Numerical modelling of Quadric-Surfaced Sludge Digesters (QSD) within Wastewater Infrastructure using 3D Printing Techniques

Tota-Maharaj, Kiran; Ramroop, Navin

Abstract

The quadric-surfaced sludge digesters (QSDs), sometimes referred to as egg-shaped sludge reactors, are becoming more popular within wastewater treatment works as of recently. These tanked systems with their shell structure provide a surface free of discontinuities which is beneficial with regards to the efficiency during mixing and sludge settleability. QSDs do not produce areas of inactive fluid motion within the tank, sludge settlement and eventual grit buildup are prevented. The first principles models examined simulated Fused Deposition Modelling (FDM) or Fused Filament Fabrication (FFF), an additive manufacturing process for QSDs, under various loading parameters. A sludge digester of 25m in height and wall thickness of 500 mm (with materials of a 3-D printed polymer) was modelled and analysed with varying fill levels of 10%, 25%, 50%, 75% and 90% respectively. These simulated sludge fill levels were for both a fixed based and base isolated structure. The stresses developed in the shell of the sludge digester vary along the meridian and equatorial diameters. For this investigation two types of data were used, namely seismic maps of the Caribbean and electronic numerical time history acceleration records. The first principles numerical models included several iterations. The peak impulsive displacements varied between each model. The highest impulsive displacement occurred in the QSD with the lowest fill level (10% fill). This occurred for both the rigid base and isolated base models because of the smaller volumetric mass coupled with a lighter convective mass. By contrast, the lowest impulsive displacement occurred at 90% fill. The results of the study found that at a height of 3.1 metres from the base of the QSD, maximum peak displacement occurs. The base and at heights between 10 and 20 metres generated low displacements due to a rigidly fixed structure. The time-history analyses yielded favourable results when compared with the harmonic analyses. This is due to the transient decay of the frequency. The analyses did show an increase in the orthogonal stresses towards the apex of the QSD. On examining the results of the analyses, it was evident that internal stresses occurred in each orthogonal direction within the QSD.

• Journal Article Type: Article
• Acceptance Date: Apr 1, 2020
• Online Publication Date: Apr 27, 2020
• Publication Date: Apr 27, 2020
• Deposit Date: May 5, 2020
• Journal: Institute of Water Journal
• Peer Reviewed: Peer Reviewed
• Issue: 4
• Pages: 25-31
• Keywords: Quadric-Surfaced Sludge Reactor, Egg-Shaped Sludge Digester, Wastewater Treatment, Shell structures, Hydraulic Infrastructure, Seismic Activity, Fused Deposition Modelling (FDM)
• Public URL: https://uwe-repository.worktribe.com/output/5954810
• Publisher URL: https://www.instituteofwater.org.uk/journal/
• Related Public URLs: http://library.myebook.com/InstituteofWaterMagazine/journal-spring-2020/2412/