Nitrogen removal from wastewater using a double-biofilm reactor with a continuous-flow method Yuan-Lynn Hsieh a, * , Szu-Kung Tseng a , Yu-Jie Chang b a Graduate Institute of Environmental Engineering, National Taiwan University, 71 Chou-Shan Road, Taipei 106, Taiwan, ROC b Department of Environmental Engineering, Tung Nan Institute of Technology, 92 Wan-Fu Hamlet, Shen-Kun Village, Taipei 222, Taiwan, ROC Received 17 July 2002; received in revised form 1 November 2002; accepted 7 November 2002 Abstract Wastewater microorganisms of nitrification and denitrification were cultivated to compose two biofilm modules, termed the permeablesupportbioreactor(PSB)andthemembranefeedingsubstratebioreactor(MFSB).PSBandMFSBwerecombinedina single tank to develop a double-biofilm reactor, which was used to treat nitrogen contaminants in wastewater. With a membrane supplementofsubstrates(O 2 andCH 3 OH),theD.O.andCODlevelswereatalowvalueinthebulksolutionthusinhibitiveeffects betweennitrificationanddenitrificationwereminimized.Simultaneousnitrification/denitrificationwasconductedinthereactorand the double-biofilm reactor achieved high nitrification and denitrification efficiency, of 96.5% and 82%, respectively. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Nitrification; Denitrification; Biofilm; PSB; MFSB; Polyvinyl alcohol 1. Introduction Advanced wastewater treatment processes for nitro- gen removal are usually separated into two biological stages, namely––aerobic nitrification and anaerobic denitrification. The operating requirements differ sig- nificantly between these two. For example, nitrification tanks need a bulk solution with high D.O. but without organic carbon, while denitrification tanks require an anaerobic environment and an organic carbon source (Benfield and Randall, 1980). Consequently, in the two-stage de-nitrogen system, residual D.O. in the ni- trification tank generally inhibits the subsequent deni- trificationprocesswhileadditionalorganiccarboninthe denitrification tank either increases the effluent COD level or influences nitrification if the water is recircu- lated. The interference from substrates between nitrifi- cationanddenitrificationtanksusuallyreducesnitrogen elimination efficiency during advanced wastewater treat- ment. Two modules introduced here probably could im- prove the traditional method for treating nitrogen con- taminants. First, a silicone membrane fed oxygen to a biofilm, a system named the permeable support biorea- ctor (PSB). Second, a silicone membrane fed methanol to a biofilm, called the membrane feeding substrate bi- oreactor (MFSB). In earlier work, combining PSB and MFSB in a single tank was noted to develop a simul- taneous nitrification/denitrification system (Chang and Tseng, 1999). However, the autotrophic nitrifying mi- croorganisms had a low growth rate and were very sensitive to environmental conditions such as pH, D.O. (Campos et al., 1999), and organic matters, immobili- zationofthenitrifierswithpolyvinylalcohol(PVA)was introducedbyHsiehetal.(2002).ThePVA-immobilized bacteria on the tube allowed the formation of biofilm with high biomass concentration and could endure a long time of operation without sloughing off. This module was investigated by Hsieh et al. (2002) to achievea95%ammoniumremovalrateandwasnamed PSBinthispaper.TheMFSBmoduleinthisworkwas adopted from Chang and Tseng (1998), and it had sev- eraladvantages:(1)achievingahighdenitrificationrate (4.5gNm 2 d 1 ) and (2) substantially reducing residual COD level ( 6 50mgl 1 ) in denitrification. In this work, PSB and MFSB were combined in a singlereactorthatconductedsimultaneousnitrification/ denitrification,andthemajorsubstrates,O 2 andcarbon Bioresource Technology 88 (2003) 107–113 * Corresponding author. Fax: +886-2-23637854. E-mail address: r7541101@ms.cc.ntu.edu.tw (Y.-L. Hsieh). 0960-8524/03/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0960-8524(02)00274-2