STUDY ON TREATMENT OF ALKALINE BLACK LIQUOR USING SULPHATE REDUCING BACTERIA

Doan Thai Hoa
Hanoi University of Technology
Tran Dinh Man
Institute of Biotechnology, VAST
Abstract. Alkaline pulping liquors are the problematic for environment due to their toxicity and
poor biodegradability. During last decade, anaerobic treatment technology has been successfully
applied to various types of pulp and paper industry effluents. In the present study, the treatment
of highly toxic pulping liquors in lab-scale has been done using sulfate reducing bacteria (SRB)
isolated from sediment samples of pulp and paper mills in Vietnam. This treatment could reduce
70 – 75% of COD after three weeks. The COD removal could achieve 82 – 88% by subsequent
aerobic treatment in 48 hours. COD of treated water was 80 – 90 mg/l.
1. INTRODUCTION
Black liquors in modern intergrated pulp and paper mills are burnt for chemical
recovery and steam generation. In Vietnam, small-scale pulp and paper mills producing
more than two third of total pulp capacity (more than one hundred thousand tons per
year) have no recovery line and treatment of pulping liquor before discharging to the
receiving water.
Alkaline pulping liquors are the problematic for environment due to their toxicity
and poor degradability. The research has led to the proposal of a detoxification stragegy
denominated upfront dilution, based on the sequenced anaerobic-aerobic treatment of the
pulping liquors [1,2,3,4,5]. In this study, the treatment of highly toxic pulping liquors in
lab-scale has been done using sulphate reducing bacteria (SRB) isolated from sediments
of pulp and paper mills in Vietnam.
2. MATERIALS AND METHODS
2.1. Bacteria
Sulphate reducing bacteria were isolated from sediments of pulp and paper mills on
the Posgate B medium in anaerobic tubes. This medium contained (in grams per liter):
KH2PO4, 0.5; CaSO4, 1.0; MgSO4.7H2O, 2.0; FeSO4.7H2O, 0.5; NH4Cl, 1.0; Sodium
lactate 3.5; ascobic acid 0.1; yeast extract 1.0; agar 15. After sterilization at 121˚C in 30
minutes, the medium was supplemented with 1 mL of trace element solution and 1 mL of
vitamins solution per liter. PH was adjusted to 7.2 by using 5% solution of NaHCO3 and
Na2S (5% solution) was added for oxygen removal.
140 Doan Thai Hoa and Tran Dinh Man
Aerobic bacteria were isolated from sediments of pulp and paper mills on the Meat
– Pepton – Agar (MPA) medium. This medium contained (in grams per liter): meat
extract 3.0; pepton 10; NaCl, 5.0; agar 15 – 20. The medium was sterilized at 121˚C in
30 minutes.
2.2. Preparation of effluents
Pulping black liquors from three pulp and paper companies (Viet Tri, Hoang Van
Thu and Van Diem) were diluted with tap water. Nutrients ware added in the ratio BOD5
: N : P = 100 : 2 : 0.1
2.3. Analytical methods
Waste sample were analyzed for COD, SS and pH according to American Public
Health Association standard methods.
3. RESULTS
Alkaline pulping liquors were shown to be highly eliminated during aerobic waste
water treatment and were problematic for anaerobic treatment due to their toxicity to
methanogens and their relatively large fraction of inert lignin.
The research on biodegradation of the lignocellulosic solid waste was investigated
under both methane producing and sulphate reducing conditions. It was shown that the
total carbon mineralization under sulphate reducing condition was 2 – 4 times higher than
in methane producing condition. The degradation of lignin, which is generally considered recalcitrant under anaerobic condition, was also detected under sulphate reducing
condition [6].
a. Study on distribution of microorganisms in sediments from pulp and paper
mills
For total bacterial counts, 10 g of each sediment was mixed in 90 mL of sterilized
water contained 0.9% NaCl. The solution was shaked for 1 hours and then was diluted to
the folder of 1…10.
Added 1 mL of each diluted solutions to anaerobic tubes. Filled the tubes with
the prepared Posgate B medium and sealed with a rubber septum. After incubation at
37˚C in the period of 4 – 7 days the formed colonies of SRB were counted. These isolated
colonies were removed using Pasteur pipet and transformed to new tube contained Posgate
B medium.
Transfered 1 mL of each above diluted solutions onto petri dishes contained MPA
medium. These dishes were incubated at 37˚C in 48 hours. The formed colonies were
counted. The number of counted SRB and aerobic bacteria was given in Table 1.
CFU = Colony Forming Unit
Numbers of SRB in sludges polluted black liquors were higher than of sample in
nature and aerobic bacteria were especially high. The chosen bacteria (VT, HVT2 and
VD2) were natively tested and mixed for the growth on the Posgate B medium contained
Study on Treatment of Alkaline Black Liquor Using Sulphate Reducing Bacteria 141
Table 1. Total bacterial counts in sludge polluted black liquors
Pulp and paper mill SRB strain Total counts (CFU/g)
SRB aerobic bacteria
Viet Tri VT 1.5 x 104 2.6 x 1010
Hoang Van Thu HVT1 3 x 105
1.8 x 109
HVT2 2.5 × 106
Van Diem VD1 2.3× 106
1.4 × 1010
VD2 1.5 × 107
black liquors insteed of sodium lactate and with deducted FeSO4. The growth of these
bacteria was examined on the optical density at the wave length of 600 nm (OD600nm).
Table 2. The growth of isolated SRB in Posgate B medium containing black liquors
Sample SRB The growth of SRB (OD600nm)
1 week 2 weeks 3 weeks
Viet Tri VT 0.159 0.204 0.132
VT+HVT2+VD2 0.122 0.162 0.138
Hoang Van Thu HVT2 0.168 0.212 0.162
VT+HVT2+VD2 0.145 0.217 0.147
Van Diem VD2 0.167 0.228 0.167
VT+HVT2+VD2 0.122 0.162 0.111
It was shown that the SRB were able to develope on the medium contained black
liquor as carbon sourse by the following reaction:
Organic matter + SO2−
4
SRB
−→ CO2 + Sulphide
The produced sulphide by the oxidation of the lignin will be distributed in the
aqueous phase in three species, i.e. H2S, HS− and S2−. The hydrogen sulphide species
can be controlled by an increased pH. At higher pH nearly all the sulphide will be as HSin the aqueous phase [6]. During treatment pH of media was increased from 7.2 to 8.8 – 9
after three weeks (Table 3).
Table 3. The change of pH during alkaline black liquor treatment
Sample SRB strain pH
1 week 2 weeks 3 weeks
Viet Tri VT 7.59 8.30 8.42
VT+HVT2+VD2 8.74 8.84 8.93
Hoang Van Thu HVT2 7.42 8.82 8.78
VT+HVT2+VD2 8.59 8.82 8.90
Van Diem VD2 7.42 8.86 8.86
VT+HVT2+VD2 7.58 8.83 8.70
b. Study on biodrgadability of alkaline black liquors
142 Doan Thai Hoa and Tran Dinh Man
Pulping black liquors from three pulp and paper mills were analyzed for COD,
BOD5, SS and pH. The results were shown in Tab.4
Table 4. Wastewater characteristics of some pulp and paper mills in Vietnam
Paper mill COD, mg O2/L BOD5, mg
O2/L
SS, mg/L pH
Viet Tri 113800 59900 42000 12.6
Hoang Van
Thu
152600 72600 36000 10.6
Van Diem 109200 52900 40000 11.6
These paper mills used alkaline pulping method have neither recovery line nor
wastewater treatment due to very small capacity and economic problem. Their black
liquor effluents directly discharge to the rivers and cause heavy pollution to the aquatic
lives and people living at the delta of the rivers.
The chosen strains were used for treatment of pulping black liquor from the native
paper mills in the anaerobic – aerobic sequence. The black liquors were diluted to the
initial COD of about 600 mg O2/L and added with 1% (v/v) of culture medium. Anaerobic
treatment is performed in plastic bottles at room temperature (about 30˚C) by the native
strains. The samples were analyzed for COD and the result is given in Fig. 1.
Fig. 1. Removal CODs of pulping black liquors during treatment by SRB
An attempt was made using mixed three strains for the treatment of the pulping
black liquor. The COD was analyzed.
Using mixed sulphate reducing trains did not show better efficiencies compared to
using separate strains. The estimated removal of COD is 70 – 75%. After detoxification
by anaerobic treatment, the wastewater samples were added with aerobic bacterial culture
(1% v/v) and shaken for two days. The treatment efficiencies during anaerobic – aerobic
treatment are shown in Fig. 2.
Study on Treatment of Alkaline Black Liquor Using Sulphate Reducing Bacteria 143
Table 5. Removal of CODs of pulping black liquors by native and mixed strains
Sample SRB strain Removal of COD (%)
1 week 2 weeks 3 weeks
Viet Tri VT 4.8 27.7 75.6
VT+HVT2+VD2 5.7 36.8 56.0
Hoang Van Thu HVT2 8.3 45.9 74.4
VT+HVT2+VD2 5.6 47.6 71.8
Van Diem VD2 4.1 57.5 70.1
VT+HVT2+VD2 4.0 42.0 70.3
Fig. 2. The anaerobic (SRB ) – aerobic treatment efficiencies of pulping effluents
Anaerobic – aerobic treatment of pulping effluents by strains isolated from the sludge
of pulp and paper mills improved COD removal to 82 – 88%. The discharged effluents have
COD in the range of 80 – 90 mg/L, which is accepted by the column B of TCVN 5945
-1995.
An attempt was made in treating more toxic black liquor. The black liquor was
diluted to COD of about 1000 mg O2/L. The result of anaerobic – aerobic treatment was
given in the table 6.
Table 6. Removal of CODs of pulping black liquors by VT and mixed strains, %
Strain Anaerobic 3 weeks Aerobic 2 days
VT 81.9 90.5
VT+HVT2+VD2 63.8 87.8
Blank 1.0 1.5
The treatment efficiency was higher in case of more concentrated black liquor. The
adequate pulping black liquor concentration should be found under specific conditions.
144 Doan Thai Hoa and Tran Dinh Man
4. CONCLUSION
Pulping black liquors are toxic and poor biodegradable. These effluents can be
treated in anaerobic (SRB) – aerobic sequence. The discharged water is acceptable. Using
SRB can decrease the “green house effect” by reducing formation of methane and carbon
dioxide. Besides, SRB can precipitate the heavy metals in the form of sulfide salts. This
study should be enlarging to pilot scale before it can feasible for both technique and
economy.
REFERENCES
1. S. Kortekaas, G. Vidal, H. Yan-Ling, G. Lettinga, and J. A. Field, Anaerobic – aerobic
treatment of toxic pulping black liquor with upfront effluent recirculation, J. Ferment.
Bioeng. 86 (1) (1998) 97-110.
2. S. Kortekaas, H. S. Doma, S. A. Potapenko, J. A. Field, and G. Lettinga, Sequenced
anaerobic – aerobic treatment of hemp black liquor, Wat. Sci. Tech. 29 (5/6) (1994)
409-419.
3. R. Sierra-Alvares, S. Kortekaas, M. van Eekert, and G. Lettinga, The anaerobic
biodegradability and methanogenic toxicity of pulping wastewaters, Wat. Sci. Tech.
24 (3/4) (1991) 113-125.
4. R.W. Wilson, K. L. Murphy, and E. G. Frenette, Aerobic and anaerobic treatment of
NSSC and CTMP effluent, Pulp Paper Can. 88 T4-8 (1987).
5. J. Rintala, and P. Vuoriranta, Anaerobic – aerobic treatment of thermomechanical
pulping effluents, TAPPI J., 71 (1988) 201-207.
6. Mastui Saburo, Control of global warming by suppressing the methane emission from
landfill sites: A proposal, UNU International Symposium on Eco-Restructuring, 5-7
July 1993.
Received January 26, 2005.