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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.

Background Phthalic acid esters, including diethyl phthalate (DEP), which are considered as top-priority and hazardous pollutants, have received significant attention over the last decades. It is vital for industries to select the best treatment technology, especially when the DEP concentration in wastewater is high. Meanwhile, anaerobic biofilm-based reactors are considered as a promising option. Therefore, in the present study, for the biological removal of DEP from synthetic wastewater, two different anaerobic biofilm-based reactors, including anaerobic fixed film baffled reactor (AnFFBR) and up-flow anaerobic fixed film fixed bed reactor (UAnFFFBR), were compared from kinetic and performance standpoints. As in the previous studies, only the kinetic coefficients have been calculated and the relationship between kinetic coefficients and their interpretation has not been evaluated, the other aim of the present study was to fill this research gap. Results In optimum conditions, 90.31 and 86.91% of COD as well as 91.11 and 88.72% of DEP removal were achieved for the AnFFBR and UAnFFFBR, respectively. According to kinetic coefficients (except biomass yield), the AnFFBR had better performance as it provided a more favorable condition for microbial growth. The Grau model was selected as the best mathematical model for designing and predicting the bioreactors’ performance due to its high coefficients of determination (0.97 < R 2). With regard to the insignificant variations of the calculated Grau kinetic coefficients (K G) when the organic loading rate (with constant HRT) increased, it can be concluded that both of the bioreactors can tolerate high organic loading rate and their performance is not affected by the applied DEP concentrations. Conclusions Both the bioreactors were capable of treating low-to-high strength DEP wastewater; however, according to the experimental results and obtained kinetic coefficients, the AnFFBR indicated higher performance. Although the AnFFBR can be considered as a safer treatment option than the UAnFFFBR due to its lower DEP concentrations in sludge, the UAnFFFBR had lower VSS/TSS ratio and sludge yield, which could make it more practical for digestion. Finally, both the bioreactors showed considerable methane yield; however, compared to the UAnFFFBR, the AnFFBR had more potential for bioenergy production. Although both the selected bioreactors achieved nearly 90% of DEP removal, they can only be considered as pre-treatment methods according to the standard regulations and should be coupled with further technology.

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.

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.

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.

A 45 m3/d field-scale anaerobic baffled reactor (ABR) was studied for its performance to remove carbonaceous organic content and suspended solids under a dynamic hydraulic loading rate (HLR) and organic loading rate (OLR). Sludge granulation effect was also assessed with and without sand as a bio-carrier aided with poly aluminium chloride. ABR was subjected to a significant variation in HLR (0.26 to 7.72 m3/m2.d) and OLR (0.03 to 8 kg COD/m3.d). Tracer study showed flow-through time was 50% of theoretical hydraulic retention time. The initial compartments of ABR were more effective for the removal of organic carbon. An overall CODTotal removal of 60 to 90% was possible for OLR in the range 1 to 8 kg COD/m3.d irrespective of low/high HLR. OLR dominated the performance of ABR compared to HLR. The compartmentalized nature of ABR was visualized through a two-phase system of anaerobic digestion as alkalinity increased while VFA decreased from the first to last compartment even under dynamic conditions. Sludge granulation with sand and PAC increased the size of granule from 629 to 1,471 μm, decreased sludge depth by 20% and enhanced CODTotal removal within a month. ABR is sturdy to sustain low/high HLR with low/high OLR conditions without impairing CODTotal removal efficiency significantly.

In this study, a decentralized new sewage water treatment system is suggested and designed in Ar Riyadh, Saudi Arabia, to safeguard the environment and reuse treated water for irrigation purposes. The system consists of a primary treatment (septic tank), a subsurface horizontal flow constructed wetland (HSSF-CW), and a storage ground tank. The research methodology employed in this study is (i) to define the wastewater characteristics, where air temperature in winter is 18.6 °C, the wastewater flow per person (q) is 150 L/d, demonstrating an inlet design discharge of 300 m3/d, the influent pollutant concentrations for biological oxygen demand (BOD), total suspended solids (TSS), chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), and fecal coliforms (FC) are 350, 1000, 700, 50, 12 mg/L, and 106 CFU/100 mL, respectively; (ii) to design the septic tank based on a retention time of two days and a surfacing load rate of 1.5 m/d; (iii) the P-k-C* model was used to determine the HSSF-CW surface area based on reed beds of Phragmites australis (common reed) and papyrus plants, where the removal rate was constant at 20 °C for BOD, TP, and FC in the effluent concentrations not exceeding 20 mg/L, 3.0 mg/L, and 2000 CFU/100 mL in order to satisfy Saudi Arabia’s wastewater reuse requirements; and (iv) to design the clean water tank for a hydraulic retention time of 10 h. The results demonstrate that the removing pollutants design area is 1872 m2 divided into nine cells, each of width 8 m and length 26 m, with a hydraulic loading rate (LR) of 0.16 m/d and a hydraulic resident time (RT) of 1.1 d. The effluent pollutant concentrations for the BOD, FC, TN, and TP were 245 mg/L, 103 CFU/100 mL, 35, and 8.5 mg/L, respectively. The wastewater treatment system total removal efficiencies for BOD, TN, TP, and FC were estimated to be 91.8, 70, 57, and 98.5%, respectively. Design curves were developed to ease the design steps. The HSSF-CW is a green wastewater treatment technology that offers greatly decreased investment costs, and service particularly for small-scale applications up to 6000 persons.