Organics Recovery from Waste Activated Sludge In-Situ Driving Efficient Nitrogen Removal from Mature Landfill Leachate: An Innovative Biotechnology with Energy Superiority

The sustainable recovery and utilization of sludge bioenergy within a circular economy context has drawn increasing attention, but there is currently a shortage of reliable technology. This study presents an innovative biotechnology based on free nitrous acid (FNA) to realize sustainable organics recovery from waste activated sludge (WAS) in -situ , driving efficient nitrogen removal from ammonia rich mature landfill leachate by integrating partial nitrification, fermentation, and denitrification process (PN/DN-F/DN). First, ammonia ((1708.5 +/- 142.9) mg center dot L -1 ) in mature landfill leachate is oxidized to nitrite in the aerobic stage of a partial nitrification coupling denitrification (PN/DN) sequencing batch reactor (SBR), with nitrite accumulation ratio of 95.4% +/- 2.5%. Then, intermediate effluent (NO 2 - -N = (1196.9 +/- 184.2) mg center dot L -1 ) of the PN/DN-SBR, along with concentrated WAS (volatile solids (VSs) = (15 119.8 +/- 2484.2) mg center dot L -1 ), is fed into an anoxic reactor for fermentation coupling denitrification process (F/DN). FNA, the protonated form of nitrite, degrades organics in the WAS to the soluble fraction by the biocidal effect, and the released organics are utilized by denitrifiers to drive NO x - reduction. An ultra -fast sludge reduction rate of 4.89 kg center dot m -3 center dot d -1 and nitrogen removal rate of 0.46 kg center dot m -3 center dot d -1 were realized in the process. Finally, F/DN-SBR effluent containing organics is refluxed to PN/DN-SBR for secondary denitrification in the post anoxic stage. After 175 d operation, an average of 19 350.6 mg chemical oxygen demand organics were recovered per operational cycle, with 95.2% nitrogen removal and 53.4% sludge reduction. PN/DN-F/DN is of great significance for promoting a paradigm transformation from energy consumption to energy neutral, specifically, the total benefit in equivalent terms of energy was 291.8 kW center dot h center dot t -1 total solid. (c) 2023 THE AUTHORS. Published by Elsevier LTD on behalf of Chinese Academy of Engineering and Higher Education Press Limited Company. This is an open access article under the CC BY -NC -ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).