Drinking Water Supply and

Transcription

1 Drinking Water Supply and Health

2 Engineered Water Systems

3 Water and Health 80% of sickness in the world is caused by inadequate water supply or sanitation 40% of the world population does not have access to safe drinking water It is estimated that water-borne diseases kill 25,000 people per day In many populated areas of the world, water-borne diseases represent the leading cause of death

4 Malaysian Interim Water Quality Standards (INWQS) Table 1: Water Use Classes in the National Water Quality Standards Updated 2008 Class Uses CLASS I Conservation of natural environment water supply 1 - practically no treatment necessary. Fishery 1 - very sensitive aquatic species CLASS IIA Water Supply II - conventional treatment required Fishery ll - sensitive aquatic species CLASS IIB Recreational use with body contact CLASS III Water Supply lll - extensive treatment required Fishery lll - common, of economic value, and tolerant species livestock drinking CLASS IV Irrigation CLASS V None of the above

5 Malaysia : National Guidelines for Raw Drinking Water Quality Table 2 : National Guidelines for Raw Drinking Water Quality (Revised December 2000) Parameter Symbol Benchmark Sulphate SO mg/l Hardness CaCO 3 SO 500 mg/l Nitrate NO 3 SO 10 mg/l Coliform - Must not be detected in any 100 ml sample Manganese Mn 0.1 mg/l Chromium Cr 0.05 mg/l Zinc Zn 3 mg/l Arsenic As 0.01 mg/l Selenium Se 0.01 mg/l Chloride Cl 250 mg/l Phenolics mg/l TDS mg/l Iron Fe 0.3 mg/l Copper Cu 1.0 mg/l Lead Pb 0.01 mg/l Cadmium Cd mg/l Mercury Hg mg

6 Sizes of Particles in Water

7 Palatable vs. Potable Palatable aesthetically pleasing considers the presence of chemicals that do not pose a threat to human health palatability affected by chloride, color, corrosivity, iron, manganese, taste and odor, total dissolved solids, turbidity

8 Potable Water Potable safe to drink not necessarily aesthetically pleasing potability affected by microbials (e.g. Giardia, Cryptosporidium) organic chemicals (e.g., alachor, chlordane, cis-1,2-dichloroethylene, disinfection byproducts) inorganic chemicals (e.g., cadmium, copper, lead, mercury) radionuclides

9 Palatable and Potable The goal of municipal water treatment is to provide water that is both palatable and potable Palatability and Potability regulated under Safe Drinking Water Act Palatability: Secondary Maximum Contaminant Levels (SMCLs) Potability: Primary Maximum Contaminant Levels (MCLs) - (for systems serving more than 25 persons per day for greater than 60 days per year)

10 Primary MCLs (mg/l)

11 Primary MCLs (mg/l)

12 Primary MCLs (mg/l)

13 Primary MCLs (mg/l)

14 Secondary MCLs (mg/l)

15 Sources of Drinking Water Groundwater shallow wells deep wells Surface water rivers lakes reservoirs

16 Ground- vs. Surface Water Groundwater constant composition high mineral content low turbidity low color low or no D.O. high hardness high Fe, Mn Surface water variable composition low mineral content high turbidity colored D.O. present low hardness taste and odor

17 Surface Water Treatment Primary objectives are to 1. Remove suspended material (turbidity) and color 2. Eliminate pathogenic organisms Treatment technologies largely based on Treatment technologies largely based on coagulation and flocculation

18 Surface Water Treatment Surface water from supply Rapid Sand Filter Screen Rapid Mix Disinfection Flocculation Basin Storage Sedimentatio n basin Sludge To Distribution System

19 Surface Water Treatment

20 Surface Water Treatment Main treatment Adding Polyaluminum chloride (PAX) and other coagulants to to raw water to promote coagulation and flocculation Sedimentation Filtration Disinfection using chlorine gas or UV light ph adjustment using sodium hydroxide (NaOH) to hinder corrosion in pipes

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22 Treatment Processes 1. Rapid Mix - From the aerators, the water flows into the rapid mix tank where it is combined with the lime. The purpose of the rapid mix tank is to provide a complete mix, allowing the lime to come in contact with the dissolved minerals. Detention time in this tank is just a few seconds. 2. First-Stage Mixing - Lime is mixed with the water for 20 to 30 minutes in mix tank. Motor-driven paddles keep the mixture moving and prevent settling in the mix tanks.

23 Treatment Processes 3. Second-Stage Mixing - The flow then proceeds to Mix Tanks. Some ph reduction can be achieved at this point by blending the lower ph of bypassed raw water with the high ph of the first-stage mix. During mixing and flocculation, the particles attach to one another to form larger solids that will be settled by gravity and removed during another stage of treatment. As slow proceeds through each tank the force and speed of the mixing is gradually reduced, allowing the particles to grow as large and heavy as possible. 4. Polymer- an anionic polymer is added to aid in coagulation and enhance settling. The polymer acts like a "glue, holding together the particles and allowing them to grow even larger.

24 Treatment Processes 5. Settling - Next, the water flows to quiet settling tanks, or clarifies, where previously formed particles settle to the bottom as lime sludge. Flow-through time here is two to three hours. Part of this sludge is returned to the mixing tank to assist in coagulation; the remainder is drawn off continuously to holding ponds or lagoons. 6. Chlorination - To ensure bacteriological safety of the water supply a calculated dose of chlorine was added. The chlorine disinfects the water and protects against microbial contamination after the water leaves the treatment plant. Dose of chlorine will also protect treated water from growth of algae if exposed to direct sun.