INTRODUCTION:

Pulp and paper industry is one of the highly polluting industries. The industry uses on an average 250 to 300 cubic meter of fresh water per ton of paper and nearly 75% of which is discharged as effluent.⁽¹⁾An important consideration of modern pulp and paper mill design and operation is to minimize losses from the process and to treat mill effluent so that their impact on the environment is minimum and essentially non-polluting. The driving force for pollution abatement is the protection of the quality of the environment for the benefit of present and future citizens. These concerns are translated by regulating agencies into specific criteria for limiting or controlling mill discharge. The implantation of pollution abatement programmes within pulp and paper industry is generally capital intensive and entails significant operating cost. This incremental cost attributed to pollution abatement is now accepted as a cost of operation and is usually passed on to the in the form of higher priced products.

The environmental impact of small pulp mills without chemical recovery in terms of BOD and COD is acute. Since several mills are operating at a capacity less than 100 tpd, chemical recovery option appears to be not techno economical viable.

A 30 tpd mill without recovery releases as much BOD and COD load as 300 to 500 ton per day modern mill. Increasing yield slightly improves this situation¹ From the lab experiments it has been clear shown that the new chemical additive phthalic anhydride (PA) has a positive effect towards pulp-yield and reduction in kappa number^{2, 3}. Although the work has been carried for wood, which has been adopted by, large paper mills where chemicals and energy is being recovered from the pulping liquor. The problem will be minimized if phthalic anhydride addition is adopted by the small paper mills based on non-conventional raw material where conventional recovery is not economic viable and pulping liquor mixed with other liquor with different stages is being discharged as a effluent contributing to major pollution loads and at the same time loosing energy in the form of both organic bio-mass and inorganic chemicals.⁴ Thus it is important to study the quality of effluent generated using new chemical additive phthalic anhydride. The object of the study was to evaluate the liquor for the pollution load vis-à-vis effect of phtahlic anhydride towards pollution loadin terms of COD and BOD.BOD is determined by measurement of dissolves oxygen (DO) in the sample. The DO content of 4 mg/l is essential for aquatic flora and fauna.^5,6 For this reason the BOD test is widely used to determine the pollution loads and the efficiency of waste water treatment system.COD is the measure of oxygen consumed during the oxidation of the oxidizable organic matter by a strong oxidizing agent. The intrinsic limitation of the tests lies in its ability to differentiate between the biologically oxidizable and biologically inert material.COD determination in that results can be obtained in about 4.5hours as compared to 5 days required for BOD tests.⁷ The ratio of COD/BOD predicts the suitability and ease of biological treatment or biodegradability of the effluent. Higher the ratio of COD/BOD lesser would be the response of the system towards the biological treatment.^8-11

EXPERIMENTATION:

Eucalyptus tereticornis (300 gms O.D) chips were cooked by kraft process in a electrically heated rotatory digester at different total alkali conc. (14 % to 18 %) using chemical additive (phthalic anhydride) or without additive (control) under conditions of total active alkali = 14 % to 18 %, Sulfidity = 20 %, Raw material to liquor ratio = 1:3.5, Temperature of cooking = 170 ⁰C, Temperature at 170 ⁰C = 90 minutes, Chemical additive (phthalic anhydride)doses = 0.2 %, 0.5 %,1.0 %,1.5 %

The cooked material was squeezed out on a nylon cloth and the spent liquor was collected in a bottles and the liquor was evaluated for its pollution properties like BOD^12,13and COD¹⁴ by standard methods

RESULT AND DISCUSSION:

The characteristics of spent liquor effluent obtained after pulping in terms of COD and BOD are shown in the folowing tables:

Table: 1.0 COD Values at different Chemical Charge

Additive Dose (%)	COD (kg/ton) Values at Different Alkali Concentration
Additive Dose (%)	14%	15%	16%	17%	18%
Control	45.6	45.9	46.25	46.65	46.95
0.2	45.10	45.30	45.90	46.35	46.50
0.5	44.40	45.00	45.60	46.05	46.35
1.0	44.44	45.00	45.60	46.05	46.35
1.5	44.44	45.00	45.62	46.08	46.35

Table: 2.0 BOD Values at different Chemical Charge

Additive Dose (%)	BOD (kg/ton) Values at Different Alkali Concentration
Additive Dose (%)	14%	15%	16%	17%	18%
Control	15.20	15.30	15.45	15.55	15.65
0.2	15.0	15.10	15.30	15.45	15.50
0.5	14.80	15.00	15.20	15.35	15.45
1.0	14.80	15.00	15.20	15.35	15.45
1.5	14.80	15.05	15.21	15.35	15.46

From the Table 1.0 and 2.0 it was observed that COD and BOD values of control spent liquor samples (without additive) were on slightly higher side in comparison to the spent liquor samples, where chemical additive phthalic anhydride was added with pulping chemicals.

The reduction in BOD was due to stabilization of carbohydrates against degradation; as a result less amount of hemicellulose comes in spent liquor after pulping, which decreases the BOD values

Fig. 1.0 and 2.0 shows that COD and BOD values of spent liquor decreases on increasing the additive doses up to 0.5 % and after 0.5 % it remains constant. There was no further decrease in COD and BOD values after 0.5 %, it means that same amount of biodegradable matter i.e. carbohydrate portion is present in spent liquor, hence the BOD remains constant after 0.5% additive.

The reduction in COD values of spent liquor at additive doses 0.2 % and 0.5 % at 14 % total active alkali was 1.10 % to 2.63 % against control. The reduction in COD at additive doses 0.2 % and 0.5 % at 15 %, 16, 17, 18 % total active alkali was 1.31 to 2.22 %, 0.76 % to 1.41 %, 0.64 to 1.29 % and 0.96 % to 2.16 % against control.

The reduction in BOD values at additive doses 0.2 % and 0.5 % at 14 % total active alkali was 1.32 % to 2.63 % against control. The reduction in BOD at additive doses 0.2% and 0.5% at 15%, 16, 17, 18% total active alkali was 1.31% to 1.29% and 0.96% to 1.28% against control.

The reduction of BOD and COD in chemical additive spent liquor samples in comparison to control samples was attributed due to stabilization of carbohydrate by phthalic anhydride when added along with pulping chemical to 2.00%, 0.97% to 1.62%, 0.64%

CONCLUSION:

Stringent legislation for pollution control has forced the paper industry to go in for suitable treatment of the effluents. However, before deciding the treatment system to be installed, it is essential to estimate the pollution load. The pollution load in any industry is measured in terms of its BOD, COD and TOC values, color etc. In the present work pollution load of is measured in terms of its COD, BOD, as these are the most commonly used parameters. The result reveals that there was reduction in COD and BOD values were phthalic anhydride chemical additive was used during pulping. The reduction in BOD is due to stabilization of carbohydrates against degradation during pulping ,as a result less amount of hemicellulose goes in spent liquor after pulping, which lead to reduction in BOD values. Hemicellulose is a main constituent that is responsible for increasing the BOD values, because lignin is non- biodegradable it does not take part in increasing the BOD values of any sample.

REFERENCES:

1. Singh, S.V., Naithani, S., Trends in Pulp and Paper Research and Development,IndianForestry New Trend, p.171,(1991)

2. Naithani Sanjay and Singh S.V.Chemical additives for accelerating delignification, IPPTA Vol 11, No3,Sept 1999.

3. Naithani Sanjay, Bhawana and Singh S.V Chemical additives for accelerating delignification Part II -Kraft pulping of Eucalyptus tereticornis,IPPTA Vol -13, No-1 , March 2001

4. Gupta, A., Studies on chemical composition and physicochemical properties of spent liquor from pulping of bagasse. Ph.D. Thesis, H.N.B. Garhwal University (1993)

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Received on 15.05.2011 Modified on 22.05.2011

Asian J. Research Chem. 4(8): August, 2011; Page 1302-1304