Treatment of fresh leachate by microaeration pretreatment combined with IC-AO2 process: Performance and mechanistic insight

Wastewater from natural gas Cansolv desulfurization process: Comprehensive characterization and effective removal of organic compounds

The wastewater generated by the solvent amine desulfurization process in natural gas purification plants is characterized by its recalcitrant organic compounds and high salinity. Without effective treatment, it has the potential to inflict severe environmental harm. The composition of organic matter, however, exerts a profound influence on the outcomes of oxidation processes. To rectify the limitations associated with indiscriminate oxidation that yields suboptimal results, this investigation meticulously performed a molecular-level analysis of organic matter. Based on the organic matter composition in the influent, this study compared the treatment efficacy of three oxidation processes and determined O3/H2O2-Fenton as the optimal joint approach. After O3/H2O2 oxidation, long-chain unsaturated organic compounds (C > 40,DBE > 20) underwent degradation into short-chain aldehydes and low-molecular-weight fatty acids, with priority given to reactions involving CC, CO, and OH over CH reactions. Subsequent Fenton oxidation effectively removed the refractory organics (CHOS, CHONS) and significantly reduced the diversity of organic matter (from 7730 to 4237). The carboxylation, demethylation, and dehydrogenation reactions further facilitated the removal of recalcitrant organic compounds. In light of these findings, this study substantiates that the conversion of extended-chain unsaturated compounds into abbreviated-chain saturated compounds within the system through O3/H2O2 oxidation significantly enhances the subsequent efficacy of Fenton oxidation in organic matter removal. These insights offer valuable perspectives for the efficient remediation of analogous high-salinity organic wastewater scenarios.

Distribution, removal and ecological risk assessment of antibiotics in leachate from municipal solid waste incineration plants in Shanghai, China

Leachate from Municipal Solid Waste (MSW) incineration plants contains multiple antibiotics. However, current knowledge of antibiotics in such leachate is very limited compared to landfill leachate. In this study, the distribution, removal and ecological risks of 8 sulfonamides (SAs), 4 quinolones (FQs), and 4 macrolides (MLs) antibiotics in leachate from three MSW incineration plants in Shanghai were investigated. The results showed that 12 types of target antibiotics were detected at high concentrations (7737.3-13,758.7 ng/L) in the fresh leachate, exceeding the concentrations reported for landfill leachate. FQs were the dominant antibiotics detected in all three fresh leachates, accounting for >60 % of the total detected concentrations. The typical "anaerobic-anoxic/aerobic-anoxic/aerobic-ultrafiltration" treatment process removed the target antibiotics effectively (89.0 %-93.4 %), of which the anaerobic unit and the primary anoxic/aerobic unit were the most important antibiotic removal units. Biodegradation was considered to be the dominant removal mechanism, removing 78.11 %-92.37 % of antibiotics, whereas sludge adsorption only removed 1.02 %-10.89 %. Antibiotic removal was significantly correlated with leachate COD, pH, TN, and NH3-N, indicating that they may be influential factors for antibiotic removal. Ecological risk assessment revealed that ofloxacin (OFX) and enrofloxacin (EFX) in the treated leachate still posed high risks to algae and crustaceans. This research provides insights into the fate of antibiotics in leachate.

Investigation with ESI FT-ICR MS on sorbent selectivity and comprehensive molecular composition of landfill leachate dissolved organic matter

Molecular characterization of landfill leachate dissolved organic matter (LDOM) is essential for developing effective processing techniques. However, the molecular selectivity of extraction method and ionization modes often leads to the bias of molecular characterization of LDOM. Here, seven representative sorbents were selected and electrospray ionization negative ion mode (ESI (-)) and positive ion mode (ESI (+)) Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were used to investigate the molecular composition of different LDOM samples. Obvious sorbent selectivity during extraction procedure was observed, resulting in the underestimation of molecular diversity of LDOM from 32.7% to 69.3%. Totally, 14,000-18,000 unique molecules were obtained in a single sample, indicating the unprecedented molecular diversity of LDOM. Lignins, proteins and lipids are three major molecular groups in LDOM, and N or S containing molecules occupied 83%. Although much of total organic carbon was removed during biochemical treatment process, the molecular diversity of LDOM was not reduced because a considerable of bio-recalcitrant molecules was produced. The results uncover the sorbents selectivity and ionization modes selectivity in LDOM analysis and provided a comprehensive change of LDOM molecular composition during biochemical treatment, which benefits the development of accurate methods to remove organic carbon in landfill leachate.

Conversion and impact of dissolved organic matters in a heterogeneous catalytic peroxymonosulfate system for pollutant degradation

Dissolved organic matters (DOM) are widely present in different water sources, causing significant effects on water treatment processes. Herein, the molecular transformation behavior of DOM during peroxymonosulfate (PMS) activation by biochar for organic degradation in a secondary effluent were comprehensively analyzed. Evolution of DOM was identified and inhibition mechanisms to organic degradation were elucidated. DOM underwent oxidative decarbonization (e.g., -C₂H₂O, -C₂H₆, -CH₂ and -CO₂), dehydrogenation (-2H) and dehydration reactions by ^·OH and SO₄^·-. N and S containing compounds witnessed deheteroatomisation (e.g., -NH, -NO₂+H, -SO₂, -SO₃, -SH₂), hydration (+H₂O) and N/S oxidation reactions. Among DOM, CHO-, CHON-, CHOS-, CHOP- and CHONP-containing molecules showed moderate inhibition while condensed aromatic compounds and aminosugars exhibited strong and moderate inhibition effects on contaminant degradation. The fundamental information could provide references for the rational regulation of ROS composition and DOM conversion process in a PMS system. This in turn offered theoretical guidance to minimize the interference of DOM conversion intermediates on PMS activation and degradation of target pollutants.

Advanced nitrogen removal from mature landfill leachate based on novel step-draining partial nitrification-denitrification and Anammox process: Significance of low volume exchange ratio

To save external carbon source dosage and simplify NH4+ to NO2- ratio control strategy, this study established a novel step-draining based partial nitrification-denitrification and Anammox (PND-AMX) system for advanced nitrogen removal from mature landfill leachate. Separation of partial nitrification and denitrification was realized based on step-draining, achieving 74.8 % nitrogen removal. 25 % was the optimal volume exchange ratio for synergistic removal of organics and nitrogen, allowing full use of carbon source. NH4+ to NO2- ratio was easily controlled by varying the volume ratio of the first and second effluent of PND reactor. Brocadia, Kuenenia and Jettenia collectively accounted for 13.61 % in AMX reactor, contributing 21.0 % of nitrogen removal. Nitrogen removal efficiency and nitrogen removal rate reached 98.3 ± 1.2 % and 3.07 ± 0.09 kgN/(m3∙d), respectively. Partial Anammox process based on step-draining was easier to realize and of practical significance for application in treatment of landfill leachate.

A comprehensive study on simultaneous enhancement of sludge dewaterability and elimination of polycyclic aromatic hydrocarbons by Fe2+ catalyzing O3 process

Simultaneous removal of polycyclic aromatic hydrocarbons (PAHs) in the process of enhancement of sludge dewaterability via oxidation of hydroxyl radicals (•OH) and flocculation of Fe³⁺ by Fe²⁺-catalyzing O₃ were investigated as a novel research focus. The results showed that capillary suction time (CST) and water content of dewatered sludge cake (Wc) were reduced from 57.9 s and 85.1% to 13.6 s and 69.65% under the optimum usage of 60 mg/g dry solids (DS) O₃ and 80 mg/g DS FeSO₄, respectively. The relevant dewatering mechanism of Fe²⁺-catalyzing O₃ treatment was elucidated. It was found that extracellular polymeric substances-bound (EPS-bound) and intracellular water was dramatically released through destroying sludge cells and EPS gel-like structure by produced •OH. In addition, the results of X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and ¹³C NMR spectroscopy revealed that •OH oxidized and mineralized hydrophilic organic matters intensifying hydrophobicity of sludge surface. Moreover, Fe³⁺ generated by oxidation of Fe²⁺ agglomerated fragmented fine particles into large aggregates and decreased exposure of hydrophilic sites by neutralizing negative charge, which promoted water-solids separation. Meanwhile, sludge surface roughness was decreased which was determined by material type upright confocal laser microscope (CLM). As a consequence, •OH and Fe³⁺ were mainly responsible for enhancement of sludge dewaterability. Moreover, more than 40% of removal rate of PAHs was accomplished by Fe²⁺-catalyzed O₃ treatment mitigating the environmental risks of PAHs spread.

Enhanced waste activated sludge dewaterability by the ozone-peroxymonosulfate oxidation process: Performance, sludge characteristics, and implication

Dewatering treatment is an essential step to diminish sludge volume, cut down transportation costs, and improve subsequent disposal efficiency. In this study, ozone-peroxymonosulfate (O₃/PMS) oxidation process was employed to ameliorate sludge dewaterability. Sludge capillary suction time (CST) and water content (Wc) of dewatered sludge cake could reduce from 70.5 s and 81.93% to 26.7 s and 65.65%, respectively, under the optimal dosage of 30 mg/g TS O₃ and 0.4 mmol/g TS PMS. The increased sludge zeta potential, particle size, and fluidity promoted sludge dewatering performance apparently. The decreased hydrophilic, fluorescent EPS components and proteins/peptides-like + Lipids percentage in EPS as well as the ratio of α-helix/(β-sheet + random coil) of treated EPS protein secondary structure was greatly responsible for the enhanced sludge dewaterability. SO₄^- and OH were detected in ozone-peroxymonosulfate process to crack sludge flocs, eliminate hydrophilic substances and liberate bound water. Moreover, the concentrations of both heavy metals and polycyclic aromatic hydrocarbons (PAHs) of sludge after O₃/PMS conditioning were decreased, and the stability and toxicity of heavy metals were also reduced, except Zn. In conclusion, this work offered a comprehensive insight based on ozone-peroxymonosulfate (O₃/PMS) advanced oxidation for improving the sludge dewaterability and environmental implication.