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Lime treatment of wastewater in a plywood industry to achieve the zero liquid discharge
Journal of Cleaner Production 240 (2019) 118176
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Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Lime treatment of wastewater in a plywood industry to achieve the zero liquid discharge Hari Prasad a, Rajesh Kumar Lohchab a, *, Bhupender Singh b, Anil Nain a, Mikhlesh Kumari a a b
Department of Environmental Science & Engineering, Guru Jambheshwar University of Science & Technology, Hisar, Haryana, India Department of Basic & Applied Sciences, Bhagat Phool Singh Mahila Vishwavidyalaya, Khanpur Kalan, Sonepat, Haryana, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 9 April 2019 Received in revised form 8 August 2019 Accepted 25 August 2019 Available online 27 August 2019
The plywood manufacturing process involves debarking of log, peeling and pressing of ribbons of wood after glueing with proper resin, trimming, sanding and finishing. Washings of glue mixer, resin kettle and a glue spreader generate solids and various hazardous chemicals like phenol, sodium hydroxide and formaldehyde. To protect the environment and human health, it is necessary to treat and reuse the wastewater of plywood manufacturing. There are several methods available for the treatment of plywood industries wastewater and use of lime is one of them. In the present study viability of lime treatment was performed to achieve zero liquid discharge in a Plywood Industry. An optimum lime dose of 1.5 g/L was applied to the wastewater of melamine urea formaldehyde and phenol formaldehyde resin units. After treatment, removal of 28.6% and 41.2% total dissolved solid and 36.8% and 37.5% total suspended solid were observed in melamine urea formaldehyde and phenol formaldehyde resin units wastewater. Phenol and chemical oxygen demand removals were more than 38% and 40% from the wastewater of both units. Lime treated wastewater was used to prepare melamine urea formaldehyde and phenol formaldehyde glue/resin by mixing chemicals. The prepared resins exhibit characteristics within prescribed limits of plywood manufacturing. The mechanical and physical properties of plywood specimen have also found satisfactory. © 2019 Elsevier Ltd. All rights reserved.
Handling editor. Prof. S Alwi Keywords: Plywood Wastewater Chemical oxygen demand Total suspended solid Phenol Lime Phenol formaldehyde resin Melamine urea formaldehyde resin
1. Introduction With modernization, improved economic conditions and high living standards, the consumption of wood-based products i.e. paper, furniture, and plywood, a composite wood product etc., are growing day by day throughout the world. The composite materials have been widely used in industries like marine ships, space structures, automobiles and oil industries etc. (Her and Liang, 2004). Plywood is a composite laminated, unidirectional, fibre reinforced material. The original solid tree wood has major demerits such as material heterogeneity, anisotropy and dimensional instability so, it cannot be directly used for applications (Islam et al., 2012). Plywood is the most important homogenous composites
* Corresponding author. E-mail addresses: [email protected] (H. Prasad), rajeshlohchab@gmail. com, [email protected] (R.K. Lohchab), [email protected] (B. Singh), [email protected] (A. Nain), [email protected] (M. Kumari). https://doi.org/10.1016/j.jclepro.2019.118176 0959-6526/© 2019 Elsevier Ltd. All rights reserved.
wood product obtained from different trees species having their own superior merits as compared to solid wood that obtained directly from a tree (Younquist, 2000). It is preferred over plain wood due to better properties i.e. imperviousness, breaking strength, texture, shrinkage, twisting and swelling. Two types of plywood are prepared in the industry i.e. boiling water resistance (BWR) and moisture resistance (MR). BWR grade plywood is prepared by using PF resin. It is of better strength, high quality and high water resistance than MR grade plywood. The BWR costs high and used for exterior work. MR grade plywood is prepared by using urea formaldehyde based resin. It is of low strength and poor water resistance ability limiting its applications for interior work. The plywood manufacturing process involves debarking of log, peeling to make a continuous ribbon of wood and pressing of these ribbons after glueing with proper resin, trimming, sanding and finishing of plywood (Fig. 1). Various hazardous chemicals are being used in the woodbased industry for veneer bonding to make the plywood. Most of these chemicals not only affect the health of workers who are
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H. Prasad et al. / Journal of Cleaner Production 240 (2019) 118176
Fig. 1. Generic diagram of plywood manufacturing process and nature of waste generates.
associated with the industry and treatment plant but also affect the health of people in the vicinity of the industry. The ingredients for the preparation of resins are usually formaldehyde, phenol, sodium hydroxide, urea and acetic or formic acids. Out of these chemicals, phenol, sodium hydroxide and formaldehyde are more hazardous to human. The sources of these chemicals are washings of glue mixer, resin kettle and a glue spreader. The wastes are generated in different forms through all processes of wood conversion from raw material to the final product. Generally, plywood mills utilize preservative chemicals to treat wood, veneer and plywood. In plywood industry, the liquid wastewater generated from the washing of glue mixing machine and glue spreading machine forms the major share of total wastes generated. The wastewater generated from wood industry is mainly associated with lignin and its derivates, that resist the microbial degradation, and very less concentrations of it cause hormonal and toxic effects in aquatic environments (Klauson et al., 2015; Leiviska et al., 2009). Residues of formaldehyde and phenol in wastewater, even in traces, have longterm adverse impacts on human health (Table 1). To avoid degradation of environment and their impacts on the health of workers and people in the vicinity of the industry, adequate preventive steps should be an essential part of industrial actions and for disposal practices in plywood industry (Nath and Dhanapal, 2012). The major characteristics of plywood industry effluent are high chemical oxygen demand (COD), ammonia, phenol and total suspended solids (Sunny et al., 2016). The plywood industry wastewater is treated by several methods depending upon the type of waste generated, amount of solid contents and wastewater volume. The chemical precipitation technique is simple in operation and requires low capital cost, but it uses a large quantity of inorganic chemicals. The operational cost of such techniques is high due to the removal and disposal of a large quantity of sludge from the bottom of settling chamber (Kurniawan et al., 2006). Lime and limestone are the precipitants most commonly used due to their low cost and easy availability in most of the countries (Mirbagheri and Hosseini, 2005). Lime works very fast and removes a large no. of impurities within a specific time. Lime increases the pH of
wastewater, which enhances the precipitation and effective in removal of suspended impurities and organic matters. Lime neutralizes the suspended impurities resulting in destabilization of charged particles and their aggregation. Now it is possible to achieve zero liquid discharge (ZLD) by reducing the consumption of water and wastewater generation (Boller, 1997). Zero liquid discharge is a purposeful technique for wastewater management by recycling all type of liquid effluents that discharged from the plant or facility. It maximizes the water use efficiency and eliminates the risk of pollution corresponded with wastewater discharge, thereby making a balance in the exploitation of water and preservation of aquatic environment (Tong and Elimelech, 2016). The present study has been conducted to achieve the zero liquid discharge from MUF and PF resin units of plywood industry. In this research, wastewater originated from plywood industry was treated with lime and used to prepare the glue. This glue has been used for the manufacturing of plywood, and various properties of the plywood were studied to analyze the effects of wastewater reuse. 2. Material and methods The study was conducted in Parvatiya Plywood Pvt. Ltd. located at village Shivlalpur of Ramnagar in district Nainital of Uttrakhand, India. The industry has melamine urea formaldehyde (MUF) and phenol formaldehyde (PF) resin units that generated about 130 L and 310 L wastewater per week. Lime treated wastewater was used for the preparation of the resin without compromising the quality of plywood. The above process of plywood manufacturing by utilizing lime treated wastewater in resin/glue preparation was used to achieve zero liquid discharge. 2.1. Sample collection and analysis In both PF and MUF resin units wastewater contains large woody solid particles in suspension. To remove these particles, presedimentation was done before the lime treatment and the sludge was collected in different containers. After that, a dose of 0.5e2.5 g/L of lime was applied, and contents were mixed properly and allowed to settle for 2 h. Based on the removal of suspended solids, an optimum lime dose of 1.5 g/L was found suitable to treat liquid wastewater originated from PF and MUF resin units (Fig. 2). After settling of sludge, treated wastewater was used for the glue preparation. Treated as well as untreated wastewater samples were analyzed at the Department of Environmental Science and Engineering, GJU&ST, Hisar. Total dissolved solids (TDS), total suspended solids (TSS), total volatile solids (TVS), total Kjeldahl nitrogen (TKN), chemical oxygen demand (COD) and phenol of both samples were analyzed by using standard methods (APHA, 2005). Analysis of glue/resin flow time and solid content properties were observed by using B4 cup test of IS: 3944e1982 and ASTMD1259-06-2012 in Parvatiya Plywood Pvt. Ltd. according to standard methods of IPIRTI (Indian Plywood Industries Research and Training Institute).
Table 1 Effects of major chemicals on human health. Sr. No
Chemicals
Effects on Human Being
1. 2.
Formaldehyde Phenol
Gastrointestinal mucosa, respiratory distress, nausea, bleeding, vomiting, renal failure, pain, may be carcinogenic Coagulate protein; blister on skin, taken internally may cause death.
Source: Sharma (1994).
H. Prasad et al. / Journal of Cleaner Production 240 (2019) 118176
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3.1. Total solids
Fig. 2. TSS removal efficiency of lime for MUF and PF Unit's wastewater.
Total suspended solids (TSS), total dissolved solids (TDS) and total volatile solids (TVS) were analyzed and results are shown in Table 3. Total solids in untreated wastewater samples of MUF and PF resin application units were found to be 1900 mg/L and 1200 mg/L. After lime treatment, 36.8% and 37.5% removal of TSS was observed from the wastewater of the MUF and PF resin application units. TSS and turbidity are removed by using lime but their removal may be further increased by use of ferrous sulphate, ferric chloride etc. (Teh et al., 2016). The removals of 28.6% and 41.2% TDS and 38.7%, and 34.8% TVS were observed from wastewater of MUF and PF resin units. It is well established that the amount of lime, which increases the pH of the mixture to 12, is the most effective for flocculation (Aktas et al., 2001). Slightly higher removal of TSS and TDS was observed in case of treated wastewater of PF resin application unit. Our results were consistent with Mishra and Mohapatra (2012); they observed 24% removal of TDS with lime application in industrial wastewater treatment. 3.2. Total Kjeldahl nitrogen
Physico-mechanical testing such as glue shear strength, adhesions of piles, static bending strength and nail holding strength of plywood and other wood products manufactured using resin was done as per IS 1734(Part-4)-1983, IS 1734(Part-5)-1983, IS 1734(Part-11)-1983 and IS1734(Part-19)-1983. The weather resistance like shrinkage or swelling of plywood and wooden board were tested in a water bath container at 110 C as per IS 303e1989. The modulus properties of plywood specimens were observed using the static bending testing machine. The moment of elasticity (MOE) and moment of rupture (MOR) for plywood specimens were analyzed by using the standard method of practice (IS: 4990e2011).
Total Kjeldahl nitrogen (TKN) is the total concentration of ammonia and organic nitrogen. The untreated wastewater was having TKN content of 270 mg/L in the MUF resin application unit and 310 mg/L in PF resin application unit. After lime treatment, the wastewater of MUF and PF resin application units were comprised with TKN of 140 mg/L and 175 mg/L (Table 3). Removal of TKN from wastewater of MUF and PF resin application units were 48.1% and 43.6%. The higher removal of TKN was observed during the treatment of wastewater from the MUF resin application unit. 3.3. Phenol
3. Results and discussion Various methods had been used by a number of researchers for wood based industries wastewater treatment (Table 2). In present study, wastewater originated from MUF and PF resin application units of plywood industry was treated with lime and change in different parameters of wastewater are discussed below:
Phenol is highly toxic to human being, phytoplankton and zooplankton if present in wastewater beyond the permissible limit of discharge. It has adverse impacts on eyes, skin and mucous membranes in humans after acute inhalation or dermal exposures. Phenol concentration was 720 mg/L, and 1310 mg/L in wastewater originated from MUF and PF resin application units. After lime treatment, its removal was 50% and 38.5% with final concentration of 425 mg/L and 805 mg/L in wastewater of MUF and PF resin
Table 2 Wood based industries wastewater treatment by different processes. Treatment
Dose
Effluent
Parameters
Removal (%)
Reference
Lime
1.5 g/L
Wastewater of MUF & PF Unit (Plywood)
10 g/L
Wastewater (Olive Mill)
Lime
10 g/L
Wastewater (Olive Mill)
Alum
0.8 g/L
Black Liquor (Paper & Pulp)
Ferrous Sulphate
0.8 g/L
Black Liquor (Paper & Pulp)
Aluminium Chloride
0.8 g/L
Black Liquor (Paper & Pulp)
Ferric Chloride
0.8 g/L
Black Liquor (Paper & Pulp)
Ultrafiltration
e
Wastewater (Olive Mill)
40 36.8 & 37.5 41 & 38.5 48.1 & 43.6 41.5e46.2 29.3e46.9 60.5e80.1 72 73 60 11 46 12 42 13 48 16 50 60 37 30
Present study
Lime
COD TSS Phenol TKN COD Total Solid TKN COD TSS Phenol COD TSS COD TSS COD TSS COD TSS COD Total Solid Phenol
Aktas et al. (2001)
Boukhoubza et al. (2009)
Irfan et al. (2017) Irfan et al. (2017) Irfan et al. (2017) Irfan et al. (2017) El-Abbassi et al., 2014
4
H. Prasad et al. / Journal of Cleaner Production 240 (2019) 118176
Table 3 Physico-chemical properties of wastewater of MUF and PF resin unit. Sr. No.
1 2 3 4 5 6
Chemical Properties
COD (mg/L) TSS (mg/L) TVS (mg/L) TDS (mg/L) TKN (mg/L) phenol (mg/L)
MUF Application Unit
PF Application Unit
Untreated Wastewater
Lime treated waste water
Untreated wastewater
Lime treated waste water
4500 1900 815 210 270 720
2700 1200 500 150 140 425
4925 1200 675 340 310 1310
2950 750 440 200 175 805
application units (Table 3). The permissible limits of phenol are 1 mg/L and 5 mg/L for wastewater disposal in inland surface water and public sewers. Even after lime treatment, phenol in wastewater was found to be much higher in concentration than general standards of effluent discharge prescribed by Environment (Protection) Rules in schedule VI, Govt. of India. The advanced techniques using H2O2/UV-C process of phenol removal can be used to dispose off plywood industrial wastewater in inland surface water and public sewer (Rueda-Marquez et al., 2016). 3.4. Chemical oxygen demand Prior to biological treatment, initial COD and lignin removal is carried out by coagulation-flocculation process (Teh et al., 2016; Kamali and Khodaparast, 2015; Pokhrel and Viraraghavan, 2004). After addition of lime, the suspended impurities including resins were settled down at the bottom of the basin. It helps in the removal of COD and other pollutants from wastewater. COD of wastewater originated from MUF and PF resin application units were 4500 mg/L and 4925 mg/L. After lime treatment, COD of wastewater of MUF and PF resin application units was reduced to 2700 mg/L and 2950 mg/L (Table 3). About 40% removal in COD has been observed from wastewater of both the resin application units. The results of COD removal corresponded with the finding of Klauson et al. (2015). They achieved 37% COD removal in wood soaking basin water of plywood industry through coagulation. 3.5. Resin properties The quantity of wastewater collected after treatment was only 5e6% of the total water requirements of 4600e4700 L in resin manufacturing. The glue/resin was prepared by mixing chemicals in lime treated wastewater and make-up fresh water, and then its physico-chemical properties of viscosity and solid contents have been studied as below. 3.5.1. Viscosity The viscosity of glue affects the strength of joints. Greater the flow time, lesser will be the viscosity and it leads to a decrease in strength of joints (Budakci, 2010). The flow time observed at 85 C was 15 and 16 s for PF and MUF resins. The flow time recorded was within the standard value of 14e16 s of IPIRTI report. At room temperature, the flow time of PF and MUF resin was 25 and 26 s. These values were within the standard limits of 25 ± 2 s (IPIRTI, 2004e05). 3.5.2. Solid content Solid content is responsible for the stagnation of glue on veneer that affects the strength of plywood. Solid content reduces the emission of volatile gases like formalin if its value is within 48e50% (Bal and Bektap, 2014). As per IPRTI standards, solid content in resin should range from 48% to 52%. Solid content was observed 49.7% and 49.2% in PF resin and MUF resin, which was well within the
prescribed standard value. Similarly, Oh and Kim (2011) have reported 49% solid content in MUF resin, and Bekhta et al. (2015) observed 50% solids content in PF resin. 3.6. Physico-mechanical properties of plywood The resin prepared by using treated wastewater was used for adhesion of veneer for the manufacturing of plywood. The adhesion property of plywood has been tested with a standard size of the knife and 90e95% surface remained rigidly attached to adjacent veneers. Kamala et al. (1999) have been reported that about 95% of upper surfaces remain cohered and after water boiling it was 70e80%. The weather resistance of plywood and wooden board was tested in water bath container at 110 C and shrinkage, or swelling of both surfaces showed a dimension change within tolerance limit and categorized AA grade as per IS 303e1989. 3.6.1. Nail holding strength The nail holding power of plywood was observed 1320 kg/mm2 and 1275 kg/mm2 for wooden board and plywood specimens. The standard minimum value for nail holding strength is 1000 kg/mm2 (IS: 2202 1999). The values observed in our case were found to be greater than the standard value. Kamala et al. (1999) observed 1185 kg/mm2 of nail holding power of plywood. 3.6.2. Glue shear strength Glue shear strength for minimum average and a minimum individual test of three dry and moist plywood specimens has been conducted for BWR and MR grade of plywood and results are shown in Table 4. Glue shear strength of dry and moist specimens of BWR grade plywood was 1430 N/mm2 and 1140 N/mm2 for minimum average test and 1190 N/mm2 and 890 N/mm2 for a minimum individual test. For MR grade plywood, shear strength on the minimum average basis of three specimens was 1120 N/mm2 and 910 N/mm2 and on minimum individual basis was 840 N/mm2 and 720 N/mm2 for dry and moist specimens. A study by Gothwal and Mohan, 2010) reported 1472 N/mm2 and 1302 N/mm2 shear strength using PF resin at wood failure at 95% and 85% in the dry and moist state. 3.7. Modulus properties of plywood Modulus properties of plywood specimens observed using the static bending testing machine are shown in Table 5. For BWR and MR grade plywoods average values of MOE along the direction of grains observed for three specimens were 8009.2 and 6710.2 N/ mm2 and average values of MOR were 79.9 and 49.8 N/mm2. Minimum individual value observed for any specimen of BWR and MR grade plywood was 5472.6 and 5109.9 N/mm2 for MOE property and 67.1 and 39.5 N/mm2 for MOR property. For BWR and MR grade plywood, the average value of MOE for three specimens across the direction of grains observed was 4190.8 and 3984.5 N/ mm2 and the average value of MOR across the direction of grains
H. Prasad et al. / Journal of Cleaner Production 240 (2019) 118176
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Table 4 Shear strength observations of BWR and MR grade (N/mm2) plywood. Sr. No
Grade of plywood
Standard Minimum value
Dry specimen
Shear strength (N/mm2) Moist specimen
1350 1100 1100 800
1140 890 910 720
Result value 1
BWR
2
MR
Minimum Minimum Minimum Minimum
average Individual average Individual
1430 1190 1120 840
Standard value
Standard value
Result value 1000 800 900 650
Table 5 Elastic modulus (MOE) and Rupture modulus (MOR) of BWR and MR grade plywood. Sr. No
Grade of plywood
Along/Across the direction of Grains
Standard Minimum value
Static Bending Strength (N/mm2) MOE (N/mm2)
1
BWR grade
Along the direction Across the direction
2
MR grade
Along the direction Across the direction
Minimum Minimum Minimum Minimum Minimum Minimum Minimum Minimum
was 32.6 and 24.9 N/mm2. Minimum individual value observed for any specimen of BWR and MR grade was 2953 and 3428.2 N/mm2 for MOE and 30.8 and 21.2 N/mm2 for MOR. Islam et al. (2012) have been also reported similar findings. In the present study, it was found that utilization of lime treated wastewater for preparation of resin without compromising the quality of plywood is a best and effective way to handle wastewater in an environmentally sound manner to achieve zero liquid discharge in a plywood industry. A 1.5 g/L dose of lime was found to be satisfactory to treat wastewater and treated wastewater used in making resin. The characteristics of resin were found within prescribed limits of plywood manufacturing. The mechanical and physical properties of plywood specimens were greater than the standards prescribed values.
4. Conclusion Lime treatment of wastewater originated from MUF, and PF resin units showed 28.57%e48.14% removals of different pollutants like Phenol, TKN, suspended and dissolved solids and COD. Even after lime treatment, the concentration of these pollutants was much higher than the general standards of effluent discharge prescribed by The Environment (Protection) Rules in schedule VI. To safeguard the environment and health of people further treatment of this waste is required before their final disposal in inland surface water and public sewers. The wastewater, even after lime treatment may have various pollutants in a concentration much above the prescribed standard limits, but found suitable for preparation of resin without compromising the quality of plywood. The use of treated wastewater in resin preparation is found to be an effective way to deal with the problem in an environmentally sound manner to achieve zero liquid discharge. The resin characteristics were observed within the prescribed limits of plywood manufacturing. The mechanical and physical properties of plywood specimens were found greater than given Indian standards. The study may help in achieving the zero liquid discharge in plywood industry by using the suggested process.
average Individual average Individual average Individual average Individual
MOR (N/mm2)
Result value
Standard value
Result value
Standard value
8009.2 5472.6 4190.8 2953 6710.2 5109.9 3984.5 3428.2
5000 4500 2500 2200 4000 3600 2000 1800
79.6 67.1 32.6 30.8 49.8 39.5 24.9 21.2
40 36 20 18 30 27 15 13
Acknowledgements Authors are thankful to Shri Akhilesh Pratap Saraswat, Parvatiya Plywood (P) LTD., Village Shivlalpur, P.O. -Ramnagar, Nainital, Uttrakhand, India for his help and guidance in data collection and conduction of experiments inside industry premises. References ASTM D1259e06, 2012. Standard Test Methods for Nonvolatile Content of Resin Solutions. American Society for Testing and Materials e ASTM. Aktas, E.S., Imre, S., Ersoy, L., 2001. Characterization and lime treatment of olive mill wastewater. Water Res. 35 (9), 2336e2340. APHA, 2005. Standard Methods for the Examination of Water and Wastewater, twenty-first ed. American Public Health Association, Washington DC, p. 1220. Bal, B.C., Bektap, Y., 2014. Some mechanical properties of plywood produced from eucalyptus, beech, and poplar veneer. Maderas Cienc. Tecnol. 16 (1), 99e108. Bekhta, P., Ortynska, G., Sedliacik, J., 2015. Properties of modified phenolformaldehyde adhesive for plywood panels manufactured from high moisture content veneer. Drv. Ind. 65 (4), 293e301. Boller, M., 1997. Small wastewater treatment plantsda challenge to wastewater engineers. Water Sci. Technol. 35 (6), 1e12. Boukhoubza, F., Jail, A., Korchi, F., Idrissi, L.L., Hannache, H., Duarte, J.C., Hassani, L., Nejmeddine, A., 2009. Application of lime and calcium hypochlorite in the dephenolisation and discolouration of olive mill wastewater. J. Environ. Manag. 91 (1), 124e132. Budakci, M., 2010. The determination of adhesion strength of wood veneer and synthetic resin panel (laminate) adhesives. Wood Res. 55 (2), 125e136. El-Abbassi, A., Kiai, H., Raiti, J., Hafidi, A., 2014. Application of ultrafiltration for olive processing wastewaters treatment. J. Clean. Prod. 65, 432e438. Gothwal, R.K., Mohan, M.K., Ghosh, P., 2010. Synthesis of low cost adhesives from pulp and paper industry waste. J. Sci. Ind. Res. 69 (1), 390e395. Her, S.C., Liang, Y.C., 2004. The finite element analysis of composite laminates and shell structures subjected to low velocity impact. Compos. Struct. 66 (1), 277e285. IPIRTI report, 2004-05. Improvement of Urea Formaldehyde (UF) Resin. SORIT/521. Irfan, M., Butt, T., Imtiaz, N., Abbas, N., Khan, R.A., Shafique, A., 2017. The removal of COD, TSS and colour of black liquor by coagulationeflocculation process at optimized pH, settling and dosing rate. Arab. J. Chem. 10 (2), S2307eS2318. IS 1734, 1983. Indian Standard Method of Testing for Plywood. Part 1-20. Bureau of Indian Standards, New Delhi. IS 2202, 1999. Wood Flush Door Shutters Solid Core Type-Specification. Bureau of Indian Standards, New Delhi. IS 303, 1989. Plywood for General Purposes-Specification. Bureau of Indian Standards, New Delhi. IS 3944, 1982. Method for Determination of Flow Time by Use of Flow Cups. Bureau of Indian Standards, New Delhi). IS 4990, 2011. Plywood for Concrete Shuttering Works-Specification. Bureau of
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Lime treatment of wastewater in a plywood industry to achieve the zero liquid discharge Hari Prasad a, Rajesh Kumar Lohchab a, *, Bhupender Singh b, Anil Nain a, Mikhlesh Kumari a a b
Department of Environmental Science & Engineering, Guru Jambheshwar University of Science & Technology, Hisar, Haryana, India Department of Basic & Applied Sciences, Bhagat Phool Singh Mahila Vishwavidyalaya, Khanpur Kalan, Sonepat, Haryana, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 9 April 2019 Received in revised form 8 August 2019 Accepted 25 August 2019 Available online 27 August 2019
The plywood manufacturing process involves debarking of log, peeling and pressing of ribbons of wood after glueing with proper resin, trimming, sanding and finishing. Washings of glue mixer, resin kettle and a glue spreader generate solids and various hazardous chemicals like phenol, sodium hydroxide and formaldehyde. To protect the environment and human health, it is necessary to treat and reuse the wastewater of plywood manufacturing. There are several methods available for the treatment of plywood industries wastewater and use of lime is one of them. In the present study viability of lime treatment was performed to achieve zero liquid discharge in a Plywood Industry. An optimum lime dose of 1.5 g/L was applied to the wastewater of melamine urea formaldehyde and phenol formaldehyde resin units. After treatment, removal of 28.6% and 41.2% total dissolved solid and 36.8% and 37.5% total suspended solid were observed in melamine urea formaldehyde and phenol formaldehyde resin units wastewater. Phenol and chemical oxygen demand removals were more than 38% and 40% from the wastewater of both units. Lime treated wastewater was used to prepare melamine urea formaldehyde and phenol formaldehyde glue/resin by mixing chemicals. The prepared resins exhibit characteristics within prescribed limits of plywood manufacturing. The mechanical and physical properties of plywood specimen have also found satisfactory. © 2019 Elsevier Ltd. All rights reserved.
Handling editor. Prof. S Alwi Keywords: Plywood Wastewater Chemical oxygen demand Total suspended solid Phenol Lime Phenol formaldehyde resin Melamine urea formaldehyde resin
1. Introduction With modernization, improved economic conditions and high living standards, the consumption of wood-based products i.e. paper, furniture, and plywood, a composite wood product etc., are growing day by day throughout the world. The composite materials have been widely used in industries like marine ships, space structures, automobiles and oil industries etc. (Her and Liang, 2004). Plywood is a composite laminated, unidirectional, fibre reinforced material. The original solid tree wood has major demerits such as material heterogeneity, anisotropy and dimensional instability so, it cannot be directly used for applications (Islam et al., 2012). Plywood is the most important homogenous composites
* Corresponding author. E-mail addresses: [email protected] (H. Prasad), rajeshlohchab@gmail. com, [email protected] (R.K. Lohchab), [email protected] (B. Singh), [email protected] (A. Nain), [email protected] (M. Kumari). https://doi.org/10.1016/j.jclepro.2019.118176 0959-6526/© 2019 Elsevier Ltd. All rights reserved.
wood product obtained from different trees species having their own superior merits as compared to solid wood that obtained directly from a tree (Younquist, 2000). It is preferred over plain wood due to better properties i.e. imperviousness, breaking strength, texture, shrinkage, twisting and swelling. Two types of plywood are prepared in the industry i.e. boiling water resistance (BWR) and moisture resistance (MR). BWR grade plywood is prepared by using PF resin. It is of better strength, high quality and high water resistance than MR grade plywood. The BWR costs high and used for exterior work. MR grade plywood is prepared by using urea formaldehyde based resin. It is of low strength and poor water resistance ability limiting its applications for interior work. The plywood manufacturing process involves debarking of log, peeling to make a continuous ribbon of wood and pressing of these ribbons after glueing with proper resin, trimming, sanding and finishing of plywood (Fig. 1). Various hazardous chemicals are being used in the woodbased industry for veneer bonding to make the plywood. Most of these chemicals not only affect the health of workers who are
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H. Prasad et al. / Journal of Cleaner Production 240 (2019) 118176
Fig. 1. Generic diagram of plywood manufacturing process and nature of waste generates.
associated with the industry and treatment plant but also affect the health of people in the vicinity of the industry. The ingredients for the preparation of resins are usually formaldehyde, phenol, sodium hydroxide, urea and acetic or formic acids. Out of these chemicals, phenol, sodium hydroxide and formaldehyde are more hazardous to human. The sources of these chemicals are washings of glue mixer, resin kettle and a glue spreader. The wastes are generated in different forms through all processes of wood conversion from raw material to the final product. Generally, plywood mills utilize preservative chemicals to treat wood, veneer and plywood. In plywood industry, the liquid wastewater generated from the washing of glue mixing machine and glue spreading machine forms the major share of total wastes generated. The wastewater generated from wood industry is mainly associated with lignin and its derivates, that resist the microbial degradation, and very less concentrations of it cause hormonal and toxic effects in aquatic environments (Klauson et al., 2015; Leiviska et al., 2009). Residues of formaldehyde and phenol in wastewater, even in traces, have longterm adverse impacts on human health (Table 1). To avoid degradation of environment and their impacts on the health of workers and people in the vicinity of the industry, adequate preventive steps should be an essential part of industrial actions and for disposal practices in plywood industry (Nath and Dhanapal, 2012). The major characteristics of plywood industry effluent are high chemical oxygen demand (COD), ammonia, phenol and total suspended solids (Sunny et al., 2016). The plywood industry wastewater is treated by several methods depending upon the type of waste generated, amount of solid contents and wastewater volume. The chemical precipitation technique is simple in operation and requires low capital cost, but it uses a large quantity of inorganic chemicals. The operational cost of such techniques is high due to the removal and disposal of a large quantity of sludge from the bottom of settling chamber (Kurniawan et al., 2006). Lime and limestone are the precipitants most commonly used due to their low cost and easy availability in most of the countries (Mirbagheri and Hosseini, 2005). Lime works very fast and removes a large no. of impurities within a specific time. Lime increases the pH of
wastewater, which enhances the precipitation and effective in removal of suspended impurities and organic matters. Lime neutralizes the suspended impurities resulting in destabilization of charged particles and their aggregation. Now it is possible to achieve zero liquid discharge (ZLD) by reducing the consumption of water and wastewater generation (Boller, 1997). Zero liquid discharge is a purposeful technique for wastewater management by recycling all type of liquid effluents that discharged from the plant or facility. It maximizes the water use efficiency and eliminates the risk of pollution corresponded with wastewater discharge, thereby making a balance in the exploitation of water and preservation of aquatic environment (Tong and Elimelech, 2016). The present study has been conducted to achieve the zero liquid discharge from MUF and PF resin units of plywood industry. In this research, wastewater originated from plywood industry was treated with lime and used to prepare the glue. This glue has been used for the manufacturing of plywood, and various properties of the plywood were studied to analyze the effects of wastewater reuse. 2. Material and methods The study was conducted in Parvatiya Plywood Pvt. Ltd. located at village Shivlalpur of Ramnagar in district Nainital of Uttrakhand, India. The industry has melamine urea formaldehyde (MUF) and phenol formaldehyde (PF) resin units that generated about 130 L and 310 L wastewater per week. Lime treated wastewater was used for the preparation of the resin without compromising the quality of plywood. The above process of plywood manufacturing by utilizing lime treated wastewater in resin/glue preparation was used to achieve zero liquid discharge. 2.1. Sample collection and analysis In both PF and MUF resin units wastewater contains large woody solid particles in suspension. To remove these particles, presedimentation was done before the lime treatment and the sludge was collected in different containers. After that, a dose of 0.5e2.5 g/L of lime was applied, and contents were mixed properly and allowed to settle for 2 h. Based on the removal of suspended solids, an optimum lime dose of 1.5 g/L was found suitable to treat liquid wastewater originated from PF and MUF resin units (Fig. 2). After settling of sludge, treated wastewater was used for the glue preparation. Treated as well as untreated wastewater samples were analyzed at the Department of Environmental Science and Engineering, GJU&ST, Hisar. Total dissolved solids (TDS), total suspended solids (TSS), total volatile solids (TVS), total Kjeldahl nitrogen (TKN), chemical oxygen demand (COD) and phenol of both samples were analyzed by using standard methods (APHA, 2005). Analysis of glue/resin flow time and solid content properties were observed by using B4 cup test of IS: 3944e1982 and ASTMD1259-06-2012 in Parvatiya Plywood Pvt. Ltd. according to standard methods of IPIRTI (Indian Plywood Industries Research and Training Institute).
Table 1 Effects of major chemicals on human health. Sr. No
Chemicals
Effects on Human Being
1. 2.
Formaldehyde Phenol
Gastrointestinal mucosa, respiratory distress, nausea, bleeding, vomiting, renal failure, pain, may be carcinogenic Coagulate protein; blister on skin, taken internally may cause death.
Source: Sharma (1994).
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3.1. Total solids
Fig. 2. TSS removal efficiency of lime for MUF and PF Unit's wastewater.
Total suspended solids (TSS), total dissolved solids (TDS) and total volatile solids (TVS) were analyzed and results are shown in Table 3. Total solids in untreated wastewater samples of MUF and PF resin application units were found to be 1900 mg/L and 1200 mg/L. After lime treatment, 36.8% and 37.5% removal of TSS was observed from the wastewater of the MUF and PF resin application units. TSS and turbidity are removed by using lime but their removal may be further increased by use of ferrous sulphate, ferric chloride etc. (Teh et al., 2016). The removals of 28.6% and 41.2% TDS and 38.7%, and 34.8% TVS were observed from wastewater of MUF and PF resin units. It is well established that the amount of lime, which increases the pH of the mixture to 12, is the most effective for flocculation (Aktas et al., 2001). Slightly higher removal of TSS and TDS was observed in case of treated wastewater of PF resin application unit. Our results were consistent with Mishra and Mohapatra (2012); they observed 24% removal of TDS with lime application in industrial wastewater treatment. 3.2. Total Kjeldahl nitrogen
Physico-mechanical testing such as glue shear strength, adhesions of piles, static bending strength and nail holding strength of plywood and other wood products manufactured using resin was done as per IS 1734(Part-4)-1983, IS 1734(Part-5)-1983, IS 1734(Part-11)-1983 and IS1734(Part-19)-1983. The weather resistance like shrinkage or swelling of plywood and wooden board were tested in a water bath container at 110 C as per IS 303e1989. The modulus properties of plywood specimens were observed using the static bending testing machine. The moment of elasticity (MOE) and moment of rupture (MOR) for plywood specimens were analyzed by using the standard method of practice (IS: 4990e2011).
Total Kjeldahl nitrogen (TKN) is the total concentration of ammonia and organic nitrogen. The untreated wastewater was having TKN content of 270 mg/L in the MUF resin application unit and 310 mg/L in PF resin application unit. After lime treatment, the wastewater of MUF and PF resin application units were comprised with TKN of 140 mg/L and 175 mg/L (Table 3). Removal of TKN from wastewater of MUF and PF resin application units were 48.1% and 43.6%. The higher removal of TKN was observed during the treatment of wastewater from the MUF resin application unit. 3.3. Phenol
3. Results and discussion Various methods had been used by a number of researchers for wood based industries wastewater treatment (Table 2). In present study, wastewater originated from MUF and PF resin application units of plywood industry was treated with lime and change in different parameters of wastewater are discussed below:
Phenol is highly toxic to human being, phytoplankton and zooplankton if present in wastewater beyond the permissible limit of discharge. It has adverse impacts on eyes, skin and mucous membranes in humans after acute inhalation or dermal exposures. Phenol concentration was 720 mg/L, and 1310 mg/L in wastewater originated from MUF and PF resin application units. After lime treatment, its removal was 50% and 38.5% with final concentration of 425 mg/L and 805 mg/L in wastewater of MUF and PF resin
Table 2 Wood based industries wastewater treatment by different processes. Treatment
Dose
Effluent
Parameters
Removal (%)
Reference
Lime
1.5 g/L
Wastewater of MUF & PF Unit (Plywood)
10 g/L
Wastewater (Olive Mill)
Lime
10 g/L
Wastewater (Olive Mill)
Alum
0.8 g/L
Black Liquor (Paper & Pulp)
Ferrous Sulphate
0.8 g/L
Black Liquor (Paper & Pulp)
Aluminium Chloride
0.8 g/L
Black Liquor (Paper & Pulp)
Ferric Chloride
0.8 g/L
Black Liquor (Paper & Pulp)
Ultrafiltration
e
Wastewater (Olive Mill)
40 36.8 & 37.5 41 & 38.5 48.1 & 43.6 41.5e46.2 29.3e46.9 60.5e80.1 72 73 60 11 46 12 42 13 48 16 50 60 37 30
Present study
Lime
COD TSS Phenol TKN COD Total Solid TKN COD TSS Phenol COD TSS COD TSS COD TSS COD TSS COD Total Solid Phenol
Aktas et al. (2001)
Boukhoubza et al. (2009)
Irfan et al. (2017) Irfan et al. (2017) Irfan et al. (2017) Irfan et al. (2017) El-Abbassi et al., 2014
4
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Table 3 Physico-chemical properties of wastewater of MUF and PF resin unit. Sr. No.
1 2 3 4 5 6
Chemical Properties
COD (mg/L) TSS (mg/L) TVS (mg/L) TDS (mg/L) TKN (mg/L) phenol (mg/L)
MUF Application Unit
PF Application Unit
Untreated Wastewater
Lime treated waste water
Untreated wastewater
Lime treated waste water
4500 1900 815 210 270 720
2700 1200 500 150 140 425
4925 1200 675 340 310 1310
2950 750 440 200 175 805
application units (Table 3). The permissible limits of phenol are 1 mg/L and 5 mg/L for wastewater disposal in inland surface water and public sewers. Even after lime treatment, phenol in wastewater was found to be much higher in concentration than general standards of effluent discharge prescribed by Environment (Protection) Rules in schedule VI, Govt. of India. The advanced techniques using H2O2/UV-C process of phenol removal can be used to dispose off plywood industrial wastewater in inland surface water and public sewer (Rueda-Marquez et al., 2016). 3.4. Chemical oxygen demand Prior to biological treatment, initial COD and lignin removal is carried out by coagulation-flocculation process (Teh et al., 2016; Kamali and Khodaparast, 2015; Pokhrel and Viraraghavan, 2004). After addition of lime, the suspended impurities including resins were settled down at the bottom of the basin. It helps in the removal of COD and other pollutants from wastewater. COD of wastewater originated from MUF and PF resin application units were 4500 mg/L and 4925 mg/L. After lime treatment, COD of wastewater of MUF and PF resin application units was reduced to 2700 mg/L and 2950 mg/L (Table 3). About 40% removal in COD has been observed from wastewater of both the resin application units. The results of COD removal corresponded with the finding of Klauson et al. (2015). They achieved 37% COD removal in wood soaking basin water of plywood industry through coagulation. 3.5. Resin properties The quantity of wastewater collected after treatment was only 5e6% of the total water requirements of 4600e4700 L in resin manufacturing. The glue/resin was prepared by mixing chemicals in lime treated wastewater and make-up fresh water, and then its physico-chemical properties of viscosity and solid contents have been studied as below. 3.5.1. Viscosity The viscosity of glue affects the strength of joints. Greater the flow time, lesser will be the viscosity and it leads to a decrease in strength of joints (Budakci, 2010). The flow time observed at 85 C was 15 and 16 s for PF and MUF resins. The flow time recorded was within the standard value of 14e16 s of IPIRTI report. At room temperature, the flow time of PF and MUF resin was 25 and 26 s. These values were within the standard limits of 25 ± 2 s (IPIRTI, 2004e05). 3.5.2. Solid content Solid content is responsible for the stagnation of glue on veneer that affects the strength of plywood. Solid content reduces the emission of volatile gases like formalin if its value is within 48e50% (Bal and Bektap, 2014). As per IPRTI standards, solid content in resin should range from 48% to 52%. Solid content was observed 49.7% and 49.2% in PF resin and MUF resin, which was well within the
prescribed standard value. Similarly, Oh and Kim (2011) have reported 49% solid content in MUF resin, and Bekhta et al. (2015) observed 50% solids content in PF resin. 3.6. Physico-mechanical properties of plywood The resin prepared by using treated wastewater was used for adhesion of veneer for the manufacturing of plywood. The adhesion property of plywood has been tested with a standard size of the knife and 90e95% surface remained rigidly attached to adjacent veneers. Kamala et al. (1999) have been reported that about 95% of upper surfaces remain cohered and after water boiling it was 70e80%. The weather resistance of plywood and wooden board was tested in water bath container at 110 C and shrinkage, or swelling of both surfaces showed a dimension change within tolerance limit and categorized AA grade as per IS 303e1989. 3.6.1. Nail holding strength The nail holding power of plywood was observed 1320 kg/mm2 and 1275 kg/mm2 for wooden board and plywood specimens. The standard minimum value for nail holding strength is 1000 kg/mm2 (IS: 2202 1999). The values observed in our case were found to be greater than the standard value. Kamala et al. (1999) observed 1185 kg/mm2 of nail holding power of plywood. 3.6.2. Glue shear strength Glue shear strength for minimum average and a minimum individual test of three dry and moist plywood specimens has been conducted for BWR and MR grade of plywood and results are shown in Table 4. Glue shear strength of dry and moist specimens of BWR grade plywood was 1430 N/mm2 and 1140 N/mm2 for minimum average test and 1190 N/mm2 and 890 N/mm2 for a minimum individual test. For MR grade plywood, shear strength on the minimum average basis of three specimens was 1120 N/mm2 and 910 N/mm2 and on minimum individual basis was 840 N/mm2 and 720 N/mm2 for dry and moist specimens. A study by Gothwal and Mohan, 2010) reported 1472 N/mm2 and 1302 N/mm2 shear strength using PF resin at wood failure at 95% and 85% in the dry and moist state. 3.7. Modulus properties of plywood Modulus properties of plywood specimens observed using the static bending testing machine are shown in Table 5. For BWR and MR grade plywoods average values of MOE along the direction of grains observed for three specimens were 8009.2 and 6710.2 N/ mm2 and average values of MOR were 79.9 and 49.8 N/mm2. Minimum individual value observed for any specimen of BWR and MR grade plywood was 5472.6 and 5109.9 N/mm2 for MOE property and 67.1 and 39.5 N/mm2 for MOR property. For BWR and MR grade plywood, the average value of MOE for three specimens across the direction of grains observed was 4190.8 and 3984.5 N/ mm2 and the average value of MOR across the direction of grains
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Table 4 Shear strength observations of BWR and MR grade (N/mm2) plywood. Sr. No
Grade of plywood
Standard Minimum value
Dry specimen
Shear strength (N/mm2) Moist specimen
1350 1100 1100 800
1140 890 910 720
Result value 1
BWR
2
MR
Minimum Minimum Minimum Minimum
average Individual average Individual
1430 1190 1120 840
Standard value
Standard value
Result value 1000 800 900 650
Table 5 Elastic modulus (MOE) and Rupture modulus (MOR) of BWR and MR grade plywood. Sr. No
Grade of plywood
Along/Across the direction of Grains
Standard Minimum value
Static Bending Strength (N/mm2) MOE (N/mm2)
1
BWR grade
Along the direction Across the direction
2
MR grade
Along the direction Across the direction
Minimum Minimum Minimum Minimum Minimum Minimum Minimum Minimum
was 32.6 and 24.9 N/mm2. Minimum individual value observed for any specimen of BWR and MR grade was 2953 and 3428.2 N/mm2 for MOE and 30.8 and 21.2 N/mm2 for MOR. Islam et al. (2012) have been also reported similar findings. In the present study, it was found that utilization of lime treated wastewater for preparation of resin without compromising the quality of plywood is a best and effective way to handle wastewater in an environmentally sound manner to achieve zero liquid discharge in a plywood industry. A 1.5 g/L dose of lime was found to be satisfactory to treat wastewater and treated wastewater used in making resin. The characteristics of resin were found within prescribed limits of plywood manufacturing. The mechanical and physical properties of plywood specimens were greater than the standards prescribed values.
4. Conclusion Lime treatment of wastewater originated from MUF, and PF resin units showed 28.57%e48.14% removals of different pollutants like Phenol, TKN, suspended and dissolved solids and COD. Even after lime treatment, the concentration of these pollutants was much higher than the general standards of effluent discharge prescribed by The Environment (Protection) Rules in schedule VI. To safeguard the environment and health of people further treatment of this waste is required before their final disposal in inland surface water and public sewers. The wastewater, even after lime treatment may have various pollutants in a concentration much above the prescribed standard limits, but found suitable for preparation of resin without compromising the quality of plywood. The use of treated wastewater in resin preparation is found to be an effective way to deal with the problem in an environmentally sound manner to achieve zero liquid discharge. The resin characteristics were observed within the prescribed limits of plywood manufacturing. The mechanical and physical properties of plywood specimens were found greater than given Indian standards. The study may help in achieving the zero liquid discharge in plywood industry by using the suggested process.
average Individual average Individual average Individual average Individual
MOR (N/mm2)
Result value
Standard value
Result value
Standard value
8009.2 5472.6 4190.8 2953 6710.2 5109.9 3984.5 3428.2
5000 4500 2500 2200 4000 3600 2000 1800
79.6 67.1 32.6 30.8 49.8 39.5 24.9 21.2
40 36 20 18 30 27 15 13
Acknowledgements Authors are thankful to Shri Akhilesh Pratap Saraswat, Parvatiya Plywood (P) LTD., Village Shivlalpur, P.O. -Ramnagar, Nainital, Uttrakhand, India for his help and guidance in data collection and conduction of experiments inside industry premises. References ASTM D1259e06, 2012. Standard Test Methods for Nonvolatile Content of Resin Solutions. American Society for Testing and Materials e ASTM. Aktas, E.S., Imre, S., Ersoy, L., 2001. Characterization and lime treatment of olive mill wastewater. Water Res. 35 (9), 2336e2340. APHA, 2005. Standard Methods for the Examination of Water and Wastewater, twenty-first ed. American Public Health Association, Washington DC, p. 1220. Bal, B.C., Bektap, Y., 2014. Some mechanical properties of plywood produced from eucalyptus, beech, and poplar veneer. Maderas Cienc. Tecnol. 16 (1), 99e108. Bekhta, P., Ortynska, G., Sedliacik, J., 2015. Properties of modified phenolformaldehyde adhesive for plywood panels manufactured from high moisture content veneer. Drv. Ind. 65 (4), 293e301. Boller, M., 1997. Small wastewater treatment plantsda challenge to wastewater engineers. Water Sci. Technol. 35 (6), 1e12. Boukhoubza, F., Jail, A., Korchi, F., Idrissi, L.L., Hannache, H., Duarte, J.C., Hassani, L., Nejmeddine, A., 2009. Application of lime and calcium hypochlorite in the dephenolisation and discolouration of olive mill wastewater. J. Environ. Manag. 91 (1), 124e132. Budakci, M., 2010. The determination of adhesion strength of wood veneer and synthetic resin panel (laminate) adhesives. Wood Res. 55 (2), 125e136. El-Abbassi, A., Kiai, H., Raiti, J., Hafidi, A., 2014. Application of ultrafiltration for olive processing wastewaters treatment. J. Clean. Prod. 65, 432e438. Gothwal, R.K., Mohan, M.K., Ghosh, P., 2010. Synthesis of low cost adhesives from pulp and paper industry waste. J. Sci. Ind. Res. 69 (1), 390e395. Her, S.C., Liang, Y.C., 2004. The finite element analysis of composite laminates and shell structures subjected to low velocity impact. Compos. Struct. 66 (1), 277e285. IPIRTI report, 2004-05. Improvement of Urea Formaldehyde (UF) Resin. SORIT/521. Irfan, M., Butt, T., Imtiaz, N., Abbas, N., Khan, R.A., Shafique, A., 2017. The removal of COD, TSS and colour of black liquor by coagulationeflocculation process at optimized pH, settling and dosing rate. Arab. J. Chem. 10 (2), S2307eS2318. IS 1734, 1983. Indian Standard Method of Testing for Plywood. Part 1-20. Bureau of Indian Standards, New Delhi. IS 2202, 1999. Wood Flush Door Shutters Solid Core Type-Specification. Bureau of Indian Standards, New Delhi. IS 303, 1989. Plywood for General Purposes-Specification. Bureau of Indian Standards, New Delhi. IS 3944, 1982. Method for Determination of Flow Time by Use of Flow Cups. Bureau of Indian Standards, New Delhi). IS 4990, 2011. Plywood for Concrete Shuttering Works-Specification. Bureau of
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