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Treatment of high strength wastewater from fruit juice industry using integrated anaerobic/aerobic system
a b s t r a c t
This work aimed to study the treatment of wastewater generated from fruit juice industry (24–30 m3/batch). Three treatment schemes have been investigated. The first treatment scheme was a batch activated sludge (AS) system and was operated at different aeration time up to 48 h. The second scheme was two-stage upflow anaerobic sponge reactors (UASR 升流式厌氧海绵反应器s). Two-stage UASR 升流式厌氧海绵反应器s were operated at a total hydraulic retention time (HRT 水力停留时间) of 13 h corresponding to an organic loading rate (OLR 有机负荷率) of 8.7 kg COD/m3 d. While, the third treatment scheme consisted of a two-stage UASR 升流式厌氧海绵反应器 followed by an AS system which was operated at three different HRT 水力停留时间s namely 10, 12, and 14 h. Long term experiments indicated the superiority of the third treatment scheme which operated at a total HRT 水力停留时间 of 23 h (UASR 升流式厌氧海绵反应器s: 13 h and AS: 10 h) in terms of chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total suspended solids (TSS) and oil & grease removal. The integrated system achieved an overall removal efficiency of 97.5% for COD, 99.2% for BOD5, 94.5% for TSS and 98.9% for oil & grease. The treated wastewater produced from the UASR 升流式厌氧海绵反应器–AS system complied with the standards set by the Egyptian law regulating the reuse of treated wastewater in agricultural purposes
Article history:
Received 23 September 2009
Received in revised form 9 November 2009
Accepted 10 November 2009
Available online 5 December 2009
Keywords:
Fruit juice industry
UASR 升流式厌氧海绵反应器
Activated sludge process
Agricultural reuse
1. Introduction
Food-processing industries in Egypt are under increasing pressure
to reduce the impact of their wastewater streams on the environment.
The production of large volumes of untreated wastewater can thus
become a very serious financial burden. Most of the wastewater
generated from food industries is highly contaminated with organic
matter, dissolved solids, suspended solids and oil & grease [1].
Wastewater must be properly treated to the degree necessary to
comply with the regulatory standards for discharge into surface water
or reuse for agricultural application [2,3].
Anaerobic digestion technology has been applied for treatment of a
wide variety of industrial wastewaters with high organic matter
content, including dairy wastewater [4], cheese whey wastewater [5],
distillery spent wash water [6], starch wastewater [7], and slaughterhousewastewater
[8]. The up-flowanaerobic sludge bed (UASB 升流式厌氧污泥床) reactor
technology is considered a breakthrough in the development and
application of anaerobic high-rate technology for industrialwastewater
especially for wastewaters coming from food-processing industries [9].
Problems with the UASB 升流式厌氧污泥床 reactor treating wastewater result from
washout of biomass which deteriorates the effluent quality [10]. In the
anaerobic biofilm reactors, the support medium acts as a physical protective
factor against washout, thus being potentially attractive for
biomass retention in the reactor. El-Gohary et al. [11] compared
between classical UASB 升流式厌氧污泥床 and anaerobic hybrid reactor (AHR 厌氧复合反应器) for the
treatment of pre-treated catalytically oxidized olive mill wastewater
(OMW) at an HRT 水力停留时间 of 24 h and an OLR 有机负荷率 of 2 kg COD/m3 d. After reaching
the steady state, the AHR 厌氧复合反应器 removed 64% of the CODwhich was higher by
14% than that obtained in the UASB 升流式厌氧污泥床 reactor.
In this study, the polyurethane foam was used as packing media and
randomly distributed in anaerobic reactors 厌氧反应器 to: (i) improve the solids–
microbial contact, and even the contact between the solids and the extracellular
enzymes, (ii) overcome washout of suspended solids, (iii) enhance
hydrolysis of the particulate organicmatter, (iv) increase the sludge
residence time (SRT 污泥停留时间), and reduces the applied hydraulic retention time.
However, the effluent of the anaerobic reactors 厌氧反应器 generally does not
comply with standards for discharge into receiving water bodies.
Therefore, post-treatment is required. Malaspina et al. [12] investigated
the integrated system consisting of down-flow–up-flow hybrid reactor
(DUHR) followed by sequencing batch reactor (SBR) as post-treatment
system for treatment of dairy wastewater. The whole system achieved
more than 90% removal of COD, nitrogen and phosphorus. In another
study, Wahaab and El-Awady [13] investigated the feasibility of using
rotating biological contactors (RBC 旋转生物接触器) as post-treatment system for
treatment of pre-anaerobically meat processing wastewater. RBC 旋转生物接触器 was
operated at an OLR 有机负荷率 of 0.288 kg BOD5/m2 d. RBC 旋转生物接触器 system achieved a
substantial reduction of COD, BOD5, TSS and oil & grease resulting effluent
quality with residual values of 132, 40, 44 and 10 mg/L, respectively.
Thiswork presents a feasibility study for the treatment ofwastewater
generated from fruit juice industry. The factory produces natural
concentrated syrups of different fruits (Apple, Orange, Cherry etc.).
Wastewater generated from the factory varied from 24 to 30 m3/batch.
Wastewater is characterized by high BOD5 and COD values representing
their high organic content. These effluents may cause serious problems,
in terms of organic load on the local sewerage system. Therefore, appropriate
treatment is required prior to reuse treated effluent in irrigation
purposes [14]. So, the aim of this research work was to investigate a
simple, low-cost integrated system for treatment of high strength fruit
juice wastewater to produce treated wastewater complies with the
national regulatory standards for reuse in agricultural application.
2. Materials and methods
In this study, three treatment schemes have been designed and
manufactured. The first scheme was an activated sludge (AS) system.
The second scheme was a two-stage up-flow anaerobic sponge reactor
(UASR 升流式厌氧海绵反应器). While, the third one was a two-stage UASR 升流式厌氧海绵反应器 followed by an AS
system. The three schemes were located out-door and were operated
at a temperature of 25 °C. A schematic block diagram of the experimental
layout is shown in Fig. 1.
2.1. The first treatment scheme
The activated sludge (AS) system used in this experiment was a
batch scale complete mixed reactor model. The bioreactor system was
made from glass with a working volume of 2 L. The bioreactor was
initially inoculated with 1 L biomass. The used biomass (3.6 g VSS/L and
SVI of 62mL/g TSS)was taken from a near-by full scale activated sludge
plant treating domestic wastewater (Zeneen, Cairo). AS system was
aerated through an air diffuser, under these conditions the dissolved
oxygen concentration 浓度 in the reactor was kept between 2 and 3 mg/L. To
attain the acclimated state, the AS system was fed twice a day with a
mixture of domestic and industrial wastewater for 1 week. This was
followed by 2 weeks of operation using the raw industrial wastewater.
After reaching the acclimated state, the AS system was fed with 1 L of
raw wastewater and then 100 mL of the mixed liquor was taken from
the AS system at a different aeration time. The mixed liquor was allowed
to settle for 1 h, and then the supernatant was withdrawn and analyzed
to determine the optimum contact time from COD removal standpoint.
This experiment was repeated six times.
2.2. The second treatment scheme
This experiment was carried out using a two-identical-stage UASR 升流式厌氧海绵反应器.
UASR 升流式厌氧海绵反应器s were manufactured from PVC and were connected in series.
Each UASR 升流式厌氧海绵反应器 (5 L) consisted of a cylindrical column with a conical
shaped bottom and gas solid separator (GSS). The UASR 升流式厌氧海绵反应器 had a height
of 70 cm, and an internal diameter of 10 cm (Fig. 2).
Each reactor was seeded with sludge obtained from the pilot plant
anaerobic hybrid reactor treating municipal wastewater [15]. The
sludge had a concentration 浓度 of 22 g/L for total solids at 105 °C, 13.6 g/L
for volatile solids at 550 °C and 44.5 mL/gTS for SVI. The total amount
of sludge added to the reactor was approximately 2 L which
represented 40% of the total reactor volume.
The floating polyurethane foam was used as packing media and was
randomly distributed in the anaerobic reactors 厌氧反应器. The dimensions of the
used sponge (cylindrical shape) amounted to 27mmin height×22mm
in diameter. The polyurethane material used in this study was
supported by a polypropylene plastic material with fins. The sponge
characteristics parameters were surface area (256m2/m3), density
(30 kg/m3), void ratio (0.9), and pore size (0.63mm). The total amount
of sponge added to the reactor was approximately 1.5 L.
The UASR 升流式厌氧海绵反应器s were operated at a total HRT 水力停留时间 of 13 h, throughout the
study. OLR 有机负荷率's varied from5.49 to 15.5 kg COD/m3 d with an average value
of 8.7 kg COD/m3 d. During start-up, the reactor was operated at 25 °C
with a total HRT 水力停留时间 of 24 h to allow sludge adaptation to fruit juice
wastewater. Afterwards, the HRT 水力停留时间 was gradually shortened with the
corresponding increase in organic load to reach the desired HRT 水力停留时间 (13 h).
For calculating the SRT 污泥停留时间 of the UASR 升流式厌氧海绵反应器s, it is assumed that the effluent
VSS 可挥发性悬浮物had the same SRT 污泥停留时间 as the excess sludge. The SRT 污泥停留时间 of the UASR 升流式厌氧海绵反应器s were
calculated according to Eq. (1).
SRT 污泥停留时间 =V ⋅XQw⋅ Xw + Q ⋅Xe
where V is the reactor volume (L), X is the average sludge concentration 浓度
in the reactor (g VSS/L), Qw is the excess sludge (L/d), Xw is the concentration 浓度
of the excess sludge (g VSS/L), Q is the wastewater flow rate
(L/d), and Xe is VSS 可挥发性悬浮物concentration 浓度 in the effluent (g VSS/L).
2.3. The third treatment scheme
The UASR 升流式厌氧海绵反应器s effluent (pre-treated effluent)was subjected directly into
an activated sludge system as post-treatment step. To attain the acclimated
state, the AS system was fed twice a day with a mixture of
domestic and industrial wastewater for 1 week. After reaching the acclimated
state, the AS system was fed continuously with the anaerobic effluent
andwas operated at three different HRT 水力停留时间s namely, 10, 12 and 14 h.
2.4. Fruit juice wastewater 果汁饮料废水
The end of pipe effluent used in this study was collected from a fruit
juice factory. The wastewater that was generated from the factory
varied from 24 to 30m3/batch.Wastewater was mainly produced from
production lines, equipments and floor cleaning operations. Fruit juice wastewater 果汁饮料废水 contains a relatively high biodegradable organic matter 可生物降解有机物
(BOD5/COD ratio=0.61). The pH of the raw wastewater was slightly
acidic. So, to provide buffering capacity, 1.5–2 mol of bicarbonate was
added to ensure that the wastewater pH did not drop below7.4 [16,17].
2.5. Sample collection and analysis
The performance of the treatment schemes was monitored by implementing
an extensive sampling and analysis program. Samples from
influent and effluent of each treatment step were collected for analyses.
The analyses covered: pH-value, chemical oxygen demand (COD),
biochemical oxygen demand (BOD5), total suspended solids (TSS), total
kjeldahl nitrogen (TKN), total phosphorous (Total-P), sulfate, hydrogen
sulfide and oil& grease. The raw sample was used for COD and BOD5, and
a 0.45 μm membrane filtered the samples for soluble COD and BOD5,
respectively. The particulate COD and BOD5 were calculated by the
difference between COD and CODsoluble, and BOD5 and BOD5 soluble,
respectively.
Moreover, sludge characteristics including: sludge volume, total
solids, volatile solids and sludge volume index were also carried out.
All analyses were carried out according to APHA [18].
2.6. Kinetics modeling
The kinetics modeling used in this study was based on basic Monod
model. Two limiting cases of the Mono, d model were considered.
2.6.1. Zero order model
In the cases of constant biomass concentration 浓度s with low biomass
change, i.e., ΔX≪X0, and high substrate concentration 浓度 (S≫Ks),
Monod equation can be reduced to a zero order reaction [19]:
dS
dt
= kX: ð2Þ
Therefore, the kinetics constants “kX” can be measured by zero
order linear regression using substrate S versus time plot, with the
slope being equal to the product乘积 of “k” and X. Thus “k” is the slope of
the zero order coefficient versus biomass concentration 浓度 (X).
2.6.2. First order model
On the other hand, based on the same constant biomass concentration 浓度
condition, with Ks≫S, Monod equation can be simplified to a first
order reaction:
dS
dt
=
kXS
Ks
ð3Þ
Therefore, the first order biodegradation kinetics coefficient “kX/Ks”
can be determined from ln(S/S0) versus time plot. The slope of the first
order biodegradation coefficient versus biomass is thus k/Ks.
2.7. Engineering studies
Based on the results of treat ability study, engineering design
related to final recommendations was carried out. Preparation of
preliminary cost estimation for the suggested scheme was conducted.
3. Results and discussion
3.1. Wastewater characteristics
The characteristics of the investigated wastewater are presented in
(Table 1). Available data indicates great fluctuations in the strength of
the wastewater during the study period; this could be due to
variations in the production processes. COD varied from 2280 to
10,913 mg/L with an average value of 5157 mg/L. Corresponding
BOD5 varied from 1650 to 6900 mg/L with an average concentration 浓度
of 3134 mg/L. The average TSS and oil & grease concentration 浓度s were
323 mg/L and 74 mg/L, respectively.
3.2. Treatment schemes
3.2.1. The first treatment scheme
The temporal variation of COD in the batch scale operated with
Fruit juice wastewater 果汁饮料废水 at initial substrate to microorganism ratio of
1.11 mg COD/mg VSS 可挥发性悬浮物is depicted in Fig. 3. As apparent from Fig. 3, COD
removal was accomplished within 30 h, and no further reduction in
COD was observed after that, with the steady state COD stabilizing at
30–50 mg/L. Furthermore, the results of this test clearly show that
COD removal efficiencies ranged from 10 to 99.5% with about 1% of the
initial COD was non-biodegradable even after 30 h of treatment. This
is to be excepted since any organic loading above the maximum
microbial uptake will be untreated.
As elaborated upon earlier, both limiting cases of the Monod model
i.e., zero order and first order kinetics were investigated. A summary
of the zero order and first order coefficients for the various batches is
listed in Table 2 together with the various correlation coefficients.
Fig. 4 illustrates graphically the fit of the data from the batch AS
system to the first order kinetic model. It is apparent from the data
that the first order kinetic model fit the data well; with an R2 value of
0.921 from the first order kinetics. The reasonably good fit of the data
to the first order model approximations may be explained by a
varying biomass concentration 浓度 or prevalence of wide values in
substrate concentration 浓度s within the vicinity of this Ks value in any given batch.
The results presents in Fig. 5 show that by increasing HRT 水力停留时间 from 28
to 30 h, the COD, BOD5 and TSS concentration 浓度s in the final effluent
significantly dropped from 175 to 30, 38 to 8 and 82 to 36 mg/L,
respectively. However, further removal of COD and BOD5 did not
occur by increasing the HRT 水力停留时间 to 48 h. On the other hand, TSS
concentration 浓度s in the final effluent significantly dropped from 36 to
5 mg/L by increasing HRT 水力停留时间 from 30 to 48 h to produce effluent with
quality complying with the national allowable limits which regulate
the reuse of treated wastewater in agricultural purposes
(COD=80 mg/L, BOD5=60 mg/L and TSS=50 mg/L). This excellent
performance towards the removal of organic matter can be attributed
to the high active biomass present in the system. Moreover, the
results also clearly demonstrate that the activated sludge system can
produce an effluent quality containing low concentration 浓度 of TSS. The
suspended matter could be adsorbed on and/or enmeshed into the
biomass and then hydrolyzed by extra-cellular enzymes [12].
Sludge analyses showed that, the sludge volume index ranged
from 50 to 83 mL/gTS which gives an indication for the good settle
ability of sludge. Microscopic examination of the sludge indicated the
presence of many colonies of protozoa, especially stalked ciliates such
as Vorticella, Opercularia and Rotatoria (not shown).
3.2.2. The second treatment scheme
The two-stage UASR 升流式厌氧海绵反应器s were operated at a total constant HRT 水力停留时间 of
13 h, throughout the study. OLR 有机负荷率's varied from 5.49 to 15.5 kg COD/
m3d with an average value of 8.7 kg COD/m3d due to a change in the
influent composition. Despite variations in OLR 有机负荷率, the reactors provided
effluent quality of around 2033 mg/L for COD, and 910 mg/L for BOD5
corresponding to the percentage removal values of 61 and 70%,
respectively (Fig. 6a). Also the results clearly show that, a substantial
reduction of TSS was achieved resulting in an average percentage
removal of 69%. This indicates the high efficiency of the UASR 升流式厌氧海绵反应器s for the
removal of suspended solids at a relatively high suspended solids
loading rate of 0.8 kg TSS/m3 d. This relatively good performance
could be attributed to the long sludge residence time (SRT 污泥停留时间=76 d)
which would effectively increase the efficiency of hydrolysis and
subsequent digestion of organic matter.
In this investigation, COD removal was lower than that previously reported
for UASB 升流式厌氧污泥床 reactor treating cheese production wastewater at a lower
OLR 有机负荷率 (1.5–1.9 kg COD/m3d) and substantially longer HRT 水力停留时间 (30–40 h) [20]
and also lower than those obtained from the UASB 升流式厌氧污泥床 reactor treating dairy
wastewater at an OLR 有机负荷率 ranging from 2.4 to 13.5 kg COD/m3d and shorter
HRT 水力停留时间 of 3 h. The COD removal ranged from 61 to 95.6% [4].
The adsorption phenomena play an important role for COD and TSS
removalwhich occurs in anaerobic treatment of complex fat containing
effluents, it is acceptable to assume that in an anaerobic reactor, the
sludge bed acts as a filter retaining the organic matter which leads to
the growth of sludge [21]. Once the storage capacity is exhausted,
unintentional washout of the sludge together with the effluent takes
place. This indicates that the sludge bed of the anaerobic reactor had
lost its adsorption or retention capacity originating a breakthrough
phenomenon similar to that common in an adsorption column. In this
study, the washout of biomass did not occur; this was due to the use of
floating polyurethane foam at the top portion of the reactor.
Residual total phosphorous, TKN and oil &grease in the treated effluent
were 9.1, 28.4 and 21.6 mg/L corresponding to average percentage
removal of 11, 51 and 70%, respectively (Fig. 6b). Apparently, the removal
of phosphorous and nitrogenwas due to precipitation,while the removal
of oil and grease was due to entrapment/adsorption to the sludge bed of
the UASB 升流式厌氧污泥床 reactor [22].
The characteristics of the retained and excess sludge from the twostage
UASR 升流式厌氧海绵反应器s are presented in Table 3. The VS/TS ratio of wasted sludge
was 0.66 which indicates that the wasted sludge was almost
stabilized. The mean value of the net sludge yield coefficient was
found to be 0.2 g VSS/g COD removed per day, corresponding to 20% of
the total influent COD. This is a very important feature of the UASR 升流式厌氧海绵反应器,
since it is significantly lower than that normally found in conventional
aerobic systems. Sludge production in the UASR 升流式厌氧海绵反应器s may be attributed to
flocculation of non-biodegradable particulate matter, forming the
inert sludge mass fraction and the biological sludge mass that is
generated as a result of anaerobic conversion in the UASR 升流式厌氧海绵反应器 [23,24].
3.2.3. The third treatment scheme
The effluent quality of the anaerobic step does notmeet the standards
set regulating the reuse of treated wastewater in agricultural purposes.
Therefore, the activated sludge system has been investigated as a posttreatment
for the UASR 升流式厌氧海绵反应器s effluent. The AS system was operated at three
different HRT 水力停留时间s namely, 10, 12 and 14 h.
The obtained results show that by increasing the HRT 水力停留时间 from 10 to
14 h the removal efficiency of COD, BOD5 and TSS in the AS system
increased. The residual values in the AS effluent at HRT 水力停留时间 of 14, 12 and
10 h were 21, 50 and 65 mg/L for COD; 10, 10 and 16 mg/L for BOD5
and 3, 5 and 15 mg/L for TSS, respectively (Fig. 7a). The results
presented in Fig. 7b show no significant improvement in the removal
efficiency of Total-P and TKN by increasing the HRT 水力停留时间.
These results are comparable to the results obtained by Malaspina
et al. [12] who used a sequencing batch reactor for treatment of the
anaerobic down-flow–up-flow hybrid reactor effluent and activated
sludge system treating the anaerobic reactor effluent [25]. Over 90% of
COD was removed at a sludge age of 20 days.
Consequently, residual values of the pollution parameters in the
final effluent of the anaerobic–aerobic system complied with the
national allowable limit which regulates the reuse of wastewater for
irrigation purposes.
3.3. Cost estimation of the proposed wastewater treatment plant
In most developing countries, industrial wastewater treatment
and disposal is a matter of concern that needs to be addressed. The
prospects for economic and social development, poverty and
priorities for industrial investments are the main obstacles in making
decisions about wastewater facilities. Since financing, constructing,
operation and maintenance of wastewater treatment plants are quite
costly, most developing countries [26] including Egypt, avoid these
projects.
Based on the above results, the preliminary cost estimation for a
Fruit juice wastewater 果汁饮料废水 treatment plant was conducted. Fig. 8 shows
the schematic diagram of the proposed system, which consists of:
two-stage UASR 升流式厌氧海绵反应器s as pre-treatment step followed by an AS step. The
fixed capital cost was 1,554,000 LE. The values shown are based on the
available market prices of 2009 for similar works. The work shall
comprise supply of all materials, construction of civil work, and supply
and erection of all mechanical and electrical equipments. While the
annual operation and maintenance (O&M) cost including electrical
energy cost, labor cost, insurance cost... etc. was 100,000 LE.
4. Conclusion and recommendation
In this study, three treatment schemes have been manufactured
and studied for the treatment of Fruit juice wastewater 果汁饮料废水. The first
scheme consists of an AS system. The second scheme is a two-stage
UASR 升流式厌氧海绵反应器. While, the third one is a two-stage UASR 升流式厌氧海绵反应器 as a pre-treatment
followed by an AS system. Based on the available results, the following
conclusions were drawn:
(1) The two-stage UASR 升流式厌氧海绵反应器 is an efficient technique for the pretreatment
of Fruit juice wastewater 果汁饮料废水 at an HRT 水力停留时间 of 13 h. The
reactor achieved percentage removal values of 61% for COD,
70% for BOD5, 69% for TSS, 51% for TKN, 11% for Total-P and 70%
for oil & grease.
(2) The wasted sludge from the UASR 升流式厌氧海绵反应器 reactor was almost stabilized
(VS/TS ratio=0.66). The sludge yield coefficient was around
0.2 g VSS/g COD totally removed per day, corresponding to 20%
of the total influent COD. Moreover, the use of polyurethane
foam as a packing media sheets overcome the washout out of
biomass which occur in a classical UASB 升流式厌氧污泥床 reactor.
(3) The combination of the two-stage UASR 升流式厌氧海绵反应器 and the AS system
represents a very promising option for the treatment of juice
industry wastewater. The combined system achieved an
average removal efficiency of 97.5% for COD, 99.2% for BOD5,
94.5% for TSS and 98.9% for oil & grease. The effluent quality of
the integrated anaerobic/aerobic system complies with the
national allowable standards required for reuse in agricultural
purposes.
(4) Accordingly, the proposed system can thus be recommended as
a techno-economically feasible Fruit juice wastewater 果汁饮料废水 treatment
system.
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