Changes of dissolved organic matter fractions and formation of oxidation byproducts during electrochemical treatment of landfill leachates: Development of spectroscopic indicators for process optimization

A novel single-chamber bio-electro-Fenton for E2-3S removal: Insights into the effects of wastewater-derived DOM composition from molecular and species levels

This study developed a novel single-chamber bio-electro-Fenton (SCBEF) system by innovating the wettability and catalyst of the air cathode, and investigated the effect of wastewater-derived dissolved organic matter (DOM) on the removal of 17β-estradiol-3-sulfate (E2-3S) by the system. Results indicated that prepared hydrophilic interface catalytic layer was more suitable for the in-situ generation of H2O2 in the SCBEF system, with the highest H2O2 and coulombic efficiencies achieved at an LA132/SP ratio of 0.6. Air cathodes loaded with developed bimetallic nitrogen co-doped carbon catalyst could efficiently catalyze H2O2 into ·OH radicals, with the ·OH radical yield significantly higher than that of cathodes loaded with a monometallic catalyst. The volumetric power density and ·OH radical yield of the SCBEF system based on the developed air cathode were significantly improved (>30 %). E2-3S was effectively removed in SCBEF system, with a removal rate of 99 %. Although the SCBEF remained effective in degrading E2-3S after the introduced wastewater-derived DOM, the degradation kinetics of E2-3S varied significantly across groups. The variations in DOM composition and bacterial community were further analyzed by ultrahigh-resolution mass spectrometry and high-throughput sequencing, and combined with electrochemical assay and network analysis to reveal the relationships explaining how DOM composition affects E2-3S degradation by regulating microbes and ·OH radicals. DOM composition reshaped degrading and electricity-producing microbes and participated in the competition for ·OH radicals, which were considered potential causes affecting the degradation of E2-3S. Relevant findings provide valuable insights for the development and optimization of the SCBEF system.

Strategy for repurposing waste anion exchange resins to construct a biofilter for removing dissolved organic matter: performance and mechanism

Anion exchange resins are widely employed in wastewater and drinking water treatment plants to remove dissolved organic matter (DOM). However, the degradation of resin performance necessitates the discontinuation of these treatment projects, resulting in the idling of underperforming resins, referred to as waste anion exchange resins (WAER). Given the substantial investment in operational costs, determining how to economically utilize WAER is essential for restarting the treatment projects. Therefore, this study proposed a strategy for repurposing WAER to construct a biofilter for DOM removal. A biofilter, termed biological anion exchange resin (BAER), was developed using WAER and compared with two conventional biofilters: biological activated carbon (BAC) and sand filter. After the acclimatization period, the BAER biofilter achieved a removal of up to 21.42 % of dissolved organic carbon (DOC), which is 5.8 times greater than the removal rate of the sand filter and comparable to the BAC. Notably, BAER exhibited the highest removal rate of aromatics, achieving 41.04 % UV254 removal, which are precursors to disinfection byproducts (DBPs). Consequently, BAER demonstrated superior control of DBPs, with a removal efficiency of 39.59 %. Additionally, BAER demonstrated effective removal of humic substances due to the bioregeneration of its adsorption sites, which led to significant differences in both the structural composition and functional expression of the biological community in BAER compared to other biofilters. This study also revealed that the bioregenerated adsorption sites primarily capture DOM through electrostatic attraction rather than ion exchange. Overall, these findings confirm the promising application of the BAER biofilter constructed with WAER and offer valuable insights into the associated removal processes.

Transformation processes of total suspended solids and dissolved organic matter in rivers: Influences of different land use sources and degradation processes

The riverine dissolved organic matter (DOM) pool constitutes the largest and most dynamic organic carbon reservoir within inland aquatic systems. Human activities significantly alter the distribution of organic matter (OM) in rivers, thereby affecting the availability of DOM. However, the impact of total suspended solids (TSS) on DOM under anthropogenic influence remains insufficiently elucidated. This study employed Fourier transform ion cyclotron resonance mass spectrometry, DOC characterization, and incubation experiments to investigate how land use and degradation processes influence TSS-DOM transformation in rivers. Our findings revealed that geographical patterns cause significant variations in both DOM composition and TSS content. Anthropogenic impacts led to an increase in autochthonous TSS content and an enhanced relative intensity (RI) of nitrogen (N)- and sulfur (S)-containing compounds in riverine DOM. The presence of TSS increased the bioavailability of DOM from 29.97 % to 33.57 %. However, during both photodegradation and combined degradation processes, the presence of TSS reduced the bioavailability of DOM. The degradation rate constant (k) of DOM decreased as degradation time increased. The k values were significantly correlated with the CHO components in natural rivers and with N- and S-containing components in human-influenced rivers. The degradation rates of DOC under different land uses were 0.05 ± 0.04 d-1, 0.07 ± 0.06 d-1, and 0.08 ± 0.06 d-1 in forested, urban, and cropland-influenced rivers, respectively. The content of aliphatic compounds and the number of CHOS molecules in TSS-containing water were higher than in TSS-free water during the combined process of photochemical and microbial degradation, while the saturation and aromaticity of the compounds were lower. The characteristics of autochthonous DOM were more pronounced under the influence of TSS photorespiration. During drinking water disinfection, these small molecules derived from autochthonous TSS may contribute to an increase in disinfection by-products (DBPs) in drinking water. This study enhanced our understanding of how changes in autochthonous TSS content, driven by geographical heterogeneity and human activities, influence the biogeochemical processes of DOM in water, as well as the underlying molecular mechanisms and implications for water quality safety.

Improving biodegradability of dissolved organic matter (DOM) in old landfill leachate by electrochemical pretreatment: The effect mechanism of polarity

Enhancing the biodegradability of old landfill leachate is vital for the efficient treatment or resource utilization of municipal solid waste. Electrochemical pretreatment emerges as a promising technology for transformation of refractory dissolved organic matter (DOM). However, the specific impact of polarity on improving biodegradability of DOM remains unclear. In this study, a divided electrolyzer was used to explore the changes in the biodegradability of DOM in old landfill leachate during electrolysis. Meanwhile, the correlation mechanism between BOD5 variation and DOM evolution was explored by spectroscopy and Maldi-TOF-MS analysis. Results shown that different polarities all have positive effect on enhancing the biodegradability of DOM, while the structural changes related with BOD5 are depending on the polarity. In the anode chamber, electrochemical oxidation (EO) generates and eliminates carboxyl groups. Additionally, EO concurrently eliminates humic-like substances, which are challenging for microorganisms to degrade, and protein-like substances, which are easily degradable by microorganisms. This creates a competitive mechanism that coexist the promotion and inhibition for biodegradability. In the cathode chamber, electrochemical reduction (ER) transforms DOM components, accumulating easily useable protein components for microorganisms. Kinetic studies show that EO related BOD5 changes are aptly described by a competition model, considering both generation and removal of bioavailable components. ER related BOD5 changes suit a pseudo-first-order kinetic model. These insights into the transformation of old leachate DOM support the development of methods predicting BOD5 evolution, crucial for future process optimization.

Performance evaluation of the effect of humic acid on Anammox granular sludge: Apparent morphology, nitrogen removal and microbial community

Humic acid (HA) is a typical refractory organic matter, so it is of great significance to investigate its effect on the performance of Anammox granular sludge. When the dosage of HA ≤ 50 mg/L, HA promotes the total nitrogen removal rate (NRR) to 1.45 kg/(m3·day). When HA was between 50 and 100 mg/L, the NRR of Anammox was stable. At this time, the adsorption of HA causes the sludge to gradually turn from red to brown, but the activities of heme and enzymes showed that its capacity was not affected. When HA levels reached 250 mg/L, the NRR dropped to 0.11 kg/(m3·day). Moderate HA levels promoted the release of extracellular polymeric substance (EPS), but excessive HA levels lead to a decrease in EPS concentrations. HA inhibited Anammox activity, which indirectly hindered the transmission of substrate and accumulated substrate toxicity. Although HA promoted the increase of heterotrophic microbial abundance in Anammox system, the microbial diversity decreased gradually. With the increase of HA concentration, the abundance of Candidatus_Brocadia, the main functional microorganism of Anammox system, decreased gradually, while the abundance of Candidatus_Kuenenia increased gradually.

Development of an electrochemical separation-Rhodopseudomonas palustris electrolysis cell-coupled system for resourceful treatment of mature leachate landfill

Electrochemical technology is a promising technique for separating ammonia from mature landfill leachate. However, the accompanying migration and transformation of coexisting pollutants and strategies for further high-value resourceful utilization of ammonia have rarely received attention. In this study, an electrochemical separation-Rhodopseudomonas palustris electrolysis cell coupled system was initially constructed for efficient separation and conversion of nitrogen in mature landfill leachate to microbial protein with synchronously tracking the transport and conversion of coexisting heavy metals accompanying the process. The results revealed that ammonia concentration in the cathode increased from 40.3 to 49.8% with increasing the current density from 20 to 40 mA/cm2, with less than 3% of ammonia transformation to NO2--N and NO3--N. During ammonia separation, approximately 95% of HM-DOMs (Cr, Cu, Ni, Pb, and Zn) were released into the anolyte due to humus degradation and further diffused to the cathode. A significant correlation was observed between the releases of HM-DOMs. Cu-DOMs accounted for 70.2% of the total Cu content, which was the highest proportion among the heavy metals (HMs). Among the HMs in anolyte, 57.4% of Pb, 52.5% of Ni, and 50.6% of Zn diffused to the cathode, and most of the HMs were removed in the form of hydroxide precipitations due to heavy alkaline catholyte. Compared with the open-circuit condition, the utilization efficiency of NH4+-N in the R. palustris electrolysis cell increased by 445.1% with 47% and 50% increases in final NH4+-N conversion rate and R. palustris biomass, respectively, due to bio-electrochemical enhanced phototrophic metabolism and acid generation for buffering the strong alkalinity of the electrolyte to maintain suitable growth conditions for R. palustris.

Different Fenton treatments on diverse landfill organics: Discover the underestimated effect of derived-DOM

Fenton is one of the most promising processes for the removal of dissolved organic matter (DOM). It has always been highly suspected that derived-DOM would be generated during Fenton reaction, but there is lack of direct evidence at the molecular level. The present study explored the molecular properties of the derived-DOM of five common Fenton technologies for degradation of nine landfill organics including leachates and concentrates based on UPLC Orbitrap MS/MS analysis. The comparative results confirmed that DOM derivation was essential for Fenton technologies, with the DOM derivation rate as high as 17.3%-70.3%. The derived-DOM are dominated by trace organic contaminants (CHON-DOM), and typical new contaminants (PPCPs, flavors, etc.). Heterogeneous Fenton had significantly lesser derived-DOM (35.1% ± 16.9%) than other Fenton technologies. Among all landfill organics, medium leachate was most likely to derive DOM (51.4% ± 13.9%), while unexpectedly old leachate had the lowest derivation rate (32.0% ± 5.3%). In the overall membrane treatment process, the secondary membrane concentrate is more susceptible to DOM derivation (43.4% ± 5.5%-49.6% ± 3.8%) than the primary membrane concentrate (40.7% ± 14.1%), and the elements and subcategories composition and molecular property indexes of the derived-DOM become more complex. On the contrary, the DOM derivatization rate of the biological treatment effluent after Fenton treatment was much lower than that of the various concentrates after Fenton treatment and the molecular property are simpler. Therefore, Fenton may replace the membrane process directly as a deep treatment process after biological treatment of landfill leachate. These information would help the selection and application of Fenton technologies.