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Predicting the parameters that influence colloidal phosphorus (CP) release from soils under different land uses is critical for managing the impact on water quality. Traditional modeling approaches, such as linear regression, may fail to represent the intricate relationships that exist between soil qualities and environmental influences. Therefore, in this study, we investigated the major determinants of CP release from different land use/types such as farmland, desert, forest soils, and rivers. The study utilizes the structural equation model (SEM), multiple linear regression (MLR), and three machine learning (ML) models (Random Forest (RF), Support Vector Regression (SVR), and eXtreme Gradient Boosting (XGBoost)) to predict the release of CP from different soils by using soil iron (Fe), aluminum (Al), calcium (Ca), pH, total organic carbon (TOC) and precipitation as independent variables. Results show that colloidal-cations (Fe, Al, Ca) and colloidal-TOC strongly influence CP release, while bioclimatic variables (precipitation) and pH have weaker effects. XGBoost outperforms the other models with an R2 of 0.94 and RMSE of 0.09. SHapley Additive Explanations described the outcomes since XGBoost is accurate. The relative relevance ranking indicated that colloidal TOC had the highest ranking in predicting CP. This was supported by the analysis of partial dependence plots, which showed that an increase in colloidal TOC increased soil CP release. According to our research, the SHAP XGBoost model provides significant information that can help determine the variables that considerably influence CP contents as compared to RF, SVM, and MLR. [Display omitted] • SHAP XGboost performed better than RF, SVM and MLR. • Colloidal TOC ranked as the most important factor followed by Fe, Ca, Al. • Increasing colloidal TOC leads to an increase in the release of Colloidal P. [ABSTRACT FROM AUTHOR]

Soil water-dispersible colloidal phosphorus (WCP) presents high mobility, however, the regulatory effect of biochar-coupled organic fertilizer is rarely known, especially under different cropping patterns. This study investigated the P adsorption, soil aggregate stability, and WCP in three paddy and three vegetable fields. These soils were amended with different fertilizers (chemical fertilizer, CF; substitution of solid-sheep manure or liquid-biogas slurry organic fertilizer, SOF/LOF; substitution of biochar-coupled organic fertilizers, BSOF/BLOF). Results presented that the LOF averagely increased the WCP contents by 50.2% across the sites, but the SOF and BSOF/BLOF averagely decreased their contents by 38.5% and 50.7% in comparison with the CF. The WCP decline in the BSOF/BLOF-amended soils was mainly attributed to the intensive P adsorption capacity and soil aggregate stability. The BSOF/BLOF increased the amorphous Fe and Al contents in the fields in comparison with the CF, which improved the adsorption capacity of soil particles, further improving the maximum absorbed P (Q max) and reducing the dissolved organic matter (DOC), leading to the improvement of > 2 mm water-stable aggregate (WSA >2mm) and subsequent WCP decrease. This was proved by the remarkable negative associations between the WCP and Q max (R2 = 0.78, p < 0.01) and WSA >2mm (R2 = 0.74, p < 0.01). This study manifests that biochar-coupled organic fertilizer could effectively reduce soil WCP content via the improvement of P adsorption and aggregate stability. [Display omitted] • Biochar addition decreased soil water–dispersible colloidal P content. • Biochar addition increased soil P adsorption capacity. • Biochar addition improved soil aggregate stability. [ABSTRACT FROM AUTHOR]

Soil colloids have been shown to play a critical role in soil phosphorus (P) mobility and transport. However, identifying the potential mechanisms behind colloidal P (P coll) release and the key influencing factors remains a blind spot. Herein, a machine learning approach (random forest (RF) coupled with partial dependence plot analyses) was applied to determine the effects of different soil physicochemical parameters on P coll content in three colloidal subfractions (i.e., nano- (NC): 1–20 nm, fine- (FC): 20–220 nm and medium-sized colloids (MC): 220–450 nm) based on a regional dataset of 12 farmlands in Zhejiang Province, China. RF successfully predicted P coll content (R2 = 0.98). Results showed that colloidal- organic carbon (OC coll) and minerals were the major determinants of total P coll content (1–450 nm); their critical values for increasing P coll release were 87.0 mg L−1 for OC coll , 11.0 mg L−1 for iron (Fe coll) or aluminium (Al coll), 2.6 mg L−1 for calcium (Ca coll), 9.0 mg L−1 for magnesium (Mg coll), 2.5 mg L−1 for silicon (Si coll), and 1.4 mg L−1 for manganese (Mn coll). Among three colloidal subfractions, the major factors determining P coll were soil Olsen-P (P Olsen ; 125.0 mg kg−1), Ca coll (2.5 mg L−1), and colloidal P saturation (21.0%) in NC; Mn coll (1.5 mg L−1), Mg coll (6.8 mg L−1), and P Olsen (135.0 mg kg−1) in FC; while Mn coll (1.5 mg L−1), Al coll (2.5 mg L−1), and Fe coll (3.8 mg L−1) in MC, respectively. OC coll had a considerable effect in the three fractions, with critical values of 80.0 mg L−1 in NC or FC, and 50.0 mg L−1 in MC. Our study concluded that the information gleaned using the RF model can be used as crucial evidence to identify the key determinants of different size fractionated P coll contents. However, we still need to discover one or more easy-to-measure parameters that can help us better predict P coll. [Display omitted] • Effects of different soil physicochemical factors on colloidal P content were investigated. • Random Forest showed good performance to predict colloidal P content in agricultural soils. • Colloidal organic carbon and minerals were the key determinants of colloidal P content. [ABSTRACT FROM AUTHOR]

The agricultural use of manure fertilizer increases the phosphorus (P) saturation of soils and the risk of colloidal P (P coll) release to aquatic ecosystems. Two experiments were conducted to identify whether Pteris vittata plantation can decrease P coll contents in two soils (Cambisol and Anthrosol) amended with various manure P rates (0, 10, 25, and 50 mg P kg−1 of soil). The total P coll contents in manured soil without P. vittata were 1.14–3.37 mg kg−1 (Cambisol), and 0.01–2.83 mg kg−1 (Anthrosol) across manure-P rates. The corresponding values with P. vittata were 0.97–2.33 mg kg−1 (Cambisol) and 0.005–1.6 mg kg−1 (Anthrosol). Experimentally determined colloidal minerals (Fe, Al, Ca), colloidal total organic carbon, Mehlich−3 nutrients (Fe, Al, and Ca), and the degree of P saturation were good predictors of P coll concentrations in both soils with and without P. vittata plantation. In unplanted soils, P adsorption decreased and the degree of P saturation increased which released more P coll. However, P. vittata plantation decreased the P coll release and P loss risk due to the increase of P adsorption and reduced DPS in both soils. The P fractions (NaOH, NH 4 F, and HCl–P) contributed to increase the P pool in planted soils which enhanced the bioavailability of P coll and increased the P. vittata biomass. It suggested that P. vittata plantation was an effective approach to reduce P coll release from manure amended soils. [Display omitted] • Soils with maximum P adsorption capacity reduce colloidal phosphorus release. • Pteris vittata plantation increase bioavailability of colloidal phosphorus. • Maximum Degree of P saturation promoted colloidal phosphorus release. [ABSTRACT FROM AUTHOR]

Understanding the processes and mechanisms that shape the distribution patterns and variations of biodiversity along spatial gradients continues to be a priority for ecological research. We focused on the biodiversity of benthic diatom communities within a large near‐natural watershed. The objectives are: (1) to explore the overall spatial patterns of benthic diatom biodiversity; (2) to investigate the effects associated with watercourse position and environmental variables, as well as both common and rare species on two facets (i.e., taxonomic and functional) of alpha and beta diversity; and (3) to unveil the mechanisms underlying their spatial variations. Alpha diversity indices along the stream watercourse showed a clear increasing trend from upstream to downstream sites. Results of random forest regression identified conductivity as the primary factor influencing functional alpha diversity, while elevation emerged as the predominant factor for taxonomic alpha diversity. Beta diversity partitioning revealed that taxonomic beta diversity generally exceeded functional beta diversity. These diversity measures exhibited different patterns along the watercourse position: taxonomic beta diversity remained relatively consistent along the watercourse, whereas functional total beta diversity and its two components of middle stream sites were lower than those of upstream and downstream sites. Functional beta diversity was sustained by dominant and common species, while rare species made significant contributions to taxonomic beta diversity. Both taxonomic and functional beta diversity and its components displayed a stronger influence from spatial factors than from local environmental, geo‐climatic, and nutrient variables. Collectively, taxonomic and functional alpha and beta diversity demonstrated distinct responses to the main environmental gradients and spatial factors within our catchment, highlighting their different insights into diatom diversity. Furthermore, research is required to assess the generalizability of our findings to similar ecosystems. In addition, this study presents opportunities for expansion to include other taxa (e.g., macroinvertebrates and fish) to gain a comprehensive understanding of the driving mechanisms behind stream biodiversity. [ABSTRACT FROM AUTHOR]

Understanding the processes and mechanisms that shape the distribution patterns and variations of biodiversity along spatial gradients continues to be a priority for ecological research. We focused on the biodiversity of benthic diatom communities within a large near‐natural watershed. The objectives are: (1) to explore the overall spatial patterns of benthic diatom biodiversity; (2) to investigate the effects associated with watercourse position and environmental variables, as well as both common and rare species on two facets (i.e., taxonomic and functional) of alpha and beta diversity; and (3) to unveil the mechanisms underlying their spatial variations. Alpha diversity indices along the stream watercourse showed a clear increasing trend from upstream to downstream sites. Results of random forest regression identified conductivity as the primary factor influencing functional alpha diversity, while elevation emerged as the predominant factor for taxonomic alpha diversity. Beta diversity partitioning revealed that taxonomic beta diversity generally exceeded functional beta diversity. These diversity measures exhibited different patterns along the watercourse position: taxonomic beta diversity remained relatively consistent along the watercourse, whereas functional total beta diversity and its two components of middle stream sites were lower than those of upstream and downstream sites. Functional beta diversity was sustained by dominant and common species, while rare species made significant contributions to taxonomic beta diversity. Both taxonomic and functional beta diversity and its components displayed a stronger influence from spatial factors than from local environmental, geo‐climatic, and nutrient variables. Collectively, taxonomic and functional alpha and beta diversity demonstrated distinct responses to the main environmental gradients and spatial factors within our catchment, highlighting their different insights into diatom diversity. Furthermore, research is required to assess the generalizability of our findings to similar ecosystems. In addition, this study presents opportunities for expansion to include other taxa (e.g., macroinvertebrates and fish) to gain a comprehensive understanding of the driving mechanisms behind stream biodiversity. [ABSTRACT FROM AUTHOR]

The metacommunity theory proposes that community structure and biodiversity are influenced by both local processes (such as environmental filtering) and regional processes (such as dispersal). Despite the extensive use of traditional bioassessments based on species‐environment relationships, the impact of dispersal processes on these assessments has been largely overlooked. This study aims to compare correlations between various bioassessment indices, including Shannon Weiner (H′), Biological Monitoring Working Party (BMWP), average score per taxon (ASPT), biotic index (BI), and EPT taxa index (EPT), based on macroinvertebrates collected from 147 sampling sites in a subtropical Chinese near‐natural catchment. Modified indices were calculated by removing species strongly influenced by dispersal processes to address the influence of dispersal processes. Their relationship with environmental factors was then compared to the original indices. The study employed random forest regression (RFR) to compare the explanatory power of environmental factors using the two sets of indices. The spearman rank correlation analysis was conducted to examine the correlation between indices and environmental factors. The river health assessment was performed based on both modified and original indices. The results reveal significant differences between original and modified indices (especially H′ and BI) providing a more accurate reflection of environmental conditions. Furthermore, the sensitivity of the different indices to various environmental factors varied, leading to differences in the bioassessment results between the modified and the original indices. Notably, original H′, BMWP, and ASPT overestimated the bioassessment results, whereas the original BI underestimated them. These findings offer valuable insights into bioassessment and river health assessment evaluation within the catchment and other interconnected freshwater ecosystems, such as lakes, reservoirs, and wetlands. Our study underscores the importance of assessing and mitigating the impact of dispersal processes on bioassessment to obtain a more precise representation of the status of freshwater ecosystems. [ABSTRACT FROM AUTHOR]

We are still challenged to fully understand to what extent controlling irrigation inputs is important for limiting phosphorus (P) losses from paddy soils and how this affects the contribution of dissolved P (DP), particulate P (PP), and colloidal P (P coll) fractions in P losses. For this investigation, an internet-based smart irrigation system was developed to precisely implement different irrigation scenarios––flooding irrigation (FI) and two water-saving irrigation (WSI) scenarios of intermittent (II) and controlled irrigation (CI). A simulation experiment was conducted and the concentrations of total P (TP), DP, PP, and P coll released to floodwater (FW) and leachate (LW) were determined during a rice season after the addition of different P forms (chemical fertilizer (CP), biogas slurry (BP), and manure (MP)) at a rate of 40 kg P·ha−1. The results revealed that the CI scenario effectively decreased P losses in FW (∼51%) and LW (∼63%) with a positive WSI ratio (39.1%), while II reduced it in FW by ∼11% and in LW by ∼27% with a WSI ratio of 11.0% compared with FI. The BP and MP additions caused a higher risk of P losses than CP under FI, with lower risk under WSI. DP largely contributed to P losses (FW: 30%–71%; LW: 42%–66%); however, more PP was released to FW under II (37%–54% of TP). The P coll (FW: 5%–23% and LW: 6%–24%) was more sensitive to release at initial periods after fertilization on account PP. This work provides a promising approach to timely control irrigation inputs, which could limit P losses from paddy soil; however, there remains a need to assess and generalize our initial evidence at field scales. [Display omitted] • An internet-based irrigation approach was proposed to limit P losses from paddy soil. • The controlled irrigation scenario had a better performance for limiting P losses. • Colloidal and dissolved P were more release under flooding irrigation. • The intermittent irrigation triggered more particulate P release to floodwater. • Colloidal P was more sensitive to release at initial periods after fertilization. [ABSTRACT FROM AUTHOR]

Ammonium is strongly related to eutrophication and a key control of eutrophication in aquatic systems, especially in agricultural runoff. In this study, a novel Fe–Mn binary oxide‐modified lava (FMML) granular adsorbent was synthesized for ammonium removal from aqueous solutions by co‐precipitation method. The kinetic data were described by pseudo‐second‐order kinetic model well and intraparticle diffusion had effects on ammonium adsorption. For pH between 4.0 and 10.0, the adsorption efficiency was >80%, and its optimum was recorded at pH 7.0. FMML exhibited strong ammonium adsorption selectivity under the single presence of cations like Na+, K+, Ca2+, and Mg2+. The optimum adsorbent dose and particle size were 4 g/L and 3–5 mm, respectively, for an aqueous solution containing 10 mg/L of ammonium under normal conditions (298 K and pH 7.0). Furthermore, the adsorption process was endothermic, following both the Langmuir (R2 > 0.98) and Freundlich (R2 > 0.96) models. Compared with other adsorbents, the FMML can be prepared following a simpler protocol. After 30 times of adsorption–regeneration cycle, the FMML also had a relatively high ammonium adsorption capacity; hence, we see it as a prospective adsorbent for ammonium adsorption from aqueous solutions. Practitioner points: Fe–Mn binary oxide‐modified lava with Fe/Mn ratio 3:1 was prepared using co‐precipitation method.Adsorption maximum of modified lava was 20.8 mg/g (298 K and pH 7.0).Adsorption was sensitive to changes in adsorbent dose, particle size, and pH.Inorganic cations decreased ammonium adsorption in order of Na+ > K+ > Ca2+ > Mg2+.Mechanisms for ammonium removal by FMML include diffusion, electrostatic attraction, oxidation, and complexation reaction. [ABSTRACT FROM AUTHOR]

Excessive application of phosphorus (P) fertilizer to the agriculture soil can lead to the P loss to the aquatic ecosystem. Three soils from different land use (tea, paddy, and vegetable soils) were treated with biogas slurry (BS) at rate of 79.8 kg ha−1, anionic polyacrylamide (PAM) at rate of 12.5, 25 and 50 kg ha−1, Gypsum (Gy) at rate of 5t ha−1, and the control (Ck) without treatment, to control P losses in a laboratory batch experiment. The soil solution was analyzed for total P (TP), dissolved reactive P (DRP) and total dissolved P (TDP). Particulate P (PP) and dissolved unreactive P (DURP) were calculated by subtracting DRP from TP and TDP, respectively. The DRP was within a range of 68–98% of TP whereas PP varied in a range of 2–32% of TP and DURP was within a range of 0.1–19% of TP, depending on soil types and different treatments. The addition of PAM at a high rate and Gy together on the soil after BS application reduced the release of TP by 54, 46, and 51% and that of DRP by 61, 49, and 53% for tea, paddy and vegetable soils, respectively. However, the application of BS with PAM alone promoted the release of DRP by 77, 86, 70% for tea, paddy, and vegetable soils, respectively. This study suggests that the synergic application of PAM and Gy on soils after BS addition can be a good strategy to reduce P losses. • Biogas slurry and PAM applied with Gypsum was effective in reducing all P forms. • Biogas slurry and PAM applications promoted the release of dissolved reactive P. • Dissolved reactive P was the predominant fraction of total P released. • Soil pH, texture, and TOC may be the main factors influencing P released. [ABSTRACT FROM AUTHOR]

Phosphorus (P) availability and loss risk are linked to P species; however, their alternations in the soil amended with biochar-blended organic fertilizer is not well known, particularly under contrasting soil properties and land management. In this study, the variance of soil P species extracted by sequential chemical extraction (SCE) and 31P NMR techniques, as well as the degree of P saturation (DPS), were investigated throughout three paddy and three vegetable fields. These fields were amended with three different fertilizers at the same P application rate: chemical fertilizer (CF), organic fertilizer substitution (sheep manure/biogas slurry, SM/BS), and biochar-blended organic fertilizer substitution (BSM/BBS). Results showed that the BSM/BBS and SM increased the total P contents by 7.5% and 5.9% (TP) and available P contents by 30.1% and 19.2% (AP), but decreased the DPS values by 19.4% and 11.7%, compared to the CF treatment. Yet, the BS decreased the TP and AP contents but increased the DPS values across the experimental sites. In the BSM/BBS amended soils, high AP contents were due to the increased inorganic P (NaHCO 3 -P i), while the increased organic P (monoester and DNA) induced low DPS values and reduced soil P loss risk. Our study highlights that biochar-blended organic fertilizer is an effective agronomic way for improving P availability and decreasing P loss risk via the alteration of soil P species. [Display omitted] • High proportion of organic P and low P loss risk in the paddy fields. • Biochar addition increased stable P dissolution and organic P retention. • Biochar addition improved soil P availability and retention. [ABSTRACT FROM AUTHOR]

The Fe3+-loaded NaBiO 3 was prepared for photocatalytic removal of tetracycline hydrochloride (TCH) from swine wastewater. Fe3+ greatly reduced the recombination efficiency of the photoinduced electron–hole pairs of NaBiO 3. Moreover, the TCH photocatalytic degradation rate constant of Fe3+-loaded NaBiO 3 was two-times higher than that of Vis+NaBiO 3 after 100 min of reaction. Fe-NaBiO 3 combined with PS (100 mg L−1) favored TCH (10 mg L−1) degradation rate (98.8%) at neutral pH. Moreover, the oxidation system was not inhibited by the fulvic acid, and showed a good photocatalytic stability. The superoxide radicals were the main active species involved in the catalytic degradation. [Display omitted] • A new bismuth-based material was prepared by simple ultrasonic agitation. • Vis+Fe-NaBiO 3 + PS system exhibited excellent removal rates of tetracycline hydrochloride. • The dynamic equilibrium of Fe2+/Fe3+ in the catalytic system greatly contributed to PS activation. • The strong resistance to organic interference exhibited broad prospects in actual wastewater. [ABSTRACT FROM AUTHOR]

• Colloidal P was closely related to Olsen-P in paddy soils on a regional scale. • Cattle manure biochar amendment decreased colloidal P in paddy soils. • Cattle manure biochar amendment increased available P in paddy soils. Colloidal phosphorus (P coll) and available phosphorus (AP) are of fundamental importance in the nutrient cycle in soil solutions and subsurface drainage of ecosystems. Although many studies have been conducted on soil P loss and P availability, there remains limited focus on the relationship between P coll and AP. In this regional-scale study, soils with loam texture were collected from 63 paddy fields in southern China to explore the relationships between P coll and AP as well as other soil parameters. Subsequently, three typical paddy soils (sandy loam, silt loam, and clay loam) were incubated to study the effect of cattle manure biochar (CMB) amendment on P coll and AP at three application rates (0, 1, and 2%, w/w) for 30 d. The results showed that P coll was closely related to AP (R 2 = 0.453, P < 0.05) and pH (R 2 = 0. 487; P < 0.05) on a regional scale. In addition, clay loam soils contained higher P coll than the other soil types. The CMB amendment increased the AP by 129.0–872.0% but reduced the P coll by 9.65–22.95%, in which colloidal molybdenum-nonreactive phosphorus (MUP coll) was reduced by 7.69–34.15% and colloidal molybdenum-reactive phosphorus (MRP coll) was reduced by 5.13–22.73%. Multiple linear regression revealed that the release potentials of P coll (R2 = 0.735), MRP coll (R2 = 0.543), and MUP coll (R2 = 0.512) could be predicted by the dissolved organic carbon, total carbon, pH, and AP. Overall, this study confirmed that the application of CMB reduced the loss of P coll from paddy soils and enhanced the soil AP content. [ABSTRACT FROM AUTHOR]

• Phosphorus (P) input and crop type cause differences in P loss via runoff. • Modified biochar reduced the runoff P concentration and loss load in all cropping systems. • Solid organic fertilizer decreased particulate P and colloidal P losses. • Biogas slurry increased the P loss in the runoff of the rice-wheat rotation system. Agricultural cropping systems involve the application of high fertilizer rates, which lead to phosphorus (P) losses via surface runoff to the aquatic environment, thereby resulting in severe eutrophication. Here, to evaluate the nutrient loss, we established three monitoring stations in Zhejiang Province, China, in each of which the crop types were double cropping rice, rice–wheat rotation, and vegetable cultivation. Field experiments were conducted with four treatments and three replications over a whole planting year. The four treatments at the same P application rate were: 1) no fertilization (control; CK), 2) chemical fertilization (CF), 3) substitution of 30 % chemical P in CF by organic P in solid sheep manure (OF) or in liquid biogas slurry (BS), and 4) substitution of 30 % chemical P in CF by organic P fertilizers (solid sheep manure or liquid biogas slurry) +1.5 t ha−1 polyacrylamide modified BC (PSB). The runoff losses of various P forms, that is, the total P, total dissolved P, particulate P, and colloidal P losses were analyzed. The total P concentration varied greatly with the crop growth stages. Compared with CF treatment, PSB treatment significantly reduced the concentration of P fractions in the runoff in all three cropping systems, while the OF treatment significantly reduced the particulate P and colloidal P concentrations by coating colloidal particles with organic carbon. However, BS treatment increased particulate P and colloidal P concentrations. Compared with CF treatment, PSB treatment reduced total P loss by 41.1 %, 29.7 %, and 37.8 % in the double cropping rice, rice–wheat, and vegetable systems, respectively. The PSB and OF treatments significantly reduced the particulate P and colloidal P losses, while BS treatment increased the loss of various P forms. Compared with the CF treatment, the PSB treatment significantly increased the available P contents by 12.7–85.4 mg kg-1, and decreased the colloidal P contents by 26.7 %–51.4 % in the soils examined. The results of the redundancy analysis confirmed that P loss via runoff was mainly caused by differences in the P inputs and crop types. The results of this study highlight the important role of PSB in reducing P loss via runoff from agricultural cropping systems. [ABSTRACT FROM AUTHOR]

One of the key environmental limitations in coal usage is selenium emission whose removal is focused in this study. We employed hydrothermal treatment to remove Se element and upgrade low rank Huainan coal at 200–300 °C. Pyrolysis temperature given during coal treatment was evaluated to simulate coal transformation into high-rank industrial grade by emphasizing O/C ratio, removal of oxygen functional groups and moisture and chemical structure stability. Following hydrothermal treatment, different characterization techniques including XPS, FTIR, XRD and Raman spectroscopy were used to determine the chemical structure of coal. Findings revealed that hydrothermal treatment process has an important influence on the crystalline structures of low rank coals. The results of XRD and Raman spectroscopy analysis demonstrated much graphitized and aromatic microcrystalline structure. The chemical structure developed was orderly, stable and dense. Selenium XPS spectra comprising of 3D peaks has confirmed several oxidation states including selenide, selenates and oxide species. The removal proportion of Se was significant and increased up to 50.7% with increased HTT temperature (300 °C). This study provides some unique findings pertaining to solubility of sub-critical water and rate of change in pyrolysis temperature as determinant factors in the removal of Se. Our simulation model further concludes that transformation of low rank coal into high rank is a function of temperature treatment coupled with optimization of fixed carbon. We infer that hydrothermal treatment derived coal possesses sufficient lucid attributes to be considered as environmentally safe fuel. Image 1 • Huainan LRC was upgraded by HTT upgrading approach. • Aliphatic carbons in LRC decreased while aromatics increased after HTT process. • XPS spectra confirmed multiple oxidation states (selenide, selenates, oxides). • HTT influence in terms of Se removal was revealed in LRC. [ABSTRACT FROM AUTHOR]