Effect of different aerobic and anoxic time periods on the effluent water quality of a sequence batch reactor in a meat processing plant
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Date
2015
Journal Title
Journal ISSN
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Uva Wellassa University of Sri Lanka
Abstract
product
manufacturing. It contains high concentrations of organic matter, oil and grease and
nitrogenous compounds. Hence, releasing waste water to the environment causes many
environmental problems such as contamination of groundwater and eutrophication of surface
waters (Rodriguez et al., 2010). The treatment of waste water is especially important in this
view. Treatment of wastewater by means of biological process has been widely implemented
from urban to industrial wastewater. Sequencing batch reactor (SBR) is a modification of
activated sludge process and operates by a cycle of periods consisting of fill, react
(alternatively aerobic and anoxic periods), settle, decant, and idle (Mahvi, 2008).
In the SBR process there is no standard time combination for aerobic and anoxic period. It
will depend on the effluent waste water components and vary plant to plant. Currently aerobic
and anoxic period is operated as 2 hr aerobic and 1 hour anoxic period in the waste water
treatment plant of CIC meat processing company. The present investigation was undertaken
to study best time combination of aerobic and anoxic time period for simultaneous carbon
oxidation, nitrification and denitrification performance of sequencing batch reactor to treat
slaughterhouse wastewater.
Methodology
The current study was carried out at CIC Poultry Farms Pvt Ltd (Processing Plant),
Badalgama. Laboratory analysis was done at CIC Processing Plant Laboratory and Uva
Wellassa University laboratories. Model structure of aeration tank which has the capacity of
600 L was used to conduct the research experiments. 180 mL of sludge from SBR unit in CIC
meat processing plant and 420 mL volume of wastewater was fed to tank each day of the
treatment. Air was supplied to the reactor during aerobic phase of react period with the help
of diffused aeration system and Anoxic conditions were maintained by switching off the
aerators. Eight different combinations of aerobic and anoxic periods were used. Every
sequence was operated totally for 20 hrs of react period by alternating the aerobic and anoxic
period according to selected different time combinations (Table 01).
Table 01: Selected time Combinations for Aerobic and Anoxic time periods
Control T1
T2
T3
T4
T5
T6
T7
T8
Aerobic (Hours)
2
2
3
3
4
4
4
4
Anoxic (Hours)
1
2
1
2
1
2
3
4
The best combination of aerobic and anoxic time period was determined by analyzing water
quality parameters as, COD, BOD, ammonium nitrogen, total nitrogen, TSS, TDS and pH.
Complete Randomized Design (CRD) was conducted and data obtained from chemical and
physical tests were analyzed using analysis of variance (ANOVA) using the General Linear
Model (GLM) procedure of SAS (SAS Institute Inc., 2000). Significant means of treatments
were separated using the Least Significant Difference (P< 0.05) test.
Results and Discussion
There was a significant difference (P<0.05) between aerobic and anoxic time combinations
regarding COD removal, BOD removal, TN removal and ammonium nitrogen removal. 4 hour
aerobic and 2 hour anoxic period showed higher COD removal (95%), BOD removal (90%),
TN removal (89%), and ammonium nitrogen removal (92%). There was no significant
difference (P>0.05) regarding phosphorus removal, TSS removal and TDS removal among
different aerobic and anoxic time combinations.
Highest COD and BOD removal occurred in 4 hour aerobic and 2 hour anoxic cycle. Second
highest COD removal (92%) was achieved during 4-1 react period. This might be due to
during 4-2 hr and 4-1 sequence total aerobic react time is higher than other react cycles.
Therefore, longer aeration was achieved. Longer aeration period has been found to be
effective in achieving higher degree of nitrification and COD, BOD removal according to the
findings of Debsarkar et al. (2006).
Due to less total aeration time in 4-3 and 4-4 hr cycles, less COD and BOD removal was
achieved. That means one cycle was alternatively operated for 20 hrs totally and in the 4-3
and 4-4 cycles has high anoxic time periods. Therefore, less COD and BOD removal occurred
(Kundu et al., 2013).
Treatment 6 (4-2) is significantly different from other treatments and also treatment 5 has high
BOD removal. This may be due to long aeration time and effective denitrification. According
to Kishida et al. (2003), BOD concentration of the effluent was relatively high because the
oxygen demand by nitrifying bacteria increased the total BOD, when the NH,-N concentration
of the effluent was too high (average = 187.1 mg/L). NH,-N concentration of the effluent was
high due to partial denitrification. According to this experiment ammonium nitrogen
concentration also affect to the BOD removal. And treatment 6 had low level of ammonium
nitrogen concentration in effluent water (1.048 mg/L 1.07 mg/L).
Longer aeration period (5 hour) has been found to be effective in achieving higher degree of
nitrification from Debsarkar et al. (2006). But according to preliminary study at the middle of
hour pH is reached to 6.9, but optimum pH for nitrification is 8.2. Therefore, in this
experiment longest aeration time per one cycle was selected as 4 hr.
According to the statistical analysis, there is no significant difference (P> 0.05) between
different aerobic, anoxic time combinations and total dissolved solid and total suspended
solids removal. This might be due to activated sludge treatment is not intended to remove
dissolved or suspended solids (Sustarsic, 2009).
Conclusions
The combination of 4 hours aerobic react period and 2 hours anoxic react period has been
found to be optimum from the view point of both nitrification and denitrification, and COD,
BOD removal. When total aeration time period is low, removal of COD, BOD is not efficient
in 4 hr aerobic – 4 hr anoxic and 4 hr aerobic – 3 hr anoxic time combinations.
Description
Keywords
Animal Sciences, Meat Production, Environmental Science, Water Chemistry