Enhanced total nitrogen removal performance in a modified Orbal oxidation ditch system with internal nitrate recycle

Abstract

h i g h l i g h t sAn Orbal oxidation ditch with nitrate recycle for enhanced TN removal was developed. The optimal DO for SND was 0.15-0.25 mg/L. The highest TN removal was achieved at internal recycle ratio of 9.4. Nitrogen mass balances confirmed SND coupled with pre-denitrification. Nitrogen removal was closely related to bacterial community composition. a r t i c l e i n f o b s t r a c tA pilot-scale modified Orbal oxidation ditch with internal recycle of the nitrified liquor was developed to significantly enhance total nitrogen (TN) removal through simultaneous nitrification/denitrification (SND) coupled with pre-denitrification under the aerated-anoxic condition. Long-term operational results showed that the highest TN removal efficiency was achieved at very low dissolved oxygen (DO) of 0.15-0.25 mg/L and oxidation-reduction potential (ORP) of 10-40 mv within the outer channel. Appropriate internal recycle ratio played a significant role for increasing nitrates reduction within the outer channel, however, excessively high recycle flow deteriorated nitrogen removal instead because of diluted carbon source. At recycle ratio of 9.4, TN removal efficiency further increased to about 87% at optimal DO and pre-denitrification was responsible for TN removal improvement according to nitrogen mass balances. Molecular biology analysis revealed the correlation between variations in nitrogen removal and changes in bacterial community composition.

Nitrite oxidizing bacteria (NOB) dominating in nitrifying community in full-scale biological nutrient removal wastewater treatment plants

“…Research has shown that simultaneous nitrification and denitrification (SND) will be stimulated in an Oxidation Ditch, which benefits high TN removal (Zhou et al 2013). In this research, similar results were observed.…”

Identification and evaluation of SND in a full-scale multi-channel oxidation ditch system under different aeration modes

“…It was concluded that such a relatively low DO concentration was sufficient for nitrification, meanwhile, without inhibitory effects on denitrification at the presence of large macroscopical aerated-anoxic environment of the outer channel [17,27,28]. According to above results, it was likely that obvious SND was efficiently accomplished at a moderately low level of oxygen supply [13,16] in the outer channel which provided continuous alternation between anoxic and micro-aerobic conditions both in space and time to maintain equally high dynamic balances between nitrification and denitrification rates. force depended on the number of disc aerators under identical operational parameters.…”

“…Until now, SND phenomenons have already been successfully observed in lab- [11], pilot- [11][12][13][14] and even full-scale OD systems [15][16][17]. There were some principal explanations or presumptions for nitrogen removal via SND in oxidation ditches: (1) repeatedly swift alternation is between aerobic (after aerators) and anoxic zones (before aerators) of the mixed liquor in the same aerated channel based on inhomogeneous oxygen distribution [18]; (2) low-oxygen nitrification occurs at low sludge loading rate or long HRT and SRT [14,16,17], despite its nitrification rate is generally maximum value at DO of above 2.0 mg L À1 ; (3) anoxic zones are developed inside the activated-sludge flocs under aerobic conditions [14,19]; (4) novel microbes such as aerobic denitrifiers and nitrifiers adapted to low-oxygen conditions [16,20] are capable of performing SND.…”

Pilot Experimentation with Complete Mixing Anoxic Reactors to Improve Sewage Denitrification in Treatment Plants in Small Communities

“…Of particular interest are the experiences described by US-EPA, which shows how to upgrade plants in order to achieve fluctuation control [1], and in which more cautious design criteria are recommended for wastewater treatment plants (WWTPs) serving small communities [2]. With specific reference to the effects on biological denitrification, the scientific literature provides abundant information on nitrogen removal [3][4][5][6][7][8][9][10][11], but rarely refers to small WWTPs. The effects of raw sewage C/N ratio variations in small community WWTPs have been highlighted in the technical literature [12][13][14], which also show the possible negative side effects of dissolved oxygen accumulation in the denitrification stage.…”