Journal of Environmental Protection, 2011, 2, 888-894
doi:10.4236/jep.2011.27101 Published Online September2011 (http://www.SciRP.org/journal/jep)
Evaluation of Filter Material for Treatment of
Different Types of Wastewater
Britt-Marie Svensson1, Lennart Mathiasson2, Lennart Mårtensson1, Pille Kängsepp2,3
1School of Education and Environment, Kristianstad University, Kristianstad, Sweden; 2Center for Analysis and Synthesis, Depart-
ment of Chemistry, Lund University, Lund, Sweden; 3The School of Natural Sciences, Linneaus University, Kalmar, Sweden.
Received July 8th, 2011; revised August 9th, 2011; accepted September 11th, 2011.
ABSTRACT
This paper presents an eva luation of the suitability o f a mixed absorbent ba sed on peat and carbon-con taining ash for
treatment of wastewaters, such as wastewater from professional car washes, landfill leachate and stormwater. This
mixture is very attractive, since it is a low-cost material which has a ca pability to simultaneously remove inorganic as
well as organic pollutants. Since any filter material eventually needs to be replaced either due to saturation of pollut-
ants or reduced infiltration capacity, it is important that the residual can be handled at low cost and that the environ-
ment will be not impaired. The tested mixture, used in filter beds, showed low leaching values and high simultaneous
removal efficiency of metals as Cu, Cd and Pb, non-pola r o rganic compound s such as PCBs. Polar organ ic compound s
as phenols were also efficiently removed by microbial and/or ch emical degrada tion in the stud ied treatment plan ts with
the filter bed acted as a biofilter. Filter material used for three years in a full-scale plant for leachate treatment and
four years in treatmen t plants for wastewater from car washes, had sufficien tly high energy content indica ting that en-
ergy recovery is a good alternative for handling after its usage. Results show that the presented filter material is excel-
lent for both small sca le applicatio ns (e.g. treatmen t systems fo r car wash wastewater with capa city between 250 - 3000
m3 per year) as well as large-scale applications (e.g. filter systems for landfill leachates with capa city above 30,000 m3
per year).
Keywords: Wastewater Treatment, Industrial Landfill, Car Wash, Batch Test, Leaching Test, Peat, Carbon-Containing
Ash
1. Introduction
There are large needs in the world for treatment of dif-
ferent types of wastewater, including leachate from land-
fills as well as wastewater from other facilities such as
professional car washes. Landfill leachate has a very
complex composition and usually contains a large num-
ber of inorganic and organic pollutants of different types,
which present a threat to the environment [1-3]. Thus,
during the last decades, demand has increased for carry-
ing out local treatment of landfill leachate before dis-
charge of leachate to a municipal wastewater treatment
facility or directly to a recipient [4,5]. Wastewater from
car wash, similarly to leachate, contains a number of
harmful substances [6], which should not be released into
the recipient. As result there is an increasing demand
from Swedish municipalities that wastewater from such
activities must also be treated. The volumes to handle of
these two types of waters are several millions of tons per
year in a country like Sweden (with 9 million inhabi-
tants). To take care of such large volumes construction of
any treatment system must be relatively cheap with cost
effective maintenance.
Natural systems with retention ponds followed by a
soil-plant irrigation system or filter-based system (with
low-cost filter material) combined with a pond, are two
attractive approaches. With respect to the complexity of
the investigated wastewaters, filters must be able to re-
move organic as well as inorganic pollutants. To keep the
costs low it is also desirable that the filter material is
cheap and has high adsorption and hydraulic capacity.
Furthermore, once the filter material has been saturated
with pollutants and must be replaced, it should be simple
to take care of.
One type of material, a mixture of peat and car-
bon-containing ash, which has previously been investi-
gated in depth for landfill leachate, fulfills the require-
ments of efficient removal of both inorganic and organic

Evaluation of Filter Material for Treatment of Different Types of Wastewater889
pollutants [7-10]. Other types of wastewaters, which in-
clude these pollutants, might be successfully treated by
this filter material. Accordingly, in this study we have
extended the investigations on this material by including
wastewaters from professional car washes and by also
considering environmental aspects on handling of the
residue, once it needs replacement.
2. Experimental
The filter material mentioned above and further investi-
gated here is a mixture of peat and carbon-containing ash.
The mixture had a peat to ash volume ratio 3:1. Due to
different densities and water content the mass ratio is
about 1:4. The peat originates from the south of Sweden,
and has been classified as H5, according to the von Post
decomposition rating scale (ranging from 1 to 10). The
carbon-containing ash is a residual product, obtained
from an incomplete combustion process at a pulp and
paper industry in the south of Sweden. This filter mate-
rial is supplied by Laqua Treatment AB, Sweden [11].
Three plants for car wash wastewater treatment and
one plant for leachate treatment that included a filtration
step with this mixture, were selected for investigation.
All of these plants were located in Sweden. The filter
volumes at the car wash wastewater treatment plants
varied between 10 m3 and 35 m3 and the filters had a ca-
pacity of about 1500 m3 to 3000 m3 wastewater per year.
Before each filter an oil separator has been installed [12].
Samples from solid filter material from the car wash
treatment plants were taken after two years (one with ID
4.6 m) and four years (one with ID 6.4 m) of use. Water
samples from effluent from each car wash wastewater
treatment plant were taken during the years 2008-2011.
The full-scale on-site plant for treatment of an indus-
trial landfill leachate, consists of a pond and four parallel
vertical-flow filters. Solid sub-samples from the filters
were taken before and after three years of operation, with
a drill at a depth of 0 to 0.6 m at 16 sampling points,
spread equally over one of the four 180 m2-area filter.
These sub-samples were then combined to form one
sample. A detailed description of the leachate treatment
plant and chemical composition of the leachate are pre-
sented elsewhere [10].
In order to characterise the mixtures from the plants,
the compositions of the unused and used filter materials
were determined. To eliminate the possibility of leakage
of hazardous compounds from fresh and used filter mate-
rial, the standardised leaching test for solid waste, the
batch test SS-EN 12457-4 [13] proposed by EU [14], was
used. The batch test methodology is in short as follows:
dried material (100 g) is placed in 2-litre polypropylene
bottles and 1 litre of tap water is added to obtain a liq-
uid-to-solid ratio (L/S) of 10. The bottles are agitated on
a shaking table at 110 rpm for 24 hours at room tem-
perature (about 20°C). The eluate is filtered through a
filter paper (quality 1003, Munktell, Sweden) and then
through a glass micro-fibre filter with retention of 1.2 m
(GF/C, Whatman, England). Samples of eluates are col-
lected in polyethylene high density (PEHD) bottles and
stored at −18C, and investigated with respect to pollut-
ants. To check that the equipment did not contribute to
the pollutants, blank tests were performed.
The analytical procedure included determination of a
number of parameters, in effluent from car washes, in
elautes from leaching tests and in solid filter materials.
Water samples from the car wash facilities were ana-
lyzed for metals (As, Cd, Co, Cr, Cu, Mo, Ni, Pb, Zn and
V), dissolved organic carbon (DOC), biological oxygen
demand (BOD) and oil-index at commercial laboratories
(Eurofins Environment Sweden AB, Lidköping, Sweden
and ALS Scandinavia, Täby, Sweden). Eluates from the
batch tests were analysed with respect to DOC and met-
als at a reference laboratory (Section for Plant Ecology
and Systematics, Department of Ecology, Lund Univer-
sity, Sweden). The solid materials were analysed with
respect to metal concentrations at the same laboratory.
The metals As, Cd and Hg were determined on an axial
inductively coupled plasma mass spectrometer (ICP-MS)
using an Elan 6000 (Perkin Elmer, USA), and the ele-
ments Al, Br, Ca, Cl, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni,
Pb, S, Sb, Sn and Zn were determined with an axial in-
ductively-coupled plasma atomic emission spectrometer
(ICP-AES) using an Optima 3000 DV (Perkin Elmer,
USA). The ICP instruments were calibrated according to
Tyler and Olsson [15]. The DOC was measured with a
TOC-analyser model 500 (Shimadzu, Japan). Conductiv-
ity and pH of the eluates were measured immediately
after the filtration steps with a Crison 524 (Crison In-
strument S.A., Spain) and Knick Portamess 912 (Knick
Elektronische Meßgeräte GmbH & Co., Germany), re-
spectively.
In addition, knowing the energy content of the material
may inform a decision on the use of the filter material
after its usage in such treatment plants. The effective
heating value on the used material was determined at a
commercial laboratory (Eurofins Environment Sweden
AB, Lidköping, Sweden).
3. Results
3.1. Characterization of the Filter Material
3.1.1. Composition of Unused and Used Filter
Materials
Information about the composition of the unused and the
used filter material is presented in Table 1.

Evaluation of Filter Material for Treatment of Different Types of Wastewater 890
In general there are no dramatic absolute changes in
the metal concentrations between unused and used filter
material. There are obviously concentration decreases in
the used material for some metals, especially those known
to have high mobility like Ca and Al. For metals like Cu,
Sb and Cd with expected high affinity to peat from the
wastewaters, the concentrations in the used filter material
had increased. The concentrations of metals in the used
materials are similar to soil which can be used for less
sensitive areas according to general criteria for
polluted soil from the Swedish EPA [16], except for Cu
in used material from leachate treatment (300 mg·kg−1
compared to criteria value of 200 mg·kg−1). The metal
concentrations in used mixtures are similar to values
usually found in peat in the Swedish environment [17].
3.1.2. Leakage of Pollutants from Used Filter
Materials
Leakage of pollutants after using the materials in the fil-
ter systems for purification of wastewater from car
washes and landfill leachate are presented in Table 2.
Table 1. Concentrations of metals in solid filter materials given as average values for unused mixture, used mixture from
full-scale leachate treatment plant and for used mixture from car washes. (na = not analysed).
Used filter material from treatment systems for Metals
(mg·kg−1) Unused mixture leachate car wash
Al 33,000 20,000 16,500
As <2.5 4.6 6.0
Br 17 100 na
Ca 26,000 14,000 16,000
Cd 0.34 0.84 0.75
Co 21 8.6 9.2
Cr 46 19 28
Cu 47 300 110
Fe 14,000 13,000 8900
Hg 0.86 0.28 0.19
K 4300 4500 2500
Mg 4800 5900 1600
Mn 210 700 160
Mo na na 3.7
Na 4000 5500 1100
Ni 46 41 25
Pb 29 31 22
S 4100 2000 3000
Sb 0.04 0.28 0.45
Sn 0.44 5.1 na
Zn 60 130 300
Table 2. Average concentrations (n = 2 - 3) from the batch test on used filter material from leachate and car wash water
treatment systems. Units for DOC and elements are mg·kg−1. For comparison are included Proposed limit values (PLV) for
non-hazardous waste from NFS 2004:10 [16], L/S fraction = 10 L·kg−1. (na = not analysed).
Used filter material from treatment systems for
Parameter / Component leachate car wash PLV
pH 8.3 7.6 >6
Conductivity mS·m−1 170 41
*
DOC 1200 280** / 810*** 800
As 0.07 0.14 2
Cd 0.005 0.002 1
Cr 0.07 0.12 10
Cu 2.4 0.45 50
Hg 0.01 0.003 0.2
Ni 0.29 0.07 10
Pb 0.08 0.03 10
Sb 0.05 0.05 0.7
Sn 0.05 na 0.5
Zn 1.0 2.6 50
* no proposed limit value is available; ** plant ID 4,6 m (filter has been in operation for two years); *** plant ID 6,4m (filter has been in operation for four
years).

Evaluation of Filter Material for Treatment of Different Types of Wastewater 891
The values are compared with the proposed limit values
included in waste acceptance criteria for non-hazardous
waste [16].
For used filter material the values of different compo-
nents in the eluent are generally low (μg·kg−1 level), and
much lower than proposed limit values. However, there
is an exception for DOC where the eluent values are
slightly higher than the PLV-value. This is not unex-
pected since the material used is mainly organic and,
furthermore colloid particles of humic substances ema-
nating from peat may pass the filter system used during
sample preparation and will thus be considered as water
soluble substances.
3.1.3. Effective Heating Value of Used Material
The effective heating value for homogenised samples
from used mixture from landfill leachate and car washes
were 16.5 MJ·kg−1 and 17.5 MJ·kg−1 (in dry weight),
respectively. This is similar to values obtained for bio-
logical materials considered for incineration, which are
usually between 17.2 MJ·kg−1 and 21.5 MJ·kg−1, e.g. 21.5
for peat, 19.2 for bark chips and 17.4 for straw [18].
3.2. Treatment of Different Pollutants in Car Wash
Wastewater
Residual concentrations of pollutants in wastewater from
car wash after passage of the peat and carbon-containing
ash filter are shown in Table 3.
Concentrations of pollutants are in most cases more
than one order of magnitude lower than the critical val-
ues recommended for wastewater to recipient from
Swedish water [19]. Exceptions are Zn, where the values
are about half the critical value, and Cd which can be
detected in 7 of 10 samples and should according to the
guidelines not be present in wastewater. However, the Cd
concentrations are below the limit value for drink-
ing-water (5.0 µg·L−1) [20].
In Sweden each municipality is responsible for the
demands for wastewater purification from car washes,
but there is some general advice from the Swedish EPA.
In Table 4 the actual values from one professional car
wash are compared with guidelines values recommended
by Kristianstad municipality, Sweden.
Concentrations of pollutants are in all cases markedly
Table 3. Average concentrations and RSD (%) of metals, DOC, BOD, and oil-index at different occasions (n = 4 - 12) in the
effluent from three car wash treatment plants, compared with critical values for wastewater to recipient [19].
Treatment plants for car wash wastewaters
Parameter Unit
Effluent, Average (n) RSD (%)
Critical
values
As µg·L−1 1.4 (4) 45 10
Cd µg·L−1 0.15 (10) 54 **
Co µg·L−1 1.5 (4) 70 *
Cr µg·L−1 2.9 (10) 55 50
Cu µg·L−1 19 (10) 46 200
Mo µg·L−1 2.2 (4) 40 *
Ni µg·L−1 9.1 (6) 36 50
Pb µg·L−1 0.93 (9) 25 50
Zn µg·L−1 98 (10) 71 200
V µg·L−1 0.94 (4) 25 *
BOD mg·L−1 40 (10) 138 *
COD mg·L−1 170 (10) 104 *
Oil index µg·L−1 1000 (12) 152 50,000
* no proposed limit value is available; ** should not be present, but can be allowed to contain same concentration as actual drinking-water
which is 5.0 µg·L−1.
Table 4. Average amounts (n = 4) and RSD (%) of metals and oil-index expressed as mg per passenger car, from one car wash
and local guideline values in policy document from Kristianstad municipality, Sweden [21].
Treatment plant for car wash wastewater
Parameter Unit
Effluent RSD (%)
guideline values
Pb + Cr + Ni mg·car−1 1.3 56 5
Cd mg·car−1 0.04 44 0.1
Zn mg·car−1 28 62 50
Cu mg·car−1 2.3 57 75
Oil index mg·car−1 300 185 1500

Evaluation of Filter Material for Treatment of Different Types of Wastewater 892
below recommended values. It should be noted that sam-
ples of the effluent water from this actual car wash were
taken over two periods of two years, which means that
this type of filter has good long-term performance for
treating wastewater from car washing.
4. Discussion
When using a filter system for treating complex waste-
waters it is of general value that the filter material has
ability to remove both organic and inorganic pollutants at
the same time. Since these types of pollutants differ con-
siderably with respect to their chemical structure, filter
material with high adsorption capacity and different
properties is needed. A single given adsorbent material is
probably not optimal to fulfill the requirements. When
two adsorbents are mixed, different types of pollutants
can be removed simultaneously, and at the same time
construction and maintenance cost will typically be re-
duced, since one filter is constructed instead of two.
In this paper a filter material based on a 3:1 mixture
(v/v) of peat and carbon-containing ash from a combus-
tion station is described. This filter mixture has shown
very good removal of organic pollutants and inorganic
pollutants in leachate water from landfills [8-10] and
showed that pollutants in effluents from car wash facili-
ties can be successfully removed. A filter of peat alone
can give a good removal of important metals as discussed
by Kalmykova et al. [22] and Brown et al. [23] but the
removal of organic pollutants is enhanced if car-
bon-containing ash is included as previously observed by
Mårtensson et al. [8] and Kängsepp et al. [7]. If only
physico-chemical processes like adsorption, ion-ex-
change processes and complexation would operate, even
this type of peat and carbon-containing ash filter would
give insufficient long-term removal efficiency for very
water-soluble organic substances such as phenols. How-
ever, with time there is an establishment in this type of
filter of bacterial communities including phe-
nol-degrading bacteria, which e.g. for phenolic com-
pounds leads to high reductions (often about 95%). This
has been shown in column [7], pilot plant [9] as well as
in a full scale plant for leachte treatment, which now has
been in operation for four years [10].
The size of the filter system can be adapted to different
volumes of wastewater treatment by altering number and
size of filter units. There are now in operation 15 treat-
ment plants for handling wastewater from car washes
with filter volumes between ca 10 and 35 m3 which can
handle wastewater volumes between ca 250 and 3 000 m3
per year [24], and filters with volumes of about 700 m3 to
handle landfill leachate volumes of 35000 m3 per year.
The results show that low-cost carbon-containing ash is a
good substitute for activated carbon for removal of or-
ganic (hydrophobic) compounds from the wastewaters,
and can especially be considered due to its cheapness.
Both the cost of the materials and their local availability
are of great importance when such treatment plants are
established where large volumes need to be treated.
The described peat and carbon-containing ash mixture
(3:1 v/v) has high capacity for pollutants and a good
structure, which permits high loadings of wastewater per
time unit and low clogging tendency over time. These
two features assure long-term operation of the same filter
mass; in fact filters of the type described have been used
for more than three years in a full-scale leachate water
treatment plant, and 2 to 4 years in car wash wastewater
treatment systems.
As shown in a previous study of a full-scale leachate
treatment plant [10,25], the peat and carbon ash filter
markedly reduces the concentration of solid particles in
the wastewaters and also takes care of high concentra-
tions of soluble iron and manganese in the leachate,
which become oxidized and precipitated in oxidative
areas of the filter. Thus, there is naturally always a risk of
long-term clogging, which also may be trigged by the
existence of microbial communities. This risk can, how-
ever, be further reduced by introducing an aerated reten-
tion pond before the filter system for precipitation of
particles and hydroxides of major pollutants such as iron
and manganese.
For characterization of filter materials, the proposed
batch test SS-EN 12457 [13] is to be preferred compared
to the alternative percolation procedure SIS-CEN/TS
14405:2004 [26]. This batch test is relatively fast, re-
quires only ordinary laboratory equipment, small space
and demands less manual work. However, to estimate the
treatment efficiency of polar organic substances in a fil-
ter with possibility for microbial activity a longer ex-
perimental time is needed. Our own experiments show
that the percolation method recommended by EU for
characterization of solid waste might be a good alterna-
tive, which would decrease the need to wait for results
from a pilot plant, which may take months to construct.
The study reported in this paper was restricted to a mix-
ture of peat and carbon-containing ash, but the described
methodology should be suitable for testing other filter
materials as well.
The possibility to classify filter material given by the
batch test, discussed above, should be complimented
with a determination of the heat content of the used filter
materials. Both these features give important information
for further decisions. For example the concentration of
DOC, as revealed by the batch test was too high (1200
mg· kg −1) compared to the proposed value of 800 mg·kg−1
to allow the material to be treated at a landfill for
non-hazardous waste. This makes incineration, which is

Evaluation of Filter Material for Treatment of Different Types of Wastewater893
also the alternative proposed by the EU, more feasible
than landfilling. With all other values of analysed pa-
rameters below proposed limit values for hazardous
waste, concentrations of metal and high energy content
are close to the values normally found in Swedish peat
[17], which already is used for energy production. Thus,
for the filter material described, incineration in a com-
bustion plant offers a low cost, environmentally sound
alternative. Furthermore, the technique of co-combustion
of peat in fuel blends is already well established in power
plants [27]. Anyhow by this approach the life cycle of the
residue has been extended.
5. Conclusions
The procedure developed for investigating filter materials,
based on a combination of a Batch test (SS EN 12457)
and a Percolation test (SIS-CEN/TS 14405:2004) for
leaching from solid waste recommended by EU, ensures
that the material used is appropriate for wastewater treat-
ments (i.e. sufficient removal efficiency) and that sound
decisions concerning appropriate destruction of used ma-
terials can be made. This procedure should be possible to
use for other filter based treatment systems as well.
The filter material investigated, based on a mixture of
peat and carbon-containing ash, can efficiently treat dif-
ferent types of wastewaters containing different pollut-
ants. The size of the filter is not critical and filter systems
with a simple and basically same construction can be
used for filter volumes of a few cubic meters (for car
wash facilities) up to several hundred cubic meters (for
landfill leachate). The high filter capacity for a wide va-
riety of pollutants and a structure that minimizes clog-
ging tendency makes this type of filter based treatment
plants operational for long periods of time (several years)
without any need for substitution of the filter material.
This gives a good treatment economy. Once the used
material is replaced its good energy value makes it con-
venient to destruct at a low price in an incineration plant
for energy production. Altogether this should make the
filter material presented useful for many types of waste-
waters.
6. Acknowledgements
The authors acknowledge the financial support of Stena
Recycling AB (Sweden) and the Knowledge Foundation
(Sweden). S Söderlund, M Eliasson and L Ivarsson (di-
ploma workers at Kristianstad University, Sweden) are
acknowledged for help with sampling and laboratory
work.
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