Remote Monitoring of Floating Covers Using UAV Photogrammetry

Abstract

High-density polyethylene (HDPE) is commonly the material of choice for covered anaerobic lagoons (CAL) at wastewater treatment plants. The membrane floats on the wastewater, and hence is called a “floating cover”, and is used for odour control and to harvest the methane-rich biogas as a renewable resource to generate electricity. The floating cover is an expensive and high-value asset that demands an efficient methodology for the determination of a set of engineering quantities for structural integrity assessment. Given the dynamics of the anaerobic activities under the floating cover, the state of deformation of the floating cover is an engineering measurand that is useful for its structural health assessment. A non-contact measurement strategy is preferred as it offers practical and safety-related benefits over other methods. In collaboration with Melbourne Water Corporation (MWC), an unmanned aerial vehicle (UAV) assisted photogrammetry approach was developed to address this need. Following the definition of the appropriate flight parameters required to quantify the state of deformation of the cover, a series of periodic flights were operated over the very large floating covers at MWC’s Western Treatment Plant (WTP) at Werribee, Victoria, Australia. This paper aims to demonstrate the effectiveness and practicality of this inspection technique to determine the state of deformation of the floating covers measured over a ten-month period.

Detection of Defects in Geomembranes Using Quasi-Active Infrared Thermography

“…q = q conv + q rad (2) where q denotes the combined heat flux, and the subscripts identify the two contributions. According to Newton's law of cooling [22,23],…”

“…processes that go on in these lagoons and release biogas, odours, and greenhouses gases. These biogases also constitute a renewable energy source and each floating cover can capture up to 65,000 m 3 of biogas per day, which is used to produce 7 MW of electrical energy [2]. The expected service life of the membrane is from 50-90 years at an operating temperature of 50 °C, and more than a thousand years at 20 °C [3].…”

“…These covers capture the anaerobic processes that go on in these lagoons and release biogas, odours, and greenhouses gases. These biogases also constitute a renewable energy source and each floating cover can capture up to 65,000 m 3 of biogas per day, which is used to produce 7 MW of electrical energy [ 2 ].…”

“…The accumulation of scum can increase to various volumes and hardness. Some may stick to the underside of the cover and/or solidify over time [ 2 ]. Large accumulations of consolidated solid matter under the cover are called scumbergs.…”

Quasi-Active Thermography for Structural Health Assessment of Large Geomembranes

“…Since the raw sewage is untreated when entering the lagoon system, fats, oils, solids or other fibrous materials may eventually be transported to the surface of the lagoon under the cover [2]. This material, known as scum, can expand in spread and depth and become harder over time, potentially developing into a large solid mass that is referred to as a "scumberg" as parts of it may rise above the water surface level even when under the cover.…”