Sri Lanka's forest sector and wood-based manufacturing industry play an important role in the national economy, contributing over USD 176 million to the country's GDP, with over 50,000 employees (Annual Report of Central Bank of Sri Lanka 2019). This sector is diverse and typically characterized by sawmill, furniture manufacturing, construction, parquet flooring, wood-based panel products, and carvings industries (Perera et al. 2006, Perera and Vlosky 2009). The industries depend primarily on the local wood supply for raw materials (Perera and Vlosky 2009, Caldera and Amarasekera 2015) for domestic markets, while a relatively smaller number of manufacturers target export markets (Perera et al. 2006, Bandara and Vlosky 2012). Although small craft-based wood industries have dispersed all over the country, furniture and woodworking mills are geographically clustered in few areas, such as Moratuwa and Ambalangoda, which are traditionally known for concentrated woodworking clusters (Fig. 1) (Perera et al. 2006, Perera 2015).
Citation: Forest Products Journal 71, 4; 10.13073/FPJ-D-21-00042
The Moratuwa Woodworking Industry Cluster (MWIC), which is the focus of this research, is a major wood-based production cluster of traditional wood craft carpenters, furniture manufacturers, sawmills, and other wood processing industries in the Moratuwa Municipal Council Area in the Western Province of Sri Lanka. Historical information from the British colonial era shows that the Moratuwa area has been a well-known area for furniture manufacturing and carpentry going back to the 1800s (Scriver and Prakash 2007). At present, the MWIC is dominated by hundreds of small-to-medium scale wood working industries, with the majority being traditional family-owned businesses catering to the local markets. Sawmills, timber and furniture retail shops, and timber seasoning facilities (kiln drying facilities that provide dried timber to MWIC industries) comprise the rest of the industries in MWIC. Although the MWIC has numerous constraints, such as socio-technological knowledge and policy barriers for expansion, the majority of firms in the cluster are dependent on furniture manufacturing and other craft woodwork as their main source of income (Liyanage et al. 2019).
The MWIC has been identified by the Government of Sri Lanka as a priority area for economic development (Central Bank of Sri Lanka 2019). The State Ministry of Technology and Innovation in 2019 introduced a geographical-based trademark to brand the furniture produced in the MWIC along with support to transform Sri Lanka's MWIC wood and timber industry into a high-tech global export market (State Ministry of Technology and Innovation 2019). These efforts have been challenging, with many negative attributes being exacerbated; the MWIC has undergone gradual transformations over the last few decades with noticeable declines in production (Central Bank of Sri Lanka 2019). The inefficiency in wood resource utilization has been identified as one of the main factors affecting the low profitability and productivity of the MWIC (Gunatilake and Gopalakrishnan 2010, Jayawardhane et al. 2015, Caldera and Amarasekera 2015, Liyanage et al. 2019). For instance, recent studies have highlighted the inefficiency and waste of MWIC sawmills and called for improved technological, sawmilling efficiencies, and training interventions (Caldera and Amarasekera 2015, Perera 2015, Abeykoon and Amarasekara 2017).
Within the MWIC, wood residues are primarily produced while processing logs into lumber. Wood residues from primary processing of logs (conversion of logs into sawn timber) include bark, slabs, sawdust, chips, coarse residues, planer shavings, peeler log cores, and end trimmings, while secondary processing (conversion of sawn timber into finished products such as furniture) typically produces chips, sawdust, sander dust, end trims, coarse residues, and planer shavings (Tatàno et al. 2009, Saal et al. 2017). Despite wood residues produced by primary and secondary wood products industries being used for fuel for energy production and other minor uses, much of the wood waste generated in MWIC goes unused and enters the waste stream, causing pollution of water bodies and related health risks to the community (Samarasekara 2017).
The Study
Conceptual framework
The conceptual framework of industrial ecology (IE) is applied to this research. It aims to minimize the inefficiencies within an industrial system and thereby attempt to reduce waste generation by mimicking the cyclic flows of materials in natural ecosystems in industrial systems (Ayres and Ayres 2002, Chertow 2007). Industrial symbiosis (IS)—a process that aims to reduce the ecological impact of industrial processes through the exchange of by-products and waste between components in a system and thereby reducing the consumption of virgin material and other inputs—is a key ideology within the framework of IE (Desrochers 2004, Sokka et al. 2011a). Such conceptual models have been applied to forest industry complexes in different countries to improve the overall efficiency (Pakarinen et al. 2010, Sokka et al. 2011a, Wahrlich and Simioni 2019). Numerous studies further highlight the overall environmental benefits of the application of IE and IS concepts to forest sector industry clusters (Sokka et al. 2011b, Hildebrandt et al. 2019). In this context, the geographically concentrated wood-based industries in the MWIC provide plausible opportunities for public planners and policymakers to explore IS options.
An understanding of the factors that affect the generation and use of wood residues in MWIC is critical for the efficient use of wood resources. Sound data on the availability, quantity and production rates, types of wood residues being produced, current markets, and current disposal practices of wood residues are essential for policymakers and businesses to take advantage of the market opportunities that exist for wood residues.
This research was undertaken to address the lack of quantitative information on wood residues generated within the MWIC. Furthermore, MWIC manufacturers have limited information on markets for wood residues (Liyanage et al. 2019). Identification of the types and quantities of wood residues generated in the MWIC and how they are being used is vital in addressing issues associated with the generation and management of wood residues.
Quantification and understanding the current flow of wood residues in MWIC will provide information to industries that both generate and use wood residues to plan business strategies that incorporate the use of wood residues.
Hence, this study aimed to estimate the volume of wood residues generated in MWIC, understand the current utilization patterns, and estimate the amount of wood residue that may be potentially available for use by other industries within an industrial symbiosis model. These industries may include any industry that has the capacity to use wood waste as an input in its manufacturing process and new business start-ups based on the availability of wood waste.
Methodology
Study location
The MWIC is located in the southern boundary of the Colombo District, about 24 km away from Colombo city on the coastal plain of the west in the Western Province of Sri Lanka (Fig. 1). The MWIC spans over an area of 23.4 km2 and includes the entire Moratuwa Municipal Council area. The total population in the MWIC is 166,857, with 41,459 families, the majority of whom are dependent on wood-based manufacturing industries for their livelihoods.
Sample selection
Initially, a preliminary analysis was carried out in the MWIC area to gain insights into the industry structure, composition, and the types of wood residues generated during manufacturing activities. According to Moratuwa Municipal Council (2019) sources, there are 1,631 registered wood-based businesses in the MWIC belonging to six major categories (i.e., carpentry shops, sawmills, integrated sawmills, sawn timber retailers, furniture retail shops, and wood seasoning and processing facilities) defined by the Forest Department of Sri Lanka (2017).
Since sawn timber retailers, furniture retail shops, and wood seasoning and processing centers have a negligible contribution to wood-waste generation in MWIC, the effective sampling population was determined as 730 businesses belonging to industry categories of integrated sawmills (n = 404), sawmills (n = 156), and carpentry shops (n = 170). Accordingly, a 25% sample (with a 95% confidence interval and a 5% margin of error) from the sampling population was selected using a stratified random sampling method (Table 1).
Data collection
A structured questionnaire was used to gather wood-waste generation information from wood-based manufacturing businesses in the MWIC. Research team members visited all business facilities in the sample to gather information between the period of May and September 2019. During the reconnaissance survey, it was revealed that the most common method of collecting and disposing of wood waste is to collect waste into gunny sacks (dimensions of approximately 115 cm × 70 cm). Hence, the respondents were asked to report the wood waste in their respective facilities in terms of the number of sacks. Those who are currently selling wood waste separated the wood waste into sizes/types (i.e., sawdust, wanes, and offcuts). The questionnaire further collected information on timber species used, typical equipment available, and current waste disposal practices of the industries.
To validate the wood-waste generation data collected from the questionnaire survey and quantitatively estimate the wood-waste generation, a wood-waste residue survey was further undertaken at selected manufacturing facilities. Accordingly, 24 wood-based industries were randomly selected (12 integrated sawmills, 6 sawmills, and 6 carpentry shops) for a wood-waste residue survey. The sample represented wood-based manufacturing facilities of different scale/magnitude and used different wood-waste disposal practices. Selected facilities were provided with gunny sacks of 115 cm × 70 cm and were asked to collect the daily wood residues. The selected manufacturing facilities were visited once a month between the period of May and October 2019, and a count of the number of sacks and the weights of five randomly selected sacks were measured using a portable hook-type weighing scale. For those who currently sort the wood waste into sawdust (fine sawdust, coarse sawdust/planer shavings, unsorted/mixed saw dust, and finishing sawdust), wanes and offcuts, two sacks from each type were measured.
Based on the mean weights of each wood-waste type, the average monthly generation of wood residues/waste from a manufacturing facility (Wf) was approximated as Wf = Σws + wa + ww (where ws, wo, and ww denote average monthly weights of sawdust, offcuts, and wanes). Accordingly, the average monthly generation of wood residues/waste from each industry type (sawmills, integrated sawmills, and carpentry shops) and wood-waste type were estimated by multiplying the mean weights derived from the sample by the respective number of manufacturing facilities. Subsequently, the monthly generation of wood waste by different industry types in the entire MWIC was determined using the sample data.
The structured questionnaire designed to collect information on wood-waste generation further gathered information on current wood-waste utilization and existing markets for wood waste. The quantity of wood taken up by current wood-waste users was determined based on the volume of wood waste traded (measured by the number of sacks) by manufacturing industries captured in the sample.
Data analysis
There was greater variability in wood-waste generation among the industries in the sample. For analysis, the industries in the sample were grouped into the small scale (SS), medium scale (MS), and large scale (LS) wood-waste generating industries using a median split of data by referring to the wood-waste generation data obtained from the study (Table 2).
One-way analysis of variance (ANOVA) was used to compare the differences in quantities and types of wood-waste generated among the three categories. All analyses were performed using IBM SPSS® Statistics (18.0) software package. Based on the estimates of wood waste generated and used in the MWIC, a wood-waste flow diagram was developed to illustrate the current wood-waste generation and utilization scenario.
Results
Timber species utilization
Tectona grandis (38.7%) and Swietenia macrophylla (28.8%) were the most common timber species used by MWIC (Table 3). Both species were predominantly used in furniture manufacturing (items such as tables, chairs, wardrobes, beds) by the carpentry industries. Hence, teak and mahogany accounted for the greater share of sawlogs used by the sawmills and integrated sawmills.
Machinery used
The survey results revealed that different machine types are used by different industrial categories (Fig. 2). In the sawmills, the circular saw was the most frequently used saw type (Fig. 3). It was observed that even though a sawmill has band saws or other saw types as the head rig, the circular saw is still used as a cross-cutting saw or a resaw. The main tools used by carpentry shops included the planer saw or the planer machine, which is used for surface shaving. Industries that produce sawn timber and furniture at the same premises used circular saws, planer saws, and jig saws (Fig. 4).
Citation: Forest Products Journal 71, 4; 10.13073/FPJ-D-21-00042
Citation: Forest Products Journal 71, 4; 10.13073/FPJ-D-21-00042
Citation: Forest Products Journal 71, 4; 10.13073/FPJ-D-21-00042
Main types of wood waste
The wood-waste residue survey identified three main types of wood wastes in the MWIC. These include sawdust, offcuts, and wanes. The reconnaissance survey showed that modern technology has replaced some of the traditional woodworking tools, such as the wand wood planer. Consequently, the generation of wood shavings was nonsignificant in the MWIC and was considered under coarse sawdust. Table 4 describes the main types of wood waste in the MWIC, along with their sources of origin.
Wood-waste generation by industry
The carpentry industry generated sawdust (80.3%) and offcuts (19.6%) as the main wood wastes. Integrated sawmills generate sawdust (64.8%), offcuts (18.6%), and wanes (16.6%). The sawmilling industry contributes to sawdust (83.0%) and wanes (17.0%). One-way ANOVA tests revealed significant differences among the mean quantities of wood-waste generation among SS, MS, and LS firms of the three industry types (Table 5). Total wood waste generated by carpentry shops, sawmills, and integrated sawmills further varied significantly (F169.193, P = 0.00*) among the three industries.
When considering the 730 wood-waste generating industries in the MWIC, sawmills accounted for 65.9% of the monthly wood-waste generation in the MWIC, while integrated sawmills and carpentry industries accounted for 30.8% and 3.2% of the monthly wood-waste generation, respectively (Table 6). Despite the comparatively high number of integrated sawmills in the MWIC, sawmills were the largest industry category generating wood waste.
The total wood-waste generation in MWIC is 6,489.9 MT/mo. Out of this, sawdust accounted for 76.5% (4,966.830 MT/mo). The total monthly generation of offcuts within the MWIC is 450.1 MT (6.9%), while 1,072.9 MT (16.5% of total wood waste) of log wanes were further added to the wood-waste stream.
Current status of wood-waste utilization in MWIC
Survey results revealed that approximately 23.2% of sawdust, 100% offcuts, and 86.1% of wanes generated in the MWIC are currently used through different channels. Approximately 77.8% of different types of sawdust and 13.9% of wanes are unused (Table 7). The survey results further revealed that 36.5% of carpentry shops and 9.0% of integrated sawmills are disposing of their wood waste by burning, burying, or dumping wood waste into the Bolgoda Lake, bordering the MWIC (Table 8). Further, an inflow of 99 MT/mo of offcuts into the MWIC was estimated according to wood-waste utilization information in MWIC.
Average market prices of coarse sawdust varied from $US 4 to $US 18 per 1,000 kg, while the fine sawdust was sold at an average rate of $US 6 to $US 22 per 1,000 kg. The price of offcuts and wanes ranged from $US 21 to $US 11 per 1,000 kg and $US 8 to $US 11 per 1,000 kg, respectively. The price range of mixed wood waste is $US 7 to $US 11 per 1,000kg, the lowest prices in the market. Carpentry was the only sector that sold finishing sawdust at $US 17 per 1,000 kg (exchange rate of conversion is 1.00 USD is equal to Rs. 180.00) (Fig. 5).
Citation: Forest Products Journal 71, 4; 10.13073/FPJ-D-21-00042
Wood-waste flow in MWIC
Figure 6 summarizes the wood-waste/residue generation within the MWIC and the flow of wood waste. There is an inflow of 99 MT of offcuts from outside sources into the MWIC. Accordingly, there is 3,586 MT of unused wood waste, which can be channeled as inputs to other industries.
Citation: Forest Products Journal 71, 4; 10.13073/FPJ-D-21-00042
Discussion
Dwindling forest resources and increasing imports of wood products are likely to have negative effects on the wood-based manufacturing industries of Sri Lanka in the future (Jayawardhane et al. 2015, Perera 2015). As such, improving the efficiency of wood utilization and exploring the potential of lesser-known native timber species have been recognized as alternative approaches to forest conservation and review of the wood-based manufacturing industries of Sri Lanka (Gunatilake and Gopalakrishnan 2010, Amarasekera 2012, Ruwanpathirana 2014, Perera 2015). The geographical concentration of a variety of wood-based industries in the MWIC provides enticing opportunities to explore possible industrial synergies to promote efficient wood utilization in the largest cluster of wood-based industries in Sri Lanka. The material flow analysis approach has been used to reveal and quantify the relationship between the resources and uses of wood resources elsewhere (Parobek et al. 2014). Using a similar approach, this study provided the vital baseline estimates of wood-waste generation, current utilization pathways and the quantities that are unutilized to support informed decision-making by policymakers, planners, and entrepreneurs.
The sawn timber requirement of carpentry and other woodworking industries in the MWIC is almost entirely satisfied by sawmills in the MWIC. The study revealed that teak and mahogany are the dominant timbers used in the MWIC, as they have been for the last three decades, suggesting the largely unchanged preference of woodworkers for traditional timbers (Amarasekara 1995, Perera et al. 2006, Perera et al. 2012, Jayawardhane et al. 2015). As such, teak and mahogany account for the largest share of wood waste generated in the MWIC. Wood density is a key determinant in wood-waste utilization options (Ogunwusi 2014). Both teak and mahogany are considered to be medium-density timbers (Perera et al. 2012, Ruwanpathirana 2014) and, hence, may find use in wood-based composite production and energy briquettes (Najafi et al. 2006, Rominiyi et al. 2017).
According to study findings, sawmills in the MWIC demonstrated better wood-waste sorting practices, which have increased the market opportunities for wood waste. Sawmills produce a greater share of fine sawdust (73.5%) and the unsorted/mixed sawdust accounted for only 5.7%. It was evident that sorted sawdust has a better market compared to unsorted/mixed sawdust as reflected by the current market prices study for different wood-waste types reported in this study. This is probably because sorting sawdust by particle sizes makes it easy for secondary utilizers to put them to specific end uses. The current market for sorted wood waste is largely driven by the demand from biomass energy users and energy briquette manufacturer (Sandupama and Arachchige 2019, Anusha and Bandara 2020). Hence, strengthening the supply chain for sorting, collecting, transporting, and processing will have a positive effect on wood-waste utilization in the MWIC (Shahidul et al. 2020). Integrated sawmills produced all three main types of wood waste as they perform both sawmilling operations and carpentry works.
The main use of both fine and coarse sawdust is to burn as fuel in industrial boilers and household furnaces. More recently, the possibility of using sawdust in aggregate concrete production has been tested, but the presence of a large amount of bark can be a limiting factor in the use of coarse sawdust (Ganiron 2014). Both medium-density hardwood and softwood sawdust have been used in the production of light-weight hollow construction blocks (Adebakin et al. 2012). Fine and coarse sawdust are used in particleboard production and wood–plastic composites (composite decking and composite flooring). However, better sorting and wood-waste management practices are required at the wood-waste generating facilities to ensure that sawdust is dry, grit-free, and not contaminated with wood bark (Akinyemi 2016, Abdulkareem and Adeniyi 2017).
There is a greater potential for sawdust to be used in the manufacturing of energy briquettes (Odusote et al. 2016, García et al. 2018, Song et al. 2020). Different biodegradable solid wastes have been successfully combined to produce biomass energy briquettes and pellets (Ogwu et al. 2014, Shiferaw et al. 2017, Alam et al. 2019, Arulprakasajothi et al. 2020). The sludge produced by the large-scale municipal wastewater treatment facility located within the MWIC and the invasive aquatic weeds covering the Bolgoda River, which borders the MWIC, can be effectively combined to produce biomass energy briquettes (Supatata et al. 2013, Davies and Abolude 2012, Kim et al. 2016, Rezania et al. 2016). As such, these can be identified as potential opportunities for business start-ups under a framework of industrial symbiosis for MWIC.
Wood offcuts have a variety of uses, from direct use as fuel to technology-intensive uses such as the production of engineered wood products (particle boards, medium density fiber boards). A major advantage of offcuts as a raw material is that they do not contain wood bark due to the debarking process at sawmills (Chaharmahali 2010). At present, offcuts are used for secondary wood product manufacturing, such as small furniture, pet cages/enclosures, wooden toys, briquettes, curtain poles and knobs, etc. There is a sizeable group of industries in the MWIC that use wood offcuts as raw materials. The study revealed a monthly influx of 99 MT to the MWIC, and this suggests the excessive demand of industries within the MWIC for offcuts.
Wanes typically consist of the outermost parts of logs and contain a higher percentage of bark and other nonwood components (such as soil, mud, and sometimes metal pieces) attached during log harvesting and transport (Erhabor 2015). The greater heterogeneity and variable quality make wood wanes challenging to use in value-added products, as it necessitates substantial investments and processing time (Jansone et al. 2017). Hence, the current demand for wanes produced in the MWIC predominantly comes from industries that operate boilers on wood biomass (Anusha and Bandara 2020). The present study further revealed that approximately 73% of the wood wanes are used to fuel boilers, often sourced free from primary wood processing facilities. With rising fuelwood prices in the country due to limitations in supply, the demand for wood wanes is likely to increase in the future. This calls for improved wood-waste collection and sorting at the source and strengthening of the supply chain to fetch better prices for discarded wood wanes.
The types of machinery used by industries largely determine the practical size of sawdust and other wood residues (Owoyemi et al. 2016). Sawdust (course sawdust, fine sawdust, and finishing sawdust) and offcuts were the main types of wood waste from carpentry shops. In integrated sawmills, circular saw and the planer saw were used as the main sawing equipment, producing 1,227 MT/mo of sawdust. The commonly used circular saws in sawmills produced 3,575 MT of sawdust per mo.
A variety of factors affect wood-waste generation, especially in sawmilling. For instance, Caledra and Amarasekera (2015) reported that loss in conversion during sawmilling in MWIC varies with sawmill management and technological parameters, such as type of machinery employed, sharpening frequency, sawyer's experience, saw set, availability of log alignment equipment and saw guards, oversizing, and sawn timber sizes. They further reported a 53.1% mean percentage loss in conversion for teak and mahogany timber for all types of sawmills (i.e., sawmills employing circular saws, band saws, and frame saws) in the MWIC. The high wood-waste generation in sawmills employing circular saws compared with those using band saws is consistent with the findings of Caldera and Amarasekera (2015). The sawdust generation in band saws is determined by factors such as high kerf, poor lubrication, and lower tensioning pressure (Abeykoon and Amarasekara 2017). General improvement of sawmill management practices and replacement of obsolete machinery has been recommended to reduce the timber waste and increase efficiency (Caldera and Amarasekera 2015, Abeykoon and Amarasekara 2017).
Conclusion
The monthly wood-waste generation in MWIC was estimated to be 6,490 MT. The most common timber species used in the MWIC is teak (38.7%), followed by mahogany (28.8%) and Alstonia macrophylla (7.4%). Hence, most of the wood waste in MWIC is originating from medium-density wood. Sawdust, wanes, and offcuts are the three types of wood waste generated within the MWIC, accounting for 76.5%, 16.5%, and 6.9%, respectively. Sawmills were the biggest generator of wood waste, followed by integrated sawmills and carpentry shops. Approximately 55% of the wood waste generated in MWIC is currently used by a variety of secondary users. About 45% of wood waste enters the waste stream. Disposal of wood waste in mixed form reduces the market acceptability and the ability of secondary users to use wood waste as inputs. Hence improved wood-waste disposal practices will substantially increase the opportunities for industrial synergies and new business start-ups in MWIC for optimal use of wood waste.
