This project aims at developing a biological alternative to the currently applied chemical pulping and bleaching methods by using microbes which produce lignin peroxidases.
The project is aimed at enlarging the use of biological catalysts to the processes of biopulping and biobleaching. The use of these bioprocesses can be expected to enhance the economies of the process as well as reduce the detrimental effects of present technology to the environment. The physiological studies which were aimed at evaluating and selecting strains isolated were successfully carried out. One of the target strains, Aspergillus niger was found to be able to cause extensive alterations on the lignin despite failure to detect the peroxidases known to effect lignin depolymerization in white rots. The A niger produces high levels of xylanases indicate that there are excellent prospects in being able to use this microorganism in the biobleaching of paper pulp.
Fermentation conditions necessary for the optimal solid state fermentation (SSF) for wheat straw delignification using P eryngii and T versicolour have been determined at laboratory scale.Work in the large scale SSF of straw is now in progress to evaluate the inherent energy saving during refining.
Research into biopulping and bleaching currently being carried out by Technology for Society (TNO) scientists could help paper manufacturers significantly improve their environmental credentials by drastically reducing energy consumption and cutting down on the use of dangerous chemicals.
In an attempt to overcome the shortcomings of mechanical and chemical pulping a biopulping process is being developed which relies on specially selected fungi to break down the lignin structure of wood. Assessments are also being made of the extent to which this process can be combined with enzymic bleaching. It has already been shown that increasing the concentration of hydrogen peroxide during this stage of the papermaking process will promote enzymic bleaching, but that high peroxide concentrations tend to restrict fungal growth. Research is therefore continuing to find the optimum concentration balance.
Electrolytic techniques are currently being used to generate hydrogen peroxide from oxygen already present in the reactive medium. Electrochemical methods are seen as being particularly promising as they are easy to control (by simply adjusting the electric current) and have no specialized transport and storage requirements.
By employing fungi to break down the lignin present in wood chips and to assist in the bleaching process, it is calculated that energy requirements could be cut by as much as a third. Added to this, fewer chemicals are likely to be required, which could significantly reduce the possibility of harmful pollutants being released into the environment.
The specific tasks of the project are: to isolate and characterize new microorganisms useful for application to lignin bio-degradation and compare them with already available ones;
to isolate the ligninase genes and study compatible host organisms for gene cloning, systems of preference will be the fungi Aspergillus niger or Penicillium chrysogenum and the yeast S. cerevisiae;
to clone and express the genes in one of these hosts and to compare the bleaching and pulping activity of the recombinant strains;
to compare in situ nonenzymatic and enzymatic peroxide producing systems;
to optimize the reactor design for the novel application of these biological systems to biopulping of straw, biobleaching of a kraft pulp paste and to the re-utilization of newspaper paste;
to conduct the experimental studies at pilot scale for making a technical and economical evaluation of an integrated biopulping and biobleaching process.
Funding SchemeCSC - Cost-sharing contracts
3700 AJ Zeist
W1R 8AL London