Acid-like Substances Research Articles

NaOH-Enhanced Wet Air Oxidation of Municipal Sludge for High-Quality Carbon Source Production

Many volatile fatty acids (VFAs) are produced after wet air oxidation, which could be a potential carbon source. In this study, we investigated the impact of NaOH on the removal of hazardous organics and the changes in the produced carbon source. The total and soluble chemical oxygen demand (SCOD) removal rates decreased to 47.9% and 55.3% with 51.6% NaOH addition. The removal rates of total suspended solids (82–85%) and volatile suspended solids (97–99%) remained stable under all conditions. Additionally, the concentrations of acetic acid and isovaleric acid increased with a high pH value. Fluorescent substances closely related to aromatic protein and fulvic acid-like substances were identified and degraded significantly with the addition of NaOH. Moreover, 41.3% NaOH addition (initial pH 13.0) could yield a VFAs/SCOD ratio of 30.5%, demonstrating the good biocompatibility of the carbon source. The effect of the nitrogen element was also considered, with the ratio of the 5-day biological oxygen demand to the total nitrogen being 7.2, indicating that the oxidation solution could provide an abundant carbon source. Thus, the sludge-derived carbon source is suitable to supply biological treatment units for municipal wastewater.

EXTRACTION OF THE HUMIC-LIKE SUBSTANCES FROM COFFEE HUSK-DERIVED BIOCHAR: DETERMINE PARAMETERS OF EXTRACT PROCESS

Dissolved organic carbon (DOC) with a humic acid-like composition is a very important component of biochar in agricultural production applications. DOC extraction from biochar derived from coffee husks at different pyrolysis temperatures using a KOH solution was performed. The investigated parameters of the DOC extraction process included biochar pyrolysis temperature (300, 450, and 600℃), KOH content (0.5; 1.0 and 2.0 M), homogenization speed (4000, 6000, and 8000 rpm), extraction time (1, 2 and 3h) and biochar dosage used (50, 100 and 150 g/L). The optimal extraction process parameters were determined based on the DOC extraction efficiency and the contribution of humic acid-like substances. The results showed that the optimal extraction parameters selected were biochar pyrolyzed at 300℃, 2M KOH; homogenization speed of 6000 rpm, extraction time of 2 h, and biochar dosage of 100 g/L. The DOC extraction efficiency reached 33.7% and the main components of DOC were the humic-like substance with high molecular weight. The findings in this study not only determine the optimal parameters for the extraction of organic matter from biochar but also provide a theoretical basis for the use of biochar-based extracts as liquid organic fertilizers or soil conditioners.

Effect of rhamnolipid on the performance of compound thermophilic bacteria agent pretreatment system for waste sludge hydrolysis.

This study innovatively introduced rhamnolipid (RL) to compound thermophilic bacteria (TB) agent pretreatment system for further accelerating the waste sludge hydrolysis and substrates transformation. The results showed that combined pretreatment was beneficial for the sludge extracellular polymers (EPS) rupture and dissolved organic matters (DOM) release. In the optimal dosage of 40mg/g SS RL, the activities of protease and α-glucosidase increased by 20.7% and 33.3% than that without RL addition, respectively. The addition of RL enhanced efficient contacts between hydrolases and organic substrates, and excitation emission matrix (EEM) spectrum revealed that combined pretreatment with 40mg/g SS RL could achieve higher soluble microbial by-products occupancy (54%) and lower fulvic acid-like substances (6%) occupancy in DOM, promoting the waste sludge biodegradability. High organics availability conducted to more shifts in microbial community structure, compared with TB agent pretreatment, the relative abundance of genus Geobacillus and norank_f__Synergistaceae were enhanced by 29.08 and 0.33 times in combined pretreatment system, respectively, which was conducive to sludge hydrolysis and subsequent anaerobic fermentation process.

Membrane fouling behaviors in membrane Fenton process without acid-base agents controlled by current density for nanofiltration concentrate treatment

Effective generation of H+ and OH− in the Fenton by electrodes is crucial for addressing the impact of acidity and alkalinity on the environment. In this study, electrolysis was coupled with membrane Fenton for nanofiltration concentrate treatment and membrane fouling behaviors were investigated. The effects of current density and dosage (H2O2 and Fe2+ ) were studied. According to the Box-Behnken design results, both current density and the dosages of H2O2 and Fe2+ positively influenced the removal of organic pollutants, with the former showing the most significant effect. Hydroxyl radical (•OH) oxidized the organic pollutants into intermediates, realizing a removal efficiency of 74.50 %. The anode oxidation and Fenton process effectively degraded fluorescent components, particularly humic acid-like substances. Ammonia nitrogen was degraded by active chlorine produced at the anode, with an average removal rate of 51.36 %. Additionally, an increase in current density enhanced ion exchange membrane fouling. Chemical composition analysis suggested that the membrane was primarily covered with hydroxide crystal substances. The ultrafiltration (UF) membrane analysis indicated that cake layer formation was responsible for the trans-membrane pressure (TMP) increase, and cake-complete was the primary mechanism contributing to UF membrane fouling. The membrane Fenton process without acid-base agents exhibits significant potential for contaminants removal from nanofiltration concentrate and is advantageous for cleaning membrane fouling.

Research on the Properties of DOM from the Microalgal Treatment Process for Leachate from Incineration Fly Ash Based on EEM-PARAFAC Analysis

Fly ash derived from the incineration of garbage is known to contain hazardous materials that can affect the growth of plants and animals and pose a threat to human health. In this study, we explored how treatment of fly ash leachate with microalgae could alter the properties of dissolved organic matter (DOM). Fly ash leachate samples obtained from a landfill site in Wenzhou were treated with the microalgae Chlorella vulgaris or Scenedesmus obliquus without and with the addition of ammonium ferric citrate (C6H8FeNO7) for 24 days, and changes in DOM levels and types were measured using excitation emission matrix fluorescence technology. The following results were obtained: Analysis of three-dimensional fluorescence spectral indices indicated that the algal treatment process consistently generated new autogenous DOM, with most of the organic matter being newly formed. Additional nutrients had a minor effect on the production and composition of DOM in the system. Using a parallel factor model to analyze the three-dimensional fluorescence spectral matrices of water samples from various systems revealed common components in each group, including arginine, tryptophan-like proteins and fulvic acid-like substances. This study aimed to explore the changes in DOM properties during microalgae treatment of fly ash leachate from the perspective of three-dimensional fluorescence.

Minimization of algogenic organic matter from cyanobacteria-laden water by electrochemical oxidation: molecular degradation signature of disinfection by-products precursors by electro-oxidation and electro-Fenton

Algogenic organic matter (AOM) generated from cyanobacteria-impacted reservoirs poses a significant risk to drinking water. This study aimed to investigate the molecular degradation signature of Microcystis aeruginosa (MA)-derived AOM by electrochemical oxidation and the corresponding disinfection by-product formation potential (DBPFP). Boron-doped diamond (BDD)-based electro-oxidation (EO) and electro-Fenton (EF) were implemented at pH 3 and 10 mA cm−2 within 1 h. The fluorophore of extracellular organic matter (EOM), the mixture of EOM and intracellular organic matter (IOM), were characterized, and their corresponding molecular weight (MW) were fractionated. The results showed that dissolved organic carbon (DOC) degradation efficiency for BDD-EF treatment is superior and maintains DOC attenuation up to 84% for the EOM suspensions alone, while a low degradation efficiency occurs for IOM-EOM mixture. In contrast, BDD-EO exhibits a maximum DOC degradation around 66% for EOM suspensions alone, but DOC reduction is as low as 20% for IOM-EOM mixture. The H2O2 generated by BDD-EO preferentially degrades humic acid-like substances in EOM suspensions, whereas BDD-EF effectively degrades multiple fluorescent AOM by •OH. For IOM-EOM mixture, BDD-EO efficiently decomposes humics, but BDD-EF preferentially minimizes soluble microbial product-like and aromatic protein-like substances. Meanwhile, BDD-EF favors degrading biopolymers, humics, and low-MW substances, while BDD-EO merely degrades partial biopolymers and humic substances. After either EF or EO, specific DBPFP decreases as EOM presents alone where the toxicity of corresponding DBPs is mitigated effectively, instead the increased specific DBPFP appears for IOM-EOM mixture where the toxic potency ([DBP]/LC50) of corresponding DBPs increases. In summary, EO and EF are powerful in attenuating MA-derived DBP precursors of EOM in the absence of IOM, depending on the molecular signature.

Laccase modified fulvic acid-like substance from paper spent cooking liquor: Chemical structure optimization, functional group reconstruction and bioactivity improvement

Identifying a recovery technology for paper spent cooking liquor and converting it into useful material is important for the sustainable development of paper industry. Previous research reported that paper spent cooking liquor-derived fulvic acid-like substances (molecular weight < 5 kDa, PFA) promotes rice growth under salt stress but not as well as natural fulvic acid, which restricts its application as a fertilizer synergist. The ability of PFA to promote rice growth was positively associated with functional groups content. Laccase was used to modify the chemical structure of PFA to further improve its bioactivity. Results showed that laccase modification increased carboxyl and phenolic group contents through oxidation and demethylation with 60 min as optimal reaction time. Under this condition, carboxyl and phenolic group content were increased by 33 %-68.9 % and 19.1 %-208.4 %, respectively. In addition, laccase lowered the molecular weight of PFA (the fraction of molecular weight < 1 kDa increased by 21 %-35.76 %), promoted the degradation of lignin, and increased the relative abundance of tannins (containing phenolic compounds) by 42.89 %-89.41 %. Moreover, laccase-modified PFA (PFA-Ms) promoted rice growth under salt stress than that of PFA. Correlation analysis verified that the promoting effect of PFA-Ms on the elongation of rice roots was associated with carboxylic-C and tannin contents. The antioxidant and root growth-promoting functions of the phenolic and carboxyl groups were confirmed by experiments using phenol and acetic acid, respectively. This study provides an attractive perspective for the sustainable utilization of paper spent cooking liquor as a fertilizer synergist in agriculture.

The interplay of Brown carbon (BrC) surrogates and copper: Implications for the oxidative potential of ambient particles

Atmospheric particulate matter (PM) poses adverse effects on human via producing reactive oxygen species (ROS). Oxidative potential (OP, ability to generate ROS) can be induced by various chemicals in PM, while their interplay remains poorly characterized. Here, we systematically assessed influences of Cu2+ on OP of Brown carbon (BrC) (e.g., imidazoles) using dithiothreitol (DTT) assay. Results showed DTT consumption rate exhibited an initial rise and later decline (0.25 −0.56 µM/min) along with increase of BrC concentration (0.1 − 2 µM), while no general trend was observed for •OH formation. Although Cu2+ showed either antagonism or synergism with BrC against DTT consumption, Cu2+ displayed antagonism with most BrC against •OH generation. Fluorescence quenching experiments provided evidence of complexation between Cu2+ and water-soluble organic compounds (WSOCs, from ambient PM2.5), which was influenced by Cu2+ concentration. Further parallel factor analysis of spectra showed that polycarboxylate-type humic acid-like substances (complexation site number (n): 0.46, complexation equilibrium constant (k): 0.51) and fulvic acid-like compounds (n: 0.42, k: 0.62) were the main components in WSOCs that complexed with Cu2+. Our results suggest the interactions of BrC and copper play a crucial role in PM OP and highlight complexation in evaluation of PM OP.

Pollution of organophosphorus pesticides in the Dongting Lake, China and its relationship with dissolved organic matter: Occurrence, source identification and risk assessment

The escalating global demand for food and industrialization has placed significant pressure on the integrity and management of inland lake ecosystems. Herein, the organophosphorus pesticides (OPPs) pollution status and their relationship with dissolved organic matter (DOM) in Dongting Lake were investigated to identify the ecological risks and potential sources of OPPs. The total concentrations of 18 detected OPPs were in the range of 13.49–375.24 ng/L, with higher concentration observed in east and west lake regions. Among these, fenthion was the dominant contributor, accounting for 64% of total OPPs, posing significant ecological risk to aquatic organisms. Nearly all of sites showed high combined risk of total OPPs. Parallel factor analysis (PARAFAC) and fluorescence regional integration (FRI) technique showed that DOM was mainly composed of terrestrial humic-like and tryptophan-like substances. Moreover, correlation analysis revealed a close association between DOM optical parameters and OPP concentrations. Specifically, OPPs exhibited a significantly positive correlation with tyrosine-like substances, while displaying a negative correlation with fulvic acid-like substances. These results indicated that OPP concentrations may decrease with increasing humification levels and declining tyrosine-like substance contents. This study underscores the critical role of DOM in assessing the occurrence and sources of OPPs in aquatic environments, providing valuable insights for effective environmental management strategies.

Polystyrene microplastics enhanced the photo-degradation and -ammonification of algae-derived dissolved organic matters

Algae-derived organic matter (ADOM) is a key source of chromophoric dissolved organic matter (CDOM) in natural waters. When exposed to solar irradiation, ADOM undergoes gradual degradation and transformation. The escalating presence of microplastics (MPs) can act as a novel type of environmental photosensitizer, however its impacts on ADOM photodegradation remains largely unexplored. Thus, in this study, ADOM were extracted from four common algal species (Microcystis aeruginosa, Synechococcus sp., Chlorella pyrenoidosa and Scenedesmus obliquus) and exposed to UV irradiation with or without polystyrene (PS) MPs, namely ADOM+PS groups and ADOM groups, respectively. The results indicated that a more rapid degradation of amino acid-like substances (∼38 % vs. ∼22 %) and more ammonia products (1.86 vs. 1.21 mg L−1) were observed in the ADOM+PS groups compared to the ADOM groups after a five-day exposure. This enhanced photodegradation might be attributed to the production of environmentally persistent free radicals and reactive species during the photoaging of PS. Furthermore, PS-derived high electron transfer belt activity of ADOM led to the production of highly aromatic and humified products. These humic-like products could potentially accelerate the degradation of amino acid-like compounds by exciting the generation of excited triplet CDOM. This study underscores the role of MPs as environmental photosensitizers in promoting ADOM degradation and ammonia generation, providing insights on the transformation of ADOM mediated by emerging pollutants and its impact on aquatic carbon and nitrogen cycles.

Unveiling the effects of dissolved organic matter (DOM) extracted from coastal algae and river on the photooxidation of arsenite

The coastal environment is an important ecosystem connecting land and sea, and arsenite (As(III)) in coastal seawater can seriously affect human health through the food chain. However, the effects of dissolved organic matter (DOM) extracted from coastal algae and rivers on As(III) photooxidation remain unclear. Results show that coastal algal DOM (CA-DOM) is significantly more effective than Suwannee River natural organic matter (SRNOM) in photooxidation of As(III), with a rate 8.3 times higher after correcting for light screening effects. CA-DOM accelerates As(III) photooxidation mainly through the 3DOM⁎ pathway, contributing 78.7 % to the process, whereas 3NOM⁎ contributes only 37.2 % for SRNOM. CA-DOM consists primarily of low-excited tyrosine and tryptophan-like protein substances, whereas SRNOM consists of humic and fulvic acid-like substances. Thus, CA-DOM exhibits a higher steady-state concentration of 3DOM⁎, and the 3DOM⁎ reacts much faster with As(III) than the 3NOM⁎. The increase in CA-DOM concentration can significantly accelerate the photooxidation of As(III), whereas the effect of SRNOM concentration is negligible. Increased salinity can accelerate As(III) photooxidation for all types of DOM. Our results provide new insights into the role of DOM from different sources in the photooxidation of As(III) in the natural environment or engineering applications.

Carbon, nitrogen, and phosphorus release characteristics and underlying mechanisms in fish manure from recirculating aquaculture systems under alternating aerobic-anaerobic conditions

To mitigate the adverse environmental impacts of aquaculture operations, recirculating aquaculture systems (RASs) have emerged as promising alternatives to traditional aquaculture methods. Fish manure is the primary pollutant in RASs, and oxygen fluctuations significantly influencing the release of pollutants. However, the release characteristics and underlying mechanisms of carbon (C), nitrogen (N), and phosphorus (P) during alternating aerobic-anaerobic conditions in RASs remain poorly understood. This study conducted batch incubation experiments to examine the release dynamics of C, N, and P from fish manure under simulated alternating aerobic-anaerobic conditions. Results showed that the overlying water exhibited anaerobic and reductive conditions, with both COD and TOC concentrations decreasing over time. NH4+-N levels significantly decreased from days 1–9, while NO3--N concentrations peaked on day 16. Furthermore, the alternating aerobic-anaerobic conditions significantly increased TP concentration in the overlying water. Soluble microbial byproduct-like substances in the overlying water transformed into humic acid-like substances over time. The relative abundance of Proteobacteria and Firmicutes decreased by 13.6 % and 6 %, respectively, while the relative abundance of Actinobacteria, Bacteroidota, and Chloroflexi increased by 7 %, 12.8 %, and 1.4 %, respectively. Overall, both abiotic and biotic factors influenced the release of C, N, and P from fish manure. The coupled effects of abiotic factors, specific bacterial communities, and functional genes played a critical role in the release and transformation of these elements. These findings provide new insights into the release behaviours and mechanisms of pollutants in RASs, contributing to improved environmental risk management in RASs.

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.

Alkaline hydrothermal cracking effect and substance transformation characteristics of caprolactam-containing sludge

Caprolactam is a crucial chemical intermediate, but its wastewater treatment process generates a significant amount of caprolactam-containing sludge. This study represented the first exploration of the effects of alkaline hydrothermal technology on the cracking and transformation of substances in this sludge. The cracking effect of caprolactam-containing sludge during hydrothermal treatment increased with rising reaction temperature and longer reaction time. With NaOH dosage in hydrothermal treatment increasing from 0 to 2 wt%, the volatile suspended solids (VSS) removal rate of the sludge increased from 44.5% to 74.8%, soluble chemical oxygen demand (SCOD) in the cracking liquid increased from 12772 mg/L to 22976 mg/L, and ammonia nitrogen concentration increased from 398.0 mg/L to 851.2 mg/L. However, the addition of Ca(OH)2 did not significantly affect the changes of sludge suspended solids, VSS and SCOD concentration, but increased the leaching of ammonia nitrogen (up to 745.0 mg/L). This was due to the secondary flocculation of Ca2+, which rebound with dissolved non-proteinaceous organic matter. Increasing temperature, reaction time, and alkaline dosage all enhanced the fluorescence intensity of dissolved organic matter (DOM). Moreover, higher reaction temperature and alkaline dosage reduced the proportion of proteinaceous products in DOM while increasing the proportions of fulvic acids, soluble microbial metabolites, and humic acid-like substances. The study provided crucial theoretical support for engineering application of this technology.

Nano Fe3O4 improved the electron donating capacity of dissolved organic matter during sludge composting

The effect of Fe3O4 nanoparticles (Fe3O4 NPs) on the electron transfer process in aerobic composting systems remains unexplored. In this study, we compared the electron transfer characteristics of DOM in sludge composting without additives (group CK) and with the addition of 50 mg/kg Fe3O4 NPs additive (group Fe). It was demonstrated that the electron transfer capacity (ETC) and electron donating capacity (EDC) of compost-derived DOM increased by 13%–29% and 40%–47%, respectively, with the addition of Fe3O4 NPs during sludge composting. Analyzing the composition and structure of DOM revealed that Fe3O4 NPs promoted the formation of humic acid-like substances and enhanced the aromatic condensation degree of DOM. Correlation analysis indicated that the increase in EDC of DOM was closely associated with the phenolic group in DOM and influenced by quinone groups and the degree of aromatization of DOM. The higher EDC and the structural evolution of DOM in group Fe reduced the bioaccessibility of Cu, Cr, Ni, Zn. This study contributes to a deeper understanding of the redox evolutionary mechanism of DOM in sludge composting and broadens the application of iron oxides additives.

Refractory COD removal from bio-treated paper wastewater using powdered activated coke adsorption technology with ozonation regeneration: Performance and molecular insights

The present study employed powdered activated coke (PAC) for the adsorptive removal of refractory COD from the bio-treated paper wastewater (BTPW). The adsorption reached equilibrium after 3 h, resulting in a decrease in the COD concentration from 98.9 mg L−1 in BTPW to 42.6 mg L−1 when utilizing a PAC dosage of 5 g L−1. The dominant fractions of dissolved organic matter in BTPW were hydrophilic acids (HIA), hydrophilic neutrals (HIN), and hydrophobic acids (HOA), accounting for 48.8%, 34.2%, and 17.0% of the total dissolved organic carbon, respectively. Three fractions were all predominantly composed of humic/fulvic acid-like substances, while the HOA fraction exhibited highest susceptibility to adsorption by PAC, followed by the HIA and HIN fractions. FT-ICR MS data revealed PAC preferentially adsorbed the unsaturated and oxygen-rich substances containing more carboxyl groups. Additionally, the spent PAC was regenerated through ozonation and subsequently utilized in the adsorption cycles. The regeneration was successfully conducted under an ozone concentration of 1 mg L−1 for a duration of 10 min, and the regeneration efficiency remained about 87.0% even after undergoing five-cycle of adsorption-regeneration. The findings of this study demonstrate that PAC adsorption is a viable and efficacious treatment technology for efficiently removing refractory COD from BTPW.

Alkali-assisted hydrothermal preparation of artificial humic acid from litchi wood and electrochemical performance of its hydrochar

Utilizing soluble alkalis such as KOH and NaOH, hydrothermal humification technology (HTH) facilitates the conversion of biomass into artificial humic acid-like substances. However, the impact of less soluble bases like Ca(OH)2 has been underexplored. In this study, we investigates the use of Ca(OH)2 as an alternative to KOH in converting waste litchi wood into artificial humic acid (AHA) under hydrothermal conditions, and examined the potential of residual hydrochar in the field of electrochemistry. Under optimal conditions (20 % Ca(OH)2 addition, 225 ℃, and 4 h), 16.77 ± 0.49 % AHA was produced, with a yield and structure comparable to those obtained with KOH. During the hydrothermal process, Ca(OH)2 promotes the formation of small molecules that contribute to AHA formation, which then complex with Ca2+ and incorporate into the solid phase. This process significantly reduces carbon gas emissions by decreasing the loss of soluble sugars and absorbing CO2 (5.22 % with Ca(OH)2vs. 18.24 % with KOH). Additionally, after simple pyrolysis, the hydrochar exhibited a specific capacitance of 88.15 F−1 at 0.5 A g−1 and maintained over 97 % of its capacitance at 10 A g−1 after 10,000 cycles. This study highlights the potential of Ca(OH)2 in the hydrothermal humification and offers a novel approach for the sustainable utilization and high-value application of litchi wood and other biomass.

Mechanisms underlying the detrimental impact of micro(nano)plastics on the stability of aerobic granular sludge: Interactions between micro(nano)plastics and extracellular polymeric substances

Microplastics (MPs) and nanoplastics (NPs) present in wastewater can pose a negative impact to aerobic granular sludge (AGS). Herein, this study found that MPs and NPs (20 mg/L) deteriorated the sludge settleability and granule integrity, resulting in a 15.7 % and 21.9 % decrease in the total nitrogen removal efficiency of the AGS system, respectively. This was possibly due to the reduction of the extracellular polymeric substances (EPS) content. The subsequent analysis revealed that tyrosine, tryptophan, and humic acid-like substances in EPS exhibited a higher propensity for chemisorption and inhomogeneous multilayer adsorption onto NPs compared to MPs. The binding of EPS onto the surface of plastic particles increased the electronegativity of the MPs, but facilitated the aggregation of NPs through reducing the electrostatic repulsion, thereby mitigating the adverse effects of MPs/NPs on the AGS stability. Additionally, comprehensive analysis of the extended Derjaguin-Landau-Verwey-Overbeek theory indicated that the suppressed aggregation of microorganisms was the internal mechanisms contributing to the inadequate stability of AGS induced by MPs/NPs. This study provides novel insights into the detrimental mechanisms of MPs/NPs on the AGS stability, highlighting the key role of EPS in maintaining the structural stability of AGS when exposed to MPs/NPs.

Co-hydrothermal carbonization of waste biomass and phosphate rock: promoted carbon sequestration and enhanced phosphorus bioavailability

Co-hydrothermal carbonization (co-HTC) of phosphorus rock (PR) and corn straw (CS) was investigated to prepare hydrochar-based materials as soil conditioners, focusing on the morphological transformation and solid–liquid migration of carbon and phosphorus. Various analytical methods, including elemental analysis, chemical quantification, FT-IR, XRD, 3D-EEM, TG, and XANES, were used to understand the synergistic interactions of PR and CS during co-HTC and determine the properties of the resultant products. The results indicated the acidic solution and humic acid-like substances produced by HTC of CS reduced the crystallinity of the PR and served as the activating agent for PR, allowing the PR to be easily dissolved and reconstituted, producing calcium carbonate and apatite-like materials, and the formation of C–O–PO3, C–PO3, C=O, and O=C–O chemical bonds. At 220 °C, adding 5% PR significantly promoted a 10.3% rise in the yield of CS hydrochar, a 4.3% rise in carbon recovery of CS, and a 4.8% rise in carbon sequestration potential of CS. The formation of Ca–P was notably promoted and the content of AP in co-HTC hydrochar was up to 89.9%, with 39% Hydro-P and 33% CaHPO4. In the case of artificial humic acid (HAa), its content was also remarkably increased by 5.9% in the hydrochar by co-HTC. In addition, the hydrochar produced by co-HTC of CS and PR was composed of carbon with an increased aromatic degree, rich organic matter, and biologically effective mineral nutrient elements and exhibited high stability. The present study provided a promising approach for value-added utilization of waste biomass and low-grade PR towards soil application.Graphical

A novel fungal and bacterial consortium promotes the degradation of rice straw: Conditions optimization and degradation properties

The rapid development of agriculture has led to the production of a large amount of crop straw, necessitating effective strategies for its management. Microbial degradation offers a promising method. In this study, a novel microbial consortium composed of Phanerochaete chrysosporium, Aspergillus niger, and Streptomyces griseorubens, known for their robust lignocellulose degradation capabilities, was constructed for rice straw degradation. The establishment of this microbial consortium was based on the growth curve and antagonistic tests. Orthogonal optimization revealed that Streptomyces griseorubens played a predominant role in the degradation of rice straw. The optimal degradation conditions were determined as follows: nitrogen source concentration of 2.5 gL−1, material-liquid ratio of 40 g L−1, inoculum size of 3%, and pH value of 9. Under these conditions, the degradation efficiency reached 42% within 15 days. The decomposition of lignocellulosic components in the straw was confirmed through various characterization methods. Additionally, as the degradation process progressed, there was a noticeable decrease in protein-like substances and an increase in humic acid-like substances in the degradation solution.