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Interaction between wastewater microorganisms and geopolymer or cementitious materials: Biofilm characterization and deterioration characteristics of mortars

Drugă, Bogdan, Ukrainczyk, Neven, Weise, Kira, Koenders, Eddie, Lackner, Susanne
International biodeterioration & biodegradation 2018 v.134 pp. 58-67
X-ray diffraction, acid tolerance, biofilm, calcium, cell respiration, cement, concrete, copper, light microscopy, microorganisms, municipal wastewater, polymers, scanning electron microscopy, sludge, thermogravimetry, wastewater treatment
This paper compares the biofilm formation during field exposure to real municipal wastewaters on geopolymer and copper-doped geopolymer mortar, with plain Portland cement and calcium aluminate cement as controls. The samples were submerged in a wastewater treatment plant at three different stages for 35 days (primary clarifier, activated sludge and final effluent), which led to diverse chemical and biological exposure conditions due to the different organic load of the three environments. The deterioration characteristics of the four different mortars were analyzed using X-ray diffraction, thermogravimetric analysis and optical microscopy. The formed biofilm was characterized by measuring the protein concentration at the sample surface and bacterial respiration. After wastewater exposure, the protein concentration on the Portland cement samples was 50% higher as compared to the geopolymer mortars, while the respiration rates on the Portland/calcium aluminate cement samples was 2.5 times higher than on the geopolymer doped with copper, suggesting a lower bioreceptivity for the latter material. Scanning electron microscopy revealed the presence of biofilm on mortar surfaces, especially on the samples exposed to organic-rich wastewaters. After being exposed to wastewater, the degree of degradation of the geopolymer-based mortars was much lower than the two controls. This may suggest that these materials can be a potential alternative to conventional cement-based binders in order to limit the growth of microorganism on concrete surfaces as well as exhibiting an enhanced acid resistance.