Fulvic-like Acid Research Articles

Sodium lignosulfonate-assisted alkaline hydrothermal pretreatment improves the production of humic-like substances from lignocellulosic biomass waste residues

In order to provide key precursors for humic-like substances formation via alkaline hydrothermal pretreatment (AHP), this study introduced an innovative approach by incorporating sodium lignosulfonate (SL) into the AHP to boost the production of humic-like acid (HLA) and fulvic-like acid (FLA) from biomass wastes. The SL-AHP conditions were optimized, and structural analysis of HLA was performed. The highest HLA yield reached 21.90 %, and FLA content reached 13.38 g/L after SL-AHP at 200 °C for 2 h with 15 g/L SL. The inclusion of SL led to a 19.67 % increase in HLA yield and a 5.25-fold enhancement in FLA content compared to that without SL. The probable reason underlying SL's facilitation of HLA and FLA formation involved the effective dissolution of lignin and hemicelluloses to produce more precursors, as well as the incorporation of SL structure into the HLA molecule. SL acted as both a surfactant and a precursor for the production of HLA and FLA. In addition, an increase in acidic groups improved the quality of HLA.

Removal of refractory humic acid-like components from UF filtrate of landfill leachate through pH adjustment and coupled electrochemical process

Mature landfill leachate contains large quantities of a wide range of hazardous and refractory pollutants, especially humic acid-like (HA) and fulvic acid-like (FA) substances. These have poor biodegradability and a considerable ultraviolet-light quenching capacity, severely inhibiting the performance of wastewater treatment and post ultraviolet-light disinfection, but this aspect has attracted little previous research. The Fenton reaction has proved to be a feasible method for removing ultraviolet-quenching substances (UVQSs) but in conventional systems it is unable to completely mineralize organic contaminants. In this study, a novel electro-oxidation process was developed consisting of a flow-through reactor with a Cu2O cathode to catalyze Fenton-type reactions, and oxidation at a RuO2 anode. The combination of pH adjustment and electro-oxidation was evaluated for the treatment of real ultrafiltration (UF) filtrate of mature landfill leachate. A series of analytical techniques were used to determine the performance for the removal of HA and FA. Under optimal conditions, the elimination of fluorescence characteristics of HA and FA reached 100 % and 99.3 %, respectively, according to PARAFAC results based on EEM spectra. TOC was removed by 25.5 %∼30.4 % during the pH adjustment step and 51 % by electrochemical oxidation. Changes in the molecular weight distribution and fluorescence content showed that pH adjustment played an important and significant role in removing UVQSs, and the remaining TOC after electrochemical oxidation was attributed to bioavailable amino acid-like substances. Overall, the results have demonstrated the successful development of an effective method of treating the UF filtrate from mature landfill leachate, with particular respect to the removal of the problematic HA and FA content.

Changes in the Glucose Concentration Affect the Formation of Humic-like Substances in Polyphenol-Maillard Reactions Involving Gibbsite.

The polyphenol-Maillard reaction is considered one of the important pathways in the formation of humic-like substances (HLSs). Glucose serves as a microbial energy source that drives the humification process. However, the effects of changes in glucose, particularly its concentration, on abiotic pathways remain unclear. Given that the polyphenol-Maillard reaction requires high precursor concentrations and elevated temperatures (which are not present in soil), gibbsite was used as a catalyst to overcome energetic barriers. Catechol and glycine were introduced in fixed concentrations into a phosphate-buffered solution containing gibbsite using the liquid shake-flask incubation method, while the concentration of glucose was controlled in a sterile incubation system. The supernatant fluid and HLS components were dynamically extracted over a period of 360 h for analysis, thus revealing the influence of different glucose concentrations on abiotic humification pathways. The results showed the following: (1) The addition of glucose led to a higher degree of aromatic condensation in the supernatant fluid. In contrast, the supernatant fluid without glucose (Glu0) and the control group without any Maillard precursor (CK control group) exhibited lower degrees of aromatic condensation. Although the total organic C (TOC) content in the supernatant fluid decreased in all treatments during the incubation period, the addition of Maillard precursors effectively mitigated the decreasing trend of TOC content. (2) While the C content of humic-like acid (CHLA) and the CHLA/CFLA ratio (the ratio of humic-like acid to fulvic-like acid) showed varying increases after incubation, the addition of Maillard precursors resulted in a more noticeable increase in CHLA content and the CHLA/CFLA ratio compared to the CK control group. This indicated that more FLA was converted into HLA, which exhibited a higher degree of condensation and humification, thus improving the quality of HLS. The addition of glycine and catechol without glucose or with a glucose concentration of 0.06 mol/L was particularly beneficial in enhancing the degree of HLA humification. Furthermore, the presence of glycine and catechol, as well as higher concentrations of glucose, promoted the production of N-containing compounds in HLA. (3) The presence of Maillard precursors enhanced the stretching vibration of the hydroxyl group (-OH) of HLA. After the polyphenol-Maillard reaction of glycine and catechol with glucose concentrations of 0, 0.03, 0.06, 0.12, or 0.24 mol/L, the aromatic C structure in HLA products increased, while the carboxyl group decreased. The presence of Maillard precursors facilitated the accumulation of polysaccharides in HLA with higher glucose concentrations, ultimately promoting the formation of Al-O bonds. However, the quantities of phenolic groups and phenols in HLA decreased to varying extents.

Transformation of dissolved organic matter during groundwater arsenite removal using air cathode iron electrocoagulation

Dissolve organic matters (DOM) usually showed negative effect on the removal of inorganic arsenic (As) in groundwater by electrochemical approaches, yet which parts of sub-component within DOM played the role was lack of evidence. Herein, we investigated the effects of land-source humic-like acid (HA) on groundwater As(III) removal using air cathode iron electrocoagulation, based on the parallel factor analysis of three-dimensional excitation–emission matrix and statistical methods. Our results showed that the land-source HA contained five kinds of components and all components presented significantly negative correlations with the removal of both As(III) and As(V). However, the high aromatic fulvic-like acid and low aromatic humic-like acid components of land-source HA presented the opposite correlations with the concentration of As(III) during the reaction. The high aromaticity fulvic-like components of land-source HA (Sigma-Aldrich HA, SAHA) produced during the reaction facilitated the oxidation of As(III) due to its high electron transfer capacities and good solubility in wide pH range, but the low aromaticity humic-like ones worked against the oxidation of As(III). Our findings offered the novel insights for the flexible activities of DOM in electron Fenton system.

Bacteria Affect the Distribution of Soil-Dissolved Organic Matter on the Slope: A Long-Term Experiment in Black Soil Erosion

Soil erosion results in dissolved organic matter (DOM) loss and is one of the main paths of soil carbon loss. Bacteria affect the generation and transformation of DOM. However, the effect of bacteria on the composition and slope distribution of DOM has rarely been investigated under field conditions. Based on a long-term experiment of three gradients (3°, 5°, 8°) in a black soil erosion area of Northeast China, the content, composition, and source of DOM were studied. The results showed that the DOM of the 3° and 5° slope was enriched midslope, and the DOM of the 8° slope was enriched downslope. Parallel factor (PARAFAC) analysis indicated that the main substances in DOM were fulvic-like acid, humic-like acid, tryptophan-like protein, and soluble microbial metabolites. The upslope and downslope soils of 3° and 5° slopes showed high DOM bioavailability, while the downslope soil of the 8° slope showed high DOM bioavailability. The content of new DOM in downslope soil increased with the gradient. Bacteria played an important role in the synthesis and transformation of DOM and affected its composition and slope distribution. Verrucomicrobiota, Firmicutes, Planctomycetota, and Gemmatimonadota were the main factors affecting soil DOM. The results could be helpful in understanding the loss mechanism of DOM in eroded black soil and provide support for soil carbon sequestration.

Waste milk humification product can be used as a slow release nano-fertilizer

The demand for milk has increased globally, accompanied by an increase in waste milk. Here, we provide an artificial humification technology to recycle waste milk into an agricultural nano-fertilizer. We use KOH-activated persulfate to convert waste milk into fulvic-like acid and humic-like acid. We mix the product with attapulgite to obtain a slow-release nano fulvic-like acid fertilizer. We apply this nano-fertilizer to chickweeds growing in pots, resulting in improved yield and root elongation. These results indicate that waste milk could be recycled for agricultural purposes, however, this nano-fertilizer needs to be tested further in field experiments.

Effective treatment of leachate concentrate from waste incineration plant by combination of coagulation and direct contact evaporation

In order to verify that coagulation as pre-treatment can reduce the temperature of the hot air used for direct contact evaporating the leachate concentrate (LC) and low-grade waste heat such as exhaust steam in the waste incineration plant can be used to evaporate the LC. The supernatants after coagulation using polymerized ferrous sulfate (PFS), polymeric-aluminum (PAC), polymeric silicate aluminum ferric (PSAF) and poly-aluminum ferric chloride (PAFC) as coagulants were further treated in a lab-scale direct contact evaporation system. The results showed that the best performance with removal efficiencies of COD and NH3–N of 58.70% and 29.09% was achieved after coagulation when PAFC dosage = 15 g/L, PAM dosage = 30 mg/L and initial pH of supernatant = 6. After coagulation, a large amount of the fulvic-like acid and aromatic heterocyclic compounds were removed and the degree of complexity and aromaticity of organics decreased. After direct contact evaporation, using PAFC as coagulant still was the best selection due to its lowest concentrations of COD and NH3–N (22 mg/L and 1.02 mg/L) in the condensate produced by this two-stage treatment when initial pH of supernatant was 6 during evaporation and the condensate produced by this two-stage treatment met the water quality standard for using as supplying water for circulating cooling water system when temperature of hot air used for heating LC was at low temperature (250 °C). The fulvic-like acid and aromatic heterocyclic compounds in the condensate continuously reduced. Phenol, adamantane, 1-isocyanato, phthalic anhydrid, tri(2-chloroethyl) phosphat, Heptadecane, 2-methyl, ginsenol and Octadecane, 2-methyl- in the condensate obviously decreased. The effect of four coagulants as pretreatment on reducing the temperature of hot air used for evaporating LC was ranked as PAFC > PFS > PAC > PSAF. PSAF was not recommended due to the large amount of NH3–N produced when using PSAF to treat the LC.

Accelerated spent coffee grounds humification by heat/base co-activated persulfate and products’ fertilization evaluation

Coffee, as the second most common beverage in the world, produced 60% of spent coffee grounds (SCG) with per ton of coffee beans processed. SCG is a typical lignocellulosic-rich organic waste and mainly disposed via composting or incineration. In this study, a rapid humification approach was proposed for the recycling of SCG using heat/base co-activated persulfate (heat/KOH/PS) advanced oxidation process. The yields of humic-like acid (HLA) and fulvic-like acid (FLA) reached 45 (3.96%) and 192 mg/g (19.2%) under the optimal humification conditions of 1% PS and 4% KOH at 100 ℃ in 1 h. The typical active groups of -OH and -COOH in FA standard were observed with higher amounts in the product compared to SCG, which may be related to occurrence of hydroxylation, carboxylation and Maillard reactions during humification. Radicals of •OH and SO4•- were identified in heat/KOH/PS system and made significant contribution to SCG humification. A slow-release nano FLA fertilizer (SNFF) was prepared by mixing treated SCG with attapulgite and showed good slow-release behaviors of HLA and FLA. In pot experiments with acid soil, SNFF increased the average root length of chickweeds by 233% compared with blank. Meanwhile, SNFF also contributed to increased abundance and richness of soil microbial community as well as a pH rise from 5 to 6.7, which was conducive to acid soil amendment. The earthworm test indicated positive ecological safety of SNFF. Overall, this study highlights an efficient humification method for the recycling of organic biowaste such as SCG in green agriculture.

Integrated production of humic-like acid, fulvic-like acid, and fermentable sugars from industrial xylooligosaccharides manufacturing waste residues via hydrothermal pretreatment

Commercial humic substances (HS) are usually extracted from non-renewable resources such as lignite and coal. In this study, artificial HS (mainly humic-like acid (HLA) and fulvic-like acid (FLA)) was produced from renewable biomass-alkaline xylooligosaccharides manufacturing waste residue (XOR) of corncob via hydrothermal pretreatment (HP), as well as fermentable sugars were coproduced. The HLA yield was highest at 1.5% and the content of FLA was 9.6 g/L after HP at 210 °C for 8 h. The glucose yield of HP-pretreated XOR reached 98.8% at CTec 2 dosages of 20 FPU/g glucan. Structural characterization analysis proved that the structures and compositions of HLA were similar to those of commercial humic acid. The results of mass balance indicated that 100 g of XOR yielded 1.5 g of HLA, 9.6 g of FLA, and 60.4 g of monosaccharides (46.9 g of glucose and 13.5 g of xylose). Therefore, this work provides a promising strategy for valorization of lignocellulosic biomass in producing HLA, FLA, and fermentable sugars.

Black carbon derived from pyrolysis of maize straw and polystyrene microplastics affects soil biodiversity

Understanding the environmental correlation of microbial community under external stimulation is significant for ecological restoration. However, few studies focused on the response of soil biodiversity induced by black carbon (BC) derived from pyrolysis of straw and microplastics (MPs) due to their widespread existence in natural environment. In this study, polystyrene MPs (PS) and maize straw with different mass ratios were used as raw materials to prepare BC by pyrolysis. The surface morphology, chemical composition and sequential variations of different functional groups of BC were systematically analyzed. The leachate from BC was identified by three-dimensional excitation emission matrice (3D-EEM). The corresponding results showed that yield, value of O/C and N element content of BC decreased with more PS. The changed C content and oxygen-containing functional groups occurred. The order of functional groups of BC formed by co-pyrolysis was: C=C > C-O > C-H > Si-O-Si. The main component of leaching from BC was humic-like and fulvic-like acid. Simultaneously, the input of exogenous BC into soil affected abundance, composition and metabolic pathways of microorganisms. The study helps to understand environmental implication of BC which was pyrolyzed from maize straw and MPs, providing an idea for improving biogeochemical cycle process in soil.

Combined impacts of algae-induced variations in water soluble organic matter and heavy metals on bacterial community structure in sediment from Chaohu Lake, a eutrophic shallow lake

Many lakes are suffering from eutrophication and heavy metals-contamination. However, the combined impacts of algae bloom and its induced variations in heavy metals on microbial community in sediment from eutrophic lakes remain unclear. In this study, we performed field experiments to investigate how algae bloom impacted water soluble organic matter (WSOM) and heavy metals in sediment from Chaohu Lake, a eutrophic shallow lake, and probed their combined impacts on sediment bacterial community structure. The results showed that algae bloom increased WSOM quantity, in particular, the soluble microbial by-product-like (SMP) and fulvic acid-like (Fa-L) components markedly enhanced by 203.70 % and 70.17 %, respectively. We also found that algae bloom redistributed the spatial patterns of heavy metals and altered their chemical species in sediment, then promoted contamination degree and potential ecological risk of heavy metals in sediment. Moreover, sediment bacterial community richness and diversity obviously decreased after algae bloom, and the variance partitioning analysis (VPA) results showed that combined impacts of algae-induced changes in WSOM and heavy metals explained 66.56 % of the variations in bacterial community structure. These findings depicted how algae bloom influence sediment WSOM and heavy metals, and revealed the combined impacts of algae-induced variations on microbial community structure in shallow eutrophic lake.

Component Properties and Heavy Metal Accumulation Characteristics of Contaminated Rice Straw Biochar During Oxygen-controlled Pyrolysis

Pyrolysis is an important technology to achieve the harmlessness and recycling of contaminated biomass. In this study, the effects of oxygen-controlled atmosphere on the component properties and heavy metal accumulation characteristics of contaminated rice straw biochar were studied. The results showed that low-oxygen pyrolysis could effectively produce biochar using contaminated rice straw and improve the stability of heavy metals in biochar. Under the nitrogen atmosphere, the yield of rice straw biochar was 29.4%-34.9%. The aromatization index (SUVA254) of dissolved organic matter (DOM) increased first and then decreased with the increase in pyrolysis temperature, whereas the fluorescent components were mainly humic-like acid substances. Meanwhile, Ca mainly existed in the form of CaCO3 in biochar. Compared with the pure nitrogen condition, the biochar yield was reduced by 5.6%-13.5% and 14.9%-15.7% under the pyrolysis atmosphere containing 10% and 20% oxygen content, respectively. Ca existed in the form of CaO in biochar, which increased the pH value of the biochar by more than 0.5 units. The oxygen of the pyrolysis atmosphere accelerated the degradation of the lignin component, resulting in the gradual decrease in SUVA254 of DOM. With the increase in oxygen content in the pyrolysis atmosphere, humic-like acid substances in DOM were transformed into fulvic-like acid substances. Under the conditions of 400℃ and a 10% oxygen-containing atmosphere, the exchangeable fractions of Cu, Cd, Pb, Ni, and As in biochar were decreased by 5.2%, 3.7%, 1.7%, 0.8%, and 0.7%, respectively, indicating that heavy metals are transformed into more stable states. The results suggested that the higher biochar yield and heavy metal stability could be obtained by introducing a proper amount of nitrogen into the air (controlling the oxygen content of approximately 10%) for pyrolysis treatment of contaminated rice straw, providing an economic and feasible technology for the achievement of harmlessness and recovery of contaminated rice straw.

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.

Priming Effects of Maillard Reaction Precursors on Rice Straw Decomposition at Different Incubation Temperatures

To verify the priming effects of Maillard reaction precursors on the microbial decomposition of rice straw at different incubation temperatures, the method of indoor incubation at a constant temperature was adopted. In the process, the addition of glucose, catechol or glycine solution alone or in mixed solution was conducted at incubation temperatures of 10 °C, 15 °C and 28 °C, respectively. The C content of humic-extracted acid (CHLE), humification index (the ratio of C content of humic-like acid to fulvic-like acid, CHLA/CFLA), ∆logK value of humic-like acid (HLA), and C content of humin-like acid (CHLu) were dynamically analyzed at 0, 30, 60, and 90 d, respectively. At the same time, the differences in the atomic ratio and FTIR spectra before and after incubation were systematically analyzed. The results showed that (1) the additions of glucose alone and mixed precursors were both beneficial to increasing the CHLE content at three tested temperatures, especially at two low temperatures (10 °C and 15 °C), and glucose alone manifested the most significant improvement in CHLE. In contrast, following the addition of glycine alone, the CHLE content decreased by 2.4% at 15 °C and 4.6% at 28 °C after incubation. (2) Glucose as the sole precursor was more beneficial to improving the quality of the humic substance (HS) at 28 °C, but only enhanced the condensation degree of HLA molecules at 15 °C. Compared with the results at 15 °C and 28 °C, the HLA molecules had the lowest condensation degree at 10 °C, regardless of whether a single precursor or mixed Maillard precursors were used. (3) After incubation, the amounts of N compounds in the HLA molecules decreased to varying degrees, especially at 28 °C. The O-containing functional groups, such as carboxyl groups, from HLA molecules decreased following the addition of a single precursor, while the mixed precursors resulted in an increase in O-containing functional groups. Increasing the catechol content directly enriched the unsaturated bonds of HLA. With the decomposition of rice straw, regardless of how the precursors were added, the polysaccharide content decreased to different degrees. The decomposition of polysaccharides in HLA was more temperature-sensitive, and an increase in temperature might encourage more polysaccharide consumption. Under each temperature, the molecular structure of HLA was simplified initially and then gradually became complex. Finally, the addition of glucose alone at 15 °C was more favorable for the complexity of HLA molecules, while at 28 °C, it could only alleviate the degree of simplification of the HLA molecular structure to a certain extent. (4) At the three tested temperatures, compared with the CK control, either one precursor or a mixture of three precursors could more effectively promote the decomposition of CHLu. Under the conditions of 10 °C and 15 °C, the addition of mixed precursors was more beneficial to the decomposition of CHLu, causing the CHLu content to decrease by 37.9% and 44.7%, respectively, followed by the addition of glucose alone.

Removal of refractory organics from landfill leachate by in situ electrogenerated H2O2 combined with an Fe0 Fenton-like process.

Landfill leachate contains a large amount of refractory organic matter, which will cause harm to the environment if not appropriately treated. In this study, the refractory organic matter in landfill leachate has been treated by in situ electrogenerated H2O2 combined with an Fe0 Fenton-like process, aiming to explore a cleaner and more efficient process for leachate treatment. The results showed that the current, initial pH and oxygen flow rate have significant influences on H2O2 production. The current and oxygen flow rate are positively correlated with H2O2 production, and neutral conditions are more favourable. Under the conditions of a current of 200 mA, an initial pH of 7.0 and an oxygen flow rate of 0.3 L/min, H2O2 production reached 2.81 mM, the current efficiency was close to 80% and the highest removal efficiency of organic matter reached 40.70%. The absorbance at 280 nm (E280) decreased from 0.1669 to 0.1180, and the ratios E240/E420, E250/E365 and E300/E400 in the UV and visible regions changed from 0.7825, 5.4492 and 0.2422 to 1.3135, 7.3745 and 0.2966, respectively. The maximum fluorescence intensities due to humic-like acid and fulvic-like acid substances decreased from 1275 and 1246 to 595.9 and 711.0, respectively. Spectral analysis further showed that the complex structure of refractory organic matter in the landfill leachate was obviously destroyed, and the relative content of humus decreased significantly. This study may provide a theoretical basis for the effective treatment of refractory organic matter in landfill leachate by in situ electrogenerated H2O2 combined with a Fenton-like process.

Chemical Characteristics of Dark-Brown Humic-like Substances Formed from the Abiotic Condensation of Maillard Precursors with Different Glycine Concentrations

The Maillard reaction is a type of nonenzymic browning process, and it is also an abiotic humification process of sugars, amino acids and phenols catalyzed by δ-MnO2. It is considered to be one of the possible pathways for the formation of humic-like substances (HLS). The change in the ratio of the Maillard precursors inevitably affects the chemical characteristics of HLS, among which the effect of amino acids concentration on the humification pathway and HLS formation has not yet been reported. In view of this, the glucose, glycine and catechol were chosen as tested objects for the present study, and the method of liquid shake-flask culture was adopted. Both catechol and glucose with fixed concentrations were added into a phosphate buffer solution (pH 8.0) containing δ-MnO2, and only the glycine concentration was adjusted in the sterile culture system. The supernatant solution and dark-brown residue were collected dynamically within 360 h through the centrifugation method. The E4/E6 ratio and total organic C (TOC) of the supernatant solution, the C content of the humic-like acid (CHLA), CHLA/CFLA (C content of fulvic-like acid) ratio and FTIR spectra of the dark-brown residue and the E4/E6 ratio and atomic ratio of humic-like acid (HLA) extracted from the dark-brown residue were systematically analyzed to reveal the effect of different glycine concentrations on the abiotic humification pathways and the characteristics of related products from the Maillard reaction under abiotic processes. The results showed that (1) Under the influence of the addition of different glycine concentrations, the structure of organic molecules in the supernatant after culture tended to be simplified, and the addition of three lower concentrations (0, 0.03 and 0.06 mol/L) of glycine made the E4/E6 ratios increase by 100.4%, 57.7% and 33.0%, respectively, and obtained a simpler structure of organic molecules in the supernatant than that of 0.12 and 0.24 mol/L glycine, which made the E4/E6 ratios increase by 5.6% and 18.0%, merely. After culture, the TOC content in the supernatant solution of each treatment decreased to varying degrees, and the addition of Maillard precursors effectively inhibited the loss of TOC in the supernatant solution, especially the addition of glycine at a concentration of 0.06 mol/L, which only reduced the TOC content by 0.1%. (2) The greater the concentration of glycine added, the higher proportion of aromatic C structure existed in the dark-brown residue. O-containing functional groups from the dark-brown residue and δ-MnO2 were bound to each other through hydrogen bonding, and (3) During the culture process, the CHLA treated with the addition of Maillard precursors was significantly higher than that of the CK control. Compared with the result at 0 h, the addition of higher concentrations of glycine (0.12 and 0.24 mol/L) were more conducive to the formation of HLA, making the CHLA increase by 666.2% and 422.7%, which were much more than these results for 256.6%, 282.2% and 360.0% from three concentrations of glycine (0, 0.03 and 0.06 mol/L) at the end of culture. After culture, the structure of HLA molecules treated by the addition of Maillard precursors became more complex, and the overall performance showed that the higher the concentration of added glycine, the more complex the HLA molecules became. Under the coexistence of glucose and catechol, the addition of glycine could promote abiotic condensation and improve the condensation degree of HLA molecules, among which the addition of 0.12 mol/L glycine had the most significant effect. Compared with the CK control, the addition of Maillard precursors could achieve a higher increase in the CHLA/CFLA ratio, which was more beneficial to the improvement of humus quality.

Effect of ozone pretreatment on biogranulation with partial nitritation - Anammox two stages for nitrogen removal from mature landfill leachate.

Due to the extremely low C/N ratio, high concentration of ammonia nitrogen and refractory organic matter of mature landfill leachate (MLL), appropriate processes should be selected to effectively remove nitrogen and reduce disposal costs. Partial nitritation (PN) and anaerobic ammonia oxidation (AMX) have been used as the main nitrogen removal processes for MLL, and the sludge granulation in PN and AMX processes could contribute to high biological activity, good sedimentation performance, and stable resistance to toxicity. In this study, the O3-PN-AMX biogranules process was selected to effectively remove nitrogen from MLL without carbon addition and pH adjustment. Without uneconomical NH4+-N oxidation and wasting the alkalinity of MLL, ozone pretreatment achieved color removal, decreased humic- and fulvic-like acid substances, and alleviated the MLL toxicity on ammonia oxidizers. In addition, the ozonation of MLL could shorten the start-up time and improve the treatment efficiency and biogranules stability of PN and AMX processes. Efficient and stable nitritation was achieved in PN reactor without strict dissolved oxygen (DO) control, which was attributed to the unique structure of granular sludge, ozone pretreatment, and alternating inhibition of free ammonia and free nitric acid on nitrite oxidizers. Through the application of ozone pretreatment and granular sludge, the nitrogen removal rate (NRR) and nitrogen removal efficiency (NRE) of the O3-PN-AMX biogranules process reached 0.39kg/m3/day and 85%, respectively, for the undiluted MLL treatment. This study might provide a novel and effective operation strategy of combined process for the efficient, economical, and stable nitrogen removal from MLL.

Removal of Microcystis Aeruginosa by oxidation-assisted coagulation: Effect of algogenic organic matter fraction changes on algae destabilization with Al hydrates

Oxidation-assisted coagulation has been widely applied to destabilize algae and improve algae removal through a flocculation-sedimentation process in drinking water treatment plants (DWTPs). However, oxidation poses a potential threat to drinking water safety with increasing algal organic matter (AOM) in the algae-polluted surface water. This study investigated the effect of sodium hypochlorite (NaOCl) oxidation-assisted polyaluminum chloride (PACl) coagulation on algae removal, along with the identification of the optical properties for AOM fractions. The results have demonstrated that the increased NaOCl oxidant dose coupled with PACl coagulation induced by sweep flocculation is more effective in Microcystis aeruginosa (MA) cells destabilization and removal, where the highest algae removal rate around 99 %. However, NaOCl oxidation coupled with PACl coagulation fails to reduce the dissolved organic carbon (DOC) in MA suspension attributed to the released AOM. Strong free chlorine destroys MA cells in response to the increases in humic acid-like (HAL) and fulvic acid-like (FAL) substances, while it is sufficient to degrade soluble microbial product-like (SMPL) and aromatic protein-like (APL) substances. In oxidation-assisted coagulation, bigger diameter (483–640 μm) with lower fractal dimension (1.31–1.39) of M. aeruginosa flocs are formed at low chlorine dosing ratio (Cl2:DOC = 1:1), while higher fractal dimension (2.39–2.75) with smaller diameter (143–395 μm) is reached at high chlorine dosing ratio (Cl2:DOC = 3:1). It is concluded that the changes in fluorescent organic matter fraction during chlorination dominantly affect coagulation performance for AOM removal in oxidation-coagulation process.

Efficient cyclic oxidation of macro long-chain alkanes in soil using Fenton oxidation with recyclable Fe

Recyclable Fe in soil was prepared by using fermented food waste supernatant. The efficient cyclic oxidation of long-chain alkanes in oil-contaminated soils could be achieved by Fenton oxidation with the recyclable Fe. The oxidation efficiency of macro long-chain alkanes (C27-C30) from the first cycle (63.4%) to the last cycle (60.1%) showed no significant decrease during three-cycle Fenton oxidation with the recyclable Fe. However, for the oil-absorbing Fe prepared by HA and Fe-SOM prepared by Cs, the oxidation efficiency of C27-C30 could not be efficiently cyclic oxidized during three-cycle Fenton oxidation. Further analysis showed that the proportion of Fe(III) in the recyclable Fe was higher than that in the oil-absorbing Fe or the Fe-SOM, where the iron content was similar. Moreover, more fulvic-like acid and humic-like acid were found in the recyclable Fe, and thus many Fe(III) ions simultaneously combined with the fulvic-like acid and humic-like acid through –C–O–C and C˭O bonds in the recyclable Fe. It was the recyclable Fe with such a stable structure that could still maintain high catalytic activity and efficiently cyclic oxidize macro long-chain alkanes during three-cycle Fenton oxidation, which is valuable for its repeated use.

Effects of the virgin forests to the dissolved organic matters in small forested watershed: a case study of the Tangwang River in Northeast China.

Making clear of the background values of different watersheds is an important mission for water resource management and assessment. The background values of the virgin forested watershed with less human activities sometimes have high COD values. In order to investigate this issue, this study take the Tangwang River watershed as a study case, analyzing the monitoring data of COD, BOD, and DO from the year of 2014 to 2018, and taking the water samples in the wet, normal, and dry season of 2019 to make clear the relationships between COD and DOM, the composition, and source of DOM. The non-degradation and terrigenous source DOM contributed to the most of COD values through the fitting analysis. The DOM in the Tangwang River mostly consisted of the humic-like acid and fulvic-like acid. Along with the river, the concentration of DOM had a little decrease, but the composition of DOM did not change obviously, so that the DOM coming from the virgin forest did not degrade in the river, and the river water only had the dilution effect with the tributaries fed in spatially. The organic matters in the virgin forest were easily washed away, so that the DOM concentration had an increase in the wet season temporally. The background COD values of the small virgin forested watershed were usually high as for the leaching effects of the organic matters from the forest, which was worthy noted when conducting the management project of this kind of watershed, in order to adjust measures to local conditions.