Lecture 6: Wastewater treatment BIO410- Ecology and Environmental Engineering FALL 2016 By Jasmin Šutković 13h Nov. 2016 Lecture 6: Wastewater treatment

Outline INTRODUCTION COAGULATION AND FLOCCULATION SETTLING FILTRATION DISINFECTION

Introduction Many aquifers and isolated surface waters are high in water quality and may be directly pumped in order to supply human consumption, irrigation, industrial processes, or fire control. However, not everyone has the benefit of having many natural springs and isolated surface waters, particularly regions where the population is dense or where there is heavy agricultural use.

Typical aquifer cross-section An aquifer is an underground layer of water-bearing permeable rock, rock fractures or unconsolidated materials (gravel, sand, or silt) from which groundwater can be extracted using a water well.

Impurities enter water as it moves through the atmosphere, across the earth’s surface, and between soil particles in the ground. Heavy metals, various chemicals from industry, from agriculture, enter the water supply. Thus, water needs to be treated, using various treatments methods

A typical water treament plant is diagrammed in Fig. 7-1 A typical water treament plant is diagrammed in Fig. 7-1. It is designed to remove odors, color, and turbidity as well as bacteria and other contaminants. Raw water entering a treatment plant usually has significant turbidity caused by colloidal clay and silt particles. These particles carry an electrostatic charge that keeps them in continual motion and prevents them from colliding and sticking together. Chemicals like alum (aluminum sulfate) are added to the water both to neutralize the particles electrically and to aid in making them “sticky” so that they can coalesce and form large particles called flocs. This process is called coagulation and flocculation and is represented in stages 1 and 2 in Fig. 7-1.

COAGULATION AND FLOCCULATION Take a look : https://www.youtube.com/watch?v=KMP9-49I1U4 Naturally occurring sediments and other particles in raw water are very small, often colloidal in size, and possess negative charges.. Before they can be removed form water, by settling method, first their charges must be neutralized. The charge neutralization is called coagulation, and the building of larger flocs from smaller particles is called flocculation.

Aluminum sulfate- Al2(SO4)3 Alum has an advantage in addition to its high positive charge. Therefore, its use as flocculating agent (causing contaminating particles to clump into larger, more easily trapped particles) is essential!!

SETTLING Flocs must be removed from water! This is invariably done in gravity settling tanks that allow the heavier-than-water particles to settle to the bottom.

FILTRATION Water from the settling basins enters the filter and seeps through the sand and gravel bed, through a false floor, and out into a clear well that stores the finished water The solid impurities in the water are removed by many processes in the filtration process, the most important of which are straining, sedimentation ,interception, diffusion and inertia.

Mechanism of filtration Straining Sedimentation Interceptions Diffusion Inertia http://nptel.ac.in/courses/105104102/Lecture%2010.htm

Straining Straining, possibly the most important mechanism, takes place exclusively in the first few centimeters of the filter medium. As the filtering process begins, straining removes only particles in the water large enough to get caught in the pores

Sedimentation In sedimentation, larger and heavier particles do not follow the fluid streamline around the sand grain, and settle on the bottom. The sedimentation process removes many particles including clay and silt based turbidity, natural organic matter, and other associated impurities. These impurities include microbial contaminants, toxic metals, synthetic organic chemicals, iron, manganese and humic substances

Interception Interception of particles is common for large particles. If a large enough particle follows the streamline, that lies very close to the sands particles, finally being caught by them

Diffusion Movement due to kinetic energy of particles, implicating chance of interaction of these particles with sand granules. Diffusion towards sand particles occurs for very small particles, such as viruses. This mechanism is only important for particles with diameters < 1 micron.

Inertial compaction Attachment by inertia occurs when larger particles move fast enough to travel off their streamlines and bump into media grains.

DISINFECTION After filtration, the finished water is often disinfected with chlorine! Disinfection kills the remaining microorganisms in the water, some of which may be pathogenic. Chlorine oxidizes the microorganisms Chlorine gas is rapidly hydrolyzed in water to form hydrochloric acid and hydrochlorous acid, by the reaction At the temperatures usually found in water supply systems, the hydrolysis of chlorine is usually complete in a matter of seconds, while the ionization of HOCl is instantaneous. Both HOCl and OC1- are effective disinfectants and are called free available chlorine in water.

Alternatives for Disinfection OZONE – Super Charged oxygen Bromide Chloride Chloride Dioxide UV..

The Municipal Water Treatment Process https://www.youtube.com/watch?v=89I9e4f381Q

Project Presentations by Doaa and Esma… 