RESEARCH ARTICLE BOD biosensors for pulp and paper industry wastewater analysis Merlin Raud & Marti Tutt & Eerik Jõgi & Timo Kikas Received: 28 May 2011 / Accepted: 9 February 2012 / Published online: 29 February 2012 # Springer-Verlag 2012 Abstract Introduction Two semi-specific microbial biosensors were constructed for the analysis of biochemical oxygen demand (BOD) in high-cellulose-content pulp and paper industry wastewaters. The biosensors were based on living cells of Bacillus subtilis and Paenibacillus sp. immobilized in an agarose gel matrix. Semi-specific microorganisms were iso- lated from various samples (decaying sawdust and rabbit manure) and were chosen based on their ability to assimilate cellulose. Materials & methods The biosensors were calibrated with the Organization for Economic Cooperation and Development synthetic wastewater, and measurements with different waste- waters were conducted. Results The response time of biosensors using the steady-state method was 20–25 min, and the service life of immobilized microorganisms was 96 days. Detection limit was 5 mg/l of BOD 7 while linear ranges extended up to 55 and 50 mg/l of the BOD 7 for B. subtilis- and Paenibacillus sp.-based biosensors, respectively. Repeatability and reproducibility of both biosensors were within the limits set by APHA—less than 15.4%. In comparison, both biosensors overestimated the BOD 7 values in paper mill wastewaters and underestimated the BOD 7 in aspen pulp mill wastewater. Conclusions The semi-specific biosensors are suitable for the estimation of organic pollution derived from cellulose, while the detection of pollution derived from tannins and lignins was minor. Better results in terms of accuracy and repeatability were gained with Paenibacillus sp. biosensor. Keywords Biochemical oxygen demand . BOD . Biosensor . Semi-specific biosensor . Bacillus subtilis . Paenibacillus sp. . Pulp and paper industry . Industrial wastewater 1 Introduction The pulp and paper industry has been considered to be a major consumer of natural resources (wood, water) and energy (fossil fuels, electricity) and a significant contributor to pollutant discharges into the environment. The paper manufacturing generates significant quantities of wastewa- ter, as high as 60 m 3 /t of paper produced (Thompson et al. 2001). This kind of industrial wastewater is very heteroge- neous and can potentially be very harmful to nature (Maximova and Dahl 2007). The major water pollutants are wood polymers, fillers, process and auxiliary chemicals, and their reaction products in the form of suspended solids and colloidal and dissolved matter. Concentrations of wood extractives in discharged wastewaters from kraft pulp mills and mechanical pulp mills vary between 0.4 and 11 kg per ton of pulp. Therefore, monitoring of pollution in pulp and paper industry wastewater is essential. Responsible editor: Philippe Garrigues M. Raud (*) : M. Tutt Institute of Chemistry, University of Tartu, Ravila 14a, 50411 Tartu, Estonia e-mail: merlin.raud@ut.ee E. Jõgi Institute of Technology, University of Tartu, Nooruse St 1, 50411 Tartu, Estonia T. Kikas Institute of Technology, Estonian University of Life Sciences, Kreutzwaldi 56, Tartu 51014, Estonia Environ Sci Pollut Res (2012) 19:3039–3045 DOI 10.1007/s11356-012-0817-0