Iranian Journal of Environmental Health, Science and Engineering Iranian Association of Environmental Health (IAEH) ISSN: 1735-1979 Vol. 4, Num. 2, 2007, pp. 77-84

Iranian Journal of Environmental Health Science & Engineering,Vol.
4, No. 2, 2007, pp. 77-84
PERFORMANCE EVALUATION OF AN ANAEROBIC BAFFLED REACTOR TREATING
WHEAT FLOUR STARCH INDUSTRY WASTEWATER
 1H. Movahedyan, *2A. Assadi, 1A. Parvaresh
 1Department of Environmental Health Engineering, Isfahan University of Medical Sciences,
  Isfahan, Iran

  2Department of Environmental Health Engineering, Zanjan University of Medical Sciences, Zanjan, Iran
*Corresponding author-Email: assadi@zums.ac.ir Tel: +98 241 7281301,
Fax: +98 241 7281317 
 Received 19 December 2006; revised 15 January 2007; accepted 30 March 2007 
Code Number: se07012
ABSTRACT
 Feasibility of the anaerobic baffled reactor process was investigated for
  the treatment of wheat flour starch wastewater. After removal of suspended
  solids by simple gravity settling, starch wastewater was
  used as a feed. Start-up of a reactor (with a volume of 13.5 L and five compartments)
  with diluted feed
  of approximately 4500 mg/L chemical oxygen demand was accomplished in about
  9 weeks using seed
  sludge from anaerobic digester of municipal wastewater treatment plant. The
  reactor with hydraulic
  retention time of 72h at 35°C and initial organic loading rate of 1.2 kgCOD/m3.d
  showed 61% COD removal efficiency. The best performance of reactor was observed
  with an organic loading rate of 2.5
  kgCOD/m3.d or hydraulic retention time of 2.45 d and the COD conversion of
  67% was achieved. The
  system also showed very high solids retention with effluent suspended solids
  concentration of about 50
  mg/L for most organic and hydraulic loadings studied. Based on these observations,
  the ABR process
  has potential to treat food industrial wastewater as a pretreatment and is
  applicable for extreme
environmental conditions.
 Key words: Anaerobic baffled reactor, starch wastewater, COD removal, organic loading
INTRODUCTION 
During the last 30 years, there has been 
  an increasing demand for more efficient systems 
  for the treatment of wastewater due to 
  increasingly stringent discharge standards now widely 
  adopted by various national and international 
  agencies (Akunna and Clark, 2000). The treatment of 
  both domestic and industrial wastewater is usually carried out using biological methods due to 
  their lower costs compared to chemical methods (Langenhoff et al., 2000). Great advances have been made over the last 20 years in 
  anaerobic reactor design and in understanding the 
  complex processes that occur in anaerobic 
  digestion (Langenhoff and Stucky, 2000). The 
  successful application of anaerobic systems to the 
  treatment of industrial wastewater is critically dependent 
  on the development and use of high rate anaerobic bioreactors. These reactors achieve a 
  high reaction rate per unit reactor volumes in terms 
  of kgCOD/m3.d by retaining the biomass Solid Retention Time, (SRT) in the reactor 
independently of the incoming wastewater Hydraulic 
Retention Time, (HRT), (Barber and Stucky, 1999). 
Such separation allows the slow growing anaerobic bacteria remain within the reactor independent 
of the wastewater flow. This allows higher 
volumetric loads and produces significantly enhanced 
removal efficiencies (Akunna and Clark, 2000). In 
contrast to domestic wastewater, industrial effluents 
pose many problems for treatment and such 
effluents are subject to daily and sometimes 
seasonal fluctuations with respect to both their flow 
and strength (Nachaiyasit and Stucky, 1997a). The characteristics of food-processing wastes 
show high variation in Biological Oxygen Demand (BOD), Total Suspended Solids (TSS) and 
flow rate. The wastes may be highly alkaline or 
highly acidic. Mineral materials (N and P) may be 
absent or may be present in excess of the ratio 
necessary to promote good environmental conditions 
for biological treatment (Nemerow and Dusgopta, 1991). Wheat starch is an important agro-based product found in many parts of the world. 
The starch extraction process includes 
preprocessing of wheat flour, starch extraction, separation 
and drying (Rausch, 2002). It produces large 
volume of wastewater up to 20-60 m3/T of 
starch produced. Water pollution problems related to 
the starch industry are serious. The wastewater is highly organic and acidic by nature with COD 
up to 25000 mg/L and pH between 3.8-5.2 (Annachhatre and Amatya, 2000). High 
rate anaerobic processes offer an attractive 
alternative for treatment of starch industry 
wastewater (Lettinga, 1996). The most common high 
rate anaerobic reactor in the world today is the 
Upflow Anaerobic Sludge Blanket (UASB), with many existing full-scale reactors for the treatment 
of wastewater from the food and beverages 
industries (Austermann-Houn et al., 1999). The success 
of the UASB depends on the formation of active and settlable granules. These granules are involved 
in aggregations of anaerobic bacteria and self-immobilized into compact forms (Yan and 
Tay, 1997). Due to the relatively low densities of 
the UASB granules, the loss of biomass with 
effluent poses problems, especially during increased 
 loading rates (Angenent et al., 2002). One of 
the many types of high rate reactors presently attracting growing interests is the 
Anaerobic Baffled Reactor (ABR) developed by 
McCarty and coworker (1981) at Stanford University. 
The ABR has been described as a series of UASBs which does not require granulation for its 
operation. Therefore, it has lower start-up period than 
the other high rate reactors. It includes a series 
of vertical baffles to force the wastewater to 
flow under and over them, and therefore the 
wastewater comes into contact with a large active 
biomass (Nachaiyasit and Stucky, 1997a). This 
reactor system has been reported to have many advantages over other systems. The 
most significant advantage of the ABR is its ability 
to separate acidogenesis and methanogensis longitudinally down the reactor, allowing the 
reactor to behave as a two-phase system without 
the associated control problems and high costs 
(Barber and Stucky, 1999). It is simple in design and 
requires no gas separation systems. Moreover, the hydrodynamic pattern reduces bacterial washout and enables it to retain biomass without the use 
of any fixed media (Grove et al., 1999; Vossoughi  et al., 2003). The separation of two phases 
causes an increase in protection against toxic material 
and higher resistance to changes in environmental parameters such as pH, temperature and 
organic loading (Barber and Stucky, 2000; Uyanik et al., 2002). Among high rate reactors, ABR 
was recommended by several researchers as a promising system for industrial and also 
domestic wastewater treatment (Nachaiyasit and 
Stucky, 1997b; Barber and Stucky, 1999; Wang et 
al., 2004). The objective of this study was 
evaluation of the performance of the ABR during 
various hydraulic and loading conditions.
MATERIALS AND METHODS 
Experimental set-up  
The laboratory scale ABR was constructed 
  from 6mm thick transparent Plexiglas, with 
  external dimensions of 53cm long, 16cm width and a 
  depth of 30cm, with the working volume 13.5L. Fig.
  1 shows a schematic diagram of the reactor. The reactor was divided into five equal 2.7 
  L compartments by vertical baffles, each compartment having down comer and riser 
  regions created by a further vertical baffle. The width 
  of up comer was 2.6 times of the width of down 
  comer. The lower parts of the down comer baffles 
  were angled at 45º in order to direct the flow 
  evenly through the up comer. This produced 
  effective mixing and contact between the wastewater 
  and anaerobic sludge at the base of each riser. 
  Each compartment was equipped with sampling ports 
  that allowed biological solids and liquid samples to 
  be withdrawn. The operating temperature was maintained constant at 35±0.5ºC by putting 
  the reactor in a water bath equipped with a 
  temperature regulator. The influent feed was pumped using 
  a variable speed peristaltic pump (Master flux 
  L/S). The outlet was connected to a glass U-tube 
  for level control and to trap solids. The produced 
  gas was collected via portholes in the top of the 
  reactor and daily volume was determined using the 
  gas-water displacement technique. 
Wastewater characteristics  
The combined starch wastewater from a 
  wheat starch factory in the central province of Iran (Ardineh starch CO, Isfahan) was used as 
feed. Wheat starch industry combined wastewater 
has low pH, high suspended solids and high COD. 
The supernatant of the combined wastewater after 
the simple gravity settling used in the investigation, 
had lower TSS, as approximately 90% of the solids were removed. Typical characteristics of 
the wheat starch wastewater are given in Table 1.
The supernatant wastewater was diluted to 
achieve the COD concentration required for each 
loading rate with tap water. In order to pH and 
alkalinity adjustment, the supernatant was neutralized 
by NaOH and NaHCO3.  A COD:N:P ratio of 
300:5:1 was kept during operation using 
NH4Cl and K2HPO4. The micro-nutrient deficiency 
was added occasionally to correct growth 
conditions according to Angenent et al., (2002).
Seed sludge 
The reactor was seeded with anaerobic 
  digested sewage sludge taken from an anaerobic 
  digester an Isfahan south municipal sewage treatment works. It was first sieved (<2mm) to remove 
any debris and large particles and was then 
introduced into five compartments of reactor. Each compartment was filled with 50% sludge 
which had a suspended solids composition of 30980 
mg TSS/L and 20880 mg Volatile Suspended Solids (VSS) per liter giving a total of 140.94 g VSS 
in the reactor. This value (10.44 g VSS/L) is in accordance with the initial VSS value used in 
other studies with ABR (Barber and Stucky, 1999). 
The remaining parts of each compartment were 
filled with tap water. After seeding the reactor, the 
lids were sealed. The reactor was then allowed to stabilize for 24h without further modification 
before starting the experiments.
Analysis 
Monitoring included the analysis of samples 
  from influent and each compartment of the ABR 
  system for COD, TSS, VSS, alkalinity and pH. All 
  samples were analyzed according to the standard 
  methods for examination of water and wastewater (APHA,1995). pH and temperature 
  were monitored daily.
RESULTS 
Reactor start-up 
In order to reactor start-up, the batch operation of ABR was
  started using an initial sludge concentration of 10440 mg VSS/L. The system
  was run on batch for 2 weeks. During this time the content of the reactor was
  recycled
for homogeneity. After these weeks the ABR was run continuously and observation
  were made for 42 days with an initial organic loading rate of
1.2 kgCOD/m3.d with influent COD in the range 
of 4225-5975 mg/L. When there was no more fluctuation in COD in each compartment, then 
the Organic Loading Rate (OLR) was increased up to 1.5 
kgCOD/m3.d for one week and then OLR were increased gradually up to 10 
kgCOD/m3.d for 40 days. At the end of this period, the 
biogas production rate increased (data not shown).
COD removal 
OLR and HRT employed during the 
  reactor operation period are shown in Fig.
  2. As can 
  be seen, there were an inversely relationship 
  between OLR and HRT. Fig.
  3 shows the effects of increase of influent COD concentration on 
COD removal rate under steady-state conditions. It 
also indicates the reactor effectiveness as percent 
COD removal. According to Fig.
  2 and Fig.
  3, the 
COD conversion during the start-up period was 
obtained up to 61%, with HRT of 3 days (OLR of 1.5 
kgCOD/m3.d). After each increase in OLR 
the COD concentration in effluent increased. 
When the OLR was increased to 2.5, 5 and 10 
kgCOD/m3.d at HRT in the range of 1.43-2.45 d, 
the efficiency of COD removal was achieved as 67%, 55% and 40%, respectively. Fig.
  4 shows the 
COD removal efficiency based on organic loading 
rates. The best performance of reactor was observed 
with an OLR of 2.5 kgCOD/m3.d (HRT of 2.45 
d) and the COD conversion of 67% was achieved 
(Fig.
  4). The variations of COD in the reactor are illustrated in Fig.
  5. 
Alkalinity and pH 
As shown in Fig.
  6, the feed alkalinity after 
  pH adjustment was approximately 1000-3000 mg/L, while the effluent alkalinity was always in the 
  range of 2000-5000 mg/L. The results of pH 
  variations along with the reactor showed that the pH decreases in compartments 1 and 2 upto 
pH<6.5 during the reactor operation. However, 
although the pH in compartments 3-5 returned to 
near neutrality, compartment 1 stayed at 
approximately pH=6.4 for the rest of the experiment. This 
is clearly shown in Fig.
  7. 
Sludge characterization 
The average TSS and VSS concentration 
  and VSS/TSS ratio in the reactor at different 
  times are presented in Fig.
  8. At the time of reactor 
  start-up, VSS/TSS was 0.67. The VSS/TSS ratio increased upto 0.77 by day 42 and later it 
  slightly decreased till the end of operation. Sludge 
  washout was negligible in the experiments since the 
  effluent suspended solids concentrations were in the 
  range of 14-272 mg TSS/L, which indicates that the 
  ABR was stable to high shock loads. Details of 
  reactor operation data are shown in Table 2.
DISCUSSION  
The reactor operation lasted for three 
  months. Because of increment different influent COD 
  at each period from wide range of 4225 to 14300 mg/L, the COD removal rate (in term of 
  mg/L.d) increased in accordance with OLR 
  increasing. However, in spite of incremental trend in 
  COD removal rate, when the reactor was fed with an organic loading rate of 5 
  kgCOD/m3.d after 69 days, the treatment removal efficiency 
  decreased. This is obviously illustrated in Fig.
  3. It is 
  evident from data that the COD removal rate did not 
  gratify in comparison with lower organic loading 
  rates. Since in the present study at higher OLR, 
  the influent COD concentration and volume of flow rate increased significantly and affected 
  the quantity of COD removal rate. It also led to 
  high COD concentration in the effluent. The 
  relatively poor performance of  ABR at higher 
  organic loading rates can be attributed to the presence 
  of high substrate gradient. In this study, the 
  best reactor performance was observed with an OLR of 2.5 
  kgCOD/m3.d and 67% COD removal efficiency was obtained (Fig.
  4). The highest 
  OLR tested (10 kgCOD/m3.d) resulted in only 
  40% decrease in the COD concentration and the remaining high COD in the effluent. This high 
OLR and high flow rate probably caused channeling through the biomass bed, resulting in 
poor substrate-biomass contact and minimal 
degradation of the incoming COD. This provides 
further support to the earlier supposition that under 
plug-flow conditions, incoming substrate remains in 
the reactor for one retention time allowing 
maximum time for conversion. However, the high 
substrate concentration resulting from lack of dispersion 
may inhibit bacterial activity (Sallis and Uyanik, 2003).
These results support the findings of the 
  other studies. Kalyuzhnyi et al., (1998) worked 
  with UASB reactor for chip-processing industry wastewater. The organic loading rate achieved 
  in the lab scale reactor had approximately 14 gCOD/L.d with treatment efficiencies higher than 
  75% and 63% on the basis of centrifuged and total 
  COD of the effluent. Grover et al., (1999) have 
  shown that a maximum COD reduction of about 60% at an organic loading rate of 5 
  kgCOD/m3.d at hydraulic retention time of 2d and 35ºC 
  was recorded with anaerobic baffled reactor 
  treating pulp and paper liquors. In other study to 
  treat tapioca starch industry wastewater with UASB process, COD removal upto 95% has been obtained at an OLR of 16 
kgCOD/m3.d (Annachhatre and Amayta, 2000). A 
comparison of the results achieved with those reported for 
other anaerobic treatment systems and for similar wastewaters illustrate that our results 
are satisfactory, though an actual comparison 
between various data sets can be based only on 
experiments where the same wastewater and reactors 
of comparable size with the same operation temperature are used. 
The variation in the COD profile in ABR was shown in Fig.
  5. As it can 
be seen, most of COD was removed in compartment 1 (35%), increasing the initial OLR enhanced 
the biological oxidation upto a certain point at 
which OLR started to inhibit the degradation rate. Because in strong wastewater containing 
high organic load, significant amounts of fatty acids 
can develop from partial degradation of substrate 
and these can inhibit the methanogenic population 
in the reactor (Uyanik et al., 2002). 
According to Fig.
  6, the effluent alkalinity was 
  always more than the feed alkalinity. The most likely explanation for this observation is 
  the formation of HCO3- due to the reaction of 
  OH- with CO2 produced during anaerobic 
  degradation (Annachhatre and Amayta, 2000). The pH 
  levels in the reactor followed a similar pattern 
  throughout the experiment, dropping rapidly to pH less 
  than 6.4 at reactor start-up and at higher OLR (Fig.
  7). The pH decrease in compartments 1 and  2 can be attributed to the fact that high concentration 
  of volatile fatty acids (VFAs) were present in 
  these compartments, while in later compartments 
  due to conversion and stabilization of 
  intermediate products i.e. VFAs to methane and activity 
  of methanogenic bacteria the pH value increased to neutral range (Uyanik et al., 2002). Very little washout of the reactor solids occurred in 
  the reactor operation (Table 2), which show that 
  the reactor was stable to severe shocks loads. This 
  is consistent with the published literature which indicates that ABR process is stable to 
  large transient shock loads (Nachaiyasit and 
  Stucky, 1997b). Determination of VSS/TSS ratio 
  gives correlation to the biomass growth and its 
  quality. As it can be seen in Fig.
  8, at the start-up 
  of reactor, VSS/TSS ratio was 0.67 and increased 
  to 0.77 by day 42 at OLR of 1.2 
  kgCOD/m3.d. After this period, it gradually decreased over the 
entire course of experiment to 0.73 by day 79 at OLR 
of 10 kgCOD/m3.d. This provides further support 
to the earlier hypothesis that biomass growth rate 
is limited in high organic loading rate (Metcalf 
& Eddy, 2003). As a final conclusion, it could 
be concluded that this type of reactor 
configuration has potential in treating food industrial 
wastewater that vary in both flow and concentration. 
Also because of equalization characterization ABR process is a good system as pretreatment for 
other anaerobic or aerobic wastewater treatment processes.
ACKNOWLEDGEMENTS 
The authors are grateful for the financial support 
  of the research vice chancellor of Isfahan University of Medical Sciences; Project 
  # 83389. Also, special thanks go to valuable cooperation 
  of Ardineh Starch CO., for providing feed samples.
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