Humic Acid-like Compounds Research Articles

The accumulation and inhibition mechanism of extracellular polymeric substances of Chlorella vulgaris during cycling cultivation under different light qualities.

The secretion, accumulation, and composition of extracellular polymeric substances (EPS) are pivotal factors influencing microalgal growth as well as wastewater recycling. Until now, the accumulation and inhibition mechanism of EPS of Chlorella vulgaris during cycling cultivation is not fully understood. The purpose of this study was to explore how different light qualities regulate the secretion, chemical composition, and structure of microalgal EPS, and subsequently influence the recycling of culture wastewater. After four cycles of cultivation, C. vulgaris under green light produced the highest EPS production and lowest biomass production, which were 82% higher and 17% lower, respectively, compared to white light, which yielded the least EPS production and the highest biomass production. EPS under different light qualities all exhibited a fibrillar structure with a sheet-like surface, but differed in composition. Compared with the other groups, EPS under green light showed a significant increase in polysaccharides, proteins, and humic acid-like compounds, as well as an increased proportion of arabinose and rhamnose, according to monosaccharide composition analysis. Transcriptome analysis indicated that the up-regulation of metabolic pathways linked to glycolysis/gluconeogenesis, TCA cycle, lipid synthesis, and ABC transporters promoted EPS accumulation. Additionally, EPS could target light-harvesting complex (LHC) and electron transport chain, down-regulating the photosynthetic pathway, which ultimately inhibited microalgal growth under green light. This study provides a theoretical foundation for the light regulation and circulation culture of microalgae, as well as for microalgal wastewater treatment.

Understanding microplastic aging driven by photosensitization of algal extracellular polymeric substances

The aging of microplastics (MPs) is extremely influenced by photochemically-produced reactive intermediates (PPRIs), which are mediated by natural photosensitive substances. Algal extracellular polymeric substances (EPS) can produce PPRIs when exposed to sunlight. Nonetheless, the specific role of EPS in the aging process of MPs remains unclear. This work systematically explored the aging process of polystyrene (PS) MPs in the EPS secreted by Chlorella vulgaris under simulated sunlight irradiation. The results revealed that the existence of EPS accelerated the degradation of PS MPs into particles with sizes less than 1 µm, while also facilitating the formation of hydroxy groups on the surface. The release rate of dissolved organic matter (DOM) from PS MPs was elevated from 0.120 mg·L-1·day-1 to 0.577 mg·L-1·day-1. The primary factor contributing to the elevated levels of DOM was humic acid-like compounds generated through the breakdown of PS. EPS accelerated the aging process of PS MPs by primarily mediating the formation of triplet excited states (3EPS*), singlet oxygen (1O2), and superoxide radicals (O2∙-), resulting in indirect degradation. 3EPS* was found to have the most substantial impact. This study makes a significant contribution to advance understanding of the environmental fate of MPs in aquatic environments impacted by algal blooms.

Membrane fouling in engineering nanofiltration process for drinking water treatment: The spatial and chemical aspects

Nanofiltration (NF) has become an established process for advanced treatment of drinking water, while membrane fouling remains as the main issue slowing the widespread application of the process. In this study, the key foulants were identified, and their spatial distribution and potential interactions were investigated based on a two-stage NF engineering project for municipal drinking water treatment. Over half a year of operation showed that the membrane fouling was mostly chemically reversible. Characterizations of the cleaning waste revealed that inorganic fouling dominated at both stages, which was mainly caused by the deposition of Al, Ca, and Si. While the overall fouling was much more severe at Stage 2, the organic fouling was the reverse. Autopsy of one full-size membrane element from each stage indicated that in addition to Al, P and humic acid-like compounds were abundant in the fouling layer for both stages despite the spatial differences. The spatial distribution of foulants was influenced by both concentration effects and presence of feed channel spacers. For the free membrane area, inorganic foulants and humic acid-like compounds had higher contents at Stage 2 than Stage 1. While for the membrane area contacting with spacers, Al and P at Stage 1 were 0.74 and 1.51 times higher than those at Stage 2, respectively. Moreover, statistical analysis, complexation experiments and engineering operation strongly supported that the residual Al and natural organic matter (NOM) were key foulants for the NF process, mainly by forming Al-NOM complexes. Besides the Al-NOM complexes, condensed phosphate, primarily sourced from the dosed phosphate-containing antiscalants, might also co-precipitate with Al or Al-NOM complexes.

A novel fungal-algal coupling system for slaughterhouse wastewater treatment and lipid production

In this study, a novel fungal-algal coupling system was established for slaughterhouse wastewater treatment with Chlorella sp. DT025 and a new fungus, Penicillium sp. AHP141. With the optimization of cultivation conditions for the fungal-algal coupling system, the harvest efficiency of Chlorella sp. DT025 reached 99.79%. The mechanism of microalgae harvest of the fungal-algal system was revealed to be related to the morphological characteristics, surface charge, and the secretion of humic acid-like compounds and tryptophan on the surface of the fungi cells. For the original slaughterhouse wastewater treatment, the fungal-algal coupling system had a better removal efficiency of COD, TN, and TP than both monoculture systems. In the high-concentration artificial slaughterhouse wastewater, COD removal of the fungal-algal system reached more than 5350 mg/L. The lipid production of the fungal-algal coupling system in the high-concentration artificial slaughterhouse wastewater treatment was improved by 343.33% to 1.33 g/L compared to the microalgae monoculture treatment.

Influences of Anthropogenic Pollution on the Dynamics of Sedimentary Fulvic Acid Fractions as Revealed via Spectroscopic Techniques Combined with Two-Dimensional Correlation Spectroscopy

To identify the influences of anthropogenic activities on the composition, spatial distribution, sources, and transformation mechanism of sedimentary fulvic acid (FA) fractions from different reaches of an urban river were tracked via excitation-emission matrix (EEM) fluorescence spectroscopy with parallel factor (PARAFAC) analysis and two-dimensional correlation spectroscopy (2D-COS). Sediment samples were collected from Baitapu River (BR) along gradients with human activities (e.g., rural, town, and urban sections) in Shenyang, northeast China, from which FA fractions were extracted and then determined via EEM fluorescence spectroscopy. According to optical indices, the autochthonous sources of sedimentary FA fractions in BR were more significant than the terrestrial sources. Among the sections, the contribution from autochthonous sources decreased in the following order: Rural > Urban > Town. Six components of sedimentary FA fractions were identified via EEM–PARAFAC: C1 comprised tryptophan-like (TRL) compounds; C2 was associated with microbial humic-like (MHL) compounds; C3, C4, and C5 were associated with FA-like (FAL) compounds; and C6 comprised humic acid-like (HAL) compounds. The proportion of sedimentary FA fractions decreased in the following order: MHL + FAL + HAL (humus, 77.37–88.90%) > TRL (protein, 11.10–22.63%) for the three sections, showing that humus dominated. The town section exhibited the highest sedimentary FA fractions (5328.87 ± 1315.82 Raman unit [R.U.]), followed by the urban (4146.49 ± 535.75 R.U.) and rural (2510.56 ± 611.00 R.U.) sections. Three pollution sources were determined via principal component analysis (i.e., the dominant industrial source, domestic wastewater, and agricultural effluent). Additionally, the results from 2D-COS revealed that sedimentary FA fractions tended to stabilize as the protein-like component was transformed into the HAL component. Furthermore, we used the structural equation model to validate the critical environmental variables affecting the FA fraction transformation. The results can elucidate the influences of human activities on the dynamics of sedimentary FA fractions in urban rivers.

Structure of the humic acid-like compounds of raw and hydrothermally treated sewage sludge

Humic acids are of great interest in many fields; however, they are inhibitors of fermentative processes applied to hydrothermally treated sewage sludge. Hence, the structure and composition of soluble and bound humic acid-like fractions from raw and hydrothermally treated sewage sludge were studied. Lipid, polysaccharide, protein and aromatic fractions were identified, as well as a high nitrogen content (7–10 %) and low solubility in alkaline media. Thus, they do not strictly meet the chemical definition of ‘humic acids’. The soluble humic acid-like compounds had more aromatic and less protein content. Thermal hydrolysis of sewage sludge increased their aromaticity to the detriment of protein and polysaccharide fractions, while wet oxidation caused an increase in all structural fractions. Regarding the bound compounds, lipid, polysaccharide and aromatic fractions increased markedly during both treatments, although oxygen produced higher degradation of the protein fraction and, from 1 h, the partial degradation of aromatic compounds and an increase in the C/N atomic ratio (from 5.0 to 18.7 after 2 h). Therefore, hydrothermal treatments have a positive impact on the hydrolysate biodegradability due to the organic matter solubilisation, but also a negative impact linked to the higher solubilisation of the humic acid-like compounds and their structural changes.

Fulvic acid enhanced peroxymonosulfate activation over Co–Fe binary metals for efficient degradation of emerging bisphenols

Bisphenol F (BPF) and bisphenol S (BPS) are emerging bisphenols, which have become the main substitutes for bisphenol A (BPA) in industrial production and are also considered as new environmental pollution challenges. Thus, the necessity for an effective approach to remove BPF and BPS is essential. In this study, fulvic acid (FA) was used to modify Co–Fe binary metals (CFO) for peroxymonosulfate (PMS) activation. The characterization results demonstrated that CFO changed significantly in morphology after compounding with FA, with smaller particle size and 5.6 times larger specific surface area, greatly increasing the active sites of catalyst; Moreover, humic acid-like compounds increased the surface functional groups of CFO, especially phenolic hydroxyl, which could effectively prolong the PMS activation. The concentration of all reactive species, such as SO4•−, •OH, O2•−, and 1O2 increased in FA@CFO/PMS system. As a result, the degradation efficiency of CFO for both BPF and BPS was significantly improved after compounding FA, which also had a wide range of pH applications. The degradation pathways of both BPF and BPS were proposed based on liquid chromatography-mass spectrometry (LC-MS) analysis and the density functional theory (DFT) calculations. Our findings are expected to provide new strategies and methods for remediation of environmental pollution caused by emerging bisphenols.

Study of the Humification Process and Humic Acid-like Structure Characteristics of Kitchen Waste with the Addition of Biochar

The majority of the studies on humification culture presently use livestock and poultry manure as the primary raw material. There is significantly less research on the changes and structural characteristics of humic acid-like compounds (HAL) formed by humification using real food waste as the raw material. This paper aims to study the changes in humic components and the structure of HAL in the humification process through the addition of biochar to pre-meal waste and post-meal swill as the primary raw materials. Kitchen waste + corn straw (KC) and kitchen waste + corn straw + biochar carbon (KCBr) were humified for 24 days, respectively, using the indoor static composting method, where the samples were collected at days 0, 12, and 24 of incubation. The HAL were analyzed using elemental analysis, infrared spectroscopy, and differential thermal techniques. The results demonstrated that KCBr first entered the high-temperature phase, which lasted for 12 days above 50 °C. The total organic carbon (TOC) demonstrated a decreasing trend in both treatments, while the total nitrogen (TN) demonstrated an upward trend. The HAL and fulvic acid-like (FAL) contents of the two treatments increased and decreased with an increase in the incubation time, respectively. The relative HAL content and humification index (PQ%) of KCBr and KC at the end of humification were 22.76% and 19.69% and 74.30%, and 73.11%, respectively. In terms of the HAL structure, the KCBr treatment demonstrated lowered condensation, reduced oxidation, decreased aliphatic, enhanced aromatization, and increased thermal stability of HAL compared with the KC treatment.

Characterization of dissolved black carbon and its binding behaviors to ceftazidime and diclofenac pharmaceuticals: Employing the molecular weight fractionation

As the ubiquitous component of the aquatic environment, dissolved organic matter (DOM) readily bind with residual pharmaceutical contaminants (PCs) and influence their environmental behaviors. However, the binding mechanisms between dissolved black carbon (DBC), a vital part of the natural DOM pool, and PCs were poorly researched. In this study, the bulk DBC was divided into four fractions in molecular weight (MW) via an ultrafiltration system, and the properties of DBC and their binding interaction with two kinds of typical PCs (ceftazidime (CAZ) and diclofenac (DCF)) were explored concretely. The results showed that low MW component was the main contributor to bulk DBC, and the aromaticity increased with the increase of MW. The categories of chemical structures and fluorescent substances in different MW DBC were similar. Multispectral techniques showed that the oxygen-enriched compounds in DBC had the higher affinity to CAZ/DCF. The –NH–, –COOH, –NH2 groups in CAZ molecules appeared to form the hydrogen bond with DBC. Fluorescence quenching experiments were analyzed, and the binding mechanisms were specifically expounded from the thermodynamic perspective. The fluorophore of fulvic acid-like compounds (FA) were quenched by both static and dynamic quenching mechanisms, while only static quenching occurred for humic acid-like compounds (HA). For bulk DBC, the hydrogen bond and van der Waals force were the major forces in the HA-CAZ system, while the hydrophobic force made the primary contribution to the HA-DCF system, which might be ascribed to the higher hydrophobic nature of DCF. Notably, with the increase of HA MW, the main binding mode of HA-CAZ/DCF changed from hydrophobic force to hydrogen bond and van der Waals force gradually, which also directly proved that various noncovalent interactions co-driven the binding processes. Our findings are beneficial to better assess the fate of DBC and PCs and the corresponding complexes in the aquatic environment.

Effects of different dissolved organic matter on peroxymonosulfate activation over Co-Fe binary metal: Experiments and density functional theory

The role of dissolved organic matter (DOM) on sulfate radical (SO4•−)-mediated advanced oxidation processes (AOPs) remains poorly studied. In this work, we systematically investigated the effects of hydrochar-derived DOM (hyDOM), humic acid (HA), and fulvic acid (FA) on peroxymonosulfate (PMS) activation over Co-Fe bimetallic catalysts (CoFeO). The results showed that the functional groups and surface oxygen vacancies of CoFeO composite were increased after compounding with DOM, which could provide more reactive sites for catalytic reaction and improve the electronic conductivity. More importantly, hydroxyl groups of the loading humic acid-like compounds on hyDOM-CoFeO and FA-CoFeO composites could accelerate the reduction of Co(III) and Fe(III), thus enhancing the PMS activation greatly. Not surprisingly, the degradation efficiency for 10 mg L−1 Bisphenol A (BPA) in PMS activation by composites within 10 min followed the order: FA-CoFeO > hyDOM-CoFeO > HA-CoFeO, and the kinetics constant (k) was 3.6, 2.6, and 8.2 times higher than that of CoFeO composite, respectively. The electron paramagnetic resonance (EPR) and quenching experiments indicated that more reactive oxygen species (ROS) were generated after compounding DOM, and SO4•− was the dominant ROS in the degradation process. Furthermore, the LC-MS analysis and density functional theory (DFT) calculation were conducted to prove the proposed degradation pathways of BPA. Our work is expected to clarify the effects of DOM on Co-Fe bimetallic catalysts/PMS system for environmental remediation.

Ozone and Fenton oxidation affected the bacterial community and opportunistic pathogens in biofilms and effluents from GAC

Granular activated carbon (GAC) filtration impacts pathogen colonization and bacterial communities in drinking water. However, the effects of ozone and heterogeneous Fenton oxidation on microbial community composition, in particular opportunistic pathogens (OPs), and their metabolic potential in biofilms and effluents from GAC filtration are not fully understood. The results of our pilot-scale test indicated that Fenton-GAC filtration removed more dissolved organic carbon (DOC, 1.25 mg/L) than ozone-GAC filtration (0.98 mg/L). Excitation-emission matrix (EEM) results showed that Fenton-GAC removed more tyrosine-like proteins and fulvic acid-like materials, while ozone-GAC removed more humic acid-like compounds and tryptophan-like proteins. Illumina HiSeq analysis indicated that Curvibacter and Hydrogenophaga dominated in the Fenton-GAC biofilm, while Bradyrhizobium, Aquabacterium and Limnobacter were predominant in the ozone-GAC biofilm. Functional prediction suggested that the microbial functional gene related to glyoxylate and dicarboxylate metabolism (the pathway for carbohydrate metabolism) was higher in the Fenton-GAC biofilm, resulting in higher contents of protein in extracellular polymeric substances (EPS) in the Fenton-GAC biofilm. Therefore, there were fewer bacteria that detached from the biofilm into the water during the Fenton-GAC filtration process. The lower EPS content in the effluents from Fenton-GAC resulted in bacteria, including OPs, being easier to remove by chlorine. However, ozone oxidation removed more bacteria, including different OPs, than Fenton oxidation, which contributed to fewer bacteria and OPs in the effluents from ozone-GAC. Overall, our results provide a Fenton-GAC treatment process to remove DOC and control OPs in drinking water systems, the cost of which was comparable to that of ozone-GAC.

Pretreatment of rice straw by newly isolated fungal consortium enhanced lignocellulose degradation and humification during composting

The slow decomposition rate of the reluctant structure of lignocellulose in agricultural waste is the great limitation of composting processes, which can be averted by pretreatment-strategies. This study focused on the impacts of pretreating rice straw using a consortium of newly isolated fungal species on lignocellulose degradation and humic substances during composting. Fungal pretreatment had a significant impact on lignocellulose degradation (84%) of rice straw by producing higher lignocellulytic enzymes than chemical pretreatments (79%) or the control (61%). The compost with fungal pretreated rice straw (FPT) showed significantly high composting temperature in the late mesophilic stage, which enhanced the degradation of lignocellulose. The fluorescence excitation emission spectroscopy revealed that significantly more humic acid-like compounds were formed in FPT. These findings suggest that fungal pretreatment is a feasible method to accelerate straw degradation and humification.

Biochar and nitrogen fertilizer co-application changed SOC content and fraction composition in Huang-Huai-Hai plain, China

Biochar can significantly enhance soil organic carbon (SOC) and crop yield, and it is therefore the preferred material for soil improvement in medium-low yield fields. In this study, a field experiment was designed to explore the impacts of biochar application on SOC content and fraction composition. Results indicated that incorporation of biochar into soil increased the SOC content by 26.9%–65.3% in the surface layer (0–10 cm) and 30.3%–63.0% in the subsurface layer (10–20 cm) of soil, while water-soluble organic carbon (WSOC) of the two layers was increased by 2.2–40.0% and 2.3–39.8%, respectively. Microbial biomass carbon decreased under conventional nitrogen treatments and increased with biochar addition under increased nitrogen application. The C:N value increased with biochar application, while the water-soluble C:N value of soil applied with 30 t ha−1 biochar was lower than that of soil applied with 15 t ha−1 biochar, both in the two tested soil layers. Wheat yield is evidently correlated with SOC, with the correlation coefficients of 0.919 and 0.952 in the surface and subsurface soil layers (P < 0.01), respectively. Particularly, increasing fulvic and humic acid-like compounds of WSOC promoted the bioavailability of nutrient elements, thereby increasing the crop yields. Therefore, biochar application is an effective means to fertilize middle-low yield soils through increasing SOC sequestration and nutrient reserves, or adjusting soil C:N value to a proper range, thereby reducing nutrient loss and increasing wheat yield.

Applied research on aquatic macrophyte fermentation broth in SBR denitrification.

In the traditional biological process for nitrogen removal, an insufficient carbon source is often the limiting factor. To solve this problem, reed fermentation broth was selected as the source of denitrification carbon for nitrogen removal in a SBR, and the influence of different C/N conditions on the denitrification and the characteristics of bacteria in the reactor were examined. Leaching experiments with reeds employed fluorescence excitation-emission spectrophotometry and revealed that the reed material had a high capacity for carbon release, the average dissolved organic carbon release content proportion was 11.3mg/g, and the dissolved organic matter mainly consisted of humic acid-like compounds. Using reed fermentation broth as an additional carbon source promoted the denitrification of wastewater by microbes. When reed fermentation broth was added at a C/N ratio of 6, the best nitrogen efficiency for nitrogen removal was 88.3-96.4%. Analyses of microbial diversity indicated that in the SBR reactor, the relative abundance of denitrifying bacteria at the genus level reached 38.5%. These results revealed that reed fermentation broth promoted the growth of anaerobic denitrifying bacteria and improved the efficiency of denitrification. The findings will contribute to a better understanding of the use of reed fermentation broth as an external carbon source that increases the efficiency for denitrification of wastewater. PRACTITIONER POINTS: Using fluorescence excitation-emission spectrophotometry and parallel factor analysis to evaluate the supply capacity of DOMs released from reed. Research the feasibility of reed fermented broth as external carbon source under the condition of extremely low carbon source. Provides theoretical guidance for deep denitrification in sewage treatment plant with SBR process.

Oxidative treatment of bisphenol A in municipal wastewater reverse osmosis concentrate using Ferrate(VI)

Reverse osmosis concentrate (ROC) resulting from the municipal wastewater recycling processes poses significant environmental and health risks as it contains significant concentrations of harmful compounds, including phenolic chemicals including bisphenol A (BPA). In this study, the effect of ferrate(VI) (or Fe(VI)) oxidation on the degradation of BPA (50 µg L−1) in a typical ROC matrix was investigated. The influence of process variables including the [Fe(VI)]/[BPA] ratios (7–50), initial pH (5.0–8.0) and reaction temperature (15–25 °C) was studied. Fe(VI) was found to be highly effective in degrading BPA in the complex ROC matrix with various operating conditions. At 25 °C, over 90% degradation of BPA was achieved at the [Fe(VI)]/[BPA] ratio of 50, and an initial pH of the ROC at 8.0 after 90 min of reaction. Under such conditions, the reduction in dissolved organic carbon (DOC) was found to be 34% accompanied by a 95% reduction in UV254 absorbance (initial value 0.750 cm−1) with 96.4% SUVA reduction. Additionally, the residual concentration of Fe(III) at pH 8.0 was the lowest compared to other pH conditions at a fixed [Fe(VI)]/[BPA] ratio of 50. Fluorescence regional integration (FRI) analyses revealed that Fe(VI) preferentially react with fulvic acid-like and humic acid-like compounds, and aromatic protein II in the ROC. This indicated Fe(VI) effectively breaking down electron-rich moieties groups including phenols and other organics in ROC. The apparent second-order rate constant (kapp) for BPA degradation was determined to be 2.27 × 102 M−1 s−1 at pH 8.0 at a [Fe(VI)]/[BPA] ratio of 50, and the value of reaction rate constant increased proportionally with increasing molar ratio at the range studied. The effectiveness of Fe(VI) in the degradation of BPA in the ROC demonstrates the potential of using Fe(VI) as an efficient oxidant to remediate the micropollutants present in water and wastewater.

Characteristics of the chromophoric dissolved organic matter of urban black-odor rivers using fluorescence and UV-visible spectroscopy.

Urban black-odor water (BOW) is a typical phenomenon seen in the urban water environment; it is caused by excessive pollution by organic matter and other pollutants, such as nitrogen and phosphorous. Chromophoric dissolved organic matter (CDOM) is a major optical fraction of dissolved organic matter. In this study, optical properties and components of CDOM were obtained from 178 river samples collected from five cities in China, the sample were investigated using absorption and fluorescence spectroscopy. The collected included 89 ordinary water (OW) samples, 63 mild BOW (MBOW), and 26 heavy BOW (HBOW) samples. Significant differences were found in the absorption spectra of the HBOW, MBOW, and OW samples, particularly in their optical parameters (the slope of the spectrum (S275-295), and the ratio of two absorption coefficients of CDOM (E2:E3)). Additionally, the fluorescence intensity of the humic acid-like component (F5) and soluble microbial by product-like component (F4) obtained via the fluorescence regional integration (FRI) method were 3 and 4.2 times higher in HBOW than in OW, respectively; this could be used as an indicator to distinguish OW from BOW in urban rivers. The results obtained using the redundancy method and the strong negative correlation between F4 and dissolved oxygen (DO) (r=- 0.56) suggested that the composition of CDOM could change significantly under different urban water environments (p<0.01). Different correlations were also found between F5, and a355, E2:E3, S275-295 in different BOW levels, suggesting that the optical parameters of CDOM were mainly determined by the polluted organic matter originating from terrestrial sources with large molecular humic acid-like compounds; optical parameter a355 could distinguish BOW from OW. These findings are conducive in understanding the dynamics of organic matter pollution and to discover the composition and optical properties of the CDOM in urban BOW and OW, thereby providing an effective method for tracking the spatial characteristics of BOW in urban rivers using remote sensing technologies in areas with multiple sources of pollution.

Sunlight-induced changes in naturally stored reclaimed water: Dissolved organic matter, micropollutant, and ecotoxicity

Natural sunlight is a vital environmental element and plays a significant role in the ecological storage of reclaimed water (RW), but its impacts on RW quality are poorly understood. In this study, sunlight-induced changes in RW with a focus on dissolved organic matter (rDOM) and 52 residual micropollutants were investigated in the field during the summer and winter seasons. The results indicated that sunlight exposure led to the dissipation of chromophoric DOM (CDOM) in the summer (55% loss) and winter (19% loss) after 14 consecutive sunny days. During open storage of RW, CDOM absorption in UVC regions was preferentially removed in the summer, while during the winter there was preferential removal of CDOM in UVA regions. The results also showed higher fluorescent DOM (FDOM) removal in summer than in winter (49% and 28%, respectively). Results in both seasons indicated that humic acid-like compounds were the most photolabile fractions and were preferentially removed under sunlight exposure. Sunlight also induced attenuation of micropollutants in the summer and winter at reductions of 66% and 24% from the initial values, respectively. Significant attenuation (>75%) was only observed for endocrine-disrupting chemicals, pharmaceuticals, and sunscreens in the summer, but they accounted for 76% of the total concentrations. Vibrio fischeri toxicity tests demonstrated that sunlight constantly decreased the luminescent bacteria acute toxicity of RW, which was estimated to be caused mainly by the sunlight-induced changes of FDOM and CDOM, while the detected micropollutants could only explain 0.02%–2% of acute toxicity. These findings have important implications regarding our understanding of the ecological storage of reclaimed water and the contribution of management strategies.

Recycled utilization of Iris pseudacorus in constructed wetlands: Litters self-consumption and nitrogen removal improvement

Aquatic plants litters from constructed wetlands might become pollutants without proper treatment. Due to its high carbon and low nitrogen contained, Iris pseudacorus litters have potential to be used as carbon source to enhance denitrification process in advanced treatments of secondary effluent from wastewater treatment plants. This study investigated the characteristics of carbon release form Iris pseudacorus litters and its performance on enhancement of nitrogen removal. The batch experiment showed that the organic carbon release process can be simulated by combining dissolution and hydrolysis process, and it was found that dissolved organic matters mainly consisted of 60% sugar and 35% humic acid-like compounds from the neutral detergent solution and hemicellulose of litters. The long-term operation of lab-scale constructed wetlands revealed a high nitrogen removal of 78.81–90.39% in treating the synthetic wastewater treatment plants effluent with the equivalent dosage of 25–150 g litters m−2 d−1. Furthermore, it is possible to establish an Iris pseudacorus self-consumed constructed wetland to reuse all of the litters produced during the operation. These findings can contribute to the understanding of the dynamics of carbon release from Iris pseudacorus litters and recycled utilization of plant biomass in the constructed wetlands.

Enhancing peroxymonosulfate activation of Fe-Al layered double hydroxide by dissolved organic matter: Performance and mechanism

In this study, peroxymonosulfate (PMS) activation of FeAl layered double hydroxide (FeAl-LDH) was enhanced by compounding dissolved organic matter (DOM). The characterization and catalytic performance of FeAl-LDH and DOM-LDH were investigated. The results revealed that the physicochemical properties of DOM-LDH were superior to FeAl-LDH: (i) The higher proportion of Fe(II) was found in DOM-LDH, mainly existed in the form of trans-coordinated octahedral Fe(II); (ii) DOM-LDH showed a flower-like morphology with larger specific surface area, pore width and pore volume; (iii) More functional groups and surface oxygen vacancies were found in DOM-LDH. Moreover, DOM promoted the process of PMS activation by accelerating Fe(III) reduction with humic acid-like compounds. The results of electron paramagnetic resonance (EPR) and quenching experiments indicated that more reactive oxygen species (ROS) were generated in DOM-LDH/PMS system, •OH was considered as the dominant ROS for Bisphenol A (BPA) degradation. As a result, the degradation efficiency for BPA (20 mg L−1) in FeAl-LDH/PMS system was increased from 60% to 93% within 60 min after the introduction of DOM. This work is expected to facilitate the design and application of Fe(II)/PMS system for environmental protection.

Dynamics, biodegradability, and microbial community shift of water-extractable organic matter in rice–wheat cropping soil under different fertilization treatments

Although fertilization plays an important role in determining the contents of soil dissolved organic matters or water-extractable organic matter (DOM, WEOM), knowledge regarding the dynamics, biodegradability, and microbial community shifts of WEOM in response to different fertilization treatments is very limited, particularly in rice–wheat cropping soil. Thus, in the present study, we performed biodegradation experiments using WEOM extracted from samples of soil that had been subjected to four different fertilization treatments: unfertilized control (CK), chemical fertilizer (CF), 50% chemical fertilizer plus pig manure (PMCF), and 100% chemical fertilizer plus rice straw (SRCF). UV spectrum and fluorescence 3D excitation–emission matrix analyses applied to investigate the chemical composition of WEOM revealed that all examined WEOMs were derived from microbial activity and the dominant portion comprised humic acid-like compounds. After the incubation, 31.17, 31.63, 43.47, and 33.01% of soil WEOM from CK, CF, PMCF, and SRCF treatments, respectively, were biodegraded. PMCF- derived WEOM had the highest biodegradation rate. High-throughput sequencing analyses performed to determine the microbial community before and after the incubation indicated that Sphingomonas, Bacillus, and Flavisolibacter were the predominant bacterial genera in the original inoculum derived from the four fertilization treatments. Following biodegradation, we observed that the dominant bacteria differed according to fertilization treatments: Curvibacter (43.25%) and Sphingobium (10.47%) for CK, Curvibacter (29.68%) and Caulobacter (20.00%) for CF, Azospirillum (23.68%) and Caulobacter (13.29%) for PMCF, and Ralstonia (51.75%) for SRCF. Canonical correspondence analysis revealed that, shifts in the microbial community were closely correlated with pH and specific UV absorbance at 254 nm. We speculated that the inherent traits of different WEOM and the properties of soil solutions under different fertilization treatments shaped the soil microbial community structure, thereby influencing the biodegradation of WEOM.