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School of Natural Sciences
Degree project work
Name: Henric Svensson
Subject: Environmental science
Level: D
Nr: 2010:M2
Leaching Test with Sawdust from Different Tree Species – Appropriateness of using them as adsorption media in wastewater and in stormwater treatment
Leaching Test with Sawdust from Different Tree Species
– Appropriateness of using them as adsorption media in wastewater and in stormwater
treatment
Henric Svensson
Environmental Science 240 hp
Degree project work, Environmental Science
30 hp Master of Science
Supervisor: William Hogland, Professor, Linnaeus University, Sweden
Co- Supervisors: Marcia Marques, Professor, Linnaeus University, UERJ Brazil
Examiner: Pasi Peltola, PhD, Research associate, Linnaeus University, Sweden
Sponsors
Abstract
Bio energy in form of woodchips and sawdust is today commonly stored outdoors in heaps on
hardened surfaces, exposed to weather and wind. Any water leaching from these heaps have the
potential to be toxic to the environment.
This paper examines the quality of the water leaching from heaps of four different tree species (oak,
pine, maple and beech), by analysing different parameters such as pH, conductivity, colour, COD,
BOD7, tannins & lignins (T&L) and phenols.
The results show significant higher leaching values of COD, phenols, T&L and colour from oak
compared to the other tree species (pine, maple and beech). These leached substances from
woodchips and sawdust were shown in the BOD7 tests and BOD7/COD ratio values to be hard to
biodegrade and are therefore not easily removed from the water.
Hence it is important that wood-based fuel storage conditions are considered in bio energy generation
schemes to ensure that the environmental benefits of using woodchips and sawdust instead of
traditional fuel are not offset by the potential harm of inappropriate storage.
The investigation further showed that leaching of highly toxic substances such as phenols can be up to
10 times higher for one tree type (oak) than another (pine, beech and maple). This difference could
potentially be found for other tree species not characterized in this study. Therefore, it is important
to consider the constitution of the heaps to be able to apply appropriate storage conditions to avoid
these toxic substances in the leached water reaching sensitive watercourses. As some of these
substances are hard to biodegrade the treatment applied need a long retention time.
Another problem is the carbon: nutrient ratio, this water has a high carbon content compared to
phosphorus and nitrogen content which might prevent an efficient biodegradation. Adjusting C:N:P
ratio with low cost amendments might raise the performance of the biodegradation in for instance, a
constructed wetland.
Preface
This thesis is part of a Master of Science (one year) in Environmental Science, at the School of Pure
and Applied Natural Sciences. It is the result of a sub-project within a larger scientific project
developed at the University of Kalmar namely “Development of an Integrated Approach for Industrial
Wastewater and Stormwater Management in the Wood-industry Sector” conducted by the
Environmental Engineering Research Group which works on developing low cost, easy-to-operate
and nature-based waste water treatment methods to reduce the contribution to the environmental
pollution from the wood industry. The project seeks for solutions that use as much as possible waste
fractions from the industry for the development of treatment systems. This sub project has been
focused on the leachate from sawdust in contact with water under different solid: water ratios.
Therefore this study addresses water-related issues of companies in the wood sector. Another
Master of Science student has at the same time, investigated electrocoagulation technique as a
possible pre or post-treatment option for wastewater and stormwater from the same industrial
sector. This project is sponsored by the KK-Foundation (KK-Stiftelsen) in cooperation with four
companies in the wood sector.
For many years the environmental focus has been on the large wood industries such as the pulp and
paper mills (Ali et al. 2001; Thompson et al. 2001). For this kind of, many types of water treatment
systems have been developed (Pokhrel et al. 2004). Now it is the time to change focus to the smaller
and medium size wood manufacturing industries such as floor and furniture manufacturers, which do
not have water as part of the manufacturing processes but do use water for washing and cleaning
surfaces, machineries and floors, generating low-volume of highly polluted wastewater. It is
therefore, the purpose of the main project to which this sub-project is connected, to find solutions
that are economically attractive not only for large but also for the small and medium size companies.
This sub-project has been focused on comparative leaching from sawdust of different tree species.
In this study, the leachate from 4 different tree species (oak, pine, maple and beech) has been characterized for the following parameters: pH, conductivity, colour, COD, BOD7, tannin & lignin (T & L) and phenols. The selected test methods used in this thesis have been chosen for the following reasons:
To carry out a pre-study investigation about the appropriateness of using sawdust as an adsorption material in treatment schemes;
To use the knowledge gained about sawdust leaching to support ongoing work with developing system for stormwater and wastewater;
To contribute to the assessment of potential water pollution resulting from wood material in contact with water.
Since large heaps of sawdust and wood heaps, as well as log yards are stored outdoors, once in contact with rain and snowfall, these wood materials can potentially release a number of substances that pollute recipient water bodies. Based on these objectives the discussion in this report is divided in two main chapters: one for the
adsorption study and one for the stormwater treatment.
Rio de Janeiro 10th of August 2009
Henric Svensson
Sammanfattning (Summary in Swedish)
Denna avhandling är en del av en Master of Science (ett år) i miljövetenskap. Den är resultatet av ett
delprojekt inom ett större vetenskapligt projekt vid Högskolan i Kalmar nämligen "Development of an
Integrated Approach for Industrial Wastewater and Stormwater Management in the Wood-industry
Sector". Projektet genomförs av en miljöteknisk forskargrupp och målet är att utveckla lågkostnad,
enkel och naturbaserad hantering av processvatten för att minska miljöbelastningen från
skogsindustrin, och om möjligt använda delar av avfallet från industrin i behandlingen av
processvattnet. Detta delprojekt är fokuserat på lakvatten från sågspån vid olika L/S förhållande.
Denna studie riktar sig speciellt till företag inom träsektorn och andra civilingenjörsstudenter som
studera natur och miljövetenskap. Projektet stöds av KK-stiftelsen i samarbete med fyra företag inom
träsektorn.
Under många år har fokus på miljöarbetet inom träindustrin legat på de storskaliga massa- och
pappersbruken (Ali et al 2001, Thompson et al. 2001). För denna typ av industrier finns många olika
system tillgängligt för vattenrening (Pokhrel et al 2004). Nu är det dags att byta fokus till mindre och
medelstora aktörer inom träindustrin, såsom golv- och möbelindustrin. Dessa industrier har inte
vatten som en del av tillverknings processen utananvänder vatten för rengöring av ytor och maskiner
och golv. Dessa processer skapar låga volymer av kraftigt förorenade vatten. Det är därför det
övergripande projektet har till syfte att finna lösningar som skulle vara ekonomiskt attraktiva för de
små och medelstora företagen. Detta delprojekt har varit inriktat på att jämföra lakvatten från
sågspån.
I denna rapport har lakvatten från fyra olika trädslag (ek, tall, lönn och bok) karakteriserats för
följande parametrar: pH, konduktivitet, färg, COD, BOD7, tanniner & ligniner och fenoler. Syftet
med de valda testmetoderna i denna avhandling har valts efter följande anledningar:
För att utgöra en förstudie och undersöka användbarheten av sågspån som ett
adsorptionsmaterial.
För att använda kunskapen i pågående arbete med att utveckla system för dagvatten
och avloppsvatten.
Att bidra till bedömning av eventuella vattenföroreningar orsakade av trämaterial i kontakt
med vatten.
Eftersom stora högar med sågspån och trädrester lagrars utomhus kommer dessa i kontakt med
regn vid denna kontakt lakas det ut ett antal ämnen som förorenar mottagare
vattenförekomster.
Baserat på dessa mål är diskussionen i denna rapport är uppdelad i två kapitel: en för
adsorptionsstudien och en för dagvattenbehandling.
Rio de Janeiro 10 augusti 2009
Henric Svensson
Contents
Terms and Acronyms ........................................................................................................................... 1
1 Introduction ...................................................................................................................................... 3
1.1 Pollutants generated in the wood industry............................................................................... 4
2 Objectives ................................................................................................................................... 6
3 Material and methods ...................................................................................................................... 7
3.1 Sawdust preparation ................................................................................................................. 7
3.2 Methods .................................................................................................................................... 8
3.3 Chemical analyses ................................................................................................................... 10
4 Results ............................................................................................................................................ 11
4.1 Units ........................................................................................................................................ 11
4.2 Results of chemical analyses ................................................................................................... 11
4.3 Solid to liquid ratio (S/L) .......................................................................................................... 17
4.4 Batch leaching over time ......................................................................................................... 17
4.5 Repeated washing of batches ................................................................................................. 17
4.6 Testing the effect of metals on colour of leachate ................................................................. 18
4.7 Effect of contact time on leaching according to studied variables ......................................... 20
4.8 Simulating the relative contribution of sawdust from different species ................................ 22
5. Discussions .................................................................................................................................... 24
5.1 Stormwater .............................................................................................................................. 25
5.2 Effects of metals on the leachate colour ................................................................................. 25
5.3 Proposal of wetland for leachate treatment ........................................................................... 26
5.4 Proposal for further research .................................................................................................. 26
Conclusions ........................................................................................................................................ 27
Acknowledgements ........................................................................................................................... 28
List of Figures ..................................................................................................................................... 29
References ......................................................................................................................................... 30
1
Terms and Acronyms
COD Chemical oxygen demand
BOD Biochemical oxygen demand
L/S Liquid solid ratio
DOC The fraction of organic particles below 0.45µm
T&L Tannins and lignins
Grey-water The water from dish washing, laundry and bathing.
Leachate The extracted substances dissolved in a liquid medium, from a solid material.
Wood debris The unsorted rest products of wood handling included sawdust and wood chips.
Wood chips Pieces of wood (bigger than sawdust) chopped to pieces. Up to 10 cm
Sawdust Pieces of wood up to 4 mm.
Resins acids Toxic compound found in the wood, produced by the tree to act as a protective
and preservative substance.
Hypoxia Reduced of dissolved oxygen content of a body of water to a level detrimental to
aerobic organisms.
Phenols Substance found in wood that is water-soluble and acidic. Many of the phenolic
compounds found in wood are there due to their micro-biocide and insecticidal
effects.
2
3
1 Introduction
The wood-industry, and in particular the paper and pulp industry, is often associated with large scale
pollution of various water courses and coastal areas (Ali et al 2001; Thompson et al. 2001). A
considerable amount of research applicable to this industry has been conducted during the years to
try to find processes for pulp mills to only use renewable materials and make good use of all output
materials from the mills i.e. reducing waste production. For example, between 1996 and 2002
MISTRA (The Foundation for Strategic Environmental Research) conducted a project called KAM - The
Ecocyclic Pulp Mill, costing over 100 million SEK. As a result of this and other factors nowadays there
exist high technological treatment systems available for these types industries. However, for the
smaller manufacturers within the wood industry, such as furniture and floor manufacturers that do
not have water in the manufacturing processes but generate low volume of highly polluted
wastewaters, much less investigations have been carried out, mainly due to lack of focus and
investments for this type of wastewater. These companies have a need for low cost and easy-to-
operate technologies that can be adapted locally. Today there are few conventional functional
systems available for the treatment of small quantities of wastewaters for their specific needs.
Although the generated volume can be small, the wastewaters can have high concentrations of
various constituents which in many cases can contain very industry-specific contaminants. Thus,
there is a need to further development of wastewater treatment options for such purposes. In south-
eastern Sweden one of these companies is the wooden floor manufacturer AB Gustaf Kähr in Nybro.
This company processes annually about 83000 ton of raw wood. During the processing of wood to
produce wood floors, it generates several small but highly polluted wastewater streams. Today,
these wastewaters are left untreated and are discharged into the municipal sewage net or the
stormwater network, thus potentially either causing direct harm to the local environment or adding
load to the communal wastewater treatment plant.
The aim of the main large project as a whole is to develop water cleaning systems that implement
integrated waste water management including process water, stormwater and perhaps also leachate
from their landfills, located within the factory area. The aim of this sub-project is to evaluate sawdust
as an adsorbent material to be used in wastewater treatment schemes.
Sawdust has successfully been used as an adsorbent for many different types of pollutants in earlier
studies, as for instance, textile dyes (Izadyar et al 2007; Dulman et al 2009) and metals (Acemioglu et
al. 2004; Ahmad et al. 2005; Ajmal et al. 1998; Kaczala et al. 2009). Using sawdust to remove metals
may have as a side effect, which is the COD raising. In this project, in particular, it is of importance
that the COD concentration does not raise as a result of the sawdust usage. Here, increased COD
could be detrimental to small recipient water bodies and perhaps outweigh the benefit of removing
specific organic substances it is intended to be used for. Thus, before using sawdust as an adsorbent
in these settings, its own leachate must be characterised. The industry in question uses many wood
species and the remainders of the production, such as sawdust, are available to be used as
adsorbents.
It is also important to evaluate the various physical characteristics such as the particle sizes and
quality of the wood waste fractions. However, the various wood species can differ in their adsorbing
capacity as well as causing various leachates. Almost all wood industries have storage of wood (logs,
4
debris and sawdust) outdoors. Precipitation (rainfall and snowmelt) as well as irrigation water, used
to avoid cracks and to protect against pests, causes leachate. Toxic concentrations of for instance
phenols, T&L, resin acids, terpenes and for some wood species a low pH in the leachate have been
reported (Hedmark et al. 2008; Tao et al. 2005; Rupar et al. 2004). COD is a proxy indicator that
indirectly quantifies the amount of chemically oxidizing substances in the leachate. The main
problem with leachate from wood industries is that high COD can create oxygen depletion in water
courses and in addition contains some toxic organic substances (Hedman 2008).
The runoff has traditionally been assumed to be clean and it has been discharged untreated to the
nearest recipient such as forest ditches or rivers. Another problem is the colour of the runoff water
that can have an impact on the photosynthesis in the watercourse. This colouring is probably cause
by T&L and humic acids (Tao et al. 2005).
Figure 1 illustrates how stormwater or snow melt come in contact with storage areas for sawdust,
wood chips and log yards and impervious surfaces creating a water pollutant transport problem.
Figure 1: Stormwater from a storage area for oak wood chips at Kährs and stormwater runoff and collection in a downstream pond
1.1 Pollutants generated in the wood industry
COD: is a way to measure the amount of the oxygen needed to oxidize all organic compounds in the
sample. COD is usually measured in mg/l or ppm. A high COD value could in a stream or lake
theoretically cause hypoxia, depending on the amount of wastewater and the size of the lake or
stream. A high COD value does not obligatorily reflect the presence of toxic substances and it does
not show what kind of oxygen consuming substances is measured. According to Swedish
Environmental Agency (Naturvårdsverket rapport 4913), a concentration of COD over 16 mg/l is
considered a very high concentration in natural watercourses. In this project some of the leachate
obtained from the sawdust presented COD over 4 000 mg/l (calculated as 80 000 mg/kg dry matter).
In comparison to the process water that requires treatment within the project, concentrations
5
between 30 000 – 150 000 mg/l have been reported for different process streams (Kaczala, 2009).
The leachate obtained from the sawdust is in the error range of detection limits for the process
waters (Kaczala, 2009).
BOD: “Biochemical Oxygen Demand” is a way to measure the amount of oxygen uptake, under a
limited time by microbial activity. The idea is that a sample with a determined amount of oxygen is
kept in a dark place for 5 days (BOD5) or 7 days (BOD7), which is the most common time period used
in measurements in Sweden. At the end of the period the amount of oxygen is determined again and
the difference in oxygen content in the water before and after is calculated. The BOD value gives a
relatively good indication of how easy the organic matter in the water is biodegraded. However, in
many cases 5 or 7 days are too short incubation periods to degrade many substances. Even though,
this test gives a good indication of how difficult it is. In order to determine the degradation capacity
in a wastewater the ratio BOD/COD often is calculated. A high ratio indicates easily degradable water
and a low value shows that it’s hard to biodegrade the organic compounds in the water.
Phenols: All phenols are characterized by a common functional group, the phenolic hydroxyl group
(Asger et al. 2008). This compound is water-soluble and acidic. Many of the phenolic compounds
found in wood are there due to their micro-biocide and insecticidal properties (Samis 1999). This
might explain why the phenolic compound constitutes the most toxic compound found in wood
leachate (Goudey 1992).
Tannins & Lignins (T& L); are substances which comprise one or more phenol functional groups. They
are common in plants and have different functions; Lignin Is the substance that joins the wood cells
together (Samis 1999), whereas tannins function as a defence to stop fungi and bacteria attacking
the wood (Chung et al. 1998). Both tannins and lignin are hard to biodegrade (Tao et al. 2005).
Resin acids are also toxic compounds found in wood (Peng et al. 2000). The different types of resin
acids are also part of the trees defence system against insects and microorganisms (Keeling et al.
2006). These compounds are not analysed or investigated in this thesis.
6
2 Objectives
The main objective for this thesis is to investigate and carry out a pre-study to characterise the
leachate from sawdust from four tree species in order to give basic information about the potential
the sawdust from these trees have as an adsorption material and to look at the leachate impact on
the stormwater from outdoor wood areas.
Due to time constrictions the adsorption test itself was not conducted. Knowledge of how sawdust
reacts in a liquid phase is required to use sawdust as an adsorption material. The basic questions to
be answered are: What happens when sawdust is mixed with water? To gain knowledge about this,
leaching tests of sawdust from different tree species were made. To support and gain pre-required
knowledge on this subject, a literature survey was conducted. The leaching study contributed to the
large project, since one of the contaminants in the industry’s stormwater is the leachate from wood
debris stored outdoors.
The following sub-goals are included in the project:
to investigate the leaching from sawdust and characterize the leachate;
To investigate the effect of different L/S ratios;
To investigate the effect of sawdust particle size;
To investigate the effect of exposure time;
To investigate if there are any difference in leachate composition and quantity between
different tree types;
To suggest a treatment system for stormwater.
Previous studies have shown a difference between the colour of the leachate from batch test and
field studies and the presence of metals are suspected to be the reason for that. Therefore, this
issue was also matter of a preliminary investigation. To support these sub-goals, a literature
survey on the possibility to use sawdust as an adsorbent for organic compounds was also
conducted.
7
3 Material and methods
In this project, sawdust from oak (Quercus robur), maple (Acer platanoides), pine (Pinus sylvestris)
and beech (Fagus sylvatica) were used. The definition of sawdust in this project is industrial wood
debris with a maximum size of 4 mm. Wood chips are larger and are produced using a chipper that
grinds wood to sizes up to 10 cm.
The sawdust used in the tests was collected from a single tree (plank) from each one of the four
species; it was not known where the trees had been grown. There are most likely differences in the
quality of the sawdust related to where the tree has lived, due to local and geological conditions and
the age of the tree when it was harvested. If these variables result in significant differences it is not
known and it was not investigated during this study, although the hypothesis should be raised.
3.1 Sawdust preparation
The sawdust used in this report was collected from AB Gustaf Kähr factory in Nybro, Sweden. In
order to homogenize the sawdust and ensure the particle sizes were below 4 mm, which is a
requirement to apply the standard method used for this study (test 1 “Batch leaching over 24
hours”), the sawdust was sieved through a sieve of 4 mm grid.
Then, one portion of the sawdust is used to calculate the moisture content in the sawdust. This is
carried out by drying the sawdust in an oven during approx. 24 h at 105 ˚C.
The sawdust used in the tests is not dried in the oven but the moisture content is accounted for as
detailed in the standard.
When wood chips were used it contained larger pieces of the wood from a chippers or shredder with
varying sizes and it was not sieved.
8
3.2 Methods
The overall research diagram is presented in Figure 2.
3.2.1 Batch leaching test over 24 hours
This is a leaching test (Figure 3) based on the standard method (SS 12457-2:2002) with small
modifications. Because of the absorption capacity of sawdust, to work with the liquid solid ratio 10:1
which is prescribed in the standard method was not feasible. Instead, higher liquid solid ratios 20:1
and 40:1 were used in this test. The liquid/solid ratio is calculated using the following adjusted
equation to calculate the amount of water:
L20=20-(MC/100)*Md
L40=40-(MC/100)*Md
Where:
MC= moisture content (%)
Md= dry mass of the test portion (Kg)
L= amount of water to add for L/S 20:1 and 40:1
Figure 3: Picture of the setup of sawdust leaching test.
Selecting the tree
species for the tests &
obtaining the material
Batch leaching
test over 24 hours
Washing of the
sawdust (as pre-
treatment)
Batch leaching
test with
sampling over
time
Testing the effect s of
metals on the colour
of the leachate
Data analysis.
Figure 2: Flowchart of research methodological approach.
9
The amount of sawdust used in each test was 0.009 Kg (dry weight) sawdust and then, mixed with
distilled water or rainwater according to the equation in the standard method. The agitation was
conducted using magnetic stirrers for 24 h. After 24 h the test portion was filtrated over a GF/C
Whatman 0.45 µm microfiber filter. The analyses1 were then conducted on the filtrate. This test was
repeated with rainwater instead of distilled water. The rainwater was collected as rainwater from a
sheet metal roof located next to The School of Pure & Applied Natural Sciences, in Kalmar, Sweden
about 30 km south east from Kalmar. It was stored refrigerated in 6 ˚C before use. The pH was 5.3
and the conductivity 35 µS/m COD, value too low to be analysed with available equipment.
3.2.2 Sawdust washing as pre-treatment
To establish the sawdust properties after washing, a series of tests were conducted with sawdust
that was reused after the 24 hours test. In this case, the sawdust was treated exactly as in “4.1 Batch
leaching test over 24 hours” but a larger amount of sawdust was used (0.018kg). After the test the
sawdust was sieved with a 125 µm sieve. The sawdust was then dried in the oven before being used
in a new 24 h leaching test. A smaller amount (average lost 1 mg each turn) than specified was used
due to the fact that some of the sawdust was lost in the sieving procedure. The L/S properties were
recalculated so that the L/S ration remained constant. This procedure was repeated to a total
amount of 6 times. After that, the leaching concentration from the sawdust was too low for the
analysing method used.
3.2.3 Batch leaching test with sampling over time
This is a further development of the ”4.1 Batch leaching test over 24 hours”. In this test a higher L:S
ratio of 1:40, was used (0.018kg dry weight sawdust). Then, a small sample with aprox. 20 mg of the
liquid/solid mixture was extracted at different time intervals. The samples were extracted with a
modified syringe. The sampling procedure was based on the principle that if the extracted sample
has the same liquid: solid ratio as the batch where it is taken from, the L/S ratio will not change
significantly in the batch. Therefore the syringe had a big inlet to also allow the larger particles to be
collected. After the extraction, the test portion was filtrated with 0.45 µm filters and directly
afterwards the analyses were conducted on the sample, when it was not possible to make analyses
on the same day the sample were stored in refrigerator to the next day and then analyzed. The pH
and conductivity measurements were made directly in the beaker.
3.2.4 Testing the effect of metals on colouring of leachate
Test 1: Distilled water and sawdust from oak was mixed by shaking. In a E-flask 500 ml half-filled with
sawdust (100 g), distilled water was added (500 ml) to a level so it covered the sawdust. Three
batches were prepared of which, the first one contained only oak and water, the second one
contained oak, Fe powder (about ½ teaspoon or 20 mg) and water;-and the last one contained oak,
Fe (about ½ teaspoon), water and oxygen, which was added in form of compressed air.
1 See ”Types of analyses in this report
10
Test 2: Separate batches of pine, oak, beech and maple mixed with Fe. The same procedure
described in test 1 was applied.
Test 3: In order to find out if other metals than Fe would have the same effect as Fe, a batch using
aluminium (Al) powder was prepared in the same way as “Test 2”, where instead of Fe powder, Al
powder was used.
3.3 Chemical analyses
The analyses were carried out with at least 3 replicates and sometimes up to 6 replicates. The tests
over time2 and the rain water test3 have only 2 replicates per tree species.
The analytical procedures described below were used for all tests.
The pH was analysed with a Mettler Toledo SG2. The pH was measured directly after filtration, under
the “4.3 Batch leaching test with sampling over time” the pH was measured in the batch not in the
filtrate. The pH is presented as the negative 10th logarithm of hydrogen ions concentration at 20 oC to
the base 10 (pH).
Conductivity was analysed with a WTW Multi 342 and the results were presented as µS/m. The
conductivity was measured directly after filtration, under the “4.3 Batch leaching test with sampling
over time” the conductivity was measured in the batch not in the filtrate.
Colour was analysed with Lovibond daylight 2000 unit and the unit used is Pt/L. Dilution to high
degree of the leachate was needed to get the samples inside the equipments operating range, which
gives an uncertainty in the results (related to dilution effect and ocular reading of the colour).
Phenols were analysed using Dr Lange kit4 (LCK 346, 5-200mg/L). In some cases, dilution was made to get the sample inside the operating range of the kit. The result was then recalculated and presented as mg/dry matter of sawdust.
To analyse the tannins and lignin’s the Standard Method “5550 tannin and lignin” (U.S Water Environment Federation.) was used. The results were then recalculated and presented as mg/dry matter sawdust.
Analyses of COD were made using a Dr Lange kit5 (LCK 114 150-1000mg/L). In some cases dilution was made to get the sample within the operating range of the kit. The result was then recalculated and presented as mg/dry matter sawdust.
Analyses were made according to the European Standard “ISO 5815:1989”. The bottle used was a 250 ml Winkler bottle. The result was then recalculated and presented as mg/dry matter sawdust. Seeding water was not used but it was assumed that the leachate itself contained a sufficient amount of biodegrading microbial organisms.
2 Se Methods ” Batch leaching test with sampling over time”
3 All the values when rainwater is used
4 Pre-prepared cuvettes test that is determining concentration using a spectrophotometer.
5 Preprepared cuvettes test that is determining concentration using a spectrophotometer.
11
4 Results
4.1 Units
For this project it was decided to present the values as mg/kg dry mater according to the standard
method (SS 12457-2:2002). Another way to present these results is as concentration (mg/l). In the
last case the low L/S ratio will have the highest pollutant concentration values (Table 1). In the case
the result is presented as the amount of leaching mg/kg dry matter then the high L/S will have the
highest pollutant concentration values. This happens because more water in the high L/S ratio
samples result in that even if the concentration is lower more pollutants have been leaching in to the
solution, which is visible when data is presented in mg/kg dry matter. Therefore, it is always
important to think of the unit selected when interpreting the data.
Table 1: Leachate quality with leaching tests using oak at different L/S ratios.
Tree type L/S
COD mg/l
mg/kg dry matter COD
Oak 40 2 365 94 600
Oak 40 2 340 93 600
Oak 40 2 170 86 841
Oak 20 4 060 81 200
Oak 20 4 310 86 200
Oak 20 4 100 82 077
4.2 Results of chemical analyses
Differences between oak and the other three species (pine, maple and beech) where clear shown for
basically all parameters analysed. This shows that it is important to know what type of three species
a storage heap consists of, to foresee the leachate that can be released from the heap, once in
contact with water.
In order to get a fuller picture of leachate content and properties, each species have to be studied
separately as it became clear each species have it very own properties. Statistical tests (two way
ANOVA) show that there is a significant difference between leaching for all of the four tree types
except between maple and beech.
pH: The leachate pH values for all four wood species under four different treatments are shown in
Figure 4. The liquid solid ratios tested seem to be of no significance for the pH of the leachate.
However, the specie that generated the sawdust is clearly significant. This means that it might be
possible to regulate/adjust pH in water for different purposes, with the use of different types of
wood debris. However, the effect of this is not analysed and the buffering capacity of sawdust has to
be tested.
The test using rain water instead of distilled water seems only to have a significant difference for the
two species, maple and beech, close to pH neutral, with the pH slightly higher for the rainwater tests.
12
Figure 4: The pH of maple, pine, oak and beech leachate after 24 hours leaching test at different solid/liquid (S/L) ratio, for distilled-, rainwater and after washing treatment. Result is shown with SD (number of independent observations: 4 > n <6).
Conductivity: The conductivity of the leachate does not differ much among different tree species.
On the other hand there is a difference for the different solid to liquid ratios: S/L 1:20 and the 1:40
(Figure 5). This is probably because the dilution of the ions from the sawdust is bigger at the S/L ratio
1:40. All of the values found are below the levels in ordinary lakes in Sweden (average in Swedish
lakes 200 to 2000 µS/M) which would imply that sawdust would have a low impact on conductivity in
water (Bydén et al. 2003). This also indicates that the leachate does not contain high values of
metals, or salts that should have increased the conductivity values.
Figure 5: The conductivity of leachate obtained from maple, pine, oak and beech after 24 h of leaching test at different S/L ratios, with distilled and rainwater. Bars show S.D. (number of independent observations: 4 > n <6).
Colour: The colour of the leachate is measured as Pt/L. This is not an exact way to measure the
colour and to get these waters within the range of the equipment capabilities high dilutions were
made, which increase uncertainties. However, the difference in colour between oak and the other
three species was easy to distinguishable (Figure 6). According to (Bydèn et al. 2003) a lake with
colour values over 10 is considered coloured and with a value over 100 it is considered highly
3
4
5
6
7
8
Maple Pine Oak Beech
pH
pH
S/L 1:40 Washed
S/L 1:40
S/L 1:30 Rain water
S/L 1:20
S/L 1:20 Rain Water
3
53
103
153
203
Beech Maple Oak Pine
µS/
m
Conductivity
S/L 1:20
S/L 1:40
S/L 1:30 Rain water
S/L 1:20 Rain water
13
coloured. Based on this classification, the leachates from all species studied were considered as
highly coloured water.
Figure 6: Colour of maple, pine, oak and beech leachate after 24 hours of leaching test at different L/S ratios; bars show S.D. (number of independent observations: 4 > n <6).
COD: The differences are large when comparing the COD values of oak leachate with the leachate
from the other 3 species (beech, maple and pine). Oak had about five times the COD amount
compared to the others. However, the oak’s wood chips do not leach the same amount in 24 h as the
sawdust. The probable explanation is that it takes longer time for the water to penetrate the wood
chips and wash out the substances and the contact surface is a lot lesser for the wood chips. The
effect of the pre-washing is almost the same for both oak and beech, and gives approximately 70%
less COD after washing (Figure 7). In Sweden there are no general threshold limits given for COD in
stormwater according to the authorities. The limits and the level accepted is determined individually
by the companies and the local environmental authorities. From 2009 on, the environmental
authorities in Sweden have planned to establish limits for emission of this parameter, due to the EU
Water Framework Directive-WFD (Vinrot, 2007).
0
500
1000
1500
2000
2500
Beech Maple Oak Pine
Pt/
L
Colour
S/L 1:20
S/L 1:40
14
Figure 7: COD in leachate from maple, pine, oak, beech and oak chips (with and without pre-washing treatment) after 24 h of leaching test at different S/L ratios using distilled and rainwater. “Oak chips 48” are wood chips that have been allowed to leach previously for 48 hours. The error bars show S.D. and the number of independent observations is: 4 > n <6.
Phenols: Regarding phenols, oak gives about ten times more phenol substances in the sawdust
leachate after 24 h of leaching test than the three other species. When pre-treatment of the
material by washing it is carried out, only about 30% of the phenol compounds amounts are leaching
from the sawdust for beech and oak (Figure 8). An interesting aspect observed is that the ratio for
phenols and COD (Phenols/COD) seems to be almost the same for wood chips in the 24 hours and 48
hours test as for the sawdust 24 hours (Figure 6). Phenols are acute toxic to freshwater invertebrates
such as Daphnia magna at levels ranging between 7mg/l to 200mg/l (WHO, Environmental Health
Criteria 161, 1994). If it is assumed that the first leaching (24 hours) at this low L/S (20:1) is about
50%6 (Mclaughlan et al. 2009) of the total amount that could be released. Therefore one kilogram of
dry oak releases about 6 000 mg of phenolic compounds. This means that on kilogram of oak sawdust
can cause toxic effect in about 800 l of water, only taking into consideration, phenol content
(therefore, without considering the T&L effect). Phenols stand for about 1-3% of the total COD
content in the leachate (Figure 9).
6 See chapter “4.4 Washing”
0
20000
40000
60000
80000
100000
Beech Maple Oak Pine Oak chips 24
Oak chips 48
CO
Dm
g/k
g d
ry m
atte
r COD S/L 1:40
S/L 1:30 Rain waterS/L 20:1
S/L 1:20 Rain waterS/L 1:40 Washed
15
Figure 8. Phenols content in leachate from Maple, Pine, Oak, Beech and Oak chips (with and without pre-washing) after 24 h of leaching test at different S/L ratios with distilled water and rainwater. “Oak chips 48” are wood chips that have been leaching previously for 48 h. Error bars show S.D. The number of independent observations is: 4 > n <6.
Figure 9. Ratio of COD/phenols after 24 hours leaching test for beech, maple, oak, pine, and oak chip. Oak chips 48 are chips that have been allowed to leach previously for 48 h.
T&L: Tannins and lignin are analysed as one group of substances (Figure 10); it is therefore
impossible to find out how much tannins relatively to lignin is found in the samples using the
selected method. However, there is one indicator which appears to be related to tannin respectively
lignin content: tannins and iron react and give a black colour7 to the leachate. This indicates that a
higher amount of the pine T&L is tannins than for beech and maple. Oak have a much higher amount
of total T&L but the ratio of tannins respectively lignin cannot be distinguished (Figure 11). There is a
potential problem with the type of analysis used in this study; the analysis of tannins & lignins is
based on the colouring that appears when tannins & lignin react with folin phenol. However,
according to Samis (1999) many other reducing compounds might also react with folin phenol giving
7 See chapter ” Testing the effect of metals on colouring of leachate “.
0
1000
2000
3000
4000
Beech Maple Oak Pine Oak chips 24
Oak chips 48
mg
/kg
dry
mat
ter Phenols S/L 1:40
S/L 1:30 Rain water
S/L 1:20
S/L 1:20 Rain water
S/L 1:40 Washed
0,0
1,0
2,0
3,0
4,0
Beech Maple Oak Pine Oak chips 24
Oak chips 48
CO
D/P
hen
ols
Ration Phenols
S/L 1:40
S/L 1:30 Rain water
S/L 1:20
S/L 1:20 Rain water
16
the same colouring therefore, inflating test results. It has to be established that no other reducing
compounds are present in the sample to have a correct correlation between T&L content and
amount of folin phenol.
Figure 10. T&L content of maple, pine, oak, beech and oak chips leachate after 24 hours leaching test at different S/L ratio and after washing treatment. Oak chip 48 is chips that have been allowed to leach for 48 hours. Error bars show S.D. (number of independent observations: 4 > n <6).
Figure 11. T&L/COD ratio in leachate after 24 h of leaching test for beech, maple, oak, pine, and oak chip. Oak chip 48 is chips that have been allowed to leach for 48 hours.
BOD7: The BOD7 values are surprisingly low; only about 20% of the COD (Figure 12)This indicates that
the organic substances in the samples were hardly biodegradable and/or it’s not enough time with 7
days (Bydèn et al. 2003). Especially phenol compounds and T&L celluloses are known as substances
that are hard to biodegrade.
Figure 12: BOD/COD ratio in the sawdust leachate after 24 h of leaching from beech, maple, oak and pine at different S/L ratios.
0
10 000
20 000
30 000
40 000
Beech Maple Oak Pine Oak chips 24
Oak chips 48
mg/
kg d
ry m
atte
r
Tannins & Lignins
S/L 1:40
S/L 1:20
S/L 1:40 Washed
0,00
0,10
0,20
0,30
Beech Maple Oak Pine
BO
D/V
OD
Ration COD/BOD
S/L 1:40
S/L 1:20
17
4.3 Solid to liquid ratio (S/L)
Based on Figure 13, there is no existing difference between the S/L ratios. However, if looking at
Figure 6 is the difference very big. But this is the concentration in the leachate and that differs
according to the S/L not to the total leaching. So the total leaching of substances doesn’t matter on
the S/L ratio but the concentration of substances in the leachate does. However, at a bigger
difference of the S/L ratio for example 1:200 a small difference in the total amount might exist. This
because there might be an equilibrium relationship between the water and the sawdust and at a
higher S/L ratio a greater amount could leach from the sawdust. This is not proved and only
speculations.
Figure 13: The COD concentration of beech, maple, oak and pine for leachate after 24 hours leaching test at different S/L ratio. Error bar = SD; Number of independent observation: 4 < n > 6.
4.4 Batch leaching over time
The main result of this test is that after 24 h the equilibrium is reached for all water quality variables
included in this study. No significant leaching happened after 24 h. This shows that beyond 24h, it’s
the S/L ratio that is the most important factor for the quality of the leachate from the sawdust and
not the contact time. The wobbling pattern found in the T&L (Figure 21) is probably related to the
uncertainty in the test. If the test had been made on wood chips the graph would most likely show a
longer contact time before the leaching would reach this equilibrium.
4.5 Repeated washing of batches
The profile of COD concentration after repeated washing of batches oak and beech sawdust with
distilled water is presented in (Figure 14).
0
1000
2000
3000
4000
5000
Beech Maple Oak Pine Oak chips 24
Oak chips 48
mg/
L
COD
S/L 20:1
S/L 1:40
18
COD (% of total leaching)
0 2 4 6 80
20
40
60
80
100Oak
Beech
%
No. of washes
Figure 14: The effect of washing sawdust repeatedly. No of independent observations: 4. The standard deviation (S.D.) were too small to be seem in the graph.
The experimental data showed that the COD concentration in the leachate decreased to about 40%
after the second wash, which is similar to the effect previously described by Maclaughlan et al.
(2008) who found that about 50% of COD released was removed by the first washing. COD
concentration dramatically reduced after the second washing. High reduction of COD in the first
washing might be due to the release of organic particles attached to the surface of sawdust and also
some chemical substances (for instance, cellulose, T&L and phenol) from sawdust itself. However,
the COD concentration was almost constant after the third washing and onward. The final COD
concentration contained in leachate was less than 5% of initial COD after washed 6 times.
4.6 Testing the effect of metals on colour of leachate
Based on preliminary observations it could be assumed that some compounds leaching from the oak
sawdust reacts with iron (Fe) and produce a black colour on both wood leaching and water. Fe in a
low pH environment by itself produces a black colour (Figure 15, 16) but not the distinct one
observed in the water when in contact with oak. The result does not exclude that other metals could
have this similar effect but after the test with Aluminium (Al), for instance (Figure 17) it is concluded
that not all metals have this effect. After consulting with professionals within the wood industry,
indications are that that Zinc and Lead could have the same effect as Iron but this has not been
investigated neither confirmed in this study.
19
Figure 15: The colour after mixing sawdust with Iron (Fe), batch: (1) oak; (2), oak and Fe; (3) oak and Fe and O2.
Figure 16: The colour after different combinations of mixing sawdust and iron (Fe). Batch (1) oak; (2), oak and Fe; (3) oak and Fe and O2; (4); pine and Fe; (5) beech and Fe; (6) maple and Fe; (7) solution with pH 4 and Fe.
20
Figure 17: The mixing of different tree species and aluminium, (Al), batch (1), pine; (2), pine and Al; (3) oak; (4) oak and Al; (5) maple and Al; (6) beech and Al.
4.7 Effect of contact time on leaching according to studied variables
The effect of the contact time on the values of pH, phenols, COD and T&L (tannins and lignin) is
shown in Figures 18, 19, 20 and 21. Excluding the variations registered during the first hours, with a
trend for increasing concentration of phenols, COD and T&L and decreasing pH during the first 24
hours, no fluctuation of importance was observed after this contact period for any of the analysed
parameters.
Figure 18: Leachate pH development over time during leaching tests with maple, pine, oak and beech sawdust and L/S 40:1. Error bars show S.D. (number of independent observations: 2).
3,5
4,5
5,5
6,5
0 24 48 72 96 120 144 168 192 216 240
pH
Hours
pH change over time
Maple
Pine
Oak
Beech
21
Figure 19: Phenol concentration over time during leaching tests with maple, pine, oak and beech sawdust and S/L 1:40 (logarithmic scale at the x-axis). Error bars show S.D. (number of independent observations: 2).
Figure 20 COD concentration over time during leaching tests with maple, pine, oak and beech sawdust and S/L 1:40. Error bars show S.D. (number of independent observations: 2).
100
400
1600
0 24 48 72 96 120 144 168 192 216 240
mg/
kg d
ry m
atte
r
Hours
Phenols
Maple
Pine
Oak
Beech
0
20 000
40 000
60 000
80 000
100 000
0 24 48 72 96 120 144 168 192 216 240
mg
CO
D/k
g d
rym
atte
r
Hours
CODOak
Pine
Maple
Beech
22
Figure 21: T&L concentration over time during leaching tests with maple, pine, oak and beech sawdust, and S/L 1:40 (logarithmic scale at the x-axis). Error bars show S.D. (number of independent observations: 2).
4.8 Simulating the relative contribution of sawdust from different species
Putting the results of this study into the context of existing wastewater streams and measurement
precision of analytical methods, one can calculate the amount of sawdust from different species that
can be added to the wastewater with treatment purposes (removal of metals, for instance), without
the side effect of increasing COD due to leaching from the sawdust itself.
For example, the glue water at Kährs (the wastewater generated after cleaning cleaning/washing of
gluing machine) has about 25 000 mg/l of COD (Laohaprapanon, 2009). The COD concentration is
measured with a Dr Lange kit (LCK 114 150-1000mg/L), which has a confidence interval of about
8% (± 4%). This means that for one cubic meter of the glue water analysed the error can be about
2,000,000 mg (2 Kg) of COD. The question is then how much sawdust is needed to affect the water
quality significantly e.g. above the error (Figure 22). In this calculation it is assumed that the total
leaching from one Kg of sawdust in the lower S/L ratio ratio (1:20) will be the double than the
amount leached at S/L 1:20. This assumption is based on the observation previously mentioned that
the first (after 24h) leaching is 50% of the total leaching from the sawdust8 (Mclaughlan et al, 2009).
The results show that not before the use of about 12 kg of oak, and 30 kg of pine per m3 of water the
leaching is in the size of the error of the analysing test for the glue water. This means that quite a lot
of sawdust - almost 80 kg of beech and maple - could be used for adsorption without even affecting
the waters in a notable way.
8 See chapter ”4.4 Washing”
1000
10000
0 24 48 72 96 120 144 168 192 216 240
mg
T&L/
kg d
ry m
atte
r
Hours
Tannins and lignins
Maple
Pine
Beech
Oak
23
Figure 22: The leaching from sawdust from four different tree types in one cubic meter of water. Based on at this low S/L the leaching is about double that the one at S/L 1:20.
0
500 000
1 000 000
1 500 000
2 000 000
2 500 000
3 000 000
0 10 20 30 40 50 60 70 80
mg
CO
D i
n o
ne
kub
ik
met
er w
ater
kg dry sawdust
Maple
Beech
Oak
Pine
24
5. Discussions
The two main goals in this project was to perform a preliminary study to assess the appropriateness
of using sawdust as a low-cost absorbent material for removal of pollutants from industrial
wastewater and; characterize selected compounds that are leaching from sawdust and their leaching
patterns. A question raised was how to manage the stormwater mixed with the leachate leaching
from sawdust heaps stored outdoors.
The main result from the tests is that there are big differences in the leachate composition generated
by different tree species. Sawdust from oak, for instance, gives high values of the pollutants
analyzed, compared to the other species. Most parameters analyzed (tannins & lignin, phenols, COD)
are known to have negative impact on aquatic ecosystems. These results are not surprising, as oak is
known as a hard wood that is resistant against degradation. The fact that fungi and bacteria cannot
easily degrade oak might be explained by the high values of tannins and phenols (Samis et al, 1999)
found in this type of wood and the low pH of these substances providing the trees with natural
defence against microbial degradation. The high values of lignins (measured by high tannins and
lignin content) would explain the hardness of oak wood. Lignins are the substance that keeps the
cellulose cells together in the wood (Samis et al, 1999). For the other tree species, no big difference
was found for these parameters, but for pH. The pH varied from 4.1 (oak) up to 6.8 (maple), which is
also an interesting information from the environmental impact viewpoint, in particularly when
considering the size of the receiving water body.
If it is true that high concentrations of T&L, phenol, etc are associated to high resistance to
biodegradation, other resistant species such as European Larch (Larix decidua), Speckled Alder (Alnus
incana) and Wych Elm (Ulmus glabra) (SLU, 2009), are expected to also give high values of pollutant
in the leachate and attention shall be paid to the selected storage method.
The knowledge gathered by this study could be useful when designing integrated wastewater
treatment systems for the wood industry. It has been demonstrated, for instance, that sawdust from
P. sylvestris shows a good efficiency as adsorbent to remove some toxic metals from wastewater
(Kaczala et al, 2009). The sawdust from different species might also be useful for regulation of the pH
in a wastewater stream. Flocculation of different pollutants is often pH dependent. The leaching
from sawdust stored areas might be a good pH adjuster. The sawdust can also work as a filter and
when it has been used the sawdust could be removed, dried and then burned as disposal method
depending on the organically pollutants that have been flocked. This would have a further benefit
gaining energy through the burning process.
In a trade-off approach, the adsorption of toxic substances must be better for the environment than
the eventually negative effect caused by leaching of compounds from the sawdust. One constraint
that might be raised regarding the use of sawdust as an adsorbent for treating different wastewaters
is the risk of leaching of other pollutants and increasing COD concentration in the water. The
simulation of this phenomenon using a real wastewater composition (glue water) from Kährs
demonstrated that this is not the case.
25
One real problem is that the leachate from the sawdust of all studied species is not easily
biodegradable (which is the case of wastewaters with BOD/COD ratio below 0.3 as stated by Bydèn
et al. 2003 among others). Potential low-cost adsorbents studied during the last years are mainly
straws, tree bark, peat and sawdust. Adsorption of metals by sawdust has been described by Shukla
et al. (2002); Acemioglu et al. (2004); Ahmad et al. (2005); Kaczala et al. (2009); Ajmal et al. (1998).
Sawdust has also been used to remove nitrogen from groundwater (Schipper et al. 1998). Removal of
different types of dyes by sawdust has also been described (Hamdaoui, 2005). These small streams of
contaminated water as for example the “glue water” consisting of about 500 l/week is highly
contaminated with around COD 25 000 mg/l (Laohaprapanon, 2009). However it is not likely that
sawdust will adsorb sufficient COD given substances from this kind of highly contaminated
wastewaters.
5.1 Stormwater
Investigations have been carried out by the main project to which this sub-project is linked during more than one year when leaching from a field-scale storage heap of oak chip at Kährs in Nybro have been regularly monitored (Kaczala, 2009). The runoff from the storage areas with wood debris and wood chips did not have as high values as at the leachate analysed in the present leaching lab study. This might be due the fact that the leaching from the field storage heap was probably diluted with stormwater runoff from surroundings before the sampling point. Even though, the concentrations found were high enough to require some kind of treatment before discharging the stormwater into recipient water bodies. Since this stormwater has also low BOD/COD ratio, and therefore, low biodegradability, and considering the level of precipitation in the Nybro area in Sweden the design of on-site treatment sytem would require a big equalization pond for this water to be collected, which might not be a feasible solution for several reasons such as space and economics. The stormwater with the leachate from the heap studied in Nybro is currently discharged into a forest ditch that about 15 km downstream discharges into the “Natura 2000” classified river Ljungbyån. Therefore, it is of importance to find out the concentration and the total load of pollution in the water discharged into the ditch and also investigate the pollution situation at the point the water reaches the river Ljungbyån. It is likely that a dominating part of the pollutants already have been degraded or percolated into the groundwater along the river before it reaches the recipient river. One way to treat the runoff is to make a constructed wetland which would have a further benefit of increasing the biodiversity in the area. The wetland and the collection of the stormwater would require a quite large area on the industry area and also a new stormwater collection system. Another way to reduce the amount of leachate sufficiently which would also generate higher energy efficiency is to store the wood debris indoors. This might even reduce the risk of fire by self ignition through reducing the heat producing microbial activity in the storage of the heaps. This ought to be considered for storage of any oak, as oak releases very high amount of toxic compounds (phenol, T&L plus lowering pH).
5.2 Effects of metals on the leachate colour
Because oak reacts with Fe giving colour, it might not be a good absorbent to use, as a metal free
environment is not likely to occur in the industry. The colouring depends on a reaction between
tannins and iron (Koch, 2008; Kreber, 1994; Williams et al, 2002). Although no toxic effect is related
to the dark colour, besides an esthetical problem, is likely that it has a negative impact in the
photosynthesis in aquatic ecosystems.
26
5.3 Proposal of wetland for leachate treatment
Besides high COD content and low biodegradability, some studies point out high nutrients content
(Jonsson et al, 2004) and others, high carbon content to nutrient as a constraint for treatment of
these wastewaters in constructed wetlands (Tao et al 2004; Tao et al 2005). A BOD:N:P ratio of
about 100:17:3 is recommended (Hammer et al. 2001). Studies have shown that a well adjusted
BOD:N:P ratio raises the treatment efficiency of the wetland (Masbough et al. 2005). Masbough et al.
(2005) investigated the removal of pollutants from stormwater generated from a log yard. They
managed to remove BOD between 52-63% and COD between 25-51%. The study shows that adding
nutrients (phosphorus and nitrogen as urea) successfully removed more pollutants from the
stormwater than without. Low amount of nutrients can limit the organisms in the wetland to work
efficiently (Gopal, 1999; Kadlec et al, 1996). In Masbough et al (2005) study is the oxygen level in the
outlet of the treatment system very low (0.3mg/l) which indicates that the breakdown of organic
matter mostly is done by anaerobic processes. This might suggest that if more oxygen is added to the
system an even better uptake of COD might be reached inside the system.
Reduction of nitrogen and phosphorus is often the goal for constructed wetlands. This is usually done
by combining anaerobic and aerobic conditions in wetlands. In the wood industrial sector which is
the focus of the main project, the goal is to reduce the high COD. The problem would therefore be
how to transfer oxygen to the water, which could be done by water overflow or by harvesting to
stimulate biomass production through photosynthesis.
Thypha latifolia is suggested because it`s well-known as a resistant specie to heavy loads of
pollutants (Masbough et al. 2005) but maybe in the later parts of the system, submerged plants and
algae could be used to increase oxygen levels. To ensure optimal conditions for photosynthesis in the
water shadowing should be avoided.
Another strategy to construct a wetland is to use an anaerobic wetland with high retention time
(Hunter et al, 1993; Tao 2004).
5.4 Proposal for further research
One area of importance for further investigations is to clarify how aging affects the sawdust leaching
pattern; as a result of microbiological activities in storage heaps.
Another practical aspect to clarify is related to the need of sawdust pre-treatment with washing or
other treatment methods before using it as adsorbent, even when stored for long periods and
leached by rainwater.
Investigation about the effectiveness of using sawdust to regulate the pH for different types of
wastewater and the buffering capacity of sawdust leachate is also suggested. Furthermore, it would
also valuable to know the leachate behaviour at different osmotic conditions that might occur in
wastewater. Is the leaching the same when the water already have 20 000 mg/l in COD? Is there a
chemical equilibrium function that makes the sawdust leaching less?
Adsorption tests for different types of wastewaters are suggested in order to verify if other
pollutants besides metals are effectively absorbed by the sawdust.
27
Conclusions
There is a significant difference in leachate quantity and composition of organically
substances depending on the tree species.
Oak is leaching higher amounts of toxic substances to the environment than maple, beech
and pine.
The high colouring of leachate from oak is likely to be caused by tannins reacting with metals
in water, the metal probably being iron.
The leachate from wood is hard to biodegrade.
One kilogram of dry oak sawdust is leaching enough of phenolic substances to make 800 L of
water toxic to aquatic organisms.
No literature supports the idea of using sawdust as an adsorbent for organic substances.
Sawdust has been used successfully for treating metal’s and dyes.
28
Acknowledgements
First of all I would like to acknowledge Professor William Hogland for giving me this opportunity to
write my master thesis under his supervision, and helping to structure this thesis from a technical
and scientific point of view. It has been very interesting to have the opportunity to work within a
large research project, having close contact with other MSc students, PhD students, professors and
students from different countries.
I know that I will have an enormous use of the knowledge gained concerning the management of
large research projects in cooperation with the industry and international cooperation in teaching
and research. I have learnt how to manage projects with the industry, in particular, how to prepare
myself and the group for research group meetings, for meetings with the companies and meetings
with international students, professors and scientists.
I also want to thank professor Marcia Marques together with professor Hogland for giving me the
possibility to finalise the thesis and discuss my results with students and researchers in Brazil with
the financial support from STINT (The Swedish Foundation for International Cooperation in Research
and Higher Education) and for giving me valuable constructive criticisms on the report and assistance
with statistical analyses.
Furthermore, I want to acknowledge the other research members of KK-Stiftelsen project for their
support and, in particular the PhD students Mr Fabio Kaczala and Ms Sawanya Laohaprapanon for
their help with the daily work in the laboratory and field studies as well as many cultural and sporty
activities during our spare time.
The support of KK-Stiftelsen and the companies AB Gustaf Kähr, KalmarEnergi AB, AczoNobel and
Becker Acroma AB to the main project to which, this work is related is highly acknowledged.
29
List of Figures
Figure1: Stormwater from a storage area for oak wood chips at Kährs and stormwater runoff and
collection in a downstream pond ............................................................................................................ 7
Figure 2: A conceptual research methodology......................................................................................10
Figure 3: Picture of the setup of sawdust leaching test ........................................................................ 10
Figure 4: The pH of maple, pine, oak and beech leachate after 24 hours leaching test ....................... 14
Figure 5: The conductivity of leachate obtained from maple, pine, oak and beech after 24 h of
leaching test .......................................................................................................................................... 14
Figure 6: Colour of maple, pine, oak and beech leachate after 24 hours of leaching test ................... 15
Figure 7: COD in leachate from maple, pine, oak, beech and oak chips . ............................................. 16
Figure 8: Phenols content in leachate from Maple, Pine, Oak, Beech and Oak chips .......................... 17
Figure 9: Ratio of COD/phenols after 24 hours leaching test ............................................................... 17
Figure 10: T&L content of maple, pine, oak, beech and oak chips leachate after 24 hours leaching test
............................................................................................................................................................... 18
Figure 11: T&L/COD ratio in leachate after 24 h of leaching test ......................................................... 18
Figure 12: BOD/COD ratio in the sawdust leachate after 24 h of leaching. .......................................... 19
Figure 13: : The COD concentration of beech, maple, oak and pine for leachate after 24 hours
leaching test. ......................................................................................................................................... 19
Figure 14: The effect of washing sawdust repeatedly .......................................................................... 20
Figure 15: The colour after mixing sawdust with Iron .......................................................................... 21
Figure 16: The colour after different combinations of mixing sawdust and iron ................................. 21
Figure 17: The mixing of different tree species and aluminium ........................................................... 22
Figure 18: Leachate pH development over time during leaching tests ................................................ 22
Figure 19: Phenol concentration over time during leaching tests ........................................................ 23
Figure 20: COD concentration over time during leaching tests ............................................................ 23
Figure 21: T&L concentration over time during leaching. ..................................................................... 24
Figure 22: The leaching from sawdust from four different tree types in one cubic meter of water .... 25
30
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