Search

As the "carbon peaking and carbon neutrality" strategy advances, carbon emissions have gradually become a significant indicator in selecting and evaluating sewage and sludge treatment solutions. This study compared the carbon footprints of different digested sludge post-treatment routes, taking the Lu'an project in China as an example. Considering anaerobic digestion and digested sludge post-treatment options, the carbon footprints are as follows: 347.7 kg CO2 (land application) < 459.7 kg CO2 (composting-involved land application) < 858.4 kg CO2 (brickmaking). In general, land application was superior to brickmaking from the perspective of carbon footprints. The power consumption incurred by aerating and turning and the direct N2O and CH4 emissions during composting increase the composting-involved land application carbon footprint. However, digested sludge that is not subject to high-temperature sterilization and compost is phytotoxic and can be fetid, which is a limitation of its applicability. And the composted sludge has a lower N ratio and water content, so the same N input means more sludge usage, which is conducive to solving the disposal problem of large amounts of sludge. Thus, if possible, composting-involved land application should be a preference, and improvements to the technique are required to minimize energy consumption and direct N2O and CH4 emissions. [ABSTRACT FROM AUTHOR]

NO 3 - is an undesirable environmental pollutant that causes eutrophication in aquatic ecosystems, and its pollution is difficult to eliminate because it is easily converted into NH 4 + instead of N 2 . Additionally, it is a high-energy substance. Herein, we propose a novel denitrification fuel cell to realize the chemical energy recovery of NO 3 - and simultaneous conversion of total nitrogen (TN) into N 2 based on the outstanding ability of NH 4 + generation on a three-dimensional copper nanowire (CNW)-modified copper foam (CF) cathode (CNW@CF). The basic steps are as follows: direct and highly selective reduction of NO 3 - to NH 4 + rather than to N 2 on the CNW@CF cathode, on which negative NO 3 - ions can be easily adsorbed due to their double-electron layer structure and active hydrogen ([H]) can be generated due to a large number of catalytic active sites exposed on CNWs. Then, NH 4 + is selectively oxidized to N 2 by the strong oxidation of chlorine free radicals (Cl • ), which originate from the reaction of chlorine ions (Cl - ) by photogenerated holes (h + ) and hydroxyl radicals (OH • ) under irradiation. Then, the electrons from the oxidation on the photoanode is transferred to the cathode to form a closed loop for external power generation. Owing to the continuous redox loop, NO 3 - completely reduces to N 2 , and the released chemical energy is converted into electrical energy. The results indicate that 99.9% of NO 3 - can be removed in 90 min, and the highest yield of electrical power density reaches 0.973 mW cm -2 , of which the nitrate reduction rates on the CNW@CF cathode is 79 and 71 times higher than those on the Pt and CF cathodes, respectively. This study presents a novel and robust energy recycling concept for treating nitrate-rich wastewater.

Removal of NO 3 - is a challenging problem in wastewater treatment. Electrocatalysis shows a great potential to remove NO 3 - but selectively converting NO 3 - to N 2 is facing a low efficiency. Here, a novel 3D Pd-Cu(OH) 2 /CF cathode based electrocatalytic (EC) system was proposed that can rapidly and selectively convert NO 3 - to NH 4 + , and further convert to N 2 simultaneously. The special designs for the system include: Cu(OH) 2 nanowires were firstly grown on copper foam (CF) with excellent conductivity that features high specific surface area in enhancing NO 3 - absorption and conversion to NO 2 - . Then, palladium (Pd) with a superior photons activation capacity was doped on the Cu(OH) 2 nanowires to promote the reduction of NO 2 - to NH 4 + . Then NH 4 + was quickly oxidized into N 2 by active chlorine. Finally, total nitrogen (TN) could easily be removed completely via above exhaustive cycle reactions. The 3D Pd-Cu(OH) 2 /CF cathode exhibits a 98.8 % conversion of NO 3 - to NH 4 + in 45 min with the reported highest removal rate of 0.017 cm -2  min -1 , which is 19.4 times higher than that of CF. The converted NH 4 + was finally exhaustively oxidized to N 2 with a 98.7 % of TN removal in 60 min., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The direct conversion of SO 2 to SO 3 is rather difficult for flue gas desulfurization due to its inert dynamic with high reaction activation energy, and the absorption by wet limestone-gypsum also needs the forced oxidation of O 2 to oxidize sulfite to sulfate, which is necessary for additional aeration. Here, we propose a method to remove SO 2 with highly synergistic H 2 O 2 production based on a novel dual-function photoelectrocatalytic (PEC) system in which the jointed spontaneous reaction of desulfurization and H 2 O 2 production was integrated instead of nonspontaneous reaction of O 2 to H 2 O 2 . SO 2 was absorbed by alkali liquor then oxidized quickly into SO 4 2- by a nanorod α-Fe 2 O 3 photoanode, which possessed high alkali corrosion resistance and electron transport properties. H 2 O 2 was produced simultaneously in the cathode chamber on a gas diffusion electrode and was remarkably boosted by the conversion reaction of SO 3 2- to SO 4 2- in the anode chamber in which the released chemical energy was effectively used to increase H 2 O 2 . The photocurrent density increased by 40% up to 1.2 mA·cm -2 , and the H 2 O 2 evolution rate achieved 58.8 μmol·L -1 ·h -1 ·cm -2 with the synergistic treatment of SO 2 , which is about five times than that without SO 2 . This proposed PEC cell system offers a cost-effective and environmental-benign approach for dual purpose of flue gas desulfurization and simultaneous high-valued H 2 O 2 production.

An efficient and inexpensive catalyst for oxygen reduction reaction (ORR), polyaniline (PANI) and β-MnO 2 nanocomposites (PANI/β-MnO 2 ), was developed for air-cathode microbial fuel cells (MFCs). The PANI/β-MnO 2 , β-MnO 2 , PANI and β-MnO 2 mixture modified graphite felt electrodes were fabricated as air-cathodes in double-chambered MFCs and their cell performances were compared. At a dosage of 6 mg cm -2 , the maximum power densities of MFCs with PANI/β-MnO 2 , β-MnO 2 , PANI and β-MnO 2 mixture cathodes reached 248, 183 and 204 mW m -2 , respectively, while the cathode resistances were 38.4, 45.5 and 42.3 Ω, respectively, according to impedance analysis. Weak interaction existed between the rod-like β-MnO 2 and surficial growth granular PANI, this together with the larger specific surface area and PANI electric conducting nature enhanced the electrochemical activity for ORR and improved the power generation. The PANI/β-MnO 2 nanocomposites are a promising cathode catalyst for practical application of MFCs., (Copyright © 2018. Published by Elsevier Ltd.)