Steady-state Mass Balance Model Research Articles

Predictions of Serum Phosphate Concentration during Continuous Renal Replacement Therapy Using a Steady-State Mass Balance Model

Introduction: Hypophosphatemia is common during continuous renal replacement therapy (CRRT), but serum phosphate levels can potentially be maintained during treatment by either intravenous phosphate supplementation or addition of phosphate to renal replacement therapy (RRT) solutions. Methods: We developed a steady-state phosphate mass balance model to assess the effects of CRRT dose on serum phosphate concentration when using both phosphate-free and phosphate-containing RRT solutions, with emphasis on low CRRT doses. Results: The model predicted that measurements of serum phosphate concentration prior to (initial) and during CRRT (final) together with clinical data on CRRT dose, treatment duration, and phosphate supplementation can determine model patient parameters, that is, both the initial generation rate and clearance of phosphate prior to CRRT. Model parameters were then calculated from average patient data reported in several previous publications with a standard or high CRRT dose. Using representative model parameters for typical patients, predictions were then made of the effect of low CRRT dose on the change in serum phosphate levels after implementation of CRRT. The model predicted that CRRT at a low dose using phosphate-free RRT solutions will limit, but not eliminate, the incidence of hypophosphatemia. Further, the model predicted that CRRT at a low dose will have virtually no influence on the incidence of hyperphosphatemia when using phosphate-containing RRT solutions. Conclusions: This report identifies the clinical measurements to be used with the proposed model for individualizing the CRRT dose and RRT phosphate concentration to maintain serum phosphate concentrations in a desired range.

Persistent Ascaris Transmission Is Possible in Urban Areas Even Where Sanitation Coverage Is High.

In low-income, urban, informal communities lacking sewerage and solid waste services, onsite sanitation (sludges, aqueous effluent) and child feces are potential sources of human fecal contamination in living environments. Working in informal communities of urban Maputo, Mozambique, we developed a quantitative, stochastic, mass-balance approach to evaluate plausible scenarios of localized contamination that could explain why the soil-transmitted helminth Ascaris remains endemic despite nearly universal coverage of latrines that sequester most fecal wastes. We used microscopy to enumerate presumptively viable Ascaris ova in feces, fecal sludges, and soils from compounds (i.e., household clusters) and then constructed a steady-state mass-balance model to evaluate possible contamination scenarios capable of explaining observed ova counts in soils. Observed Ascaris counts (mean = -0.01 log10 ova per wet gram of soil, sd = 0.71 log10) could be explained by deposits of 1.9 grams per day (10th percentile 0.04 grams, 90th percentile 84 grams) of child feces on average, rare fecal sludge contamination events that transport 17 kg every three years (10th percentile 1.0 kg, 90th percentile 260 kg), or a daily discharge of 2.7 kg aqueous effluent from an onsite system (10th percentile 0.09 kg, 90th percentile 82 kg). Results suggest that even limited intermittent flows of fecal wastes in this setting can result in a steady-state density of Ascaris ova in soils capable of sustaining transmission, given the high prevalence of Ascaris shedding by children (prevalence = 25%; mean = 3.7 log10 per wet gram, sd = 1.1 log10), the high Ascaris ova counts in fecal sludges (prevalence = 88%; mean = 1.8 log10 per wet gram, sd = 0.95 log10), and the extended persistence and viability of Ascaris ova in soils. Even near-universal coverage of onsite sanitation may allow for sustained transmission of Ascaris under these conditions.

Isotope-based water balance assessment of open water wetlands across Alberta: Regional trends with emphasis on the oil sands region

Study regionWater sampling for stable isotopes (18O and 2H) was carried out during 2009–2019 across Alberta, Canada, as part of a survey targeting 1022 open water wetlands. The study presents the first site-specific wetland water balance assessment spanning Grassland, Parkland, Foothills, Mountains, and Boreal regions, including the oil sands region, a corridor of rapid development. Study focusClimate reanalysis, watershed data, and isotopic data for wetlands were incorporated into a steady-state isotope mass balance model, and applied to estimate site-specific evaporation losses from the wetlands, as well as runoff, groundwater inflow, total outflow, and seasonal drawdown. Regional-scale water balance fluxes, water balance indicators and site-specific classifications were mapped and described. New hydrological insights for the regionSystematic variations in evaporation losses, watershed runoff to wetlands, wetland discharge, and net groundwater inflow are revealed across the major subregions of Alberta including the oil sands region. Isotope balance calculations suggest that 13% of wetlands are predominantly evaporative, 87% have surface and/or groundwater outflow, 90% have positive water yields, 47% likely have groundwater inflow, and 2% are apparently fed by allochthonous water sources (either snow or glacial melt). For the 3 oil sands regions, a scoping survey suggests that between 20% and 40% of wetlands within the bitumen zones are detectably groundwater reliant compared to 35–50% in the wider vicinity of the deposits.

Radiation exposure due to 222Rn, 220Rn and their progenies in three metropolises in China and Japan with different air quality levels

Radiation exposure due to radon contributes most of the ionizing radiation exposure to people among natural radiation sources. This research measured the 222Rn, 220Rn by the RADUET and their progeny concentrations by the improved deposition based 222Rn and 220Rn progeny monitor, and the contribution of outdoor PM2.5 concentrations to indoors by a modified steady-state mass balance model in Beijing, Changchun, China and Aomori, Japan. Based on these results, we preliminarily explored the relevance between the city level outdoor PM2.5 exposure and indoor 222Rn, 220Rn inhalation exposure in these three metropolises with different air quality levels. The average equilibrium equivalent radon concentration (EERC) and equilibirum equivalent thoron concentration (EETC) indoor were 17.2 and 1.1 Bq m−3 in Beijing, 19.4 and 1.3 Bq m−3 in Changchun, and 10.8 and 0.9 Bq m−3 in Aomori, respectively. The indoor EERC and EETC in Beijing showed 1.4 and 2.2 times as high as that measured in 2006. The indoor radiation dose due to inhalation presented in a descending order as Changchun, Beijing and Aomori, which were in accordance with their outdoor 222Rn concentrations. The indoor radiation doses due to 220Rn contributed 30% of the total dose in the three cities, indicating that 220Rn cannot be neglected when evaluating indoor radiation dose. It should be noted that, the indoor PM2.5 concentrations of outdoor origin presented strong correlation (r = 0.772) with indoor EETC and moderate correlation (r = 0.663) with indoor EERC, indicating that the PM2.5 of outdoor origin can break the concentration balance of the indoor PM2.5, then affect the indoor 222Rn and 220Rn behaviors, and further affect the inhalation exposure of radon.

Application of phosphorus loading models to understand drivers of eutrophication in a complex rural lake-watershed system

Several lakes in southwestern Nova Scotia, Canada have experienced reoccurring algal blooms and possess concentrations of phosphorus (P) that are in the eutrophic to hypereutrophic range (>35 μg/L). In this study a mass balance modeling approach was used to evaluate the relative contribution of P sources within these watersheds and lakes. Primary sources of P included land runoff, septic systems, agricultural activities including mink fur farming, aquaculture, as well as internal loading. These sources were assessed for three different study years (1983, 2008, and 2017), based on availability of water quality data, and to quantify the relative impact of the mink farming industry as it rapidly expanded during this time period. A novel method to estimate P loads from intensive fur farming operations was developed, using agricultural census, remote sensing, and publicly available spatial data. A suite of simulations were generated, using a steady state mass balance model, to examine lake P concentrations and sources for baseline conditions (no anthropogenic sources), no mink farming, and varying levels of P retention on mink farms (25%, 50%, 75%) scenarios. An additional scenario was also constructed which involved calibrating mink farm P retention coefficients using available water quality data. In the baseline scenario it was predicted that all study lakes would be oligotrophic, indicating that cultural eutrophication of these lakes has occurred. In the no mink farming scenario, it was predicted that all study lakes would be oligotrophic except for Hourglass Lake, which was predicted to be mesotrophic due to inputs from an aquaculture facility. Internal loading of P from lake sediments was also identified as an important potential P loading mechanism, which will likely be exacerbated by climate change. These findings indicate that the P from mink farms is the primary driver of cultural eutrophication in the study lakes, and highlights the need to consider these nutrient sources within watershed management plans. It is recommended that lake remediation efforts continue to focus on reducing P inputs from mink farms, and on controlling P loading from any new anthropogenic development in these watersheds.

Stable isotopes of deep soil water retain long-term evaporation loss on China's Loess Plateau

Evaporation from the land surface enriches heavy isotope ratios (2H/1H and 18O/16 O) in shallow soils, and downward water movement will carry the fractionation signal to deep soils. However, how to acquire the evaporation from water stable isotopes in deep soils remains untested. Here, we measured water stable isotope composition in the deep soils (2–10 m) across 20 sites on China's Loess Plateau. Our results show that the line-conditioned excess (lc-excess) in deep soils of these sites was invariable with depth at each site, but ranged between −14.0‰ and − 4.1‰ among these sites, indicating differing degree of enrichment in heavy water isotopes between sites. Moreover, the mean lc-excess in deep soils water was significantly correlated to mean annual precipitation (R2 = 0.57), potential evapotranspiration (R2 = 0.25), and the Budyko dryness (R2 = 0.68), indicating that deep soil water lc-excess reflects land surface climate conditions. Furthermore, the deep soils correspond to a timescale of approximately 100 years at one site and more than 27 years at the remaining sites. These results together indicate that stable isotopes of deep soil water retained long-term land surface evaporation effects. Further, by implementing the steady-state isotope mass balance model into the lc-excess framework, we derived a new method to estimate evaporation loss fraction (f). Our f estimates at these sites varied between 5% and 15%, which may represent the lower bound of the actual evaporation to precipitation ratio. Nevertheless, our work suggests that in these and the other similar regions, deep soil is a novel archive for long-term soil evaporation loss, and f may be estimated through a snapshot field campaign of stable isotope measurements.

A comparison of radon, heat tracer and head gradient methods to quantify surface water - groundwater exchange in a tidal wetland (Kooragang Island, Newcastle, Australia)

Subsurface flow plays an important role in the functioning of wetlands and in the maintenance of their ecosystem services. Specifically, the transport and exchange of dissolved matter between sediments and surface waters is regulated by subsurface flow, which can strongly affect ecological zonation and productivity. Having a quantitative understanding of this subsurface flow is therefore important. Field techniques based on Darcy’s equation or natural tracers are often used separately to assess flows. Here, radon and heat (both natural groundwater tracers) and Darcy’s equation are used simultaneously to quantify the subsurface flow in a tidal wetland (Kooragang Island, Newcastle, Australia) and the results of the independent methods are compared. A steady-state radon mass balance model indicated an overall net subsurface exfiltration of 10.2 ± 4.2 cm/d while a 1D, vertical fluid heat transport model indicated a net exfiltration of 4.3 ± 2.9 cm/d. Flow estimated from analysis of hydraulic heads indicated an exfiltration rate of 3.2 ± 1.8 cm/d. The difference in flow rates is likely due to the localised measurement of the heat and head methods relative to radon, and therefore, these methods are less likely to capture zones of preferential subsurface flow. The main advantage of radon is that it provides the total subsurface flow regardless of the driving force. While head gradient or heat tracer method have the advantage of temporally quantify infiltration and exfiltration, we highlight that these methods may underestimate subsurface flows in highly dynamic coastal systems, such as tidal wetlands where a large portion of the subsurface flow is recirculated seawater. This could potentially lead to errors in solute flux estimates. This study highlights the importance of employing a multi-tracer approach and has implications towards quantifying the hydrological export of dissolved constituents (e.g., carbon and nitrogen) in coastal wetlands.

Impacts of implementing Healthy Building guidelines for daily PM2.5 limit on premature deaths and economic losses in urban China: A population-based modeling study

Given a large fraction of people’s exposure to urban PM2.5 occur indoors, reducing indoor PM2.5 levels may offer a more feasible and immediate way to save substantial lives and economic losses attributable to PM2.5 exposure. We aimed to estimate the premature mortality and economic loss reductions associated with achieving the newly established Chinese indoor air guideline and a few hypothetical indoor PM2.5 guideline values. We used outdoor PM2.5 concentrations from 1497 monitoring sites in 339 Chinese cities in 2015, coupled with a steady-state mass balance model, to estimate indoor concentrations of outdoor-infiltrated PM2.5. Using province-specific time-activity patterns for urban residents, we estimated outdoor and indoor exposures to PM2.5 of outdoor origin. We then proceeded to use localized census-based concentration-response models and the value of statistical life estimates to calculate premature deaths and economic losses attributable to PM2.5 exposure across urban China. Finally, we estimated potentially avoidable mortality and corresponding economic losses by meeting the current 24-hour based guideline and various hypothetical indoor limits for PM2.5. In 2015 in urban areas of mainland China, the city-specific annual mean outdoor and indoor PM2.5 concentrations ranged 9–108 μg/m3 and 5–56 μg/m3, respectively. Indoor exposures contributed 62%–91% daily and 68%–83% annually to the total time-weighted exposures. The potential reductions in total deaths and economic losses for the scenario in which daily indoor concentrations met the current guideline of 75 μg/m3, 37.5 μg/m3, and 25 μg/m3 were 16.9 (95% CI: 0.7–62.1) thousand, 87.7 (95% CI: 9.7–197.7) thousand, and 165.5 (95% CI: 30.8–304.0) thousand, respectively. The corresponding reductions in economic losses were 5.7 (95% CI: 0.2–34.8) billion, 29.4 (95% CI: 2.4–109.6) billion, and 55.2 (95% CI: 7.7–168.0) billion US Dollars, respectively. Deaths and economic losses would be reduced exponentially within the range of 0–75 μg/m3 for hypothetical indoor PM2.5 limits. The findings demonstrate the effectiveness of reducing indoor concentrations of outdoor-originated PM2.5 in saving substantial lives and economic losses in China. The analysis provides quantitative evidence to support the implementation of an indoor air quality guideline or standard for PM2.5.

Steady-State Mass Balance Model for Predicting Particle-Gas Concentration Ratios of PBDEs.

Assuming equilibrium partitioning between the gas and particle phases has been shown to overestimate the fraction of low-volatility chemicals in the particle phase. Here, we present a new steady-state mass balance model that includes separate compartments for fine and coarse aerosols and the gas phase and study its sensitivity to the input parameters. We apply the new model to investigate deviations from equilibrium partitioning by exploring model scenarios for seven generic aerosol scenarios representing different environments and different distributions of emissions as the gas phase, fine aerosol, and coarse aerosol. With 100% of emissions as the particle phase, the particle–gas concentration ratio in our model is similar to the equilibrium model, while differences are up to a factor of 106 with 100% of emissions as the gas phase. The particle–gas concentration ratios also depend on the particle size distributions and aerosol loadings in the different environmental scenarios. The new mass balance model can predict the particle–gas concentration ratio with more fidelity to measurements than equilibrium models. However, further laboratory-based evaluations and calibrations of the standard sampling techniques, field investigations with preferably size-resolved measurements of aerosol particle composition, together with the appropriate process modeling for low-volatility chemicals are warranted.

Hydrogeological controls on heterogeneous groundwater discharge to a large glacial lake

Lacustrine groundwater discharge (LGD) can be an important pathway for delivering pollutants to large lakes but this pathway is often neglected. This is in part because characterizing the magnitude and spatial variability of LGD to large lakes is highly resource intensive. To better target efforts, particularly in glacial environments where the hydrogeology is often highly complex, there is a need to understand linkages between spatial LGD patterns and hydrogeological features. The objective of this study was to evaluate the magnitude and spatial variability of nearshore LGD to Lake Simcoe (area = 722 km2) and use this information to explore hydrogeological controls on the observed spatial LGD patterns. LGD was quantified by applying a steady state mass balance model to radon-222 (222Rn) data obtained from boat surveys conducted along ~80% of the lake’s shoreline. Overall, LGD was highly spatially variable with total LGD to Lake Simcoe estimated to range from 7 ± 1% to 16 ± 2%, respectively, of the total volume of tributary inputs during summer. No large regional scale differences in LGD were found despite the diverse hydrogeological conditions around the lake. Rather, discrete shoreline areas with high LGD were observed around the lake. Areas with high LGD were related to permeable nearshore surficial sediments and tunnel channel aquifers which provide connectivity between large recharge features (moraines), regional aquifer units, and the lake. The study findings are needed to inform actions aimed at managing non-point pollution sources to large glacial lakes including LGD.

Triple oxygen isotope signatures of evaporation in lake waters and carbonates: A case study from the western United States

Evaporation can increase the δ18O values of lake waters and carbonates by several per mil. If not accounted for in geological studies, this can lead to substantial misinterpretation of δ18O values in terms of paleoclimate and paleoelevation. Evaporation also leads to a lowering in residual waters of Δ17O, a measure of the departure of δ′17O from a characteristic relationship with δ′18O. We present new triple oxygen isotope data from waters and carbonates from lakes and their source rivers in the western United States (Bear Lake, Great Salt Lake, Lake Tahoe, Mono Lake, and Pyramid Lake). Consistent with predictions from steady-state isotopic mass balance models, the data illustrate marked lowering of Δ17O in closed basin lakes and freshwater lakes relative to their source rivers. The evaporation slope in triple oxygen isotope space (λlake) is similar for these lakes, averaging 0.5229 and ranging between 0.5219 and 0.5239. Moreover, models and data both show that the evaporation slope correlates with Δ17O, meaning that the slope can be estimated on the basis of the measured Δ17O value of the carbonate. We show how triple oxygen isotopes in lake waters and carbonates and ‘clumped isotopes’ (Δ47) in carbonates can be combined to reconstruct the δ18O values of primary (unevaporated) catchment precipitation (δ18Orucp). We use our lacustrine carbonate data as a test case for this approach, and find that δ18Orucp values closely approximate independently-measured δ18O values of catchment precipitation. However, the δ18Orucp values are consistently higher than δ18O of catchment precipitation by ∼2‰, which may reflect present incomplete understanding of a number of triple oxygen isotope parameters used in the calculation, such as the fractionation exponent for carbonate-water equilibrium, the evaporation slope λlake, and the Δ17O values of unevaporated meteoric waters. In conclusion, triple oxygen isotope analysis of lake waters and lacustrine carbonates is a promising new method for studying evaporation in fossil lake systems, but will benefit from additional research into triple oxygen isotope systematics relevant to meteoric waters, lake systems, and carbonate–water fractionation.

A Mass Balance Model to Assess Food Limitation in Commercial Oyster Nurseries

This work aims to provide oyster farmers a tool to estimate the stock biomass to hold in their nursery. Herein, a steady-state single-compartment mass balance model, which includes the feeding activity of oyster spat, was developed. This model applies to nurseries such as floating upweller systems or land-based tanks and estimates (1) the optimal stock as a function of external food concentration or (2) the food concentration required for a given stock. The model was implemented for the Pacific oyster (Crassostrea gigas Thunberg) and is available online: http//seaplusplus4.com/oysterspatbud.html. The model was evaluated using published data and further tested by simulating a general rule of thumb regarding the spat-holding capacity for a given nursery. According to a general rule of thumb, 1 hectare of a shallow pond can hold between 1 and 3 tons of spat. The model allows to further specify the rule depending on the spat grade to stock. If the spat is around 0.38 g, the model estimates a holding stock within the range of the rule of thumb; however, if the spat is around 0.04 g, the biomass stock sustained is lower (between 0.7 and 2 tons).

Potential Exposure and Cancer Risk from Formaldehyde Emissions from Installed Chinese Manufactured Laminate Flooring.

Lumber Liquidators (LL) Chinese-manufactured laminate flooring (CLF) has been installed in >400,000 U.S. homes over the last decade. To characterize potential associated formaldehyde exposures and cancer risks, chamber emissions data were collected from 399 new LL CLF, and from LL CLF installed in 899 homes in which measured aggregate indoor formaldehyde concentrations exceeded 100μg/m3 from a total of 17,867 homes screened. Data from both sources were combined to characterize LL CLF flooring-associated formaldehyde emissions from new boards and installed boards. New flooring had an average (±SD) emission rate of 61.3 ±52.1μg/m2 -hour; >one-year installed boards had ∼threefold lower emission rates. Estimated emission rates for the 899 homes and corresponding data from questionnaires were used as inputs to a single-compartment, steady-state mass-balance model to estimate corresponding residence-specific TWA formaldehyde concentrations and potential resident exposures. Only ∼0.7% of those homes had estimated acute formaldehyde concentrations >100μg/m3 immediately after LL CLF installation. The TWA daily formaldehyde inhalation exposure within the 899homes was estimated to be 17μg/day using California Proposition 65 default methods to extrapolate cancer risk (below the regulation "no significant risk level" of 40μg/day). Using a U.S. Environmental Protection Agency linear cancer risk model, 50th and 95th percentile values of expected lifetime cancer risk for residents of these homes were estimated to be 0.33 and 1.2 per 100,000 exposed, respectively. Based on more recent data and verified nonlinear cancer risk assessment models, LL CLF formaldehyde emissions pose virtually no cancer risk to affected consumers.

Issue Highlights

The Canadian Journal of Chemical EngineeringVolume 95, Issue 6 p. 1022-1022 Issue HighlightsFree Access Issue Highlights First published: 21 April 2017 https://doi.org/10.1002/cjce.22849AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat 1023 Benchmarking the Timmins Process - A Novel Approach for Low Energy Pre-Combustion Carbon Capture in IGCC Flowsheets Bart Hallmark, Julian Parra-Garrido, Andrew Murdoch, Ian Salmon and Chris Hodrien The Timmins Process is a novel pre-combustion carbon capture process that combines industrially-tested unit operations in a novel and unique configuration, with the aim of providing high levels of carbon capture with minimal energy penalty. This paper reports an initial benchmarking study of this process in the context of an IGCC flowsheet, and concludes that the net efficiency of the plant incorporating the Timmins Process varies between 33.8 % and 34.3 % at a carbon capture level of 91.8 % (on a mass basis) depending on the process configuration and the cooling water temperature.1 1093 A Soft Sensor for the Sulphur Dioxide Converter in an Industrial Smelter Jianjun He, Junfeng Zhang and Helen Shang A catalytic reactor that converts sulphur dioxide to sulphur trioxide is a key operation in a sulphuric acid plant. The sulphur dioxide conversion ratio represents an important performance indicator for a sulphur dioxide converter. In this paper, a soft sensor is developed for the sulphur dioxide conversion ratio and outlet concentration. The soft sensor is built based on the steady state mass balance model of the converter and industrial dynamic data analysis. It provides a real-time estimate of the unmeasured variables from available industrial real-time measurement.2 1171 Modelling of Dynamic Mass Transfer in a Vapour Extraction Heavy Oil Recovery Process Qiong Wang, Xinfeng Jia and Zhangxin Chen This study presents a new method to determine the effective diffusivity between a vaporized solvent and a crude heavy oil in a vapour extraction heavy oil recovery process. It is found that both constant and variable diffusivities can achieve a satisfactory match in cumulative oil production data, but the latter gives more accurate characterization of transition zone properties. Some correlations are also regressed to convert a constant diffusivity to an equivalent variable diffusivity. Moreover, back-calculated constant effective diffusivity is found to be about 10–30 times of the corresponding molecular diffusivity measured in the laboratory.3 References 1 B. Hallmark, J. Parra-Garrido, A. Murdoch, I. Salmon, C. Hodrien, Can. J. Chem. Eng. 2017, 95, 1023. 2 J. He, J. Zhang, H. Shang, Can. J. Chem. Eng. 2017, 95, 1093. 3 Q. Wang, X. Jia, Z. Chen, Can. J. Chem. Eng. 2017, 95, 1171. Volume95, Issue6June 2017Pages 1022-1022 ReferencesRelatedInformation

A soft sensor for the sulphur dioxide converter in an industrial smelter

In metal productions from sulphide ores, sulphur dioxide (SO2) is generated when the ore concentrate is smelted. To minimize emission of SO2 to the atmosphere, sulphuric acid plants are used to convert SO2 gas into sulphuric acid product in smelters. A SO2 to sulphur dioxide (SO3) converter, where SO2 is oxidized to SO3 with the help of catalyst, is the key unit in a sulphuric acid plant. For monitoring the converter, temperature of the reactor is extensively measured at various locations, but the concentration of SO2 is barely measured or only measured at very limited points due to the difficulty and costs involved. In this paper, a soft sensor is developed to estimate the conversion ratio and concentration of SO2. The soft sensor is derived based on the steady state mass balance model of the converter and dynamic data analysis. From the proposed soft sensor, conversion ratio and concentration of SO2 can be estimated from available industrial real‐time measurement.

Assessment of the maximum allowed acid deposition load at current stage in China

Soil acidification caused by acid deposition has been significant in some forests in southern China. We present an approach for assessing the current stage maximum allowed load (SML) of acid deposition for terrestrial system in the country. The main idea was that soil base cation exchange as a finite buffer to acidity was included in the soil acidity mass balance calculation at current acidification stage. We calculated the SML for five forests in southern China. The usual critical loads for the same forests were also calculated by the steady state mass balance model for comparison. The results showed that the SML is a more tolerant limit than the critical load for the forests with soils not acidified seriously at current stage. However, the SML become a more stringent limit to acid deposition when the forest soils have acidified seriously to very low base cation saturation. In this case the SML assessment is beneficial for the soils recovering from a serious acidified state. Based on a national scale database, the SML mapping for non-agricultural soil system in China was carried out.

Temporal 222Rn distributions to reveal groundwater discharge into desert lakes: Implication of water balance in the Badain Jaran Desert, China

Summary How lake systems are maintained and water is balanced in the lake areas in the Badain Jaran Desert (BJD), northeast of China have been debated for about a decade. In this study, continuous 222Rn measurement is used to quantify groundwater discharge into two representative fresh and brine water lakes in the desert using a steady-state mass-balance model. Two empirical equations are used to calculate atmospheric evasion loss crossing the water–air interface of the lakes. Groundwater discharge rates yielded from the radon mass balance model based on the two empirical equations are well correlated and of almost the same values, confirming the validity of the model. The fresh water and brine lakes have a daily averaged groundwater discharge rate of 7.6 ± 1.7 mm d−1 and 6.4 ± 1.8 mm d−1, respectively. The temporal fluctuations of groundwater discharge show similar patterns to those of the lake water level, suggesting that the lakes are recharged from nearby groundwater. Assuming that all the lakes have the same discharge rate as the two studied lakes, total groundwater discharge into all the lakes in the desert is estimated to be 1.59 × 105 m3 d−1. A conceptual model of water balance within a desert lake catchment is proposed to characterize water behaviors within the catchment. This study sheds lights on the water balance in the BJD and is of significance in sustainable regional water resource utilization in such an ecologically fragile area.

Metabolic Flux Distribution during Defatting of Steatotic Human Hepatoma (HepG2) Cells.

Methods that rapidly decrease fat in steatotic hepatocytes may be helpful to recover severely fatty livers for transplantation. Defatting kinetics are highly dependent upon the extracellular medium composition; however, the pathways involved are poorly understood. Steatosis was induced in human hepatoma cells (HepG2) by exposure to high levels of free fatty acids, followed by defatting using plain medium containing no fatty acids, or medium supplemented with a cocktail of defatting agents previously described before. We measured the levels of 28 extracellular metabolites and intracellular triglyceride, and fed the data into a steady-state mass balance model to estimate strictly intracellular fluxes. We found that during defatting, triglyceride content decreased, while beta-oxidation, the tricarboxylic acid cycle, and the urea cycle increased. These fluxes were augmented by defatting agents, and even more so by hyperoxic conditions. In all defatting conditions, the rate of extracellular glucose uptake/release was very small compared to the internal supply from glycogenolysis, and glycolysis remained highly active. Thus, in steatotic HepG2 cells, glycolysis and fatty acid oxidation may co-exist. Together, these pathways generate reducing equivalents that are supplied to mitochondrial oxidative phosphorylation.

Surface exposure chronology of the Waimakariri glacial sequence in the Southern Alps of New Zealand: Implications for MIS-2 ice extent and LGM glacial mass balance

During the late Quaternary, the Southern Alps of New Zealand experienced multiple episodes of glaciation with large piedmont glaciers reaching the coastal plains in the west and expanding into the eastern alpine forelands. Here, we present a new 10Be exposure age chronology for a moraine sequence in the Waimakariri Valley (N-Canterbury), which has long been used as a reference record for correlating glacial events across New Zealand and the wider Southern Hemisphere. Our data indicate that the Waimakariri glacier reached its maximum last glaciation extent prior to ∼26 ka well before the global last glaciation maximum (LGM). This was followed by a gradual reduction in ice volume and the abandonment of the innermost LGM moraines at about 17.5 ka. Significantly, we find that during its maximum extent, the Waimakariri glacier overflowed the Avoca Plateau, previously believed to represent a mid-Pleistocene glacial surface (i.e. MIS 8). At the same time, the glacier extended to a position downstream of the Waimakariri Gorge, some 15 km beyond the previously mapped LGM ice limit. We use a simple steady-state mass balance model to test the sensitivity of past glacial accumulation to various climatic parameters, and to evaluate possible climate scenarios capable of generating the ice volume required to reach the full local-LGM extent. Model outcomes indicate that under New Zealand's oceanic setting, a cooling of 5 °C, assuming modern precipitation levels, or a cooling of 6.5 °C, assuming a one third reduction in precipitation, would suffice to drive the Waimakariri glacier to the eastern alpine forelands (Canterbury Plains). Our findings demonstrate that the scale of LGM glaciation in the Waimakariri Valley and adjacent major catchments, both in terms of ice volume and downvalley ice extent, has been significantly underestimated. Our observation that high-lying glacial surfaces, so far believed to represent much older glacial episodes, were glaciated during the LGM, challenges the conventional geomorphic model of glaciation in New Zealand where the vertical arrangement of glacial landform-associations is used to assign successively older glaciation ages.

Assessment of the removal of estrogenicity in biological nutrient removal wastewater treatment processes

The removal of estrogenicity in a University of Cape Town-biological nutrient removal (UCT-BNR) wastewater treatment process was investigated using pilot and bench scale systems, batch experiments and mathematical modeling. In the pilot BNR process, 96±5% of the estrogenicity exerted by the influent wastewater was removed by the treatment process. The degradation efficiencies in the anaerobic, anoxic and aerobic zones of the pilot BNR bioreactor were 11±9%, 18±2% and 93±10%, respectively. In order to further understand the performance of the BNR process in the removal of estrogenicity from wastewater, a bench scale BNR process was operated with synthetic wastewater dosed with E1 and E2. The removal of estrogenicity in the bench scale system (95±5%) was comparable to the pilot BNR process and the degradation efficiencies were estimated to be 8±0.8%, 38±4% and 85±22% in the anaerobic, anoxic and aerobic zones, respectively. A biotransformation model developed to predict the fate of E1 and E2 in batch tests using the sludge from the BNR process was calibrated using the data from the experiments. The biotransformation rate constants for the transformation of E2 to E1 were estimated as 71±1.5, 31±3.3 and 1±0.9LgCOD−1d−1 for the aerobic, anoxic and anaerobic batch tests, respectively, while the corresponding biotransformation rate constants for the transformation of E1 were estimated to be 7.3±1.0, 3±2.0, and 0.85±0.6L·gCOD−1d−1. A steady state mass balance model formulated to describe the interactions between E2 and E1 in BNR activated sludge reasonably described the fate of E1 and E2 in the BNR process.