Water Pollution Control in Pulp and Paper Industry
Water Pollution Control in Pulp & Paper Industry: Status & Overview<br />By:<br />VaibhavNautiyal<br />M.E. – Environmental Engineering<br />(2009-2011 Batch)<br />Roll No. – ME/ENV/04<br />Guided By:<br />Prof. (Dr.)S.K. Singh (Professor & Dean)<br />Deptt. Of Civil & Environmental Engineering<br />Dr. Bharat Jhamnani(Assistant Professor)<br />Deptt. Of Civil & Environmental Engineering<br />
Introduction<br /><ul><li>One of India’s oldest and core industrial sector
Highly capital, energy and water intensive industry
Highly polluting process and requires substantial investments in pollution control equipment
In India, around 905.8 million m3 of water is consumed and around 695.7 million m3 wastewater is being discharged anually by this sector</li></li></ul><li>Contd…<br /><ul><li>India’s current average fresh specific water consumption of about 150 m3/tonne of product is far above the global best specific water consumption of 28.66 m3/tonne (for large scale wood based pulp and paper mill).
This large gap is attributed to the use of obsolete technology/equipments and poor water management practices.
Indian Paper Industry accounts for 1.6% of the world’s production of paper and paperboard.</li></li></ul><li>Contd….<br />India produces 9.37 million tonnes of paper per year (2008-2009) through 525 paper manufacturing units with a capacity utilization of only 60%.<br />Large paper mill category is defined for those having a chemical recovery process and the production in excess of 24,000 TPA.<br />There are about 80 large pulp and paper mills with a total installed capacity to make 2.45 million tonnes per annum<br />
Segregation of Indian Mills (Basis: Raw material Use)<br />
Raw Materials<br />Hardwood<br />Bamboo<br />Various types of reeds and grasses<br />Agricultural Residues like wheat straw and bagasse<br />Note: Of these, bamboo accounts for nearly 60 to 70% of the total tonnage<br />
PULPING PROCESS<br /> It is the process by means of which the wood or agricultural residues are converted to a fibrous mass for onward processing into paper and board products.<br /><ul><li>Groundwood Pulping
White Water from Paper Machine</li></li></ul><li>Contd….<br />Gaseous Wastes<br />Evaporation Loss (Wood Preparation Stage)<br />Blow-system Emission<br />Smelt tank emission, Lime kiln emission, Recovery furnace emission, Evaporation emission from Evaporation Stage<br />Heat losses through Paper Machine<br />
Contd….<br />Solid Wastes<br />Bark Refuse, Wood particles and slivers sawdust<br />Knots fibres (Screening Stage)<br />Fiber losses during Washing and Thickening Stages<br />Fibers, Fillers and Brokes from Paper Machine<br />Broke and coatings during finishing and coating stage<br />
BLEACHING PROCESS<br /><ul><li>The principal aim is to increase the brightness of the pulp.
In the production of dissolving pulps, it is also regarded as part of the refining process.
In less highly refined pulps, it is regarded as removing wood extractives and bark specks and conferring superior strength characteristics.
Mechanical pulps are bleached using oxidative chemicals, predominantly hydrogen peroxide.</li></li></ul><li>
Chemical Oxidation<br /><ul><li>Complete oxidation to Carbon Dioxide and Water of organics found in Pulp, Paper & Paperboard mill wastewaters is the significant advantage
Oxidation with air under extreme temperature and pressure, and under ambient condition, in the presence of excessive amount of strong oxidants or Catalysts.
Oxidants used are Ozone (O3), Hydrogen Peroxide (H2O2) and Chlorine Dioxide (ClO2) whereas Catalysts used are certain metal oxides.</li></li></ul><li>Chemical Precipitation<br /><ul><li>Used to remove the colloids and colour from the wastewater streams.
Two processes are generally followed i.e. HOWARD Process and STRELLENERT Process.
The Howard Process is a precipitation with lime as a coagulant, in 3 stages to a final pH of 11.
The Strellenert Process is similar to Howard Process except the coagulant used is gypsum, and the liquors are heated to 160oC in pressure vessels; sulphur dioxide is evolved and reused in cooking liquors; lignin is precipitated and used as a fuel.</li></li></ul><li>BIOLOGICAL TREATMENT METHODS<br />
Anaerobic Lagoons<br /><ul><li>Have been used for the treatment of strawboard wastes and pulp and paper mill wastes.
A full scale anaerobic lagoon treating about 18,000 cu m/day of pulp mill wastewater gives 50 to 60% reduction in BOD in 20 days.
BOD Loading, g/m3/d - 30.0 – 45.0</li></li></ul><li>
Aerated Lagoons<br /><ul><li>One of the most popular low cost biological treatment methods.
Typical oxygen transfer devices utilize between 3 and 5 HP per 1000 cu m of wastewater and detention time ranging from 4 to 6 days, with nearly 80% BOD removal.
Dissolved oxygen content of 0.2 to 0.5 mg/l is necessary to sustain aerobic condition.
Mostly, aerated lagoons are used for treating total effluent from kraft pulp mills and can be used for treatment when land cost is moderate.</li></li></ul><li>
Activated Sludge Process<br />Most successful methods for treating pulp and paper mill wastewaters and these operate at high oxygen levels.<br />The normal drawbacks in the system are foaming in aeration tank, cost of nutrients and colour intensification.<br />If properly designed and operated, an activated sludge process will give very good treatment result.<br />
Drawbacks of ASP Systems<br /><ul><li>High solids content in clarified effluent due to too high or too low solids retention time and growth of filamentous micro-organisms.
Rising sludge, occurring when sludge that normally settles rises back to the surface after having settled.
Bulking sludge, which settles too slowly and is not compactable, caused by the predominance of filamentous organisms.
Insufficient reduction of organic load, probably caused by a low solids retention time; insufficient amount of nutrients such as P or N (rare in fisheries wastewaters); short-circuiting in the settling tank, poor mixing in the reactor and insufficient aeration or presence of toxic substances.
Odours, caused by anaerobic conditions in the settling tanks or insufficient aeration in the reactor.</li></li></ul><li>Plastic Media Trickling Filters<br /><ul><li>They can be operated at much higher hydraulic and organic loadings compared to the conventional filters.
Trickling filters that use plastic packing have been built in round, square, and other shapes with depths varying from 4 to 12 m (14 to 40 ft).
The plastic packings have a high surface area per unit volume (100 m2/m3), a high void ratio (95%) and are designed to provide uniform distribution of the wastewater.
Steam for Reuse in Pulp and paper Mills<br />Sale to Road Industry<br />Sale to Food Industry<br />Sale to Regional Market<br />Sulphate Furnace<br />Road Binder Plant<br />Vanillan Plant<br />Sale to Regional Market and Internal Use<br />Dry Sludge<br />Sulphite Liquor Reused<br />Incinerated<br />Sulphite<br />Reused<br />Sulphite<br />WasteLiquor<br />Fines<br />Fines<br />Paperboard Plant<br />Low Grade Wrapping Paper<br />Excess Fines<br />Ca(HSO3)2<br />Pulp Product<br />NaHSO3<br />Wood <br />Pulp<br /> Mill<br />Bark<br />Logs<br />Pressed Hardboard<br />Groundwood Pulp Plant<br />Steam Plant<br />Sale to Regional Market<br />Sale to World Market<br />Fine PaperMill<br />Concentrate Sulphate Binder Reuse<br />
Assuming that the total production of fine paper is 1000 tonnes per day. The remaining quantities are calculated based on this production as below:<br />Computation of trees at the complex<br />Production of fine paper = 1000 tonnes/day (907.2 kg/day X 103)<br />Fiber loss from papermill = 1.68% of production.<br />Therefore, suspended solids going into waste streams from papermill<br /> = 1.68/100 X 1000 = 16.8 tonnes/day (15.24 kg/day X 103)<br />Total wood pulp produced per day<br /> = 1000 + 16.8 = 1016.8 tonnes (922.44 kg X 103)<br />Quantity of sulphite liquor generated in wood pulp mill<br /> = 300 gallon/ton (1.24 X 10-3/kg) of pulp produced<br />White concentration of dissolved solids in sulphite liquor = 11%<br />Thus, dissolved solids going in sulphite liquor<br /> = 110,000 X 8.34 X 300 X 10-6<br /> = 275.22 lb/ton (1.376 X 10-1 kg/kg) of pulp<br />Total sulphite wastewater dissolved solids produced per day<br /> = 275.22 lb/tonnes X 1016.8 tonnes/day X tonnes/2000 lb<br /> = 139.9 tonnes/day (1.269 X 10-5 kg/day)<br />On an assumption that the amount of bark produced is generally 15% (by weight) of the pulp production. Therefore, bark production<br /> = 15/100 X 1016.8 = 152.5 tonnes/day (1.38 X 105 kg/day)<br />Total tonnage of trees used in the complex<br /> = 1016.8 + 139.9 + 152.5 = 1309.2 tonnes/day (1.187 X 106 kg/day)<br />
Groundwood pulp production<br />Recovery of suspended solids from paper mill = 16.8 tonnes/day (1.52 X 104 kg/day). <br />Assume that 100 tonnes (907.2 X 102 kg) of ground pulp is required for production every day.<br />Fiber loss in the groundwood pulp plant = 0.6 tonnes/100 tonnes of the groundwood pulp<br /> = 0.6/100 X 100 = 0.6 tonnes/day (544.3 kg/day)<br />Total groundwood pulp produced and lost per day<br /> = 100 + 0.6 = 100.6 tonnes/day (912.6 X 102 kg/day)<br />Therefore, used newspaper required<br /> =100.6 – 16.8 = 83.6 tonnes/day (758.4 X 102 kg/day)<br />Assuming 50% of the groundwood pulp is recycled and the remaining is used in the production of paperboard.<br />
Paperboard production<br />Loss of fines from groundwood pulp production is about 0.5% of the production.<br />Let us say that paperboard production = X tonnes/day<br />X + 5/100 X = 50 tonnes pulp/day (543.59 X 102 kg/day)<br />1.005 X = 50<br />X = 49.75 tonnes paperboard/day (451.32 X 102 kg/day)<br />Fines recovered from paperboard waste = 50 – 49.75 = 0.25 tonnes/day (226.79 kg/day)<br />0.25 tonnes/day of fines can be used to produce low grade wrapping paper and pressed hardboard. With no loss of fines and with a 50-50 product production split, 113.64 kg of each product can be manufactured.<br />
Sulphite Recovery<br />The solids concentration of spent sulphite liquor drawn from the digestors may vary from 6 to 16% with an average value of 11%. These solids may contain as much as 68% lignosulphonic acid, 20% reducing sugars, and 6.7% calcium. Complete evaporation of the sulphite waste liquor produces both a fuel which can be burned without an additional outside fuel supply and a salable by-product such as synthetic vanillan and road binder.<br />
Energy Management<br /><ul><li> Integrated production complexes have a significant advantage over conventional plants from the energy management standpoint.
Waste heat from one section of the complex can be used as a process heat for another section, the concept being minimization of waste heat. It is accepted that thermal discharges may result in anomalous stratification in the receiving basin, lowering of capacity to hold oxygen, increased reaction rates and metabolism. These effects vary significantly with the chemical and meteorological conditions associated with the water body.
The lethal effects of thermal pollution are sometimes obvious, whereas the sub-lethal effects on food chains and waste assimilative capacities are not easy to foresee without careful study.
The present industrial complex outlined can reduce waste heat discharged to the hydrosphere and atmosphere. The two significant areas of concern are:
Utilization of solid wastes from the plant to achieve energy efficiency.
Utilization of low grade heat from one section in another suitable section.</li></li></ul><li>Comparative Benchmarks(National & International)<br />
Status of R&D & Quality Control<br />One of the major reasons for the slow modernization of Indian pulp and paper industry till recent past has been a low level of investments on Research and Development (R&D) for the development of indigenous new technologies, process modifications, environmental management etc.<br />On an average, the R&D investment in pulp and paper sector of the country is less than 0.1% of the total turnover compared to more than 5% in developed countries.<br />Nearly 50% of the R&D investment comes from government agencies.<br />Most of the laboratories are equipped with instruments/testing facilities required for quality control of paper products. Only a few mills have full fledged testing facilities for other areas of paper making like raw material evaluation, black liquor analysis and environmental monitoring<br />
Cleaner Production Programme<br />Most of the mills are implementing cleaner production techniques and programme for improving their product quality as well as environmental status<br />Areas like raw material development and use, efficient water utilisation, adoption of energy efficient and green technologies, generation of green energy and careful control and management of environmental problems are being accorded top priority by most of the mills.<br />Mills are also working towards resource recovery/ optimisation by employing process automation and upgrading paper machines.<br />There has been increasing efforts by the mill for recycling/ reuse of process back water to reduce the effluent discharge and water consumption.<br />The application of biotechnology particularly enzymatic pre-treatment of pulp before bleaching is now gaining importance. The use of enzymatic pre-treatment of pulp has been demonstrated successfully in saving of bleaching chemicals (chlorine 12-15%) & AOX reduction by 20-25%.<br />