The current political situation imposes high demands on the economic feasibility of biogas plants. High prizes for biogas substrates and a trend to reduced feed‐in tariffs generated an increasing need to optimize substrate exploitation and operation conditions. This includes a comprehensive and reliable biogas process monitoring. For that purpose a number of different process monitoring methods like CH4 production rate, FOS/TAC (ratio of organic acid/total inorganic carbon alkalinity), pH or (auto)fluorescence are successfully applied. This paper will evaluate whether the surface charge — a parameter, which has not been in use so far — might also be suitable for biogas process monitoring. Since it is known that the surface charge is correlated with the adherence and floc formation capability of microbial cells, a change in surface charge might also reflect a change in the biogas process efficiency, or vice versa. To test this hypothesis, samples for the investigations were taken from a continuously stirred laboratory‐scale tank biogas reactor with continuously increased substrate load. The impact of the load change was measured with both, surface charge and a number of more established monitoring parameters as given above. It was found that the “surface charge” reflected well short‐term process changes (within hours) caused by an increasing substrate load in the reactor, though the highest short‐term monitoring sensitivity was obtained with the “FOS/TAC” monitoring. Different from other monitoring parameters like CH4, pH, or FOS/TAC the value of the parameter “surface charge” decreased with every feeding, eventually indicating a continuous deterioration of the biogas process conditions. Surface charge might therefore be of particular use as a complementary tool especially for the long‐term monitoring of biogas process conditions.

No abstract

The monitored natural attenuation (MNA) of groundwater contamination is in many cases considered to be a cost-effective and appropriate strategy to manage the remediation of contaminated aquifers. A prerequisite for the public acceptance of such NAremediation approaches is that the efficiency of the presumed NA-processes should be proven. This proof must be based on an extensive hydrogeological and in-situ characterization of the ongoing aquifer processes. Additional investigations of aquifer samples in the laboratory (microcosms) are often questioned because they are not representative. The aim of this research was therefore to evaluate and compare the microcosm-monitoring of degradation activity directly to results obtained from field investigations at the same site, a former coking plant in Castrop-Rauxel in Germany. The in-situ monitoring of the contaminant degradation at this site revealed a clear decrease in the concentration of the major contaminants, benzene and naphthalene along the flow direction of the plume. Furthermore, comparative isotopic analysis of the sulfur pools indicated that sulfate-reducing processes could play a predominant role in this degradation process. However, attempts to prove the microbial degradation of the organic contaminants directly by analysis of the isotopic fractionation of the contaminant carbon failed, especially in the case of benzene and naphthalene. The assumption that a very active microbial population was actually involved in the natural attenuation process of the prevalent contaminants at the site could be shown more convincingly with laboratory microcosm experiments. The two monitoring approaches therefore complemented each other very well and should therefore both be implemented in standard natural attenuation monitoring programs.

No abstract

No abstract