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 isolated 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 wastewaters 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.