Phosphorus recovery from sludge by pH enhanced anaerobic fermentation and vivianite crystallization

Phosphorus (P) shortage is a global issue. However, P recovery from waste activated sludge (WAS) has huge potential. In this study, an innovative method for the recovery of P from WAS via pH adjustment-enhanced anaerobic fermentation (AF) and vivianite crystallization was developed. The results indicate that P could be effectively released from WAS to the supernatant under an appropriate pH during AF. P release efficiency increased by 31.6 % at pH 5.0 and 26.1 % at pH 11.0 compared to the control. Over 99 % of the P in the liquid could be recovered by subsequent vivianite crystallization, and similar to 60 % total P recovery efficiency was obtained. The scanning electron microscopy and X-ray diffraction analyses showed that the co-precipitation of Ca2+ and Mg2+ affected vivianite purity. The recovered vivianite purity from the pH 11.0 supernatant (91.39 %) was higher than the pH 5.0 supernatant (85.44 %) because of lower Ca2+ and Mg2+ ions in the former. In addition, the heavy metals in the recovered vivianite were lower than their own risk thresholds. This study provides new insights into the recovery of P from WAS by pH adjustment-enhanced AF and vivianite crystallization

New insights into the degradation of chloramphenicol and fluoroquinolone antibiotics by peroxymonosulfate activated with FeS: Performance and mechanism

SO4?- and ?OH are recognized as valid reactive species in the FeS-activated persulfate system. However, whether other reactive species are generated in this process remains unclear. In this study, a FeS-based peroxymonosulfate (PMS) (FeS/PMS) system was developed for the degradation of chloramphenicol (i.e., chloramphenicol (CAP) and thiamphenicol (TAP)) and fluoroquinolone (i.e., ciprofloxacin (CIP) and norfloxacin (NOR)) antibiotics. In addition to SO4?- and ?OH, Fe(IV) was identified as another reactive species by using methyl phenyl sulfoxide (PMSO) and methyl phenyl sulfone (PMSO2) as probe compounds. Although Fe(IV) participated in antibiotic degradation, the contribution of Fe(IV) was smaller than that of SO4?- due to its low redox potential and weak competition ability. Efficient degradation of antibiotics was achieved in the FeS/PMS system within 120 min using 6 mM PMS and 0.6 g/L FeS at initial pH of 7.0, with removal percentages of 93.5%, 98.5%, 100% and 100% for CAP, TAP, CIP and NOR, respectively. The S2- acted as an electron donor to facilitate continuous Fe(III) reduction and Fe(II) regeneration. Based on the degradation intermediates of antibiotic, the reaction pathways were proposed to involve side chain cleavage, hydroxylation, denitration, deoxygenation, decarboxylation and dehalogenation. In addition to its performance in simulated waters, the FeS/PMS system also presented effective antibiotic degradation in real surface water. This study provides new insights into the mechanism of multiple reactive species generation in the FeS-activated PMS process and extends the potential engineering applications in antibiotic degradation and in situ water quality remediation

A novel combination of bioelectrochemical system with peroxymonosulfate oxidation for enhanced azo dye degradation and MnFe2O4 catalyst regeneration

Advanced oxidation process (AOP) based on peroxymonosulfate (PMS) activation was established in microbial fuel cell (MFC) system with MnFe2O4 cathode (MFC-MnFe2O4/PMS) aimed to enhance azo dye degradation and catalyst regeneration. The effects of loading amount of MnFe2O4 catalyst, applied voltage, catholyte pH and PMS dosage on the degradation of Orange II were investigated. The stability of the MnFe2O4 cathode for successive PMS activation was also evaluated. The degradation of Orange was accelerated in the MFC-MMnFe2O4/PMS with apparent degradation rate constant increased to 1.8 times of that in the MnFe2O4/PMS control. A nearly complete removal of Orange II (100 mg L-1) was attained in the MFC-MnFe2O4/PMS under the optimum conditions of 2 mM PMS, 10 mg cm(-2) MnFe2O4 loading, pH 7 -8 and 480 min reaction time. MFC driven also extended the longevity of the MnFe2O4 catalyst for PMS activation due to the in-situ regeneration of congruent to Mn2+ and congruent to Fe2+ through accepting electrons from the cathode, and over 80% of Orange II was still removed in the 7th run. Additionally, the MFC-MnFe2O4/PMS system could recover electricity during Orange II degradation with a maximum power density of 206.2 +/- 3.1 mW m(-2). PMS activation by MnFe2O4 was the primary pathway for SO4 generation, and SO4 based oxidation was the primary mechanism for Orange II degradation. MFCs driven coupled with PMS activated AOP systems provides a novel strategy for efficient and persistent azo dye degradation. (C) 2018 Elsevier Ltd. All rights reserved

Decorated reduced graphene oxide transfer sulfides into sulfur and sulfone in wastewater

Sulfides cannot be completely removed using oxidation due to the production of sulfate. In this work, a reduced graphene oxide (RGO)/Fe3O4 hybrid material was synthesized via a simple in situ chemical method for sulfide removal. The adsorption capacity of RGO/Fe3O4 was evaluated by sulfide removal from aqueous solution, and different experimental parameters including contact time, solution pH, adsorbent dosage, ion strength and temperature were investigated. The equilibrium data were in accordance with the Langmuir linear isotherm with a maximum uptake capacity of 173 mg g(-1). The adsorption of sulfide by the RGO/Fe3O4 hybrid material can be attributed to the synergistic effect of both chemical and physical adsorption according to kinetic, adsorption isotherm and thermodynamic studies. The RGO/Fe3O4 material with oxygenated functional groups could convert sulfides to stable elemental sulfur and sulfone organics. The external magnetic field could easily separate the magnetic RGO/Fe3O4 adsorbent from the liquid. This research provides a novel strategy for the green and low-cost treatment of sulfide-containing wastewater by the RGO/Fe3O4 hybrid material

Reductive degradation of chloramphenicol by Geobacter metallireducens

Geobacter metallireducens is known to be capable of removing nitroaromatic compounds via an oxidation mode. However, little attention has been paid to investigate the reductive removal of chlorinated nitroaromatic compounds by G. metallireducens. In this study, G. metallireducens was used to reduce chloramphenicol (CAP), a typical chlorinated nitroaromatic antibiotic. Cyclic voltammograms and chronoamperometry highlighted a higher peak current for CAP reduction by G. metallireducens compared to the control without bacteria. G. metallireducens efficiently reduced CAP (20 mg/L) with acetate as the sole electron donor, and the removal efficiency reached (97.6 +/- 4.9)% within 6 d. Aromatic amine (AMCl2), AMCl (dechlorinated AMCl2) and AM (dechlorinated AMCl) were identified as reduction products by liquid chromatography-mass spectrometry. However, the removal efficiency declined to (25.0 +/- 3.6)% when the CAP dosage increased to 80 mg/L. Transcriptomic analysis indicated the significant upregulation of genes related to electron transfer, such as pilus assembly protein gene (2.8 folds), NADH-quinone oxidoreductase subunit K2 gene (4.5 folds) and many c-type cytochrome genes such as cytochrome c biogenesis protein ResB (Gmet 2901, 4.6 folds), cytochrome c (Gmet 0335, 4.4 folds) and cytochrome c7 (Gmet 2902, 3.4 folds). Furthermore, a gene related to chlorinated contaminant removal (Gmet 1046, 5.4 folds) was also upregulated, possibly resulting in enhanced CAP reduction. This work deepened our knowledge of the bioremediation ability of G. metallireducens with respect to environmental contaminants and provided a potential strategy to treat antibiotics with electrochemically active bacteria

In situ fabrication of gold nanoparticles into biocathodes enhance chloramphenicol removal

The development of highly conductive biofilms is a key strategy to enhance antibiotic removal in bioelectrochemical systems (BESs) with biocathodes. In this study, Au nanoparticles (Au-NPs) were in situ fabricated in a biocathode (Au biocathode) to enhance the removal of chloramphenicol (CAP) in BESs. The concentration of Au(III) was determined to be 5 mg/L. CAP was effectively removed in the BES containing a Au biocathode with a removal percentage of 94.0% within 48 h; this result was 1.8-fold greater than that obtained using a biocathode without Au-NPs (51.7%). The Au-NPs significantly reduced the charge transfer resistance and promoted the electrochemical activity of the biocathode. In addition, the Au biocathode showed a specifical enrichment of Dokdonella, Bosea, Achromobacter, Bacteroides and Petrimonas, all of which are associated with electron transfer and contaminant degradation. This study provides a new strategy for enhancing CAP removal in BESs through a simple and eco-friendly electrode design. (c) 2021 Elsevier B.V. All rights reserved

A new insight into the strategy for methane production affected by conductive carbon cloth in wetland soil: Beneficial to acetoclastic methanogenesis instead of CO2 reduction

Conductive materials/minerals can promote direct interspecies electron transfer (DIET) between syntrophic bacteria and methanogens in definedco-culture systems and artificial anaerobic digesters; however, little is known about the stimulation strategy of carbon material on methane production in natural environments. Herein, the effect of carbon cloth, as a representative of conductive carbon materials, on methane production with incubated wetland soil was investigated. Carbon cloth significantly promoted methanogenesis. With the application of electrochemical technology, calculation of the apparent electron transfer rate constant showed that carbon cloth significantly increased electron transfer rate (ETR) compared with the control experiment in presence of cotton cloth, from 0.0017 +/- 0.0003 to 0.0056 +/- 0.0015 s(-1). Results obtained from both stable carbon isotope measurements and application of specific inhibitor (CH3F) for acetoclastic methanogenesis indicated that carbon cloth obviously promoted acetoclastic methanogenesis instead of CO2 reduction. High-throughput sequencing showed that methane production may stem from the involvement of Methanosarcina for both treatments. Our findings suggested that conductive carbon material can promote acetoclastic methanogenesis instead of CO2 reduction in a natural environment. (C) 2018 Elsevier B.V. All rights reserved