Optimal and suboptimal control of anaerobic digesters

Anaerobic digester failure due to entry of inhibitors or sudden changes in the feed substrate concentration may be encompassed beneficially by applying optimal control theory. An almost proportional relationship between the dilution rate and the methane production rate leads to a simple suboptimal control law with only minor loss in performance, after the occurrence of the above mentioned events.     

Transient modeling of trickling filters for biological ammonia removal

A dynamic model for nitrifying trickling filters is developed, based on material balances in the biofilm and the bulk liquid. The model predicts the profile of ammonia as a function of the operating parameters (volumetric flow rate and feed ammonia concentration) and the biofilm thickness as a function of filter depth and time. This revised version was published online in July 2006 with corrections to the Cover Date.     

Copper fractionation with dissolved organic matter in natural waters and wastewater--a mixed micelle mediated methodology (cloud point extraction) employing flame atomic absorption spectrometry

A cloud point extraction-preconcentration methodology for the speciation analysis of free and organically complexed metal species in natural waters is presented. The method is based on the neutralization of the electrostatic charge of the humate-metal complexes with a positively charged surfactant in a high ionic strength solution environment. The resulting complexes are conveniently solubilized in the micelles of a non-ionic surfactant medium and are thus separated from the bulk aqueous phase. Free metal species are also determined by complexation with a conventional chelating agent under mild conditions. The overall procedure is easy, rapid and allows for a high sample throughput in terms of massive analysis of many samples in the same time period. The method offers substantially low detection limits of 8.5 and 0.9 micrograms l-1 for bound and labile species respectively, with a calibration curve rectilinear in the wide range 40-150 micrograms l-1 for the humate associated and 4-40 micrograms l-1 for the free metal species. The method is free from interferences yielding recoveries in the range 97-102% for various samples of different matrixes.     

Driving in mild cognitive impairment: The role of depressive symptoms

Objectives: Previous studies indicate a negative association between depression and driving fitness in the general population. Our goal was to cover a gap in the literature and to explore the link between depressive symptoms and driving behavior in individuals with mild cognitive impairment (MCI) through the use of a driving simulator experiment.

Methods: Twenty-four individuals with MCI (mean age = 67.42, SD = 7.13) and 23 cognitively healthy individuals (mean age = 65.13, SD = 7.21) were introduced in the study. A valid driving license and regular car use served as main inclusion criteria. Data collection included a neurological/neuropsychological assessment and a driving simulator evaluation. Depressive symptomatology was assessed with the Patient Health Questionnaire (PHQ-9).

Results: Significant interaction effects indicating a greater negative impact of depressive symptoms in drivers with MCI than in cognitively healthy drivers were observed in the case of various driving indexes, namely, average speed, accident risk, side bar hits, headway distance, headway distance variation, and lateral position variation. The associations between depressive symptoms and driving behavior remained significant after controlling for daytime sleepiness and cognition.

Conclusions: Depressive symptoms could be a factor explaining why certain patients with MCI present altered driving skills. Therefore, interventions for treating the depressive symptoms of individuals with MCI could prove to be beneficial regarding their driving performance.     

Exposure to major volatile organic compounds and carbonyls in European indoor environments and associated health risk

This paper summarizes recent data on the occurrence of major organic compounds (benzene, toluene, xylenes, styrene, acetaldehyde, formaldehyde, naphthalene, limonene, α-pinene and ammonia, classified by the European Commission's INDEX strategy report as the priority pollutants to be regulated) and evaluates accordingly cancer and non-cancer risks posed by indoor exposure in dwellings and public buildings in European Union (EU) countries. The review process indicated that significant differences in indoor air quality exist within and among the countries where data were available, indicating corresponding differences in sources and emission strength of airborne chemicals, identified or not. Conservative exposure limits were not exceeded for non-carcinogenic effects, except for formaldehyde; for carcinogenic agents the estimated risks were up to three orders of magnitude higher than the one (10(-6)) proposed as acceptable by risk management bodies. However, the risk assessment evaluation process faces crucial difficulties, either due to the relative paucity of indoor air quality measurements in many EU countries, or by the lack of sampling consistency in the already existing studies, indicating the need for additional measurements of indoor air quality following a harmonized sampling and analytical protocol. Additionally, uncertainties embodied in the cancer potency factors and exposure limit values impose further difficulties in substance prioritization and risk management.     

Dynamics of a chemostat with three competitive hydrogen oxidizing denitrifying microbial populations and their efficiency for denitrification

In this work, competition for two nitrogen resources (nitrate-, nitrite-nitrogen) between three hydrogen oxidizing denitrifying populations (Acidovorax sp. strain Ic3 (X₁), Paracoccus sp. strain Ic1 (X₂), and Acinetobacter sp. strain Ic2 (X₃)) was examined. The dynamics of three systems of microbial populations (system I: X₁ − X₃, system II: X₂ − X₃, and system III: X₁ − X₂ − X₃), grown in a chemostat, was studied using bifurcation analysis. The chemostat is the most common type of biological reactor used for the study of microbial growth under controlled conditions. The effect of the operating parameters (i.e., dilution rate and feed nitrate nitrogen concentration) on the long-term behavior of the systems showed that X₃ was the predominant population for a wide range of combinations of dilution rate and feed nitrate nitrogen concentration. Also, coexistence of two populations (X₂X₃, X₁X₃) was observed. The results of the bifurcation analysis were also used to determine the denitrification rate and the nitrite nitrogen accumulation for each of the three systems as a function of the dilution rate (up to 0.17 h⁻¹) and the feed nitrate nitrogen concentration (up to 300 mg/L). The highest denitrification rate was achieved by system I (28 mg/Lh). A comparison between the three systems showed that the nitrite nitrogen concentration in system I was less than the one in system III, while the two systems gave similar denitrification rates. The second system had the greatest accumulation of nitrites with the lowest denitrification rate.     

Multi-objective optimization of air quality monitoring

A new method for multi-objective optimization of air quality monitoring systems based on satellite remote sensing of the troposphere is described in this work. The technique uses atmospheric turbidity as surrogate for air pollution loading. Through inverse chemical modeling and ancillary information the respective patterns of primary gaseous and particle pollutants are inferred. The optimization algorithm uses the resulting maps of ambient air pollution as input. It focuses on the gain of information with regard to human exposure to high pollution, potential impact on cultural heritage, compliance to ambient air quality standards, monitoring key point and area source emissions, as well as on the associated cost. Application of the method in Brescia, Italy showed its significant potential for improving the cost-effectiveness of air quality monitoring networks at the urban and regional scales.     

Exposure Modeling of Benzene Exploiting Passive–Active Sampling Data

The objective of the present study is the exploitation of active sampling personal exposure data in assessing the factors that affect exposure to benzene in combination with the widely accepted scheme of passive sampling—time microenvironment–activity diaries (TMAD). The campaign included personal exposure measurements with both passive and active sampling in several microenvironments, evaluation of TMAD kept by the volunteers, and a variety of environmental data (ambient air benzene determination, traffic and meteorological observations). Due to the relatively elevated benzene traffic emissions, average personal exposure was determined to be equal to 8.9 μg/m³, ranging between 5 and 20 μg/m³, which is a value highly related to the average urban concentration (9.2 μg/m³). The information gained from TMAD was embedded (in terms of spatial and temporal distribution) into three zones respectively, in order to draw statistically significant conclusions about the exposure levels and the activity patterns. The contribution of the activities to the overall amount of exposure was further quantified and refined by active sampling measurements. These data revealed that driving in a traffic-congested road was the main activity leading to elevated exposure levels (up to 70 μg/m³), followed by walking on the roadside of a congested road (up to 35 μg/m³). Indoor exposure to benzene was in general lower than outdoor (indicating that traffic is the dominant source of benzene emissions in the wider area), and it was significantly affected by the presence of environmental tobacco smoke. The higher significance of the regression coefficients obtained by statistical analysis of the active sampling data was fundamental for the development of a regression-based prediction exposure model. The model was evaluated through comparison with the passive sampling data, which were considered as an unknown but realistic data exposure pattern. The model performed very well in terms of expressing the variance of the exposure data with an average score of R ² equal to 0.935. All of the above indicate that active sampling is a necessary albeit more laborious tool that needs to be used as a complement to passive sampling for precise quantification of the factors determining personal exposure patterns.     

Human mortality in Cyprus: the role of temperature and particulate air pollution

Climatic change results in increased occurrence of heat waves, and the thermal stress caused by such phenomena is leading to higher levels of heat-related mortality worldwide. This study is the first to examine the effect of extreme weather on mortality in Cyprus. It investigates the individual effect of meteorological indicators on mortality, as well as the role of particulate air pollution (PM₁₀). A generalized linear model (GLM) with quasi-Poisson regression was implemented. GLM included a temperature function and was adjusted for relative humidity and seasonality. The temperature function was developed under a newly developed framework of distributed lag nonlinear models, which capture nonlinearities and delayed effects of heat simultaneously. GLM was extended to examine the confounding effect of air pollution. All the results on heat effects are presented. High temperatures had a significant effect on mortality with increased mortality rates, independent of humidity and seasonality. Mortality risk increased steeply above a temperature threshold. A direct heat effect was shown, with higher risk on the current and next day of a severe heat event. PM₁₀ was not found to have a confounding effect on the temperature–mortality relationship, since the strength of this relationship remained after the inclusion of PM₁₀ in the model. Differences existed between urban and coastal areas.     

Release,distribution, and impacts of polychlorinated biphenyls (PCB) induced by dredged material disposal activities at a deep-water estuarine site

The aquatic disposal field investigation initiated in Elliott Bay, Puget Sound, WA, in February 1976, was designed to evaluate the ecological effects of open-water disposal of dredged material. The experimental disposal site was located at a depth of 60 m in marine estuary with generally weak circulation. Approximately 114,000 m³ of dredged material contaminated with polychlorinated biphenyls (PCBs) were dumped at the site from split-hull barges. The material presented in this paper is limited to a discussion of PCB impacts. It imcludes (a) a summary of results from the studies conducted between 1976 and 1977 to assess short-term impacts during and after the disposal of PCB contaminated sediments at the Elliott Bay disposal site; (b) a presentation of preliminary results from the continuation studies initiated in February 1979 to determine long-term impacts of the disposal operations. The preliminary data indicate that both dredged-material deposit and the associated PCBs appear to be stable. No major long-term impact on benthic organisms is apparent from this analysis.