Low Energy High Rate Anaerobic – Aerobic Digestion (HRAAD) and Applications

Conventional aerobic technologies based on activated sludge processes have been widely applied for the treatment of domestic wastewater due the high efficiency realized, the possibility for nutrient removal, and high operational flexibility [1].  Unfortunately, the high capital and operation costs that coincide with the introduction of aeration-based technologies likewise impose significant financial constraints upon city and county that process large amounts of dilute wastewater [2].  The dissolution of oxygen is energy intensive, and results in the growth of significant quantities of biomass known as sludge, which requires further treatment/stabilization prior to disposal [3].  As such; reliable, unsophisticated, and cost effective treatment technologies have been proposed, including anaerobic treatment under anoxic conditions, as well as combined forms of anoxic with anaerobic treatment [4].  Of these, anaerobic pretreatment is perhaps the simplest and most conceptually attractive approach for domestic wastewater due to its relatively low construction and operational cost, operational simplicity, low production of excess sludge, production of energy in the form of biogas and applicability in small or large scale [5]. 

Anaerobic digestion can also be used as a pretreatment step prior to facilitate the use of low energy aerobic treatments used as a polishing step - reducing the organic load flowing into the aeration treatment basins can result in the production of less sludge that will, in turn, will reduce the amount of energy used in sludge handling (e.g., pumping, dewatering through belt presses, drying, trucking, and placing in landfills) [6].  In this presentation on-going research to design high rate anaerobic –aerobic digestion (HRAAD) reactors will be presented, as will results from their deployment in industry at demonstration scale.  Commentary on how the HRAAD can be integrated into businesses to achieve sustainable use of fresh water supplies in isolated city communities will also be presented along with the application of sand filtration to this system to produce an R1 effluent for agriculture.  Finally, the design of a novel unit operation that combines the elements of both a sand filter and a microbial fuel cell will also be discussed. 

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1.             Gavrilescue, M., et al., Acta Biotechnology, 19(2), 111-145 (1999).

2.             Kassab, G., et al., Bioresource Technology, 101(10), 3299-310 (2010).

3.             Dufresne, L., et al., Evaluation of Energy Conservation Measures for Wastewater Treatment Facilities. 2010, Environmental Protection Agency: Washington D.C.

4.             Chan, Y.J., et al., Chemical Engineering Journal, 1(55), 1-18 (2009).

5.             Lettinga, G., Antonie van Leeuwenhoek, 67, 3-28 (1995).

6.             Gohil, A., et al., Bioresource Technology, 97, 2141-2152 (2006).