BOD5 estimation for pulp and paper mill effluent using UV absorbance

A novel method based on UV absorbance, is presented for estimating the BOD5 in pulp and paper mill effluent. This method could eventually be incorporated into an on-line sensor for BOD5 that is suitable for process control applications. Two streams, the reactor entrance and the final effluent, from two different mills were studied. One mill employed the Kraft pulping process, while the second mill was a thermo-mechanical one. The absorbance over the range 200-350 nm showed significant differences between the two mills. Because the two mills use very distinct processes, separate correlations were used to relate the absorbance to the BOD5 for both the mills. Results indicate that prediction of reactor entrance BOD5 was reasonable, whereas prediction of final effluent BOD5 was inaccurate, for both mills. Also studied was the effect of aeration on BOD5 results obtained at low BOD5 values for the Kraft mill.