Performance Evaluation of Drinking Water Treatment Plant (Case Study: Gambella Town Drinking Water Treatment Plant)
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Date
2013-01
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Addis Ababa University
Abstract
The conventional water treatment plant, especially in developing countries, faces major
challenges in terms of assessing its operation and performance due to inappropriate
technologies, insufficient equipment and deficiency in skilled expertise. Simple but efficient
technologies are therefore necessary for reasonable evaluation of the daily performance of
the plant. Turbidity is thought of as a convenient surrogate to give favorable indication of the
biological and physical quality of the treated water thus by extension provide a fair gauge of
the performance of the treatment plant with respect to water purification. Besides, it is fairly
simple to measure, cheap and can easily be understood by the operators. In this study the
performance of Gambella town water treatment plant was assessed. The study was conducted
by assessing unit process capability, design, operation and maintenance potential to meet
optimized goals. From results of the assessments, root factors limiting optimum performance
were identified and improvement options were proposed. Major unit processes were
evaluated to project their design capabilities to meet current peak water demand by selecting
appropriate loading rates as basis criteria. The results of the assessment found that all units
had the capability to satisfactorily treat water at peak daily demand of 2000 m
/day. The
study assessed turbidity performances of sedimentation and filtration units by setting
optimized turbidity goals. The assessment results indicated that, settled water turbidity was
measured less than 10 NTU. And filter turbidity spike of 6.5 NTU following backwash with
a reduction to 0.6 NTU after one hour was observed. Generally optimized performance goals
were not being achieved. This indicated high risk of microbial pathogens that could pass the
filtration barriers in the finished water. Jar test experiments were conducted to evaluate the
effectiveness of Aluminum Sulphate (recently used by the treatment plant), Ferric chloride
and Ferric Sulphate by comparing the optimum dose at optimum pH for highest turbidity
removal and relative costs. From the jar test results Aluminum Sulphate was found to be the
effective chemical with 45 mg/l optimum dose at pH 7.1 and the treatment plant was
recommended to continue using Aluminum Sulphate at the optimum dose for the raw water
characteristics during the evaluation period. Treated water samples were collected from the
clear-water well to test 14 water quality parameters according to the standard methods for
water and waste water examinations. The collected samples were intended to show the characteristics of the finished water only during the evaluation period. The samples were
analyzed at the laboratory of GWTP and results were compared with WHO standards and
guidelines for drinking water. Results of the analysis showed that all of the measured
parameters were within the acceptable range. In the assessment of factors limiting
performance of the treatment plant; major factors were categorized as design, operational and
maintenance. No single factor was responsible for poor plant performance, although in
general the study found that all factors influence the plant’s ability to work properly. Some of
the primary operational problems and the intake structure’s adequacy significantly affected
performance. Operational factors were found to have the highest rank. This finding, coupled
with the fact that the plant had adequate capability, indicates that improving process control
could significantly improve performance.
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Keywords
Water Treatment Plant, Drinking Water, Gambella Town