Scientist E-1, CPPRI, Environmental Management Division, Saharanpur, U.P., India
Environmental Management Division, CPPRI, Saharanpur, India
Environment Research Institute, University of Petroleum & Energy Sudies, Dehradoon, India
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Release of AOX (Adsorbable Organic Halide) from pulp and paper industry is now the main environmental concern after statutory authorities notified and set the standard norms for AOX. To meet the norms, the source of release of AOX compounds and its concentration must be known for the treatment of effluent in a better way. This paper deals with the source of release of AOX compounds and its concentration in the particular effluent. The main source of release of AOX compounds are bleach plant effluent. Characterization of bleach plant effluents (Chlorination-stage, Extraction-stage, Hypo-Stage and Combined Stage) collected from agro based small pulp & paper mills and wood based large pulp & paper mills are done to know the AOX value in both type of industries. Characterization of bleach plant effluent shows that the E-stage effluent of bleach plant have high AOX value (88-109 mg/L) as compared to the other stage of agro and wood based mill. On other hand in agro based mills, AOX value is in higher range (95-109 mg/L) as compared to wood based mills (88 -98 mg/L) in E-stage effluent.
AOX, COD, BOD, Bleach plant effluent, C-stage, E-stage, H-stage.
The increased environmental awareness and strengthening of green movement and consciousness of the public in developed countries and developing countries has made adsorbable organic halide (AOX) a major environmental issue. The pulp and paper industries are considered as one of most pollutant releasing industries in the world which releases different type of pollutant including AOX (Thompson et al. 2001). Organically-bound chlorine, arising from the chlorination of lignin and extractives, is found in significant concentrations in bleached kraft pulp (Reeve, 1991). Identification & quantification of individual chloroorganic compounds is exceedingly complex and so generic measurement was desirable whereby the total total amount of chlorine bound to organic matter was quantitively determined (Odendahl, et al. 1990). The amount of AOX formed was linearly proportional to the total consumption of elemental chlorine in Cl2 & ClO2 (Axegard, 1989). The chloroorganic compounds collectively known as AOX formed during bleaching of the pulp with chlorine based chemicals was known to cause toxicity of aquatic life and tendency to bioaccumulate (Fraser and Reeve, 1992). Organochlorines are a group of chemicals including dioxins and furans, at least some of which are highly toxic to humans. Organochlorines are formed as a byproduct of the chlorine bleaching process in pulp mills (Hocking, 1991). Neilson (1991), has reported that the chlorophenolic compounds can become bound to natural matrices-particularly sediments-but there are inherent problems on the bioavailability of the compounds. Martinsen, et al. (1988), has optimized the process of determination of organo chlorine in the water and fish. The AOX measurement in the soil and water have shown that the halogenated compounds are more widespread than previously assumed and that there is substantial natural production of organo halogen in natural environment (Dahlman, et al. 1993). Many chlorinated phenolic compounds have been identified in influent of either commercial or laboratory bleaching of wood pulps with chlorine containing reagents (Suntio, et al. 1988). Bleach plant effluent from pulp mills contain chlorinated organic materials which are toxic and also highly coloured (Bajpai and Bajpai, 1994). The Indian pulp and paper mills use conventional pulping and bleaching process and use high elemental chlorine to attain the desired brightness. The effluent discharge from bleaching section contains large amounts of chlorinated organics and can be problematic in the environment, and the paper industry would prefer them not be discharged prior their characterization and treatment (Prasad and Joyce, 1993). Consequently, the level of AOX released in Indian pulp and paper mills are normally high as compared to developed countries. AOX value in bleach plant effluent is also depend upon the COD carry over with pulp going to bleaching section. In Indian condition COD carry over is high resultant in to high AOX value. At certain COD carry over, AOX discharge from softwood pulp bleaching were clearly higher than the hard wood pulp bleaching (Bloomberg, 1990). The recognition of large scale environmental contamination by organochlorines due to their formation in bleach plants, the industry implemented a number of process internal changes and continued to develop process external treatment processes. Understanding the factors controlling AOX and finding alternative institutional arrangements for implementation of control measures of AOX, before this the characterization of bleach plant effluents of wood based large mill and agro based small mills are necessary.
Bleach plant effluents from C –E-H stage (Chlorination, Extraction, Hypo Stage) and combined stage were collected from large wood based mill and small agro based mills and were characterized for different pollution parameter specially AOX levels.
Procedure for the Determination of Adsorbable Organic Halides (AOX)
It involves the adsorption of chlorinated organics onto activated carbon and then combustion at higher temperature in presence of oxygen followed by micro- coulometric titration of produced halides. This procedure was standardized in Germany in 1985 and known as DIN 38 409 Tail 14 AOX procedure. It has been adopted as a legally enforceable measure for control of chlorinated organic compounds in effluents.
The AOX procedure is considered to be the most suitable for adoption to the pulp mill effluents due to its simplicity, more accuracy and better reproducibility. The values of AOX are generally higher (Average 20%) than the TOCl values due to recovery of volatile chloro-organics. The advantages of AOX over the TOCl method are
- Better reproducibility
- Lower detection limit
- Higher percentage of recovery of volatile chlo- rinated organic compounds. Today AOX has been accepted as an standard monitoring and regulatory parameter for pulp and paper mill effluents world wide in preference to TOCl.
The testing procedure is given below
The organic halides adsorbed onto the activated carbon decomposed in presence of oxygen at 1000 ± 50 0C and thus formed hydrogen chloride is precipitated by silver ions in an acetic acid solution in microcoulometric titration cell. The silver ions consumed are replaced electrochemically and the generating current is integrated and displayed digitally as chlorine in test sample.
AOX Analyzer (Analytickjena, Germany) Method
DIN method is followed to measure AOX in liquid samples. The measurement of AOX involves;
- Pretreatment or Adsorption
- Microcoulometric analysis
Characterisation of Bleach Plant Effluent Collected From the Pulp and Paper Mills
Studies were initiated with the objective to determine the potential of AOX generation by conventional bleaching of pulp produced from raw materials commonly used in Indian pulp and paper industry i.e. agro based and wood based.
The three composite bleach plant effluent samples from C-stage, E-stage, H-stage and combined stage were collected from the one wood based mill and one agro based mill using conventional bleaching sequence These samples were characterized for various pollutional parameter main emphasis on Adsorbable Organic Halide (AOX). The wood based mill was mainly on based on woody mixed raw material and agro based mill was rice straw and bagasse.
The Characterization of bleach plant effluents collected from agro and wood based mill for different pollution parameters are given in the Table 1-2.
Pulp and Paper Mills in India are highly polluting industry and the level of pollution loads generated in Indian industries is higher compared to same industries operating in developed countries. The main reason of high pollution loads in the Indian pulp and paper mills are due to the use of mixed raw materials, obsolete technology and use of conventional bleaching technology (CEH). Bergbauer and Eggert, (1992), reported that bleaching of pulp fiber was done by chlorine as bleaching agent in chlorination stage and subsequently extraction stage which contribute most of the pollution load as AOX. Only few pulp and paper mills in India have adopted modern technology for reduction of AOX generation but others could not switch over to new and modern technology for reduction of pollution load at source due to high costs. The pollution load in the small pulp and paper mills using agro based raw material are higher than large pulp and paper mills using wood based raw material& this is due to most of the small agro based mills have not chemical recovery system and not any controlled over chemical consumption for bleaching of pulp. Gonzales and Zaroor, (2000) reported that softwood pulp contains high amount of resin and fatty acid and require high bleaching chemicals during conventional bleaching sequence as compared to hard wood pulp and resultant in high amount of AOX released in the effluent.
Characterization of different samples of bleach plant effluent collected from agro and wood based mill shows that agro based mill was having high pollution load in comparison to wood based mill. The level of AOX in agro based mill was higher as compared to that of wood based mill due to high usage of chlorine in agro based mill.
- The level of AOX in the C-stage effluent in agro based mill was varying from 72 to 83 mg/L but in wood based it was 41 to 55 mg/L.
- In the E-stage effluent of agro based mill the AOX level was 95 -109 mg/L and in wood based the AOX level was 88 - 98 mg/L.
- AOX level in H- stage of agro based mill was 45 -65 mg/L & 46 -60 mg/L in wood based mill. H stage effluent was having low AOX value in compared to other stage bleaching and all most total effluent recycled during bleaching stage
- AOX level in Combined bleach plant effluent of agro based mill was 55 - 76 mg/L and in wood based mill was 50 - 58 mg/L.
Mohta and Upadhyaya (2001) reported that about 70 % AOX level was contributed by first two stage of bleaching sequence, i.e., chlorination stage and extraction stage effluent. The level of AOX was higher in the Agro Mills due to use of high amount of elemental chlorine and no controlled over chemical consumption during bleaching stage for gain of higher brightness of pulp. Milosevich and Hill, (1992), also studied and shows that bleach plant effluent carry high value of AOX than the other stream. But large wood based mill used controlled and optimum dose of chlorine for bleaching purpose. Actually mills are using elemental chlorine due to low cost involved. Gergov, et al. (1988) also reported that toxicity of Extraction stage filtrate was rather high as compared to other stage effluent and it was even higher during bleaching with a higher chlorine dioxide concentration.
Other pollutional parameters like COD, BOD, Color, etc were also in higher range in bleach plant effluent of agro mills as compared to the wood based mill. Differences in level of other pollutional parameters like COD, BOD, TSS etc. may also be attributed to difference in nature of raw material used, process conditions, chemical used etc.
However, in India, the mills are still using conventional pulping and chlorine based bleaching processes resulting in high level of AOX toxic compounds which exerts toxicity to fauna and flora. The presence of inorganic salts makes bleach plant effluents unsuitable for reuse in the process primarily due to accumulation of inorganic salts, corrosion etc. As such in most of the mills the bleach plant effluent is just drained out to effluent treatment plant (ETP). Agro based mill require more strict watch on proper pulping with less carry over of black liquor and chlorine consumption in bleach stage is to be optimized for reduction of AOX level. Adoption of modern technologies to reduce AOX and other pollutants are capital intensive and so most of the Indian mills need to expand their pulp mill capacity to make these technologies viable. These mills are however required to operate the pulp mill under controlled conditions to reduce the kappa number and also to modify their pulp washing system to minimize the carry over of black liquor along with pulp in order to reduce the discharge of AOX compounds.
Mr. Akash Pandey is sincerely thankful (Director) Dr. N. Endley, Dr. S. Mishra and Dr. R.M. Mathur of Central Pulp & Paper Research Institute, Saharanpur U.P. India for their co-operation & encouragement during my work. He also appreciates, all other Scientists for their motivation and help during work.