Chapter Seven: Water Treatment

1 Chapter Seven Water Treatment

1.1 Introduction

In this chapter, different categories of the unit operations that are utilized to achieve different water treatment levels are described. It is followed by description of the recommended approach of design of treatment plant components. Emphasis should be given to potential water sources that have undergone investigations on the variability of both the quality and quantity for at least two years. The data gathered should be used for selection of appropriate treatment flow sheets and designing it.

Classification of the qualities of water sources found in Tanzania according to the complexity of its treatment Water treatment is any process that improves the quality of water to make it more acceptable for human consumption. Production of drinking water treatment involves the removal of contaminants from raw water to produce water that is pure enough for human consumption without any short term or long term risk of any adverse health effect.

The processes involved in removing the contaminants from water include physical processes such as settling and filtration, chemical processes such as disinfection and coagulation and biological processes such as slow sand filtration. Table 7.1 and Figures – 7.8 presents the recommended flow Sheets for the Most Common Water Sources in Tanzania. Water contaminants removal processes are best represented in water treatment flow sheets (Figures 7.1 – 7.8).

1.1.1 Table 7.1: Recommended water treatment flow sheets for the most common water sources in Tanzania

S/No	Nature of the Water Source	Recommended Flow Sheet(Minimum)	Remarks
1	Rainwater harvesting	Periodic disinfection	Assuming design allows flushing of first rains
2	Deep well with no minerals	Residual chlorination	Assuming water is supplied through a distribution line and storage tank.
3	Shallow wells with no pollution	Periodic chlorination	Well used by many families
4	Highland stream with no soil erosion	Screens, grit chamber or sand trap, sedimentation with lamella plates, Slow Sand Filtration (SSF),chlorination	Water supplied via distribution pipes and storage tanks.
5	Deep well with Iron and Manganese	Aeration,sedimentation, SSF or RSF, chlorination	Assume water is supplied via distribution pipe and storage tanks
6	Deep well with Fluoride	Sedimentation tank, Bone char, chlorination or Sedimentation, UF/MF, NF, disinfection.	Energy for pumps needed & chlorine not used to avoid corrosion of Polyamide fibres.
7	Surface water with low pH	Screens, Lime, sedimentation with lamella plates, RSF, disinfection
8	Surface water with Nitrate & Sulphate	Screens, Coagulation, Flocculation, Sedimentation with lamella plates,RSF,disinfection. Or Screens,UF/MF, NF, disinfection
9	Surface water with Cadmium, Selenium, Arsenic, Mercury, Lead, Copper,Uranium, Chromium,Cyanide, Nickel	Screens, Coagulation, Flocculation, Clarifier, RSF, UF/MF, NF.	Areas near mining sites with metal recovery possibility.
10	Surface water with pesticides	Screens, Lamella settlers, RSF, UF/MF, NF	Areas with intense large scale agriculture

Floculation ← Coagulation ← Grit Chamber/Sand trap ← Screens ← ↓ Clarifier → RSF → Disinfection