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Electro-hydraulic loading system (EHLS) has been widely utilized in rail grinding industry for rail maintenance. Accurate tracking of the desired grinding force is critical to keep the rail surface at expected level. However, uncertain nonlinear friction, unmodeled nonlinearities of hydraulic systems, and high-frequency motion disturbances caused by random rail corrugations usually deteriorate the force tracking performance. To resolve this problem, a neural adaptive dynamic surface control strategy is designed. To efficiently address the uncertainties and disturbances of the single-rod EHLS, a radial basis function neural network (RBFNN) is developed and trained by adequate measurement data to approximate the nonlinear friction, then two nonlinear disturbance observers that integrate the RBFNN are constructed to estimate the matched and unmatched disturbances. Furthermore, the neural network weights are updated adaptively via the tracking error, which enhance the dynamic learning ability of the neural network. And, dynamic surface control (DSC) instead of traditional backstepping method is applied to construct the composite controller to avoid the “explosion of complexity”. Simulation and experimental results of force tracking prove the effectiveness and potential application value of the designed control strategy.

Effluent concentrations from horizontal flow (HF) treatment wetlands can be estimated by using the Tanks-In-Series model for describing hydraulics and first-order removal rate coefficients for describing pollutant removal. In the design of conventional wastewater treatment plants, volumetric removal rate coefficients (kV) are traditionally used in conjunction with the theoretical hydraulic retention time. Areal removal rate coefficients (kA) coupled with the applied areal hydraulic loading rate are widely used in the literature. Despite this, supporting evidence of its appropriateness is scarce in the literature. The objective of this study is to investigate the adequacy of both approaches by analyzing the influence of liquid depth on kV and kA. Data from 74 HF wetlands were collected, covering biochemical oxygen demand and chemical oxygen demand, and diverse types of influents (raw sewage and primary, secondary and tertiary effluents). For these conditions, kV decreased with depth of the wetland system. Regression analyses between depth and removal rate coefficients were performed, and the equations indicated that kV was approximately related to the inverse of depth, while kA was almost independent of depth. These findings endorse the utilization of the areal-based approach for design purposes. The volumetric-based approach can also be used, but the value of kV must be provided together with the depth being considered.

Operation conditions considerably affect the removal efficiency of wastewater treatment systems, and yet we still lack data on how these systems function under extreme dilution rates and climatic conditions at high altitudes. Here, we applied two modified First-Stage French Vertical Flow Constructed Wetlands (FS-FVFCWs) for sewage treatment in Northern Tropical Andes. Specifically, within 18 months, we conducted a pilot-scale experiment at two hydraulic loading rates (HLRs) of 0.94 and 0.56 m d−1, representing 2.5 and 1.5 times the recommended design values, with two different feeding/resting periods to investigate the impact of HLRs and operational strategy on system performance. We found that chemical oxygen demand (COD) and total suspended solids (TSS) removal was satisfactory, with average values of 53 ± 18 and 69 ± 16%, respectively. Moreover, reducing HLRs resulted in higher removal efficiency for COD, from 46 ± 15 to 64 ± 15%, but had no impact on TSS removal, with 3 days of feeding and 6 days of resting. For an equal time of feeding and resting, COD and TSS removals were not affected by the modified HLR. These findings suggest that high HLRs can be applied to FS-FVFCW without compromising the system operation and obtaining satisfactory results, leading to opportunities to reduce areas and costs.

Biofilters based on earthworms–microorganisms represent, particularly in developing countries, an interesting alternative for domestic wastewater treatment due to their easy operation and low cost. However, there are several operational aspects that should be better understood in order to improve their performance. This paper studies the effect of using intermittent hydraulic loading rates to improve organic matter and nutrient removal from domestic wastewater using these biofilters. Three laboratory-scale columns, operating at a 2.5 m3 m−2day−1 hydraulic loading rate, were used. The B1–24 h, B2–8 h, B3–4 h column loading rates indicate that the columns were operated continuously for 24, 8 and 4 h, respectively. Each column (biomass biofilm/earthworms, redox potential, and head loss) and its corresponding operational performance parameters (TCOD, NH4+, NO3−, NO2−, TP) were monitored. The results showed that the B2–8 h intermittent hydraulic loading rate results in the best global performance, with 74%, 57%, and 20% average removal efficiencies for TCOD, nitrogen, and phosphorus, respectively. Moreover, it showed the best biomass growth (biofilm and earthworms), activity (as redox potential changes) and the lowest clogging effects (up to −1.0 cm). The intermittent operation influences the behavior of the earthworm–microorganism biofilters and offers the possibility of optimizing its global performance and achieving a resilient technology.

Sludge management is one of the most costly and technically challenging components of municipal wastewater treatment, highlighting the need for sustainable and low-cost stabilization technologies. This study evaluated a pilot-scale vermifiltration system for municipal sewage sludge stabilization under varying hydraulic and organic loading conditions. Three vermifilter pilots incorporating Eisenia andrei earthworms were operated using lightweight expanded clay aggregate (LECA), high-density polyethylene (HDPE) plastic media, and mineral pumice. The systems were tested at hydraulic loading rates (HLRs) of 150, 300, and 450 L/m2·d. Performance was assessed using chemical oxygen demand (COD), total solids (TS), volatile solids (VS), VS/TS ratio, sludge volume index (SVI), and sludge dewaterability indicators, including specific resistance to filtration (SRF) and time to filtration (TTF). Optimal performance occurred at an HLR of 150 L/m2·d, achieving maximum reductions of 49% in COD, 30% in TS, and 40% in VS, along with an SVI reduction of up to 78%. Increasing HLR significantly reduced treatment efficiency due to shorter retention times and biofilm washout. A regression analysis showed the strongest association between COD removal and organic loading rate (R2 = 0.63) under the coupled HLR–OLR conditions tested, while weaker correlations were observed for SVI and VS/TS. Dewaterability improved markedly after vermifiltration, particularly in the LECA-based system. Although filter media type did not significantly affect COD or SVI removal, pumice and plastic media provided greater hydraulic stability at higher loadings. These results demonstrate that vermifiltration is an effective and environmentally sustainable option for municipal sludge stabilization when operated under controlled hydraulic conditions.

Rapid population growth and urbanization has put a lot of stress on existing water bodies in most developing countries such as the Marriott Lake of Egypt. Three constructed wetland configurations including Typha angustifolia planted with enhanced atmospheric aeration by using perforated pipes networks (CWA), planted without perforated pipe network (CWR), and a control non-planted and without perforated pipes wetland (Control) were used in the study. Changes in physicochemical properties and microbial community over four seasons and hydraulic loading rate (HLR) (50, 100, 200, 300, and 400 L day −1  m −1 ) were monitored using influent from Marriott Lake in Egypt. Overall, the removal performance followed the sequence CWA>CWR>control . Turbidity removal of 98.4%; biochemical oxygen demand (BOD 5 ) removal of 83.3%; chemical oxygen demand (COD) removal of 95.8%; NH 3 -N removal of 99.9%; total nitrogen (TN) removal of 94.7%; NO 3 − -N and NO 2 − -N increased; total P (TP) removal of 99.7%, Vibrio sp. of 100%, Escherichia coli 100%; total bacterial count of 92.3%; and anaerobic bacteria reduction of 97.5% were achieved by using CWA. Seasonal variation and variation in HLRs had significant effect on performance. The modified planted CWA system enhances the removal of pollutants and could present a novel route for reducing the cost associated with integrating artificial aeration into wetlands.

Effects of seasons and hydraulic loading rates (HLR) on the treatment performance and the response of the microbial community of vertical flow constructed wetland treating tail water were investigated. The seasonal treatment performance was evaluated at four HLR of 125, 250, 375 and 500 mm/d, respectively. The microbial community was detected by MiSeq Illumina platform at HLR 125 and 375 mm/d. The wetland showed significantly higher chemical oxygen demand (COD) and total nitrogen (TN), total phosphorus (TP) at HLR 125 mm/d, compared with other HLR. Overall removal efficiency was 61.47%, 71.40% and 76.31% for COD, TN and TP, respectively, while no significant differences for COD, TN and TP removal were found at HLR of 250, 375 and 500 mm/d. The best removal efficiency for COD and TN was achieved in summer and autumn, while the best TP removal was achieved in winter. Nitrification bacteria (Nitrosomonas and Nitrospira) were significantly higher in HLR 125 mm/d, whereas sequences associated with denitrification had no significant difference at the two HLR. The results can partially explain the significantly higher NH4+-N removal in HLR 125 mm/d and relatively low nitrogen performance in winter.

Surface runoff in mining areas transports dissolved and suspended particles into water bodies, known as mine spoil rainwater, contributing to increases in turbidity. The aim of this study was to evaluate the effectiveness of horizontal flow wetlands, free water surface (FWS), and subsurface flow (HSSF) in reducing turbidity >1500 NTU from a synthetic mine spoil rainwater. Macrophytes, support media, hydraulic retention time (HRT), and hydraulic loading rate (HLR) were analyzed. The HSSF T. domingensis in gravel #1 achieved a 99% reduction for 4-day HRT, with residual turbidity of 7 ± 3 NTU for 27.43 L m−2 d−1 HLR. The FWS P. stratiotes achieved a 99% reduction for 6-day HRT, with residual turbidity of 11 ± 5 NTU for 36.53 L m−2 d−1 HLR. P. stratiotes free root structures promoted interception of suspended colloidal particles, resulting in a better performance. The dense root structure of T. domingensis spreading through the pores of the substrate provided better efficiency than N. humboldtiana. However, N. humboldtiana proved to be promising as a native species. The use of small granulometry alkaline support media (9 to 19 mm) was highlighted. Therefore, this research proves the efficiency of constructed wetlands in reducing high turbidity and provides optimized parameters for this technology application.

With the utilization of underground space, backward erosion piping (BEP) has been observed in many underground structures. Different from BEP in embankments or river dikes, the BEP in underground structures is usually triggered by a sudden flow of water and persists in a “progression phase,” in which the piping process can always reach an equilibrium before higher hydraulic loads are employed. In this study, the progression of BEP with sudden and gradual hydraulic loads was investigated using a radial Hele-Shaw cell. The test results indicated that the progression of BEP could be strongly influenced by the hydraulic loading speed. Once a faster hydraulic loading method was employed, the erodible medium could organize itself and show a greater resistance to erosion; additionally, the erosion pattern could be more uniform. These findings were included in a discussion of the erosion mechanism.

The study evaluates optimum hydraulic loading rate (HLR) based on the fish and plant production performance and nutrient removal percentage in aquaponics. The growth of Gotukola (Centella asiatica (L.))—a leafy vegetable as well as traditional medicinal plant—and koi carp (Cyprinus carpio var. koi.)—a high demand ornamental fish—were evaluated at three different HLRs, viz. 2.6 m day−1 (T1), 7.8 m day−1 (T2), and 13.0 m day−1 (T3). Treated aquaculture wastewater was utilized in a combination of the freshwater in 1:1 ratio with 2.1 kg m−3 fish stocking density. The highest fish mean length; weight; feed conversion ratio; specific growth rate; NH3, NO2−, and NO3− removal percentage; and plant growth parameters were observed. Considering fish (koi carp) and plants (Gotukola) growth parameters as well as nutrient removal percentages, a HLR of 7.8 m day−1 was found to be the optimum in aquaponics.