Degradation of antipyrine in water with activated persulfate aided with biochar of olive pomace.

The degradation of antipyrine (AP) in water has been studied using persulfate activated with biochar obtained from gasification of olive pomace (BC) combined with ferric salts in the presence of UV-A radiation. Firstly, the adsorption of AP on biochar was evaluated. The data were adjusted using various kinetic models verifying that AP adsorption on BC occurs in three stages and follows pseudo-second order kinetics. Degradation tests show that the presence of iron or persulfate (PS) in binary systems with BC produces increases AP degradation when no radiation is used, reaching 75.7 % due to the ability of BC to donate electrons. On the other hand, addition of PS showed an increase in efficiency in the presence of BC (up to 79%). For ternary systems the best result was found when UVA/PS/Fe was used (100% of AP degradation in 30 min). The addition of UV-A radiation to the BC/PS system improves the degradation of the contaminant by only 6.7%, while the presence of iron in the studied conditions does not cause any improvement. A Central Composite Factorial Design of experiments was used to optimize the UVA/BC/PS/Fe system, leading to an 89.3% AP degradation rate in 90 min (k = 0.0134 min-1) under optimal conditions ([Fe(III)] = 10 mg/L, [PS] = 379 mg/L, [BC] = 500 mg/L). Although the best results were obtained for the UVA/PS/Fe process without BC, systems based on BC/PS can be considered as an alternative in cloudy days or when simple processes are selected due to economical/technical reasons.

Solar photo-degradation of aniline with rGO/TiO2 composites and persulfate.

The solar photodegradation of aniline using reduced graphene oxide-based composites (rGO/TiO2) and different electron acceptors such as H2O2 and persulfate (PS) has been studied. To this end, an innovative self-sufficient drum reactor (operating with solar irradiation and artificial UV light) has been employed. The role of radicals and the new graphene morphology is evaluated. Finally, changes in the degradation/mineralization mechanism are explained according to intermediates evolution (obtained from mass spectroscopy). In the Solar/rGO/TiO2/H2O2 system, hydroxyl radicals react with the reduced graphene oxide (rGO) producing oxidized rGO (OrGO). The process creates new pores increasing surface area favouring adsorption. Also, other radicals such as superoxide or singlet oxygen are also formed, affecting the degradation mechanism. The hole reacts with adsorbed aniline to form the aniline-radical-cation. Nitrosobenzene is then formed with the active participation of superoxide radical anion, finally yielding azobenzene. It was found that the addition of 2.5% wt of rGO increases mineralization from 0 to 14% during the solar stage after 120 min, reaching 82.5% when lamps are switched on after 240 min. On the other hand, activation of PS with UV-C light is a very efficient process, since aniline is wholly degraded in 10-20 min depending on PS initial concentration, reaching a high mineralization degree close to 90% in 120 min. During this process, degradation occurs in a very different route, via the formation of phenol. In the first stage (t < 25 min), sulfate radical is the primary oxidant involved to yield benzoquinone. In a second step (t > 25 min), hydroxyl radicals play the leading role to reach C2-C6 organic acids.

Operation costs of the solar photo-catalytic degradation of pharmaceuticals in water: A mini-review.

The removal of pharmaceuticals present in wastewater is receiving more and more attention since most of them are refractory to traditional biological treatments. Many advanced oxidation processes have been reported in literature. However, cost estimations are not available for most of them. Recently, more environment friendly processes using solar radiation are gaining importance. The solar photo-Fenton process has been used with different reactor configurations and scales and seems to be the most promising technology for reducing operation costs. In addition, the use of ferrioxalate-aided systems allows the use of pHs close to neutrality, that reduces costs before disposal (not calculated here). The possible use of photovoltaic panels for an energy-free process makes it very interesting for an economic evaluation. Results for the homogeneous solar photo-Fenton process show that when pure compounds are present in water, mineralization is in the range 18-21% with an estimated operation cost of 0.739-0.85 €/m3. An increase in mineralization up to 60-80.6% requires either the use of ferrioxalate (slightly increasing costs to 1.1-1.56 €/m3) or the addition of very high concentration of H2O2, that rises costs substantially. The presence of pharmaceuticals in a Waste Water Treatment Plant effluent reduces mineralization (maximum of 20%) also increasing costs. On the other hand, published results confirm that heterogeneous photocatalysis with TiO2 (both suspended or immobilized) is still far to compete with homogeneous photo-Fenton process in operation costs. The development of new reactor systems and modified photo-catalysts are needed to compete as an efficient applicable technology in the near future.

Environmental sustainability of the solar photo-Fenton process for wastewater treatment and pharmaceuticals mineralization at semi-industrial scale.

The environmental sustainability of a semi-industrial solar photo-Fenton reactor, treating real effluents emanating from a pharmaceutical laboratory, is assessed herein. The life cycle assessment/analysis (LCA) methodology was employed and real life cycle inventory (LCI) data was collected from a ferrioxalate-assisted homogeneous solar photo-Fenton wastewater treatment plant (WWTP), at Ciudad Real, Spain. Electricity was provided by photovoltaic (PV) panels in tandem with a battery bank, making the plant autonomous from the local grid. The effective treatment of 1m3 of secondary-treated pharmaceutical wastewater, containing antipyrine, was used as a functional unit. The main environmental hotspot was identified to be the chemical reagents used to enhance treatment efficiency, mainly hydrogen peroxide (H2O2) and to a smaller degree oxalic acid. On the other hand, land use, PV panels, battery units, compound parabolic collectors (CPC), tanks, pipes and pumps, as materials, had a low contribution, ranging from as little as 0.06% up to about 2% on the total CO2eq emissions. Overall, the solar photo-Fenton process was found to be a sustainable technology for treating wastewater containing micropollutants at semi-industrial level, since the total environmental footprint was found to be 2.71kgCO2m-3 or 272mPtm-3, using IPCC 2013 and ReCiPe impact assessment methods, respectively. A sensitivity analysis revealed that if the excess of solar power is fed back into the grid then the total environmental footprint is reduced. Depending on the amount of solar power fed back into the grid the process could have a near zero total environmental footprint.

A novel combined solar pasteurizer/TiO2 continuous-flow reactor for decontamination and disinfection of drinking water.

A new combined solar plant including an annular continuous-flow compound parabolic collector (CPC) reactor and a pasteurization system was designed, built, and tested for simultaneous drinking water disinfection and chemical decontamination. The plant did not use pumps and had no electricity costs. First, water continuously flowed through the CPC reactor and then entered the pasteurizer. The temperature and water flow from the plant effluent were controlled by a thermostatic valve located at the pasteurizer outlet that opened at 80 °C. The pasteurization process was simulated by studying the effect of heat treatment on the death kinetic parameters (D and z values) of Escherichia coli K12 (CECT 4624). 99.1% bacteria photo-inactivation was reached in the TiO2-CPC system (0.60 mg cm-2 TiO2), and chemical decontamination in terms of antipyrine degradation increased with increasing residence time in the TiO2-CPC system, reaching 70% degradation. The generation of hydroxyl radicals (between 100 and 400 nmol L-1) was a key factor in the CPC system efficiency. Total thermal bacteria inactivation was attained after pasteurization in all cases. Chemical degradation and bacterial photo-inactivation in the TiO2-CPC system were improved with the addition of 150 mg L-1 of H2O2, which generated approximately 2000-2300 nmol L-1 of HO● radicals. Finally, chemical degradation and bacterial photo-inactivation kinetic modelling in the annular CPC photoreactor were evaluated. The effect of the superficial liquid velocity on the overall rate constant was also studied. Both antipyrine degradation and E. coli photo-inactivation were found to be controlled by the catalyst surface reaction rate.