Fate of Lignin in the Process of Aerobic Biological Treatment of Paper Mill Wastewater

Abstract

Although lignin is known to be not readily biodegradable the concentration of dissolved lignin decreased during aerobic biological treatment of paper mill wastewater performed in sequencing batch reactors (SBR). Systematic lab scale batch tests were conducted to clarify whether the observed removal of lignin was the result of biodegradation or adsorption onto the activated sludge. For the batch tests, sludge samples were taken from sequencing batch reactors operated at solid retention times (SRT) of 10, 15, 20, 30, and 40 days, respectively. The amount of lignin present in the bulk liquid and in the sludge samples was quantified by an analytical procedure comprising pyrolysis, gas chromatography and mass spectrometry (py‐GC/MS analysis). It was found that lignin adsorbs onto the activated sludge by up to 30%[TH]w/w. This demonstrates the sludge excellent adsorption properties. The ultimate removal of lignin is achieved by sludge wasting. The highest overall removal rate was found when sludge was used from the SBR run at SRT of 20 days.

Effects of biological treatment on the chemical structure of dissolved lignin-related substances in effluent from thermomechanical pulping

“…The pyrogram of PTE lignin indicated the typical lignin fragments found in spruce milled wood lignin, viz guaiacol and aromatics with a guaiacyl moiety, for example 4-methyl guaiacol, 4-vinyl guaiacol, isoeugenol, vanillin, homovanillin, and coniferyl alcohol (Helmreich et al 2001;Galletti and Bocchini 1995;Meier and Faix 1992). The vinyl, ethyl, or methyl substituents identified in the fragments are residues of the propanoic chains present in the original lignin molecules (Helmreich et al 2001;Galletti and Bocchini 1995).…”

“…The vinyl, ethyl, or methyl substituents identified in the fragments are residues of the propanoic chains present in the original lignin molecules (Helmreich et al 2001;Galletti and Bocchini 1995). The peak pattern from the PTE sample was analogous to the results for bleached TMP lignin .…”

“…Treated effluent, however, still contains various compounds that are difficult to remove by biological treatment. One such group of compounds is lignin-related substances, which persist despite the treatment and contribute significantly to the COD of the treated wastewater (Widsten and Laine 2003;Smook 2002;Helmreich et al 2001;Magnus et al 2000;Franta et al 1994). Growing demand for high brightness products has prompted the extensive use of bleaching chemicals (Lindholm 1999).…”

“…Removal of lignin in biological effluent treatment plants has been subject to investigation (Widsten and Laine 2003;Helmreich et al 2001;Magnus et al 2000;Jansson 1980;Ganczarczyk and Obiaga 1973). Several authors ascribe lignin removal to a combination of partial degradation and sorption to the biomass in the treatment plant (Magnus et al 2000;Helmreich et al 2001;Levine et al 1985;Ganczarczyk and Obiaga 1973).…”

“…Several authors ascribe lignin removal to a combination of partial degradation and sorption to the biomass in the treatment plant (Magnus et al 2000;Helmreich et al 2001;Levine et al 1985;Ganczarczyk and Obiaga 1973). There is, however, little information on how, and to what extent, lignin-related substances are affected by the mechanisms in activated sludge treatment plants.…”