Monitoring of the composting process using a mediator-type biochemical oxygen demand sensor

The pH, electrical conductivity, ammonia-nitrogen, chemical oxygen demand, carbon-to-nitrogen ratio, total organic carbon and biochemical oxygen deman d (BOD5) of compost extract solution and the moisture content and organic m atter content of solid compost samples were investigated as parameters for monitoring the composting process. It was observed that the BOD5 value of t he compost sample decreased dramatically from 355 to 33 mg L-1 during the p rocess. Compared with other parameters, the BOD5 value showed the largest c hange. However, the conventional method of BOD5 determination is not suitab le for process control owing to its time-consuming nature and the complicat ed procedures required. Thus, compost monitoring using a mediator-type BOD sensor consisting of Pseudomonas fluorescens biovar. V and potassium ferric yanide was investigated. In order to realize rapid and reproducible measure ments, we developed a 10-channel potentiostat system incorporating screen-p rinted disposable chips incorporating microorganisms immobilized in sodium alginate gel. Using sludge extract solutions as standard solutions for cali bration, it was found that aqueous extracts of the compost were most suitab le for BOD determination. In conclusion, the relative change in BOD sensor values determined using our system corresponded well with the BOD5 values o btained using the standard 5 d method during 58 d of composting.