Bio-Utilization of Pulping and Bleaching Waste Waters
Report No 1367/1/05
Efforts are made by the pulp and paper industry to reduce the
chloroorganic and chloride discharges by the substitution of
chlorine-containing chemicals with other more environmentally friendly
bleaching agents such as hydrogen peroxide, oxygen and ozone. In
response to the environmental concerns and stringent emission
standards, modifications of the production process at the pulping and
bleaching stages have been developed that can reduce the levels of
absorbable organic halogen and toxic effect of the pulping and
bleaching waste waters. The bio-utilization of industrial waste waters
in production of high-value products such as enzymes and the use of
enzymes in bio-bleaching to reduce the chemical consumption of
chlorine-based bleaching agents present new environmentally sound
technologies that can significantly minimize the environmental impact
of the pulp and paper industry.
- Development of a bioremediation and biobleaching technology
to minimize the use of hazardous chlorine-based bleaching chemicals
which would produce certain economical benefits as well as reduce the
environmental impact of the pulp and paper industry.
- Development of a microbial fermentation technology of
pulping waste waters to obtain high-value products such as enzymes to
be utilized in a biobleaching process for environmental clean-up and
upgrading the quality of pulp and paper products.
Remediation of industrial waste waters from the pulp and paper industry
was investigated using bleaching with enzymes, biomimetic systems
(polyoxometalates) and microbial fermentation processes. The waste
waters under study were derived from the pulping and bleaching stages
of pulp production. Two industrial pulp types were examined for their
bleachability with enzymes: hardwood soda-aq pulp and bagasse soda-aq
pulp. Following enzymatic treatments, pulp properties such as
brightness, viscosity, kappa number, etc. were determined according to
the Standard Methods of the Technical Association of the Pulp and Paper
Industry (TAPPI, Atlanta, USA). Most of the waste water analyses such
as chemical oxygen demand, colour, solid content, etc. were carried out
as described in the Standard Methods for Examination of Water and Waste
Water (APHA, American Public Health Association, Washington, DC, USA).
Fermentation experiments for enzyme production were carried out in
shake flasks and bioreactors in batch and fed-batch cultures.
Evaluation of cultivation conditions was based on the levels of
xylanase activity produced. The efficiency of various approaches of
waste water bioremediation was evaluated mainly based on the impact on
chemical load, toxic effect, chloride content and chlorinated organic
waste water bioremediation
- Polyoxometalate (POM) pretreatment of hardwood soda-aq pulp
enabled chlorine dioxide savings of 10% compared to alkaline oxygen
control and 50% compared to the acid oxygen control while retaining
brightness at the control level.
- POM pretreatment of bagasse soda pulp could replace the
entire chlorine bleaching step without loss in final pulp quality. In
addition, up to 50% of the hypochlorite charge could be reduced without
deterioration of bagasse pulp properties.
- The use of POM in pulp bleaching represents an alternative
bleaching technology that can offer a significant reduction of the
consumption of chlorine-containing bleach chemicals with reduced
environmental impact. However, further studies are required to
demonstrate the reusability and economical viability and determine the
environmental impact of this technology.
Bio-utilisation of waste
water for xylanase production with the fungi Aspergillus oryzae and Aspergillus phoenicis
- It has been demonstrated that implementation of the enzyme
bleaching technology in the pulp and paper industry could improve the
existing technology of pulp and paper manufacture in a cost-effective
and environmentally friendly way.
- Biobleaching of bagasse pulp with xylanase (X) afforded
reductions in sodium hypochlorite (32%) and sodium hydroxide (20%).
Similarly, reductions of chlorine dioxide (30%) and sodium hydroxide
(20%) were possible during biobleaching of soda-aq pulp.
- Overall improvements in the bleach filtrate quality could
be achieved when xylanase treatment was employed prior to bleaching.
The major impact of the reduction of the active chlorine charges during
biobleaching was on the chloride, adsorbable organic halides (AOX) and
toxic effect levels (as determined by the bacterial growth inhibition
test) of the bleach waste waters. Overall, the AOX content correlated
well with the bacterial growth inhibition caused by the bleach
filtrates. It was evident that the use of chlorine containing chemicals
during bleaching was the major cause of bacterial growth inhibition in
the resulting waste waters. In addition, the reduction of the amount of
chlorinated compounds would minimize also their teratogenic effect.
- Introduction of a washing step between X and D1 stages
during soda-aq bleaching might prevent problems such as the overloading
of the plant waste water treatment system. The wash waters from the
xylanase stage might be treated separately or even utilised for
biotechnological applications. Alternatively, the xylanase-stage
chemical oxygen demand (COD) can be sent to the recovery system of the
mill where the organic matter will be utilized for heat generation and
use in the mill.
- The reductions in the use of bleaching chemicals would not
only minimize the impact of the pulp and paper waste waters on the
environment, but also lead to cost savings for the industry.
For instance, savings of 5.25 kg of ClO2/t pulp and 1.4 kg NaOH/t pulp
could be obtained as result of the enzyme bleaching. This can be
translated into cost savings in excess of R2 million per annum.
- A comparison of xylanase activities obtained with Aspergillus oryzae
NRRL 3485 showed that higher xylanase activities of up to 200 U/ml were
obtained in batch cultures than in shake flasks (30 U/ml) cultures
using the concentrated spent sulfite liquor (SSLc) as carbon feedstock
at 20-fold dilution.
- The fed-batch cultivation of A. oryzae NRRL 3485
using SSLc as carbon substrate yielded activities of up to 200 U/ml,
which was two-fold higher than activities obtained in batch cultures
under similar conditions (40-fold dilution).
- The chemical composition of the SSL waste waters revealed
that concentrating the waste water reduced the amount of acetic acid,
thereby minimising the inhibitory effect the acid may have on microbial
growth during utilisation of SSLc as carbon feedstock.
- The considerably high biomass concentrations obtained with
SSLc as carbon feedstock could be attributed to the utilisation of
additional carbon present in the SSLc, as is indicated by the total
organic carbon (TOC) results.
- Xylanase production using SSLc as carbon feedstock
indicated that the SSLc acted as inducer. Being a cheap
carbon substrate, xylanase production costs would be greatly reduced
and possibly enhance the economic viability of the biobleaching
- Xylanase production using SSLc was favoured by a high
culture pH of 7.5. The agitation rates between 400 to 800 rpm
did not have any adverse effect on xylanase production. A
better understanding of the limiting factor would enable even higher
activities being achieved.
- The xylanases from both A. oryzae NRRL and A. phoenicis
ATCC 13157 exhibited multiplicity. The A. oryzae xylanase
showed unusual pH and temperature optima not generally exhibited by
fungal xylanases. A higher level of pH stability was shown by
the xylanase preparations from this fungus.
- The application of SSL-grown fungal xylanases in
biobleaching resulted in a reduction in the use of active chlorine of
up to 30 %. The xylanases increased the pulp brightness by up
to 1.5 brightness points over the control. The application of
these xylanase enzymes, produced with SSLc as carbon feedstock is
- Xylanase production using SSLc as carbon feedstock
indicated that the SSLc acted as carbon source and enzyme
inducer. Overall, the xylanase yields in shake flasks
obtained with both A. oryzae and A. phoenicis on SSL-based growth media
were about 2-fold higher than those produced on xylan-based media.
Furthermore, the xylanase activities induced in batch cultures on SSL
and xylan were comparable.
- Since the carbon source in general constitutes 30-50% of
the total enzyme production costs, the eventual replacement of xylan
with SSL as inexpensive and abundant carbon substrate would result in
significant cost reductions associated with xylanase production and
enhance the economic viability of the biobleaching technology.
- It has been demonstrated that the implementation of the
enzyme bleaching technology in the pulp and paper industry could
improve the existing technology of pulp and paper manufacture in a
cost-effective and environmentally friendly way. The use of enzymes can
reduce the amount of chlorine-containing chemicals employed in
bleaching. This impacts directly on the levels of toxic effects,
chlorides and adsorbable organic halides of the waste waters.
- The use of polyoxometalates in pulp bleaching represents an
alternative bleaching technology that can offer a significant reduction
or complete elimination in the use of
chlorine-containing bleach chemicals. However, further studies are
required to demonstrate the reusability and economical viability and
determine the environmental impact of this
- The potential of pulp mill waste waters for biotechnical
utilization has been demonstrated. The bio-utilization of these waste
waters would alleviate problems associated with their discharge.
Furthermore, the xylanase enzymes produced on the spent sulphite liquor
could be successfully applied in biobleaching of pulp. This would
further contribute to the overall reduction of the environmental impact
of the bleach waste waters.