Performance of electrochemical oxidation and photocatalysis in terms of kinetics and energy consumption. New insights into the p-cresol degradation.

This work reports the comparative performance of two Advanced Oxidation Processes (AOPs), electrochemical oxidation and photocatalysis, as individual technological alternatives for the treatment of effluents containing p-cresol. First, the influence of operating parameters in the oxidation and mineralization yield was carried out together with kinetic analysis. Boron Doped Diamond (BDD), RuO2 and Pt as anodic materials, Na2SO4 and NaCl as supporting electrolytes and different current densities were evaluated in electrochemical oxidation whereas the effect of TiO2 concentration and radiation was studied in the photocatalytic degradation. Then, the parameter Electrical Energy per Order (EEO) was calculated to compare the energy consumption in both AOPs, concluding that under the studied conditions the electrochemical treatment with BDD, Na2SO4 and 125 A m-2 showed the best energy efficiency, with an EEO of 5.83 kW h m-3 order-1 for p-cresol and 58.05 kW h m-3 order-1 for DOC removal, respectively.

Electrocoagulation-electrooxidation for mitigating trace organic compounds in model drinking water sources.

In-situ water treatment can be accomplished using electrochemical treatments such as electrocoagulation (EC), which generates coagulants, and electrooxidation (EO), which generates oxidants (e.g., free chlorine and reactive oxygen species) via electrolysis using boron-doped diamond electrodes. In sequential EC-EO, EC can remove oxidant scavengers present in dissolved organic carbon (DOC), thereby improving the efficacy of downstream oxidation via EO. This study evaluated sequential EC-EO (and each process independently for comparison) for mitigating the trace organic compounds (TOrCs) acyclovir (ACY), trimethoprim (TMP), and benzyldimethyldecylammonium chloride (BAC-C10) in model groundwaters and surface waters. EO-only removed greater than 70% of ACY and TMP but negligible BAC-C10 in model groundwaters. In model surface waters, EO-only removed ∼55-75% BAC-C10, but had less removal for ACY and TMP (∼20-55%), primarily due to DOC interference. Sequential-EC-EO was investigated to better gauge the potential process improvement due to the addition of EC ahead of EO. EC removed 74 ± 7% DOC from model surface water and improved downstream EO treatment relative to EO-only by a factor of 3.4 for ACY, 1.7 for TMP, and 1.4 for BAC-C10. When treating model groundwater, EC-EO resulted in no improvement compared to EO-only for ACY and TMP. BAC-C10 removal was attributed to the particle separation step between EC and EO rather than electrochemical inputs. EO-only treatment was more energy efficient for model groundwater compared to model surface waters based on electrical energy per order (EEO) values. Sequential EC-EO further improved the energy efficiency for treating model river water.

Evaluation and prospects of nanomaterial-enabled innovative processes and devices for water disinfection: A state-of-the-art review.

This study provided an overview of established and emerging nanomaterial (NM)-enabled processes and devices for water disinfection for both centralized and decentralized systems. In addition to a discussion of major disinfection mechanisms, data on disinfection performance (shortest contact time for complete disinfection) and energy efficiency (electrical energy per order; EEO) were collected enabling assessments firstly for disinfection processes and then for disinfection devices. The NM-enabled electro-based disinfection process gained the highest disinfection efficiency with the lowest energy consumption compared with physical-based, peroxy-based, and photo-based disinfection processes owing to the unique disinfection mechanism and the direct mean of translating energy input to microbes. Among the established disinfection devices (e.g., the stirred, the plug-flow, and the flow-through reactor), the flow-through reactor with mesh/membrane or 3-dimensional porous electrodes showed the highest disinfection performance and energy efficiency attributed to its highest mass transfer efficiency. Additionally, we also summarized recent knowledge about current and potential NMs separation and recovery methods as well as electrode strengthening and optimization strategies. Magnetic separation and robust immobilization (anchoring and coating) are feasible strategies to prompt the practical application of NM-enabled disinfection devices. Magnetic separation effectively solved the problem for the separation of evenly distributed particle-sized NMs from microbial solution and robust immobilization increased the stability of NM-modified electrodes and prevented these electrodes from degradation by hydraulic detachment and/or electrochemical dissolution. Furthermore, the study of computational fluid dynamics (CFD) was capable of simulating NM-enabled devices, which showed great potential for system optimization and reactor expansion. In this overview, we stressed the need to concern not only the treatment performance and energy efficiency of NM-enabled disinfection processes and devices but also the overall feasibility of system construction and operation for practical application.

Evaluation of advanced oxidation processes for water and wastewater treatment - A critical review.

This study provides an overview of established processes as well as recent progress in emerging technologies for advanced oxidation processes (AOPs). In addition to a discussion of major reaction mechanisms and formation of by-products, data on energy efficiency were collected in an extensive analysis of studies reported in the peer-reviewed literature enabling a critical comparison of various established and emerging AOPs based on electrical energy per order (EEO) values. Despite strong variations within reviewed EEO values, significant differences could be observed between three groups of AOPs: (1) O3 (often considered as AOP-like process), O3/H2O2, O3/UV, UV/H2O2, UV/persulfate, UV/chlorine, and electron beam represent median EEO values of <1 kWh/m3, while median energy consumption by (2) photo-Fenton, plasma, and electrolytic AOPs were significantly higher (EEO values in the range of 1-100 kWh/m3). (3) UV-based photocatalysis, ultrasound, and microwave-based AOPs are characterized by median values of >100 kWh/m3 and were therefore considered as not (yet) energy efficient AOPs. Specific evaluation of 147 data points for the UV/H2O2 process revealed strong effects of operational conditions on reported EEO values. Besides water type and quality, a major influence was observed for process capacity (lab-vs. pilot-vs. full-scale applications) and, in case of UV-based processes, of the lamp type. However, due to the contribution of other factors, correlation of EEO values with specific water quality parameters such as UV absorbance and dissolved organic carbon were not substantial. Also, correlations between EEO and compound reactivity with OH-radicals were not significant (photolytically active compounds were not considered). Based on these findings, recommendations regarding the use of the EEO concept, including the upscaling of laboratory results, were derived.