Structural transformation of lignin from eucalyptus during chlorine dioxide bleaching

Enzymatic/mild acidolysis lignin was extracted from both unbleached and bleached eucalyptus pulp, and the difference in lignin structures was analyzed by nuclear magnetic resonance spectroscopy. The unbleached pulp lignin was chlorinated with chlorine dioxide, and the mechanism of adsorbable organic halide (AOX) formation was investigated. Chlorinated reaction products were detected by gas chromatography-mass spectrometry. There is a possibility of producing three different chlorobenzene or chlorophenol products from S/S lignin dimers that are connected with β-O-4 bonds. Based on quantum chemistry theory, three reaction pathways were investigated using molecular simulation techniques. The results showed that pathway 1 possessed the lowest reaction activation energy, which made it the most favored thermodynamically. The β-O-4 bond of the lignin dimer was cleaved. Following that scission, 2-chloro-3,5-dimethoxy-methyl benzene was the most likely product to be generated from the chlorination reaction of the syringyl unit. These results provide theoretical guidance for further reduction of AOX in chlorine dioxide bleaching.

Verification of a Method for Microcoulometric Determination of Adsorbable Organic Halide Pollutants in Natural, Drinking, Waste, and Treated Waters

A microcoulometric method is described for the determination of organic-halide pollutants at 2-2000 μg/L in natural, drinking, waste, and treated waters. The conditions for the adsorption of organic halides, using a microcolumn with activated charcoal-and for the desorption of inorganic halides-as well as for the pyrolysis process, were optimized for the successful determination of priority organic halide pollutants. An appropriate criterion was proposed to stop the desorption step. The mean recovery was 100.3%, and the mean relative standard deviation was 9.9%. The detection limit based on 3 times the standard deviation of the blank sample was 2 μg/L.

Decolorization and Detoxification of Extraction-Stage Effluent from Chlorine Bleaching of Kraft Pulp by Rhizopus oryzae

ABSTRACT Rhizopus oryzae, a zygomycete, was found to decolorize, dechlorinate, and detoxify bleach plant effluent at lower cosubstrate concentrations than the basidiomycetes previously investigated. With glucose at 1 g/liter, this fungus removed 92 to 95% of the color, 50% of the chemical oxygen demand, 72% of the adsorbable organic halide, and 37% of the extractable organic halide in 24 h at temperatures of 25 to 45°C and a pH of 3 to 5. Even without added cosubstrate the fungus removed up to 78% of the color. Monomeric chlorinated aromatic compounds were removed almost completely, and toxicity to zebra fish was eliminated. The fungal mycelium could be immobilized in polyurethane foam and used repeatedly to treat batches of effluent. The residue after treatment was not further improved by exposure to fresh R. oryzaemycelium.

Biotreatability test of bleach wastewaters from pulp and paper mills

Research is focused on an integrated way to simultaneously optimize the bleaching operations and subsequent wastewater treatment for pulp and paper mills. Bleach wastewaters from ClO2-bleached pulping studies at Institute of Paper Science and Technology (IPST) were used as the feed for batch reactors to test and rank the treatability and kinetics. The key aspect of the system is the use of sequential anaerobic/aerobic phases to enhance reductive dehalogenation of chloro-organic materials. Two continuous reactor systems, one operated in an anaerobic-aerobic mode and a second in an aerobic-aerobic mode, received bleaching wastewater obtained from a full-scale plant. Acclimated cultures from both continuous reactors were used to quantify the AOX (Adsorbable Organic Halide) and COD removal from various bleaching wastewaters. In general, the sequential anaerobic/aerobic treatment of bleach wastewater can improve both biotreatability and degradation rates.

Adsorbable Organic Halide Removal Mechanisms in a Pulp and Paper Mill Aerated Lagoon Treatment System

The aerated lagoon treatment system of a New Zealand pulp and paper mill exhibited 65% removal of adsorbable organic halide (AOX). This value is high compared to published data and an assessment was made of possible mechanisms for the observed AOX removal. Much of this removal took place in a short section (3.3 hour residence time) of the system's main lagoon. The initial AOX decrease in the aqueous phase could be achieved in part by settling of AOX-containing suspended solids from the influent wastewaters and by alkaline dehalogenation. In addition, lime and bacterial solids present in the treatment system were able to adsorb AOX from the influent wastewaters. Only a small proportion of the organic chlorine removed was found in sludges. A mass balance of aqueous and solid phases indicated that over 99% of the removed AOX was mineralised.

Anaerobic-Aerobic Lagoon Treatment of Kraft Mill Effluent for Enhanced Removal of AOX

A continuous-flow sequential anaerobic-aerobic lagoon treatment process was developed and evaluated for removal of adsorbable organic halide (AOX) from whole-mill kraft effluent at both laboratory and pilot-scale. The rationale underlying the development of the process was that the AOX removal efficiency of aerated lagoons currently in use might be significantly increased through relatively simple modification. Bench-scale studies showed that sequential anaerobic-aerobic treatment of whole-mill kraft effluent resulted in AOX-removal efficiencies of over 70% at hydraulic retention times (HRTs) of 10 days, 5 days and 2 days. In contrast, only 20%, 35% and 36% removal was obtained in a control aerobic lagoon. Pilot-scale studies showed that up to 65% removal of AOX from whole-mill kraft effluent was consistently obtained at HRTs ranging from 5 to 10 days. This compares with typical AOX removal efficiencies in conventional aerated lagoons of about 25%. Conversion of the anaerobic section in the pilot-scale lagoon from a simple sludge blanket to a combination of sludge blanket and submerged biofilm further increased AOX removal efficiencies to about 70%.

Investigation of Anaerobic Removal and Degradation of Organic Chlorine from Kraft Bleaching Wastewaters

A study of anaerobic removal of adsorbable organic halide (AOX) from kraft bleaching wastes has been conducted, using bottle bioassay techniques. The anaerobic cultures were fed either acetate or hydrogen and were able to remove from 40 to 65% of the AOX. The removal mechanism and the role of an adapted anaerobic consortium has been investigated with results indicating some biological removal, but significant amounts of sorption or degradation that does not seem to require microbial activity. Significant inhibition of methanogenic activity has also been found in some of the tests.

The Effects of Chlorination Conditions on the AOX and Chlorinated Phenol Content of Kraft Bleach Plant Wastewaters

A central composite experimental design was used to develop models of the yields of Adsorbable Organic Halide (AOX) and chlorophenolic compounds in wastewaters produced by bleaching oxygen delignified kraft pulps. The following five variables were used to control the bleaching conditions: total available chlorine, chlorine dioxide substitution, incoming kappa number, chlorination time and temperature. The total available chlorine and the chlorine dioxide substitution were the most important parameters in all the models developed. The yields (g.tonne−1) of AOX and total chlorophenolic compounds increased linearly with increasing total chlorine application. Elevating the level of chlorine dioxide substitution caused the yield of AOX to decrease linearly while the yield of total chlorophenols diminished in a non-linear manner. Increasing the level of chlorine dioxide substitution at a given total chlorine application is an effective means of reducing the emissions of both AOX and chlorinated phenols.