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Recently, the electrochemical treatment of wastewater polluted by recalcitrant organics and containing chlorides was shown to be significantly improved adopting proper operative conditions such as suitable anodes and cathodes and low current density. In particular, the use of suitable cathodes such as carbon felt or silver could increase the removal of TOC and reduce the formation of chlorinated by‐products. In this study, attention was focused on the utilization of carbon felt cathodes with the main aim to evaluate the effect of air pressure on the process using phenol as model organic pollutant. It was shown that, in the presence of carbon felt cathode, the use of pressurized air allows both to increase the removal of TOC and to reduce the formation of chlorate. Moreover, the effect of the nature of the anode and of the presence of FeSO4, in order to study the involvement of electro‐Fenton process, was evaluated. [ABSTRACT FROM AUTHOR]

In the last years, an increasing attention has been devoted to the utilization of anodic oxidation (AO) technologies for the treatment of wastewater polluted by recalcitrant organics. Recently, Ti4O7 was proposed as a promising anode for AO for the treatment of various organics. Here the potential utilization of commercial Ti4O7 anodes has been evaluated considering the electrochemical treatment of synthetic wastewater contaminated by three very different organic molecules (namely, oxalic acid, phenol and Acid Orange 7), all characterized by a very high resistance to AO. The performances of Ti4O7 were compared with that of two largely investigated anodes: Boron‐doped diamond (BDD), which is probably the most effective electrode for AO, and an Ir‐based anode which presents a relatively low cost. Moreover, the effect of various operative conditions (current density, mixing rate and initial concentration of the organic) was evaluated by both experimental studies and the adoption of a theoretical model previously developed for BDD anodes. It was shown that the performances of the process can be improved by a proper selection of operative conditions. Moreover, it was found that the proposed model can be effectively used to predict the effect of operative parameters at Ti4O7 anodes, thus helping the process optimization. [ABSTRACT FROM AUTHOR]

Humic-like substances are essential components of soluble organic matter in tannery wastewater. However, the tannery process can promote the abiotic humification in wastewater. Therefore, it is of great significance to clarify the pathway and degree of abiotic humification and the properties of the as-derived humic acid-like (HAL) complex polymers in the tannery process in order to control the refractory organic compounds. In the present study, considering the catechol-Maillard system and commercial humic acid (HA) as control, the polyphenol-Maillard humification in the tannery process was simulated under the catalysis of MnO2. Moreover, physicochemical and spectroscopic techniques were used to characterize the separated fractions of HAL further. As a result, it was found that the catechol-Maillard system with small molecule organic matter as precursor had higher humification degree. Furthermore, the ultraviolet-visible (UV-Vis), Fourier transform infrared (FTIR), and excitation-emission matrix (EEM) fluorescence spectrum of humic acid-like 0 (HAL0) derived from it was different from those of humic acid-like 1 and 2 (HAL1 and HAL2) of polyphenol-Maillard system, indicating the differences of polymer structure between them. In the polyphenol-Maillard system, tannin was the skeleton of polymerization or polycondensation reaction, and the high content of N and the H/C value of HAL2 indicated that in adding to amino acids, proteins promoted the humification, forming industry-specific HAL polymers with a high degree of aliphatic nature. Therefore, it can be concluded that controlling the raw materials in the tannery process (especially tannins), in order to reduce the occurrence of abiotic humification may be the key to improve the efficiency of wastewater treatment. [ABSTRACT FROM AUTHOR]

The treatment of a real wastewater characterized by low conductivity was performed by anodic oxidation at boron doped diamond (BDD) in both conventional and microfluidic cells. The electrolyses carried out in conventional cells without supporting electrolyte were characterized by very high TOC removals but excessively high energetic consumptions and operating costs. The addition of sodium sulphate, as supporting electrolyte, allowed to strongly reduce the cell potentials and consequently the energetic consumptions and the operating costs. However, under various operating conditions, the addition of Na 2 SO 4 caused a lower removal of the TOC. The best results in terms of both TOC removal, energetic consumptions and operating costs (about 1 €/m 3 ) were obtained using a cell with a very low inter-electrode distance (50 µm) with no addition of a supporting electrolyte. [ABSTRACT FROM AUTHOR]

Polyphenols are organic substances commonly involved in a wide variety of industrial processes. They are prone to polymerize with other organic chemicals during production and subsequent wastewater treatment section, which yields various persistent and recalcitrant organic chemicals. To better understand the behavior of polyphenolic polymers in wastewater treatment processes and the effect on the biodegradability of wastewater, we explored the conversion of polyphenolic polymers during aerobic biochemical treatment and their relationship with extracellular polymeric substances (EPS). The COD Cr (chemical oxygen consumption measured using potassium dichromate) removal efficiency of the polyphenolic polymers with high concentration was only 29.66% with COD Cr of 437.5 mg/L, which was far from the wastewater discharge standard (60–100 mg/L, first class standard of GB 8978–1996). In the activated sludge system with stabilized organic matter as the substrate, the effluent had the highest degree of humification with the maximum SUVA value of 6.87 L/(mg∙m). The polyphenolic polymers caused a component variation in EPS, further affecting wastewater's humification degree and degradability. In particular, the content of humic acid-like substances in loose bound EPS (LB-EPS) was up to 4 times more than control, indicating higher aromatization and humification degree and of the waste. On the contrary, the content of polysaccharides in LB-EPS decreased by about 46.2–87.7% in treatments with different concentration of polyphenolic polymer. The high-concentration polyphenol polymers somehow stimulated the microbial production like proteins and humic-like substances. The direct conversion of polyphenol polymers also contributed to the increased humification of wastewater. • The accumulation of organic polymers was observed in the aerobic biochemical treatment. • Low-concentration polyphenol polymers can be degraded by microorganisms. • High-concentration polyphenol polymers increased the humification degree of wastewater during treatment. • The humic-like substances of microbial metabolites induced by polyphenolic polymers increased significantly. [ABSTRACT FROM AUTHOR]

In the last years, large attention has been devoted to the electrochemical treatment of wastewater polluted by recalcitrant organics and containing chlorides. However, the utilization on an applicative scale of this route is limited by the fact that usually it is not possible to achieve high removals of organics without the generation of significant amounts of chlorinated by-products. Here, the role of several operative parameters on the performances of the process was systematically evaluated using phenol as a model organic pollutant. It was shown that the removal of phenol and TOC and the generation of many by-products including chlorophenols, chloroacetic acids, chlorate and perchlorate dramatically depend on the adopted operative conditions (i.e., nature of anode and cathode, current density and concentration of chlorides). The use of boron doped diamond (BDD) anode gave the highest removal of TOC but also the highest final concentrations of chlorate and perchlorate and the lowest concentrations of chloroacetic acids. Conversely, the use of Ti/IrO 2 -Ta 2 O 5 gave the lowest generation of chlorate and no perchlorate. The use of lower current densities allowed as well to reduce the concentrations of these compounds. It is worth to mention that lower amounts of chlorinated by-products were achieved using suitable cathodes. Carbon felt cathodes, as previously reported for the water disinfection, allowed to reduce the generation of chlorate. Moreover, it was shown, for the first time, that the use of silver cathodes minimized the concentrations of chloroacetic acids. In addition, it was found that the use of a system equipped with both silver and carbon felt cathodes and proper current densities allowed to increase remarkably the removals of TOC and the current efficiency and to achieve very low concentrations of chlorinated by-products. [ABSTRACT FROM AUTHOR]

Based on the concept of microbial community multi-processing in integrated spatial bacterial succession (ISBS), this study constructs a highly efficient cellular fixed-bed bioreactor that follows the growth of biological flora in the wastewater treatment process. The reactor is organically partitioned based on synergistic laws and in accordance with environmental and microbial metabolic changes, and sewage is subjected to unitized and specialized biological treatment under direct current conditions. The results show that the ISBS reactor exhibits stable nitrogen removal performance under a low-carbon source. Compared with traditional sewage biochemical treatment technology, the microbial concentration is increased by 2–3 times and even up to 12 times, and the ammonia nitrogen removal rate is maintained at 99%. The removal rate reaches 90% (hydraulic retention time of 14 h). High-throughput sequencing analysis based on 16S rDNA reveals the microbial community structure succession at different depths of the same section of the reactor. The microbial community is rich under the influence of environmental factors and exhibits different responses. The intervals vary. An analysis of the microbial community function explains why the ISBS reactor has high nitrogen removal efficiency. [ABSTRACT FROM AUTHOR]