Short communication Effect of nutrients on biomass activity in degradation of sulfate laden organics S.K. Patidar a , Vinod Tare b, * a Department of Civil Engineering, National Institute of Technology, Kurukshetra 136119, India b Environmental Engineering and Management Program, Department of Civil Engineering, Indian Institute of Technology, Kanpur 208 016, India Received 3 July 2005; received in revised form 3 July 2005; accepted 7 July 2005 Abstract The effects of key nutrients iron (Fe), nickel (Ni), zinc (Zn), cobalt (Co), and their combinations were investigated on the total methanogenic activity (TMA) and total sulfidogenic activity (TSA) of biomass metabolizing synthetic sulfate laden organics (COD/SO 4 2 ratio 3.5) in batch assays. In Phase I of the study, TMA and TSA were assessed twice for four feed changes in Cycle-I and Cycle-II. Nutrient combinations Fe–Co, Fe–Ni–Zn, Ni–Zn–Co and Zn have shown maximum TMA and/or TSA. Antagonistic effects of Ni on Co uptake by methane producing bacteria (MPB) and Zn uptake by sulfate reducing bacteria (SRB) were observed. In Phase II study, sustainability of effects of nutrients for best combinations was assessed in long duration study involving 10 feed changes. Assays with Fe and Co supplementation have shown maximum stimulation of MPB and SRB. # 2005 Elsevier Ltd. All rights reserved. Keywords: Biomass activity; Batch assays; Nutrients; Methane producing bacteria; Sulfate reducing bacteria; Sulfate laden organics 1. Introduction The performance of high rate anaerobic reactors depends on retention of highly active mixed culture biomass to metabolize complex organics using available electron acceptors. Microorganisms including methane producing bacteria (MPB) and sulfate reducing bacteria (SRB) present in mixed culture require various metal ions for enzymatic activities and growth. The trace metals have been identified as cofactors of enzymes and their bioavailability affect overall functioning of anaerobic digestion system due to their role in enzymatic activity, membrane stability, nutrient transport, and energy conservation in MPB and SRB. Fe is involved in energy metabolism and present in cytochromes, ferredoxins, hydrogenase, methyl transferase, APS reduc- tase, bisulfite reductase, formylmethanofuran dehydrogen- ase, formate dehydrogenase, ethanol dehydrogenase, lactate dehydrogenase, CO dehydrogenase, and aldehyde oxidor- eductase [1–3]. Cobalt has been found to be present in corrinoids, which are also involved in the activity of methyl transferase and CO dehydrogenase [4,5], and ATP sulfur- ylase [6]. Nickel is component of methyl coenzyme M, factor F 420 , factor F 430 , hydrogenase and CO dehydrogenase [7,8]. Zn has been found to be present in hydrogenase, CO dehydrogenase, ATP sulfurylase, and formate dehydrogen- ase [5,6]. Zn is also reported to be involved in coenzyme M activation during formation of methyl-coenzyme M [9]. Other trace metals Mo, Se and W are also reported to be present in various coenzymes. Metal ions availability depends on many factors including total metal concentration in the substrate, metal precipitation, metal chelation or complexation, and kinetics of precipitation and chelation reaction, etc. A unifying theory for the microbial availability of metal ions has not been reported [10,11]. Literature review reveals that lack of a complete understanding of the various metal transport mechanisms, synergism and antagonism between metal ions, identification of metal-specific chelators www.elsevier.com/locate/procbio Process Biochemistry 41 (2006) 489–495 * Corresponding author. Tel.: +91 512 2597792; fax: +91 512 2590260/ 2597395. E-mail address: vinod@iitk.ac.in (V. Tare). 1359-5113/$ – see front matter # 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.procbio.2005.07.001