Oxygen Control and Improved Denitrification Efficiency by Means of a Post-Anoxic Reactor

Abstract

Abstract:The presence of dissolved oxygen (DO) in biological denitrification reactors determines inhibition effects on the denitrification rate. The article shows the results of an experimental study to control the DO concentration in the pre-denitrification stage by a post-anoxic reactor. The results demonstrate that the post-anoxic reactor is very effective in improving the nitrogen removal efficiency because it causes a considerable reduction of the DO content in the mixed liquor recycle sent to the pre-denitrification reactor. This reduction is influenced by both the retention time and the F:M ratio (referred to the denitrification and the oxidation-nitrification volume). In fact, a retention time and a F:M ratio equal to 1.5 h and 0.130 kgBOD5 kgMLVSS in the pre-denitrification reactor and, consequently, a denitrification efficiency of 91%. Moreover, the contribution of the endogenous denitrification to the whole denitrification efficiency was found negligible. The paper contributes to the progress in nitrogen removal from sewage, a fundamental issue for a sustainable management of water resources. OPEN ACCESSSustainability 2015, 7 1202

Development of a Practical Tool for the Assessment of Biological Performances in Wastewater Treatment Plants

“…Biological denitrification is carried out under anoxic conditions by a broad range of heterotrophic bacteria through the process of nitrate dissimilation, in which nitrite and/or nitrate are used as the electron acceptor rather than oxygen [15]. As denitrification is often carried out after most of the organic matter has been consumed aerobically, it is necessary to add an organic carbon source [1,15,20]. The dissimilation reaction for denitrification is written to include the use of several common organic substrates, as follows: 5 CH 3 OH þ 6 NO À 3 !…”

“…Nutrient (N, P) removal is the basic requirement to reach high discharge standards in wastewater treatment plants (WWTPs). Discharge of treated wastewater with high residual nitrogen and phosphorous content may be the cause of eutrophication and reduced dissolved oxygen concentrations in receiving water bodies [1][2][3][4].…”

Trace Dissolved Oxygen Removal Using a Hydrocyclone to Enhance Denitrification

“…Several similar aeration strategies based on set points and a linear proportional‐integral (PI) controller have also been verified for feasibility , . A pre‐denitrification stage using a post‐anoxic reactor was also implemented and showed effectiveness in improving nitrogen removal due to a considerable reduction in the DO content in the mixed liquor recycle sent to the pre‐denitrification reactor . The residual DO was also decreased by less than 0.2 mg L −1 by the oxidation of Fe(II) .…”

Physico-chemical technologies for nitrogen removal from wastewaters: a review

“…communities, industrial plants, intensive livestock and farming, uncontrolled waste disposal) discharge many pollutants in water, including nitrogen (Urbini et al, 2015). Nitrogen is one of the causes of eutrophication, while some N-compounds (e.g., ammonia, ammonium, nitrite, nitrate, chloramines) can be harmful for human health.…”

“…At present, the dominant technology is pre-denitrification in activated sludge systems. Research advances in this field are mainly oriented to (i) evaluate the inhibiting effects of dissolved oxygen on denitrification rates (Raboni et al, 2014b;Torretta et al, 2014); (ii) limit, as much as possible, the presence of dissolved oxygen in the denitrification reactor (Urbini et al, 2015); (iii) highlight denitrification efficiency limitations in plants serving small communities due to strong fluctuations of the fed loads (Raboni et al, 2013a, Raboni et al, 2014a; (iv) evaluate the effects of the hydrodynamic behavior of the denitrification reactor (complete-mixing or plug-flow) on denitrification performance (Eramo et al, 1994;Farabegoli et al, 2003). With reference to industrial wastewaters, studies which highlight the inhibition effect of high ammonia concentrations on microbial activity suggest the use of alternative solutions based on physico-chemical processes.…”