The conversion of ammonia to nitrogen at Ti/PbO2 anode in non-chlorinated solution by controlling the pH value was discussed in detail in this work. The results showed the pH value made a great effect on the conversion of ammonia to nitrogen during electrolysis. Ammonia was converted to nitrogen primarily by direct oxidation in alkaline solution, whereas it was oxidized by OH radicals in acidic solution. The 80-min electrolysis at 15 mA/cm2 showed that the conversion rates of ammonia increased about 3.5 times as pH from 3.0 to 5.0 and 2.0 times from 9.0 to 11.0. High pH value caused the accumulation of NO3− with electrolysis time. The accumulation rate was 9.61 mg-N/(L ⋅ h) at pH 11.0, about six times of that at pH 9.0. For actual wastewater with the pH of 5.0, the ammonia oxidation rate was 41 mg-N/(L ⋅ h), 95% of removed ammonia converted to N2 and only 4.83% to NO3− within the electrolysis time of 120 min.

•The flow field of novel vertical-flow tubular electrochemical reactor with mesh electrodes (VTER) and traditional concentric tubular electrochemical reactor with plate electrodes (CTER) were compared.•The relationship between mass transfer coefficients and tube flow velocity and pressure drop in VTER and CTER were obtained.Electrochemical treatment is an environmentally friendly method of removing pollutants from industrial wastewater. The tubular electrochemical reactor is one kind of electrochemical reactor. The current density distribution on the electrode surface in a traditional concentric tubular reactor is not homogeneous and the working area of the anodes and cathodes is unequal. Therefore, a novel tubular electrochemical reactor based on plug flow fluid orthogonal with mesh plate electrodes is presented. In this work, fluid flow and hydrodynamics of the vertical-flow tubular electrochemical reactor, such as velocity distribution and turbulent intensity distribution using computational fluid dynamics (CFD) method, are studied by comparing them to the traditional one. The electro-oxidation of phenol simulation wastewater treatment was developed to analyze the mass transfer performance of the two types of electrochemical reactors. In the novel tubular electrochemical reactor, due to the presence of mesh electrodes, the velocity distribution tended to be more homogeneous. In fact, the turbulent intensity clearly increased by 200% around the electrode surface. The kinetics of organic compounds removal in the novel tubular electrochemical reactor was also improved. Under the same flow rate, the improvement of the mass transfer coefficient for the novel tubular electrochemical reactor was more than twice that of the traditional tubular electrochemical reactor.

In bioelectrochemically reductive dechlorination of chlorinated organic compounds (COCs), the electrons transfer from enzyme in the electrode to COCs was the key step, which determined the average current efficiency (CE) and was influenced by the pH and temperature of the systems. In this work, the effect of temperature (288–318 K) and pH (2–11) of the electrolyte on decholrination of trichloroacetic acid (TCA) was investigated in the sodium alginate/hemoglobin-multiwalled carbon nanotubes-graphite composite electrode (Hb/SA–MWCNT–GE). The results showed that the most favourable degradation conditions for TCA by Hb/SA–MWCNT–GE were found to be pH 3 and 310 K. By varying the pH of the systems, it was found that a proton accompanied with an electron transfer between the electrode and heme Fe(III)/Fe(II) of Hb during the reaction. Additionally, the activation energy of 26.2 kJ mol−1 was also calculated by the Arrhenius equation for the reaction. The total mass balance of the reactant and the products was in the range of 97–105% during the bioelectrochemically reductive reaction. The CE only decreased from 87% to 83% when the Hb/SA–MWCNT–GE was used 5 times. Based on the intermediates detected, a pathway was proposed for TCA degradation in which it underwent dechlorination process. The main degradation mechanism described by a parallel reaction rather than by a sequential reaction for dechlorination of TCA in Hb/SA–MWCNT–GE system was proposed. These data provided relevant information about the applicability of bioelectrocatalytic systems for treatment of wastewater contaminated by COCs.Graphical abstractHighlights► The electrons transfer from enzyme in the electrode to COCs was the key step. ► The average current efficiency was influenced by pH and temperature of the systems. ► The most favourable degradation conditions for TCA were found to be pH 3 and 310 K. ► The activation energy of 26.2 kJ mol−1 was also calculated by the Arrhenius equation. ► Bioelectrocatalytic mechanism of TCA was verified by kinetic expressions.

The feasibility of a novel zero discharge process for dyeing wastewater depth treatment after biochemical processes was investigated in this study. The novel process was integrated with reverse osmosis (RO) technology, electrochemical oxidation (EO) and bipolar membrane electrodialysis (BMED). The fresh water generated from the RO and BMED processes and the mixed acid and base solutions regenerated from BMED could be reused as resources. No pollutants or wastewater were discharged into the environment during dyeing wastewater depth treatment. The effects of operation parameters, such as recovery ratio, specific current and input power on RO/EO/BMED performance were explored and discussed. The experimental results indicated that the recovery ratio of wastewater by this RO/EO/BMED process reached 97%, as compared with 70% achieved by RO or nanofiltration (NF); more than 83% of the total dissolved solids (TDS) in wastewater were desalinized and converted into mixed acid and base solutions. The total operating power requirement was 24.6 kWh to treat one cubic meter of wastewater, 0.97 tons fresh water and 1.31 kg mixed acid (0.12 mol/L) and 2.16 kg base (0.18 mol/L) were produced. This work has demonstrated proof of concept for the RO/EO/BMED process; further optimization remains to be carried out.

This study was performed to investigate the variables that influence chlorobenzene (CB) degradation in aqueous solution by electro-heterogeneous catalysis. The effects of current density, pH, and electrolyte concentration on CB degradation were determined. The degradation efficiency of CB was almost 100% with an initial CB concentration of 50 mg/L, current density 15 mA/cm2, initial pH 10, electrolyte concentration 0.1 mol/L, and temperature 25°C after 90 min of reaction. Under the same conditions, the degradation efficiency of CB was only 51% by electrochemical (EC) process, which showed that electro-heterogeneous catalysis was more efficient than EC alone. The analysis results of Purge-and-Trap chromatography-mass spectrometry (P&T/GC/MS) and ion chromatography (IC) indicated that in the reaction process, the initial .OH attack could occur at the C–Cl bond of CB, yielding phenol and biphenyl with the release of Cl−. Further oxidation of phenol and biphenyl produced ρ-Vinylbenzoic acid and hydroquinol. Finally, the compounds were oxidized to butenedioic acid and other small-molecule acids.