Water, Wastewater, and Sludge Filtration

C. Visvanathan, Roger Ben Aim

• Publisher: CRC Press
• Year: 2020
• ISBN:
  9781000142044
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Engineering General
• Index: Technology & Engineering

A comprehensive and up-to-date account of filtration in solid-liquid separation processes, with a sharp focus on the influence of pro-cess variables on performance and specific applications is pre-sented in this volume. With contribu-tions from researchers with significant industrial experi-ence, as well as by senior academics, this publication fea-tures a deep bed filtration overview with informa-tion on mathematical modeling and application in wastewater treat-ment. Pre-treatment filtration techniques such as cartridge filters, pre-coat filters and micro screening are included. Membrane filtration processes to remove dis-solved and suspended solids for the recovery of valuable ma-terials and the provision of high quality water are covered. Sludge de-watering methods such as centrifuga-tion, and vacuum and pressure filtration are described. Application status data, tables, figures and diagrams are also included. This volume is of special interest to practicing engineers and technolo-gists dealing with treatment problems requiring filtration solu-tions and to graduate students in environmental engineering.

Chapter 1

OVERVIEW OF DEEP BED FILTRATION: DIFFERENT TYPES AND MATHEMATICAL MODELS

Saravanamuthu Vigneswaran and Roger Ben Aim

TABLE OF CONTENTS

I.	Introduction
II.	Improvements on Rapid Filter A. Improvements on Filter Media B. Improvements on Flow Rate C. Elimination of Some Operations from Conventional Water Treatment
III.	Filter Backwash Methods A. Choice of Backwash Method B. Backwashing with Effluent from Other Filter Units
IV.	Optimization of Filter Design
V.	Mathematical Models A. Filtrate Quality B. Headloss 1. Clean Bed 2. Clogged Bed
References

I. INTRODUCTION

Filtration technologies are classified under two major categories, depending mainly on the mode of filtration: slow sand filtration and rapid sand filtration. Slow sand filter, which includes biological activity in addition to physical and chemical mechanisms for removing impurities from the raw water, is especially suitable for small community water supplies, because of its large areal requirement. Numerous documents are available on this technology.^{1, 2, 3, 4, 5, 6, 7}

Rapid filter, on the other hand, due to its lower areal requirement (25 to 150 times less than slow sand filter) is used widely as a final clarification unit in municipal water treatment plants. It is becoming increasingly important in wastewater treatment, particularly when water reuse is envisaged. The applications of filtration in wastewater are discussed in detail in Chapter 4.

II. IMPROVEMENTS ON RAPID FILTER

A. Improvements on Filter Media

The conventional rapid filter generally uses sand with an effective size of 0.6 mm and a uniformity coefficient of 1.5 to 2. This results in stratification of filter medium after the backwash, in which the finer medium remains at the top and the coarser medium at the bottom of the filter bed. To overcome this problem, two alternatives have been proposed: dual or multimedia filtration; or coarse size, narrowly graded media filtration.

In dual-media filtration, the size and specific gravity are carefully selected to minimize intermixing. The commonly used media are anthracite coal and sand. Various research workers have given optimum size ratios to avoid intermixing (Table 1). Extensive research has been carried out to study the advantages and disadvantages of intermixing of filter media in dual media filtration.^{13, 14, 15} While a group of researchers feel that the grain size of course anthracite and fine sand should be chosen in such a way that the intermixing at the interface is minimized, others believe that controlled mixing among filter media is beneficial. A detailed design of media is discussed in the literature.^16,17

Another alternative is to replace a graded single medium with a coarse, narrowly graded medium of larger depth. This arrangement results in deeper penetration of the suspended solids and thus higher storage capacities which would lead to a longer run. The selection of size depends on the raw water and required effluent qualities. The commonly used size range is 0.9 to 1.1 mm. This arrangement can meet an increase in demand in existing units because it can be operated at a higher filtration rate. However, deeper penetration of the solids would entail a higher backwashing requirement. The rate of air and water used for backwashing depends on the size of medium. For example, sand of 2 mm effective size requires a washing rate of 90 to 110 m³/m²·h of air and 19 to 24 m³/m²·h of water.

B. Improvements on Flow ...

Table of contents

• Cover
• Title Page
• Copyright Page
• Preface
• The Editor
• Contributors
• Table of Contents
• Chapter 1 Overview of Deep Bed Filtration: Different Types and Mathematical Models
• Chapter 2 Theoretical Approach of Deep Bed Filtration
• Chapter 3 Direct Filtration
• Chapter 4 Applications of Deep Bed Filtration in Wastewater Treatment
• Chapter 5 Microstraining
• Chapter 6 Precoat Filtration
• Chapter 7 Cartridge Filtration
• Chapter 8 Reverse Osmosis
• Chapter 9 Ultrafiltration
• Chapter 10 Microfiltration
• Chapter 11 Electrodialysis
• Chapter 12 Vacuum Filtration
• Chapter 14 Centrifuges for Sludge Treatment
• Index