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Research Article
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COD and BOD Reduction of Domestic Wastewater using Activated Sludge, Sand Filters
and Activated Carbon in Saudi Arabia |
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Saad A. Al-Jlil
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ABSTRACT
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The objective of this study was to determine COD and BOD reduction from domestic wastewater using sedimentation, aeration, activated sludge, sand filter and activated carbon. Mean maximum COD and BOD reduction was 92.17 and 97.66%, respectively. Other water quality parameters such as TSS, TDS, NO2, TKN and PO4 showed significant reduction except NO3 which increased significantly using different materials in the Wastewater Treatment Plant (WTP). The sewage treatment system using different materials showed excellent potential for COD and BOD removal from domestic wastewater. Also, the concentration level of COD and BOD in the treated water was within the permissible limits for industrial cooling and agriculture use especially for landscape development.
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INTRODUCTION
Recent urban and rural expansion tremendously increased the water consumption
in and around major cities of the Kingdom which resulted in many fold increases
in wastewater production. The wastewater is a mixture of sewage water, agricultural
drainage, industrial waste effluents and hospitals facilities. It is well known
that the wastewater from domestic origin contains pathogens, suspended solids,
nutrients (nitrogen and phosphorus) and, other organic and inorganic pollutants
(Andrew et al., 1997). In order to minimize the
environmental and health hazards, these pollutants need to be brought down to
permissible limits for safe disposal of wastewater (Manju
et al., 1998; Poots et al., 1978).
Therefore, removal of the organic contaminants and pathogens from wastewater
is of paramount importance for its reuse in different activities (Ali
and Deo, 1992; Chen, 1997; Raj
et al., 1997). The conventional wastewater treatment technologies
as adopted in industrialized nations are expensive to build, operate and maintain
(Mazumder and Roy, 2000; Piet et
al., 1994; Mazumder and Kumar, 1999), especially
for decentralized communities. Research efforts are underway (Mohammed et
al., 1998; Wang et al., 2005) for the development
of treatment technologies suited to these decentralized communities. Fly ash
can be used as a promising adsorbent for removal of various types of pollutants
from wastewater (Wang and Hongwei, 2006). Low-cost adsorbents
of different origin like industrial waste material, bagasse fly ash and jute-processing
waste can also be used for removal of organic matter from wastewater (Bhatnagar,
2007; Srivastava et al., 2005; Banerje
and Dastidar, 2005). The COD and BOD concentrations play an important role
in the re-use of these waste effluents. Adsorption-based innovative technology
(Devi et al., 2002; Devi and
Dahiya, 2006) developed with low-cost carbonaceous materials showed good
potential, more so for COD removal from the domestic wastewater. Devi
and Dahiya (2008) studied COD and BOD reduction of domestic wastewater using
discarded material based mixed adsorbents (mixed adsorbent carbon, MAC and commercial
activated carbon, CAC) in batch mode. Under optimum conditions, maximum COD
and BOD reduction achieved using MAC and CAC was 95.87, 97.45, 99.05 and 99.54%,
respectively. The results showed that MAC offered potential benefits for COD
and BOD removal from wastewater.
Devi et al. (2008) assessed the reduction of
chemical oxygen demand (COD) and biological oxygen demand (BOD) of wastewater
from coffee processing plant using activated carbon made up of Avacado Peels.
The maximum percentage reduction of COD and BOD concentration under optimum
operating conditions using APC was 98.20 and 99.18%, respectively and with CAC
this reduction was 99.02 and 99.35%, respectively. As the adsorption capacity
of APC is comparable with that of CAC for reduction of COD and BOD concentration,
it could be a lucrative technique for treatment of domestic wastewater generated
in decentralized sectors.
To date, research has mainly focused on the use of intermittent sand filters
for the treatment of domestic strength wastewater (Schudel
and Boller, 1990; Gross and Mitchell, 1985; Gold
et al., 1992; Nichols et al., 1997).
Generally, these filters are designed and operated in accordance with the US
Environmental Protection Agency (1980) guidelines and have provided good
organic carbon, TSS and nutrient removal rates. Research on the use of intermittent
sand filters in the treatment of high strength wastewater is more limited. Liu
et al. (1998, 2000, 2003)
used sand filter columns to treat high-strength synthetic wastewater containing
detergent and milk fat.
Healy et al. (2006) studies the performance
of a stratified sand filter in removal of chemical oxygen demand, total suspended
solids and ammonia nitrogen from high-strength wastewater. Best performance
was obtained at a system hydraulic loading rate of 10 L/m2/d, a higher
system hydraulic loading rate (of 13.4 L/m2/d) caused surface ponding.
The system hydraulic loading rate of 10 L/m2/d gave a filter chemical
oxygen demand (COD), TSS and Total Kjeldahl Nitrogen (TKN) loading rate of 14,
3.7 and 2.1 g/m2/d, respectively and produced consistent COD and
TSS removals of greater than 99% and an effluent NO3-N concentration
of 42 mg L-1 (accounting for an 86% reduction in total nitrogen (Tot-N)).
Tan and Chua (2004) stated that proper control of the
activated sludge process is essential in ensuring production of good effluent.
The COD adsorption capacity (CAC) of the activated sludge could be used as a
control parameter. The CAC is determined by mixing the activated sludge with
the settled sewage and measuring the instantaneous COD reduction per unit mass
of activated sludge. The CAC measures substrate removal by physical adsorption
and reflects the quality of the activated sludge.
The main objective of this study was to develop low cost and effective wastewater treatment technology for the reduction of COD and BOD from wastewater using activated sludge, sand filter, activated carbon and chlorination. MATERIALS AND METHODS
The experiment was carried at the Technical College Riyadh during 2008-2009.
The domestic wastewater was passed through a series of treatment processes for
the removal of BOD and COD. The treatment process consists of the following
steps:
• | Pre-treatment
stage includes screening, oil separation and equalization |
• | Primary
treatment stage including two processes: |
• | Physical
processes which including Sedimentation in clarifiers, flocculation and
filtration |
• | Chemical
processes include precipitation, coagulation and neutralization |
• | Secondary
treatment stage includes two processes: |
• | Activated
sludge system includes aeration tank and settling tank |
• | Advanced
treatment stage or tertiary method includes three processes: |
• | Activated
carbon as an adsorbent (adsorption system) |
• | Chlorination
(disinfection) |
The schematic diagram of Wastewater Treatment Plant (WTP) is presented in Fig. 1.
Analytical procedure: The raw wastewater samples were collected from
the main outlet of wastewater from the Technical College. The raw water samples
were passed through different steps as indicated in Fig. 1
for the removal of COD and BOD. The treated and untreated wastewater samples
were collected on weekly basis and analyzed for COD, BOD, Total Suspended Solids
(TSS), Total Kjeldahl Nitrogen (TKN), Total Dissolved Solids (TDS), Nitrate
(NO3), Nitrite (NO2) and Phosphate (PO4) in
the analytical laboratory according to the methods prescribed by the American
Public Health Association (1989). The experimental duration was 5-weeks
and each treatment replicated three times. Overall percent efficiency for each
parameters was also calculated relative to the control treatment by considering
the control values equal to 100%.
| Fig. 1: | Domestic
wastewater treatment plant
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The data were analyzed by ANOVA for treatment evaluation according to Snedecor
and Cochran (1973).
RESULTS AND DISCUSSION
Biological Oxygen Demand (BOD): The BOD decreased significantly in the
treated water as compared to the untreated wastewater (LSD0.05 =
9.677) (Table 1). The results showed that the activated sludge,
sand filter and the activated carbon were very effective for the removal of
BOD from the wastewater. The reduction in BOD was 128.57 mg L-1 (raw
water) to 3.03 mg L-1 (treated water) with a mean removal efficiency
of 97.66%. Similar results were reported by Devi et al.
(2008) who assessed the reduction of BOD of wastewater from coffee processing
plant using activated carbon made up of Avacado Peels.
Chemical Oxygen Demand (COD): The COD concentration decreased significantly
in the treated water as compared to the untreated wastewater (LSD0.05
= 18.145) (Table 1). The results showed that the activated
sludge, sand filter and the activated carbon were effective for removal of COD
from the wastewater. The reduction in COD was from 130.33 mg L-1
(raw water) to 10.2 mg L-1 (treated water) with a mean removal efficiency
of 92.17%. The study results agree with those of Healy et
al. (2006) who studied the performance of a stratified sand filter in
removal of chemical oxygen demand, total suspended solids and ammonia nitrogen
from high-strength wastewater. They also stated that the system hydraulic loading
rate of 10 L/m2/d gave a filter COD, TSS and total TKN loading rate
of 14, 3.7 and 2.1 g/m2/d, respectively and produced consistent COD
and TSS removals of greater than 99% and an effluent NO3-N concentration
of 42 mg L-1 (accounting for an 86% reduction in total nitrogen (Tot-N)).
Similarly, Tan and Chua (2004) reported that proper
control of the activated sludge process is essential in ensuring production
of good effluent. COD adsorption capacity (CAC) of the activated sludge could
be used as a control parameter. CAC is determined by mixing the activated sludge
with the settled sewage and measuring the instantaneous COD reduction per unit
mass of activated sludge.
Total Suspended Solids (TSS): The TSS concentration decreased significantly
in the treated water as compared to the un-treated water with LSD0.05
value of 9.620 (Table 1). The mean TSS concentration decreased
from 111.33 to 2.7 mg L-1 in the raw water and treated water, respectively
with a mean removal efficiency of 97.58%. This suggests that the treatments
applied to the wastewater were significantly effective for the removal of TSS
from wastewater. The results agree with the findings of Healy
et al. (2006) who observed TSS removal up to 99% using sand filters.
Total Dissolved Solids (TDS): The TDS decreased significantly in the treated water as compared to the un-treated water with LSD0.05 value of 5.449 (Table 1). Although, the TDS showed decreases ranging from 593.5 mg L-1 (raw water) to 401.33 mg L-1 (treated water), but the removal efficiency was very low (32.38%). The results indicated that there was not appreciably reduction in the total water salinity. Total Kjeldahl Nitrogen (TKN): Mean TKN concentration decreased significantly in the treated effluent as compared to the raw wastewater (Table 1). Mean TKN concentration was 26.25 and 4.17 mg L-1 in the raw and treated wastewater, respectively, but the different between the two was significant (LSD0.05 = 2.93). The reduction in TKN in the treated effluent could be due to the decomposition of organic nitrogen from wastewater to other forms of nitrogen such as NH4, NO2 and NO3 in the treated water using different materials in the system. Table 1: | Effect
of treatments on different parameters (mg L-1) of wastewater |
 |
Figures in the column followed by the same letters are not
significantly different at 5% level of significance (LSD0.05).
BOD: Biochemical Oxygen Demand, COD: Chemical Oxygen Demand, TSS: Total
Suspended Solids, TDS: Total Dissolved Solids, TKN: Total Kjeldahl Nitrogen,
NO3: Nitrate, NO2: Nitrite, PO4: Phosphate,
R2: Coefficient of determination, CV: Coefficient of variation,
RMSE: Root of Mean Standard Error, TE: Treatment Efficiency |
Nitrate (NO3) and nitrite (NO2) concentration:
The NO3 concentration increased significantly in the treated effluent
than the raw wastewater (Table 1). Mean NO3 concentration
was 1.88 and 6.66 mg L-1 in the raw and treated wastewater, respectively.
The significant increase in the NO3 concentration could be attributed
to the conversion of organic form of nitrogen to nitrate form due to oxidation
reaction during the wastewater treatment process. Because, organic nitrogen
is mostly in NH4 form which might have oxidized to NO2
and finally to a more stable form of nitrogen (NO3). On the other
hand, the NO2 concentration was low than NO3 as the NO2
form of nitrogen is highly unstable and is immediately converted either to NH3
(volatile form of nitrogen) or to NO3, highly stable form of nitrogen
into the wastewater treatment system.
Phosphate (PO4) concentration: The PO4 concentration decreased significantly in the treated wastewater under various treatments processes than the raw wastewater (Table 1). The decrease in the PO4 concentration could be due to the decomposition of some organic phosphorus compound from the wastewater by the activated sludge and the activated carbon. Comparison of some chemical parameters: A comparison of some chemical parameters with the established standards showed that the concentration of BOD, COD, TSS and TDS was within permissible limits for agricultural and industrial uses (Table 2). CONCLUSIONS The study showed that by using sedimentation, aeration, activated sludge, sand filter and activated carbon COD and BOD reduction was 92.17 and 97.66%, respectively in the domestic sewage water. Other water quality parameters such as TSS, TDS, NO2, TKN and PO4 showed significant reduction except NO3 which increased significantly using different materials in the Wastewater Treatment Plant (WTP). The sewage treatment system using different materials showed excellent potential for COD and BOD removal from domestic wastewater. Besides, the final COD and BOD concentration in the treated was within the permissible limits for industrial cooling and agriculture use especially for landscape development.
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