Process Biochemistry 37 (2001) 81 – 86 Anoxic degradation of nitrogenous heterocyclic compounds by acclimated activated sludge Yongmei Li a , Guowei Gu a , Jianfu Zhao a , Hanqing Yu b, * a State Key Laboratory of Pollution Control and Resource Reuse, Tongji Uniersity, Shanghai 200092, People’s Republic of China b Department of Applied Chemistry, Uniersity of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China Received 11 September 2000; received in revised form 6 March 2001; accepted 25 March 2001 Abstract Batch experiments were conducted to investigate anoxic biodegradation of five refractory nitrogeneous heterocyclic compounds, i.e. pyridine, indole, quinoline, isoquinoline, 2-methyl quinoline, in coke plant wastewater. These compounds were effectively degraded by the denitrifiers in acclimated activated sludge within 60 h. The degradation rate was dependent upon chemical structures in the order: pyridine indole quinoline 2-methyl quinoline isoquinoline. Denitrification was a zero-order reaction, and the denitrification rate of individual compounds had a linear relationship with its corresponding molecular connectivity index. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Anoxic; Degradation; Denitrifier; Nitrate; Nitrogeneous heterocyclic compounds; Molecular connectivity index www.elsevier.com/locate/procbio 1. Introduction Wastewaters generated from coke-plants contain toxic organic pollutants, including phenols, thio- cyanate, free and complexed cyanides, polynuclear aro- matic hydrocarbons, aliphatic and heterocyclic compounds [1 – 4]. These compounds produce long-term environmental impacts, and are reported to be mutative and cancerogenic [5]. Coke-plant wastewaters also con- tain a high concentration of ammonia nitrogen, which is only partially removed by conventional biological treatment systems [6,7]. As a result, the existing biolog- ical systems are usually unable to meet discharge stan- dards in terms of organic matter and nitrogen [8–10]. It is therefore necessary to look for more efficient pro- cesses for coke-plant wastewater treatment. Nitrogenous heterocyclic compounds (NHCs) consti- tute nearly 40% total organic compounds in coke-plant wastewater [3,4,9], thus, biodegradation of these com- pounds has a substantial influence on the overall effi- ciency of a treatment system. NHCs are hardly removed, and even non-biodegradable in activated sludge processes [1,3]. Ganczarczyk [11] observed that some NHCs did not decompose in a conventional activated sludge process but accumulated in the wasted activated sludge, leading to potential pollution prob- lems when the sludge is subsequently disposed. On the other hand, NHCs can be mineralized by anaerobic bacteria [12,13]. The critical step in anaerobic degrada- tion of NHCs is partial scission of polycyclic and heterocyclic rings, cleavage of long chains, and degra- dation of these organics through anaerobic fermenta- tion [13]. The reactions involved in scission of rings and cleavage of chains include carboxylation, decarboxyla- tion, reductive deamination, dehydroxylation, demethoxylation, nitroreduction, hydration, hydrolysis, hydrogenation, and dehydrogenation [12 – 14]. NHCs generally undergo a ring reduction step in which anaer- obes produce, as a result of induction, a whole se- quence of enzymes which convert aromatic substrates into an ortho - or para -cyclohexane carboxylic acid derivatives, followed by cleavage of the ring [13,14]. These ring fission products are then funneled into the Krebs cycle through a variety of pathways, depending on the bacteria and culture conditions [15]. Unfortu- nately, anaerobic degradation of NHCs is relatively slow and thus less attractive for full-scale application [15]. * Corresponding author. Fax: +86-551-3631760. E-mail address: hqyu@ustc.edu.cn (H. Yu). 0032-9592/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII:S0032-9592(01)00176-5