Thomas Griebe

Biocide-free antifouling strategy to protect RO membranes from biofouling☆

Abstract The biofouling potential in industrial water systems consists of microbial biofilms and nutrients which can be considered as potential biomass. The basic mechanism of biofilm development involves the conversion of dissolved nutrients into locally accumulated biomass. Biofouling occurs only when the extent of biofilm growth meets a threshold of interference. It is not necessary to kill all biofilms—it is possible to live with biofilms as long as this operational defined threshold of interference is not exceeded. The concept presented involves a biofilter upstream of a system to be protected. As biofilm growth is limited by the amount of nutrients available, the growth of biofilms in the biofilter will occur at the expense of the nutrients determined as biodegradable dissolved organic carbon (BDOC). Thus, downsteam of the reactor the nutrient concentration is reduced and less biofilm develops in systems. This concept has been investigated in an heat exchanger plant system with RO-systems and proved to be feasible.

Determination of microbial respiratory and redox activity in activated sludge

The tetrazolium salt 5-cyano-2,3-ditolyltetrazolium chloride (CTC) was used for the determination of metabolically active bacteria in active sludge. The method was adapted and optimized to the conditions of activated sludge. The colorless and nonfluorescent tetrazolium salt is readily reduced to a water-insoluble fluorescent formazan product via the microbial electron transport system and indicates mainly dehydrogenase activity. After more than 2 h incubation, no further formation of new formazan crystals was observed, although the existing crystals in active cells continued to grow at the optimal CTC-concentration of 4 mM. The dehydrogenase activity determined by direct epifluorescence microscopic enumeration did not correlate with cumulative measured activity as determined by formazan extraction. The addition of nutrients did not lead to an increase of CTC-active cells. Sample storage conditions such as low temperature or aeration resulted in a significant decrease in dehydrogenase activity within 30 min. The rapid and sensitive method is well suited for the detection and enumeration of metabolically active microorganisms in activated sludge. Extracellular redox activity was measured with the tetrazolium salt 3′-{1-[phenylamino-) carbonyl]-3,4-tetrazolium}-bis(4-methoxy-6-nitro)benzene-sulfonic acid hydrate (XTT), which remains soluble in its reduced state, after extraction of extracellular polymeric substances (EPS) with a cation exchange resin.

Sorption kinetics of tributyltin on Elbe river biofilms

For the first time detailed sorption kinetics of tributyltin on native Elbe river biofilms are presented. For this purpose a modified annular rotating continuous flow reactor has been used to develop a reproducible biofilm. Important parameters, such as flow rates, sheer forces, and nutrient concentrations could be varied independently and adjusted to natural conditions. Time-resolved sorption kinetics have been carried out with tributyltin, the most toxic compound in many antifouling paints. The highest sorption rates of tributyltin were observed during the first 0–10 min (0.60±0.05 μg Sn m−2min−1) than they decreased to a value of 0.10±0.10 μg Sn m−2min−1 (10–90 min) and increased to a value of 0.20±0.05 μg Sn m−2min−1 (90–120 min).

Bestimmung der stoffwechselaktiven Bakterien im Belebtschlamm

Die Bestimmung der Stoffwechselaktivitat ist ein zentrales Anliegen der Okologie der Abwasser-Mikroorganismen, da der Abbau von organischen Wasserinhaltsstoffen und die Stoffumsatzrate nur durch physiologisch aktive Organismen bestimmt werden. In der Regel wird die Aktivitat von Mikroorganismen im Abwasser uber die summarische Bestimmung von Stoffumsatzraten und Biomasseparametern charakterisiert. Diese summarischen Kenngrosen ermoglichen keine Aussagen uber die Verteilung der Stoffwechselaktivitat in den einzelnen Populationen. Fur das Verstandnis der Populationsdynamik und der Stoffumsatzraten im Abwasser ist zunachst die Erfassung der physiologisch aktiven Mikroorganismen auf zellularer Ebene eine wesentliche Voraussetzung. Die gleichzeitige Identifikation der stoffwechselaktiven Mikroorganismen uber Gensonden, um die wirklichen Akteure und deren Bedeutung fur die Stoffumsetzung im Abwasser zu charakterisieren, stellt in einem weiteren Schritt eine wichtige Aufgabe der Okologie dar.