الفهرس 
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Abstract
Access to clean and affordable water is important for human health, economic
productivity, and environmental sustainability. Sanitary drinking water supply from
surface freshwater through Alexandria Water Company (AWCO) includes several steps;
raw water collection, pre-chlorination, coagulation, sedimentation, filtration, disinfection,
storage, and distribution.
The sedimentation process is one of the most important treatment processes for
removing settleable solids from water by gravity. In conventional water purification
plants, sedimentation occurs after coagulation/flocculation and before filtration. The
process of deposition of suspended matter has been termed sedimentation, settling, or
clarification.
Coagulation and settling play a major role in the preliminary phase of drinking
water purification by reducing or eliminating impurities. When used as a pre-treatment to
filtration and disinfection, they greatly increase the efficiency of the latter processes by
reducing or eliminating suspended particles that would clog filters or impair disinfection.
As a result, the risk of waterborne diseases is significantly reduced.
Pre-treatment using coagulation, flocculation, and sedimentation is being replaced
by newer treatment technologies providing enhanced water quality; improved
sustainability; smaller footprints; reduced chemical usage; and reduced environmental
impacts.
Lamella clarifiers or inclined plate settlers (IPS) are utilized in water treatment to
make rectangular tanks more cost-effective. The difference between conventional clarifiers
and lamella clarifiers is that the flow in the settling region is directed through inclined
parallel plates. This substantially eliminates unstable flow manners and mixing currents,
which inhibit the settling of solids.
Moreover, the main benefit of IPS is that the sedimentation unit is more compact
usually requiring only 65-80% of the area of clarifiers operating without inclined plates.
Lamella plates suggest that the clarifier can be operated with overflow rates higher than that of
the conventional clarifiers which allow a higher influent flow rate.
This study aims to assess the effectiveness of lamella clarifiers in enhancing the
sedimentation process for drinking water purification, investigating the operational
parameters that influence floc performance. Also to compare between the conventional
clarifiers and clarifiers contain inclined plate settlers to improve water quality and increase
its productivity.
A cross-sectional comparative study between the lamella sedimentation tank and
the conventional one was carried out in the pilot plant of Alexandria Water Company. The
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experiments were planned to cover the seasonal variation over one year (from October
2018 to August 2019) to cover the worst cases which affect the raw water quality.
To compare the produced water quality from the two different types of
sedimentation technologies (Conventional and Lamella), water samples were collected
from two target sites as follow; One raw water sample from the influent and two clarified
water samples from the effluent of the sedimentation tank (one after detention time 90
minutes and one after 120 minutes).
The total collected water samples of each site were 80 samples and 240 water
samples were analyzed during this study according to the Standard Methods for the
Examination of Water and Wastewater. Also, all the statistical analyses of the results were
presented using SPSS 20.0.
Water quality indicators were measured for raw and clarified water collected from
the two types of sedimentation tanks; physicochemical quality indicators were turbidity,
Total Suspended Solids (TSS), pH, residual chlorine, and residual aluminum. While
biological quality indicators were Total Heterotrophic Plate Count (THPC), Total
Coliform (TC), Fecal Coliform (FC), total algal count, and protozoa.
To fulfill the study objectives and complete the comparison between the two
different types of water purification technologies, financial factors were considered.
These factors were; produced water quantity, operational and maintenance expenses,
and finally the cost of water production. These data were collected using a data
collection sheet from the records and the annual statistical reports of Alexandria Drinking
Water Company from October 2018 to September 2019 applying the two different
technologies.
The physical water quality indicators recorded that the removal percentage of
turbidity for conventional sedimentation tank within the study year ranged from (94.5% -
98.3%), while in the case of the lamella sedimentation tank it ranged from (96.3% -
99.0%). Mann-Whitney U test showed a highly significant difference (p-value <0.001)
between the two types of sedimentation tanks in all seasons of the year for the values of
turbidity. In addition, the removal percentage of TSS for conventional sedimentation tank
within the study year ranged from (83.8% - 90.0%), but in the case of the lamella
sedimentation tank, it ranged from (90.0% - 96.5%). Mann-Whitney U test showed a
highly significant difference (p-value ≤0.001) between the two types of sedimentation
tanks in different seasons for the values of TSS.
Concerning chemical water quality indicators; pH values of raw water within the
study year range from (7.36 - 7.93). pH values of clarified water from the effluent of
conventional sedimentation tank range from (6.96 - 7.48), while for the lamella
sedimentation tank, it ranged from (6.90 - 7.42). The minimum and maximum values of
residual chlorine within the study year were (0.46 mg/L and 1.16 mg/L), respectively.
Mann-Whitney U test showed a highly significant difference (p-value ≤0.001) between the
two types of sedimentation tanks for the residual chlorine. The removal efficiency of
residual aluminum within the study year ranged from (17.5% - 29.4%). Mann-Whitney U
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test showed a highly significant difference (p-value <0.001) between the two types of
sedimentation tanks in the summer season for the values of residual aluminum.
For biological water quality indicators; the removal percentages of THPC for
conventional sedimentation tank were (85.8% - 92.1%), while in the case of the lamella
sedimentation tank were (93.5% and 98.1%). Mann-Whitney U test showed a highly
significant difference (p-value <0.001) between the two types of sedimentation tanks in
different seasons for the values of THPC. The positive samples percentage of TC for the
effluent of conventional sedimentation were (20% - 80%), while TC isn’t detected (0%) in
the effluent of lamella sedimentation tank in all seasons. Paired t-test for the positive
samples of TC throughout the study year recorded a highly significant difference (p-value
<0.001) between the two types of sedimentation tanks in different seasons for the
reduction of TC. All water samples collected from the effluent of conventional and lamella
sedimentation tanks were compatible with the limits of Egyptian drinking water quality
standards, law 458/2007 which states that all samples must be free of Basil ideal colon.
The removal percentage of TAC for conventional sedimentation tank ranged from (78.3%
- 81.8%), while for the lamella sedimentation tank ranged from (84.4% and 95.1%).
Mann-Whitney U test showed a highly significant difference (p-value <0.001) between the
two types of sedimentation tanks in different seasons after 120 minutes towards the values
of TAC. The removal percentage of protozoa for the effluent of the conventional
sedimentation tank was (30% - 70%), but for the effluent of lamella sedimentation tank
were (70% - 100%).
Cost-Effectiveness Analysis; for conventional technology calculations showed that
the average cost of produced water quantity per cubic meter during the study year is equal
to 0.784 L.E. while for lamella technology calculations showed that the average cost of the
lamella is equal to 0.011 L.E./m3 and the percentage of increase in the cost of drinking
water production due to the use of lamella is 1.4 %. This increase in drinking water
production cost is very small compared with the improvement in the produced drinking
water quality and quantity.
The produced water quality was improved when lamella was used for 90 minutes of
sedimentation detention time. Therefore, the use of lamella with the reduction of
sedimentation detention time from 120 to 90 minutes will lead to an increase of drinking
water quantity by 33.33% (one third) with a better water quality compared with water
quality produced when conventional sedimentation technology is used for 120 minutes
sedimentation detention time.
The present study concluded that the Application of using lamella clarifiers or
inclined plate settlers for drinking water purification plants of AWCO is recommended.