Impact of Resin and Fatty Acids on Full-Scale Anaerobic Treatment of Pulp and Paper Mill Effluents

Wastewater generated during pulp and paper production usually contains large amounts of organic matter that may be converted to biogas through anaerobic treatment. These effluents can also contain a variety of inhibitors such as resin acids and long-chain fatty acids (RFAs) among other compounds. A multivariate data analysis was conducted with performance and water quality data from an anaerobic reactor at a pulp and paper mill, which provides unprecedented evidence for the long-term inhibitory effects of RFAs during full-scale operation. Although RFAs in the reactor influent did not cause serious process disturbance, they significantly contributed to the variability in the percentage removal of soluble chemical oxygen demand (percent sCOD removal) (similar to 45% to similar to 75%), as well as the variability in volatile fatty acid concentration in the effluent (2 to >20meq/L). Furthermore, a linear correlation was found between RFA concentrations in the reactor sludge bed and the percent sCOD removal. An effective strategy to remove RFAs before anaerobic treatment is upfront removal of particles within the primary clarifier. Based on an exploratory model, a graphical method is introduced that allows for quick assessment of the extent to which resin acids are sorbed to particles, and associated potential for upfront settling. When the pH of high-solids wastewater is below 7, the majority of resin acids will be associated with particles and a considerable fraction of these can therefore be removed by means of settling or floatation. Finally, a novel liquid chromatography-mass spectrometry method that rapidly quantifies major RFA constituents was developed. In the full-scale reactor, dehydroabietic acid (DHA) represented the bulk (similar to 92%) of the resin acids within the granular sludge. DHA in sludge warrants special attention and should be monitored closely.