Klaus Pecher

Redox measurements in aqueous solutions — A theoretical approach to data interpretation, based on electrode kinetics

Abstract Redox electrodes are commonly used to measure redox potentials in complex natural systems. In this paper, an approach based on electrode kinetics to interpreting measured redox potentials is presented. Redox couples dissolved in aqueous solutions are classified as sensor effective redox couples (SERCs), which exchange electrons with the electrode surface at a significant rate, and sensor ineffective redox couples (SIRCs), which do not control the potential of the electrode. Going through the corresponding mathematical formalism, we arrive at a Butler-Volmer-type equation which states that a quantitative interpretation of redox potentials is not possible without understanding the nature of SERCs and their electrode kinetic parameters. A sensitivity analysis of effects of these unknown parameters on the redox potential is presented. Implications for interpretations of potential readings in natural samples are discussed. Finally, outlooks for necessary future experimental studies are given.

Tracing faecal pollution by coprostanol and intestinal bacteria in an ice-covered finnish lake loaded with both industrial and domestic sewage

The relationships existing between coprostanol (5β-cholestan-3β-ol), faecal indicator bacteria and various physico-chemical tracer and bacterial stress factors in an ice-covered Finnish lake were investigated. Field observations show that coprostanol lies below the theoretical mixing line, indicating a net removal, primarily by settling together with suspended sediments. Faecal indicator bacteria, however, are differently transported and are removed by various environmental factors e.g. industrial wastes. Thus, only faecal streptococci show a regional covariance to coprostanol. Principal component analyses reveal a strong correlation between coprostanol and faecal streptococci in water but not with coliforms and sulfite reducing sporing anaerobs. However, in sediments also coliforms are correlated significantly with coprostanol and faecal streptococci.Therefore it might be necessary to estimate the quality of those waters polluted by both industrial and faecal wastes by means of coprostanol, a principal sterol in sewage of man and higher animals, which is thus well suited as a chemical marker of faecal pollution.

Mobility of chlorofluorocarbons in deposits of shredder wastes from plastic and metal utilizing industries

Chlorofluorocarbons (CFCs) are used as propellants in spray cans, as refrigerants and as blowing agents for plastic foams, which are finally dumped together with solid wastes in landfills. We found shredder waste from plastic and metal utilizing industry to be highly contaminated with F12 (CF2Cl2) and less with F11 (CFCl3). By means of model calculations with one dimensional diffusion models, we were able to estimate the amount and rate of outgassing of CFCs. The models were validated with measured vertical gas concentration profiles. From our results we conclude that deposition of shredder wastes containing CFCs results in a quick loss of these substances to the atmosphere with halflifes of ∼ 2 d. In order to reduce CFC emission from landfills, contaminated wastes should be covered with compacted adsorbing layers (e.g., sewage sludge) immediately after their deposition.

Chemodynamics of Chlorophenols during Sequential Degradation of Solid Municipal Wastes

In laboratory reactor experiments the behaviour of chlorophenols was studied during sequential anaerobic degradation of municipal wastes. Special attention was directed to the biochemical stability and physicochemical mobility of such chemicals in the waste material. Under idealized conditions an anaerobic degradation sequence was simulated in order to investigate the influence of varying biochemical conditions on the chemodynamics of chlorophenols. The dominant process governing their fate was reductive dechlorination during methanogenic conditions. Increasing pH during acidogenic conditions led to a considerable release of chlorophenols into the leachate. This behaviour could be described with an equilibrium model assuming different adsorption isotherms for ionic and protonated species.

Behaviour of chloroform from pulp bleaching in an ice-covered finnish lake

Abstract Samples of ice and water from different depths were collected from various parts of Lake Nasijarvi, Finland. Chloroform was analysed by liquid—liquid extraction, capillary gas chromatography followed by electron capture detection and confirmation by gas chromatography/mass spectrometry. Maps of the regional variation of chloroform and sodium-lignin sulfonates (NaLS) show that under winter conditions with an inverse stratification the effluents of a pulp mill containing chloroform and NaLS fill the depressions of the lake bottom and flow as a thin, high-density waste water current downslope northeastward against the southward directed upper current of the epilimnion. Plots of chloroform against Ca indicate that there is only a weak net removal of chloroform from combined solution and suspension. Thus mass transfer to the atmosphere is confined in Lake Nasijarvi to seasons with vertical mixing of the water masses.

Chemodynamik von Chlorphenolen Während des Sequentiellen Abbaus Fester Kommunaler Abfälle (Kurzfassung)

Mit Hilfe von Laborexperimenten wurde das Verhalten von Chlorphenolen unterschiedlicher Chlorierungsgrade wahrend des phasenweisen anaeroben Abbaus fester kommunaler Abfalle untersucht. Der Schwerpunkt der Untersuchung lag auf der Ermittlung des Einflusses zeitvarianter Milieubedingungen im 3-Phasensystem Mull-Sickerwasser-Faulgas auf die Mobilitat und Stabilitat der organischen Schadstoffe. Die Milieubedingungen stellen sich dabei als Folge der biologischen Aktivitat verschiedener Mikroorganismenpopulationen ein.

Regulationsmechanismen der Spurenmetallöslichkeit beim Anaeroben Abbau Fester Kommunaler Abfälle

Das Poster diskutiert die Bedeutung biogeochemischer Prozesse wahrend des anaeroben mikrobiellen Abbaus fester kommunaler Abfalle fur die Mobilisierung der abfallburtigen Schwermetalle Eisen, Zink, Cadmium, Blei und Kupfer. Im weiteren wird der Einflus von gemeinsam mit Hausmull abgelagertem cadmiumhaltigen Klarschlamm auf die Mobilitat der Metalle dargestellt sowie die Auswirkung von Sauerstoffzufuhr zu anaeroben Schlammen diskutiert.