A novel iron molybdate photocatalyst with heterojunction-like band gap structure for organic pollutant degradation by activation of persulfate under simulated sunlight irradiation.

Advanced oxidation processes (AOPs) applied to wastewater treatment have become increasingly well developed and the ability of a single technology to remove difficult organic pollutants is limited. One of the main limiting factors is the insufficient variety and quantity of active species generated during the reaction process and catalyst failure. The coupling of the two methods is a practical and effective approach. In this study, different types of semiconductor persulfate (PS) activators, iron molybdate nanoparticles (I-FeMoO4, II-FeMoO4, and III-FeMoO4), were synthesized by simple solvothermal and calcination methods and applied to photo-assisted activation of PS systems. In addition, the relationship between the intrinsic physicochemical and optoelectronic properties of FeMoO4 and the catalytic degradation performance was revealed by a series of characterization tools, and the dominant catalysts were screened. At an unadjusted pH of 4.86, 0.6 g L-1 of PS and 0.4 g L-1 of I-FeMoO4 could achieve efficient degradation of several difficult organic dye contaminants (rhodamine b (Rh B), methylene blue (MB), malachite green (MG), methyl orange (MO), and tartrazine (TTZ)) and other antibiotic contaminants (sulfamethoxazole (SMX), tetracycline (TC), norfloxacin (NOR), and carbamazepine (CBZ)) within 5-60 min. Possible degradation mechanisms in the I-FeMoO4/PS/Light reaction system were suggested by radical trapping experiments and electron paramagnetic resonance (EPR) tests. Recovery tests demonstrated that I-FeMoO4 has good recoverable stability and did not cause secondary pollution. Finally, our study provided a new perspective on the application of coupled wastewater treatment technologies in the practical treatment of organic wastewater.

Biochar stimulates growth of novel species capable of direct interspecies electron transfer in anaerobic digestion via ethanol-type fermentation.

The study presented here was to evaluate the effects of combining biological ethanol-type fermentation pretreatment (BEFP) with biochar on the growth of novel species capable of direct interspecies electron transfer (DIET) and methanogenesis in anaerobic co-digestion (AcoD) of kitchen wastes (KWs) and waste activated sludge (WAS). The results showed that, after BEFP, the genera capable of extracellular electron transfer to Fe(III) oxides or the elemental sulfur, such as Geobacter, Sphaerochaeta and Sporanaerobacter species, were detected, which however were not detected in the seed sludge. In the presence of biochar, their abundance was further increased, suggesting that biochar stimulated their growth. With biochar, methane production rate increased by about 44% and the effluent concentration of total organic substrates further declined, compared with that without biochar. With biochar, methane production efficiency reached 241.6 mL/g-COD, more than 30% higher than that without biochar (185.0 mL/g-COD), suggesting that more energy from the oxidation of organic substrates was converted into methane. Analysis of Fourier transform infrared spectroscopy (FT-IR) and three-dimensional excitation emission matrix (3D-EEM) showed that decomposition of complex organic compounds in KWs and WAS was enhanced, since the novel species might proceed DIET with methanogens and participate in the metabolism of complex organic compounds.