Abstract
The paper summarizes the state-of-the-art of the most recent advances in biological nitrogen removal, including process design criteria and technological innovations. With reference to the Modified Ludzck Ettinger (MLE) process (pre-denitrification and nitrification in the activated sludge process), the most common nitrogen removal process used nowadays, a new design equation for the denitrification reactor based on specific denitrification rate (SDNR) has been proposed. In addition, factors influencing SDNR (DO in the anoxic reactor; hydrodynamic behavior) are analyzed, and technological solutions are proposed. Concerning technological advances, the paper presents a summary of various “deammonification” processes, better known by their patent names like ANAMMOX®, DEMON®, CANON®, ANITA® and others. These processes have already found applications in the treatment of high-strength wastewater such as digested sludge liquor and landfill leachate. Among other emerging denitrification technologies, consideration is given to the Membrane Biofilm Reactors (MBfRs) that can be operated both in oxidation and reduction mode.
Highlights
Nitrogen removal from wastewater can be achieved by means of physico-chemical or biological processes
Biological processes for nitrogen removal are generally applied to the denitrification of municipal wastewaters, and often to food and beverage processing industries, tanneries, fertilizer and petrochemical plants, as well as extensive livestock farm wastewaters
Other studies showed the effects of inhibition (Oh and Silverstein, 1999; Plòsz et al, 2003); in particular, significant effects of dissolved oxygen (DO) inhibition at concentrations as low as 0.09 mg L-1, with up to 35% denitrification reduction, were observed (Oh and Silverstein, 1999)
Summary
Nitrogen removal from wastewater can be achieved by means of physico-chemical or biological processes. As far as the former are concerned, many technologies are available, as discussed elsewhere (Raboni et al, 2013b; Capodaglio et al, 2015). The dominant technology is pre-denitrification in activated sludge systems, where an anoxic stage (DEN) is located upstream of an aerobic oxidation-nitrification (OX-NIT) stage. Research in this field is mainly focused on evaluating optimal sizing criteria for the denitrification reactor. Among the most recent developments in biological denitrification, the “deammonification” process (better known by its patented versions ANAMMOX®, DEMON®, CANON®, ANITA® and others) carried out by aerobic ammonia-oxidizing bacteria capable of degrading ammonia to nitrogen, has already found widespread application in the treatment of high-strength wastewaters such as digested sludge liquor and landfill leachate (US-EPA, 2009; 2010)
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