Application of biological early warning systems in wastewater treatment plants: Introducing a promising approach to monitor changing wastewater composition.

Wastewater treatment plants (WWTPs) are a major source of micropollutants to surface waters. Currently, their chemical or biological monitoring is realized by using grab or composite samples, which provides only snapshots of the current wastewater composition. Especially in WWTPs with industrial input, the wastewater composition can be highly variable and a continuous assessment would be advantageous, but very labor and cost intensive. A promising concept are automated real-time biological early warning systems (BEWS), where living organisms are constantly exposed to the water and an alarm is triggered if the organism's responses exceed a harmful threshold of acute toxicity. Currently, BEWS are established for drinking water and surface water but are seldom applied to monitor wastewater. This study demonstrates that a battery of BEWS using algae (Chlorella vulgaris in the Algae Toximeter, bbe Moldaenke), water flea (Daphnia magna in the DaphTox II, bbe Moldaenke) and gammarids (Gammarus pulex in the Sensaguard, REMONDIS Aqua) can be adapted for wastewater surveillance. For continuous low-maintenance operation, a back-washable membrane filtration system is indispensable for adequate preparation of treated wastewater. Only minor deviations in the reaction of the organisms towards treated and filtered wastewater compared to surface waters were detected. After spiking treated wastewater with two concentrations of the model compounds diuron, chlorpyrifos methyl, and sertraline, the organisms in the different BEWS showed clear responses depending on the respective compound, concentration and mode of action. Immediate effects on photosynthetic activity of algae were detected for diuron exposure, and strong behavioral changes in water flea and gammarids after exposure to chlorpyrifos methyl or sertraline were observed, which triggered automated alarms. Different types of data analysis were applied to extract more information out of the specific behavioral traits, than only provided by the vendors algorithms. To investigate, whether behavioral movement changes can be linked to impact other endpoints, the effects on feeding activity of G. pulex were evaluated and results indicated significant differences between the exposures. Overall, these findings provide an important basis indicating that BEWS have the potential to act as alarm systems for pollution events in the wastewater sector.

Screening innovative technologies for energy-efficient domestic hot water systems.

Domestic hot water systems are large energy consumers. With the aim of reducing the energy footprint of these systems, we selected and simulated five technologies across a wide range of technology readiness levels: established technologies - pipe insulation and low-flow faucets -, relatively new technologies - shower drain heat exchangers and an innovative pipe system - and a novel experimental technology - a heat exchanger connected to membrane bioreactor for on-site greywater treatment. Using the WaterHub modeling framework, we simulated the technologies alone and in combination and compared the energetic performance of fifteen scenarios with a validated reference domestic hot water system. Low-flow appliances as standalone technologies performed best with 30% less energy required for the boiler tank, but combining low-flow appliances with a membrane bioreactor heat exchanger performed best overall (50% reduction). Deep insights into the temperature dynamics at all locations in the system led to the identification of technological competition patterns to prevent and synergies to exploit. Through our results, we are able to discuss and recommend further investigations regarding critical aspects like hygiene and economic performance.

Modelling of aerobic granular sludge reactors: the importance of hydrodynamic regimes, selective sludge removal and gradients.

Hydraulic selection is a key feature of aerobic granular sludge (AGS) systems but existing aerobic granular sludge (AGS) models neglect those mechanisms: gradients over reactor height (Hreactor), selective removal of slow settling sludge, etc. This study aimed at evaluating to what extent integration of those additional processes into AGS models is needed, i.e., at demonstrating that model predictions (biomass inventory, microbial activities and effluent quality) are affected by such additional model complexity. We therefore developed a new AGS model that includes key features of full-scale AGS systems: fill-draw operation, selective sludge removal, distinct settling models for flocs/granules. We then compared predictions of our model to those of a fully mixed AGS model. Our results demonstrate that hydraulic selection can be predicted with an assembly of four continuous stirred tank reactors in series together with a correction code for plug-flow. Concentration gradients over the reactor height during settling/plug-flow feeding strongly impact the predictions of aerobic granular sludge models in terms of microbial selection, microbial activities and ultimately effluent quality. Hydraulic selection is a key to predict selection of storing microorganisms (phosphorus-accumulating organisms (PAO) and glycogen-accumulating organisms (GAO)) and in turn effluent quality in terms of total phosphorus, and for predicting effluent solid concentration and dynamic during plug-flow feeding.

A Research Agenda for the Future of Urban Water Management: Exploring the Potential of Nongrid, Small-Grid, and Hybrid Solutions.

Recent developments in high- and middle-income countries have exhibited a shift from conventional urban water systems to alternative solutions that are more diverse in source separation, decentralization, and modularization. These solutions include nongrid, small-grid, and hybrid systems to address such pressing global challenges as climate change, eutrophication, and rapid urbanization. They close loops, recover valuable resources, and adapt quickly to changing boundary conditions such as population size. Moving to such alternative solutions requires both technical and social innovations to coevolve over time into integrated socio-technical urban water systems. Current implementations of alternative systems in high- and middle-income countries are promising, but they also underline the need for research questions to be addressed from technical, social, and transformative perspectives. Future research should pursue a transdisciplinary research approach to generating evidence through socio-technical "lighthouse" projects that apply alternative urban water systems at scale. Such research should leverage experiences from these projects in diverse socio-economic contexts, identify their potentials and limitations from an integrated perspective, and share their successes and failures across the urban water sector.

Transformation of Nanoscale and Ionic Cu and Zn during the Incineration of Digested Sewage Sludge (Biosolids).

Engineered nanoparticles (NP) discharged to sewers are efficiently retained by wastewater treatment plants and accumulate in the sewage sludge, which is commonly digested. The resulting biosolids are either used as fertilizer or incinerated. In this study, we address the transformation of Cu and Zn during sewage sludge incineration and evaluate whether the form of Cu or Zn (nanoparticulate versus dissolved) added to the digested sewage sludge affects the fate of the metals during incineration. We spiked CuO-NP, dissolved CuSO4, ZnO-NP, or dissolved ZnSO4 into anaerobically digested sewage sludge to reach Cu and Zn concentrations of ≈2500 and ≈3700 mg/kg and maintained the sludge under mesophilic, anaerobic conditions for 24 h. Subsequently, the sludge was incinerated in a pilot fluidized bed reactor. The speciation of Cu and Zn in the sludge, derived from X-ray absorption spectroscopy measurements, was dominated by sulfidic species, with >90% of Cu and >60% of Zn coordinated to reduced sulfur groups. In the ash, both Cu (>60%) and Zn (≈100%) were coordinated to oxygen. The chemical speciation of Cu and Zn in the ashes was independent of whether they were spiked in the dissolved or nanoparticulate form and closely matched the speciation of Cu and Zn observed in ashes from full-scale incinerators.

A framework for good biofilm reactor modeling practice (GBRMP).

A researcher or practitioner can employ a biofilm model to gain insight into what controls the performance of a biofilm process and for optimizing its performance. While a wide range of biofilm-modeling platforms is available, a good strategy is to choose the simplest model that includes sufficient components and processes to address the modeling goal. In most cases, a one-dimensional biofilm model provides the best balance, and good choices can range from hand-calculation analytical solutions, simple spreadsheets, and numerical-method platforms. What is missing today is clear guidance on how to apply a biofilm model to obtain accurate and meaningful results. Here, we present a five-step framework for good biofilm reactor modeling practice (GBRMP). The first four steps are (1) obtain information on the biofilm reactor system, (2) characterize the influent, (3) choose the plant and biofilm model, and (4) define the conversion processes. Each step demands that the model user understands the important components and processes in the system, one of the main benefits of doing biofilm modeling. The fifth step is to calibrate and validate the model: System-specific model parameters are adjusted within reasonable ranges so that model outputs match actual system performance. Calibration is not a simple 'by the numbers' process, and it requires that the modeler follows a logical hierarchy of steps. Calibration requires that the adjusted parameters remain within realistic ranges and that the calibration process be carried out in an iterative manner. Once each of steps 1 through 5 is completed satisfactorily, the calibrated model can be used for its intended purpose, such as optimizing performance, trouble-shooting poor performance, or gaining deeper understanding of what controls process performance.

Modeling hydraulic transport and anaerobic uptake by PAOs and GAOs during wastewater feeding in EBPR granular sludge reactors.

New-generation bioprocesses using granular sludge aim for a high-rate removal of nutrients from wastewater with low footprint. Achieving enhanced biological phosphorus removal (EBPR) relies on the design of sludge beds and wastewater feeding conditions to optimally load the biomass and to select for polyphosphate- (PAOs) over glycogen-accumulating organisms (GAOs) and over other heterotrophs. A hydraulic-metabolic mathematical model was developed to elucidate the impact of hydraulic transport patterns and environmental conditions on the PAO/GAO competition during up-flow feeding through an EBPR granular sludge bed. Tracer experiments highlighted plug-flow regimes with dispersion under both rapid (9 m h-1 , Rebed = 1.6, Pez = 7.2, Pet = 4.6) and slow (0.9 m h-1 , Rebed = 0.2, Pez = 21.3, Pet = 3.4) feeding. Non-turbulent regimes (Rebed << 103 ) promote a safe implementation of simultaneous fill/draw. Feeding time, pH, and temperature significantly impacted bacterial competition for carbon uptake under anaerobic slow feeding. Feeding duration should be designed to avoid full depletion of intracellular storage polymers within static granules. PAOs bear twice longer feeding than GAOs by using both polyphosphate and glycogen hydrolysis to sustain anaerobic C-uptake. Alkaline conditions (pH 7.25-8.0) by, e.g., dosing lime in the feed select for PAOs independently of temperature (10-30°C). A twice higher bed is required for full anaerobic conversions at 10 rather than 20°C. Biosystem responses for anaerobic C-uptake can be anticipated using the model toward designing robust anaerobic selectors to manage the microbial resource in EBPR granular sludge. Biotechnol. Bioeng. 2017;114: 1688-1702. © 2017 Wiley Periodicals, Inc.

Growth of Nitrosococcus-Related Ammonia Oxidizing Bacteria Coincides with Extremely Low pH Values in Wastewater with High Ammonia Content.

Ammonia oxidation decreases the pH in wastewaters where alkalinity is limited relative to total ammonia. The activity of ammonia oxidizing bacteria (AOB), however, typically decreases with pH and often ceases completely in slightly acidic wastewaters. Nevertheless, nitrification at low pH has been reported in reactors treating human urine, but it has been unclear which organisms are involved. In this study, we followed the population dynamics of ammonia oxidizing organisms and reactor performance in synthetic fully hydrolyzed urine as the pH decreased over time in response to a decrease in the loading rate. Populations of the ß-proteobacterial Nitrosomonas europaea lineage were abundant at the initial pH close to 6, but the growth of a possibly novel Nitrosococcus-related AOB genus decreased the pH to the new level of 2.2, challenging the perception that nitrification is inhibited entirely at low pH values, or governed exclusively by ß-proteobacterial AOB or archaea. With the pH shift, nitrite oxidizing bacteria were not further detected, but nitrous acid (HNO2) was still removed through chemical decomposition to nitric oxide (NO) and nitrate. The growth of acid-tolerant γ-proteobacterial AOB should be prevented, by keeping the pH above 5.4, which is a typical pH limit for the N. europaea lineage. Otherwise, the microbial community responsible for high-rate nitrification can be lost, and strong emissions of hazardous volatile nitrogen compounds such as NO are likely.

From biofilm ecology to reactors: a focused review.

Biofilms are complex biostructures that appear on all surfaces that are regularly in contact with water. They are structurally complex, dynamic systems with attributes of primordial multicellular organisms and multifaceted ecosystems. The presence of biofilms may have a negative impact on the performance of various systems, but they can also be used beneficially for the treatment of water (defined herein as potable water, municipal and industrial wastewater, fresh/brackish/salt water bodies, groundwater) as well as in water stream-based biological resource recovery systems. This review addresses the following three topics: (1) biofilm ecology, (2) biofilm reactor technology and design, and (3) biofilm modeling. In so doing, it addresses the processes occurring in the biofilm, and how these affect and are affected by the broader biofilm system. The symphonic application of a suite of biological methods has led to significant advances in the understanding of biofilm ecology. New metabolic pathways, such as anaerobic ammonium oxidation (anammox) or complete ammonium oxidation (comammox) were first observed in biofilm reactors. The functions, properties, and constituents of the biofilm extracellular polymeric substance matrix are somewhat known, but their exact composition and role in the microbial conversion kinetics and biochemical transformations are still to be resolved. Biofilm grown microorganisms may contribute to increased metabolism of micro-pollutants. Several types of biofilm reactors have been used for water treatment, with current focus on moving bed biofilm reactors, integrated fixed-film activated sludge, membrane-supported biofilm reactors, and granular sludge processes. The control and/or beneficial use of biofilms in membrane processes is advancing. Biofilm models have become essential tools for fundamental biofilm research and biofilm reactor engineering and design. At the same time, the divergence between biofilm modeling and biofilm reactor modeling approaches is recognized.

Biofilm carrier migration model describes reactor performance.

The accuracy of a biofilm reactor model depends on the extent to which physical system conditions (particularly bulk-liquid hydrodynamics and their influence on biofilm dynamics) deviate from the ideal conditions upon which the model is based. It follows that an improved capacity to model a biofilm reactor does not necessarily rely on an improved biofilm model, but does rely on an improved mathematical description of the biofilm reactor and its components. Existing biofilm reactor models typically include a one-dimensional biofilm model, a process (biokinetic and stoichiometric) model, and a continuous flow stirred tank reactor (CFSTR) mass balance that [when organizing CFSTRs in series] creates a pseudo two-dimensional (2-D) model of bulk-liquid hydrodynamics approaching plug flow. In such a biofilm reactor model, the user-defined biofilm area is specified for each CFSTR; thereby, Xcarrier does not exit the boundaries of the CFSTR to which they are assigned or exchange boundaries with other CFSTRs in the series. The error introduced by this pseudo 2-D biofilm reactor modeling approach may adversely affect model results and limit model-user capacity to accurately calibrate a model. This paper presents a new sub-model that describes the migration of Xcarrier and associated biofilms, and evaluates the impact that Xcarrier migration and axial dispersion has on simulated system performance. Relevance of the new biofilm reactor model to engineering situations is discussed by applying it to known biofilm reactor types and operational conditions.

Influence of Different Sewer Biofilms on Transformation Rates of Drugs.

To estimate drug consumption more reliably, wastewater-based epidemiology would benefit from a better understanding of drug residue stability during in-sewer transport. We conducted batch experiments with real, fresh wastewater and sewer biofilms. Experimental conditions mimic small to medium-sized gravity sewers with a relevant ratio of biofilm surface area to wastewater volume (33 m2 m-3). The influences of biological, chemical, and physical processes on the transformation of 30 illicit drug and pharmaceutical residues were quantified. Rates varied among locations and over time. Three substances were not stable-that is, >20% transformation, mainly due to biological processes-at least for one type of tested biofilm for a residence time ≤2 h: amphetamine, 6-acetylcodeine, and 6-monoacetylmorphine. Cocaine, ecgonine methyl ester, norcocaine, cocaethylene, and mephedrone were mainly transformed by chemical hydrolysis and, hence, also unstable in sewers. In contrast, ketamine, norketamine, O-desmethyltramadol, diclofenac, carbamazepine, and methoxetamine were not substantially affected by in-sewer processes under all tested conditions and residence times up to 12 h. Our transformation rates include careful quantification of uncertainty and can be used to identify situations in which specific compounds are not stable. This will improve accuracy and uncertainty estimates of drug consumption when applied to the back-calculation.

Response of Simulated Drinking Water Biofilm Mechanical and Structural Properties to Long-Term Disinfectant Exposure.

Mechanical and structural properties of biofilms influence the accumulation and release of pathogens in drinking water distribution systems (DWDS). Thus, understanding how long-term residual disinfectants exposure affects biofilm mechanical and structural properties is a necessary aspect for pathogen risk assessment and control. In this study, elastic modulus and structure of groundwater biofilms was monitored by atomic force microscopy (AFM) and optical coherence tomography (OCT) during three months of exposure to monochloramine or free chlorine. After the first month of disinfectant exposure, the mean stiffness of monochloramine- or free-chlorine-treated biofilms was 4 to 9 times higher than those before treatment. Meanwhile, the biofilm thickness decreased from 120 ± 8 µm to 93 ± 6-107 ± 11 µm. The increased surface stiffness and decreased biofilm thickness within the first month of disinfectant exposure was presumably due to the consumption of biomass. However, by the second to third month during disinfectant exposure, the biofilm mean stiffness showed a 2- to 4-fold decrease, and the biofilm thickness increased to 110 ± 7-129 ± 8 µm, suggesting that the biofilms adapted to disinfectant exposure. After three months of the disinfectant exposure process, the disinfected biofilms showed 2-5 times higher mean stiffness (as determined by AFM) and 6-13-fold higher ratios of protein over polysaccharide, as determined by differential staining and confocal laser scanning microscopy (CLSM), than the nondisinfected groundwater biofilms. However, the disinfected biofilms and nondisinfected biofilms showed statistically similar thicknesses (t test, p > 0.05), suggesting that long-term disinfection may not significantly remove net biomass. This study showed how biofilm mechanical and structural properties vary in response to a complex DWDS environment, which will contribute to further research on the risk assessment and control of biofilm-associated-pathogens in DWDS.

Operating a pilot-scale nitrification/distillation plant for complete nutrient recovery from urine.

Source-separated urine contains most of the excreted nutrients, which can be recovered by using nitrification to stabilize the urine before concentrating the nutrient solution with distillation. The aim of this study was to test this process combination at pilot scale. The nitrification process was efficient in a moving bed biofilm reactor with maximal rates of 930 mg N L(-1) d(-1). Rates decreased to 120 mg N L(-1) d(-1) after switching to more concentrated urine. At high nitrification rates (640 mg N L(-1) d(-1)) and low total ammonia concentrations (1,790 mg NH4-N L(-1) in influent) distillation caused the main primary energy demand of 71 W cap(-1) (nitrification: 13 W cap(-1)) assuming a nitrogen production of 8.8 g N cap(-1) d(-1). Possible process failures include the accumulation of the nitrification intermediate nitrite and the selection of acid-tolerant ammonia-oxidizing bacteria. Especially during reactor start-up, the process must therefore be carefully supervised. The concentrate produced by the nitrification/distillation process is low in heavy metals, but high in nutrients, suggesting a good suitability as an integral fertilizer.

Effect of Ozone Treatment on Nano-Sized Silver Sulfide in Wastewater Effluent.

Silver nanoparticles used in consumer products are likely to be released into municipal wastewater. Transformation reactions, most importantly sulfidation, lead to the formation of nanoscale silver sulfide (nano-Ag2S) particles. In wastewater treatment plants (WWTP), ozonation can enhance the effluent quality by eliminating organic micropollutants. The effect of ozonation on the fate of nano-Ag2S, however, is currently unknown. In this study, we investigate the interaction of ozone with nano-Ag2S and evaluate the effect of ozonation on the short-term toxicity of WWTP effluent spiked with nano-Ag2S. The oxidation of nano-Ag2S by ozone resulted in a stoichiometric factor (number of moles of ozone required to oxidize one mole of sulfide to sulfate) of 2.91, which is comparable to the results obtained for the reaction of bisulfide (HS(-)) with ozone. The second-order rate constant for the reaction of nano-Ag2S with ozone (k = 3.1 × 10(4) M(-1) s(-1)) is comparable to the rate constant of fast-reacting micropollutants. Analysis of the ozonation products of nano-Ag2S by transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS) revealed that ozonation dominantly led to the formation of silver chloride in WWTP effluent. After ozonation of the Ag2S-spiked effluent, the short-term toxicity for the green algae Chlamydomonas reinhardtii increased and reached EC50 values comparable to Ag(+). This study thus reveals that ozone treatment of WWTP effluent results in the oxidation of Ag2S and, hence, an increase of the Ag toxicity in the effluent, which may become relevant at elevated Ag concentrations.

Formation of Chlorination Byproducts and Their Emission Pathways in Chlorine Mediated Electro-Oxidation of Urine on Active and Nonactive Type Anodes.

Chlorination byproducts (CBPs) are harmful to human health and the environment. Their formation in chlorine mediated electro-oxidation is a concern for electrochemical urine treatment. We investigated the formation of chlorate, perchlorate, and organic chlorination byproducts (OCBPs) during galvanostatic (10, 15, 20 mA · cm(-2)) electro-oxidation of urine on boron-doped diamond (BDD) and thermally decomposed iridium oxide film (TDIROF) anodes. In the beginning of the batch experiments, the production of perchlorate was prevented by competing active chlorine and chlorate formation as well as by direct oxidation of organic substances. Perchlorate was only formed at higher specific charges (>17 Ah · L(-1) on BDD and >29 Ah · L(-1) on TDIROF) resulting in chlorate and perchlorate being the dominant CBPs (>90% of initial chloride). BDD produced mainly short chained OCBPs (dichloromethane, trichloromethane, and tetrachloromethane), whereas longer chained OCBPs (1,2-dichloropropane and 1,2-dichloroethane) were more frequently found on TDIROF. The OCBPs were primarily eliminated by electrochemical stripping: On BDD, this pathway accounted for 40% (dichloromethane) to 100% (tetrachloromethane) and on TDIROF for 90% (1,2-dichloroethane) to 100% (trichloromethane) of what was produced. A post-treatment of the liquid as well as the gas phase should be foreseen if CBP formation cannot be prevented by eliminating chloride or organic substances in a pretreatment.

Role of biofilm roughness and hydrodynamic conditions in Legionella pneumophila adhesion to and detachment from simulated drinking water biofilms.

Biofilms in drinking water distribution systems (DWDS) could exacerbate the persistence and associated risks of pathogenic Legionella pneumophila (L. pneumophila), thus raising human health concerns. However, mechanisms controlling adhesion and subsequent detachment of L. pneumophila associated with biofilms remain unclear. We determined the connection between L. pneumophila adhesion and subsequent detachment with biofilm physical structure characterization using optical coherence tomography (OCT) imaging technique. Analysis of the OCT images of multispecies biofilms grown under low nutrient condition up to 34 weeks revealed the lack of biofilm deformation even when these biofilms were exposed to flow velocity of 0.7 m/s, typical flow for DWDS. L. pneumophila adhesion on these biofilm under low flow velocity (0.007 m/s) positively correlated with biofilm roughness due to enlarged biofilm surface area and local flow conditions created by roughness asperities. The preadhered L. pneumophila on selected rough and smooth biofilms were found to detach when these biofilms were subjected to higher flow velocity. At the flow velocity of 0.1 and 0.3 m/s, the ratio of detached cell from the smooth biofilm surface was from 1.3 to 1.4 times higher than that from the rough biofilm surface, presumably because of the low shear stress zones near roughness asperities. This study determined that physical structure and local hydrodynamics control L. pneumophila adhesion to and detachment from simulated drinking water biofilm, thus it is the first step toward reducing the risk of L. pneumophila exposure and subsequent infections.

Considering microbial and aggregate heterogeneity in biofilm reactor models: how far do we need to go?

A model describing a given system should be as simple as possible - but not simpler. The appropriate level of complexity depends both on the type of system and on the intended use of the model. This paper addresses the critical question of which purposes justify increased complexity of biofilm (reactor) models. Additional model features compared to conventional models considered are: (1) the inclusion of microbial diversity, distinguishing between different species performing the same function; and (2) the distinction between flocs and granules in putatively granular sludge reactors. With a multispecies model considering interspecies diversity, it was demonstrated that a given macroscopic reactor performance does not necessarily reflect steady state conditions on the microscale. In a second case study, it was shown that the addition of a small level of flocs can have a significant impact on macroscale process performance and on microbial population and activity distributions in granular sludge reactors. It was concluded that increased complexity in biofilm models, concerning microbial diversity or mesoscale aggregate architecture, is likely more useful when the focus is on understanding fundamental microscale outputs, but under specific conditions, these additional model features can be critically informative for bulk reactor behavior prediction and general understanding.

Sulfidation kinetics of silver nanoparticles reacted with metal sulfides.

Recent studies have documented that the sulfidation of silver nanoparticles (Ag-NP), possibly released to the environment from consumer products, occurs in anoxic zones of urban wastewater systems and that sulfidized Ag-NP exhibit dramatically reduced toxic effects. However, whether Ag-NP sulfidation also occurs under oxic conditions in the absence of bisulfide has not been addressed, yet. In this study we, therefore, investigated whether metal sulfides that are more resistant toward oxidation than free sulfide, could enable the sulfidation of Ag-NP under oxic conditions. We reacted citrate-stabilized Ag-NP of different sizes (10-100 nm) with freshly precipitated and crystalline CuS and ZnS in oxygenated aqueous suspensions at pH 7.5. The extent of Ag-NP sulfidation was derived from the increase in dissolved Cu(2+) or Zn(2+) over time and linked with results from X-ray absorption spectroscopy (XAS) analysis of selected samples. The sulfidation of Ag-NP followed pseudo first-order kinetics, with rate coefficients increasing with decreasing Ag-NP diameter and increasing metal sulfide concentration and depending on the type (CuS and ZnS) and crystallinity of the reacting metal sulfide. Results from analytical electron microscopy revealed the formation of complex sulfidation patterns that seemed to follow preexisting subgrain boundaries in the pristine Ag-NP. The kinetics of Ag-NP sulfidation observed in this study in combination with reported ZnS and CuS concentrations and predicted Ag-NP concentrations in wastewater and urban surface waters indicate that even under oxic conditions and in the absence of free sulfide, Ag-NP can be transformed into Ag2S within a few hours to days by reaction with metal sulfides.

Ensuring microbial water quality for on-site water reuse: Importance of online sensors for reliable operation.

A growing number of cities and regions are promoting or mandating on-site treatment and reuse of wastewater, which has resulted in the implementation of several thousand on-site water reuse systems on a global scale. However, there is only limited information on the (microbial) water quality from implemented systems. The focus of this study was on two best-in-class on-site water reuse systems in Bengaluru, India, which typically met the local water quality requirements during monthly compliance testing. This study aimed to (i) assess the microbial quality of the reclaimed water at a high temporal resolution (daily or every 15 min), and (ii) explore whether measurements from commercially available sensors can be used to improve the operation of such systems. The monitoring campaign revealed high variations in microbial water quality, even in these best-in-class systems, rendering the water inadequate for the intended reuse applications (toilet flushing and landscape irrigation). These variations were attributed to two key factors: (1) the low frequency of chlorination, and (2) fluctuations of the chlorine demand of the water, in particular of ammonium concentrations. Such fluctuations are likely inherent to on-site systems, which rely on a low level of process control. The monitoring campaign showed that the microbial water quality was most closely related to oxidation-reduction potential (ORP) and free chlorine sensors. Due to its relatively low cost and low need for maintenance, the ORP emerges as a compelling candidate for automating the chlorination to effectively manage variations in chlorine demand and ensure safe water reuse. Overall, this study underscores the necessity of integrating treatment trains, operation, and monitoring for safe on-site water reuse.

Interactions between Clostridium beijerinckii and Geobacter metallireducens in co-culture fermentation with anthrahydroquinone-2, 6-disulfonate (AH2QDS) for enhanced biohydrogen production from xylose.

To enhance biohydrogen production, Clostridium beijerinckii was co-cultured with Geobacter metallireducens in the presence of the reduced extracellular electron shuttle anthrahydroquinone-2, 6-disulfonate (AH(2)QDS). In the co-culture system, increases of up to 52.3% for maximum cumulative hydrogen production, 38.4% for specific hydrogen production rate, 15.4% for substrate utilization rate, 39.0% for substrate utilization extent, and 34.8% for hydrogen molar yield in co-culture fermentation were observed compared to a pure culture of C. beijerinckii without AH(2)QDS. G. metallireducens grew in the co-culture system, resulting in a decrease in acetate concentration under co-culture conditions and a presumed regeneration of AH(2)QDS from AQDS. These co-culture results demonstrate metabolic crosstalk between the fermentative bacterium C. beijerinckii and the respiratory bacterium G. metallireducens and suggest a strategy for industrial biohydrogen production.