A Fiber Bragg Grating (FBG)-Based Sensor System for Anaerobic Biodigester Humidity Monitoring

An operational, Fiber Bragg Grating (FBG)-based sensing system, specifically designed to monitor conditions in a harsh industrial environment is reported. The sensors used were placed inside tanks with high levels of methane (CH 4 ), carbon dioxide (CO 2 ) and hydrogen sulphide (H 2 S) gases and high relative humidity in the North Head sewage treatment plant in Sydney, Australia. The sensor system was developed primarily to monitor the effect of >98% relative humidity and temperature changes on the corrosion rates of various materials inside the tanks. Data have been obtained from the use of the system for eight months: these have been correlated with key climate data including the changing weather conditions experienced during the continued monitoring activity. The sensor system specifically developed has been shown to be sufficiently robust to work well, and safely, in such a harsh environment (due to the gaseous H 2 S and CH 4 present) with no signs of deterioration of the sensors or of the signals obtained from the system. The remote operation through flexible data transmission has allowed continuous and up-to-date monitoring of the conditions inside the tanks

Deterioration of alkali-activated mortars exposed to natural aggressive sewer environment

This study aims to evaluate the performance of low calcium fly ash based geopolymer (FA-GPm) and alkali-activated slag based mortars (AASm) in an aggressive sewer environment. Specimens were extracted from field exposure, after 6 and 12 months. Visual, chemical and physical analyses were performed to evaluate the deterioration. Surface pH was evaluated to identify the microbial induced corrosion (MIC) stage in each specimen. The neutralization depth of the specimens was measured by using the phenolphthalein indicator. Extensive microstructural analyses were carried out to assess the extent and type of deterioration of gel matrix by using techniques such as scanning electron microscopy (SEM), energy dispersive X-Ray (EDX), X-Ray diffraction (XRD) and Raman spectroscopy. Results showed greater depth of neutralization and surface pH reduction in FA-GPm as compared to AASm. Further investigation on penetration of sulphur confirmed much higher diffusion in FA-GPm as compared to AASm. XRD and SEM with EDX analysis showed the crystallization of thenardite and gypsum within the matrix of FA-GPm and AAS mortar, respectively, which was also, confirmed by Raman spectroscopy results. Extend of overall matrix deterioration was much higher in FA-GPm as a result of thenardite crystallization as compared to AASm after 12 months of exposure