Environmental Emissions From Sawmilling

The sawmilling sector is the backbone of the Malaysian wood-based industry. The conversion of saw-logs into sawn timber releases several gases into the atmosphere, and these may contribute to environmental burdens as well as environmental impacts. By Geetha Ramasamy, Jegatheswaran Ratnasingam, Edi Suhaimi Bakar and RasminaHalis, Universiti Putra Malaysia, and Neelakandan Muttiah, Energy Consultants

The Malaysian wood-based industry began in the early 1900s. While it was primarily focused on meeting the domestic demand at the time, it has been transformed into a large, export-oriented industry, producing a wide variety of value-added productions. The industry has gained a prominent socio-economic status by contributing more than RMB20 billion in annual export earnings and providing employment to almost 226,000 workers over the last few years. In 2011, a total of 3,975 manufacturing entities were operating in the Malaysian wood-based industry.

The wood-based industry has emerged as one of the most important, prominent and fastest growing manufacturing sectors in the Malaysian economy. Despite the growing importance of value-added wood product manufacturing, the sawmilling sector remains the backbone of the wood-based industry.

Sawmilling produces sawn timber and wood waste that are exploited by the other wood-based industries to be further processed into value-added products, such as furniture, wood-based panels, moulding and joinery. Since the implementation of the first Industrial Master Plan (IMP) in 1986 by the Malaysian government, the sawmilling industry has been accorded less importance.

With a reduced supply of saw-logs from natural forest in the country, which practices sustainable forest management (SFM), the capacity for utilisation of wood within the sawmilling industry in Malaysia has also suffered.

Furthermore, the technology used in the Malaysian sawmilling sector is old and obsolete. In general, sawmills fail to modernise and automate because of a lack of finances. It has been noted that the different characteristics of the tropical hardwood and softwood saw-logs, together with the variable market demands for these sawn timbers, makes the application of new technology in the Malaysian sawmilling sector uneconomical.

As a result, the Malaysian sawmilling sector suffers from low productivity and generates a large volume of waste. According to the ITTO-CITES Project report, the generation of wood waste in the sawmilling sector of Peninsular Malaysia was approximately 45-50 percent of the total volume of saw-log input. On the other hand, the sawmilling sector is also energy-intensive. 

The electrical energy consumed during the sawmilling processes is generated off-site at power stations that burn fossil fuels. During the sawmilling process, a substantial amount of thermal energy is also produced on-site. The combustion of fossil fuels for energy generation discharges gases, such as carbon dioxide, methane, nitrous oxide, mono-nitrogen oxides—which include nitric oxide and nitrogen dioxide, carbon monoxide, sulphur dioxide, non-methane volatile organic compounds, and particulates to the environment. These gases have a negative impact on the environmental air quality.

A number of studies have investigated the effects of resource consumption in sawmilling and the resultant environmental profiles. These studies have revealed that the consumption of resources results in the discharge of a variety of gases in different quantities into the environment. Environmental emissions are different between countries and sawmills as a result of the different technologies, methods and environmental standards applied.

 

Environmental Effects 

It is widely believed that the effects of sawing softwoods is less environmentally damaging compared to hardwoods, although no conclusive reports are available at this time. In addition, the emission of several gases subsequently impacts the environment in the form of global warming, acidification, human toxicity, ozone depletion, photo-oxidant formation, material depletion, energy depletion and eutrophication potentials. Consequently, the issue of environmental performance from the sawmilling industry has become a topic of intense debate at the national and international levels.

Although alternative materials, such as steel, plastic and concrete, can replace wood for many applications, this practice is not desirable, as these materials have been reported to contribute to greater environmental burdens compared to wood.

In view of this difference, research on the environmental performance of the sawmilling sector is of high interest, especially in Malaysia, which has a large wood-based industry. Therefore, a study of the environmental performance of the sawmilling sector in Peninsular Malaysia using the life cycle assessment (LCA) technique was carried out.

The study assessed the environmental performances from the sawmilling sector. Two sawmills were chosen for the study. The selection of sawmills in this environmental burdens assessment was presumed to be representative of the overall sawmilling sector that produces rough green sawn timber of meranti species in Peninsular Malaysia. The findings of the environmental performances in this investigation provided benchmark values for the sawmilling sector, which is considered the oldest wood-processing industry in the country.

The first sawmill, referred to as sawmill A, is the biggest sawmill in Peninsular Malaysia. Sawmill A was set as the base scenario for the study. Meanwhile, the second sawmill, referred to as sawmill B, is a medium-sized sawmill. The purpose to include medium-sized sawmill in this study was to determine any notable differences from resource consumption to environmental performance when compared to sawmill A. 

Small-size sawmills do exist, but mills of this type provide custom wood products only. In addition, smaller mills tend not to keep accurate production records, and even some of the large hardwood sawmills did not have primary mill data requested.

 

Product Yield

The flow of saw-logs in the manufacturing process produced rough green sawn timber as the main product. The yield of light red meranti and dark red meranti rough green sawn timber was enumerated by applying the cubic recovery technique. The method of cubic recovery was selected as it is more practical and more accurate than the lumber recovery factor.

The mean recovery of light red meranti and dark red meranti rough green sawn timber in sawmill A differed by 10.36 percent. Likewise, the mean of the sawn timber recovery for light red meranti was 10.49 percent higher than dark red meranti in sawmill B. On the other hand, in a comparison between the sawmills, sawn timber recovery for both species in sawmill B yielded greater quantities than sawmill A by 3.23 percent and 3.05 percent for light red meranti and dark red meranti respectively.

Apart from the production of rough green sawn timber, the flow of saw-logs also resulted in wood losses in the form of off-cuts, sawdust, shavings and splinters. These wood losses were not further used in sawmill A and sawmill B. Off-cuts, sawdust, shavings and splinters were eventually sold to other mills in which off-cuts were recovered for other wood products, while sawdust, shavings and splinters were used for energy generation in the boilers.

 

Energy Consumption

The sources of energy used in the sawmilling activities were identified as electrical energy and diesel fuel energy.

Electricity was used in sawmill A and sawmill B to run the motors for the sub-system unit processes comprising the primary breakdown, secondary breakdown, quality control and conveyor belt. Energy used to operate the sub-system processes was defined as process energy. 

Diesel fuel was used in sawmill A and sawmill B for off-road transportation activities. These activities involved the carrying of saw-logs and sawn timber boards within the mills themselves. Since the study was focused on the off-site transportation activity, the fuel used was the only aspect taken into consideration.

 

Environmental Burdens

The use of resources in sawmilling activities consequently discharges the wood residues, carbon dioxide, methane, nitrogen dioxide, mono-nitrogen oxides, carbon monoxide and sulphur dioxide in different types and quantities into the environment. 

The off-site electricity was generated from the burning of fossil fuels in the conventional power stations. Meanwhile, diesel fuel was combusted on-site, especially for transportation activities. Fuel comprises carbon, sulphur, nitrogen and other compounds. Inevitably, these components were emitted into the environment in different amounts, depending on the quantities and types of fossil fuel used. The release of these gases as a result of fuel consumption is categorised as anthropogenic emission, which is related to environmental burdens.

Generally, the release of carbon dioxide, mono-nitrogen oxides, carbon monoxide and sulphur dioxide from dark red meranti was greater than that of light red meranti. As a matter of fact, the result showed that wood species factor did not affect the emission of carbon dioxide, mono-nitrogen oxides, carbon monoxide and sulphur dioxide, as the findings were non-significant between the wood species. 

The saw-log’s density, length, diameter, volume, moisture content as well as the dimensions of sawn timber produced, for both wood species, were different. The observations in this study with regards to the variability in the energy consumption, particularly electricity, for light red meranti and dark red meranti saw-logs was likely caused by the differences in saw-log characteristics and physical properties. Increasing the saw-log’s length and diameter would require additional energy during the cutting processes. Furthermore, cutting small dimension sawn timber would increase the energy demand.

Saw-logs of higher density require more energy and more material for a given cutting volume. In the meantime, the sawing volume of dark red meranti in both sawmills was higher than the light red meranti, which explains the higher use of diesel fuel energy.

Perhaps, the difference in the saw logs characteristics, physical properties, and number of logs does not have strong influence in the variation in energy consumption. As a result, the weak variability in the consumption of electrical and diesel fuel energy between the light red meranti and dark red meranti did not show any significant difference in the discharged amount of carbon dioxide, methane, nitrogen dioxide, mono-nitrogen oxides, carbon monoxide and sulphur dioxide.

The release of carbon dioxide, methane, nitrogen dioxide, mono-nitrogen oxides, carbon monoxide and sulphur dioxide is capable of impacting the environment. Based on this fact, the potential environmental impacts were evaluated.

The findings indicate that the global warming, acidification, human toxicity, eutrophication and photo-oxidant formation potentials showed a mean difference between the sawmills and wood species. A statistical analysis was performed in order to determine any significant difference for each of the potential environmental impacts between the test factors. As the normality for each of the potential environmental impacts was observed to be acceptable, MANOVA statistical test was applied for further analysis.

The first part of the MANOVA test was a multivariate test. The multivariate test for sawmill, wood species and interaction of sawmill and wood species was not statistically significant. The statistical analysis was not continued to examine in detail the univariate analysis for main effect of sawmill factor, main effect of wood species factor, and interaction of sawmill and wood species because the finding for each of the potential environmental impact would be non-significant as well.

 

 

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