Ecology/environmental microbiology Performance of a horizontal-flow anaerobic immobilized biomass (HAIB) reactor and dynamics of the microbial community during degradation of pentachlorophenol (PCP) Elizabeth A. Baraldi a , Ma ´ rcia H.R.Z. Damianovic a, * , Gilson P. Manfio b , Eugenio Foresti a , Rosana F. Vazoller c a Laborato ´rio de Processos Biolo ´gicos, Escola de Engenharia de Sa ˜o Carlos, Universidade de Sa ˜o Paulo, Sa ˜o Carlos - SP, Brazil b Gereˆncia de Tecnologia Quı ´mica da Natura Inovaça ˜o e Tecnologia de Produtos Ltda., Cajamar - SP, Brazil c Laborato ´rio de Microbiologia Ambiental, Departamento de Microbiologia, Instituto de Cieˆncias Biome´dicas, Universidade de Sa ˜o Paulo, Sa ˜o Paulo - SP, Brazil article info Article history: Received 22 February 2008 Received in revised form 21 June 2008 Accepted 23 September 2008 Available online 17 October 2008 Keywords: Wastewater treatment Anaerobic biofilms Pentachlorophenol Methanogenic Archaea Methanol abstract The anaerobic biological treatment of pentachlorophenol (PCP) and methanol as the main carbon source was investigated in a horizontal-flow anaerobic immobilized biomass (HAIB) reactor at 30  1  C, during a 220-day trial period. The reactor biomass was developed as an attached biofilm on polyurethane foam particles, with 24 h of hydraulic retention time. The PCP concentrations, which ranged from 2.0 to 13.0 mg/L, were controlled by adding synthetic substrate. The HAIB reactor reduced 97% of COD and removed 99% of PCP. The microbial biofilm communities of the HAIB reactor amended with PCP, without previous acclimatization, were characterized by polymerase chain reaction (PCR) and amplified ribo- somal DNA restriction analysis (ARDRA) with specific Archaea oligonucleotide primers. The ARDRA technique provided an adequate analysis of the community, revealing the profile of the selected pop- ulation along the reactor. The biomass activities in the HAIB reactor at the end of the experiments indicated the development of PCP degraders and the maintenance of the population of methanogenic Archaea, ensuring the high efficiency of the system treating PCP with added methanol as the cosubstrate. The use of the simplified ARDRA method enabled us to monitor the microbial population with the addition of high concentrations of toxic compounds and highlighting a selection of microorganisms in the biofilm. Ó 2008 Published by Elsevier Ltd. 1. Introduction Pentachlorophenol (PCP) was the most widely distributed and commonly used of all chlorinated aromatic pesticides in most industrialized countries, and it is still used in some tropical coun- tries. The literature indicates that 80% of PCP production was destined for the preservation of wood [1]. PCP was frequently used as a solvent, similar to mineral spirits or diesel fuel. Over the years the continued use of PCP led to its accumulation in the food chain [2], causing public health problems involving increased cancer diseases. Despite Brazil’s regulations on environmental preserva- tion and recovery, some chlorinated aromatic compounds are still present in different areas as a ‘‘stock of hazardous chemicals’’, and more seriously, in areas of the southeast that underwent uncon- trolled industrialization in the early 1960s [3]. Today, the correlation between pollution and health is much more widely acknowledged in Brazil, leading to the need for the development of more research and the application of innovative technologies to treat hazardous wastes. PCP degrades in the environment by chemical and biological processes, and prokaryote and eukaryote species are active degraders of this compound in soils and sediments. These biolog- ical discoveries claim bioremediation is the best solution for the removal of toxic compounds. The reaction of reductive dehalogenation is the most well- known biochemical pathway to dechlorinate compounds such as PCP [4,5] under anaerobic conditions. Since 1990, the anaerobic process has proved to be an appropriate method for degrading PCP under methanogenic conditions. A good example of this is the fact that anaerobic treatment has already demonstrated a consistent capacity to treat chlorinated compounds such as PCP using UASB reactors [6–8], hybrid anaerobic systems and fixed film reactors [9–12], or even expanded systems using activated granular carbon as the support medium [13]. PCP removal efficiencies in the range * Corresponding author. Tel.: þ55 16 33738357; fax: þ55 16 33739550. E-mail address: marciadamianovic@terra.com.br (M.H.R.Z. Damianovic). Contents lists available at ScienceDirect Anaerobe journal homepage: www.elsevier.com/locate/anaerobe 1075-9964/$ – see front matter Ó 2008 Published by Elsevier Ltd. doi:10.1016/j.anaerobe.2008.09.004 Anaerobe 14 (2008) 268–274