Use of broken brick to enhance the removal of nutrients in subsurface flow constructed wetlands receiving hospital wastewater

The role of plant uptake in total phosphorous and total nitrogen removal in vegetated bioretention cells using vetiver and cattail

Bioretention cells have emerged as a prominent strategy for mitigating pollutant loads within urban stormwater runoff. This study delves into the role of plant uptake in the simultaneous removal of nitrogen and phosphorus compounds within these systems. Three bioretention cells-CP, P1, and P2-were constructed using local soil, C33 sand, and gravel. CP served as the unvegetated control, while P1 and P2 were vegetated with vetiver and cattail, respectively. The removal efficiencies of NO₃⁻-N, NH₃⁻-N, NO₂⁻-N, TN, TP, and COD from rainwater were evaluated under saturated and unsaturated conditions. The unvegetated control reactor (CP) achieved TN and TP removal rates of 40.44% and 82.52%, respectively. Reactor P1 (vetiver) demonstrated TN and TP removal rates of 62.92% and 97.19%, respectively. Reactor P2 (cattail) showed TN and TP removal rates of 49.71% and 87.78%, respectively. With the introduction of a saturation zone, TN removal efficiencies increased to 51.69%, 89.22%, and 79.91% for CP, P1, and P2, respectively. However, TP removal efficiencies decreased to 74.81%, 95.04%, and 84.58% for CP, P1, and P2, respectively. Plant tissue uptake tests indicated that vetiver could retain 5 times more TN and twice as much TP compared to cattail. This enhanced performance is attributed to vetiver's high photosynthetic potential as a C4 plant, resilience to varying environmental and nutrient conditions, extensive root network, secretion of oil sesquiterpenes from its root cortex, and the presence of arbuscular mycorrhizal fungi, which secrete glomalin, a substance that promotes water retention and nutrient uptake. Findings from this study indicate that the efficacy of traditional bioretention cells can be augmented through the strategic selection and integration of locally adapted plant species, coupled with the incorporation of saturation zones, to enhance pollutant removal capabilities and resilience to drought conditions.

Removal of pharmaceutical contaminants from hospital wastewater using constructed wetlands: a review

AbstractPharmaceutical compounds are a significant source of environmental pollution, particularly in hospital wastewater, which contains high concentrations of such compounds. Constructed wetlands have emerged as a promising approach to removing pharmaceutical compounds from wastewater. This paper aims to review the current state of knowledge on the removal of pharmaceutical compounds from hospital wastewater using constructed wetlands, including the mechanism of removal, removal efficiency, and future prospects. Pharmaceutical contaminants have been considered to be one of the most emerging pollutants in recent years. In this review article, various studies on constructed wetlands are incorporated in order to remove the pharmaceutical contaminants. The nature of constructed wetland can be explained by understanding the types of constructed wetland, characteristics of hospital wastewater, removal mechanism, and removal efficiency. The results of the review indicate that constructed wetlands are effective in removing pharmaceutical compounds from hospital wastewater. The removal mechanism of these compounds involves a combination of physical, chemical, and biological processes, including adsorption, degradation, and uptake by wetland plants. The removal efficiency of constructed wetlands varies depending on several factors, including the type and concentration of pharmaceutical compounds, the design of the wetland system, and the environmental conditions. Further research is necessary to optimize the performance of these systems, particularly in the removal of emerging contaminants, to ensure their effectiveness and long-term sustainability.

Dissemination of antibiotic resistance genes through soil-plant-earthworm continuum in the food production environment

Treated municipal wastewater (TMW) can provide a reliable source of irrigation water for crops, which is especially important in arid areas where water resources are limited or prone to drought. Nonetheless, TMW may contain residual antibiotics, potentially exposing the crops to these substances. The goal of this study was to investigate the dissemination of antibiotics resistance genes (ARGs) in the soil-plant-earthworm continuum after irrigation of spinach and radish plants with TMW containing trimethoprim, sulfamethoxazole, and sulfapyridine in a greenhouse experiment, followed by feeding of earthworms with harvested plant materials. Our results showed that antibiotic resistance genes (ARGs) were enriched in the soil-plant-earthworm microbiomes irrigated with TMW and TMW spiked with higher concentrations of antibiotics. The number of ARGs and antibiotic-resistant bacteria (ARB) enrichment varied with plant type, with spinach harboring a significantly higher amount of ARGs and ARB compared to radish. Our data showed that bulk and rhizosphere soils of spinach and radish plants irrigated with MilliQ water, TMW, TMW10, or TMW100 had significant differences in bacterial community (p < 0.001), ARG (p < 0.001), and virulence factor gene (VFG) (p < 0.001) diversities. The abundance of ARGs significantly decreased from bulk soil to rhizosphere to phyllosphere and endosphere. Using metagenome assembled genomes (MAGs), we recovered many bacterial MAGs and a near complete genome (>90 %) of bacterial MAG of genus Leclercia adecarboxylata B from the fecal microbiome of earthworm that was fed harvested radish tubers and spinach leaves grown on TMW10 irrigated waters, and this bacterium has been shown to be an emerging pathogen causing infection in immunocompromised patients that may lead to health complications and death. Therefore, crops irrigated with TMW containing residual antibiotics and ARGs may lead to increased incidences of enrichment of ARB in the soil-plant-earthworm continuum.

Biodegradation and sorption of nutrients and endocrine disruptors in a novel concrete-based substrate in vertical-flow constructed wetlands

Removing phosphorus and endocrine-disruptors (EDC) is still challenging for low-cost sewage treatment systems. This study investigated the efficiency of three vertical-flow constructed wetlands (VFCW) vegetated with Eichhornia crassipes onto red clay (CW-RC), autoclaved aerated concrete (CW-AC), and composite from the chemical activation of autoclaved aerated concrete with white cement (CW-AAC) in the removal of organic matter, nutrients, and estrone, 17β-estradiol, and 17α-ethinylestradiol. The novelty aspect of this study is related to selecting these clay and cementitious-based materials in removing endocrine disruptors and nutrients in VFCW. The subsurface VFCW were operated in sequencing-batch mode (cycles of 48-48-72 h), treating synthetic wastewater for 308 days. The operation consisted of Stages I and II, different by adding EDC in Stage II. The presence of EDC increased the competition for dissolved oxygen (DO) and reduced the active sites available for adsorption, diminishing the removal efficiencies of TKN and TAN and total phosphorus in the systems. CW-RC showed a significant increase in COD removal from 65% to 91%, while CW-AC and CW-AAC maintained stable COD removal (84%-82% and 78%-81%, respectively). Overall, the substrates proved effective in removing EDC, with CW-AC and CW-AAC achieving >60% of removal. Bacteria Candidatus Brocadia and Candidatus Jettenia, responsible for carrying out the Anammox process, were identified in assessing the microbial community structure. According to the mass balance analysis, adsorption is the main mechanism for removing TP in CW-AC and CW-AAC, while other losses were predominant in CW-RC. Conversely, for TN removal, the adsorption is more representative in CW-RC, and the different metabolic routes of microorganisms, biofilm assimilation, and partial ammonia volatilization in CW-AC and CW-AAC. The results suggest that the composite AAC is the most suitable material for enhancing the simultaneous removal of organic matter, nutrients, and EDC in VFCW under the evaluated operational conditions.

Impact analysis of hydraulic loading rate and antibiotics on hybrid constructed wetland systems: Insight into the response to decontamination performance and environmental-associated microbiota

Hybrid constructed wetlands (HCWs) are a promising solution for water ecology and environmental treatment, not only for conventional types of water pollution but also for antibiotics. Among the critical parameters for wetlands, the hydraulic loading rate (HLR) is especially important given the challenges of antibiotics treatment and frequent extreme rainfall. To investigate the removal performance of different HLRs on nutrients and antibiotics, as well as the response of antibiotics to nutrient removal, and the impact of HLRs on microbial communities, new HCWs with vertical flow constructed wetlands (VFCWs) and floating constructed wetlands (FCWs) in series were built. The results of the study showed that: (1) HCWs are highly effective in removing chemical oxygen demand (COD), NH4+-N, NO2--N, and total phosphorus (TP) at low HLR (L_HLR), with removal efficiencies as high as 97.8%, 99.6%, 100%, and 80.5%. However, high HLR (H_HLR) reduced their removal efficiencies; (2) The average removal efficiency of fluoroquinolones (FQs) under different HLRs was consistently high, at 99.9%, while the average removal efficiency of macrolides (MLs) was 96.3% (L_HLR) and 88.4% (H_HLR). The removal efficiency of sulfonamides (SAs) was susceptible to HLRs, and the removal of antibiotics occurred mainly in the rhizosphere zone of wetland; (3) High concentrations of antibiotics in HCWs were found to inhibit and poison plant growth and to reduce the removal efficiency of TP by 12%. However, they had a minor effect on the removal efficiency of carbon and nitrogen nutrients; (4) H_HLR altered the diversity and abundance of microbial communities in different compartments of the wetland and also reduced the relative abundance of Bacillus, Hydrogenophaga, Nakamurella, Denitratisoma and Acidovorax genera, which are involved in denitrification and phosphorus removal processes. This alteration in microbial communities was one of the main reasons for the reduced performance of nitrogen and phosphorus removal.

The dynamics and transmission of antibiotic resistance associated with plant microbiomes

Antibiotic resistance genes (ARGs) have been widely found and studied in soil and water environments. However, the propagation of ARGs in plant microbiomes has attracted insufficient attention. Plant microbiomes, especially the rhizosphere microorganisms, are closely connected with water, soil, and air, which allows ARGs to spread widely in ecosystems and pose a threat to human health after entering the human body with bacteria. Therefore, it is necessary to deeply understand and explore the dynamics and the transmission of ARGs in rhizosphere microorganisms and endophytes of plants. In this review, the transmission and influencing factors of ARGs in the microorganisms associated with plants, especially the influence of root exudates on plant microbiomes, are analyzed. Notably, the role of intrinsic genes of plants in determining root exudates and their potential effects on ARGs are proposed and analyzed. The important role of phyllosphere microorganisms and endophytes in the transmission of ARGs and co-resistance of antibiotics and other substances are also emphasized. The proliferation and transmission of ARGs associated with plant microbiomes addressed in this review is conducive to revealing the fate of ARGs in plant microorganisms and alleviating ARG pollution.

Kinetics and capacities of non-reactive phosphorus (NRP) sorption to crushed autoclaved aerated concrete (CAAC)

With growing interest in resource recovery and/or reuse, waste materials have been considered a promising alternative for phosphorus (P) adsorption because they are low-cost and easily accessible. Crushed autoclaved aerated concrete (CAAC), as representative construction waste, has been extensively studied for P removal in ecological technologies such as treatment wetlands. However, most of the previous studies focused on the adsorption of orthophosphate, namely reactive phosphorus, and lacked attention to non-reactive phosphorus (NRP) which is widely present in sewage. This study presents the first investigation on the potential and mechanism of CAAC removing four model NRP compounds. Adsorption isotherm and kinetics of NRP onto CAAC indicate that the removal of NRP was a chemisorption process and also involved a two-step pore diffusion process. The desorption experiment shows that different NRP species showed varying degrees of desorption. Most NRP was irreversibly adsorbed on CAAC. Among the model compounds considered in this study, the adsorption capacity and hydrolysis rate of organophosphorus were much less than that of inorganic phosphorus. Moreover, the adsorption of different NRP species by CAAC in the mesocosm study was different from the results of laboratory adsorption experiments, and the possible biodegradation was essential for the conversion and removal of NRP. The findings confirmed the validity of CAAC for NRP removal and the potential advantages of CAAC in terms of costs and environmental impact. This study will contribute to a better understanding of NRP conversion and environmental fate and that can be the basis for a refined risk assessment.

Towards Effective, Sustainable Solution for Hospital Wastewater Treatment to Cope with the Post-Pandemic Era

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has spread across the globe since the end of 2019, posing significant challenges for global medical facilities and human health. Treatment of hospital wastewater is vitally important under this special circumstance. However, there is a shortage of studies on the sustainable wastewater treatment processes utilized by hospitals. Based on a review of the research trends regarding hospital wastewater treatment in the past three years of the COVID-19 outbreak, this review overviews the existing hospital wastewater treatment processes. It is clear that activated sludge processes (ASPs) and the use of membrane bioreactors (MBRs) are the major and effective treatment techniques applied to hospital wastewater. Advanced technology (such as Fenton oxidation, electrocoagulation, etc.) has also achieved good results, but the use of such technology remains small scale for the moment and poses some side effects, including increased cost. More interestingly, this review reveals the increased use of constructed wetlands (CWs) as an eco-solution for hospital wastewater treatment and then focuses in slightly more detail on examining the roles and mechanisms of CWs' components with respect to purifying hospital wastewater and compares their removal efficiency with other treatment processes. It is believed that a multi-stage CW system with various intensifications or CWs incorporated with other treatment processes constitute an effective, sustainable solution for hospital wastewater treatment in order to cope with the post-pandemic era.

A review on antibiotics removal: Leveraging the combination of grey and green techniques

Antibiotics are currently a major source of concern around the world due to the serious risks posed to human health and the environment. The performance of the secondary wastewater treatment processes/technologies (representing grey process) and constructed wetlands (CWs) (typical green process) in removing antibiotics and antibiotic resistance genes (ARG) was reviewed. The result showed that the grey process mainly removes antibiotics, but does not significantly remove ARG, and some processes may even cause ARG enrichment. The overall treatment in CWs is better than WWTPs, especially for ARG. Vertical subsurface flow CWs (VFCWs) are more conductive to antibiotics removal, while horizontal subsurface flow CWs (HFCWs) have a better ARG removal. More importantly, this review admits and suggests that the combination of grey process with green process is an effective strategy to remove antibiotics and ARG. The most advantage of the combination lies in realizing complementary advantages, i.e. the grey process as the primary treatment while CWs as the polishing stage. The efficiency of such the hybrid system is much higher than either single treatment process.

Plants inhibit the relative abundance of sulfonamide resistance genes and class 1 integron by influencing bacterial community in rhizosphere of constructed wetlands

Antibiotic resistance genes (ARGs) commonly detected in wastewater can potentially lead to a health crisis. Constructed wetlands (CWs) remove ARGs and sulfonamides (SAs) from wastewater, but the importance of plants in the process is seldom reported. We compared the effect of three wetland plant species (Cyperus alternifolius, Juncus effuses, and Cyperus papyrus), sample distance from the root, and SA presence on the environmental abundance of class 1 integron (intI1) and SA resistance genes (sul) using specially designed CW rhizoboxes. Quantitative polymerase chain reaction revealed that the relative abundance of the target genes in planted CWs, especially in C. alternifolius planted CWs, was significantly lower than that in unplanted CWs (P < 0.05). The substrate in the rhizosphere or near-/moderate-rhizosphere (closest to the root) showed the lowest average relative abundance of the target genes, while the bulk substrate (without the root) showed the highest abundance of these genes, irrespective of the planted species. Further, the influence of plants was more evident after 8 weeks of wastewater treatment. The trend was the same in SA-treated and untreated groups, although the relative abundance of the target genes was significantly higher in the former (P < 0.05). The weaker correlation between the intI1 and sul genes in the rhizosphere and near-/moderate-rhizosphere in comparison to the bulk substrate in the SA group suggested that the risk of horizontal gene transfer was probably higher in the bulk substrate and unplanted CW. A partial least-squares path model revealed that dissolved organic carbon and oxygen content significantly influenced SA concentration, microbial community, and intI1 genes, and then shaping the sul genes together. Finally, redundancy analysis suggested that abundance of sul genes was influenced by bacteria enriched in the bulk substrate and unplanted CWs. The findings provide new insights into the importance for controlling risk of ARGs by wetland plants.

Effectiveness of biochar filters vegetated with Echinochloa pyramidalis in domestic wastewater treatment

The use of biochar in constructed wetlands for domestic wastewater treatment is gradually being acclaimed by environmentalists due to its high specific surface area and porosity. In this study, the effectiveness of corn cob biochar (CCB) and rice husk biochar (RHB) in vertical flow constructed wetlands vegetated with Echinochloa pyramidalis was studied with sand as common reference material. The filters were fed with primarily treated domestic wastewater at a hydraulic loading rate of about 350 L/m²/day for 6 months. Water samples were collected monthly for physicochemical and bacteriological analysis and plant growth assessed every two weeks throughout the study. Biochar filters were highly performant in wastewater improvement with no significant differences between the biochar types. Both biochars were more efficient than sand in the removal of chemical oxygen demand (COD), biochemical oxygen demand (BOD), true colour, total suspended solids (TSS) and total dissolved solids (TDS). However, sand filters performed better in the reduction of nutrients. All wetlands showed positive plant growth though the plants did not significantly affect the performance of the different filters for most parameters. However, a better plant growth was observed in the CCB filters. The study shows that CCB and RHB can effectively replace sand as substrates in constructed wetlands for wastewater treatment.

A review on hospital wastewater treatment: A special emphasis on occurrence and removal of pharmaceutically active compounds, resistant microorganisms, and SARS-CoV-2

The hospital wastewater imposes a potent threat to the security of human health concerning its high vulnerability towards the outbreak of several diseases. Furthermore, the outbreak of COVID-19 pandemic demanded a global attention towards monitoring viruses and other infectious pathogens in hospital wastewater and their removal. Apart from that, the presence of various recalcitrant organics, pharmaceutically active compounds (PhACs), etc. imparts a complex pollution load to water resources and ecosystem. In this review, an insight into the occurrence, persistence and removal of drug-resistant microorganisms and infectious viruses as well as other micro-pollutants have been documented. The performance of various pilot/full-scale studies have been evaluated in terms of removal of biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), PhACs, pathogens, etc. It was found that many biological processes, such as membrane bioreactor, activated sludge process, constructed wetlands, etc. provided more than 80% removal of BOD, COD, TSS, etc. However, the removal of several recalcitrant organic pollutants are less responsive to those processes and demands the application of tertiary treatments, such as adsorption, ozone treatment, UV treatment, etc. Antibiotic-resistant microorganisms, viruses were found to be persistent even after the treatment of hospital wastewater, and high dose of chlorination or UV treatment was required to inactivate them. This article circumscribes the various emerging technologies, which have been used to treat PhACs and pathogens. The present review also emphasized the global concern of the presence of SARS-CoV-2 RNA in hospital wastewater and its removal by the existing treatment facilities.

Field-scale baffled and biorack hybrid constructed wetland: effect of fluctuating loading rates and recirculation for domestic wastewater treatment

The conventionally used constructed wetlands require modification/s to minimize clogging problems and space requirement. In this study, a field-scale baffled and biorack hybrid constructed wetland (BBHCW) was developed as a part of 42 KLD decentralized wastewater treatment (DWT) system at Walchand College of Engineering, Sangli (M.S.), India for domestic wastewater. Brickbats were used as support medium in the baffled portion and corrugated sheets in biorack. Mixed vegetation of Typha angustifolia and Canna indica was used in both baffled and biorack portions. BBHCW was operated under the dynamic conditions of flow (0.60-9.89 m³/m² day) and strength (0.12-2.12 kg COD/m² day) for 8 months. The performance was assessed for the removal of organic carbon and nitrogen with and without recirculation of treated effluent. Tracer studies showed that the hydraulic efficiency was satisfactory. COD, BOD₃, and TKN removal is possible to an extent of 26.30 ± 1.36, 29.08 ± 2.43, and 19.39 ± 2.27%, respectively, under dynamic conditions. Recirculation enhances the removal efficiency of COD by 5.00-10.00%. However, TKN removal was not significant with or without recirculation. Morphological study showed that vegetation growth was well supported in BBHCW. The discarded corrugated sheets in BR and brickbats in BSFW are the most appropriate low-cost options. The clogging problem is reduced significantly. BBHCW is sturdy enough to absorb shock loading and space requirement can be reduced by judicious choice of HLR and OLR. BBHCW is an alternative to conventionally used sub-surface constructed wetland as a part of DWT. Novelty statementDevelopment of newly configured baffled and biorack hybrid dual-species constructed wetland (BBHCW) for field scale application.Use of discarded brickbat and cement sheets as a new support medium and bioracks.Performance assessment of field-scale BBHCW for the removal of organic carbon (expressed as COD and BOD₃), and nitrogen (expressed as TKN) from domestic wastewater under highly dynamic conditions induced by fluctuating hydraulic loading rate (0.60-9.89 m³/m² day) and organic loading rate (0.12-2.12 kg COD/m² day).

Horizontal sub surface flow Constructed Wetlands coupled with tubesettler for hospital wastewater treatment

Hospital wastewater are a lurking threat to environment and human health security for any given moment of time owing to its complexity and high vulnerability to cause disease outbreak. Though there are a number of treatment process for wastewater., there is a high need for employing cost-efficient and sustainable method of treatment. Hence a pilot scale horizontal surface flow Constructed Wetland (HSFCW) coupled with Tubesettler was installed at New Delhi, India (February to may 2019). This study reports comparative pollutants removal from hospital wastewater using Constructed Wetlands and associated tubesettler dosed with Hospital wastewater. A pilot scale CW system was used for treating 10m³/day of hospital wastewater. The system was tested for 3 Months to evaluate its performance for removing pollutants from the wastewater. The HSFCW coupled with tubesettler achieved over all removal efficiency of 94% (COD), MLSS (97%), TSS (98%), BOD₅ (96%), Phosphate (79%). However, process of nitrification was not observed and accumulation of Nitrate up to 197% was observed. The study concluded that it may be due to the presence of pharmaceuticals and other elements present in hospital wastewater. This conclusion was based on the fact that Alkalinity increased by 52% in effluent and pH value also exhibited an average increase of 12%. Further research studies are required to investigate effect of pharmaceutical originating from hospital on treatment efficiency, to incorporate anaerobic setup to complete denitrification-nitrification process and also to determine efficiency of thermophilic, mesophilic, and psychrophilic bacteria with respect to climate and temperature.

A review of emerging organic contaminants (EOCs), antibiotic resistant bacteria (ARB), and antibiotic resistance genes (ARGs) in the environment: Increasing removal with wetlands and reducing environmental impacts

Emerging organic contaminants (EOCs) include a diverse group of chemical compounds, such as pharmaceuticals and personal care products (PPCPs), pesticides, hormones, surfactants, flame retardants and plasticizers. Many of these compounds are not significantly removed in conventional wastewater treatment plants and are discharged to the environment, presenting an increasing threat to both humans and natural ecosystems. Recently, antibiotics have received considerable attention due to growing microbial antibiotic-resistance in the environment. Constructed wetlands (CWs) have proven effective in removing many EOCs, including different antibiotics, before discharge of treated wastewater into the environment. Wastewater treatment systems that couple conventional treatment plants with constructed and natural wetlands offer a strategy to remove EOCs and reduce antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) far more efficiently than conventional treatment alone. This review presents as overview of the current knowledge on the efficiency of different wetland systems in reducing EOCs and antibiotic resistance.