Secondary Wastewater Effluent Research Articles

Preparation of effective lithium-ion sieve from sludge-generated TiO2

A potential adsorbent for Li+ extraction from liquid resources is titanium-type lithium-ion sieves (LISs) because of their structural stability and high adsorption capacity. However, the adsorption efficiency and recycling stability of LISs produced with various TiO2 precursors vary significantly. Additionally, traditional TiO2 is often produced using chemical-intensive methods, resulting in large amounts of effluent containing strong acids and high concentrations of chloride/sulfate ions, posing a threat to the environment. Hence, in this study, the LIS precursors, Li2TiO3, were synthesized utilizing novel environment-friendly anatase titania made from flocculated sludges of synthetic secondary sewage effluent (S-LTO) and dye wastewater (D-LTO). The physicochemical characteristics and adsorption capacities of the synthesized LISs were then investigated. The results indicated that sludge-generated LISs could be effectively produced and had a high Li+ adsorption capacity of 35.43 mg/g for S-LTO and 34.97 mg/g for D-LTO. For the synthesized LISs, the adsorption kinetics and isotherms verified a fixed energy-based monolayer chemisorption. Furthermore, the H2TiO3 generated from sludge was extremely stable after acid pickling, reusable (4 regeneration cycles exhibited minimal performance degradation), and highly selective to Li+ in an aqueous medium, suggesting enormous industrial potentials such as seawater and brine for aqueous Li+ recovery.

Comparison of the reverse osmosis membrane fouling behaviors of different types of water samples by modeling the flux change over time

Fouling of RO membranes has long been a complex but inevitable problem in wastewater reclamation. In this study, a modified intermediate blocking model with two parameters was applied to describe the flux change of RO membranes treating various water samples, including municipal secondary effluent, treated industrial wastewater, surface water, and groundwater. The model was validated by 55 sets of data reported by 13 articles, and the results were promising, with 90% of the determination coefficient (R2) exceeding 0.90. Relatively large flux and high operational pressure were found likely to aggravate membrane fouling. Treated industrial wastewater had the highest fouling potential (fouling constant k: 0.061–2.433) compared to municipal wastewater secondary effluent, surface water, and groundwater, even with similar dissolved organic carbon concentration. With industrial wastewater excluded, water samples exhibited lower fouling potential than organic matter solutions, with the majority (25%∼75%) of k distributing in 0.03–0.12, much lower compared to the major k range of the latter (0.05–0.28). This suggested a deviation in fouling behaviors between model organic matters and real water samples. Xanthan gum and guar gum were proposed to be model polysaccharides based on their model parameters, which were relatively close to real water samples.

Enhancement of solute removal efficiency of polyamide reverse osmosis membrane without water permeability loss

This study investigates the enhancement of the solute removal efficiency of reverse osmosis (RO) membranes without water permeability loss during the treatment of secondary wastewater effluent (SWE). First, filtration experiments were performed using a synthetic SWE containing three types of solutes with different membrane transport properties, namely arsenious acid (H3AsO3), electrolyte, and rhodamine-WT (R-WT), and alginate as a representative biopolymer foulant. The flux of R-WT at 2.0 MPa decreased by up to 45% in the presence of alginate without decreasing water permeability; this trend was not observed for H3AsO3 and the electrolyte, indicating that nanoscale imperfections that allow unselective solute transport were plugged by alginate. Second, H3AsO3 and R-WT were spiked into a real SWE that was pretreated using 0.1 µm microfiltration, and the enhancement of solute removal efficiency was investigated. Membrane performance after 14 days of operation revealed that the flux of R-WT at 2.0 MPa decreased by up to 44% in the presence of the biopolymer. These results demonstrated that nanoscale imperfections in the RO membrane were plugged by the biopolymer contained in SWE and that the removal of large solutes was enhanced without forfeiting water permeability.

The fate of aqueous betrixaban during adsorption, photolysis, and advanced oxidation: Removal, kinetics, and reaction mechanisms

This study investigated the fate of aqueous betrixaban, an oral anticoagulant, during adsorption, photolysis, and advanced oxidation in the presence of radicals. Adsorption studies revealed 95% removal of betrixaban at 10 h contact time with coconut shell-based granular activated carbon (CSGAC). The adsorption kinetics and isotherms best-fitted pseudo-first-order and Freundlich models, respectively, suggesting chemisorption. UVC (254 nm) irradiation (3 J/cm2), in combination with H2O2 (0.5 mM), led to the highest degradation (>90%) of betrixaban at pH 7. An increase in the initial H2O2 dosage, light intensity, and contact time enhanced the degradation rates of betrixaban. Lower degradation rates were observed in secondary wastewater effluent than with deionized water, but reactions in both matrices obeyed pseudo-first-order kinetics. Experiments using different scavengers, including tert-butyl alcohol (TBA), potassium iodide (KI), and methanol, demonstrated hydroxyl radicals (•OH) as the major reactive species involved in degradation during the UV/H2O2 process. This is the first study on the fate of betrixaban under photolysis, advanced oxidation, and adsorption, which helps to understand betrixaban's removal efficiencies and mechanisms during these processes.

Oxidant-reactive carbonous moieties in dissolved organic matter: Selective quantification by oxidative titration using chlorine dioxide and ozone

The application of oxidants for disinfection or micropollutant abatement during drinking water and wastewater treatment is accompanied by oxidation of matrix components such as dissolved organic matter (DOM). To improve predictions of the efficiency of oxidation processes and the formation of oxidation products, methods to determine concentrations of oxidant-reactive phenolic, olefinic or amine-type DOM moieties are critical.Here, a novel selective oxidative titration approach is presented, which is based on reaction kinetics of oxidation reactions towards certain DOM moieties. Phenolic moieties were determined by oxidative titration with ClO2 and O3 for five DOM isolates and two secondary wastewater effluent samples. The determined concentrations of phenolic moieties correlated with the electron-donating capacity (EDC) and the formation of inorganic ClO2-byproducts (HOCl, ClO2−, ClO3−). ClO2-byproduct yields from phenol and DOM isolates and changes due to the application of molecular tagging for phenols revealed a better understanding of oxidant-reactive structures within DOM.Overall, oxidative titrations with ClO2 and O3 provide a novel and promising tool to quantify oxidant-reactive moieties in complex mixtures such as DOM and can be expanded to other matrices or oxidants.

Efficient removal of antibiotic-resistant bacteria and intracellular antibiotic resistance genes by heterogeneous activation of peroxymonosulfate on hierarchical macro-mesoporous Co3O4-SiO2 with enhanced photogenerated charges

Antibiotic resistance genes (ARGs) and their host antibiotic-resistant bacteria (ARB) are widely detected in the environment and pose a threat to human health. Traditional disinfection in water treatment plants cannot effectively remove ARGs and ARB. This study explored the potential of a heterogeneous photo-Fenton-like process utilizing a hierarchical macro-mesoporous Co3O4-SiO2 (MM CS) catalyst for activation of peroxymonosulfate (PMS) to inactivate ARB and degrade the intracellular ARGs. A typical gram-negative antibiotic-resistant bacteria called Pseudomonas sp. HLS-6 was used as a model ARB. A completed inactivation of ARB at ∼107 CFU/mL was achieved in 30 s, and an efficient removal rate of more than 4.0 log for specific ARGs (sul1 and intI1) was achieved within 60 min by the MM CS-based heterogeneous photo-Fenton-like process under visible light and neutral pH conditions. Mechanism investigation revealed that •O2− and 1O2 were the vital reactive species for ARB inactivation and ARG degradation. The formation and transformation of the active species were proposed. Furthermore, the hierarchical macro-mesoporous structure of MM CS provided excellent optical and photoelectrochemical properties that promoted the cycle of Co3+/Co2+ and the effective utilization of PMS. This process was validated to be effective in various water matrices, including deionized water, underground water, source water, and secondary effluent wastewater. Collectively, this work demonstrated that the MM CS-based heterogeneous photo-Fenton-like process is a promising technology for controlling the spread of antibiotic resistance in aquatic environments.

Modulation of reduced graphene oxide membrane for low-fouling wastewater filtration: Membrane structure, wastewater property, and DFT calculation

Membrane fouling is a major hurdle impeding real-world application of membranes for advanced wastewater treatment. In this study, a GO membrane and a reduced GO (rGO) membrane were examined in parallel for their anti-fouling propensities and ability to remove pharmaceutical compounds from realistic wastewater effluents. The effects of membrane properties and wastewater characteristics on the two aspects were also assessed by experiments and DFT simulation. The results showed that the transmembrane pressure (TMP) of the rGO membrane increased by 0–3.5 kPa after filtering a secondary wastewater effluent from an activated sludge system (SW), as compared to 201.6–292.1 kPa for the GO membrane. Meanwhile, slightly greater TMP increases were observed for both membranes after filtering a secondary wastewater effluent from a partial nitrification and denitrification system (PND), but the fouling remained low for the rGO membrane. Overall, chemical reduction of GO to rGO led to larger SSA and reduced negative charge, which promoted adsorptive filtration of pharmaceutical compounds. Also, the diminishing of functional groups possessed by the GO membrane mitigated attractive interlayer polar interaction and expanded membrane pore dimension, thus enhancing the permeability and anti-fouling propensity of GO membranes.

Removal of drug losartan in environmental aquatic matrices by heat-activated persulfate: Kinetics, transformation products and synergistic effects

In this study, the oxidative degradation of losartan (LOS), a widely administered medicine for high blood pressure by heat-activated persulfate was investigated. Increased temperature and persulfate concentration, as well as acidic conditions enhance the degradation efficiency of LOS, whose rate follows pseudo-first order kinetics. From the respective apparent rate constants in the range 40–60 °C, an apparent activation energy of 112.70 kJ/mol was computed. Radical scavenging tests demonstrated that both HO• and SO4•− contribute towards LOS degradation. LOS degradation was suppressed in real water matrices including bottled water (BW) and secondary wastewater effluent (WW), while other experiments indicated that the presence of bicarbonates and humic acid negatively affected its oxidation. Instead, the addition of chloride ions at 250 mg/L resulted in a positive effect on LOS removal. The combination of heat-activated PS with low-frequency ultrasound exhibited a synergistic effect, with the ratio S being 2.29 in BW and 1.52 in WW. Five transformation products of LOS were identified through HRMS suspect and non-target screening approaches, among which two are reported for the first time. Using the in-house risk assessment program, ToxTrAMs was revealed that most of the identified TPs present higher toxicity than LOS against Daphnia magna.

Characterization of the immobilized algae-based bioreactor with external ceramic ultrafiltration membrane to remove nutrients from the synthetic secondary wastewater effluent

In this study, alginate-immobilization of microalgae combined with continuous/intermittent algae-based membrane bioreactor (A-MBR) and external ceramic membrane was developed to investigate the effect of immobilization on algal growth, nutrient removal, algal organic matter (AOM) and membrane fouling control in synthetic secondary wastewater effluent treatment. First, Chlorella vulgaris and Scenedesmus quadricauda were selected to investigate the treatment performance, AOM characteristics and membrane fouling control between suspended and immobilized microalgae. The results showed the effect of immobilization on two microalgae growth was not significant and nearly complete NO3−-N and PO43−-P removals were achieved by both immobilized microalgae in batch experiments, contributing from algal uptake as well as chemical precipitation. In addition, fluorescence excitation-emission matrix spectra indicated specific intensity of protein- and soluble microbial byproduct-like peaks in AOM derived from immobilized S. quadricauda was lower than C. vulgaris and reduced recently produced AOM from two immobilized microalgae was observed, which would improve membrane fouling control. After 35-day intermittent A-MBR operation with immobilized S. quadricauda, higher concentration of microalgal biomass and 63% NO3−-N and 58% PO43−-P removals were achieved. In addition, alginate-immobilization and intermittent operation for relaxation of membrane showed slower decline of permeate flux under constant pressure mode and therefore, were beneficial for membrane fouling control. Hence, the intermittent A-MBR with immobilized microalgae has potential to cultivate microalgae, provide stable treatment performance to remove nutrients and limit membrane fouling in secondary wastewater effluent treatment.

Bi-metal oxide-modified flat-sheet ceramic membranes for catalytic ozonation of organic pollutants in wastewater treatment

Ceramic membranes have a highly porous structure and a high surface area, which provide suitable support for heterogeneous catalytic oxidation. In this study, as effective catalysts for ozonation, Mg, Ce, and Mn oxides were coated by co-precipitation onto a flat-sheet ceramic membrane to produce two catalytic ceramic membranes (CCMs), namely an Mg-Ce membrane and an Mg-Mn membrane. This technique combines ceramic membrane filtration with catalytic ozonation for advanced water and wastewater treatment. The CCM characterization showed that the metal oxide catalysts were well coated on the membrane surface and inside the membrane pores. Compared with non-catalytic ozonation, catalytic ozonation with CCMs was more effective for the degradation and removal of organic pollutants, including a dye as a model pollutant in water and residual organics in secondary wastewater effluent. At the same ozone dosage for ozonation coupled with membrane filtration, the organic removal efficiency was increased from approximately 30% for the ceramic membrane without the catalyst coating to over 80% for the CCM with the catalyst coating. Membrane catalytic ozonation also resulted in effective membrane fouling control during ultrafiltration of the secondary effluent. Based on the hydroxyl (OH) quenching test, ozonation with CCMs produced more OH free radicals than ozonation alone, which led to enhanced organic degradation. Moreover, catalytic ozonation in the membrane reactor played an effective role in mitigation of membrane fouling. Ceramic membrane-based catalytic ozonation can be used for effective removal of toxic and persistent organic pollutants from water and wastewater.

Insights on the role of periphytic biofilm in synergism with Iris pseudacorus for removing mixture of pharmaceutical contaminants from wastewater

The potential of Iris pseudacorus and the associated periphytic biofilm for biodegradation of two common pharmaceutical contaminants (PCs) in urban wastewater was assessed individually and in consortium. An enhanced removal for sulfamethoxazole (SMX) was achieved in consortium (59%) compared to individual sets of I. pseudacorus (50%) and periphytic biofilm (7%) at concentration of 5 mg L−1. Conversely, individual sets of periphytic biofilm (77%) outperformed removal of doxylamine succinate (DOX) compared to individual sets of I. pseudacorus (59%) and consortium (67%) at concentration of 1 mg L−1. Enhanced relative abundance of microflora containing microalgae (Sellaphora, Achnanthidium), rhizobacteria (Acidibacter, Azoarcus, Thioalkalivibrio), and fungi (Serendipita) in periphytic biofilm was observed after treatment. SMX treatment for five days elevated cytochrome P450 enzymes’ expressions, including aniline hydroxylase (48%) and aminopyrine N-demethylase (54%) in the periphytic biofilm. Nevertheless, I. pseudacorus showed 175% elevation of aniline hydroxylase along with other biotransformation enzymes, such as peroxidase (629%), glutathione S-transferase (514%), and dichloroindophenol reductase (840%). A floating bed phytoreactor planted with I. pseudacorus and the periphytic biofilm consortium removed 67% SMX and 72% DOX in secondary wastewater effluent. Thus, the implementation of this strategy in constructed wetland-based treatment could be beneficial for managing effluents containing PCs.

New iodine-based electrochemical advanced oxidation system for water disinfection: Are disinfection by-products a concern?

A novel electrochemical Advanced Oxidation System (AOS) has been recently developed for water disinfection where iodide is used to generate active iodine species in-situ. However, the presence of iodide during water disinfection can lead to the formation of iodinated disinfection byproducts (I-DBPs), which have been shown to be more cyto- and genotoxic than their chlorinated and brominated analogs. In this study, the formation of DBPs was assessed in ultrapure water, river water and secondary wastewater effluents treated by the AOS. A comprehensive total organic halogen and target DBP analysis was used that included 25 unregulated DBPs, and the total organic halogen (TOX) quantified as total organic chlorine (TOCl), total organic bromine (TOBr), and total organic iodine (TOI). Ultrapure water disinfection only quantified iodoform (TIM) at a maximum concentration of 0.90 ± 0.05 µg/L. River water results show that TOI increase from 1.3 ± 0.3 µg/L before disinfection (t = 0) to a maximum of 3.5 ± 1.1 µg/L. TIM and bromodiiodomethane (BDIM) were the only targeted iodo-trihalomethanes (I-THMs) that were quantified with a maximum total I-THM concentration of 0.44 µg/L. Secondary wastewater effluent disinfection results show that TOI increased from 1.8 ± 0.3 µg/L (t = 0) to a maximum concentration of 35.3 ± 0.3 µg/L. Iodide and iodate were the main iodinated species exiting the AOS system with a iodine recovery of 94–101%. The results from this study show that the AOS formed low levels of iodinated DBPs in treated water sources that are comparable to the levels found in disinfected drinking water and wastewater.

Simultaneous Disinfection and Organic Microcontaminant Removal by UVC-LED-Driven Advanced Oxidation Processes

This work presents the comparison of four advanced oxidation processes driven by UVC-LED radiation (278 nm—2 W/m2) for simultaneous bacteria inactivation (Escherichia coli—106 CFU/mL) and microcontaminant removal (imidacloprid—50 µg/L) in simulated wastewater secondary effluent. To this end, the activation of H2O2 and S2O82− as precursors of HO• and SO4•−, respectively, by UVC-LED and UVC-LED/Fe3+–NTA (ferric nitrilotriacetate at 0.1 mM) has been studied at different oxidant concentrations. For the purpose of comparison, conventional chlorination was used as the baseline along with bacterial regrowth 24 h after treatment. Disinfection was achieved within the first 30 min in all of the processes, mainly due to the bactericidal effect of UVC-LED radiation. UVC-LED/H2O2 did not substantially affect imidacloprid removal due to the low HO• generation by UVC irradiation at 278 nm, while more than 80% imidacloprid removal was achieved by the UVC-LED/S2O82−, UVC-LED/Fe3+–NTA/S2O82−, and UVC-LED/Fe3+–NTA/H2O2 processes. The most efficient concentration of both oxidants for the simultaneous disinfection and microcontaminant removal was 1.47 mM. Chlorination was the most effective treatment for bacterial inactivation without imidacloprid removal. These findings are relevant for scaling up UVC-LED photoreactors for tertiary wastewater treatment aimed at removing bacteria and microcontaminants.

Comparison of ultrafiltration and iron chloride flocculation in the preparation of aquatic viromes from contrasting sample types.

Viral metagenomes (viromes) are a valuable untargeted tool for studying viral diversity and the central roles viruses play in host disease, ecology, and evolution. Establishing effective methods to concentrate and purify viral genomes prior to sequencing is essential for high quality viromes. Using virus spike-and-recovery experiments, we stepwise compared two common approaches for virus concentration, ultrafiltration and iron chloride flocculation, across diverse matrices: wastewater influent, wastewater secondary effluent, river water, and seawater. Viral DNA was purified by removing cellular DNA via chloroform cell lysis, filtration, and enzymatic degradation of extra-viral DNA. We found that viral genomes were concentrated 1-2 orders of magnitude more with ultrafiltration than iron chloride flocculation for all matrices and resulted in higher quality DNA suitable for amplification-free and long-read sequencing. Given its widespread use and utility as an inexpensive field method for virome sampling, we nonetheless sought to optimize iron flocculation. We found viruses were best concentrated in seawater with five-fold higher iron concentrations than the standard used, inhibition of DNase activity reduced purification effectiveness, and five-fold more iron was needed to flocculate viruses from freshwater than seawater—critical knowledge for those seeking to apply this broadly used method to freshwater virome samples. Overall, our results demonstrated that ultrafiltration and purification performed better than iron chloride flocculation and purification in the tested matrices. Given that the method performance depended on the solids content and salinity of the samples, we suggest spike-and-recovery experiments be applied when concentrating and purifying sample types that diverge from those tested here.

Formation of transformation products during ozonation of secondary wastewater effluent and their fate in post-treatment: From laboratory- to full-scale

Ozonation is increasingly applied in water and wastewater treatment for the abatement of micropollutants (MPs). However, the transformation products formed during ozonation (OTPs) and their fate in biological or sorptive post-treatments is largely unknown. In this project, a high-throughput approach, combining laboratory ozonation experiments and detection by liquid chromatography high-resolution mass spectrometry (LC-HR-MS/MS), was developed and applied to identify OTPs formed during ozonation of wastewater effluent for a large number of relevant MPs (total 87). For the laboratory ozonation experiments, a simplified experimental solution, consisting of surrogate organic matter (methanol and acetate), was created, which produced ozonation conditions similar to realistic conditions in terms of ozone and hydroxyl radical exposures. The 87 selected parent MPs were divided into 19 mixtures, which enabled the identification of OTPs with an optimized number of experiments. The following two approaches were considered to identify OTPs. (1) A screening of LC-HR-MS signal formation in these experiments was performed and revealed a list of 1749 potential OTP candidate signals associated to 70 parent MPs. This list can be used in future suspect screening studies. (2) A screening was performed for signals that were formed in both batch experiments and in samples of wastewater treatment plants (WWTPs). This second approach was ultimately more time-efficient and was applied to four different WWTPs with ozonation (specific ozone doses in the range 0.23-0.55 gO3/gDOC), leading to the identification of 84 relevant OTPs of 40 parent MPs in wastewater effluent. Chemical structures could be proposed for 83 OTPs through the interpretation of MS/MS spectra and expert knowledge in ozone chemistry. Forty-eight OTPs (58%) have not been reported previously. The fate of the verified OTPs was studied in different post-treatment steps. During sand filtration, 87-89% of the OTPs were stable. In granular activated carbon (GAC) filters, OTPs were abated with decreasing efficiency with increasing run times of the filters. For example, in a GAC filter with 16,000 bed volumes, 53% of the OTPs were abated, while in a GAC filter with 35,000 bed volumes, 40% of the OTPs were abated. The highest abatement (87% of OTPs) was observed when 13 mg/L powdered activated carbon (PAC) was dosed onto a sand filter.

A novel submerged photocatalytic oscillatory membrane reactor for water polishing

A submerged photocatalytic oscillatory membrane reactor was tested for micropollutants removal from water as a tertiary treatment method for water polishing. A detailed study of the system performance at various operating conditions of membrane reactor and background water matrices including humic acid (HA) and secondary wastewater effluent (SWE) was conducted. Initially, the system was evaluated using suspended nanosized TiO2 under UV illumination and antipyrine as a model pollutant. Experiments using central composite design (CCD) and response surface analysis (RSM) were used to analyze the effects of the oscillation amplitude and frequency, and airflow rate on the antipyrine removal and the membrane flux. Optimum conditions for the reactor operation were determined using a composite desirability function. These conditions were then applied for the removal of other micropollutants with varying physiochemical properties namely, diclofenac, sulfamethoxazole, and hydrochlorothiazide. Up to 90% micropollutants removal can be achieved in Milli-Q water, although, the performance was noticeably affected in presence of background organics in SWE and HA due to either catalyst blocking and/or competition of organics, as well as catalyst agglomeration. A significant process intensification can be achieved using the proposed photocatalytic oscillatory membrane reactor configuration, which could offer a promising potential as a final polishing step for water recycling.

Importance of origin and characteristics of biopolymers in reversible and irreversible fouling of ultrafiltration membranes

The present work compares the chemical properties of isolated biopolymers of different origins and their fouling potential during ultrafiltration (UF). The biopolymers were extracted from secondary wastewater effluent as effluent organic matter (EfOM) and from surface water as natural organic matter (NOM). Multiple analytical techniques were used to characterize the isolates. The characterization results revealed that EfOM biopolymers were more enriched in protein-type structures compared to the NOM organics, and they presented significant differences in the reversibility of membrane fouling. Dissolved in pure water, EfOM biopolymers led to more irreversible fouling than that caused by NOM isolates. Dosing divalent cations (e.g., Ca2+) into the solutions increased the irreversibility of both types of fouling, while aggravating NOM fouling more significantly. Further investigation was conducted to understand the interaction between EfOM and NOM biopolymers during formation of the fouling layer. The results showed that the interaction between these two types of organics was negligible in the absence of salts. These findings highlight the importance of a comprehensive understanding of biopolymers from different origins, considering their chemical properties and water chemistry, which have valuable implications for selecting suitable membrane fouling control strategies for treating water from different origins.

Removal of Antibiotics and Nutrients by Vetiver Grass (Chrysopogon zizanioides) from a Plug Flow Reactor Based Constructed Wetland Model.

Overuse of antibiotics has resulted in widespread contamination of the environment and triggered antibiotic resistance in pathogenic bacteria. Conventional wastewater treatment plants (WWTPs) are not equipped to remove antibiotics. Effluents from WWTPs are usually the primary source of antibiotics in aquatic environments. There is an urgent need for cost-effective, environment-friendly technologies to address this issue. Along with antibiotics, nutrients (nitrogen and phosphorus) are also present in conventional WWTP effluents at high concentrations, causing environmental problems like eutrophication. In this study, we tested vetiver grass in a plug flow reactor-based constructed wetland model in a greenhouse setup for removing antibiotics ciprofloxacin (CIP) and tetracycline (TTC), and nutrients, N and P, from secondary wastewater effluent. The constructed wetland was designed based on a previous batch reaction kinetics study and reached a steady-state in 7 days. The measured concentrations of antibiotics were generally consistent with the modeling predictions using first-order reaction kinetics. Vetiver grass significantly (p < 0.05) removed 93% and 97% of CIP and TTC (initial concentrations of 10 mg/L), simultaneously with 93% and 84% nitrogen and phosphorus, respectively. Results show that using vetiver grass in constructed wetlands could be a viable green technology for the removal of antibiotics and nutrients from wastewater.

Conversion of soluble recalcitrant phosphorus to recoverable orthophosphate form using UV/H2O2

Soluble non-reactive phosphorus (sNRP), such as inorganic polyphosphates and organic P, is not effectively removed by conventional physicochemical processes. This can impede water resource reclamation facilities’ ability to meet stringent total P regulations. This study investigated a UV/H2O2 advanced oxidation process (AOP) for converting sNRP to the more readily removable/recoverable soluble reactive P (sRP), or orthophosphate, form. Synthetic water spiked with four sNRP compounds (beta-glycerol phosphate, phytic acid, triphosphate, and hexa-meta phosphate) at varying H2O2 concentration, UV fluence, pH, and temperature was initially tested. These compounds represent simple, complex, organic, and inorganic forms of sNRP potentially found in wastewater. The efficiency of sNRP to sRP conversion depended on whether the sNRP compound was organic or inorganic and the complexity of its chemical structure. Using 1 mM H2O2 and 0.43 J/cm2 (pH 7.5, 22 °C), conversion of the simple organic beta-glycerol phosphate to sRP was 38.1 ± 2.9%, which significantly exceeded the conversion of the other sNRP compounds. Although conversion was achieved, the electrical energy per order (EEO) was very high at 5.2 × 103 ± 5.2 × 102 kWh/m3. Actual municipal wastewater secondary effluent, with sNRP accounting for 15% of total P, was also treated using UV/H2O2. No wastewater sNRP to sRP conversion was observed, ostensibly due to interference from wastewater constituents. Wastewater utilities that have difficulty meeting stringent P levels might be able to target simple organic sNRP compounds, though alternative processes beyond UV/H2O2 need to be explored to overcome interference from wastewater constituents and target more complex organic and inorganic sNRP compounds.

Simultaneous removal of antibiotic resistant bacteria, antibiotic resistance genes, and micropollutants by a modified photo-Fenton process

Although photo-driven advanced oxidation processes (AOPs) have been developed to treat wastewater, few studies have investigated the feasibility of AOPs to simultaneously remove antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs) and micropollutants (MPs). This study employed a modified photo-Fenton process using ethylenediamine-N,N′-disuccinic acid (EDDS) to chelate iron(III), thus maintaining the reaction pH in a neutral range. Simultaneous removal of ARB and associated extracellular (e-ARGs) and intracellular ARGs (i-ARGs), was assessed by bacterial cell culture, qPCR and atomic force microscopy. The removal of five MPs was also evaluated by liquid chromatography coupled with mass spectrometry. A low dose comprising 0.1 mM Fe(III), 0.2 mM EDDS, and 0.3 mM hydrogen peroxide (H2O2) was found to be effective for decreasing ARB by 6-log within 30 min, and e-ARGs by 6-log within 10 min. No ARB regrowth occurred after 48-h, suggesting that the proposed process is an effective disinfectant against ARB. Moreover, five recalcitrant MPs (carbamazepine, diclofenac, sulfamethoxazole, mecoprop and benzotriazole at an initial concentration of 10 μg/L each) were >99% removed after 30 min treatment in ultrapure water. The modified photo-Fenton process was also validated using synthetic wastewater and real secondary wastewater effluent as matrices, and results suggest the dosage should be doubled to ensure equivalent removal performance. Collectively, this study demonstrated that the modified process is an optimistic ‘one-stop’ solution to simultaneously mitigate both chemical and biological hazards.