Periods Of High Load Research Articles

Improving the efficiency of a direct ethanol fuel cell by a periodic load change

We present a simple method to increase the efficiency of a direct ethanol fuel cell by a periodic modulation of the load (pulsed mode). The fuel cell was periodically short circuited with a resistor (1 Ω) for a few seconds (high load period) followed by a low load period of up to 100 s when the resistor was disconnected. The open circuit voltage (OCV) values before and after the short circuit of the cell showed an increase of up to 70 mV. The higher OCV was due to the oxidation and removal of strongly adsorbed CO during the electric short circuit when the electric potential of the anode was increased to be close to the cathode potential. The depoisoned anode surface was much more active directly after the short circuit. The slow decrease of the OCV observed after the short circuit was caused by the subsequent poisoning of the anode surface, which can be neutralized by another short circuit. In general, a stable increase in cell performance was obtained by repetition of the electric short circuit. The data showed that the pulse mode gave an increase in the power generated by the direct ethanol fuel cell by up to 51% and was 6% on average. It is anticipated that this mode of operation can be used also in different types of polymer electrolyte membrane fuel cells where CO poisoning is a problem, and after optimization of the parameters, a much higher gain in efficiency can be obtained.

Design optimization of a polygeneration plant producing power, heat, and lignocellulosic ethanol

A promising way to increase the energy efficiency and reduce costs of biofuel production is to integrate it with heat and power production in polygeneration plants. This study treats the retrofitting of a Danish combined heat and power plant by integrating lignocellulosic ethanol production based on wheat straw with the aim of minimizing specific ethanol production cost. Previously developed and validated models of the facilities are applied in the attempt to solve the design optimization problem. Straw processing capacities in the range of 5–12kg/s are considered, while plant operation is optimized over the year with respect to maximal income and with the limitations that the reference hourly district heating production has to be met while reference hourly power export cannot be exceeded.The results suggest that the specific ethanol production cost increased continuously from 0.958Euro/L at a straw processing capacity of 5kg/s to 1.113Euro/L at a capacity of 12kg/s, indicating that diseconomies-of-scale applies for the suggested ethanol production scheme. A thermodynamic evaluation further discloses that the average yearly exergy efficiency decreases continuously with increasing ethanol production capacity, ranging from 0.746 for 5kg/s to 0.696 for 12kg/s. This trend results from operating constraints that induce expensive operation patterns in periods of high district heating loads or shut-down periods for the combined heat and power plant. A sensitivity analysis indicates that the found optimum is indifferent to major variations in fossil fuel prices. The results question the efficiency of the suggested retrofitting scheme in the present energy system, and they further point toward the importance of taking operating conditions into consideration when developing flexible polygeneration plant concepts as differences between design-point operation and actual operation may have a significant impact on overall plant performance.

Characteristic Analysis of the Electricity Price Fluctuation: An Empirical Analysis Based on California’s Day-Ahead Market

The paper deals with the Day-ahead Market of California between Apr. 1st, 1998 and Jan. 31, 2001 and divided each day to high-load period and low-load period, described the characteristics of electricity price fluctuation by ARCH models. The results showed that ARCH models under t-distribution matched the volatility of the sample series quite well, captured the series’ heteroscedasticity and the obvious peak and fat tail effectively; the total risk of the day-ahead market in the sample was high, the impacts from external information on the conditional variances was permanent and sustainable, the impacts could not disappear in a short time once the price were fluctuated; the daily mean price fluctuation and low-load period price fluctuation were not asymmetric; while high-load period were significantly asymmetrical.

Effects of sustained proNGF blockade on attentional capacities in aged rats with compromised cholinergic system

Disruption in nerve growth factor (NGF) signaling via tropomyosin-related kinase A (trkA) receptors compromises the integrity of the basal forebrain (BF) cholinergic system, yielding cognitive, specifically attentional, impairments in Alzheimer’s disease (AD). Although normal aging is considered a risk factor for AD, the mechanisms underlying the selective vulnerability of the aging cholinergic system to trkA disruption is not clear. The levels of proNGF, a proneurotrophin that possesses higher affinity for p75 receptors, increase in aging. The present study was designed to test the hypothesis that cholinergic and attentional dysfunction in aged rats with reduced BF trkA receptors occurs due to the overactivation of endogenous proNGF signaling. We employed a viral vector that produced trkA shRNA to suppress trkA receptors in the corticopetal cholinergic neurons of aged rats. BF trkA suppression impaired animals’ performance on signal trials in both the sustained attention task (SAT) and the cognitively taxing distractor version of SAT (dSAT) and these deficits were normalized by chronic intracerebroventricular administration of proNGF antibody. Moreover, depolarization-evoked acetylcholine (ACh) release and the density of cortical cholinergic fibers were partially restored in these animals. However, SAT/dSAT scores reflecting overall performance did not improve following proNGF blockade in trkA knockdown rats due to impaired performance in non-signal trials. Sustained proNGF blockade alone did not alter baseline attentional performance but produced moderate impairments during challenging conditions. Collectively, our findings indicate that barring proNGF-p75 signaling may exert some beneficial effects on attentional capacities specifically when BF trkA signaling is abrogated. However, endogenous proNGF may also possess neurotrophic effects and blockade of this proneurotrophin may not completely ameliorate attentional impairments in AD and potentially hinder performance during periods of high cognitive load in normal aging.

Experiences from the full-scale implementation of a new two-stage vertical flow constructed wetland design

This paper describes the results of the first full-scale implementation of a two-stage vertical flow constructed wetland (CW) system developed to increase nitrogen removal. The full-scale system was constructed for the Bärenkogelhaus, which is located in Styria at the top of a mountain, 1,168 m above sea level. The Bärenkogelhaus has a restaurant with 70 seats, 16 rooms for overnight guests and is a popular site for day visits, especially during weekends and public holidays. The CW treatment system was designed for a hydraulic load of 2,500 L.d(-1) with a specific surface area requirement of 2.7 m(2) per person equivalent (PE). It was built in fall 2009 and started operation in April 2010 when the restaurant was re-opened. Samples were taken between July 2010 and June 2013 and were analysed in the laboratory of the Institute of Sanitary Engineering at BOKU University using standard methods. During 2010 the restaurant at Bärenkogelhaus was open 5 days a week whereas from 2011 the Bärenkogelhaus was open only on demand for events. This resulted in decreased organic loads of the system in the later period. In general, the measured effluent concentrations were low and the removal efficiencies high. During the whole period the ammonia nitrogen effluent concentration was below 1 mg/L even at effluent water temperatures below 3 °C. Investigations during high-load periods, i.e. events like weddings and festivals at weekends, with more than 100 visitors, showed a very robust treatment performance of the two-stage CW system. Effluent concentrations of chemical oxygen demand and NH4-N were not affected by these events with high hydraulic loads.

Energy efficient optimization of wireless embedded sensor networks

The energy optimization techniques developed for conventional ad hoc networks do not appropriately address the unique features of the wireless embedded sensor networks (WESNs). In the WESN environment, only reducing the overall energy consumption is not considered enough to maximize the life span of the entire network, but maintaining full network connectivity for a sufficiently long period of time is also an important design goal due to the energy constraints of each node. The wireless radio is a major energy user and is often the focus of energy conservation mechanisms, since the nodes communicate in a shared medium (air interface). The medium access control (MAC) layer of the communication protocol stack arbitrates access to the communications link by manipulating the sleep, listen, transmit, and receive states of the radio transceivers. The bursty traffic networks experience long periods of inactivity interrupted by unplanned and often short lived periods of high traffic loads. Currently available MAC protocols cannot meet application fidelity requirements of the bursty traffic networks since they are designed either for networks with periodic traffic or are not sufficiently traffic-adaptive, thereby introducing large multi-hop latency delays to realize network connectivity, overprovision during light traffic conditions, and slow ramp up at the initiation of a high traffic episode. This paper presents enhancements made to the energy efficient MAC protocol which is especially designed for the bursty traffic networks and in the process targets some available communication techniques used in the WESNs for discussion and comparison.

Neural network-based active power curtailment for overvoltage prevention in low voltage feeders

As non-controllable and intermittent power sources, grid-connected photovoltaic (PV) systems can contribute to overvoltage in low voltage (LV) distribution feeders during periods of high solar generation and low load where there exists a possibility of reverse power flow. Overvoltage is usually prevented by conservatively limiting the penetration level of PV, even if these critical periods rarely occur. This is the current policy implemented in the Northern Territory, Australia, where a modest system limit of 4.5kW/house was imposed. This paper presents an active power curtailment (APC) strategy utilizing artificial neural networks techniques. The inverter active power is optimized to prevent any overvoltage conditions on the LV feeder. A residential street located in Alice Springs was identified as a case study for this paper. Simulation results demonstrated that overvoltage conditions can be eliminated and made to comply with the Australian Standards AS60038 and AS4777 by incorporating the proposed predictive APC control. In addition, the inverter downtime due to overvoltage trips was eliminated to further reduce the total power losses in the system.

Ship impacts on the marine atmosphere: insights into the contribution of shipping emissions to the properties of marine aerosol and clouds

Abstract. We report properties of marine aerosol and clouds measured in the shipping lanes between Monterey Bay and San Francisco off the coast of Central California. Using a suite of aerosol instrumentation onboard the CIRPAS Twin Otter aircraft, these measurements represent a unique set of data contrasting the properties of clean and ship-impacted marine air masses in dry aerosol and cloud droplet residuals. Below-cloud aerosol exhibited average mass and number concentrations of 2 μg m−3 and 510 cm−3, respectively, which are consistent with previous studies performed off the coast of California. Enhancements in vanadium and cloud droplet number concentrations are observed concurrently with a decrease in cloud water pH, suggesting that periods of high aerosol loading are primarily linked to increased ship influence. Mass spectra from a compact time-of-flight Aerodyne aerosol mass spectrometer reveal an enhancement in the fraction of organic at m/z 42 (f42) and 99 (f99) in ship-impacted clouds. These ions are well correlated to each other (R2>0.64) both in and out of cloud and constitute 14% (f44) and 3% (f99) of organic mass during periods of enhanced sulfate. High-resolution mass spectral analysis of these masses from ship measurements suggests that the ions responsible for this variation were oxidized, possibly due to cloud processing. We propose that the organic fractions of these ions be used as a metric for determining the extent to which cloud-processed ship emissions impact the marine atmosphere where (f42 > 0.15; f99 > 0.04) would imply heavy influence from shipping emissions, (0.05 < f42 < 0.15; 0.01 < f99 < 0.04) would imply moderate, but persistent, influences from ships, and (f42 < 0.05; f99 < 0.01) would imply clean, non-ship-influenced air.

Measuring workload during a dynamic supervisory control task using cerebral blood flow velocity and the NASA-TLX

While automated systems have been shown to improve safety and efficiency in operational environments, automation failures can lead to abrupt shifts in workload. Subjective workload scales have been shown to be sensitive to differences in workload, but they are limited in their ability to assess dynamic, moment-to-moment workload variations. Physiological measures may be better suited to assess dynamic workload in complex environments. This study explored the feasibility of a relatively new physiological measure, Transcranial Doppler Sonography (TCD), as a candidate for adaptive automation studies. Participants performed long duration, supervisory control tasks under varying levels of taskload. In one group, enemy threats increased once late in the simulation, and in another group enemy threats increased at two points; once early and once late within the simulation. All participants completed a comparison condition in which there was no variation in the number of incoming enemy threats. Cerebral blood flow velocity (CBFV), as measured by TCD, was measured during task performance. Performance was assessed by the ability of the operator to protect a no-fly zone from enemy incursion. Subjective mental workload was assessed using the NASA-TLX. As performance decreased during periods of high load, CBFV increased, and there was a close parallel between the CBFV and performance measures. The NASA-TLX was sensitive in detecting differences in workload between the two conditions, but the patterns of results of this subjective measure were insensitive to specific task elements. The results are interpreted in terms of a resource theory of task performance and show that the CBFV measure is sensitive to dynamic changes in taskload in complex environments.

Global electric circuit modulation of winter cyclone vorticity in the northern high latitudes

Small changes in extended winter (November–March) 500hPa vorticity area index (VAI) values for the 60–80°N latitude band are shown to be positively correlated with changes in a proxy for the high latitude ionosphere-to-surface current density Jz.The proxy was obtained from low latitude Jz values, measured at Mauna Loa Observatory (MLO) during the years 1960–1961 and 1977–1982, which were taken as proportional to the global ionospheric potential Vi. Such MLO Jz values may also serve as proxies for high latitude Jz, provided that they are not used during Forbush decreases or during periods of high stratospheric aerosol loading. The MLO data were of sufficient quantity and quality to obtain high latitude Jz proxies for five northern hemisphere winters. These proxies were used in linear regressions with lagged values of anomalies in the VAI (with lags extending from −150 to +150days). For the regression analysis using VAI values from the four 1977–1982 winters, the largest R2 value occurred for a lag of +2days, and the corresponding regression coefficient was the second largest in magnitude for the 301day interval. An ANOVA test showed this result to have a statistical significance of greater than 95%. For the regression analysis using data from only the 1960–1961 winter, both the maximum slope and R2 value occurred for a lag of −3 days. However, the autocorrelation of the VAI has a width of ∼15 days, and the noise associated with the small number of data points for 1960–1961 suggests that the maxima were displaced to negative lags by noise. The overall results are consistent with Tinsley’s hypothesis that higher Jz values enhance the vorticities of relatively intense winter cyclones when latent heat is important for their development. Electric charge deposited in clouds by Jz modulates the scavenging rates for both cloud condensation nuclei and ice-forming nuclei. The hypothesis is that these modulate the updraft vigor by the Rosenfeld mechanism, thus increasing the cyclonic vorticity.

Genetic potential for N 2O emissions from the sediment of a free water surface constructed wetland

Removal of nitrogen is a key aspect in the functioning of constructed wetlands. However, incomplete denitrification may result in the net emission of the greenhouse gas nitrous oxide (N 2O) resulting in an undesired effect of a system supposed to provide an ecosystem service. In this work we evaluated the genetic potential for N 2O emissions in relation to the presence or absence of Phragmites and Typha in a free water surface constructed wetland (FWS-CW), since vegetation, through the increase in organic matter due to litter degradation, may significantly affect the denitrification capacity in planted areas. Quantitative real-time PCR analyses of genes in the denitrification pathway indicating capacity to produce or reduce N 2O were conducted at periods of different water discharge. Genetic potential for N 2O emissions was estimated from the relative abundances of all denitrification genes and nitrous oxide reductase encoding genes ( nosZ). nosZ abundance was invariably lower than the other denitrifying genes (down to 100 fold), and differences increased significantly during periods of high nitrate loads in the CW suggesting a higher genetic potential for N 2O emissions. This situation coincided with lower nitrogen removal efficiencies in the treatment cell. The presence and the type of vegetation, mainly due to changes in the sediment carbon and nitrogen content, correlated negatively to the ratio between nitrate and nitrite reducers and positively to the ratio between nitrite and nitrous oxide reducers. These results suggest that the potential for nitrous oxide emissions is higher in vegetated sediments.

Wind power impacts and electricity storage – A time scale perspective

Integrating large amounts of wind power in energy systems poses balancing challenges due to the variable and only partly predictable nature of wind. The challenges cover different time scales from intra-hour, intra-day/day-ahead to several days and seasonal level. Along with flexible electricity demand options, various electricity storage technologies are being discussed as candidates for contributing to large-scale wind power integration and these also differ in terms of the time scales at which they can operate. In this paper, using the case of Western Denmark in 2025 with an expected 57% wind power penetration, wind power impacts on different time scales are analysed. Results show consecutive negative and high net load period lengths indicating a significant potential for flexibility measures capable of charging/activating demand and discharging/inactivating demand in periods of 1 h to one day. The analysis suggests a lower but also significant potential for flexibility measures charging/activating demand in periods of several days. In addition, the results indicate a physical potential for seasonal electricity storage. In the study, a number of large-scale electricity storage technologies – batteries, flow batteries, compressed air energy storage, electrolysis combined with fuel cells, and electric vehicles – are moreover categorised with respect to the time scales at which they are suited to support wind power integration. While all of these technologies are assessed suitable for intra-hour and intra-day/day-ahead power balancing only some are found suited for responding to several days with high/low net loads and even fewer for seasonal balancing.

Impact of active power curtailment on overvoltage prevention and energy production of PV inverters connected to low voltage residential feeders

As non-controllable power sources, photovoltaics (PV) can create overvoltage in low voltage (LV) distribution feeders during periods of high generation and low load. This is usually prevented passively by limiting the penetration level of PV to very conservative values, even if the critical periods rarely occur. Alternatively, one can use active power curtailment (APC) techniques, reducing the amount of active power injected by the PV inverters, as the voltage at their buses increase above a certain value. In this way, it is possible to increase the installed PV capacity and energy yield while preventing overvoltage. This paper investigates a number of approaches for sizing and controlling the PV power generated by 12 net-zero energy houses equipped with large rooftop PV systems in a typical 240 V/75 kVA Canadian suburban radial distribution feeder. Simulations of a one year period with typical solar irradiance and load profiles are conducted with PSCAD to assess the performance of the different approaches in terms of overvoltage occurrence, sharing of the burden for overvoltage prevention per house and total energy yield of the residential PV feeder.

The links between atmospheric vorticity, radiation belt electrons, and the solar wind

The links between winter storm intensity and solar wind variations associated with Heliospheric Current Sheet (HCS) crossings are shown to be present in 1997 through 2002 data without the necessity of high stratospheric aerosol loading.The peak values of winter storm vorticity are measured in terms of the 500hPa vorticity area index (VAI) for the Northern Hemisphere, during extended winter months, November through March. Superposed epoch analyses are used, but instead of the key days being defined by heliospheric current sheet crossings as used formerly, they are defined by minima in the absolute flux of relativistic electrons (REF)>2MeV measured at geostationary orbit. Minima in the VAI were found approximately 3days after the REF minima. Corresponding VAI minima were also found in response to the deepest minima in the solar wind speed (SWS). The SWS minima occurred approximately 2days before the REF minima, and 5days before the VAI minima. These results for the 1997–2002 period of low to moderate stratospheric aerosol loading are compared to periods of high loading that occurred between 1964 and 1994. The weaker VAI response in 1997–2002 is evidently due to the reduced aerosol loading, but there is uncertainty in the amount of weakening, due to the greater sensitivity gained by analyzing with respect to the deepest minima in REF or SWS rather than to times of HCS crossings, and the possibility of secular changes in the solar wind and in the magnetospheric relativistic electron populations.

Monitoring biological and psychological measures throughout an entire season in male handball players

The aim of this study was to monitor biological markers of inflammation and oxidative stress, mood states, and recovery-stress states throughout an entire season in male handball players. Fourteen handball players (age 20.1±2.5 years) with a regular training and competitive background in handball (11.0±3.7 years) from the same club volunteered to participate. All participants completed 40 weeks of training. The training load was increased progressively throughout the season. Blood samples were collected and questionnaires were administered during preparatory, competitive, and recovery periods. Blood C-reactive protein and oxidized glutathione (GSSG) concentrations increased during periods of high load, while the reduced/oxidized glutathione ratio (GSH/GSSG) decreased. These changes were accompanied by a significant increase in total leukocyte count. Positive correlations were found between C-reactive protein, GSSG, GSH/GSSG ratio, and training load. No changes were observed in the Total Mood Disturbance score of the Profile of Mood States (POMS). However, scores on some Recovery-Stress Questionnaire for Athletes subscales, such as Injury, Physical Recovery, and Being in Shape, correlated with training load. Findings indicate that during periods of high training load, handball players developed a low grade of inflammation and oxidative state. Results support the usefulness of monitoring psychological and biological markers of inflammation, oxidative stress, and training load during season.

HIV-1 Subtype C-Infected Individuals Maintaining High Viral Load as Potential Targets for the “Test-and-Treat” Approach to Reduce HIV Transmission

The first aim of the study is to assess the distribution of HIV-1 RNA levels in subtype C infection. Among 4,348 drug-naïve HIV-positive individuals participating in clinical studies in Botswana, the median baseline plasma HIV-1 RNA levels differed between the general population cohorts (4.1–4.2 log10) and cART-initiating cohorts (5.1–5.3 log10) by about one log10. The proportion of individuals with high (≥50,000 (4.7 log10) copies/ml) HIV-1 RNA levels ranged from 24%–28% in the general HIV-positive population cohorts to 65%–83% in cART-initiating cohorts. The second aim is to estimate the proportion of individuals who maintain high HIV-1 RNA levels for an extended time and the duration of this period. For this analysis, we estimate the proportion of individuals who could be identified by repeated 6- vs. 12-month-interval HIV testing, as well as the potential reduction of HIV transmission time that can be achieved by testing and ARV treating. Longitudinal analysis of 42 seroconverters revealed that 33% (95% CI: 20%–50%) of individuals maintain high HIV-1 RNA levels for at least 180 days post seroconversion (p/s) and the median duration of high viral load period was 350 (269; 428) days p/s. We found that it would be possible to identify all HIV-infected individuals with viral load ≥50,000 (4.7 log10) copies/ml using repeated six-month-interval HIV testing. Assuming individuals with high viral load initiate cART after being identified, the period of high transmissibility due to high viral load can potentially be reduced by 77% (95% CI: 71%–82%). Therefore, if HIV-infected individuals maintaining high levels of plasma HIV-1 RNA for extended period of time contribute disproportionally to HIV transmission, a modified “test-and-treat” strategy targeting such individuals by repeated HIV testing (followed by initiation of cART) might be a useful public health strategy for mitigating the HIV epidemic in some communities.

Effect of Adaptive Cluster Sampling Design on Accuracy of Sediment Rating Curve Estimation

Adaptive cluster sampling represents a design whereby more samples during high storm hydrographs can be obtained in the field compared to the commonly used calendar-based. To compare the effect of these sampling designs on accuracy of sediment rating curve estimation, we performed a study for Gorgan-Rood River, Iran by synthesizing sample sets from daily records. The load estimates obtained by conventional, two bias-corrected, and logged mean load within discharge classes (LMLWDCs) rating curves were statistically evaluated. All rating curves derived from calendar-based sample sets–except those with a nonparametric correction factor–underestimated the average load from 25 to 76%. Rating curves derived from adaptive sample sets, however, increased the sediment load to as much as 30%. Among this group of rating curves, LMLWDC produced the most accurate results with only 3% overestimation and a coefficient of variation in the order of 14% when the sampling frequency was semiweekly. The more accurate estimates from adaptive sample sets are likely due to the inclusion of more samples from high load periods.

Fluctuation of microbial activities after influent load variations in a full-scale SBR: recovery of the biomass after starvation

Due to variations in the production levels, a full-scale sequencing batch reactor (SBR) for post-treatment of tannery wastewater was exposed to low and high ammonia load periods. In order to study how these changes affected the N-removal capacity, the microbiology of the reactor was studied by a diverse set of techniques including molecular tools, activity tests, and microbial counts in samples taken along 3 years. The recover capacity of the biomass was also studied in a lab-scale reactor operated with intermittent aeration without feeding for 36 days. The results showed that changes in the feeding negatively affected the nitrifying community, but the nitrogen removal efficiencies could be restored after the concentration stress. Species substitution was observed within the nitrifying bacteria, Nitrosomonas europaea and Nitrobacter predominated initially, and after an ammonia overload period, Nitrosomonas nitrosa and Nitrospira became dominant. Some denitrifiers, with nirS related to Alicycliphilus, Azospirillum, and Marinobacter nirS, persisted during long-term reactor operation, but the community fluctuated both in composition and in abundance. This fluctuating community may better resist the continuous changes in the feeding regime. Our results showed that a nitrifying-denitrifying SBR could be operated with low loads or even without feeding during production shut down periods.

Long-term ammonia removal in a coconut fiber-packed biofilter: Analysis of N fractionation and reactor performance under steady-state and transient conditions

A comprehensive study of long-term ammonia removal in a biofilter packed with coconut fiber is presented under both steady-state and transient conditions. Low and high ammonia loads were applied to the reactor by varying the inlet ammonia concentration from 90 to 260 ppm v and gas contact times ranging from 20 to 36 s. Gas samples and leachate measurements were periodically analyzed and used for characterizing biofilter performance in terms of removal efficiency (RE) and elimination capacity (EC). Also, N fractions in the leachate were quantified to both identify the experimental rates of nitritation and nitratation and to determine the N leachate distribution. Results showed stratification in the biofilter activity and, thus, most of the NH 3 removal was performed in the lower part of the reactor. An average EC of 0.5 kg N-NH 3 m −3 d −1 was obtained for the whole reactor with a maximum local average EC of 1.7 kg N-NH 3 m −3 d −1. Leachate analyses showed that a ratio of 1:1 of ammonium and nitrate ions in the leachate was obtained throughout steady-state operation at low ammonia loads with similar values for nitritation and nitratation rates. Low nitratation rates during high ammonia load periods occurred because large amounts of ammonium and nitrite accumulated in the packed bed, thus causing inhibition episodes on nitrite-oxidizing bacteria due to free ammonia accumulation. Mass balances showed that 50% of the ammonia fed to the reactor was oxidized to either nitrite or nitrate and the rest was recovered as ammonium indicating that sorption processes play a fundamental role in the treatment of ammonia by biofiltration.

Phytate as a novel phosphorus-specific paleo-indicator in aquatic sediments

A reliable geochemical paleo-indicator for phosphorus remains elusive, despite the importance of understanding historical changes in the nutrient status of aquatic ecosystems. We assessed the potential of phytate (salts of myo-inositol hexakisphosphate) as a novel phosphorus-specific paleo-indicator by measuring its concentrations in dated sediments from an embayment in Helsinki, Finland, with a known 200-year history of trophic changes. Phytate was extracted in a solution containing sodium hydroxide and EDTA and detected by solution 31P NMR spectroscopy with spectral deconvolution. Concentrations varied markedly with sediment depth and paralleled previously determined changes in diatom assemblages and geochemical indicators linked to trophic status. In contrast, total sediment phosphorus did not reflect phosphorus inputs to the embayment, presumably due to the mobilization of inorganic phosphate under anoxic conditions during periods of high pollutant loading. Importantly, phytate appeared to be stable in these brackish sediments, in contrast to other organic and inorganic phosphates which declined abruptly with depth. We therefore conclude that phytate represents a potentially important indicator of historical changes in phosphorus inputs to water bodies, although additional studies are required to confirm its stability under conditions likely to be encountered in lakes and coastal ecosystems.