the inactivation of free-swimming E. coli was investigated at two PAA doses (5 and 20 mg/L min). TSS reduced inactivation extent an average of 0.4 logs at 5 mg/L min and 1.5 logs at 20 mg/L min. It was hypothesized that this might be due to the formation of bacteria aggregates as defense mechanism against disinfection, enhanced by the presence of solids.

Disinfection by-products formation and ecotoxicological effects of effluents treated with peracetic acid: A review

Peracetic acid (PAA) has gained increasing attention over the last decades as a suitable and environmentally-friendly alternative to chlorine-based compounds for wastewater disinfection, claiming limited disinfection by-products (DBPs) formed and no persistent residues in the environment. The present work aims at presenting a comprehensive and updated review of the ecotoxicological effects of effluents treated with PAA, to be ascribed to residual PAA and hydrogen peroxide (H2O2) and DBP formation. Modest concentrations of DBPs have been observed after PAA treatment, mainly carboxylic acids, which are not recognized as genotoxic. Moreover, there is no evidence of any endocrine disruption potential of PAA in human health or in the ecotoxicological studies. The associated H2O2 fraction can potentially minimize the formation of halogenated DBPs and also contribute to the acute toxic effects of treated effluents. Effluents disinfected with PAA at concentrations typical of the wastewater treatment field have displayed limited toxic, mutagenic and genotoxic effects on different aquatic organisms, particularly low compared to chlorine-based disinfectants.

Smart pipe: A miniaturized sensor platform for real-time monitoring of drinking water quality

This work presents the first prototype of the Smart Pipe, a compact and intelligent wireless node hosting miniaturized sensors, embedded in a flange, for distributed and real-time monitoring of water contamination and for optimization of water treatment plants. Beyond pH and temperature, it features a low-cost and high-resolution (13 ppm, 11 ms response time) custom-designed 4-channel conductivity measurement circuit. Long-term operation and optimized on-demand maintenance are achieved by the innovative combination of an impedance sensor measuring the thickness of sludge and biofilm depositing on microelectrodes with self-cleaning capabilities offered by UV photo-regeneration of nanometric TiO2 electrodes coatings. Finally, here we also demonstrate self-powering of the unit by means of an energy harvesting control valve, regulating the flow in the water distribution network where an efficient installation of these sensors is today foreseeable.