Activated Sludge - Evaluating and Controlling Your Process by Tim Hobson (What you get out of the book.)

Table of Contents
Activated Sludge - Evaluating & Controlling Your Process
by Tim Hobson

Top of Page
Intro
Process Eval
Process Control
Troubleshooting

Introduction

This is not an introductory text about activated sludge. In this book, we discuss the observation, testing, and calculation procedures that provide data about the status of the activated sludge process. In addition, we discuss in depth how to apply this data to the business of controlling your activated sludge treatment process.

Basic activated sludge concepts are addressed in this book in the context of process evaluation and control. We focus our efforts on discussing a basic, practical system of control for the process.

The procedures discussed in this manual are equally applicable to all variations. An operator must have information about settleability, dissolved oxygen concentration, solids concentration, effluent quality, and clarifier sludge levels for consistent, efficient process performance of every type of activated sludge process. These procedures are covered in detail.

The procedures discussed are based on work done by E. B. Mallory in the 1930’s and 40’s and further developed by Alfred W. West while he was head of the Operational Technology Branch of the Environmental Protection Agency in the 1960’s and 70’s. The system, with some modifications by this author, is frequently called the “West Method” or "Sludge Quality Method" of activated sludge process control because operational controls adjustments are based on the sludge quality existing in your facility rather than on arbitrary values.

Activated Sludge

Evaluating and Controlling Your Process

Table of Contents

Part I: Process Evaluation
The testing and observation techniques covered in Part I will include:

Chapter 1: Observation
This chapter discusses important information you can gain about the activated sludge process by using your eyes and nose. We show you, through pictures and text, the information gained by observing and evaluating aeration basin turbulence, and color and foam characteristics. Secondary clarifier characteristics such as ashing, rising sludge, bulking, etc. are also discussed. The significance of each condition is briefly discussed. In Part II, we discuss each observed condition and its use in evaluating and controlling the process.

Chapter 2: Measuring sludge settleability
Sludge settleability is a key indicator of process condition. The operator makes process control adjustments in order to create a sludge that settles at the correct rate and provides a high quality effluent. Many operators tend to ignore this important test. The 60-minute settleability test described here will provide much more information than the more common 30-minute reading used for SVI calculations.

Chapter 3: Measuring concentration and amount of solids in the process
Methods for measuring solids concentration in the aeration basin, secondary clarifier, the return sludge, and waste sludge are described. Featured are the TSS and VSS tests and the centrifuge spin. The problems that you run into when trying to estimate solids concentration using a graduated cylinder or jar settling test are also discussed. Methods of calculating the amount of sludge solids in various tanks and flows are discussed and demonstrated with examples. Also featured: Calculation of settled sludge concentration and its application to defining "sludge quality".

Chapter 4: Aeration basin dissolved oxygen and oxygen profiles
Here we talk about methods of measuring the dissolved oxygen concentration in the aeration basin.

Chapter 5: Determining effluent quality
Measuring effluent quality using BOD and TSS testing is well documented. Here we discuss a couple of other quick and informative tests using a “$5.00, 1-minute” method, and also by measuring the turbidity of the effluent sample and settleometer supernatant.

Chapter 6: Measuring secondary clarifier sludge blankets
We discuss the correct methods for measuring the amount of sludge contained in the final clarifier using the sight-glass, electronic and core taker types of equipment.

Chapter 7: Microscopic examination of activated sludge
Many other resources discuss this subject extensively. Here we briefly discuss the methods and conclusions to be drawn from observing the various indicator organisms found in activated sludge.

Chapter 8: Displaying evaluation results
Here we discuss how to take all that process information you've gathered and get it into a form that allows you to see what's happening in your process. Using trendcharts, you'll be able to analyze where your process has been and where it's going.

At each step, we discuss how you can apply these testing skills to find out more about the status of your process, and what steps to take to progress toward a balanced, highly efficient state of operation.

Part II
Process Control

In Part II, we discuss how to interpret and apply the observation and test results learned in Part I:

Controlling aeration rates in diffused-air facilities and mechanically-aerated facilities

Controlling wasting rate. Determining what the best wasting rate is based on process observations and testing. Calculating wasting rates based on:

The Constant MLSS method

The Constant F/M method

The Constant MCRT method

Controlling return sludge flow rate

Discusses the relationship between return sludge flow and other factors.

Talks about the importance of good return sludge flow control

Demonstrates how to determine the best rate

Clarifier sludge depth method (commonly used but not recommended)

Mass balance method

Sludge Quality approach

Part III
Troubleshooting Guides

In Part III, Troubleshooting Guides for the activated sludge process are presented. The guides originally were applicable to the conventional activated sludge process but have been modified here to include information for operators of the extended aeration process.