الفهرس 
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Abstract
This section represents the Summary, Conclusion of the present study and its recommendations.
5.1. Summary:
Algae is a group of photosynthetic organisms. Under specific environmental conditions, the rapid increase in the population of algae in freshwater or marine water systems was occurred, and cause algae blooms.
Algal blooms in water supplies can cause several problems in conventional water treatment including bad taste, obnoxious odors, clogging of filter beds, increasing coagulants demanded, disturbing sedimentation processes, impairing the final water disinfection process, promoting microbial re-growth in the water distribution systems and being pathogenic to human. The pathogenic nature of algae arises from the production of algal toxins, which affect human health.
This study was conducted in Al -Mogran Water Purification Plant during the period March 2018 to June 2018 in order to assess the efficiency of algal removal from its intake by optimization of pre-oxidation and coagulation processes.
A total of nineteen grab raw water samples were collected, to determine the optimum conditions for the pre-oxidation and coagulation processes using jar test for algal and turbidity removal.
Experiments were designed to evaluate the effect of pre-oxidation on algal removal by using two different oxidants, chlorine with five concentrations (1, 2, 3, 4, and 5) mg/l in two detention times (15 and 30 minutes), potassium permanganate with six concentrations (0.5, 1, 2, 3, 4 and 5) mg/l, in two detention times (60 and 180 minutes), and a mixture of both with six doses (0.5 KMnO4+1 Cl2), (0.5 KMnO4+2 Cl2), (0.5 KMnO4+3 Cl2), (1 KMnO4+1 Cl2), (1 KMnO4+2 Cl2) and (1 KMnO4+3 Cl2) mg/l. followed by coagulation using two different coagulants, PAC with five concentrations (4, 6, 8, 10, and 12) mg/l and Alum with five concentrations (5, 10, 15, 20, and 25) mg/l for turbidity and algae removal.
The results of pre-oxidation revealed that chlorine and potassium permanganate for different mentioned detention times removed algal from (29.7% to 69.8%) and from (53.4% to 83.5%), respectively. It was observed that there was a gradual increase in the algae removal percentage with increasing concentrations of oxidants without any significant difference between the tested detention times either using chlorine or potassium permanganate p-value = 0.728 and 0.999, respectively. The results obtained from pre-oxidation using a mixture of chlorine and potassium permanganate showed that algae removal percent increased according to the increase of mixtures doses from 50 % to 75.5%, and the optimum dose was (1 mg/l KMnO4+1 mg/l Cl2) with algal removal 71.5%.
Pre-oxidation was less effective on turbidity reduction compared with algal reduction, the maximum reduction did not exceed 22.9%, while algal reduction exceeds 83.5%.
Considering the pre-oxidation with the optimum dose (1 mg/l KMnO4+1 mg/l Cl2) and subsequent coagulation with PAC and Alum are effective in the removal of algal and turbidity, showing that the turbidity removal increased from 90.7 % to 97.7% and algae removal increased according to the increase of PAC doses from 82.3% to 99.6. The optimum dose was 8 mg/l with algal removal value 96.6%. While Alum increased turbidity removal from 94.5% to 99.1% and algal removal increased according to the increase of Alum doses from 76.9 % to 96.4%, the optimum dose was 25 mg/l with algal removal value 96.4%. The optimum dose of PAC achieved 96.6% of algal removal and optimum dose of alum achieved 96.4% of algal removal without any significance between them p-value = 0.125. Results of water quality characteristics after application of optimum doses of combined pre-oxidation (1mg/l chlorine and 1mg/l potassium permanganate) and coagulation with PAC and Alum, for all tested parameters in the treated water, were within the maximum permissible level of Sudanese standards for drinking water (044/2015) and THMs were not detected.
As the results of Cost-Effectiveness Analysis, it can be suggested that the best alternative is coagulation at Al-Mogran WPP using the dose of 8 mg/l PAC combined with doses of 1 mg/l chlorine and 1mg/l potassium permanganate.
The study recommended the application of research results in all Drinking Water Purification Plants in Khartoum state and development of a guide for algal presence in Sudanese Water Standards.
5.2. Conclusions:
This examine study yielded the following conclusions concerning the use of pre-oxidation and coagulation to improve the efficiency of turbidity and algal removal from the intake of Al-Mogran WPP in Khartoum State:
1) The chlorine efficiency for removal of algae is about 70% at 5 mg/l dosage, while turbidity reduction reached about 18% for the same dose.
2) The potassium permanganate efficiency for algae removal is about 84% for a doe of 5 mg/l, while turbidity reduction reached 9.5%-23%.
3) The low doses of the mixture of chlorine and potassium permanganate (1 mg/l KMnO4+1mg/l CL2) can effectively remove algal from raw water with 71.5% efficiency.
4) Pre-oxidation with both pre-oxidants (chlorine, potassium permanganate, and a mixture of both of them) were less effective in the removal of turbidity (22.9%) as compared with algal removal (83.5%).
5) Trihalomethanes formation potential is reduced by using a low dose of chlorine combining it with potassium permanganate.
6) Pre-oxidation combined with coagulation enhanced turbidity and algal removal.
7) The optimum dose of PAC achieved 96.6% algal removal, optimum dose of Alum achieved 96.4% of algal removal without any significance between them (p-value = 0.125).
8) Cost-effectiveness analysis showed that the best coagulants for the algal and turbidity removal were PAC combined with (1 mg/l KMnO4+1mg/l Cl2).
9) Water quality parameters after application of optimum doses of pre-oxidation followed by coagulation followed Sudanese Standard; although the standard is established for final treated water after disinfection process. Furthermore, THMs were not detected in effluent water.
5.3. Recommendations
This study recommended the following amendments and changes to be implemented:
1- Application and use of pre-oxidation stage for removal of the majority of algal, enhancing coagulation process, minimizing the dose of coagulant, minimizing the cost of maintenance due to high turbidity, omitting taste and odor problems, and preventing the growth of algal within treatment plan (filter basin) during growth of algal blooms.
2- Application of potassium permanganate to reduced chlorine dose and control THMs formation. Use of a mixture of them followed by coagulation with PAC in drinking WPPs would reduce the turbidity and total algal count which would lead to:
• Unclogging of filters and consequently increasing run time of filter and decreasing loss of water used in filter backwash.
• Reduction of cost of electricity.
• Reduction of disinfectant dose.
• Improving water quality in the distribution system
3- The newly extended part of the Al-Mogran WPP ought to be put in operation as soon as possible. This is to mitigate the pressure on the plants and offer permission and chance for pre-treatment stage.
4- Sudanese Water Standards need to develop a guide for the presence of algae.
5- All components of plant ought to be maintained and cleaned periodically to avoid any problem of algal growth within the plant.
6- Cooperation between governmental and non-governmental sectors is of paramount importance to protect water resources in Sudan. It worth mentioning that water suppliers and authorities in some countries have developed monitoring and management strategies for the presence of algal and their toxins in WPPs that draw their water from surface water containing algal species.
7- Application of international standars for water intakes of WPPs in Khartoum State.
5.3. Recommendation for further study:
1) Conduct a pilot-scale study to assess the efficiency of algae removal from the intake of Al-Mogran WPP by optimization of pre-oxidation and coagulation processes.
2) Carry out further studies to assess effectiveness of other physical, biological and chemical applicable methods for suppressing, mitigating, or controlling algal cells.
3) Conduct a detailed study to assess the occurrence and distribution of algal and the ability to predict the timing, species composition, and toxicity of HABs at all seasons from the intake of WPPs in all Khartoum metropolitan area.