Effect of wheat crops on the persistence and attenuation of antibiotic resistance genes in soil after swine wastewater application

Swine wastewater (SW) application introduces antibiotic resistance genes (ARGs) into farmland soils. However, ARG attenuation in SW-fertigated soils, especially those influenced by staple crops and soil type, remains unclear. This study investigated twelve soil ARGs and one mobile genetic element (MGE) in sandy loam, loam, and silt loam soils before and after SW application in wheat-planted and unplanted soils. The results revealed an immediate increase in the abundance of ARGs in soil by two orders of magnitude above background levels following SW application. After SW application, the soil total ARG abundance was attenuated, reaching background levels at 54 days; However, more individual ARGs were detected above the detection limit than pre-application. Among the 13 genes, acc(6')-lb, tetM, and tetO tended to persist in the soil during wheat harvest. ARG half-lives were up to four times longer in wheat-planted soils than in bare soils. Wheat planting decreased the persistence of acc(6')-lb, ermB, ermF, and intI2 but increased the persistence of others such as sul1 and sul2. Soil type had no significant impact on ARG and MGE fates. Our findings emphasize the need for strategic SW application and the consideration of crop cultivation effects to mitigate ARG accumulation in farmland soils.

Impact of mixed microalgal and bacterial species on organic micropollutants removal in photobioreactors under natural light

Single microalgae species are effective at the removal of various organic micropollutants (OMPs), however increased species diversity might enhance this removal. Sixteen OMPs were added to 2 continuous photobioreactors, one inoculated with Chlorella sorokiniana and the other with a microalgal-bacterial community, for 112 d under natural light. Three media were sequentially used in 3 Periods: I) synthetic sewage (d 0-28), II) 10x diluted anaerobically digested black water (AnBW) (d 28-94) and III) 5x diluted AnBW (d 94-112). Twelve OMPs were removed > 30 %, while 4 were < 10 % removed. Removal efficiencies were similar for 9 OMPs, yet the mixed community showed a 2-3 times higher removal capacity (µg OMP/g dry weight) than C. sorokiniana during Period II pseudo steady state. The removal decreased drastically in Period III due to overgrowth of filamentous green algae. This study shows for the first time how microbial community composition and abundance are key for OMPs removal.

Indene, indane and naphthalene in a mixture with BTEX affect aerobic compound biodegradation kinetics and indigenous microbial community development

BTEX (benzene, toluene, ethylbenzene, xylene) are common pollutants often found in former gasworks sites together with some other contaminants like indene, indane and naphthalene (Ie, Ia, N). This study aimed to evaluate the inhibitory or stimulative substrate interactions between BTEX, and Ie, Ia, N during aerobic biodegradation. For this, batch bottles, containing originally anaerobic subsurface sediments, groundwater and indigenous microorganisms from a contaminated former gasworks site, were spiked with various substrate combinations (BTEX, BTEXIe, BTEXIa, BTEXN, BTEXIeIa, BTEXIeN, BTEXIaN, BTEXIeIaN). Subsequently concentrations were monitored over time. For the BTEXIeIaN mixture, initial concentrations were between 1 and 5 mg L-1, and all compounds were completely degraded by the microbial consortia within 39 days of incubation. The experimental data were fitted to a first order kinetic degradation model for interpretation of inhibition/stimulation between the compounds. Results showed that indene, indane, and naphthalene inhibited the degradation of benzene, toluene, ethylbenzene, o-xylene, with benzene being the most affected. M/p-xylene is the only compound whose biodegradation is stimulated by the presence of indene and indane (individually or mixed) but inhibited by the presence of naphthalene. 16S rRNA amplicon sequencing revealed differentiation in the microbial communities within the batches with different substrate mixtures, especially within the two microbial groups Micrococcaceae and Commamonaceae. Indene had more effect on the BTEX microbial community than indane or naphthalene and the presence of indene increased the relative abundance of Micrococcaceae family. In conclusion, co-presence of various pollutants leads to differentiation in degradation processes as well as in microbial community development. This sheds some light on the underlying reasons for that organic compounds present in mixtures in the subsurface of former gasworks sites are either recalcitrant or subjective towards biodegradation, and this understanding helps to further improve the bioremediation of such sites.

Impact of wastewater characteristics on the removal of organic micropollutants by Chlorella sorokiniana

Microalgae-based technologies can be used for the removal of organic micropollutants (OMPs) from different types of wastewater. However, the effect of wastewater characteristics on the removal is still poorly understood. In this study, the removal of sixteen OMPs by Chlorella sorokiniana, cultivated in three types of wastewater (anaerobically digested black water (AnBW), municipal wastewater (MW), and secondary clarified effluent (SCE)), were assessed. During batch operational mode, eleven OMPs were removed from AnBW and MW. When switching from batch to continuous mode (0.8 d HRT), the removal of most OMPs from AnBW and MW decreased, suggesting that a longer retention time enhances the removal of some OMPs. Most OMPs were not removed from SCE since poor nutrient availability limited C. sorokiniana growth. Further correlation analyses between wastewater characteristics, biomass and OMPs removal indicated that the wastewater soluble COD and biomass concentration predominantly affected the removal of OMPs. Lastly, carbon uptake rate had a higher effect on the removal of OMPs than nitrogen and phosphate uptake rate. These data will give an insight on the implementation of microalgae-based technologies for the removal of OMPs in wastewater with varying strengths and nutrient availability.

The removal of micropollutants from treated effluent by batch-operated pilot-scale constructed wetlands

Micropollutants (MPs), such as pharmaceuticals and antibiotics, are present in the environment at low concentrations (ng/L-μg/L). A constructed wetland (CW) is a nature-based wastewater treatment technology, which can be used to remove MPs from wastewater treatment plant effluent. This study aimed to improve MP removal of CWs by optimizing the design of batch-operated CW. Three pilot-scale CWs were built to study the effect of two design-features: the use of a support matrix (a mixture of bark and biochar) and continuous aeration. The use of bark-biochar as support matrix increased the removal of 11 of 12 studied MPs compared to the CW filled with conventional material sand. The highest improved removal by the addition of bark-biochar was more than 40% (median) for irbesartan, carbamazepine, hydrochlorothiazide and benzotriazole. Aerating the bed of the bark-biochar CW did not change MP removal. Besides, the presence of bark-biochar also enhanced the removal of total nitrogen during 10 months of operation, but no improvement was observed on the total organic carbon and total phosphorus removal. Considering the application in a batch-operated CW, MP removal can be greatly enhanced by replacing sand with bark-biochar that will act as MP adsorbing matrix.

Use of ion chromatographic pulsed amperometric method (IC-PAD) for measuring aqueous sulfide in synthetic and real domestic wastewater

Sulfide detection in domestic wastewater is widely demanded, as sulfide induces odour nuisance and wastewater assets corrosion. However, traditional sulfide detection methods are usually plagued by the limited detection range or interference from impurities. To address these constraints, this study improved the ion chromatographic pulsed amperometric method (IC-PAD) and tested its validity for use in domestic wastewater. Prior to sulfide detection, sulfide-containing sample collection usually requires the use of sulfide antioxidant buffers (SAOB) to minimize sulfide loss. Different sample matrixes require different SAOB recipes, which increases complexity and uncertainty when measuring different environmental samples. Therefore, this study also developed a more convenient and generic sample collection method without the addition of SAOB. The results indicated that the proposed SAOB-free sample collection method could minimize the sulfide loss during sample collection. The IC-PAD method showed a wide linear detection range up to 10 mg-S/L. The detection limit was 3 μg-S/L. Matrix effect studies showed that 1 g/L glucose, formate, acetate, methanol, ethanol, propionate, butyrate, lactate, or sulfate had no evident interference on sulfide measurement. However, 5 mM phosphate buffer led to interference, but reducing the KOH eluent concentration from 62 to 30 mM avoid this interference. Wolfe's vitamin mixture and Wolfe's modified mineral mixture could cause diminutive interference equivalent to 2.53 ± 1.32 μg-S/L sulfide. Moreover, the interference caused by chloride indicated that the IC-PAD method is more applicable for measuring sulfide in low-chloride wastewater. To this end, the IC-PAD method showed high accuracy and precision in the real domestic wastewater samples with chloride concentration of 68 mg/L. The recovery was higher than 97% and the relative standard deviation (RSD) was lower than 1.2%. This study demonstrated the potential use of IC-PAD method for measuring sulfide in real domestic wastewater and possible interference from the solution matrix to be considered.

The effect of anode potential on electrogenesis, methanogenesis and sulfidogenesis in a simulated sewer condition

Methane emissions from the sewer system are considered to be a non-negligible source of aggravating the greenhouse effect. Meanwhile, the sewer system has long been plagued by sulfide-induced corrosion problems. This study explored the possibility of using a bioelectrochemical system to intensify the competition between electroactive bacteria, methanogens and sulfate-reducing bacteria, thereby reducing the production of methane and sulfide. Dual-chamber bioelectrochemical reactors were constructed and operated in fed-batch mode with the coexistence of Electroactive bacteria, Methanogenic archaea and Sulfate-reducing bacteria. Acetate was supplied as the sole carbon source. The results indicated that electrogenesis induced by the anode potentials of -0.42 V and -0.2 V (vs. Ag/AgCl) had advantages over methanogenesis and sulfidogenesis in consuming acetate. The stimulated electrogenesis by anode potentials resulted in a decrease in pH. Methane production was suppressed in the reactors with anode potentials of -0.42 and -0.2 V compared to open circuit controls. In contrast to methane, the capacity for sulfide production was facilitated in the reactors with the anode potentials of -0.42 V and -0.2 V compared to open circuit controls. 16s rRNA gene analysis showed that Geobacter was the most abundant genus on the anode biofilm in the anode potential-controlled reactor, while acetoclastic methanogens dominated in open circuit controls. Methanosaeta and Methanosarcina were the most abundant methanogens in open circuit controls. Collectively, our study demonstrates that the use of electrodes with anode potential control can help to control methane emissions, but could not yet prevent sulfide production, which requires further research.

Mesocosm constructed wetlands to remove micropollutants from wastewater treatment plant effluent: Effect of matrices and pre-treatments

The contamination of the aquatic environment by micropollutants (MPs) brings risks for the ecosystem and human health. Constructed wetlands (CWs) were an eco-friendly technology to remove MPs from wastewater treatment plant effluent. In this study, the removal of MPs was evaluated in seven vertical flow mesocosm CWs with different configurations, including different support matrices (sand and a combination of bark-biochar), light pre-treatments (UVC and sunlight) or bioaugmentation in support matrices (activated sludge). The CWs with bark-biochar as support matrix significantly enhanced the removal of irbesartan and carbamazepine (>40 %), compared to the CW filled with the conventional support matrix sand. UVC irradiation as pre-treatment was more efficient in removing MPs than sunlight irradiation. After UVC pre-treatment, less MPs accumulated in the plants in the subsequent CW unit compared to the CW unit without any pre-treatment. Moreover, in the UVC combined CW system, less sulfamethoxazole, furosemide, mecoprop and diclofenac were accumulated in the plants (<0.5 μg) than other MPs (>3 μg). The addition of 0.5 % activated sludge combined with the aeration of influent did not improve MP removal in the CW. Considering the application, a bark-biochar based CW combined with UVC pre-treatment will result in more MP removal than a conventional sand CW.

Removal processes of individual and a mixture of organic micropollutants in the presence of Scenedesmus obliquus

Organic micropollutants (OMPs) need to be removed from wastewater as they can negatively affect aquatic organisms. It has been demonstrated that microalgae-based technologies are efficient in removing OMPs from wastewater. In this study, the removal processes and kinetics of six persistent OMPs (diclofenac, clarithromycin, benzotriazole, metoprolol, carbamazepine and mecoprop) were studied during cultivation of Scenedesmus obliquus in batch mode. These OMPs were added as individual compounds and in a mixture. Short experiments (8 days) were performed to avoid masking of OMP removal processes by light and nutrient limitation. The results show that diclofenac, clarithromycin, and benzotriazole were mainly removed by photodegradation (diclofenac), biodegradation (benzotriazole), or a combination of these two processes (clarithromycin). Peroxidase was involved in intracellular and extracellular biodegradation when benzotriazole was present as individual compound. Carbamazepine, metoprolol and mecoprop showed no biodegradation or photodegradation, and neglectable removal (<5%) by bioadsorption and bioaccumulation. Using an OMP mixture had an adverse effect on the photodegradation of clarithromycin and diclofenac, with reduced first-order kinetic constants compared to the individual compounds. Benzotriazole biodegradation was inhibited by the presence of the OMP mixture. This indicates that the presence of OMPs inhibits the photodegradation and biodegradation of some individual OMPs. These results will improve our understanding of removal processes of individual and mixtures of OMPs by microalgae-based technologies for wastewater treatment.

Urban water as an alternative freshwater resource for matching irrigation demand in the Bengal delta

Rapid changes in climate patterns, population growth, urbanization, and rising economic activities have increased the pressure on the delta's freshwater availability. Bangladesh's coastal planes suffer from a shortage of good quality irrigation water, which is crucial for peri-urban agriculture and at the same time, a high volume of untreated wastewater is discharged into the surface water. This calls for a transition towards efficiently managing and (re)using available urban water resources for irrigation, which is addressed in this paper. A quantitative match between the irrigation demand and potential freshwater supply has been assessed considering different urban water generation scenarios. The FAO AquaCrop model has been used to calculate the irrigation water demand for Boro rice during the dry period. Results indicate that 7.4 million m³ of irrigation water is needed, whereas over 8.2 million m³ of urban water is being generated during the dry season. Simultaneously, mismatches between irrigation demand and alternative water supply mainly occurred in February and March, which could be resolved with water storage capacities. However, to make urban water reuse a reality, the water management policy needs to change to facilitate the construction of required infrastructures for collection, treatment, and storage. The proposed method helps realize the urban water's hidden potential to sustain agricultural activities in the delta areas.

Microbial contamination in surface water and potential health risks for peri-urban farmers of the Bengal delta

Ensuring safe irrigation practices is vital to sustaining food production in water-scarce delta areas. Bangladesh and many other developing countries discharge untreated wastewater into their surrounding surface water bodies, serving as the primary irrigation source. This indirect irrigation of wastewater is believed to pose threats to the farmers, consumers and market vendors and may also affect crop and soil quality. To assess the risk, peri-urban farmers who use surrounding water bodies of Khulna city, Bangladesh, for crop irrigation were selected for the study. The microbial and heavy metal concentrations were measured in water samples collected from various locations over different seasons. For heavy metals As, Co, Ni, Cd, Cr, Cu and Pb, concentrations were below the detection limit, whereas Al, Fe, Mn, Ti and Zn were present but below the FAO recommendation limit for safe irrigation. The mean concentrations of microbial parameters were above the thresholds of WHO guidelines for crop irrigation intended for human consumption. Significant temporal variations in Faecal Coliform, E. coli and Enterococcus concentrations in the water samples were observed. The annual risk of infection for farmers was determined using the screening-level Quantitative Microbial Risk Assessment (QMRA). The results indicated that the annual probability of infection with pathogenic E. coli in different seasons ranges between 5 × 10^-3 to 5 × 10^-2, above the WHO's acceptable threshold for annual risk of infection for safe water reuse in agriculture. During the farmers' survey, around 45% reported health-related issues and more than 26% reported suffering from water-borne diseases after getting in contact with polluted surface water. This illustrates the actuality of the risks in practice. To ensure safe irrigation, the health risks need to be reduced below the acceptable limits. Suggested technical measures include adequate treatment of wastewater before disposal into rivers and access to protective equipment for farmers. This should be complemented by raising awareness through education programs among farmers to reduce accidental ingestion.

Phytoremediation of micropollutants by Phragmites australis, Typha angustifolia, and Juncus effuses

Micropollutants (MPs) include organic chemicals, for example, pharmaceuticals and personal care products. MPs have been detected in the aquatic environment at low concentrations (ng/L-µg/L), which may lead to negative impacts on the ecosystem and humans. Phytoremediation is a green clean-up technology, which utilizes plants and their associated rhizosphere microorganisms to remove pollutants. The selection of plant species is important for the effectiveness of the phytoremediation of MPs. The plant species Phragmites australis, Typha angustifolia, and Juncus effuses are often used for MP removal. In this study, batch experiments were conducted to select plant species with an optimal ability to remove MPs, study the effect of temperature on MP removal in plants and the phytotoxicity of MPs. This study also explored the degradation of a persistent MP propranolol in plants in more detail. Data show that all three investigated plant species removed most MPs efficiently (close to 100 %) at both 10 and 21.5 °C. The tested plant species showed a different ability to translocate and accumulate propranolol in plant tissues. Typha angustifolia and Juncus effuses had a higher tolerance to the tested MPs than Phragmites australis. Typha angustifolia and Juncus effuses are recommended to be applied for phytoremediation of MPs.Novelty statement The novelty of this study is the selection of Typha angustifolia and Juncus effuses as proper plant species for phytoremediation of micropollutants (MPs). These two plant species were selected due to their good ability to remove MPs, tolerate low temperature, and resist the toxicity of MPs. The outcomes from this study can also be applied for constructed wetlands in removing MPs from wastewater. This study demonstrates the uptake and degradation processes of persistent MP propranolol in plants in more detail. Understanding the degradation mechanisms of a MP in plants is significant not only for the application of phytoremediation on MP removal but also for the development of constructed wetland studies.

Sorption of micropollutants on selected constructed wetland support matrices

Micropollutants (MPs) are organic chemicals that are present in the environment at low concentrations (ng/L-μg/L), for example pharmaceuticals. A constructed wetland (CW) is a promising post-treatment technique to remove MPs from wastewater effluent. Selecting a suitable material for support matrix is important when designing such a CW. Nine materials were studied as potential support matrices: Light Expanded Clay Aggregates (LECA), compost, bark, granulated activated carbon (GAC), biochar, granulated cork, lava rock, sand and gravel. Batch experiments were conducted to study MP removal by nine materials in phosphate buffer with 5 or 50 μg/L MPs, or wastewater effluent with 50 μg/L of MPs. GAC and biochar removed almost all MPs in both phosphate buffer and wastewater effluent, followed by bark, compost, granulated cork. Sand, gravel, LECA and lava rock removed less than 30% of most MPs in both matrixes. Based on set criteria (e.g. removal efficiency), biochar, bark, compost, LECA and sand were selected, and used in combinations in column studies to test their overall performance. A combination of bark and biochar performed the best on MP removal, as 4 MPs were highly (70%-100%) removed, 4 MPs were moderately (30%-70%) removed while only 3 MPs were hardly removed. The main flow regime of this combination was both plug flow and dispersive flow. Moreover, we hypothesized to apply bark and biochar in a CW. Based on the assumptions and calculations, some benefits are expected, such as increasing MP removal and extending operation time.

Direct analysis of aromatic pollutants using a HPLC-FLD/DAD method for monitoring biodegradation processes

Industrial discharges resulting in contaminated groundwater is a global environmental problem. For such contaminated groundwater cases, bioremediation is a cost efficient and environmentally friendly approach. The determination and quantification of these pollutants has gained great importance and researchers are currently seeking to develop labor extensive, accurate and reliable methods for evaluating their biodegradation process. In this study, a HPLC method was developed and optimized for the quantification of 11 industrial pollutants studied as two different mixtures: benzene, toluene, ethylbenzene, o, m/p-xylene, indane, indene, and naphthalene (mixture A) and benzene, monochlorobenzene, 1,2-dichlorobenzene, and 1,4-dichlorobenzene (mixture B). The method uses two different detectors: fluorescence detection and diode array. The fluorescence detector was used for mixture A to achieve lower quantification limits and to quantify separately o-xylene and indene due to them showing similar wavelength behaviors. The limit of detection was found to be between 2 and 70 μg L^-1 for mixture A and 290 μg L^-1 for mixture B. The limit of quantitation was between 6 and 210 μg L^-1 for mixture A and 980 μg L^-1 for mixture B, respectively. The novel part of this study is that aqueous samples can be directly measured with one-step sample preparation and it comes with other advantages such as low volumes of sampling from batch bottles and also avoidance of high cost, relative to other analytical techniques. Therefore, this analytical method aims to facilitate the quantification of various aromatic hydrocarbons in laboratory batch samples and can be used as a routine monitoring tool for biological degradation processes of these 11 prevalent contaminants.

Institutional challenges and stakeholder perception towards planned water reuse in peri-urban agriculture of the Bengal delta

The indirect, unplanned use of urban wastewater by peri-urban farmers in developing countries poses a severe risk to the environment and the farmers. Planned water reuse could contribute substantially to the irrigation water demand in peri-urban agriculture and minimize the risk. However, implementing such practice requires a thorough evaluation of stakeholder's perception and the scope within the existing organizational structures. This paper aims to assess the level of awareness, perception, and willingness of different stakeholders toward current practices and the prospect of urban water reuse in Khulna City - one of the most vulnerable cities located in the southwest of Bangladesh due to the consequences of rapid climate changes in the Bengal delta. Also, institutional arrangements and their functioning were analyzed to understand the current sectoral performance. One questionnaire with 385 respondents from the urban area, 32 in-depth interviews and one focus group discussion with farmers in the peri-urban area, and ten interviews with key informants from the government and non-government organization was conducted. Results indicate an overall positive attitude among major stakeholder groups toward planned water reuse for peri-urban agriculture. More than half of the citizens (53%) are willing to pay for the treatment of wastewater and majority of the farmers (66%) are willing to pay for the supply of better-quality irrigation water. However, the public sector responsible for wastewater collection and treatment requires adjustment in rules and regulations to implement planned water reuse. Interrelated factors such as lack of transparency and coordination, shifting responsibilities to other organizations, lack of required resources need to be addressed in the updated rules and regulations. Strategies to enforce current regulations and align all stakeholders are also crucial for collection and treatment of wastewater and its subsequent use for crop production.

Bioflocculants from wastewater: Insights into adsorption affinity, flocculation mechanisms and mixed particle flocculation based on biopolymer size-fractionation

HYPOTHESIS

Microbial extracellular polymeric substances (EPS) produced from wastewater are generally heterodispersed, which is expected to influence their flocculation performances and mechanism, particularly in mixed particle systems. The different molecular weight (MW) fractions should contribute to the overall adsorption affinity and flocculation mechanism of EPS in single and dual clay systems.

EXPERIMENTS

EPS harvested from bioreactors were size-fractionated into high, medium and low MW fractions (HMW, MMW, LMW, respectively). The harvested mixed EPS and its fractions were characterised by diverse analytical techniques coupled with optical reflectometry to investigate the role of each EPS fraction in the overall flocculation mechanism of EPS in kaolinite and montmorillonite clay systems.

FINDINGS

In single clay systems, both the harvested mixed EPS and the HMW-EPS fraction showed comparable flocculation performances. However, mixed EPS proved to be more efficient than the HMW-EPS fraction for dual clay flocculation. Site blocking effects were observed in mixed EPS: the LMW and MMW EPS first adsorbed to the surface due to higher diffusivities and faster mass transfer to the interface, while the HMW-EPS were slowly transported but were attached to the surface irreversibly and stronger than the LMW/MMW-EPS. We propose from this, a mixed EPS adsorption mechanism: extended anionic polymer tails in solution, thereby enhancing particle flocculation.

Experimental Evaluation of Anion Exchange Membranes for the Desalination of (Waste) Water Produced after Polymer-Flooding

Electrodialysis (ED) has been recently proposed to desalinate polymer-flooding produced water (PFPW), a byproduct stream from the oil and gas industry rich in charged polymers. However, process performance is limited by fouling occurring on the ion-exchange membranes, particularly on the anionic ones (AEMs). Thus, this study aimed to correlate the properties of different AEMs with their performance while desalinating PFPW, ultimately evaluating their significance when fouling is to be minimized and operation improved. Six stacks containing different homogeneous and commercially available AEMs were employed to desalinate synthetic PFPW during 8-days ED experiments operated in reversal mode. AEMs recovered from the stacks were analyzed in terms of water uptake, ion-exchange capacity, permselectivity, and area resistance, and compared with virgin AEMs. Relatively small changes were measured for most of the parameters evaluated. For most AEMs, the water uptake and resistance increased, while the ion-exchange capacity (IEC) and permselectivity decreased during operation. Ultimately, AEMs with high area resistance were linked to the fast development of limiting current conditions in the stack, so this property turned out to be the most relevant when desalinating PFPW.

Regeneration and reuse of microbial extracellular polymers immobilised on a bed column for heavy metal recovery

Microbial extracellular polymeric substances (EPS) have gained increasing attention for various water treatment applications. In this study, EPS produced from nitrogen-limited glycerol/ethanol-rich wastewater were used to recover Cu²⁺ and Pb²⁺ from aqueous solutions. Continuous flow-through tests were conducted on a column packed with silica gel coated with polyethyleneimine, to which EPS were irreversibly attached as shown by optical reflectometry. These immobilised EPS excellently adsorbed Cu²⁺ and Pb²⁺, with 99.9% of influent metal adsorbed before the breakthrough points. Metal desorption was achieved with 0.1M HCl, with an average recovery of 86% for Cu²⁺ and 90% recovery for Pb²⁺. For the first time, we successfully showed the possibility to regenerate and reuse the immobilised EPS for five adsorption-desorption cycles (using Cu²⁺ as an example) with no reduction in the adsorbed amount at the breakthrough point (q_bp). Based on the mass balance of the associated metal ions participating in the adsorption process, ion exchange was identified as the major mechanism responsible for Cu²⁺ and Pb²⁺ adsorption by EPS. The results demonstrate the potential of wastewater-produced EPS as an attractive and perhaps, cost-effective biosorbent for heavy metal removal (to trace effluent concentrations) and recovery (86-99%).

Potential impact of hydrodynamic shear force in aquifer thermal energy storage on dissolved organic matter releasement: A vigorous shaking batch study

The combination of bioremediation and aquifer thermal energy storage (ATES) has become attractive because of the possibility of solving environmental and energy problems simultaneously. While the impact of ATES on groundwater quality due to temperature change has received ample attention in literature, the effect of the greatly enhanced groundwater flow velocity on groundwater quality has not yet received sufficient scientific attention. To fill this gap in understanding, we conducted a simple yet straightforward experiment to illustrate the impact of hydrodynamic shear force due to the water flow by ATES on the release of dissolved organic matter, which can potentially be advantageous to bioremediation. Vigorous shaking conditions were applied to simulate the enhanced dynamics at the ATES well center and nearby. As the indicators of dissolved organic matter, COD and TOC concentrations were significantly impacted by shaking. COD increased from 5.4 mgO₂/L to 36.3 mgO₂/L during horizontal shaking. The maximum COD level was determined as 33.8 mgO₂/L during orbital shaking, while the TOC level was growing from 6.7 to 28.7 mg C/L. Meanwhile, redox potential (with initial level -100 mV) was decreasing to -450 mV synchronously with the elevating COD and TOC level. Temperature was also revealed as a significant factor in the organic matter releasement. Microbial iron reduction was deemed to occur, yet sulfate reduction was not initiated during the whole experiment. Eventually, the structure of the soil-water matrix has been changed due to the extensive hydraulic and particle collisions, resulting in blackish appearance and thicker layer of fine particles. Overall, the findings advance our understanding of the role of the ATES-induced water flow in the subsurface biogeochemistry and give insight into the perspective of the combination of bioremediation and ATES. In general, an increase in dissolved organic matter can be expected due to the increased shear force at high flow conditions in the ATES system.

Valorization of glycerol/ethanol-rich wastewater to bioflocculants: recovery, properties, and performance

Microbial extracellular polymeric substances (EPS) were produced in two membrane bioreactors, each separately treating fresh and saline synthetic wastewater (consisting of glycerol and ethanol), with the purpose of applying them as sustainable bioflocculants. The reactors were operated under nitrogen-rich (COD/N ratios of 5 and 20) and limited (COD/N ratios of 60 and 100) conditions. Under both conditions, high COD removal efficiencies of 87-96% were achieved. However, nitrogen limitation enhanced EPS production, particularly the polysaccharide fraction. The maximum EPS recovery (g EPS-COD/g COD_influent) from the fresh wastewater was 54% and 36% recovery was obtained from the saline (30 g NaCl/L) wastewater. The biopolymers had molecular weights up to 2.1 MDa and anionic charge densities of 2.3-4.7 meq/g at pH 7. Using kaolin clay suspensions, high flocculation efficiencies of 85-92% turbidity removal were achieved at EPS dosages below 0.5 mg/g clay. Interestingly, EPS produced under saline conditions proved to be better flocculants in a saline environment than the corresponding freshwater EPS in the same environment. The results demonstrate the potential of glycerol/ethanol-rich wastewater, namely biodiesel/ethanol industrial wastewater, as suitable substrates to produce EPS as effective bioflocculants.

Glocal assessment of integrated wastewater treatment and recovery concepts using partial nitritation/Anammox and microalgae for environmental impacts

This study explored the feasibility and estimated the environmental impacts of two novel wastewater treatment configurations. Both include combined bioflocculation and anaerobic digestion but apply different nutrient removal technologies, i.e. partial nitritation/Anammox or microalgae treatment. The feasibility of such configurations was investigated for 16 locations worldwide with respect to environmental impacts, such as net energy yield, nutrient recovery and effluent quality, CO₂ emission, and area requirements. The results quantitatively support the applicability of partial nitritation/Anammox in tropical regions and some locations in temperate regions, whereas microalgae treatment is only applicable the whole year round in tropical regions that are close to the equator line. Microalgae treatment has an advantage over the configuration with partial nitritation/Anammox with respect to aeration energy and nutrient recovery, but not with area requirements. Differential sensitivity analysis points out the dominant influence of microalgal biomass yield and wastewater nutrient concentrations on area requirements and effluent quality. This study provides initial selection criteria for worldwide feasibility and corresponding environmental impacts of these novel municipal wastewater treatment plant configurations.

Enhanced pharmaceutical removal from water in a three step bio-ozone-bio process

Individual treatment processes like biological treatment or ozonation have their limitations for the removal of pharmaceuticals from secondary clarified effluents with high organic matter concentrations (i.e. 17 mg TOC/L). These limitations can be overcome by combining these two processes for a cost-effective pharmaceutical removal. A three-step biological-ozone-biological (BO₃B) treatment process was therefore designed for the enhanced pharmaceutical removal from wastewater effluent. The first biological step removed 38% of ozone scavenging TOC, thus proportionally reducing the absolute ozone input for the subsequent ozonation. Complementariness between biological and ozone treatment, i.e. targeting different pharmaceuticals, resulted in cost-effective pharmaceutical removal by the overall BO₃B process. At a low ozone dose of 0.2 g O₃/g TOC and an HRT of 1.46 h in the biological reactors, the removal of 8 out of 9 pharmaceuticals exceeded 85%, except for metoprolol (60%). Testing various ozone doses and HRTs revealed that pharmaceuticals were ineffectively removed at 0.1 g O3/g TOC and an HRT of 0.3 h. At HRTs of 0.47 and 1.46 h easily and moderately biodegradable pharmaceuticals such as caffeine, gemfibrozil, ibuprofen, naproxen and sulfamethoxazole were over 95% removed by biological treatment. The biorecalcitrant carbamazepine was completely ozonated at a dose of 0.4 g O₃/g TOC. Ozonation products are likely biodegraded in the last biological reactor as a 17% TOC removal was found. No appreciable acute toxicity towards D. magna, P. subcapitata and V. fischeri was found after exposure to the influents and effluents of the individual BO₃B reactors. The BO₃B process is estimated to increase the yearly wastewater treatment tariff per population equivalent in the Netherlands by less than 10%. Overall, the BO₃B process is a cost-effective treatment process for the removal of pharmaceuticals from secondary clarified effluents.

Pharmaceutical concentration variability at sewage treatment plant outlets dominated by hydrology and other factors

A study was conducted in which the effluent at four small to medium sized sewage treatment plants (STP) in North Rhine-Westphalia, Germany was monitored for three pharmaceutical compounds (carbamazepine, diclofenac, metoprolol) over a period of four years. Grab sampling and auto sampling campaigns were accomplished with respect to various weather conditions in the catchment area. Flow volumes and hydraulic retention times (HRT) from various sampling dates which provide information on processes causing emission changes were additionally taken into account. Monitoring results showed that concentration scattering in the effluent is related to HRT in the sewage treatment plants. Dilution effects following rain events in the catchment area were analysed for the three investigated substances. Short-term emission changes explained by dilution only could be well determined by the mathematical relation between discharge and concentration, and for carbamazepine to be solely determined by the dilution effects at all HRTs. For metoprolol, a clear decrease in concentrations was observed at HRTs above 80 h, and a significant contribution of biodegradation was supported by independent biodegradation tests. For three out of the four STPs, a decrease in concentrations of diclofenac was observed at hydraulic retention times above 80 h, indicating removal, whereas the relationship between concentration and HRT of the other STP could be explained by dilution only. The study shows that emissions can vary with weather conditions, hampering the assessment of emissions and estimation of concentrations in surface waters from generic removal rates only. Furthermore, it illustrates the importance of HRT of rather stable substances in wastewater treatment.

Combination of aquifer thermal energy storage and enhanced bioremediation: Biological and chemical clogging

Interest in the combination concept of aquifer thermal energy storage (ATES) and enhanced bioremediation has recently risen due to the demand for both renewable energy technology and sustainable groundwater management in urban areas. However, the impact of enhanced bioremediation on ATES is not yet clear. Of main concern is the potential for biological clogging which might be enhanced and hamper the proper functioning of ATES. On the other hand, more reduced conditions in the subsurface by enhanced bioremediation might lower the chance of chemical clogging, which is normally caused by Fe(III) precipitate. To investigate the possible effects of enhanced bioremediation on clogging with ATES, we conducted two recirculating column experiments with differing flow rates (10 and 50mL/min), where enhanced biological activity and chemically promoted Fe(III) precipitation were studied by addition of lactate and nitrate respectively. The pressure drop between the influent and effluent side of the column was used as a measure of the (change in) hydraulic conductivity, as indication of clogging in these model ATES systems. The results showed no increase in upstream pressure during the period of enhanced biological activity (after lactate addition) under both flow rates, while the addition of nitrate lead to significant buildup of the pressure drop. However, at the flow rate of 10mL/min, high pressure buildup caused by nitrate addition could be alleviated by lactate addition. This indicates that the risk of biological clogging is relatively small in the investigated areas of the mimicked ATES system that combines enhanced bioremediation with lactate as substrate, and furthermore that lactate may counter chemical clogging.

Sorption and biodegradation of six pharmaceutically active compounds under four different redox conditions

This study explored the removal of six pharmaceutically active compounds (PhACs) in lab-scale experiments with sediments under four redox conditions, namely aerobic, nitrate reducing, sulfate reducing, and methanogenic conditions using batch and column set-ups. Redox conditions were found to influence PhAC removal by sorption and biodegradation. The most optimal PhAC removal was observed at the outer ranges of the redox spectrum, i.e. either aerobic or deep anaerobic (sulfate reducing and methanogenic conditions), whereas nitrate reducing conditions were found least effective for PhACs biodegradation and sorption. For instance, sorption coefficient K_d values for metoprolol in column experiments were 90, 65, 42 and 11 L/kg for sulfate reducing, methanogenic, aerobic and nitrate reducing conditions, respectively. For the same conditions K_d values for propranolol were 101, 94, 55 and 55 L/kg, respectively. As expected, biodegradation efficiencies were highest under aerobic conditions, showing >99% removal of caffeine and naproxen, but no removal for propranolol and carbamazepine. The adaptive capacity of sediment was demonstrated by pre-exposure to PhACs leading to improved PhAC biodegradation. The results of this study indicate the necessity to combine diverse redox conditions, including aerobic conditions, for maximizing PhAC removal by sorption and biodegradation. Furthermore, our findings stress the need for additional treatment measures as recalcitrant PhACs are not effectively removed under any redox condition.

Production of volatile fatty acids from sewage organic matter by combined bioflocculation and alkaline fermentation

This study explored the potential of volatile fatty acids (VFA) production from sewage by a combined high-loaded membrane bioreactor and sequencing batch fermenter. VFA production was optimized with respect to SRT and alkaline pH (pH 8-10). Application of pH shock to a value of 9 at the start of a sequencing batch cycle, followed by a pH uncontrolled phase for 7days, gave the highest VFA yield of 440mgVFA-COD/g VSS. This yield was much higher than at fermentation without pH control or at a constant pH between 8 and 10. The high yield in the pH 9 shocked system could be explained by (1) a reduction of methanogenic activity, or (2) a high degree of solids degradation or (3) an enhanced protein hydrolysis and fermentation. VFA production can be further optimized by fine-tuning pH level and longer operation, possibly allowing enrichment of alkalophilic and alkali-tolerant fermenting microorganisms.

Biodegradation of cis-1,2-Dichloroethene in Simulated Underground Thermal Energy Storage Systems

Underground thermal energy storage (UTES) use has showed a sharp rise in numbers in the last decades, with aquifer thermal energy storage (ATES) and borehole thermal energy storage (BTES) most widely used. In many urban areas with contaminated aquifers, there exists a desire for sustainable heating and cooling with UTES and a need for remediation. We investigated the potential synergy between UTES and bioremediation with batch experiments to simulate the effects of changing temperature and liquid exchange that occur in ATES systems, and of only temperature change occurring in BTES systems on cis-DCE reductive dechlorination. Compared to the natural situation (NS) at a constant temperature of 10 °C, both UTES systems with 25/5 °C for warm and cold well performed significantly better in cis-DCE (cis-1,2-dichloroethene) removal. The overall removal efficiency under mimicked ATES and BTES conditions were respectively 13 and 8.6 times higher than in NS. Inoculation with Dehalococcoides revealed that their initial presence is a determining factor for the dechlorination process. Temperature was the dominating factor when Dehalococcoides abundance was sufficient. Stimulated biodegradation was shown to be most effective in the mimicked ATES warm well because of the combined effect of suitable temperature, sustaining biomass growth, and regular cis-DCE supply.

Volatile fatty acids production from sewage organic matter by combined bioflocculation and anaerobic fermentation

This work aims at exploring the feasibility of a combined process bioflocculation to concentrate sewage organic matter and anaerobic fermentation to produce volatile fatty acids (VFA). Bioflocculation, using a high-loaded aerobic membrane bioreactor (HL-MBR), was operated at an HRT of 1h and an SRT of 1 day. The HL-MBR process removed on average 83% of sewage COD, while only 10% of nitrogen and phosphorus was removed. During anaerobic fermentation of HL-MBR concentrate at an SRT of 5 days and 35 °C, specific VFA production rate of 282 mg VFA-COD/g VSS could be reached and consisted of 50% acetate, 40% propionate and 10% butyrate. More than 75% of sewage COD was diverted to the concentrate, but only 15% sewage COD was recovered as VFA, due to incomplete VSS degradation at the short treatment time applied. This shows that combined process for the VFA production is technologically feasible and needs further optimization.

Effectiveness of stimulating PCE reductive dechlorination: a step-wise approach

Reductive dechlorination of tetrachloroethene (PCE) and its daughter products in aquifers is often hampered by Fe(III) reducing conditions. Rigorous treatment to adjust the redox potential and stimulate dechlorination may be costly and potentially have negative effects on other aquifer functions. A step-wise experimental strategy was applied to investigate the effectiveness of various adjustment scenarios. Batch experiments with ascorbic acid (AA) and sodium lactate (SL) showed that 75μmol electron equivalents per gram dry mass of aquifer material was required to reach a sufficiently low redox potential for the onset of PCE dechlorination. Similar effects of either AA or SL on the measured redox potential suggest electron donors are not specific. However, the relative rates of Fe(III) and sulphate reduction appeared to be specific to the electron donor applied. While redox potential stabilised around -450mV after titration and sulphate was reduced to zero in both treatments, in the AA treatment a faster production of Fe(2+) was observed with a final concentration of 0.46mM compared to only 0.07mM in the SL treatment. In subsequent batch experiments with aquifer material that was pre-treated with AA or SL, PCE reductive dechlorination occurred within 30days. Further stimulation tests with extra electron donor or inoculum revealed that adding electron donor can accelerate the initiation of PCE biodegradation. However, bioaugmentation with dechlorinating bacteria is required to achieve complete reductive dechlorination to ethene. The findings from step-wise approaches are relevant for improving the cost-effectiveness of the design and operation of in-situ bioremediation at initially unfavourable environmental conditions.

Effects of storm runoff on the thermal regime and water quality of a deep, stratified reservoir in a temperate monsoon zone, in Northwest China

Jinpen Reservoir is a deep, stratified reservoir in Shaanxi province, located in a warm temperate zone of Northwest China. Influenced by a temperate monsoon climate, more than 60% of the annual precipitation is concentrated from late summer to autumn (July-September). In recent years, extreme rainfall events occurred more frequently and strongly affected the thermal structure, mixing layer depth and evolution of stratification of Jinpen Reservoir. The reservoir's inflow volume increased sharply after heavy rainfall during the flooding season. Large volumes of inflow induced mixing of stratified water zones in early autumn and disturbed the stratification significantly. A temporary positive effect of such disturbance was the oxygenation of the water close to the bottom of the reservoir, leading to inhibition of the release of nutrients from sediments, especially phosphate. However, the massive inflow induced by storm runoff with increased oxygen-consuming substances led to an increase of the oxygen consumption rate. After the bottom water became anaerobic again, the bottom water quality would deteriorate due to the release of pollutants from sediments. Heavy rainfall events could lead to very high nutrient input into the reservoir due to massive erosion from the surrounding uninhabited steep mountains, and the particulate matter contributed to most nutrient inputs. Reasonably releasing density flow is an effective way to reduce the amounts of particulate associated pollutants entering the reservoir. Significant turbid density flow always followed high rainfall events in Jinpen Reservoir, which not only affected the reservoir water quality but also increased costs of the drinking water treatment plant. Understanding the effects of the storm runoff on the vertical distributions of water quality indicators could help water managers to select the proper position of the intake for the water plant in order to avoid high turbidity outflow.

Electrochemical conversion of micropollutants in gray water

Electrochemical conversion of micropollutants in real gray water effluent was studied for the first time. Six compounds that are frequently found in personal care and household products, namely methylparaben, propylparaben, bisphenol A, triclosan, galaxolide, and 4- methylbenzilidene camphor (4-MBC), were analyzed in the effluent of the aerobic gray water treatment system in full operation. The effluent was used for lab-scale experiments with an electrochemical cell operated in batch mode. Three different anodes and five different cathodes have been tested. Among the anodes, Ru/Ir mixed metal oxide showed the best performance. Ag and Pt cathodes worked slightly better than Ti and mixed metal oxide cathodes. The compounds that contain a phenolic ring (parabens, bisphenol A, and triclosan) were completely transformed on this anode at a specific electric charge Q = 0.03 Ah/L. The compounds, which contain a benzene ring and multiple side methyl methyl groups (galaxolide, 4-MBC) required high energy input (Q ≤ 0.6 Ah/L) for transformation. Concentrations of adsorbable organohalogens (AOX) in the gray water effluent increased significantly upon treatment for all electrode combinations tested. Oxidation of gray water on mixed metal oxide anodes could not be recommended as a post-treatment step for gray water treatment according to the results of this study. Possible solutions to overcome disadvantages revealed within this study are proposed.

Sensitivity analysis on parameters and processes affecting vapor intrusion risk

A one-dimensional numerical model was developed and used to identify the key processes controlling vapor intrusion risks by means of a sensitivity analysis. The model simulates the fate of a dissolved volatile organic compound present below the ventilated crawl space of a house. In contrast to the vast majority of previous studies, this model accounts for vertical variation of soil water saturation and includes aerobic biodegradation. The attenuation factor (ratio between concentration in the crawl space and source concentration) and the characteristic time to approach maximum concentrations were calculated and compared for a variety of scenarios. These concepts allow an understanding of controlling mechanisms and aid in the identification of critical parameters to be collected for field situations. The relative distance of the source to the nearest gas-filled pores of the unsaturated zone is the most critical parameter because diffusive contaminant transport is significantly slower in water-filled pores than in gas-filled pores. Therefore, attenuation factors decrease and characteristic times increase with increasing relative distance of the contaminant dissolved source to the nearest gas diffusion front. Aerobic biodegradation may decrease the attenuation factor by up to three orders of magnitude. Moreover, the occurrence of water table oscillations is of importance. Dynamic processes leading to a retreating water table increase the attenuation factor by two orders of magnitude because of the enhanced gas phase diffusion.

Stability of the total and functional microbial communities in river sediment mesocosms exposed to anthropogenic disturbances

River systems are exposed to anthropogenic disturbances, including chemical pollution and eutrophication. This may affect the phylogenetic diversity as well as the abundance of various functional groups within sediment-associated microbial communities. To address such potential effects, mesocosms filled with Ebro delta sediment covered with river water were exposed to chlorinated organic compounds or to a high nutrient concentration as used for fertilization. Changes in the abundance of selected functional microbial groups, i.e. total aerobes, nitrate, sulfate and iron reducers, organohalide-respiring microorganisms as well as methanogens, were examined using culture-dependent most probable number and culture-independent PCR methods targeting phylogenetic as well as functional gene markers. It was concluded that the abundance of functional groups was neither affected by pollution with 1,2-dichloroethane and tetrachloroethene nor by elevated nutrient loads, although changes in the bacterial community composition were observed using 16S rRNA gene-targeted fingerprint techniques. This study reinforced the notion that complementary culture-dependent and molecular methods, focusing on different fractions of the microbial community (cultivable, active or total), should be used in combination for a comprehensive description of phylogenetic diversity and functional potential.

Aerobic nonylphenol degradation and nitro-nonylphenol formation by microbial cultures from sediments

Nonylphenol (NP) is an estrogenic pollutant which is widely present in the aquatic environment. Biodegradation of NP can reduce the toxicological risk. In this study, aerobic biodegradation of NP in river sediment was investigated. The sediment used for the microcosm experiments was aged polluted with NP. The biodegradation of NP in the sediment occurred within 8 days with a lag phase of 2 days at 30°C. During the biodegradation, nitro-nonylphenol metabolites were formed, which were further degraded to unknown compounds. The attached nitro-group originated from the ammonium in the medium. Five subsequent transfers were performed from original sediment and yielded a final stable population. In this NP-degrading culture, the microorganisms possibly involved in the biotransformation of NP to nitro-nonylphenol were related to ammonium-oxidizing bacteria. Besides the degradation of NP via nitro-nonylphenol, bacteria related to phenol-degrading species, which degrade phenol via ring cleavage, are abundantly present.

Degradation of 1,2-dichloroethane by microbial communities from river sediment at various redox conditions

Insight into the pathways of biodegradation and external factors controlling their activity is essential in adequate environmental risk assessment of chlorinated aliphatic hydrocarbon pollution. This study focuses on biodegradation of 1,2-dichloroethane (1,2-DCA) in microcosms containing sediment sourced from the European rivers Ebro, Elbe and Danube. Biodegradation was studied under different redox conditions. Reductive dechlorination of 1,2-DCA was observed with Ebro and Danube sediment with chloroethane, or ethene, respectively, as the major dechlorination products. Different reductively dehalogenating micro-organisms (Dehalococcoides spp., Dehalobacter spp., Desulfitobacterium spp. and Sulfurospirillum spp.) were detected by 16S ribosomal RNA gene-targeted PCR and sequence analyses of 16S rRNA gene clone libraries showed that only 2-5 bacterial orders were represented in the microcosms. With Ebro and Danube sediment, indications for anaerobic oxidation of 1,2-DCA were obtained under denitrifying or iron-reducing conditions. No biodegradation of 1,2-DCA was observed in microcosms with Ebro sediment under the different tested redox conditions. This research shows that 1,2-DCA biodegradation capacity was present in different river sediments, but not in the water phase of the river systems and that biodegradation potential with associated microbial communities in river sediments varies with the geochemical properties of the sediments.

Bioavailability and biodegradation of nonylphenol in sediment determined with chemical and bioanalysis

The surfactant nonylphenol (NP) is an endocrine-disrupting compound that is widely spread throughout the environment. Although environmental risk assessments are based on total NP concentrations, only the bioavailable fraction possess an environmental risk. The present study describes the bioavailability and biodegradability of NP over time in contaminated river sediment of a tributary of the Ebro River in Spain. The bioavailable fraction was collected with Tenax TA(R) beads, and biodegradation was determined in aerobic batch experiments. The presence of NP was analyzed chemically using gas chromatography-mass spectrometry and indirectly as estrogenic potency using an in vitro reporter gene assay (ER(alpha)-luc assay). Of the total extractable NP in the sediment, 95%+/-1.5% (mean +/- standard error) desorbed quickly into the water phase. By aerobic biodegradation, the total extractable NP concentration and the estrogenic activity were reduced by 97%+/-0.5% and 94%+/-2%, respectively. The easily biodegradable fraction equals the potential bioavailable fraction. Only 43 to 86% of the estrogenic activity in the total extractable fraction, as detected in the ER(alpha)-luc assay, could be explained by the present NP concentration. This indicates that other estrogenic compounds were present and that their bioavailability and aerobic degradation were similar to that of NP. Therefore, we propose to use NP as an indicator compound to monitor estrogenicity of this Ebro River sediment. To what extent this conclusion holds for other river sediments depends on the composition of the contaminants and/or the nature of these sediments and requires further testing.