Detection of Defects in Geomembranes Using Quasi-Active Infrared Thermography

Abstract

High-density polyethylene geomembranes are employed as covers for the sewage treatment lagoons at Melbourne Water Corporation’s Western Treatment Plant, to harvest the biogas produced during anaerobic degradation, which is then used to generate electricity. Due to its size, inspecting the cover for defects, particularly subsurface defects, can be challenging, as well as the potential for the underside of the membrane to come into contact with different substrates, viz. liquid sewage, scum (consolidated solid matter), and biogas. This paper presents the application of a novel quasi-active thermography inspection method for subsurface defect detection in the geomembrane. The proposed approach utilises ambient sunlight as the input thermal energy and cloud shading as the trigger for thermal transients. Outdoor laboratory-scale experiments were conducted to study the proposed inspection technique. A pyranometer was used to measure the intensity of solar radiation, and an infrared thermal camera was used to measure the surface temperature of the geomembrane. The measured temperature profile was analysed using three different algorithms for thermal transient analysis, based on (i) the cooling constant from Newton’s law of cooling, (ii) the peak value of the logarithmic second derivative, and (iii) a frame subtraction method. The outcomes from each algorithm were examined and compared. The results show that, while each algorithm has some limitations, when used in combination the three algorithms could be used to distinguish between different substrates and to determine the presence of subsurface defects.

Thermographic Monitoring of Scum Accumulation beneath Floating Covers

“…According to Newton's law of cooling, the rate of temperature reduction of an object is governed by the cooling constant. In the convection cooling process, the cooling constant can be used to estimate how fast the temperature of the object decreased to the ambient temperature [9][10][11]. This paper is organised into two parts.…”

“…The exponential decay law in Equation ( 8) applies strictly only for the geomembrane in contact with air or biogas. However, as shown in our previous work [9][10][11], it is also possible to allocate a value of the cooling constant for regions where the geomembrane is in contact with soil (simulating scum) by fitting the (measured or calculated) thermal transients to an exponential decay law.…”

“…The thermal properties of each material are summarised in Table 5. The emissivity of the HDPE geomembrane at the WTP is approximately 0.9 [9][10][11]. The thermal expansion effect of the HDPE geomembrane was neglected in this study because The FE model was used to analyse the temperature change on the HDPE geomembrane, using the measured solar intensity and ambient temperature as inputs.…”

“…This paper investigates the potential of a novel thermographic technique for detecting and monitoring the semi-solid and solid scum under the floating covers at the WTP. The main aim of this paper is to provide a preliminary assessment of a novel quasi-active thermographic approach [9][10][11] as a quantitative methodology to classify the state of scum formation.…”

Comparison of Optimisation Algorithms for Centralised Anaerobic Co-Digestion in a Real River Basin Case Study in Catalonia

“…This potential for biogas generation could be translated as well to a source of renewable natural gas, which has specific composition requirements that demand high-tech sensors to assure its quality no matter its origin, as those developed in [15,16]. Due to their potential for resource recovery and the further implications in the water-food-energy nexus, WWTPs have been a research focus from different areas of Sensors 2022, 22, 1857 2 of 20 expertise: from modelling and engineering design [17][18][19][20][21][22][23][24] to process dynamics, simulation and integration [25][26][27][28].…”