Vertical tubular flocculator: Alternative technology for the improvement of drinking water treatment processes in rural areas

The guarantee of access to safe drinking water for rural communities is a great challenge due to the increase in contamination and deterioration of water sources. Rural areas face technological, financial, and operational limitations, having poor water quality, generally. The purpose of this study was to evaluate the efficiency of a vertical tubular flocculator (VTF) to be used as part of the purification process in rural areas where small flows are used. An experimental treatment system (ETS) implemented in the field was used. The VTF was implemented using PVC pipes and fittings. Tests were carried out with the same raw water used from a conventional treatment plant with aluminum sulfate as a coagulant. The optimal coagulant dose applied in the ETS was determined by the jar test. In the VTF, the length, turbidity, and flow of the raw water were varied. The hydraulic behaviour of the VTF was evaluated with the analysis of the time distribution curve of concentration of a tracer applying the Wolf-Resnick model. A low residence time VTF was obtained, representing a new efficient flocculation model for the reduction of turbidity and colour. The results showed that the turbidity of the raw water, the residence time, and the degree of agitation are important parameters in the operation and efficiency of a VTF. There was a predominance of plug flow in the reactor. The obtained results were compared with the efficiency of a conventional water treatment plant used in the study site. The results obtained indicated that this ETS that integrates a VTF with settling and filtration can be a useful tool for rural areas. It was recommended to replicate this study with wastewater, other dimensions of the VTF, to establish a specific methodology for the design of the VTF, to evaluate the dosage with dose bombs for improving the results of VTF, and to elaborate a hydraulic model for VTF.

Hydraulic conductivity of GCL overlap permeated with saline solutions

Hydraulic conductivity of the overlap region of two needle-punched sodium bentonite (Na-B) geosynthetic clay liners (GCLs) permeated with CaCl₂ solutions under confining stresses of 20, 100, 250, and 500 kPa were evaluated. One of the GCLs consisted of a uniform layer of Na-B encapsulated between a nonwoven (NW) and a woven (W) geotextile, and the other one consisted of NW geotextiles on both sides. Supplemental bentonite was placed within the overlap region. Experiments were conducted with 10, 20, and 50 mM CaCl₂ solutions representing dilute and aggressive leachates. The results indicate that in most of the scenarios there is a possibility that the flow is not completely vertical (meaning flow passes through the overlap region horizontally). As the confining stress increased, the horizontal flow through the overlap region for GCLs reduced effectively when permeated with deionized water and 10 mM CaCl₂ solution, whereas the reduction of horizontal flow was limited to 20 mM and 50 mM CaCl₂ solutions.

Municipal Wastewater Treatment uses Vertical Flow Followed by Horizontal Flow in a Two-Stage Hybrid-Constructed Wetland Planted with Calibanus hookeri and Canna indica (Cannaceae)

The utilization of hybrid-constructed wetland systems has recently expanded due to more rigorous municipal wastewater discharge and also complex wastewaters treated in hybrid-constructed wetlands (HCWs). A lab-scale two-stage experimental setup of vertical flow followed by horizontal flow hybrid-constructed wetland (VFHCW-HFHCW) configuration was built. First-stage vertical flow hybrid-constructed wetland reactor with the surface area was 1963.49 cm² and second-stage horizontal flow hybrid-constructed wetland reactor with the surface area was 2025 cm². The HCW unit was planted with two type plants: Calibanus hookeri and Canna indica (Cannaceae). Influent Municipal wastewater flow rate 112.32 l/day, hydraulic loading rate (HLR) 0.55 m/day, and hydraulic retention time of 1 day. The efficiency was evaluated in municipal wastewater quality improvement and physico-chemical analysis in our laboratory. The removal rate after the second-stage horizontal flow of BOD₃ at 27 °C, COD, TSS, TP, NH₃-N, and NO₃-N reached 92.75%, 89.90%, 85.45%, 88.83%, 99.09%, and 96.05%, respectively. The results shown after both stage hybrid-constructed wetland VFHCW-HFHCW, treated effluent of Municipal wastewater produced high-quality effluent which may be reused in gardening, agriculture, and flushing in toilet purpose according to Bureau of Indian Standards (BIS) code for practices. However, in the future, hybrid-constructed wetlands could be standards design criteria developing and enhancing the performance standards and economic meets both to make more popular technology of the hybrid-constructed wetland (HCW).

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11270-022-05984-0.

Vertical flow constructed wetlands using expanded clay and biochar for wastewater remediation: A comparative study and prediction of effluents using machine learning

This study evaluated and compared the performance of two vertical flow constructed wetlands (VF) using expanded clay (VF₁) and biochar (VF₂), of which both are low-cost, eco-friendly, and exhibit potentially high adsorption as compared to conventional filter layers. Both VFs achieved relatively high removal for organic matters (i.e. Biological oxygen demand during 5 days, BOD₅) and nitrogen, accounting for 9.5 - 10.5 g^.BOD₅^.m^-2.d^-1 and 3.5 - 3.6 g^.NH₄-N^.m^-2.d^-1, respectively. The different filter materials did not exert any significant discrepancy to effluent quality in terms of suspended solids, organic matters and NO₃-N (P > 0.05), but they did influence NH₄-N effluent as evidenced by the removal rate of that by VF₁ and VF₂ being of 8₂.4 ± 5.7 and 84.6 ± 6.4%, respectively (P < 0.05). The results obtained from the designed systems were further subject to machine learning to clarify the effecting factors and predict the effluents. The optimal algorithms were random forest, generalized linear model, and support vector machine. The values of the coefficient of determination (R²) and the root mean square error (RMSE) of whole fitting data achieved 74.0% and 5.0 mg^.L^-1, 80.0% and 0.3 mg^.L^-1, 90.1% and 2.9 mg^.L^-1, and 48.5% and 0^.5 mg^.L^-1 for BOD₅_VF₁, NH₄^-N_VF₁, BOD₅_VF₂, and NH₄-N_VF₂, respectively.

Effect of different bypass rates and unit area ratio in hybrid constructed wetlands

This study presents the performance of a hybrid constructed wetland (Bp(VF + HF)_2:1) system which consists of an unsaturated vertical flow (VF) unit followed by a saturated down-flow unit simulating horizontal flow (HF) with HF/VF area ratio of 0.5 and influent bypass to the HF unit. Treating synthetic wastewater simulating municipal wastewater, optimum total nitrogen (TN) removal (57%) was reached at 39% bypass and surface loading rate (SLR) of 33 g BOD₅/m² day and 9.7 g TN/m² day (overall system). On the other hand, treating actual municipal wastewater, the system reached 63% TN removal at 30% bypass and SLR of 18 g BOD₅/m² day and 4.7 g TN/m² day. Surface removal rates reached 5.5 and 3.0 g TN/m² day for synthetic and municipal wastewater. Surface nitrification rate in the VF unit was in the range of 5.0-7.4 and 3.6-3.8 g N/m² day for synthetic and municipal wastewater, respectively, indicating a large effect of wastewater characteristics on the nitrification process. Infiltration rate in the VF unit remained high and far from clogging risk. Overall greenhouse gas emissions were 0.11 (N₂O) and 0.41 (CH₄) g/m² day which corresponded to emissions factors (relative to total organic carbon and TN influent) of 0.7% (N₂O) and 3.6% (CH₄). Compared with a similar system with a different HF/VF area ratio of 2.0, organic matter and nitrogen removal efficiency was similar, but surface removal rates were about 3 times higher.

Zero discharge: Pilot project for biodegradation of cattle effluent by pyroclastic "lapilli" treatment for fodder irrigation

Livestock effluents are a nutrient supply that is beneficial for crops, so their use is essential to guarantee the sustainability of the global management of farms. Zero discharge cattle effluent management to irrigate fodder crops is a mitigation option, so it is considered a key factor for adaptation to climate change. This paper presents the result of an "on site" pilot scale (three-stage, vertical flow filtration system using lapilli). This is a low-cost solution in terms of finance and energy, which does not require the addition of chemicals, to treat a cattle effluent. The effluent's quality obtained allowed it to be injected in a drip system with low risks of obstruction. And the pilot system allowed to obtain elimination values for the main parameters of effluent's quality (TSS and COD, 98% and 80% respectively) similar or greater than the ones obtained in other treatments of low cost and energy, and gives values contemplated in reclaimed water reuse guidelines of many countries. Furthermore, elimination rate for the BOD₅ obtained 35 mgL^-1 in treated effluent. High removal rates were obtained for N, P, K, Cu, Fe and Mn, medium for Ca, Mg and Zn and low for B and Na. These shows that the pilot system and fodder crop combination provide an optimal solution to small farms, controlling sanitary risks. The tested flow allows the use of this system by conventional small farms, which represented 94% of total cow farms in Canary Islands.

Study on the removal of hormones from domestic wastewaters with lab-scale constructed wetlands with different substrates and flow directions

Eight wastewater samples from a university campus were analysed between May and July of 2014 to determine the concentration of 14 natural and synthetic steroid hormones. An on-line solid-phase extraction combined with ultra-high performance liquid chromatography coupled with mass spectrometry (on-line SPE-UHPLC-MS/MS) was used as extraction, pre-concentration and detection method. In the samples studied, three oestrogens (17β-estradiol, estrone and estriol), two androgens (boldenone and testosterone), three progestogens (norgestrel, progesterone and norethisterone) and one glucocorticoid (prednisone) were detected. The removal of hormones was studied in primary and secondary constructed wetland mesocosms. The porous media of the primary constructed wetlands were palm tree mulch. These reactors were used to study the effect of water flow, i.e. horizontal (HF1) vs vertical (VF1). The latter was more efficient in the removal of 17β-estradiol (HF1: 30%, VF1: 50%), estrone (HF1: 63%, VF1: 85%), estriol (100% both), testosterone (HF1: 45%, VF1: 73%), boldenone (HF1:-77%, VF1: 100%) and progesterone (HF1: 84%, VF1: 99%). The effluent of HF1 was used as influent of three secondary constructed wetland mesocosms: two double-stage vertical flow constructed wetlands, one with gravel (VF2gravel) and one with palm mulch (VF2mulch), and a mineral-based, horizontal flow constructed wetland (HFmineral). VF2mulch was the most efficient of the secondary reactors, since it achieved the complete removal of the hormones studied with the exception of 17ß-estradiol. The significantly better removal of BOD and ammonia attained by VF2mulch suggests that the better aeration of mulch favoured the more efficient removal of hormones.

Impacts of design configuration and plants on the functionality of the microbial community of mesocosm-scale constructed wetlands treating ibuprofen

Microbial degradation is an important pathway during the removal of pharmaceuticals in constructed wetlands (CWs). However, the effects of CW design, plant presence, and different plant species on the microbial community in CWs have not been fully explored. This study aims to investigate the microbial community metabolic function of different types of CWs used to treat ibuprofen via community-level physiological profiling (CLPP) analysis. We studied the interactions between three CW designs (unsaturated, saturated and aerated) and six types of mesocosms (one unplanted and five planted, with Juncus, Typha, Berula, Phragmites and Iris) treating synthetic wastewater. Results show that the microbial activity and metabolic richness found in the interstitial water and biofilm of the unsaturated designs were lower than those of the saturated and aerated designs. Compared to other CW designs, the aerated mesocosms had the highest microbial activity and metabolic richness in the interstitial water, but similar levels of biofilm microbial activity and metabolic richness to the saturated mesocosms. In all three designs, biofilm microbial metabolic richness was significantly higher (p < .05) than that of interstitial water. Both the interstitial water and biofilm microbial community metabolic function were influenced by CW design, plant presence and species, but design had a greater influence than plants. Moreover, canonical correlation analysis indicated that biofilm microbial communities in the three designs played a key role in ibuprofen degradation. The important factors identified as influencing ibuprofen removal were microbial AWCD (average well color development), microbial metabolic richness, and the utilization of amino acids and amine/amides. The enzymes associated with co-metabolism of l-arginine, l-phenyloalanine and putrescine may be linked to ibuprofen transformations. These results provide useful information for optimizing the operational parameters of CWs to improve ibuprofen removal.

Effect of step-feeding on the performance of lab-scale columns simulating vertical flow-horizontal flow constructed wetlands

The effect of step-feeding (untreated wastewater by-pass) on the performance of lab-scale columns simulating a hybrid vertical flow (VF)-horizontal flow (HF) constructed wetland (CW) system was studied. Step-feeding strategies have been adopted in several kinds of CW, but this is the first report about the use of step-feeding in VF + HF hybrid systems treating domestic wastewater. Applied loading rates were 7-11 g BOD₅/m² day and 2.1-3.4 g TN/m² day (overall system). Removal efficiency reached 98% TSS and COD and 99% BOD₅ on average, whilst a 50% by-pass improved TN removal from 31 to 50%. Maximum surface nitrification rate (5.5 g N/m² day) was obtained in VF unit, whilst maximum denitrification rate (1.8 g N/m² day) was observed in HF unit. Referred to the overall system, maximum surface nitrification and denitrification rates were 2.2 and 1.6 g N/m² day, respectively. However, potential nitrifying and denitrifying activities (batch assays) were 15.0 and 58.9 g N/m² day, respectively. Even at 50% by-pass, operational conditions in HF unit (dissolved oxygen, redox, COD/TN ratio) were not suitable enough for denitrification. However, methane emissions were not observed and nitrous oxide emissions were relatively low.

Wind-induced flow velocity effects on nutrient concentrations at Eastern Bay of Lake Taihu, China

Shallow lakes are highly sensitive to respond internal nutrient loading due to wind-induced flow velocity effects. Wind-induced flow velocity effects on nutrient suspension were investigated at a long narrow bay of large shallow Lake Taihu, the third largest freshwater lake in China. Wind-induced reverse/compensation flow and consistent flow field probabilities at vertical column of the water were measured. The probabilities between the wind field and the flow velocities provided a strong correlation at the surface (80.6%) and the bottom (65.1%) layers of water profile. Vertical flow velocity profile analysis provided the evidence of delay response time to wind field at the bottom layer of lake water. Strong wind field generated by the west (W) and west-north-west (WNW) winds produced displaced water movements in opposite directions to the prevailing flow field. An exponential correlation was observed between the current velocities of the surface and the bottom layers while considering wind speed as a control factor. A linear model was developed to correlate the wind field-induced flow velocity impacts on nutrient concentration at the surface and bottom layers. Results showed that dominant wind directions (ENE, E, and ESE) had a maximum nutrient resuspension contribution (nutrient resuspension potential) of 34.7 and 43.6% at the surface and the bottom profile layers, respectively. Total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP) average concentrations were 6.38, 1.5, and 0.03 mg/L during our field experiment at Eastern Bay of Lake Taihu. Overall, wind-induced low-to-moderate hydrodynamic disturbances contributed more in nutrient resuspension at Eastern Bay of Lake Taihu. The present study can be used to understand the linkage between wind-induced flow velocities and nutrient concentrations for shallow lakes (with uniform morphology and deep margins) water quality management and to develop further models.

Integrating pretreatment and denitrification in constructed wetland systems

The aim of this work was to study the operational characteristics and the efficiency of a compact constructed wetland system for municipal wastewater treatment that integrates denitrification in the pre-treatment unit. The proposed system was simulated by two units in series with effluent recirculation, the first one being an anoxic digester, conceived as a hydrolytic up flow sludge bed for solids hydrolysis and denitrification, and the second one a sand column that simulated the operation of a vertical flow constructed wetland. The hybrid system consisted of two small columns of 4 and 10.2cm in diameter (anoxic digester and vertical flow unit, respectively). The unplanted system was operated successively with synthetic and real municipal wastewater over a period of 136days. Hydraulic loading rate ranged from 212 to 318mm/day and surface loading rate from 122 to 145g/m²·day of chemical oxygen demand and 10-15g/m²·day of total nitrogen for the overall system. The overall system reached removals of 91% to 99% for total suspended solids, chemical oxygen demand and biochemical oxygen demand whilst total nitrogen removal ranged from 43% to 61%. In addition to suspended solids removal (up to 78%), the anoxic digester provided high denitrification rates (3-12gN/m²·day) whilst the vertical flow unit provided high nitrification rates (8-15gN/m²·day). Organic matter was mainly removed in the anoxic digester (63-82% chemical oxygen demand) and used for denitrification. Final effluent concentration was lower for ammonia (7.4±2.4mgN/L on average) than for nitrate (19.8±4.4mgN/L), denitrification appearing as the limiting step in nitrogen removal in the system. CH₄ or N₂O emissions were not detected in any of the units of the system indicating very low greenhouse gas emissions.

Different leachate phytotreatment systems using sunflowers

The use of energy crops in the treatment of wastewaters is of increasing interest, particularly in view of the widespread scarcity of water in many countries and the possibility of obtaining renewable fuels of vegetable origin. The aim of this study was to evaluate the feasibility of landfill leachate phytotreatment using sunflowers, particularly as seeds from this crop are suitable for use in biodiesel production. Two different irrigation systems were tested: vertical flow and horizontal subsurface flow, with or without effluent recirculation. Plants were grown in 130L rectangular tanks placed in a special climatic chamber. Leachate irrigated units were submitted to increasing nitrogen concentrations up to 372mgN/L. Leachate was successfully tested as an alternative fertilizer for plants and was not found to inhibit biomass development. The experiment revealed good removal efficiencies for COD (η>50%) up until flowering, while phosphorous removal invariably exceeded 60%. Nitrogen removal rates decreased over time in all experimental units, particularly in vertical flow tanks. In general, horizontal flow units showed the best performances in terms of contaminant removal capacity; the effluent recirculation procedure did not improve performance. Significant evapo-transpiration was observed, particularly in vertical flow units, promoting removal of up to 80% of the inlet irrigation volume.

The use of hybrid constructed wetlands for wastewater treatment with special attention to nitrogen removal: a review of a recent development

The hybrid systems were developed in the 1960s but their use increased only during the late 1990 s and in the 2000s mostly because of more stringent discharge limits for nitrogen and also more complex wastewaters treated in constructed wetlands (CWs). The early hybrid CWs consisted of several stages of vertical flow (VF) followed by several stages of horizontal flow (HF) beds. During the 1990 s, HF-VF and VF-HF hybrid systems were introduced. However, to achieve higher removal of total nitrogen or to treat more complex industrial and agricultural wastewaters other types of hybrid constructed wetlands including free water surface (FWS) CWs and multistage CWs have recently been used as well. The survey of 60 hybrid constructed wetlands from 24 countries reported after 2003 revealed that hybrid constructed wetlands are primarily used on Europe and in Asia while in other continents their use is limited. The most commonly used hybrid system is a VF-HF constructed wetland which has been used for treatment of both sewage and industrial wastewaters. On the other hand, the use of a HF-VF system has been reported only for treatment of municipal sewage. Out of 60 surveyed hybrid systems, 38 have been designed to treat municipal sewage while 22 hybrid systems were designed to treat various industrial and agricultural wastewaters. The more detailed analysis revealed that VF-HF hybrid constructed wetlands are slightly more efficient in ammonia removal than hybrid systems with FWS CWs, HF-VF systems or multistage VF and HF hybrid CWs. All types of hybrid CWs are comparable with single VF CWs in terms of NH4-N removal rates. On the other hand, CWs with FWS units remove substantially more total nitrogen as compared to other types of hybrid constructed wetlands. However, all types of hybrid constructed wetlands are more efficient in total nitrogen removal than single HF or VF constructed wetlands.