Secondary Wastewater Treatment Research Articles

Tracking antibiotic resistance genes and class 1 integrons in Escherichia coli isolates from wastewater and agricultural fields.

Considering high concentrations of multidrug-resistant bacteria and antibiotic resistance genes (ARGs) in wastewater, agricultural reuse of treated wastewater may be a public health threat due to ARG dissemination in different environmental compartments, including soil and edible parts of crops. We investigated the presence of antibiotic-resistant Escherichia coli as an indicator bacterium from secondary treated wastewater (STWW), water- or wastewater-irrigated soil and crop samples. ARGs including blaCTX-m-32, blaOXA-23, tet-W, sul1, cml-A, erm-B, along with intI1 gene in E. coli isolates were detected via molecular methods. The most prevalent ARGs in 78 E. coli isolates were sul1 (42%), followed by blaCTX-m-32 (19%), and erm-B (17%). IntI1 as a class 1 integrons gene was detected in 46% of the isolates. Cml-A was detected in STWW isolates but no E. coli isolate from wastewater-irrigated soil and crop samples contained this gene. The results also showed no detection of E. coli in water-irrigated soil and crop samples. Statistical analysis showed a correlation between sul1 and cml-A with intI1. The results suggest that agricultural reuse of wastewater may contribute to the transmission of antibiotic-resistant bacteria to soil and crop. Further research is needed to determine the potential risk of ARB associated with the consumption of wastewater-irrigated crops.

Greenhouse gas budgets of severely polluted urban lakes in India

Inland waters are important sources of greenhouse gases and emissions from polluted subtropical systems may be contributing to the observed global increase in atmospheric methane concentrations. Here we detail a scoping study where dissolved concentrations of greenhouse gases methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O) were measured in two contrasting urban lakes in Bangalore (Bengaluru), Karnataka, India, from June 2018 to February 2020. Bellandur Lake is a severely polluted system whilst Jakkur Lake has been subject to partial restoration via treatment of organic matter inputs. Methane concentrations in Bellandur Lake were three orders of magnitude higher than in Jakkur Lake, with a mean concentration of 3.02 ± 1.57 mg CH4-C L−1 compared to 1.72 ± 1.22 μg CH4-C L−1. At Bellandur Lake, dissolved CO2 concentrations were of the same order of magnitude as for CH4, whereas at Jakkur Lake dissolved CO2 concentrations were two orders of magnitude greater than for CH4. Concentrations of N2O were negligible in both lakes. Extrapolating our data to estimate greenhouse gas fluxes, mean daily methane fluxes from Bellandur Lake were consistently in excess of 1000 mg CH4 m2 d−1, rendering the lake a source of GHGs to the order of 148,350 ± 21,790 ton yr−1 CO2-e yr−1, compared to 100 ± 37 ton CO2-e yr−1 from Jakkur Lake, with CH4 contributing primarily to this difference. We propose that the contribution of severely polluted urban lakes to global CH4 production warrants further investigation, particularly as our evidence suggests that standard secondary wastewater treatment to support restoration of these systems has the potential to significantly reduce CH4 emissions.

Evaluation of Titanium Tetrachloride (TiCl₄) as an Alternative Coagulant and Characterization of Recovered TiO₂.

Titanium tetrachloride (TiCl₄) as an alternative coagulant to remove organic matters and nutrients from the effluent of the secondary wastewater treatment was evaluated by comparison of removal efficiency of total phosphorous to Al- and Fe-based coagulants. Also, the surface characteristics, elemental contents, and crystallinity of the TiO₂ produced from wastewater sludge flocculated with TiCl₄ coagulant were investigated depending on the calcination temperatures. The more dosages of coagulants were injected, the greater concentrations of the cations (Al+3, Fe+3, Ti+4) and hydrogen ions (H+) resulted in the lower pH. Also, TiCl₄ formed larger and heavier flocs than other coagulants and resulted in greater T-P removal efficiencies with reduced amounts of dosage. The phase change of anatase and rutile crystalline structures of TiO₂ incinerated from wastewater sludges of TiCl₄ coagulant was observed at relatively high calcination temperatures due to the existence of mixtures of organic matters, nutrients, and various impurities in the wastewater sludges of TiCl₄ coagulant. Both C and P atoms were found to be mainly doped in/on TiO₂ and the C and P atom originated from residual carbon of the settled organic matters and phosphorus nutrients present in effluents from sewage treatment plant, respectively. Therefore, 600-800 °C is the optimal calcination temperatures for TiO₂ produced from TiCl₄ coagulant flocculated with effluents from sewage treatment plant.

Long‐Term Trends Show Improvements in Water Quality in the Chicago Metropolitan Region With Investment in Wastewater Infrastructure, Deep Tunnels, and Reservoirs

AbstractThe ecological degradation of streams draining urban land, known as the urban stream syndrome, is characterized by elevated nutrients and contaminants, increased hydrologic flashiness, and altered biotic assemblages. This study demonstrated an improvement in chemical characteristics by evaluating water quality trends from 1975 to 2012 and from 2013 to 2018 in the Chicago, Calumet, and Des Plaines River Systems in Cook County, Illinois. Data from 41 monitoring locations were compiled and 11 water quality parameters were analyzed for long‐term monotonic trends and differences in water quality parameters between select time periods to investigate the outcomes from improvements in water reclamation plant (WRP) and tunnel and reservoir infrastructure carried out by the Metropolitan Water Reclamation District of Greater Chicago. From 1975 to 2012, significant decreasing trends in concentrations were demonstrated at most sampling locations for total organic carbon (TOC), total Kjeldahl nitrogen (TKN), ammonium nitrogen (), total suspended solids (TSS), fecal coliform (FC), and sulfate. Significant increasing trends were demonstrated for dissolved oxygen (DO) and chloride concentrations and temperature. Total phosphorus (TP) concentrations increased downstream of the Stickney, Kirie, and Calumet WRPs from 1975 to 2012, but decreased downstream of the Kirie WRP and had no trends downstream of the Stickney and Calumet WRPs from 2013 to 2018. Improvements in TKN, , TOC, TSS, FC, TP, and DO concentrations over four decades demonstrated the benefits of expanding secondary wastewater treatment and implementing the Tunnel and Reservoir Plan System, instream and side‐stream elevated pool aeration stations, and effluent disinfection.

Changes in soil salinity under treated wastewater irrigation: A meta-analysis

In view of water shortages, the development and utilization of unconventional water resources have been studied extensively. Treated domestic or industrial wastewater used for agricultural irrigation is an unconventional water resource utilization method. Due to the particularities of water sources, previous studies have mainly focused on changes in soil heavy metals, microorganisms, and organic substances and crop responses to toxic elements; thus, attention to soil salinity is of secondary importance. After selecting qualifying research, a meta-analysis was performed to statistically analyze the data of seven variables (potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), electrical conductivity (EC), pH, and yield) to 1) estimate the mean effects of treated wastewater (TWW) irrigation on the soil salinity, soil pH and crop yield; and 2) identify the wastewater treatment grade (primary treated wastewater (PTW), secondary treated wastewater (STW), and tertiary treated wastewater (TTW)) and soil texture (sandy texture, loamy texture and clayey texture) that benefit TWW irrigation. The results showed that TWW irrigation caused a significant accumulation of soil salinity, and the increase in cation content from high to low was K (90.1%), Na (59.9%), Mg (25.2%) and Ca (17.3%). EC also increased significantly by approximately 57.2%, while there was no significant change in pH, and even the crop yield presented an average reduction of nearly 6.5%. PTW contributed to the largest salt accumulation, followed by TTW and STW. STW showed a significant increase in EC but did not show a significant change for the four ions. In terms of yield, STW can increase yield, while TTW has the opposite effect. In general, the sandier the soil texture, the higher is the salt content detected, although the retention of salt in loamy textured soil may differ depending on the ions. The yield of crops grown increased in the clayey textured soil and decreased in the loamy textured soil. Our study elucidated the response of soil salinity accumulation under TWW irrigation and could provide a reference for unconventional water resource utilization.

Application of Biofilm Carrier in Aerobic Reactors as a Method to Improve Quality of Wastewater Treatment

The research revealed in the paper considers the improvement of secondary treatment of wastewater in the aerobic reactor to provide removal of organics and nutrients. There were five types of polymer biofilm carriers taken into account initially; however, two of them were decided not to apply due to technological reasons. The main part of the research was divided into three substages to investigate each type of biofilm carrier. According to the literature review, the optimal efficiency may be reached if the carrier filling ratio is 10 to 30% of reactor volume. On this basis, there were three benches launched at each sub-stage with a corresponding filling ratio of 10, 20, and 30%. The fourth reactor at each sub-stage had no floating carrier to control the experiment. The research of all three types of carriers showed the effect of BOD removal in the range of 95–96% for benches equipped with a floating carrier, which can be considered similar to the control bench with the efficiency of 92%. In the case of ammonia nitrogen, the removal control bench showed only 55% of efficiency, while floating carriers helped to increase the efficiency up to 70–86%. Despite obtaining relatively positive results, the research has to be continued to achieve regulation requirements in treatment quality.

Fate of organic micropollutants in reverse electrodialysis: Influence of membrane fouling and channel clogging

Reverse electrodialysis (RED)-based hybrid processes (e.g., RED-ED/RO) have been proposed for more energy-efficient desalination in drinking water production. The use of secondary-treated wastewater as a low-salinity stream in RED raises concerns about enhanced membrane fouling and, especially, potential organic micropollutants (OMPs) contamination of drinking water sources. The influence of membrane fouling and channel clogging on the transport and adsorption of 25 OMPs in RED was investigated using synthetic and real seawater and secondary-treated wastewater for 40 days. Real wastewater induced more membrane fouling and channel clogging than its synthetic counterparts and real seawater, as evidenced by pressure drop increase, permselectivity decrease, and ATP levels increase. The OMP transport and adsorption in real seawater conditions were higher than their synthetic counterparts, while OMP transport and adsorption under real wastewater conditions decreased significantly compared to synthetic wastewater conditions, possibly due to: 1) higher OMP-membrane interaction compared to OMP-fouling layer interaction (steric and electrostatic mechanisms), and 2) OMP adsorption onto the effluent organic matter in real wastewater. These results provide critical implications for industrial scenarios: OMPs transport might be overestimated at the lab-scale when using synthetic streams, clearly indicating the key role of effluent organic matter and fouling in RED using impaired water.

An electro-oxidation reactor for treatment of nanofiltration concentrate towards zero liquid discharge

Nanofiltration (NF) concentrate generated from the secondary wastewater treatment contains high concentration of ammonium nitrogen and refractory organics, thus having great environmental risks. In this study, an electro-oxidation (EO) reactor built up with a boron-doped diamond (BDD) anode is utilized to treat the NF concentrate. To reach “zero liquid discharge”, a mixture of the electrolytic effluent and the raw secondary wastewater was collected and transported back to the NF module. Results show that under the current density of 30 mA·cm−2, most of ammonia nitrogen was decomposed into N-gases within 30 min due to the active chlorine radicals generated in the electrochemical process. Moreover, the EO reactor completely eliminated antibiotics, humic acids and bacteria in the NF concentrate under long electrolysis time of 60 min. In particular, the organic pollutants removal rate was kept at a stable value in the EO reactor for a long-term operation of up to 120 h. In addition, the NF membrane remained a constant permeate flux without being affected by the membrane biofouling caused by organic components in wastewater. Our study highlights the potential of the NF-EO process as a “zero liquid discharge” approach for treatment of the secondary wastewater.

Secondary wastewater treatment processes optimization

Introduction. The level of water pollution in Ukraine continues to grow, despite the strengthening of requirements for the treated water, so the existing approaches to the water treatment processes control need to be revised and improved.
 Materials and methods. Mathematical Programming methods for formalization and solving the optimization problem are used. Computer simulation research using the program developed by the authors are applied to verify the compliance of the obtained results with the normative values and data of normal operation.
 Results and discussion. The optimization of processes control was performed on the example of a typical process of secondary wastewater treatment, which is used for wastewater treatment in Kyiv and nearby settlements. The secondary treatment unit consists of an aeration tank, into which air is forcibly supplied and evenly distributed, and a secondary settling tank with recycling. The problem of optimization of biological wastewater treatment control process is formalized: minimization of pollutant concentration in treated water is chosen as the main aim of optimization, air flow to aeration tank is chosen as control parameter, quadratic deviation of current concentration values from normative ones is chosen for target function. To solve the optimization task, a software module in JavaScript was developed using a client-server architecture that works in real time and allows to obtain such values of oxygen consumption in the aeration tank, which provide a minimum deviation of the concentration of pollutants from the normative values. The simulations showed that the calculated control values provide a reduction in the concentration of pollutants to the normative values within 6-10 hours, which corresponds to the data of normal operation, and the difference between the calculated and actual data does not exceed 5%.
 Conclusions. The obtained results allow to find a set of technological influences to ensure optimal control according to the selected criterion, and are also the basis for calculating the control system. The results of calculations can be used for short-term - up to 8 hours - forecasting of water quality indicators.

Water Hyacinths (Eichhornia crassipes) – Application for Secondary Wastewater Treatment and Biomass Production

Clean water is one of the most significant challenges for our society. Efficient reuse of effluent water after treatment can becomes an effective solution to the shortage of water resources. The focus of this study is to investigate the use of Eichhornia crassipes plants for post treatment of clarified municipal residential sewage under natural conditions using a small pilot Laboratory Water Hyacinth Clarifier system. Twelve Eichhornia crassipes plants are used to investigate total phosphorus and ammonia nitrogen removal during a 20-day study period under various retention rates. The biomass gain of the Eichhornia crassipes plants was 2.4-fold from the initial weight of 1556.5 g to 3676.7 g. Total phosphorous reduction of 10.64%, 11.83%, 20.93%, 41.66%, 67.12%, and 40.13% for the 1.5, 9.0, 12.0, 24.0, 48.0 h, and 120.0-hour retention times respectively. Ammonia nitrogen removal was between 35.71%, 33.33% for the 1.50 and 9.0-hour retention time and 42.85% for the 12.0 and 24.0-hour retention time. A reduction of 71.43% resulted for the 48.0-hour retention time and an 85.71% reduction for the 120.0-hour retention time. Overall retention time of 24.0 h, 48.0 h and 120 h tend to give best removal rates for both total phosphorus and ammonia nitrogen removal. Factors such as climate, contaminant concentration, retention rate, and weather conditions play an important role for the application of Eichhornia crassipes in a tertiary treatment sequence of MRS.

Water quality index including periphyton chlorophyll-a in forested urban watersheds from Tierra del Fuego (Argentina)

The city of Ushuaia, Argentina, has experienced a rapid and unorganized population growth with possible consequences on the dynamics and functioning of urban lotic ecosystems. Urban expansion was not largely accompanied by the development of infrastructure for the provision of services such as drinking water and sewers to all the population. Currently, only 65% of the population is connected to the main sewage system (pre-treatment) and the city does not have a secondary wastewater treatment plant yet. We evaluated the impact of wastewater discharges and non-point contamination on the water quality of the three main water courses that cross the city of Ushuaia: Pipo river (PR), Buena Esperanza stream (BES) and Arroyo Grande river (AGR). We sampled four sites per watershed from spring to autumn in two consecutive years (2018 and 2019): S1 (not urbanized at the upper section), S2 (transitional section), S3 (urbanized at the middle-low section), and S4 (urbanized, close to the outlet). We developed the Fuegian Water Quality Index (F_WQI) as a tool for environmental monitoring in forest streams which includes several indicators of organic inputs (dissolved oxygen, nitrogen-ammonium, total phosphorus, fecal coliform bacteria) and periphyton chlorophyll-a (Peri Chl-a). The variables were ranked and weighed, and the index was constructed using a mathematical formula. Urbanization negatively impacted the water quality of these ecosystems; the F_WQI showed “very bad” and “bad” water quality categories at S4 in BES and AGR, both sites impacted by wastewater discharges and large percentage of urbanized area. Likewise, in the PR watershed, with less urbanization and sewage discharges, the F_WQI indicated “very good” water quality. The F_WQI summarizes the water quality of forested watersheds in a simple numerical scale, resulting in a useful tool for monitoring studies in temperate rivers and streams. We encourage the inclusion of Peri Chl-a in water quality indices, due to its ubiquity in these ecosystems and the fact that it increased the sensitivity of the index.

Performance of horizontal flow constructed wetland for secondary treatment of domestic wastewater in a remote tribal area of Central India

The purification of the primary treated domestic sewage was performed in the present study through the horizontal sub-surface flow constructed wetland (CW) of 10 × 3.5 m dimension. The study was performed using three setups of CW 1 (Unplanted CW), CW 2 (CW planted with macrophyte Typha latifolia), and CW 3 (CW planted with two species of macrophyte T. latifolia and Commelina benghalensis). The purification experiments were performed by converting one type of CW into the other form sequentially, i.e., CW 1 was built first and after the experiments, it was converted into CW 2 and then CW 3. The CW was filled with a layer of coarse and fine gravel of 70 cm depth as filter media in 1:2 ratio. Each set of wetland was operated for 3 months (12 wk) during which the treatment performance of wetlands for basic physicochemical parameters was evaluated. The CW was operated in continuous mode at an average hydraulic loading rate of 250 L h− 1 and the treated effluent was analysed twice every week at four different sampling points having hydraulic retention times (HRT) of 12, 24, 36 and 48 h for important sewage quality parameters All the three setups of CW were able to clean the primary treated sewage significantly. Among the three sets of wetlands used, CW 3 was the best performer removing 79, 77, 79, 79, and 78% of biochemical oxygen demand, chemical oxygen demand, nitrate, ammonia, and phosphate respectively in 48 h HRT. Among the three sets of wetlands, the CW 3 removed the highest percent of total coliforms, fecal coliforms, and E. coli as 64, 61 and 52% respectively.

The oxygenic photogranule for wastewater treatment process

Wastewater treatment is an energy-intensive process. During secondary wastewater treatment, unwanted characteristics like Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD) etc. are reduced to permissible levels with the help of bacteria as this is a microbe driven process. A novel method of cultivating Oxygenic Photo Granules (OPGs) which are natural aggregates predominantly consisting of cyanobacteria from the activated sludge and using it to treat the wastewater in the secondary treatment is under development. After the primary treatment, OPGs help to substitute the high energy-consuming aeration equipment which deems the secondary process more sustainable. Cultivation of OPGs is influenced by many factors including the intensity of light used during cultivation, the concentration of sludge etc. Manipulating these factors, we can cultivate OPGs in the most efficient way possible. The objective of this work is the optimization of the time constraints for developing OPG samples, then analyze the energy saving of this process at a pilot scale. OPGs substitute the aeration equipment in the secondary treatment process, and they are mix evenly with the wastewater to be treated in a sequential batch reactor. Upon continuous stirring followed by settling and decanting, the wastewater is treated and analyzed. Utilization of OPGs in wastewater treatment not only saves energy but is also efficient than the conventional method, thereby making this process a more economical option.

Solar photon-Fenton process eliminates free plasmid DNA harboring antimicrobial resistance genes from wastewater

This work aimed to assess the elimination and inactivation of resistance-conferring plasmids (RCPs) present in suspension in secondary wastewater by solar photo-Fenton as these are important vectors for the dissemination of antimicrobial resistance. Experiments were performed in synthetic secondary wastewater (SWW) and municipal wastewater treatment plant effluent (MWWTPE). Solar photo-Fenton (50 mg L−1 of H2O2 and 30 mg L−1 of Fe2+) was carried out for 60 min at neutral pH by applying the intermittent iron addition strategy. The removal of RCPs was assessed by Real-Time Polymerase Chain Reaction (qPCR). The transformation of competent non-resistant E. coli was used to evaluate the inactivation of target RCPs harboring antibiotic resistance genes (ARGs) to ampicillin (pSB1A2) or kanamycin (pSB1K3) after treatment and controls. Solar photo-Fenton completely removed RCPs initially present in both matrixes (SWW and MWWTPE), showing enhanced performance compared to the dark Fenton process. Both RCPs were inactivated after 30 min of solar photo-Fenton treatment, while 60 min were necessary to achieve the same effect for the dark Fenton reaction under similar conditions. These results indicate the potential of solar photo-Fenton to improve wastewater quality and reduce the spread of antimicrobial resistance in the environment by hampering the discharge of cell-free RCPs present in suspension in MWWTP onto environmental waters.

Low-pressure volume retarded osmosis for removal of per- and polyfluoroalkyl substances

Forward osmosis is an energy efficient process that is capable of recovering high-quality water from secondary wastewater treatment. However, regeneration of the draw solution (DS) is a problem that needs to be addressed. Herein, we developed and optimized a one-step process that does not require additional treatment for the DS. This process, called pressure assisted-volume retarded osmosis (PA-VRO), utilizes naturally occurring pressure with the aid of a small inlet pressure (< 1 bar). Poly(styrenesulfonate) was employed as the DS, for its high solubility in water and large molecular size (∼70,000 Da). Accordingly, real wastewater was employed as the feed solution for 48 h to remove perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) through PA-VRO. The rejection rates for PFOA/PFOS and poly(sodium-4-styrenesulfonate) (PSS) were observed to exceed 98%, after 24 h and 99%, after 48 h. Moreover, there were no traceable amounts of PFOA/PFOS in the DS, and hence the detected concentrations of PFOA and PFOS can be attributed to the residuals from the equipment. Therefore, this well-optimized PA-VRO process can be utilized for potable water production from treated wastewater.

A COMPARATIVE STUDY OF CONVENTIONAL EXTENDED AERATION AND MODERN MEMBRANE BIOREACTOR METHODS OF SEWAGE TREATMENT FROM THE ENVIRONMENTAL AND FINANCIAL PERSPECTIVES

The conventional extended aeration (EA) method has been considered as an effective method of secondary wastewater treatment in various installations around the world. The membrane bioreactor (MBR) method has been promoted by membrane manufacturers over the past decade as the most efficient treatment method in the industry. Research has shown the higher quality of MBR effluent compared with that of EA, but thecomparison has seldom included the financial aspects. If the effluent quality from both methods is acceptable for a given reuse application, then a major consideration in adopting either method must be financial (i.e., the capital expenditure (CAPEX) and operating expenses (OPEX) involved in their deployment). In this study, simulation of both methods is conducted for domestic wastewater treatment plants using the biological and financial models of CAPDETWorksTM. The CAPEX and OPEX findings from the simulation were re-based to October 2019 usingglobal price indices. Hydraulic loads from 500 to 5,000 m3/d were considered for three influent strengths: weak, medium, and strong. It is found that the EA method is less costly in meeting the effluent-quality requirements of certain reuse applications, while the MBR is recommended for the extra strong-strength influent especially for units smaller than 500m3/d, due to both effluent quality and lifetime cost.

Evaluation of various waste substrates for biofilm formation and subsequent use in aerobic packed-bed reactor for secondary treatment of domestic wastewater.

Immobilization of bacterial cells on suitable substrates is of utmost importance in the secondary treatment of wastewater using fixed-film reactors. Therefore, screening of efficient and cheaper materials for bacterial surface immobilization was carried out. Eleven waste materials were used as substrates, packed in a column, and bacterial surface immobilization was carried out using cow dung slurry/MLSS mixture. All the chosen substrates were screened for bacterial immobilization/biofilm formation by standard bacterial enumeration technique. The substrate with the highest biofilm-forming ability was used for secondary treatment of raw domestic wastewater. The results showed that high-density polyethylene and aluminium foil sheets have poor immobilizing characteristics with 2.2 × 108 and 2.4 × 108CFU/cm2 respectively, whereas jute fibres were observed to be the most efficient among the substrates with 5.1 × 1023CFU/cm2. The column packed with jute fibres was used for wastewater treatment. Various physico-chemical parameters were analyzed before and after treatment and there was a significant reduction in major parameters after treatment. The bacteria-immobilized jute fibres showed maximum immobilization potential and were highly efficient in wastewater treatment, and therefore these findings offer immense promise in the synthesis of composite polymers for bacterial immobilization and subsequent secondary treatment.

Fate and persistence of antibiotic-resistant bacteria and genes through a multi-barrier treatment facility for direct potable reuse

Abstract Given the availability of technological solutions and guidelines for safe drinking water, direct potable reuse of reclaimed water has become a promising option to overcome severe lack of potable water in arid regions. However, the growing awareness of the presence of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARG) in corresponding raw wastes has led to new safety concerns. This study investigated the fate of ARB and intracellular and extracellular ARG after each treatment step of an advanced water treatment facility in Windhoek, Namibia. The New Goreangab Water Reclamation Plant (NGWRP) produces drinking water from domestic secondary wastewater treatment plant effluent and directly provides for roughly a quarter of Windhoek's potable water demand. Procedures to study resistance determinants were based on both molecular biology and culture-based microbiological methods. TaqMan real-time PCR was employed to detect and quantify intracellular resistance genes sul1, ermB, vanA, nptII and nptIII as well as extracellular resistance gene sul1. The NGWRP reduced the amount of both culturable bacterial indicators as well as the resistance genes to levels below the limit of detection in the final product. The main ozonation and the ultrafiltration had the highest removal efficiencies on both resistance determinants.

Linking PFAS partitioning behavior in sewage solids to the solid characteristics, solution chemistry, and treatment processes

Per- and polyfluoroalkyl substances (PFAS) have gained increasing attention due to the potential health risks that they present. Secondary sludge and biosolids are known as notable PFAS emission routes to the environment. In this study, partitioning behavior of 14 PFAS were investigated across four secondary wastewater treatment types (activated sludge, trickling filter, biological nutrient removal, and rotating biological contactor; n = 10) and three sludge stabilization methods (composting, aerobic digestion, and anaerobic digestion; n = 6). Batch experiments were conducted to evaluate how PFAS sorption to secondary sludge and biosolid was affected by various treatment methods, solid properties, and solution chemistry parameters. Insignificant differences in compound-specific partitioning coefficients (Kd) were observed among the four secondary treatment methods. However, sludge stabilization resulted in significantly different partitioning behavior among biosolid samples, in which anaerobically digested biosolids generally had significantly higher Kd values compared to aerobically digested and composted biosolids (anaerobic digestion > aerobic digestion > composting). Multiple linear regression models were developed to explain analyte-specific Kd values across the biosolid samples and identified that solid-specific property significance was as follows: protein fraction > organic matter fraction > lipid fraction. Stabilization generally decreased the PFAS sorption capacity relative to the secondary sludge samples. Furthermore, PFAS Kd increased with elevated calcium concentrations and ionic strengths and decreased with increasing pH values in sludge and biosolid samples. These findings could inform the decision-making process to reduce the release of PFAS to the environment.

Integrated Estrogenic Effects and Semi-Volatile Organic Pollutants Profile in Secondary and Tertiary Wastewater Treatment Effluents in North China

Integrated Estrogenic Effects and Semi-Volatile Organic Pollutants Profile in Secondary and Tertiary Wastewater Treatment Effluents in North China