nitrifying granular systems: a suitable technology to obtain stable partial nitrification at room...

Separation and Purification Technology 74 (2010) 178–186 Contents lists available at ScienceDirect Sep aration and Purification T echnol ogy j o u r nal h o me p a g e : www.elsevier.com/locate/seppur Nitrifying granular systems: A suitable technology to obtain stable partial nitrification at room temperature J.R. Vázquez-Padín ∗ , M. Figueroa, J.L. Campos, A. Mosquera-Corral, R. Méndez Department of Chemical Engineering, School of Engineering, Rua Lope Gómez de Marzoa s/n, University of Santiago de Compostela, E-15782, Santiago de Compostela, Spain a r t i c l e i n f o Article history: Received 3 February 2009 Received in revised form 5 December 2009 Accepted 2 June 2010 Keywords: Aerobic granules Partial nitrification Nitrogen SBR Temperature a b s t r a c t The operation of nitrifying biomass as biofilms or granules allows the treatment of higher ammonia loads compar ed to the conventional act ivated sludgesystems, dueto the lar ge amountsof biomass accu - mulated inside the reactors. In the present work, a sequencing batch reactor (SBR) containing nitrifying granuleswith an averagediameterof1.9–2.9mm wasopera tedfor 880d atroom temper ature (18 –24 ◦ C). The obtained granule s prese nted high settli ng velocities around 100 m h −1 and low sludge volumetric index es of 30 mL (g VSS) −1 which indicated their good settling properties. When nitrogen loading rate (NLR) of 0. 4 g NH 4 + -N L −1 d −1 was fed, complete nitrification to nitrate was reached. The increase of the NLR to 0.8g NH 4 + -N L −1 d −1 caused a stable accumulation of nitrite with only 20% of nitrate production even by keeping the dissolved oxygen (DO) concentration in the bulk liquid at 8 mg O2 L −1 . Batch assays pe rf or me d ina range fr om2 to30mg O 2 L −1 of DO showedthat par tialnitrifi cat ionwasreached by fixin g the DO concentra tion in the range from 2.0 to 3.5 mg O2 L −1 in the bulk liquid. The total surface of the granul es to bulk liquid ratio was low and ranged from 58 to 216 m 2 m −3 being the oxygen mass transfer through the interface bulk liquid–granule surface the limiting step. This oxygen transfer limitation allowed reaching stable partial nitrification at room temperature. For more than one year, an effluent with a mean NO2 − /NH4 + molar ratio close to 1.0, suitabl e to feed a subseq uent Anammox reactor , was obtain ed. A maximal nitrite product ion of 1 g NO 2 − -N L −1 d −1 was reached without nitrite oxidation to nitrate. The bacteria populations in the granules belonged mainly to the genus Nitrosomonas and were placed in the external layer of the granules of 100 m. © 2010 Elsevier B.V. All rights reserved. 1. Intro ducti on Excess of nitrogen content in disposed wastewater causes oxygen deple tionand enha nces eutr ophiz atio n of the recei vingnatural streams. Nitr ogen is commonly present in wastewater in the form of ammonium, which can be removed by means of different treatment processes classified in two categories: physicochemical and biologic al proc esses. The use of the conventiona l biolo gi- cal nitrification–denitrification processes for nitrogen removal in wastewater treatment plants is recommended due to their lower costs compared to the physicochemical methods [1]. In orde r to apply this comb ined nitr ifica tion –den itrifi cation processes several aspects have to be taken into account. Firstly, the nitrification is generally the limiting process; therefore, it is important to promote the accumulatio n of large concentrations of nitrifyingbiomassinsidethe reac tors.This purpose canbe achi eved usi ng bio film sys tems where lar ge ret ent iontimes for nit rifi ers are obta ined.Nowaday s the opera tionof aerob ic gran ular biomass sys- ∗ Corresponding author. Tel.: +34 981 563100x16739; fax: +34 981 528050. E-mail address: [email protected] (J.R. Vázquez-Padín). tems is under study as a new approach to the biofilm systems. The development and operation of nitrifying granular sludge has already been reported [2–5]. Secondly, in order to achieve complete denitrification a certain amount of organic carbon source has to be available in the treated effluent. In many cases the addition of extern al org ani c matter is necessary wh ich causes an inc rease of treatment costs. In order to overcome this drawbacks several alternatives are und er stu dy bas ed on the use of the so- cal led “ni tri te route”, which is a shortc ut in th e ni trog en cy cl e based on the oxidation of ammonia to nit rit e and the fur ther reduction of the latter to nitrogen ga s. This route can be carried out according to two alternatives: (1) Combin ing the par tia l nit rifi cat ion of ammonium to nitrite and the subsequent heterotrophic denitrification using an organic carbon source as electron donor. This alternative involves the saving of aeration and addition of electron donor source costs in 25% and 40%, respectively, compared to the conventional nitrification–denitrification processes [6]. (2) Combining the partial nitr ification of half of the ammonia con- tai nedin the wa stewa ter fol lowed by the Anammox (an aer obi c ammonia oxidation) process. The Anammox process consists 1383-5866/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2010.06.003

nitrifying granular systems: a suitable technology to obtain stable partial nitrification at room...

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