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Iranian Journal of Environmental Health, Science and Engineering
Iranian Association of Environmental Health (IAEH)
ISSN: 1735-1979
Vol. 4, Num. 2, 2007, pp. 107-112
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Untitled Document
Iranian Journal of Environmental Health Science & Engineering,Vol.
4, No. 2, 2007, pp. 107-112
DEGRADATION OF AROMATIC COMPOUNDS USING MOVING BED BIOFILM
REACTORS
*B. Ayati, H. Ganjidoust, M. Mir Fattah
Tarbiat Modares University, Civil Engineering Department, Environmental Engineering Division, Tehran, Iran
*Corresponding author-Email: ayati_bi@modares.ac.ir Tel: +98 21 8833
2900, Fax: +98 21 8800 5040
Received 23 January 2007; revised 19 February 2007; accepted 27 March 2007
Code Number: se07016
ABSTRACT
For biological treatment of water, there are many different biofilm systems
in use. Examples of them are trickling filters, rotating biological contactors,
fixed media submerged biofilters, granular media biofilters
and fluidized bed reactors. They all have their advantages and disadvantages.
Hence, the Moving Bed
Biofilm Reactor process was developed in Norway in the late 1980s and early
1990s to adopt the best
features of the activated sludge process as well as those of the biofilter
processes, without including the
worst. Two cylindrical moving bed biofilm reactors were used in this study
working in upflow stream
conditions. Experiments have been done in aerobic batch flow regime. Laboratory
experiments were
conducted at room temperature (23–28°C) and synthetic wastewater
comprising a composition of phenol and hydroquinone in each reactor as the
main organic constituents, plus balanced nutrients and alkalinity
were used to feed the reactor. The ratio of influent to effluent COD was determined
at different retention
times. The results indicated that the removal efficiency of each selected compound
is affected by the
detention time. At low phenol and hydroquinone concentration (from 700 to 1000
mg/L) maximum
removal efficiency (over 80%) was obtained. By further increasing in COD loading
rate up to 3000 mg/L,
a decrease in COD removal rate was occurred. In the reactor containing pyrogallol
in COD of 1500 mg/L,
the removal rate decreased to 10 percent because of its toxicity for microorganisms.
Key words: Hydroquinone, Moving Bed Biofilm reactor, phenol, pyrogallol.
INTRODUCTION
The removal of toxic phenolic compounds
from industrial wastewater is an important issue to
be addressed. Phenolic compounds such as phenol, hydroquinone and pyrogallol are used in
different industries which end into their wastewaters.
They are considered as priority pollutants because
of their high toxicity at low concentrations. Phenol
is an important raw material in petrochemical, pharmaceutical, plastic, pesticide
production industries. Hydroquinone and its derivations
is another phenolic compound used in photographic applications, rubber industry, monomer
inhibitors, dyes and pigments, antioxidants
agricultural chemicals, and other diverse and
special applications. The largest demand for
hydroquinone is as a photographic developer, principally for
black and white film, lithography, photochemical machining, microfilm, and X-ray film (Elves et al., 1989a). Pyrogallol is also the other
phenolic compound that used in photography,
lithography and hair dyes production. It is also used as
an antioxidant and stabilizer. The use of pyrogallol
in the field of cosmetics and medicines is
currently declining because of pronounced toxicity
(Elves et al., 1989b). The presence of these pollutants
in water and soil has become significant problems. Effective methods for the removal or
treatment of them need to be pursued.
Many efforts have been made for the
biological treatments of wastewater rich in
phenolic compounds. Common commercial wastewater treatment methods utilize the combination
of physico-chemical and biological treatment.
Both chemical and biological processes were used
for many years to treat phenolic wastewater.
Activated sludge, fluidized and packed
bed reactors and recently moving bed biofilm
reactors (MBBR) were studied as biological treatment processes (Vinod et al., 2006; Murugesan et al., 2005; Hosseini et al., 2005;
Andreottola et al., 2000). Chemical processes like advanced
oxidation methods by ozone, hydrogen peroxide and
fenton like process (Ri-Sheng et al., 2006; Wu1 et al., 2002) and reduction by electrode reactor (Xiong et al., 2003) were also studied for degradation
of phenol. Laboratory experiments are done on adsorption of phenol on carbonaceous
adsorbents as an effective advanced process to
treatment phenolic wastewater (Ahmaruzzaman et
al., 2005).
The moving bed biofilm reactor process
(European Patent No.0, 575,314, US Patent no.
5,458,779) was developed in Norway in the late 1980s
and early 1990s. In 1988, the Norwegian State Pollution Control Authority made
recommendation on design of small wastewater plant (Rusten et al., 1997). These recommendations include
design of biological/chemical treatment plants based
on low loaded biofilm process with a large tank
(sludge separator) serving both as pretreatment unit,
sludge holding and equalization tank. A Norwegian company (Kaldnes Miljøtekonlogy A/S),
which was developing the so-called MBBR at the
time initiated construction of small treatment
plants according to these recommendations.
MBBR has been a commercial success.
There are presently more than 400 large-scale wastewater treatment plants based on this
process in operation in 22 different countries all over
the world. In addition there are several hundreds
small, on-site treatment units based on the MBBR
mostly in Germany. More than 50 MBBR plants are in operation at commercial fish farms, in addition
to several hundred small MBBR systems for ornamental fish.
MBBR is performed in biofilm system with relatively large (0.1 to 5 cm)
carriers. These are mixed with the wastewater and suspended in the reactor by the turbulence.
The system is located somewhere between an activated sludge and a fixed-bed biofilm
system (Maurer et al., 2001). One important
advantage of the moving bed biofilm reactor is that the
filling fraction of biofilm carriers in the reactor may
be subject to preferences. In order to be able to
move the carrier suspension freely, it is
recommended that filling fractions should be below 70%
(Rusten et al., 2006). One may, however, use as much as needed below this. A number of different
carriers have been developed. Those designed and developed in Norway, are two variants
called Kaldnes® and Natrix® (Maurer et
al., 2001). These carriers are small plastic tubes (1 to 5
cm diameter or length) made from polyethylene with density close to 1
g/cm3. The inner part of the tubes is divided into several sectors to
increase the total biofilm surface. This system is successfully used for treating of
high-strength industrial wastewater. Also other kinds of
carriers with differences in size and shape and,
therefore, in different specific surface areas have been used.
Investigations on the shape and size effect
of carrier made it clear that the key factor in
the design of a moving bed biofilm process for
organic matter removal is the effective surface area
where biomass may grow. The size and shape of
carrier may have an influence on this effective area.
The design of process should be based on organic surface area removal rate (Ødegaard et al., 2000).
MATERIALS AND METHODS
Three applied cylindrical MBBR reactors (Fig. 1) were made of Plexiglas. Each reactor had an internal diameter of 10 cm, a height of 70 cm
and wall thickness of 4 mm and five sampling
ports. The effective depth of wastewater in each
reactor was 60 cm (70% of reactor volume) filled
with plastic floating biofilm carrier (Fig. 2) described
in Table 1. Batch reactors were working in upflow stream conditions in room temperature (22-26 oC). The circulation of the biofilm carriers inside
the reactors was caused by aeration. In order to
keep the carriers in the reactors, a sieve (with 5
mm opening) was placed at the outlet of the
reactors. Filling ratio of plastic elements in the reactors
is important due to the amount of biomass, which can be supported by carriers. The reactors used
were filled about 70% (recommended percentage volumetric filling of plastic elements in
empty reactor). The synthesized wastewater has
been prepared using phenol, hydroquinone and
pyrogallol which were supplied by Merck, Germany.
In order to have C/N/P= 100/5/1 and
alkalinity, necessary nutrients (urea,
KH2PO4, K2HPO4) were
used to feed the reactor. The parameters of pH, COD (soluble COD filtered through
Vattman paper No.42) and dissolved oxygen (DO)
were measured daily. TSS, mixed liquor suspended
solids (MLSS) and mixed liquor volatile suspended
solids (MLVSS) were measured on alternative days. Volatile Fatty Acids (VFA)
and alkalinity were controlled weekly. Microscopic investigation
was done regularly. All analytical tests were done
as outlined in the Standard Methods Handbook (APHA, 1998).
RESULTS
After 20 days of starting up the reactor with
sludge obtained from Ekbatan wastewater treatment
plant as seed, solution of glucose and wastewater compound with COD of 1000
mg/L with different concentrations were used. In the adaptation
period, the amount of Organic Loading Rate (OLR)
was being increased stepwise within 60 days. In
the beginning, the COD removal rate was very low but after 4 months of the
study, it reached to 50% that are more discussed in the following
paragraphs.
Effect of detention time on COD removal rate
The effect of different retention times was
studied for each reactor. COD removal efficiency
has measured after 24, 48 and 72 hr for every step increase in COD. At low phenol and
hydroquinone concentration (from 700 to 1000 mg/L)
maximum efficiency was obtained. By further increasing
in COD loading up to 3000 mg/L, a decrease in COD removal rate was occurred.
Same behavior in reactor containing
hydroquinone was observed. However, decrease in
COD removal rate in hydroquinone reactor was
slighter. It seems that further increasing in
concentration of hydroquinone and especially in phenol
will eventually cause the physiological parameters decrease and the substrate inhibition occur.
Figs. 3, 4, and 5 indicate the removal rate for different
COD and detention times for phenol, hydroquinone
and pyrogallol, respectively.
For reactor containing pyrogallol, as shown in
Fig. 5, the COD removal efficiency exceeded 80%
for influent COD of 600 mg/L after 72 hours.
Beyond this there was a steep decrease in COD
removal efficiencies. The effect of inhibitory of pyrogallol appeared in influent COD concentrations
more than 600 mg/L and with increasing COD
loading, longer detention times did not have a
remarkable effect to improve this behavior.
Comparing COD removal efficiency
between three phenolic compounds
From Fig. 6, it can be seen that the COD
removal of wastewater containing hydroquinone had
better efficiency. The removal efficiency of
phenol wastewater with about 20% difference lies
lower than hydroquinone. This difference was more apparent in COD ranging between 1000 to
2000 mg/L and reduced by increasing influent COD. As shown in Fig. 5 there is a sudden reduction
in COD removal efficiency of wastewater containing pyrogallol comparing to phenol and
pyrogallol beyond loading of 600 mg/L. Hence,
increasing of influent COD was stopped. More decrease
in COD of 1800 mg/L could be related to low DO in the system.
DISCUSSION
As mentioned in the introduction part,
many researches have been done using chemical treatment for removal of the three compounds
used in this study from industrial wastewater. Not
much work has been reported for biological removal
of these chemicals especially for hydroquinone and pyrogallol. Some of the biological
treatment methods which could be comparable with our
study are discussed in the following paragraphs:
Two researches are recently done in
Sharif University of Technology using MBBR for removal of both molasses and phenol from
synthetic wastewater with COD of about 800 mg/L.
They have reported 95 percent COD removal
efficiency (Hosseini et al., 2001 & 2005).
Another study has been shown that after ozonation
pretreatment process of the phenol wastewater with
COD concentration of 1600 to 6000 mg/L from a petrochemical industry, MBBR with
granule activated carbon resulted in 85 to 90
percent removal efficiency (Lin et al., 2001). Not
much work has been reported using hydroquinone as
a separate wastewater by means of any biological treatment processes whereas it has been
identified as a by-product of phenol, nitro phenol and
other phenol compounds treatment (Yi et al., 2006).
Biological treatment of pyrogallol in
comparison to hydroquinone has not been significantly
studied. One of the limited research studies in this
area was the use of activated sludge process in
treating phenolic wastewater containing pyrogallol. In
this study 78 percent of COD and phenols were removed, but not much pyrogallol has
been successfully decreased (Pendy et al.,
1991). Based on the experimental results of this
study, the removal efficiency for each selected
compound was affected by the detention time. The three
used MBBR systems have shown a proper COD removal efficiency for biodegradation of
phenol and hydroquinone wastewater. It has shown
that at low phenol concentration (700 to 1000
mg/L) over 80 percent was removed. In addition, by increasing in COD loading rate up to 3000
mg/L, a decrease in COD removal rate was occurred. Similar results (between 92 to 94% at low
COD and 80% for COD 1000 to 2500 mg/L) have been observed for hydroquinone wastewater. In
the reactor containing pyrogallol (COD 500 mg/L), maximum of 82% removal efficiency
was obtained. By increasing COD to 1500 mg/L, because of its toxicity for microorganisms,
the removal decreased to 10 percent. In overall,
the results have indicated that MBBR has better effect on hydroquinone removal.
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© 2007 Tehran University of Medical Sciences Publications
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