Recalcitrant organics emerging from biological treatment of kraft mill effluents

Recalcitrant organic matter (ROM) in combined kraft mill effluents is that organic matter remaining in the effluents after primary and secondary treat ment. Recalcitrant organic matter comprises of both high molecular weight ( HMM) and low molecular weight (LMW) components and is of interest, since en vironmental regulators are considering placing limits on final effluent COD and colour. Biologically treated pulp mill effluent was fractionated by ul trafiltration to study the contributions of the high and low molecular weig ht recalcitrant organics towards final effluent COD and AOX Batch biodegrad ation tests were carried out on lab-generated biotreated effluent from lab scale sequencing batch reactors operating at 35, 45, 55 and 60 degreesC, to investigate if the residual recalcitrant fraction could be further degrade d. Biodegradation tests involved the optimization of the microbiological me dium by the addition of either an alternate carbon source (glucose) or a ca rbon-nitrogen substrate (yeast extract). Treatment temperatures and nutrien t levels were varied and the effect of each of these four factors on the bi odegradability of the recalcitrant fractions was studied. The recalcitrant portion was found to be resistant to further biodegradation, even under opt imized microbiological conditions. The HMW fraction of the ROM obtained fro m final biotreated effluent from a bleached kraft pulp mill (HMW ROMMill) w as studied for its ability to bind other organic model pollutants in an aqu eous environment. Pentachlorophenol (PCP) was tested for its binding onto t he HMW ROMMill, using toxicity as a surrogate parameter for binding, in the Microtox (TM) test. Equilibrium dialysis studies were carried out to inves tigate the ability of HMW ROMMill to bind C-14-Benzopyrene (BaP) and H-3-de hydroabietic acid (DHA). Microtox (TM) studies failed to indicate the bindi ng of PCP onto HMW ROMMill. BaP and DHA however did bind onto HMW ROMMill. BaP binding onto HMW ROMMill was higher than DHA binding, possibly due to i ts hydrophobicity. Also, increasing the dissolved organic carbon concentrat ion of HMW ROMMill led to a decrease in the partition coefficient values fo r both Bal? and DHA.