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In order to solve the advanced treatment problem of industrial wastewater and simultaneously satisfy the needs of ecological and park mode construction, the process of “efficient three-dimensional ecology + constructed wetland” was designed and applied. The technological process, ecological design, operational effect, and technical and economic analysis of the project were systematically described. After stable operation for 12 months, the average removal rates of COD cr , BOD 5 , SS, NH 3 -N, TN, and TP were 86.13%, 81.19%, 90.86%, 97.97%, 84.03%, and 80.85%, respectively. The effluent of the system could meet the Class III standard requirements of “Environmental Quality Standards for Surface Water” (GB3838-2002), achieving high-quality effluent and resource utilization.

Downstream scour at grade-control structures (GCSs) poses a serious threat to structural stability and riverbed integrity. Among various countermeasures, riprap has long been recognized as a cost-effective and readily available solution for scour protection. This research examines the role of riprap in reducing scour downstream of a vertical drop GCS, with emphasis on the influence of riprap thickness (T r /h, where h is structure height) and tailwater depth (y t /h). Experiments were conducted under clear-water conditions to monitor both the temporal and spatial development of scour and to establish new empirical relationships for normalized maximum scour depth (d s /h) and length (l s /h). The results show that riprap substantially reduces scour dimensions and accelerates stabilization. In the absence of protection, maximum scour depth reached up to 1.2 h under high discharges. Increasing riprap thickness to T r /h ≈ 0.5 reduced scour by nearly 70% and further increases to T r /h ≈ 0.66 achieved reductions exceeding 89%, with scour almost eliminated at low flows. Tailwater depth provided an additional stabilizing effect, reducing jet impact velocity and vortex intensity. Doubling the tailwater depth decreased scour by 20–30%, and when combined with thick riprap layers, reductions greater than 90% were achieved in both depth and length. The proposed empirical equations demonstrated strong predictive capability for both d s /h and l s /h, yielding R² values of 0.913 and 0.902, RMSE values of 0.107 and 0.405, and MAE values of 0.082 and 0.310, respectively. The sensitivity analysis further identified riprap thickness and tailwater depth as the most influential parameters governing the protective performance. These findings confirm the riprap effectiveness as a simple, economical, and robust strategy for mitigating downstream scour, offering valuable guidance for the hydraulics and geotechnical design of grade-control systems.

At the confluence zone, the separation zone affects the flow, pollutant transport, and damages the bed and sidewalls of the channel. In this research, the geometric characteristics of the separation zone and the tailwater effect at the 90° channel–pipe junction are investigated using experiments and numerical simulations. These characteristics are different from the previous study in the channel or river junctions. (1) The separation zone is not attached to the sidewall of the channel. The shape of the separation zone is close to an ellipse but there is depression at the inside of the separation zone. (2) There is a pair of helical cells with opposite flow directions near the sidewall, which affects the shape of the separation zone and results in the differences. (3) The volume of the separation zone is proportional to the discharge ratio and the water-surface height. Furthermore, it's found that the momentum ratio is the basic reason affecting the volume of the separation zone. (4) The tailwater effect is affected by the discharge ratio and the water-surface height. And there is a significant positive correlation between the volume of separation zone and tailwater effect.

In the process of geothermal tailwater reinjection of sandstone, the problem of plugging has been seriously restricting the continuous development of geothermal reinjection for many years, and the problems of plugging are complex and changeable. The plugging in the process of reinjection can be divided into physical plugging, chemical plugging, microbial plugging and gas plugging. Given these four types of blocking, according to the mechanism characteristics of the blocking caused by them, this paper puts forward corresponding blocking prevention measures and solves the current blocking problems by filtering, adding a scale inhibitor, intermittent reinjection, adding chlorine dioxide and regular lifting. In addition, the existing reinjection process and the equipment flow are relatively simple and cannot achieve the goal of efficient reinjection. Therefore, a complete set of reinjection processes is designed to ensure the efficient reinjection of sandstone geothermal tailwater.

The discharge of treated effluent from sewage treatment plants, commonly referred to as tailwater, can lead to particular pollution in the receiving water bodies. Constructed wetlands (CWs) represent a cost-effective and straightforward approach to tailwater treatment. However, they often have a limited capacity for removing residual chemical oxygen demand (COD) and nitrogen due to poor biodegradability of the remaining organic substances, resulting in insufficient carbon sources for denitrification. To address these constraints, a synergistic combination of plant-derived carbon sources and zeolite-loaded nano-zero-valent iron (Z-nZVI) materials were employed to enhance the nitrogen removal efficiency within CWs. Z-nZVI facilitated the transformation of nitrate (NO 3 − –N) and nitrite (NO 2 − –N) into ammonium (NH 4 + –N), which was subsequently eliminated via zeolite adsorption through physical–chemical processes. Then, introducing plant carbon source (PCS) augmented biological denitrification. Under optimized conditions with a C/N ratio of 3.5, the addition of both PCS and Z-nZVI led to removal rates of 85.34 ± 2.44% for NH 4 + –N, 85.24 ± 1.58% for NO 3 − –N, and 84.32 ± 0.77% for total nitrogen (TN) in the CW system. These represented average improvements of 17.37%, 60.48%, and 51.50% for NH 4 + –N, NO 3 − –N, and TN respectively, compared to the control wetland without intervention. This study introduces a novel strategy to boost nitrogen removal efficacy in treated wastewater within CWs, utilizing PCS and Z-nZVI, thus offering a valuable reference for treating low C/N ratio wastewater in CWs.

The operational instability of hydraulic turbine units poses a prevalent and significant challenge. Pressure pulsations occupy a prominent position among the primary factors contributing to turbine vibrations. Consequently, exploring the correlation between the internal flow field and pressure pulsations within hydraulic turbines constitutes a pivotal research focus in the contemporary vibration studies of such units. In this study, a three-dimensional geometric model of the Wudongde Francis turbine was developed. Using ICEM CFD for meshing, the internal flow conditions of the turbine’s entire flow passage were simulated in CFX software, focusing on analyzing flow characteristics and internal flow field attributes under 510 MW and 764 MW operating conditions. The results indicate the emergence of a pronounced blade vortex phenomenon under the 510 MW operating scenario, whereas at 764 MW, which approximates the rated operating condition, the runner blade vortex phenomenon diminishes markedly. Furthermore, the central vortex rope observed under the 510 MW condition induces severe pressure pulsations. Conversely, under the 764 MW condition, the central vortex rope aligns nearly vertically downward from the tailwater inlet’s center, exerting minimal influence on the adjacent flow patterns and substantially reducing pressure pulsations.

Experimental tests were carried out to investigate the effective scouring parameters downstream from stepped spillways with different flow rates and step sizes. The results indicated that the flow regime plays an important role in scour-hole dimensions such that the minimum scouring depth happens in the nappe flow regime. Moreover, step size and tailwater depth are essential parameters for maximum scouring depth. Increasing tailwater depth from 6.31 cm to 8.54 cm and then to 11.82 cm decreases the scouring depth by 18.56% and 11.42%, respectively. These alterations also decrease the scouring length by 31.43% and 16.55%, respectively. By increasing the flow rate, the particle Froude number will increase, and the increased momentum of the flow promotes scouring. In addition, the results show that scouring at the sidewalls is higher than in the middle of the cross-section. Finally, an empirical formula with root mean square error = 0.107 and R2 = 0.974 is proposed to predict the maximum scouring depth downstream from the stepped spillways. Comparisons were made between the proposed formula and experimental results. This comparison demonstrated that the formula can predict souring depth to within 3.86% and 9.31% relative and maximum errors, respectively.

The role of weirs in flow regulation in water resources infrastructure and flood control is well known. In the meantime, the study of full-width plate weirs (FWPW), due to their wide application and lacking findings, is of great importance. In this study, experimental models were conducted at Babol Noshirvani University of Technology to investigate flow passing through FWPWs with five different heights (p = 0.07, 0.09, 0.11, and 0.15 m) under eight discharge conditions (Q = 1.4 to 6.3 L/s). The experiments were carried out in a flume measuring 4 m in length, 0.6 m in width, and 0.2 m in height. The discharges were measured with a calibrated flowmeter, and the water depths upstream of the weir (h) and the tailwater depths (h1) were measured with a point gauge with an accuracy of 0.1 mm. For each test, the discharge coefficient (Cd), relative residual energy (E1/E0), and relative energy dissipation ((E0 − E1)/E0) were computed. The proposed equation for calculating discharge achieved good accuracy with RMSE = 0.0002, MAE=0.0002, and R2 = 0.997. Results show a reducing trend of Cd by increasing h/P, which is compatible with previous results. It was observed that at a constant discharge, relative residual energy reduces by an average of 47% by increasing weir height, and at a constant P, increasing flow discharge increases it a little. A novel accurate equation for relative energy dissipation in FWPW was proposed based on h/P that provided specific constant coefficients for each p value.

Conventional pretreatment and secondary biochemical treatment are ineffective methods for removing phosphorus from phosphorus-containing pesticide wastewater. In this study, coagulation-coupled ozone catalytic oxidation was used to treat secondary biochemical tailwater of phosphorus-containing pesticide wastewater thoroughly. The effects of the coagulant type, coagulant dosage, coagulant concentration, wastewater pH, stirring rate, and stirring time on the removal efficiency of chemical oxygen demand (COD), total phosphorus (TP), and chromaticity were investigated during coagulation. When the dosage of the coagulant PAFS was equal to 100 mg/L, the concentration of the coagulant, pH, stirring rate, and stirring time were 5 wt%, 8, 100 rpm, and 5 min, respectively, and the removal rates of COD, TP, and chroma in wastewater reached the maximum value of 17.6%, 86.8%, and 50.0%, respectively. Effluent after coagulation was treated via ozone catalytic oxidation. When the respective ozone dosage, H2O2 dosage, catalyst dosage, and reaction time were 120 mg/L, 0.1 vt‰, 10 wt%, and 90 min, residual COD and chromaticity of the final effluent were 10.3 mg/L and 8, respectively. The coagulation-coupled ozone catalytic oxidation process has good application prospects in the treatment of secondary biochemical tailwater from phosphorus-containing pesticide wastewater.