Suqing Wu

Vallisneria spinulosa Yan (V. spinulosa Yan), as a submerged macrophyte and herbal plant, simultaneously exhibits ecological restoration functions in water bodies and medicinal value. However, it cannot be efficiently planted and cultivated in turbid water bodies. Enclosure cultivation technology can solve this issue in real ecological engineering, and enclosure area is an important parameter. The impact of enclosure area on growth characteristics, water purification, and microbial communities of the V. spinulosa Yan growth system in the enclosure cultivation process was studied, with planting density (50 plants·m⁻²) and soil volume per pot kept constant. The results showed that enclosure area primarily shifted biomass allocation: aboveground biomass decreased, and belowground biomass increased with increasing enclosure area, with the root-to-shoot ratio rising from 0.449 (A1, 1 × 1 m enclosure area) to 1.013 (A16, 4 × 4 m enclosure area). Total biomass, leaf number, soluble protein, and soluble sugar did not differ significantly among treatments. Leaf length was significantly greatest in A1. Notably, chlorophyll a, chlorophyll b, and total chlorophyll were significantly lowest in the A4 (2 × 2 m enclosure area) treatment, while SOD (superoxide dismutase) activity was highest in A1 and POD (peroxidase) activity was lowest in A1, all surviving global multiple-comparison correction. Nutrient removal loads (TN, nitrate nitrogen, TP, and PO₄³⁻-P) were significantly higher in planted treatments than in the unplanted control, but pairwise comparisons among planted treatments showed no significant differences. Furthermore, A1 exhibited significantly higher TP (total phosphorus) and PO₄³⁻-P (phosphate) removal loads than the other planted treatments, and its TN (total nitrogen) removal load was significantly higher than that of A9 (3 × 3 m enclosure area). Overall, enclosure area primarily shifted biomass allocation and induced complex physiological responses, without uniformly improving growth or water purification performance. This study can provide valuable references for efficient cultivation of submerged macrophytes and enhancing water purification effects in real ecological engineering.

Introduction: Ecological restoration of submerged macrophytes in highly turbid waters is severely hampered by light attenuation, which imposes significant oxidative stress on plants and disrupts their physiological homeostasis. While suspended planting technology offers a solution by optimizing light exposure, the critical role of planting substrates in modulating plant stress tolerance and rhizosphere resilience remains largely unexplored—a knowledge gap that this study addresses for the first time. This study is novel in systematically linking substrate physical properties to plant redox regulation and rhizosphere microbiome assembly under turbid-water stress, providing an integrated plant–microbe perspective previously unaddressed. Methods: In this study, we cultivated Vallisneria spinulosa Yan using four suspended substrates (plastic mesh, palm mat, linen cloth, and bamboo woven strips) in outdoor flume experiments, aiming to evaluate their effects on plant physiology, water remediation, and associated microbial networks. Results: Our results demonstrated that the linen cloth substrate most effectively alleviated oxidative damage, as evidenced by significantly enhanced root development, biomass accumulation, and leaf photosynthetic pigment content, alongside a marked reduction in physiological oxidative stress markers. Functionally, all treatments achieved over 90% turbidity removal; however, the linen cloth group exhibited superior purification efficiency, with the highest total nitrogen and total phosphorus removal loads (2.32 × 10 ^-4 and 2.70 × 10 ^-4 g·m ^-2 ·d ^-1 , respectively). Critically, microbial community analysis revealed that the linen cloth substrate fostered a more complex and interconnected rhizosphere network, with a notable enrichment of a denitrifying bacterial family ( Comamonadaceae ), indicating a synergistic enhancement of plant–microbe mutualism under stress. Discussion: Collectively, our findings identify linen cloth as the optimal substrate for suspended planting, not merely as a physical support, but as a catalyst for reinforcing the plant’s antioxidant defense system and orchestrating a beneficial rhizosphere microbiome, thereby providing a robust theoretical framework for applying this redox-based ecological engineering strategy in turbid water restoration.

Stormwater and greywater are increasingly recognized as freshwater resources, and the effective separation and reutilization of nitrogen (N) and phosphorus (P) from these streams is vital for water quality improvement and urbanization sustainability. In this study, we constructed a pilot-scale hydroponic green roof wetland system planted with two economically important Chinese herbal plant species (Mentha spicata L. (ML) and Basella alba L. (BL)) to separate and reutilize N and P from synthetic stormwater/greywater. The results reveal that the highest plant biomass was obtained at an ML:BL ratio of 1:3, indicating their superior adaptation to rooftop hydroponics with synthetic stormwater/greywater. This configuration also achieved the strongest water purification, with substantial separation and reutilization efficiency of N (82.09%) and P (81.90%). Furthermore, the lowest microbial richness in the ML roots at this specific plant ratio suggested that increasing BL may enhance ML’s allelopathic effects. An increase in the BL proportion was further associated with a gradual shift in the dominant ML root-associated microorganisms toward microeukaryotic taxa. The green vegetation of the two plant species also effectively suppressed algal blooms (especially diatoms) in the hydroponic rooftop system. This study demonstrates that a Chinese herb-based green roof wetland system can effectively separate and reuse N and P from stormwater/greywater while concurrently purifying water and producing economic crops.

Due to its advantages in specific surface area and oxygen-containing functional groups, biochar was often utilized for water pollution control. In this study, biochar was prepared from three types of wetland plants—Lotus Leaf, Arundo donax L., and Canna indica L. through slow pyrolysis. This biochar was utilized to adsorb Cr(VI) from wastewater, and the adsorption performance of the biochar under different pyrolysis temperatures and KOH modification ratios was investigated. The experimental results of biochar preparation demonstrated that under the pyrolysis of 500 °C and the lotus leaf powder/KOH mass ratio of 1:3, the prepared biochar (LBC-500(1:3)) exhibited the optimal adsorption capacity for Cr(VI) at a concentration of 50 mg·L⁻¹, with an adsorption capacity reaching up to 27.88 mg·g⁻¹. The optimal pH for Cr(VI) adsorption by LBC-500(1:3) was 3, with an adsorption capacity of 32.14 mg·g⁻¹ at this pH. When the dosage amounted to 60 mg, LBC-500(1:3) demonstrated its highest adsorption capacity for Cr(VI), achieving a maximum of 19.39 mg·g⁻¹. When the initial concentration peaked at 80 mg·L⁻¹, the adsorption capacity was able to attain a value of 34.80 mg·g⁻¹. Characterization analyses of the biochar prior to and subsequent to adsorption were conducted to elucidate the adsorption mechanisms of biochar for Cr(VI). The results revealed that the primary removal mechanisms of LBC-500(1:3) for Cr(VI) were coordination, electrostatic adsorption, and pore filling. The analysis of adsorption kinetics and isotherms revealed that the biochar predominantly adsorbed the Cr(VI) through monomolecular layer chemisorption. Adsorption thermodynamics results demonstrated that the adsorption process of the biochar was a spontaneous endothermic reaction. This study provides new insights and technical support for water pollution control, which holds significant environmental importance and application value.

The presence of organic matter can alter the dewatering characteristics of river-dredged silt and affect the dewatering efficiency. This study systematically compared the dewatering effects of cationic polyacrylamide (CPAM), ferric chloride (FeCl₃), and composite flocculant (CPAM + FeCl₃) for sludge with different organic matter contents by using the combined flocculation–electro-osmotic dewatering technology. The results show that the presence of organic matter significantly hinders the dewatering of silt. After the combined treatment of low-, medium-, and high-organic-matter river-dredging sludge with composite flocculants and electro-osmotic treatment, the final water content was 39.53%, 45.08%, and 47.28%, respectively. Compared with the use of CPAM alone, its dewatering efficiency increased by 66.98%, 5.39%, and 13.72%, respectively. Three-dimensional fluorescence spectroscopy analysis (3D-EEM) indicates that the combined dewatering of flocculation and electro-osmosis can improve the dewatering performance of sludge by promoting the transformation of organic matter. Scanning electron microscopy (SEM) analysis shows that under the action of the composite flocculant, the sludge particles aggregate significantly, and after electro-osmosis, the structure becomes more compact and channels are formed, which further improves the sludge dewatering efficiency. This study provides a theoretical basis for the optimization of dewatering processes for dredged silt with different organic matter contents.

Designing phosphate adsorbents is often hindered by trial-and-error optimization that overlooks nonlinear coupling between preparation parameters and operational conditions. Here we present a unified, explainable machine-learning framework that links red mud modified biochar bead (RM/CSBC) preparation (red mud dosage, biomass dosage, and pyrolysis temperature) to operating variables (initial pH, reaction temperature, contact time, and initial phosphate concentration) and directly guides condition selection. Using 95 independent experiments, six regressors were trained and compared. Random Forest (RF) model demonstrated strong prediction accuracy, with R² values of 0.916 for the training set and 0.892 for the test set. Support Vector Regression (SVR) model showed superior performance, achieving R² values of 0.984 and 0.967 for training and test sets, respectively, with low RMSE (0.068 and 0.083) and PBIAS (5.41% and 6.86%). Feature importance analysis revealed red mud and biomass doses positively influenced phosphate adsorption, with surface active sites and phosphate concentration gradient playing significant roles. Experimental verification confirmed RF and SVR models provided accurate predictions under three representative conditions, with deviations between predictions and measurements of +0.66, +0.19, and −0.69 mg·g⁻¹ for SVR and −1.08, −0.79, and −1.15 mg·g⁻¹ for RF, offering reliable guidance for phosphate removal in wastewater using RM/CSBC. This work highlights the potential of using machine learning to optimize waste-based adsorbent materials for wastewater treatment, significantly reducing time and experimental costs.

In this study, red mud (RM) was utilized as an iron and aluminum source, and reed biomass served as a carbon precursor to prepare red mud-modified biochar beads (RM/CSBC) via the gel-calcination method. Under a pyrolysis temperature of 900 °C and an RM/biomass dosage of 3 g each, RM/CSBC exhibited an optimal balance between adsorption performance and cost. Within typical pH range of 6–9 in wastewater, RM/CSBC maintained effective adsorption performance, while metal ion leaching (Fe ≤ 0.3 mg·L⁻¹, Al ≤ 0.2 mg·L⁻¹) complied with Class II surface water standards in China. Kinetic data were well fitted by the pseudo second-order model, supported by the Elovich model, indicating the involvement of both chemical and physical adsorption mechanisms. Isotherm results showed that the Langmuir model provided the best fit, indicating monolayer adsorption, with a maximum capacity of 85.16 mg·g⁻¹ at 25 °C. XPS analysis revealed the formation of AlPO₄ and FePO₄ precipitates, confirming chemical precipitation as a key mechanism, along with electrostatic attraction and physical sorption. This study highlights the feasibility of RM/CSBC as an efficient and low-cost phosphate adsorbent and provides a theoretical basis for phosphorus removal and recovery from wastewater using waste-derived materials.

Soil acidification, salinization, and heavy metal pollution pose serious threats to global food security and sustainable agricultural development. Biochar, with its high porosity, large surface area, and abundant functional groups, can effectively improve soil properties. However, due to variations in feedstocks and pyrolysis conditions, it may contain potentially harmful substances. Industrial wastes such as fly ash, steel slag, red mud, and phosphogypsum are rich in minerals and show potential for soil improvement, but direct application may pose environmental risks. The co-application of biochar with these wastes can produce composite amendments that enhance pH buffering capacity, nutrient availability, and pollutant immobilization. Therefore, a review of biochar-industrial waste composites as soil amendments is crucial for addressing soil degradation and promoting resource utilization of wastes. In this study, the literature was retrieved from Web of Science, Scopus, and Google Scholar using keywords including biochar, fly ash, steel slag, red mud, phosphogypsum, combined application, and soil amendment. A total of 144 articles from 2000 to 2025 were analyzed. This review summarizes the physicochemical properties of biochar and representative industrial wastes, including pH, electrical conductivity, surface area, and elemental composition. It examines their synergistic mechanisms in reducing heavy metal release through adsorption, complexation, and ion exchange. Furthermore, it evaluates the effects of these composites on soil health and crop productivity, showing improvements in soil structure, nutrient balance, enzyme activity, and metal immobilization. Finally, it identifies knowledge gaps as well as future prospects and recommends long-term field trials and digital agriculture technologies to support the sustainable application of these composites in soil management.