Hydraulic Residence Time Research Articles

Hydrodynamic behavior and start-up performance of a periodic anaerobic baffled reactor in an "every second" switching manner treating traditional Chinese medicine wastewater.

Most studies focus on the "clockwise sequential" switching manner for a four-compartment periodic anaerobic baffled reactor (PABR), while the exploration of the "every second" option on the feasibility for real industrial wastewater treatment is rarely reported. Hence, a PABR-treating traditional Chinese medicine wastewater was run continuously in "every second" switching manner with both switching period T and hydraulic residence time of 48 h. Satisfactory start-up performance was achieved during the operation of a climbing average organic load rate at approximately 1, 2, 4, and 6 kg chemical oxygen demand (COD) m-3 d-1 for 12, 24, 24, and 6 days, respectively. The average COD removal was 87.20% after the second lifting of OLR and 89.98% after the third one. Denaturing gradient gel electrophoresis and its cluster analysis showed that the microbial communities in each compartment adapted their structure in response to the periodically changing micro-ecology conditions. Moreover, the residence time distribution test with tap water in the clean PABR was carried out in experiments and computational fluid dynamics (CFD) simulation, both of which were in good agreement. The CFD model output visualized the flow velocity field and hydrodynamic-mass transport inside the PABR. Optimization of operation pattern in PABR including switching manner and frequency depended on both the type of waste being treated and the flexibility of biomass to periodically changing micro-ecology conditions.

Nanofiber composite ultrafiltration membrane functionalized with cross-linked β-cyclodextrin for steroid hormone micropollutant removal

Steroid hormone (SH) micropollutants are not efficiently removed with conventional membrane processes. Cyclodextrins are macrocyclic molecules widely applied in water treatment for the removal of these micropollutants. In this study, a composite nanofiber membrane (CNM) containing cross-linked β-cyclodextrin-epichlorohydrin (βCDP) was prepared by electrospinning the functionalized nanofibers onto an ultrafiltration membrane support.The CNM membrane was evaluated for SH removal in both static adsorption and during filtration. A removal of 80 % was reached in static condition with a βCDP loading of 2.5 ng/cm2. During filtration, the hydraulic residence time, SH concentration and nanofiber matrix thickness limited SH removal and uptake. The highest removal of 76 % and uptake of 9.5 ng/cm2 were achieved with a nanofiber matrix thickness of 442 μm. Molecular dynamic simulation revealed that SH type affected the βCDP interaction and inclusion complex formation, the strongest interaction occurred with progesterone and the lowest with testosterone. This was consistent with experimental data.Overall, the results are promising for the application of this functionalized membrane for SH removal due to the high adsorption capacity and the ability to form a specific inclusion complex interaction with the SH molecules.

The stable operation of nitritation process with the continuous granular sludge-type reactor and microbial community analysis

The nitritation step is the fundament for the biological nitrogen removal regardless of the traditional nitrification and denitrification process, the nitrite shunt process or the anammox process. Thus, exploring the effective nitritation performance is an important aspect of biological nitrogen removal. This study explored the upper limit of nitritation rate by increasing hydraulic residence time with the well-mixed and continuous granular sludge-type reactor characterized with low complexity and easy operation. The results showed that with the nitrogen loading rate of 1.0 kg/m3/d, the nitrite production rate could reach up to 0.65 kg/m3/d with the nitrite production efficiency of 63.49%, which is remarkable compared to that in the previously similar research. The microbial analysis indicated that ammonia-oxidizing bacteria was successfully enriched (13.27%) and genus Nitrosomonas was the dominant bacteria type. Besides, the activity of ammonium oxidizing bacteria in the continuous flow reactor was higher than that of other reactor types. The growth of vorticella on the sludge was also found in the reactor. The test of specific sludge activity and the microbe analysis both indicated that the nitrite-oxidizing bacteria was well inhibited during the whole experiment, which indicated the strategy of simply adjusting the dissolved oxygen is effective for running of nitritation process. The phosphorus removal performance was also achieved with a removal efficiency of 23.53%. The functional composition of the microbial community in the samples was predicted and finally transformation mechanism of nitrogen in sludge was drawn. In sum, this study indicated the superior performance of the granule sludge-type nitritation process and give a reference for the application of biological nitrogen removal technology.

Modeling Method for Aerobic Zone of A2O Based on KPCA-PSO-SCN

Sewage treatment plants face significant problems as a result of the annual growth in urban sewage discharge. Substandard sewage discharge can also be caused by rising sewage treatment expenses and unpredictable procedures. The most widely used sewage treatment process in urban areas is the Anaerobic–Anoxic–Oxic (A2O) sewage treatment process. Therefore, modeling the sewage treatment process and predicting the effluent quality are of great significance. A process modeling method based on Kernel Principal Component Analysis–Particle Swarm Optimization–Stochastic Configuration Network (KPCA-PSO-SCN) is proposed for the A2O aerobic wastewater treatment process. Firstly, eight auxiliary variables were determined through mechanism analysis, including Chemical Oxygen Demand (COD) and ammonia nitrogen (NH4+) and nitrate nitrogen (NO3−) of influent water, pH, temperature (T), Mixed Liquor Suspended Solid (MLSS), Dissolved Oxygen (DO) and hydraulic residence time (HRT) in the aerobic zone. Dimensionality reduction was carried out using the kernel principal component analysis method based on the Gaussian function, and the eight-dimensional data were changed to five-dimensional data, which improved the running speed and efficiency of subsequent models. Then, according to the advantages of the particle swarm optimization algorithm, such as low calculation cost and fast convergence, combined with the advantages of stochastic configuration network general approximation performance, the PSO-SCN model was established to predict the three water quality indexes of effluent COD, NH4+, and NO3− for the aerobic zone. The experimental results proved the effectiveness of the model. Compared with classic water quality prediction algorithm models such as SCN, PSO-BP, RBF, PSO-RBF, etc., the superiority of the PSO-SCN algorithm model was demonstrated.

Research Progress on Removing Antibiotic Resistance Genes in Constructed Wetlands

Recently, the issue of environmental pollution and emerging antibiotic resistance genes (ARGs) has gradually gained attention. Antibiotic resistant bacteria (ARB) can be effectively reduced via the conventional water treatment processes. Although the ARB are completely inactivated during the disinfection process, the free ARGs can be incorporated into other microorganisms through transformation or transduction, allowing the ARGs to spread and propagate. Therefore, ARGs in wastewater must be handled by a specific process. It has been demonstrated in several studies that treatment using constructed wetland is an effective, economical, and environmentally friendly method of removing antibiotics and resistance genes from wastewater. Here, the research progress on the removal effect of constructed wetland water treatment systems on ARGs at home and abroad was reviewed. The results revealed that the removal efficiency of ARGs in subsurface flow constructed wetland was higher than that in surface flow-constructed wetlands. The composite-constructed wetland had significantly improved removal efficiency of ARGs compared to that in the ordinarily constructed wetland; however, the parameter setting of the composite process still requires further research. Several studies have reported that the removal efficiency of ARGs using constructed wetlands varies depending on the type of constructed wetland enhancement, plant, temperature, pH, and other factors. The results of the current study revealed that cross-mixing was the best way to combine plants, whereas the selection of plant species has not yet shown a clear dominant species. Temperature and pH affected the removal of ARGs by altering the microbial community in constructed wetlands. Although longer hydraulic residence time could increase the removal efficiency of ARGs, it also increased the enrichment risk of ARGs. The selection of constructed wetland substrate type should focus on fillers with a high specific surface area; the flow direction of the up-flow type was generally more efficient than the down-flow type in removing ARGs. In conclusion, the various factors (such as, the constructed wetland type, substrate type, hydraulic retention time, ambient temperature, and plant species) need to be integrated into the design of the constructed wetland system parameters to achieve the most effective treatment effect. The application of constructed wetlands in removing ARGs from the environment has broad prospects but also faces challenges.

Dissolved gas recovery from water using a sidestream hollow-fiber membrane module: First principles model synthesis and steady-state validation

This paper presents a first-principles model for the recovery of dissolved gases from liquids using a sidestream hollow-fiber membrane module. The model avoids the use of new empirical coefficients, thus providing a parametric understanding of the process behavior for future design and optimization of membrane modules. This type of first-principles model could be particularly useful when gas recovery is beneficial to biological or chemical reactions of interest, such as the acetogenesis reactions in two-stage anaerobic digesters. The steady-state behavior of the model was validated against both new experimental data for the recovery of H2, CH4 and H2–CH4 mixtures from pure water, as well as existing published data. The modeled gas recovery predictions agreed with experimental data to an absolute average error of 13%, and an average R2 value of 0.98. Parametric analysis of mixed-gas recovery suggests possible key transition points in the composition of the recovered gases. For example, at 40 °C, increasing trans-membrane pressure while keeping hydraulic residence time (HRT) under 0.5 s will result in an increase in the ratio of H2 to CH4 recovered. Otherwise, increasing trans-membrane pressure will instead decrease the ratio of H2 to CH4 recovered. The model has potential to be extended to transient analysis, but has yet to be validated with transient experimental data. This model was successfully implemented in both Python and MATLAB, and provides valuable insights for future net-energy optimization for anaerobic digestion systems with in-situ gas recovery.

Response of Nitrogen Removal Performance and Microbial Distribution to Seasonal Shock Nutrients Load in a Lakeshore Multicell Constructed Wetland

Multicell constructed wetlands (MCWs) on lakeshores are a prospective treatment technique. However, the factors affecting the nutrient removal performance of lakeshore MCWs at the field scale are unclear. This study chose a field-scale lakeshore MCW with the highest mass removal efficiency (approximately 49,175.12 mg m−2 day−1) for total nitrogen removal in the wet season to investigate the response of nitrogen removal and microbial distribution to seasonal shock nutrients load. The mass loading rates in the wet season were as high as 43~72 times over those in the dry season. Hence, a storage pond (SP), as a forebay retention cell, was necessary to mitigate the shock loads of the influent, which is beneficial to nitrogen removal of the MCW system. The two major genera in the sediments are heterotrophic nitrification–aerobic denitrification bacteria, and the abundance and species of the nitrogen-related functional genera were higher in the wet season than the dry season. According to the results of redundancy analysis, the hydraulic residence time (29.4%, F = 2.2, p < 0.1) and hydraulic loading rate (85.9, F = 36.5, p < 0.05) were the major factors explaining microbial community variation, instead of environmental factors (temperature, pH, and dissolved oxygen). The shock loads of influent and the periodic saturation in sediments contributed to a complicated oxygen and nitrogen nutrient exchange environment resulting in higher abundance and species of nitrogen-related microbes, which is beneficial to nitrogen removal in lakeshore MCWs. The results provided a scientific basis for the optimal design of constructed wetlands on lakeshores.

Using automated machine learning techniques to explore key factors in anaerobic digestion: At the environmental factor, microorganisms and system levels

Exploring key factors has important guidance for understanding complex anaerobic digestion (AD) systems. This study proposed a multi-layer automated machine learning framework to understand the complex interactions in AD systems and explore key factors at the environmental factor, microorganisms and system levels. The first layer of the framework identified hydraulic residence time (HRT) as the most important environmental factor, with an optimal range of 33–45 d. In the second layer of the framework, Methanocelleus (optimal relative abundance (ORA) = 3.0%) and Candidatus_Caldatribacterium (ORA = 1.7%) were found to be the key archaea and bacteria, respectively. Furthermore, the prediction of key microorganisms based on environmental factors and remaining microbial data showed the essential roles of Methanothermobacter and Acetomicrobium. The third layer for finding the optimal combination of data variables for predicting biogas production demonstrated that combined Archaea genera and environmental factors should be achieved for the most accurate prediction (root mean square error (RMSE) = 84.21). GBM had the best model performance and prediction accuracy among all the built-in models. Based on the optimal GBM model, the analysis at the system level showed that HRT was the most important variable. However the most important microorganism, Methanocelleus, within the appropriate survival range is also essential to achieve optimal biogas production. This research explores key parameters at various levels through automated machine learning techniques, which are expected to provide guidance in understanding the complex architecture of industrial and laboratory AD systems.

Comparative evaluation of low-cost ceramic membrane and polymeric micro membrane in algal membrane photobioreactor for wastewater treatment

Algal-bacterial membrane photobioreactor (AMPBR) is proven as a highly energy-efficient process for treating domestic wastewater. This study compared the application of polymeric micro-membrane (PMM) and a low-cost ceramic membrane (LCM) to the AMPBR process for treating domestic wastewater with low and high organic pollution levels. Experiments were conducted over 57 days using two PMM-AMPBRs and two LCM-AMPBRs, operating on a 12-h dark/light cycle in a continuous mode. Simulated wastewater containing varying levels of chemical oxygen demand (COD) was fed to reactors for a consistent hydraulic residence time (HRT) of 7 d and a flux rate of 100 L/m2/d. PMM and LCM-AMPBRs demonstrated efficient wastewater treatment capabilities, achieving COD removal rates exceeding 94% and 95% for high and low COD loadings, respectively. PMM-AMPBR achieved 54.1% TN removal at low COD loading, while LCM-AMPBR achieved 57.2%. These removal efficiencies decreased to 45.6% and 47.0% under high COD loading. Total Phosphorus (TP) removal reached 29–33% for PMM-AMPBRs and 21–24% for LCM-AMPBRs, irrespective of COD loading. LCM-AMPBRs showed significantly lower fouling frequency than PMM-AMPBRs. The biomass production rate decreased with increasing COD loading and achieved 40 mg/L/d at low COD loading for both AMPBRs. Net energy return (NER) values for both AMPBRs were close to 0.87, indicating them as energy-efficient processes. Considering the cost-effectiveness and comparable performance, LCM-AMPBR could be a viable alternative to PMM-AMPBR for wastewater treatment, particularly under low COD loading conditions.

Nitrification-denitrification co-metabolism in an algal-bacterial aggregates system for simultaneous pyridine and nitrogen removal

Photosynthetic oxygenation in algal-bacterial symbiotic (ABS) system was mainly concerned to enhance contaminant biodegradation by developing an aerobic environment, while the role of nitrification-denitrification involved is often neglected. In this study, an algal-bacterial aggregates (ABA) system was developed with algae and activated sludge (PBR-1) to achieve simultaneous pyridine and nitrogen removal. In PBR-1, as high as 150 mg·L−1 pyridine could be completely removed at hydraulic residence time of 48 h. Besides, total nitrogen (TN) removal efficiency could be maintained above 80%. Nitrification-denitrification was verified as the crucial process for nitrogen removal, accounting for 79.3% of TN removal at 180 μmol·m−2·s−1. Moreover, simultaneous pyridine and nitrogen removal was enhanced through nitrification-denitrification co-metabolism in the ABA system. Integrated bioprocesses in PBR-1 including photosynthesis, pyridine biodegradation, carbon and nitrogen assimilation, and nitrification-denitrification, were revealed at metabolic and transcriptional levels. Fluorescence in situ hybridization analysis indicated that algae and aerobic species were located in the surface layer, while denitrifiers were situated in the inner layer. Microelectrode analysis confirmed the microenvironment of ABA with dissolved oxygen and pH gradients, which was beneficial for simultaneous pyridine and nitrogen removal. Mechanism of nitrification-denitrification involved in pyridine and nitrogen removal was finally elucidated under the scale of ABA.

Continuous flow operation of solar photo-Fenton fused with NaOCl as a novel tertiary treatment

A novel strategy based on solar photo-Fenton mediated by ferric nitrilotriacetate (Fe3+-NTA) combined with NaOCl in continuous flow mode for wastewater reclamation has been studied. Escherichia coli (E. coli) inactivation attained ≥ 5 log10-units, meeting the most restrictive EU 2020/741 target (10 CFU/100 mL), and 75% of organic microcontaminant total load was removed. As a remarkable finding, trihalomethanes (THMs) concentration was insignificant, complying by far with the Italian legislation limit. To attain these results, first the effect of liquid depth on E. coli inactivation and imidacloprid (IMD) removal from spiked municipal effluents was evaluated in continuous flow pilot-scale raceway pond reactors at 60-min hydraulic residence time with low reagent concentrations (0.10 mM Fe3+-NTA, 0.73 mM H2O2 and 0.13 mM NaOCl). Disinfection was due to the bactericidal effect of chlorine. In contrast, liquid depth notably influenced microcontaminant removal, highlighting that operation at 10-cm liquid depth allows achieving treatment capacities higher than at 5 cm (16.50 vs 28.20 mg IMD/m2∙day). Next, the monitoring of THMs was carried out to evaluate the generation and degradation of disinfection by-products, along with the removal of actual microcontaminants. These promising results draw attention to the treatment potential and open the way for its commercial application.

Evaluation of a sequential anaerobic-aerobic membrane bioreactor system for treatment of traditional and insensitive munitions constituents

New energetic formulations containing insensitive high explosives (IHE), such as 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazole-5-one (NTO), and nitroguanidine (NQ) are being developed to provide safer munitions. The addition of IHE to munitions formulations results in complex wastewaters from explosives manufacturing, load and pour operations and demilitarization activities. New technologies are required to treat those wastewaters. The core objective of this research effort was to develop and optimize a dual anaerobic-aerobic membrane bioreactor (MBR) system for treatment of wastewater containing variable mixtures of traditional energetics, IHE, and anions. The combined system proved highly effective for treatment of traditional explosives (TNT, RDX, HMX), IHE (DNAN, NTO, NQ) and anions commonly used as military oxidants (ClO4−, NO3−). The anaerobic MBR, which was operated for more than 500 d, was observed to completely degrade mg L−1 concentrations of TNT, DNAN, ClO4− and NO3− under all operational conditions, including at the lowest hydraulic residence time (HRT) tested (2.2 d). The combined system generally resulted in complete treatment of mg L−1 concentrations of RDX and HMX to <20 μg L−1, with most of the degradation occurring in the anaerobic MBR and polishing in the aerobic system. No common daughter products of DNAN, TNT, RDX, or HMX were detected in the effluent. NTO was completely transformed in the anaerobic MBR, but residual 3-amino-1,2,4-triazole-5-one (ATO) was detected in system effluent. The ATO rapidly decomposed when bleach solution was added to the final effluent. NQ was initially recalcitrant in the system, but microbial populations eventually developed that could degrade >90% of the ∼10 mg L−1 NQ entering the anaerobic MBR, with the remainder degraded to <50 μg L−1 in the aerobic system. The dual MBR system proved to be capable of complete degradation of a wide mixture of munitions constituents and was resilient to changing influent composition.

Impact of mixing insufficiencies on L-phenylalanine production with an Escherichia coli reporter strain in a novel two-compartment bioreactor

BackgroundThe omnipresence of population heterogeneity in industrial bioprocesses originates from prevailing dynamic bioprocess conditions, which promote differences in the expression of cellular characteristics. Despite the awareness, the concrete consequences of this phenomenon remain poorly understood.ResultsTherefore, for the first time, a L-phenylalanine overproducing Escherichia coli quadruple reporter strain was established for monitoring of general stress response, growth behavior, oxygen limitation and product formation of single cells based on mTagBFP2, mEmerald, CyOFP1, and mCardinal2 expression measured by flow cytometry. This strain was applied for the fed-batch production of L-phenylalanine from glycerol and ammonia in a stirred-tank bioreactor at homogeneous conditions compared to the same process in a novel two-compartment bioreactor. This two-compartment bioreactor consists of a stirred-tank bioreactor with an initial volume of 0.9 L (homogeneous zone) with a coiled flow inverter with a fixed working volume of 0.45 L as a bypass (limitation zone) operated at a mean hydraulic residence time of 102 s. The product formation was similar in both bioreactor setups with maximum L-phenylalanine concentrations of 21.1 ± 0.6 g L−1 demonstrating the consistency of this study’s microbial L-phenylalanine production. However, cell growth was vulnerable to repetitive exposure to the dynamically changing conditions in the two-compartment bioreactor with maximum biomass yields reduced by 21%. The functionality of reporter molecules was approved in the stirred-tank bioreactor cultivation, in which expressed fluorescence levels of all four markers were in accordance with respective process state variables. Additional evaluation of the distributions on single-cell level revealed the presence of population heterogeneity in both bioprocesses. Especially for the marker of the general stress response and the product formation, the corresponding histograms were characterized by bimodal shapes and broad distributions. These phenomena were pronounced particularly at the beginning and the end of the fed-batch process.ConclusionsThe here shown findings confirm multiple reporter strains to be a noninvasive tool for monitoring cellular characteristics and identifying potential subpopulations in bioprocesses. In combination with experiments in scale-down setups, these can be utilized for a better physiological understanding of bioprocesses and support future scale-up procedures.

Electrodeposited copper enhanced removal of 2,4-dichlorophenol in batch and flow reaction in Cu@CC-PS-MFC system

Combination of microbial fuel cell (MFC) and advanced oxidation process (AOP) is promising for pollutant removal. In this paper, Cu0-loaded carbon cloth cathode by electrodeposition (Cu@CC-PS-MFC) was applied to enhance 2,4-dichlorophenol (2,4-DCP) degradation based on persulfate (PS) activation in microbial fuel cell. Cu0 exhibited a typical structure of face-centered cubic metal polyhedron on carbon cloth. The removal of 2,4-DCP by Cu@CC-PS-MFC (75.6%) was enhanced by more than 50% compared to CC-PS-MFC (49.2%) after 1 h of reaction. 30 mg/L 2,4-DCP in Cu@CC-PS-MFC was completely removed and achieved a high mineralization (80.6%) after 9 h of reaction under optimized condition with low dissolved copper ion concentration (0.615 mg/L). Meanwhile, more than 90% removal of 2,4-DCP was stably achieved with flow operation condition (hydraulic residence time of 7.2 h). The change of copper valent state Cu0/Cu2O/CuO was the main mechanism of PS activation with main reactive species of O•H and O21. The bioanode of MFC enhanced the in-situ regeneration of ≡Cu+ and ≡Cu0 on the catalyst surface by transporting electrons, which was believed to contribute to good catalyst lifetime and excellent 2,4-DCP removal. Electrodeposited copper contributes to the enhanced degradation of 2,4-DCP with energy recovery at the same time which can further broaden the application MFC.

Modelling and experimentation of a continuous nutrient recovery reactor – an assessment of mixing on reactor operation

Phosphorus recovery from human waste will help assure global food security, reduce environmental impact, and ensure effective stewardship of this limited and valuable resource. This can be accomplished by the precipitation of struvite (MgNH4PO4·6H2O) in a two-zone reactor, continuously fed with nutrient-rich hydrolysed urine and a magnesium solution. The solid struvite crystals are periodically “harvested”, removing accumulated crystal mass – and therefore recovered nutrients – from the process, and the operating campaign can, in principle, be continuously operated in a batch-continuous operating mode. A previously developed process model is augmented, incorporating two well-mixed volumes (upper zone and lower zone) that are coupled by intermixing forward and back flows. The intermixing back flow is parametrised and, therefore, adjusted for analysis. Crystal linear growth rate is modelled by a simple power-law kinetic, driven by the nutrient solution's saturation index (SI) of struvite. The instantaneous mass transfer rate of struvite constituents from liquid to solid phase is predicted, using the total interfacial area of the crystal population exposed to the well-mixed solution. This model describes a 12-L, laboratory reactor operated in the hybrid batch-continuous mode, although larger reactors could easily be accommodated, subject to their mixing behaviours. Experiments were performed at a 10-hour hydraulic residence time (HRT), which, importantly, is based on the volume of the well-mixed lower zone, since this is the volume of liquid that actively interacts with the suspended struvite crystals. The Mg/P feed molar ratio was varied (0.34, 0.64 and 1.29) to assess Mg feed rate-limiting behaviour. The concentration profiles of elemental P and Mg agree with experimentation, while P and Mg composition in the solid and X-ray diffraction support the production of struvite.

Relevance of photocatalytic redox transformations of selected pharmaceuticals in a copper- and iron-rich Mediterranean intermittent river

This work aimed at investigating specific attenuation pathways of pharmaceuticals in copper- and iron-rich Mediterranean intermittent and sunlit rivers by combining lab- and field-scale studies. Poorly photodegradable and biodegradable compounds such as fluconazole, oxazepam and venlafaxine attenuated in two river stretches with short hydraulic residence times (<3 h). This result was assumed to be related to their capacity to interact with photoreactive free Cu2+ and Fe3+ or their associated oxides. Lab-scale photodegradation experiments under simulated solar irradiation revealed the beneficial impact of a mixture Cu2+ and colloidal iron hydroxides at environmental concentrations and at neutral pH on the pharmaceuticals photodegradation kinetic rate constants. These latter were consistent with the in-stream attenuation rate constants of targeted contaminants which ranged from 0.104 to 0.154 h−1. Further identification of phototransformation products by LC-HRMS highlighted reductive transformation pathways including reductive dehalogenation and hydrogenation reactions. Several TPs were found to be stable under irradiation and were detected in field monitoring, accordingly. This was ascribed to the formation of a Cu/Fe composite material under solar irradiation with photocatalytic properties. The role of Cu was to trap the electron in the conduction band of the iron-based photocatalyst, which promoted separation efficiency of electron-hole pairs as well as enhanced photoreduction processes at the expense of oxidation ones. Even though, these mechanisms have been reported in water treatment field for organic micropollutants removal, their significance was demonstrated for the first time in natural settings.

Advancing aerobic digestion efficiency using ultrafine bubbles in wastewater treatment

The application of ultrafine/nanobubbles (NBs) was tested as an aeration mechanism in a laboratory scale, semi-batch, biological wastewater treatment unit and compared with a similar scale, conventional bubbling supported aerobic digestion unit. The results showed that the oxygen utilization rate (OUR) and volumetric oxygen mass transfer coefficient (kla) were doubled from 0.075 to 0.159 mg O2/min and 0.07 to 0.13 respectively, through the application of NBs compared to the use of conventional bubbles (CBs). This was achieved by exploiting the sufficient residence time NBs can have in the aqueous system along with its capacity of high mass transfer surface area to volume ratio. The twofold increment in the OUR and kla due to the application NBs improved the biodegradation rate of the organic matter from 5.83 to 17.5 mg/l.hr compared to the application of CBs. Thus, 60 % of the hydraulic residence time reduction was achieved by the application NBs compared to CBs to achieve a similar amount of organic waste degradation. Moreover, the membrane filtration results also showed a reduction in the sludge load and fouling rate for aerobic membrane bioreactors supported by NB systems. A possible mechanism for sludge reduction was also proposed based on the results achieved.

Continuous solar photo-Fenton for wastewater reclamation in operational environment at demonstration scale

For the first time, a continuous flow solar photo-Fenton demonstration plant has been assessed for wastewater reclamation according to the EU 2020/741 regulation. The treated water qualities achieved under two operating strategies (acidic and neutral pH) in a 100-m2 raceway pond reactor were explored in terms of liquid depth, iron source, reagent concentrations, and hydraulic residence time over three consecutive days of operation. The results obtained at acidic pH showed removal percentages of contaminants of emerging concern (CECs) > 75% and water quality classes B, C and D according to EU regulation at both assessed operating conditions, with treatment capacities up to 1.92 m3 m-2 d-1. At neutral pH with ferric nitrilotriacetate (Fe3+-NTA), 50% of CEC removal and only water quality class D were achieved with the most oxidizing condition assessed, giving a treatment capacity of 0.80 m3 m-2 d-1. The treatment capacities obtained in this work, which have never been achieved with solar water treatments, demonstrate the potential of this technology for commercial-scale application.

Modeling an acid-phase digester in BioWin with parameter optimization from site data

Organic acid digesters are reactors of growing interest for municipal nutrient recovery technologies, but the industry standard BioWin modeling software does not accurately predict their performance. A BioWin configuration using default parameters will over-predict volatile fatty acid production in an acid digester, yielding an unrealistically low pH. We have characterized the effects of parameters for local pH inhibition thresholds, growth and decay kinetics, and hydraulic residence times to successfully facilitate more accurate modeling of acid phase digestion reactors in BioWin. These changes show improvements in a range of treatment train models without affecting accuracy in other reactors. Results were calibrated against a municipal acid phase digester to accurately predict pH, VFA concentration, and gas production. In particular, an acid digester with a measured suspension pH of 5.14 was predicted by BioWin using default parameters to exist at pH 4.35 with highly sensitive biogas methane content, but our parameter changes were able to correct the predicted suspension pH and VFA concentrations over a range of values. We also demonstrate that several intuitive or traditional parameters a BioWin user may attempt, such as growth and fermentation kinetics, do not yield meaningful results. Refinements incorporated into BioWin should allow future operators to easily model acid digesters for their specific treatment trains or allow users to predict changes while testing new wastewater treatment technologies.

Unraveling mechanisms behind reduced nitrate leaching with graphite nanomaterials addition with fertilizers in soil column experiments

Overuse or mistimed application of nitrogen fertilizer can cause nitrate contamination in groundwater and surrounding surface waters. Previous greenhouse studies have explored the use of graphene nanomaterials, including graphite nano additive (GNA), to reduce nitrate leaching in an agricultural soil while growing lettuce crops. To investigate the mechanism of GNA addition in suppressing nitrate leaching, we conducted soil column experiments using native agricultural soils under saturated or unsaturated flow conditions to simulate varied irrigation. We investigated the effects of temperature (4 °C compared with 20 °C) on microbial activity and dose effect of GNA was also explored (165 mg/kg soil and 1650 mg/kg soil) for biotic soil column experiments whereas a single temperature condition (20 °C) and GNA dose (165 mg/kg soil) was employed for abiotic (autoclaved) soil column experiments. Results showed GNA addition had minimal effects on nitrate leaching in saturated flow soil columns due to short hydraulic residence times (∼3.5 h). In comparison, longer residence times (∼3 d) in unsaturated soil columns reduced nitrate leaching by 25–31% relative to control soil columns without GNA addition. Furthermore, nitrate retention in the soil column was found to be suppressed at 4 °C compared with 20 °C, suggesting a bio-mediated mechanism for GNA addition to reduce nitrate leaching. In addition, the soil dissolved organic matter was found to be associated with nitrate leaching, where less nitrate leaching occurring when higher dissolved organic carbon (DOC) was measured in leachate water. Following studies of adding soil-derived organic carbon (SOC) resulted in greater nitrogen retention in the unsaturated soil columns only when GNA was present. Overall, the results suggest that GNA-amended soil reduces nitrate loss through increased N immobilization in the microbial biomass or loss of N in gaseous phase through enhanced nitrification and denitrification process.