Variation Of Residence Time Research Articles

Study of anaerobic biofilter tofu wastewater treatment with bioball media and phytoremediation by kiambang (salviniamolesta)

Small and medium industries such as tofu industry are characterized as industries with high levels of pollution because it lacks or does not have a wastewater handling system. Tofu wastewater contains high level of chemical oxygen demand (COD) and total suspended solid (TSS). If referring to the standard quality of wastewater, tofu wastewater requires treatment before being discharged into water bodies. This research aims to find out the effect of residence time and plant mass variation on the efficiency of reducing COD and TSS in tofu wastewater. This research were used anaerobic reactors with bioball media and phytoremediation reactors using kiambang (salviniamolesta) with plant mass variations of 50, 100, 150, 200 and 250 grams. The research begins with the process of seeding to breed microorganisms derived from tofu wastewater then proceed with running on the anaerobic reactor until the reduction in COD reaches 60% -70%. On the 6th day of running, the reduction in COD has reached 66.66% so that it can be continued flowing tofu wastewater to the phytoremediation reactor. The process of running on phytoremediation is done with variations in plant mass and residence time of 0, 1, 2, 3, 4, 5, 6, and 7 days. The results showed that the variation of residence time affected the level of COD and TSS reduction. In phytoremediation reactors, the best plant mass in reducing COD levels is 250 grams with removal efficiency at D-7 reaching 59.61% while the best plant mass in reducing TSS levels is 50 grams with removal efficiency at D-7 reaching 89.41 %.

Prototype Alat Olah Limbah Sistem Semi Batch Untuk Pengolahan Limbah Cair Laboratorium Kimia

Chemical laboratory liquid waste Environmental Pollution Control Techniques Cilacap State Polytechnic is liquid waste originating from practical or research activities of lecturers / students. Most of the waste contains organic and inorganic substances that are harmful to the environment. In the initial analysis the results of the wastewater content were in the form of lead ˂0.251 mg / L, Hardness 213.33 mg / L, TDS 4690 ppm, and pH 1.6. One parameter that needs to be addressed is TDS because dissolved solids can affect the O2 levels contained in the waters. In this research, a prototype of a waste processing tool was used to process the waste. In this research the method used is the process of coagulation, electrocoagulation and sedimentation in batch with a variation of residence time which affects the product. In addition, the filtration and adsorption process uses a continuous system, so that overall the tool uses a semi-batch system. In this study the chemicals used for processing were CaCO3 and citric acid. Then the adsorbent used is zeolite and activated charcoal as absorbent of dissolved solids. This waste treatment tool is considered quite effective in reducing TDS with a final result of 2950 ppm.

Continuous‐Flow Synthesis of ZIF‐8 Biocomposites with Tunable Particle Size

AbstractZeolitic imidazolate framework (ZIF) biocomposites show the capacity to protect and deliver biotherapeutics. To date, the progress in this research area is based on laboratory batch methods. Now, the first continuous flow synthetic method is presented for the encapsulation of a model protein (bovine serum albumin, BSA) and a clinical therapeutic (α1‐antitrypsin, AAT) in ZIF‐8. The in situ kinetics of nucleation, growth, and crystallization of BSA@ZIF‐8 were studied by small‐angle X‐ray scattering. By controlling the injection time of ethanol, the particle growth could be quenched by ethanol‐induced crystallization from amorphous particles to ZIF‐8 crystals. The particle size of the biocomposite was tuned in the 40–100 nm range by varying residence time prior to introduction of ethanol. As a proof‐of‐concept, this procedure was used for the encapsulation of AAT in ZIF‐8. Upon release of the biotherapeutic from the composite, the trypsin inhibitor function of AAT was preserved.

Continuous-Flow Synthesis of ZIF-8 Biocomposites with Tunable Particle Size.

Zeolitic imidazolate framework (ZIF) biocomposites show the capacity to protect and deliver biotherapeutics. To date, the progress in this research area is based on laboratory batch methods. Now, the first continuous flow synthetic method is presented for the encapsulation of a model protein (bovine serum albumin, BSA) and a clinical therapeutic (α1‐antitrypsin, AAT) in ZIF‐8. The in situ kinetics of nucleation, growth, and crystallization of BSA@ZIF‐8 were studied by small‐angle X‐ray scattering. By controlling the injection time of ethanol, the particle growth could be quenched by ethanol‐induced crystallization from amorphous particles to ZIF‐8 crystals. The particle size of the biocomposite was tuned in the 40–100 nm range by varying residence time prior to introduction of ethanol. As a proof‐of‐concept, this procedure was used for the encapsulation of AAT in ZIF‐8. Upon release of the biotherapeutic from the composite, the trypsin inhibitor function of AAT was preserved.

Effect of Temperature and Residence Time Torrefaction Palm Kernel Shell On The Calorific Value and Energy Yield

Torrefaction was thermochemical processes to make biomass a fuel that had better properties, such as increased carbon content and calorific value. It was a temperature-sensitive process that was effective between 200 °C and 300 °C in an inert environment with a residence time of 20-60 minutes. Palm kernel shell was one of the biomass that has the potential to be used as fuel, where its availability was abundant and has good physical properties. In this study of palm kernel shell torrefaction was carried out from 0.5 cm sieve with three variations in temperature and residence time follows 250 °C - 300 °C and 20-40 minutes. The results obtained were the increase in temperature and holding time causes an increase in the calorific value but relatively on energy yield because of a large mass loss at a temperature of 300 °C. The optimum process for torrefaction of palm kernel shell according to calorific value and energy yield was 275 °C with residence time 20 minutes.

Flame dynamics and stability of premixed methane/air in micro-planar quartz combustors

The flame dynamics and stability of methane/air premixed combustion in micro-planar quartz combustors were numerically studied with detailed chemical reaction mechanism. The computed flame characteristics were quantitatively and qualitatively in good agreement with experimental phenomena. The oscillating flame was observed from the perspective of three-dimensional simulation for the first time. Parametric analysis associated with channel height and channel length was performed. Results indicated that the blowout limit was found to increase first and then decrease as increasing the channel height due to the tradeoff relationship between increased areas for heat flux and the extended timescales for energy diffusion. The change in channel length can lead to the variation in residence time of mixture in channel and heat loss from the external wall. It was found that there existed a critical point of channel length, above which the flame stability was improved marginally. Furthermore, it was shown that wall thermal conductivity had effect on both the flame structure and flame location, especially at relatively high inlet velocities. Further analyses indicated that the mechanism of enhanced flame stability with sufficient high wall thermal conductivity can be attributed to the lower strain rate and smaller deflection of streamlines in flame front.

Affinity, binding kinetics and functional characterization of draflazine analogues for human equilibrative nucleoside transporter 1 (SLC29A1)

In the last decade it has been recapitulated that receptor-ligand binding kinetics is a relevant additional parameter in drug discovery to improve in vivo drug efficacy and safety. The equilibrative nucleoside transporter-1 (ENT1, SLC29A1) is an important drug target, as transporter inhibition is a potential treatment of ischemic heart disease, stroke, and cancer. Currently, two non-selective ENT1 inhibitors (dilazep and dipyridamole) are on the market as vasodilators. However, their binding kinetics are unknown; moreover, novel, more effective and selective inhibitors are still needed. Hence, this study focused on the incorporation of binding kinetics for finding new and improved ENT1 inhibitors.We developed a radioligand competition association assay to determine the binding kinetics of ENT1 inhibitors with four chemical scaffolds (including dilazep and dipyridamole). The kinetic parameters were compared to the affinities obtained from a radioligand displacement assay. Three of the scaffolds presented high affinities with relatively fast dissociation kinetics, yielding short to moderate residence times (RTs) at the protein (1–44 min). While compounds from the fourth scaffold, i.e. draflazine analogues, also had high affinity, they displayed significantly longer RTs, with one analogue (4) having a RT of over 10 h. Finally, a label-free assay was used to evaluate the impact of divergent ENT1 inhibitor binding kinetics in a functional assay. It was shown that the potency of compound 4 increased with longer incubation times, which was not observed for draflazine, supporting the importance of long RT for increased target-occupancy and effect.In conclusion, our research shows that high affinity ENT1 inhibitors show a large variation in residence times at this transport protein. As a consequence, incorporation of binding kinetic parameters adds to the design criteria and may thus result in a different lead compound selection. Taken together, this kinetic approach could inspire future drug discovery in the field of ENT1 and membrane transport proteins in general.

Potensi dan Pengaruh Batang Pisang Sebagai Media Filter Pada Pengolahan Air Limbah Pencucian Kendaraan Bermotor

Wastewater vehicle washing that discharged directly into water bodies can increase pollution levels. Wastewater treatment of small-scale vehicle washing businesses must be efficient, no need large areas, easy to operate and economical. The alternative technology is using simple wastewater filtration system. Banana stems can be used for filter media. Previous studies mention banana stems have cellulose content and have high hygroscopic ability. High cellulose content allows the potential to be used as an absorbent media. Hygroscopic properties are useful for absorbing harmful inorganic chemicals. The study was conducted by making a filtration reactor using banana stem filter media with a variation of residence time and filter media thickness. Sample testing by analyzing COD, TSS and Detergent parameters. The test results significant decrease in TSS and detergent parameters. The highest percentage decrease in TSS reached 91% and detergent 96%. COD decreased during the filtration treatment directly, but after that increased with the length of duration. This is due to biological influence and the high percentage of organic matter and biomass of banana stems. It can be concluded that the banana stem potential as a filter media for direct wastewater treatment and effective in reducing TSS and detergents for washing vehicles wastewater.

Seasonal Variation in Residence Times of Two Neighboring Bays with Contrasting Topography

Residence time is an important parameter for evaluating the physical and biochemical characteristics of estuaries and bays. The residence times of two neighboring South Korean bays with contrasting topographies, Gwangyang Bay and Jinju Bay, were calculated for winter and summer using a three-dimensional model. Gwangyang Bay, with considerable industrial development nearby, has a relatively large volume and depth, whereas Jinju Bay is shallow and is primarily used for aquaculture. River discharge in the two bays is high in summer and low in winter, in part due to the influence of the East Asian Monsoon. Temperature and salinity in both bays are vertically homogeneous during winter but stratified in summer. The mean residence time in Gwangyang Bay is more than 20 days in winter due to its large volume, but less than 5 days in summer due to increased gravitational circulation driven by large volumes of river discharge and a horizontal density gradient. However, the mean residence time of Jinju Bay is less than 5 days in both seasons due to its small volume and shallow depth. These results reveal that Gwangyang Bay is vulnerable to industrial pollution during winter, but that it may remove pollutants efficiently in summer. The shallower Jinju Bay is likely to remain free from anthropogenic eutrophication caused by nutrient inputs from aquaculture due to its short residence time throughout the year.

Hydrogeological processes and near shore spatial variability of radium and radon isotopes for the characterization of submarine groundwater discharge

Inadequate characterization of variability in natural tracers of submarine groundwater discharge (SGD) introduces large errors into tracer-derived SGD estimates. To address this gap, we investigated spatial variability in the natural SGD tracers 223Ra, 224Ra, 226Ra, 228Ra and 222Rn using a high-density array of piezometers and seepage meters over a nearshore area where discharging groundwater transitioned from fresh to saline. Seepage meters and piezometers were used to sample groundwater and to quantify fluxes and salinity. A series of spatial patterns was distinguished beyond the normal salinity impact on Ra activity. The discharge in the interface between saltwater and freshwater was characterized by higher activities of the longer-lived isotopes (226Ra and 228Ra), while areas dominated by benthic exchange had higher activities of the shorter-lived isotopes (223Ra and 224Ra). Spatial differences in Ra activities were associated with variation in salinity and residence time in the aquifer and were indicative of underlying hydrogeological processes. At the freshwater-saltwater interface, fresh discharge is driven by terrestrial hydraulic gradients and saline discharge is driven by density gradients; both result in long residence times in the aquifer. Benthic exchange of saltwater has shorter residence times, much less than required to enrich long-lived isotopes and reach secular equilibrium. The highest activities of 222Rn were detected in the fresh discharge zone, and the lowest activities in areas dominated by benthic exchange. Direct sampling at discharge points allowed comparison between groundwater collected from inland wells and the water discharging to the bay, and indicated significant differences in the activities despite the short distance from wells to the discharge area. Substantial spatial variability in Ra and Rn was observed on the meter scale, with trends that reflected groundwater origin and residence time. Inadequate characterization of variability, trends, and fluxes introduces large errors into tracer-derived estimates of submarine groundwater discharge. Thus, the study of submarine groundwater discharge with radioactive tracers requires adequate hydrogeological knowledge to identify processes that have strong impacts on Ra and Rn activities and associated fluxes to the ocean.

Continuous-feed carbonation of waste incinerator bottom ash in a rotating drum reactor

Carbonation is a key process in the aging of waste incinerator bottom ash (BA). The reaction with CO2 decreases the BA alkalinity and lowers the leachability of amphoteric trace metals. Passive ageing over several months is usually performed in intermittently mixed BA heaps. Here we aimed at accelerating the process in a rotating drum reactor continuously fed with the BA and the reactant gas (10 vol-% CO2, volumetric flow rate 60 L/min). In one test, the gas was heated and humidified. Since carbonation depends on the specific CO2-supply, experiments were conducted at varied BA residence time (60, 80, and 100 min). Residence time was calculated by mass balancing and confirmed by the breakthrough time of two tracers. Leachates and solid phase properties of the treated BA served to evaluate the carbonation performance. The residence time of BA could be adequately controlled by the reactor loading and feed rate. A residence time of 80 min was sufficient to reduce the BA leachability such as to comply with the German regulatory standards for non-hazardous waste, whereas the untreated BA was hazardous waste. Decreased alkalinity was indicated by lower leachate pH and Ca(OH)2 contents of the BA as compared to the input. Leachate concentrations of amphoteric trace metals (Pb, Zn, Cu) decreased by at least one order of magnitude while oxyanions became slightly more mobile upon carbonation. In view of relatively short residence times and stable process performance, the rotating drum reactor seems promising for a full-scale implementation of BA carbonation.

The atmospheric carbon sequestration potential of man-made tidal lagoons

Understanding sequestration of carbon by coastal ecosystems is central to addressing the role they play in climate change mitigation. To quantify this process, accurate measurements of CO2 fluctuation, coupled with variations in residence time of coastal water-bodies are required. Nearshore ecosystems, including coastal lagoons, may provide an effective sink for atmospheric carbon dioxide, particularly those containing productive biota such as seagrass. However, the rate and pattern of carbon sequestration in seagrass meadows across a range of environmental settings is still poorly constrained. In this study, we utilize a robust physical tidal model, along with biogeochemical dissolved inorganic carbon (DIC) assessment, to estimate water residence time and net sequestration of atmospheric CO2 in an intertidal lagoon containing a seagrass (Zostera noltii) meadow. Total alkalinity and pH measurements taken from advected water mass exchanged with the open ocean at inlet boundaries are used to calculate DIC and pCO2. A predictive model of hydrodynamics provides good approximation of mean water residence time to within 6 h (±3 s.d). Results indicate that during the daytime study period the lagoon is a sink for carbon, having a mean net ecosystem productivity (NEP) of 3.0 ± 0.4 mmol C m−2 hr−1. An equivalent diel NEP range of between 15.23 and −9.24 mmol C m−2 d−1 is calculated based on reported shallow water pelagic respiration rates. Moreover, approximately 4% of DIC availability occurs from atmospheric CO2 transfer to lagoon water. However, a negative diel rate of −82 ± 81 mmol C m−2 d−1 is found, assuming overnight respiration ascertained from converted Zostera noltii O2 utilization. We hypothesize that analogous regional nearshore ecosystems provide baseline study sites suitable to elucidate the carbon capture potential of planned, nearby tidal range energy schemes.

Removal of metals (Pb, Cd, Cu, Cr, Ni, and Co) from drinking water by oxidation-coagulation-absorption at optimized pH

Removal of some metals, viz., Cd, Pb, Ni, Cr, Cu, and Co by oxidation-coagulation-adsorption at optimized pH (OCOP), an efficient and low cost method for simultaneous removal of As, Fe and Mn from groundwater has been studied. NaHCO3, KMnO4 and FeCl3 are used in OCOP as pH conditioner, oxidant and coagulant, respectively. The effects of variation of initial concentration and residence time on the removal of the heavy metal ions have also been studied. The removal of the chosen metals from initial concentration of 2 mg/L by the method has been found to increase in the order Cd (79.0%) << Co (94.8%) < Ni (94.4%) << Cu (98.0%) < Cr (98.3%) < Pb (99.5%). Analyses by atomic adsorption spectrophotometer, Energy dispersed X-ray spectrophotometer and powder X-ray diffraction indicate adsorption of the heavy metals on the surface of coagulates/precipitates as oxides and complexes of the heavy metals. The highly active absorber coagulates/precipitates formed in FeOOH, 5Fe2O3.9H2O, MnO2, and Mn3O4, also strongly adsorb other metals in addition to removal by precipitations of oxy-complexes in cases of Cd and Pb. The relatively lower removal of Cd has been attributed to its soft acidic nature and higher removal of Cr is due to its hard acidic nature. The present study shows that the OCOP method is capable of removing the heavy metals of Cd, Pb, Ni, Cr, Cu and Co, very well, in addition to efficiently removing As, Fe and Mn from water.

Correlation of combustor lean blowout performance to supercritical pyrolysis products

Studies to assess correlations between fuel pyrolysis products and fuel-to-air equivalence ratio at combustor lean blowout (LBO) were conducted. Eighteen fuels, including conventional and alternative fuel formulations and blends, single compounds and binary surrogates of hydrocarbon compounds, were studied. The pyrolysis tests consisted of thermally cracking the fuels in a flow reactor at supercritical conditions of 4.14 MPa and up to 625 °C, at varying residence times. The liquid and gaseous pyrolysis products were analyzed via gas chromatography to correlate yields to the fuel LBO data acquired in a previous study on a single-nozzle swirl-stabilized combustor. Focus was given to correlate LBO with primary decomposition products, since it is hypothesized that fuel combustion characteristics, particularly ignition and flame extinction, are related to the rate and type of products formed upon initial thermal decomposition of the parent fuel. Therefore, only the range of conversions for which low molecular weight products had a near-constant formation rate was considered. Results show that the highly branched fuels primarily decomposed to branched C4 and methane, while fuels with high concentration of linear alkanes show greater yields of C2-C4 alkanes and 1-alkenes. Regression analyses of the pyrolysis gas and LBO data show very strong correlations (R2 > 0.90) for several pyrolysis products for the conventional and alternative fuels, with ethane, ethylene and iso-butylene yields providing the best correlations to LBO. The calculated LBOs based on regression parameters and concentrations of the pyrolysis gases were within 2% of the measured LBO for most fuels tested. These initial results suggest that despite the vast differences in fuel reaction timescales in the flow reactor (∼0.2–11 s) and combustor environments (<0.5 ms), fuel pyrolysis species in a flow reactor environment are relevant and may be used to predict fuel combustion behavior. If further validated, this method provides a capability to identify fuel components that can improve combustion performance via their primary pyrolytic product slates, potentially providing a more cost-effective alternative to combustion testing for determination of fuel combustion performance metrics. Results of the pyrolysis tests of all fuels, and future efforts are discussed.

Impacts of combustion phasing, load, and speed on soot formation in spark-ignition engines

The premixed prevaporized engine operation method was used to study the effects of main combustion thermodynamic properties and residence time on soot formation in a spark-ignition engine. Select cases were repeated under early-injection, nearly homogeneous, spark-ignition direct-injection operation to determine if the impact of the investigated parameters was the same or if the impact of in-cylinder liquid fuel injection and the resulting heterogeneous fuel-air mixture alters the trends. The original premixed prevaporized study hypothesized that soot is more likely to form after main combustion than during the main combustion event under completely homogeneous conditions. This hypothesis was tested in this study by performing premixed prevaporized combustion phasing sweeps at equivalence ratios (Φs) of 1.35 and 1.40. Both sweeps showed low sensitivity of the particle size distribution to significant changes in peak temperature and pressure during combustion, providing supporting evidence for the original hypothesis. This information was then used to design experiments to isolate the impacts of pressure (engine load) and residence time (engine speed). A premixed prevaporized load sweep showed that particulate emissions increase as a function of load/pressure. A spark-ignition direct-injection load variation showed similar pressure dependence for cases with in-homogeneous in-cylinder fuel-air distributions. A premixed prevaporized residence time variation (performed by changing engine speed) demonstrated an increase in soot formation with increased residence time. The results for identical spark-ignition direct-injection residence-time variations suggest a trade-off in soot formation between the effects of increased mixing time and increased residence time for spark-ignition direct-injection operation. The premixed prevaporized load and speed points were each investigated using Φ sweeps to determine the critical enrichment threshold for soot formation (ΦC) and the dependence of soot formation for Φ &gt; ΦC. The spark-ignition direct-injection investigations were performed at Φ = 0.98, such that any soot formation above the non-fuel-related baseline particle size distribution could be attributed either to mixture heterogeneity or in-cylinder fuel films.

Dynamics of water exchange and salt flux in the Macuse Estuary, central Mozambique, southern Africa

Studies of water-particle flow dynamics in shallow estuarine systems show that tidal currents control water exchange, salt flux and residence time. We used the 3D Estuary, Lake and Coastal Ocean Model (ELCOM) to estimate the dynamics of tidal currents, salt flux and residence time in the Macuse Estuary, central Mozambique. The model was calibrated using data acquired from field-data measurements obtained in 2014 with an acoustic Doppler current profiler and conductivity-temperature-depth (CTD) casts and a tide-gauge. The water flow dynamics that were tracked indicated that tidal currents of 100 cm s−1 were dissipated by friction caused by bathymetric morphology during both the spring and neap tides. The water dissipation was translated into a phase-difference delay of ∼15 min between the catchment zone and the outlet during flood and ebb tides. The study showed that tidal currents and river discharges controlled the salt flux (2.07 × 105 g kg−1 m3 s−1) and the variation in residence time from hours to 40 days. The water ages were mostly driven by U-velocity tidal currents, bathymetric gradients and seasonal river discharges of ∼500 m3 s−1. River discharges seasonally affected salinity changes between 15 and 30, and changes in the concentration of suspended sediments of ∼300 mg l−1. In addition, it was shown that ELCOM was able to track the water-particle dynamics well, indicating the model’s suitability. These results contribute to our understanding of the effect of water-exchange dynamics on residence time and salt flux in shallow coastal inlet systems.

Reconstruction of Holocene coupling between the South American Monsoon System and local moisture variability from speleothem δ18O and 87Sr/86Sr records

Investigating controls on past variability of South American hydroclimate is critical to assessing its response to future warming scenarios. δ18O records from South America offer insight into past variability of the South American Monsoon System (SAMS). The controls, however, on precipitation δ18O values can be decoupled from precipitation amount at a given site and, thereby, limit local moisture condition reconstructions. Here we use a principal components analysis to assess the coherence of speleothem and lake core Holocene δ18O records in tropical and subtropical South America to evaluate the extent to which δ18O variability reflects changes in SAMS intensity at different sites across the region. The main mode of variability across Holocene δ18O records (PC1) closely tracks austral summertime insolation, consistent with existing work. Sites towards the periphery of the continent are heavily weighted on PC1, whereas interior sites as not. Further δ18O variability at interior sites bear little similarity to each other and implicate controls, beyond regional monsoon intensity, on these δ18O records. Further, we develop speleothem 87Sr/86Sr records spanning the Holocene from Tamboril Cave (Brazilian Highlands), Paraíso Cave (eastern Amazon Basin), Jaraguá Cave (Mato Grosso do Sul Plateau), and Botuverá Cave (Atlantic coastal plain) to investigate coupling between reconstructed monsoon variability (reflected by PC1) and local moisture conditions (interpreted from 87Sr/86Sr records). We interpret speleothem 87Sr/86Sr variability as a proxy of local moisture conditions, reflecting the degree of water-rock interaction with the cave host rock as driven by variations in water residence time. Speleothem 87Sr/86Sr records from all the sites, except Botuverá cave, do not co-vary with PC1, suggesting that local moisture conditions do not necessarily follow variations in regional monsoon intensity at these interior sites. These speleothem 87Sr/86Sr records generally suggest dry mid-Holocene conditions relative to the early- and late-Holocene, consistent with interpretations of other paleo-moisture records in the region, but timing of wet-dry transitions varies between sites. These results highlight that controls, in addition to SAMS variability, might influence δ18O variability. Further, our results suggest spatially variable local moisture conditions at interior sites that do not uniformly respond to regional monsoon intensity, and stress the need for δ18O-independent reconstructions of moisture conditions.

Residence Time Controls on the Fate of Nitrogen in Flow‐Through Lakebed Sediments

AbstractFor many glacial lakes with highly permeable sediments, water exchange rates control hydrologic residence times within the sediment‐water interface (SWI) and the removal of reactive compounds such as nitrate, a common pollutant in lakes and groundwater. Here we conducted a series of focused tracer injection experiments in the upper 20 cm of the naturally downwelling SWI in a flow‐through lake on Cape Cod, MA. We systematically varied residence time and reactant controls on nitrate processing, using isotopically labeled 15N nitrate to monitor the effect of these changes on nitrate removal via denitrification. The addition of acetate, a labile carbon compound, triggered the lake SWI to switch from net production to net removal of nitrate. When acetate was combined with increased residence time created by controlled reductions in water flux, we observed a fivefold increase in nitrate removal, a 26‐fold increase in N2 production, and a 42‐fold increase in N2O production. We demonstrate that water residence time is an important control on the fate of nitrate in these lake SWIs and illustrate that seasonal conditions that alter lake exchange rates and variability in lake carbon may predict dynamic nitrate removal across the SWI. Additionally, observed N2O production during the oxic pore water experiments paired with geophysical characterization of the sediment porosity revealed that the lake SWI has less mobile pores occupying upward of 50% of the total porosity volume, which function as reactive microzones for nitrate processing.

Catalytic hydrothermal deoxygenation of the lipid fraction of activated sludge

The need for sustainable wastewater treatment and search for cheap feedstock for renewable energy production have driven investigators to evaluate the potential of producing biofuels from waste materials such as sewage sludge. The current work is aimed at assessing the potential for producing hydrocarbons from the lipid fraction of activated sludge via a catalytic hydrothermal decarboxylation reaction under varying residence time. Impacts of platinum on carbon (Pt/C) and palladium on carbon (Pd/C) catalysts were evaluated at 290 °C and residence time of 0.5, 1, 3 and 4 h. The analyses of the lipids and hydrocarbons were done using high-temperature gas chromatography. The results show that at the optimum conditions of 1 h, 290 °C, 20 mg of catalyst, 100 mg of lipid extract and 15 mL of water, the maximum yield of hydrocarbon was 23.2% of pentadecane obtained using Pt/C. This shows that the dominant hydrocarbon is pentadecane and that Pt/C exhibited greater catalytic effect than did Pd/C. The hydrocarbons might be used directly as renewable diesel and as such will contribute to the mitigation of climate change since emission of greenhouse gases will be reduced, and the use of activated sludge as the feedstock is expected to help minimize the cost of production and to ensure sustainable wastewater treatment.

Dynamic Hyporheic Zones: Exploring the Role of Peak Flow Events on Bedform‐Induced Hyporheic Exchange

AbstractDischarge varies in space and time, driving hyporheic exchange processes in river corridors that affect biogeochemical cycling and ultimately control the dynamics of biogeochemical hot spots and hot moments. Herein, we use a reduced‐order model to conduct the systematic analysis of the interplay between discharge variability (peak flow intensities, duration, and skewness) and streambed topography (bedform aspect ratios and channel slopes) and their role in the flow and transport characteristics of hyporheic zones (HZs). We use a simple and robust conceptualization of single peak flow events for a series of periodic sinusoidal bedforms. Using the model, we estimate the spatial extent of the HZ, the total amount of exchange, and the residence time of water and solutes within the reactive environment and its duration relative to typical time scales for oxygen consumption (i.e., a measure of the denitrification potential). Our results demonstrate that HZ expansion and contraction is controlled by events yet modulated by ambient groundwater flow. Even though the change in hyporheic exchange flux (%) relative to baseflow conditions is invariant for different values of channel slopes, absolute magnitudes varied substantially. Primarily, peak flow events cause more discharge of older water for the higher aspect ratios (i.e., for dunes and ripples) and lower channel slopes. Variations in residence times during peak flow events lead to the development of larger areas of potential nitrification and denitrification in the HZ for longer durations. These findings have potential implications for river management and restoration, particularly the need for (re)consideration of the importance of hyporheic exchange under dynamic flow conditions.