Molecular characterization of dissolved organic nitrogen during anoxic/oxic and anammox processes using ESI FT-ICR MS

Novel strategy for treating high salinity oilfield produced water: Pyrite-activated peroxymonosulfate coupled with heterotrophic ammonia assimilation

Existing conventional biological treatment techniques face numerous limitations in effectively removing total petroleum hydrocarbons (TPHs) and ammonia (NH4+-N) from oilfield-produced water (OPW), highlighting the pressing need for innovative pre-oxidation and biological treatment processes. In this study, a pyrite-activated peroxymonosulfate (PMS)-coupled heterotrophic ammonia assimilation (HAA) system was established to achieve satisfactory system performance for OPW treatment. Pyrite sustained-release Fe2+-activated PMS was used to produce SO4•- and •OH, and 71.0 % of TPHs were effectively removed from the oil wastewater. The average TPHs and NH4+-N removal efficiencies in the test group with pre-oxidation were 96.9 and 98.3 %, compared to 46.5 and 77.1 % in the control group, respectively. The maximum fluorescence intensities of tryptophan protein and aromatic protein in the test group declined by 83.7 %. Fourier transform ion cyclotron resonance mass spectrometry revealed that pre-oxidation degraded more long-chain hydrocarbons and aromatic family compound, whereas the HAA process produced more proteins and carbohydrates. Pyrite-PMS promoted the enrichment of ammonia-assimilating bacteria, alleviating the explosive increase in extracellular polymeric substances and reducing sludge settleability. The low cost, efficiency, green chemistry principles, and synergies of this approach make it a powerful solution for practical OPW treatment to reduce environmental impacts and promote sustainable wastewater treatment.

Molecular insights into the dissolved organic matter of leather wastewater in leather industrial park wastewater treatment plant

Leather wastewater (LW) effluent is characterized by complex organic matter, high salinity, and poor biodegradability. To meet the discharge standards, LW effluent is often mixed with municipal wastewater (MW) before being treated at a leather industrial park wastewater treatment plant (LIPWWTP). However, whether this method efficiently removes the dissolved organic matter (DOM) from LW effluent (LWDOM) remains debatable. In this study, the transformation of DOM during full-scale treatment was revealed using spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry. LWDOM exhibited higher aromaticity and lower molecular weight than DOM in MW (MWDOM). The DOM properties in mixed wastewater (MixW) were similar to those in LWDOM and MWDOM. The MixW was treated using a flocculation/primary sedimentation tank (FL₁/PST), anoxic/oxic (A/O) process, secondary sedimentation tank (SST), flocculation/sedimentation tank, denitrification filter (FL₂/ST-DNF), and an ozonation contact reactor (O₃). The FL₁/PST unit preferentially removed the peptide-like compounds. The A/O-SST units had the highest removal efficiencies for dissolved organic carbon (DOC) (61.34 %) and soluble chemical oxygen demand (SCOD) (52.2 %). The FL₂/ST-DNF treatment removed the lignin-like compounds. The final treatment showed poor DOM mineralization efficiency. The correlation between water quality indices, spectral indices, and molecular-level parameters indicated that lignin-like compounds were strongly correlated with spectral indices and CHOS compounds considerably contributed to the SCOD and DOC. Although the effluent SCOD met the discharge standard, some refractory DOM from LW remained in the effluent. This study illustrates the composition and transformation of DOM and provides theoretical guidance for improving the current treatment processes.

Enhancing nitrate attenuation in groundwater via selectively applying surface agricultural practices: A novel and sustainable strategy for non-point source pollution mitigation

Non-point nitrate pollution in groundwater has been accelerated by agricultural development, but sustainable nitrogen removal is a challenge because of its wide distribution and negative side effects. Surface agricultural practices (SAPs), which are demonstrably effective in driving the downward infiltration of dissolved organic carbon (DOC), have not been well explored for their potential to enhance nitrate attenuation in groundwater. Therefore, a combination of soil column and groundwater incubation experiments was performed to investigate the carbon and nitrogen responses to different SAPs (manure fertilization, lucerne planting, and straw return). The soil column experiment showed that SAPs promoted DOC and reduced nitrate leaching into groundwater, and straw treatment witnessed the highest DOC leaching flux (252.71 g m^-2 yr^-1) and lowest nitrate leaching flux (9.51 g m^-2 yr^-1). The groundwater incubation experiment showed that leachates from the straw treatment displayed the best denitrification-enhancement performance, with the highest NO₃^--N reduction efficiency (92.93%) and rate (1.627 mg/day), N₂ selectivity (99.78%), and net nitrogen removal (0.09 mg). Furthermore, Fourier transform ion cyclotron resonance mass spectrometry confirmed that CHOS molecules with lower double bond equivalents (0-5) and larger carbon numbers (10-15) were more accessible to denitrifiers. This study provides a new path for the sustainable control of non-point source nitrate pollution.