A Simplified Multiple Jar Test Procedure for Activated Sludge Evaluation

 by Richard G. Weigand, CET and Michael R. Weigand

Overview

Developing and maintaining good floc structure is critical for proper mixed liquor settling and ultimate clarification. The flocculation of mixed liquor solids within the aerobic process and the subsequent de-flocculation due to downstream agitation or pumping can dramatically affect clarifier performance and effluent quality.

This procedure describes a methodology where a Phipps & Bird JarTester™ (six-paddle stirrer) can be used to evaluate the flocculation and de-flocculation ability of a mixed liquor.  A six-paddle jartester, commonly found in a drinking water plant lab, is used to stir mixed liquor samples.  Various mixing schemes are applied to both typical and agitated samples.  After settling, TSS and turbidity analyses are performed on the supernatant to assess the impacts of mixing on effluent quality.  Conclusions and  practical plant applications are described.

Introduction

The basic principal behind all activated sludge type wastewater treatment processes is the growth of microorganisms that colonize into settleable floc particles.  Under ideal conditions these floc particles are allowed to settle forming a sludge blanket and leaving a clear supernatant free of organic material and suspended solids.  Floc particles can vary greatly in size and density due to a variety of treatment factors.  Mixed liquor floc particles can be subjected to a wide range of environmental, mechanical and chemical factors which can influence their settleability.

In an effort to simplify the evaluation of mixed liquor flocculation and potential de-flocculation a six-paddle jar tester can be utilized.  Such equipment is widely used in the water treatment process to determine proper dosages of coagulants.  An easy methodology has been developed that can provide useful operational information in addition to such traditional process control tests as MLSS concentration, SVI and 30-minute settleometer.

Procedure

First, collect approximately 8 liters of activated sludge mixed liquor sample after the aerator has run for a few minutes.  Measure out the mixed liquor in six 1-liter samples into each of six Phipps & Bird 2000ml B-KerLab Jars using a 1000 ml graduated cylinder.

Mixing is done using the Phipps & Bird JarTester.  A programmable stirrer (Phipps & Bird PB-900™ Programmable JarTester) makes adjusting RPM and setting time intervals easier but is not required.  
A manually-operated model (Fig. 1) and a timer are sufficient.
  
                                                                                                                                                          Fig. 1 

Phipps & Bird PB-700™ JarTester

Table 1 summarizes a suggested mixing scheme for each of the jars.  Jar #1 receives unmixed, unagitated mixed liquor.  This serves as a control in an attempt to simulate a conventional settleometer test.  Jar #2 is first stirred quickly at 50 RPM for 30 minutes and then slowly at 15 RPM for 15 minutes.  Jar #3 is stirred at 50 RPM for 15 minutes and 15 RPM for 15 minutes.

The sample in Jar #4 is first agitated in the large jug for 5 minutes.  Then it is stirred for 15 minutes at 50 RPM followed by 15 minutes at 15 RPM.  Jar #5 is also agitated for 5 minutes before it is stirred for 15 minutes at 15 RPM.  The sixth and final jar is agitated for 5 minutes and received no mixing.  These mixing speeds are suggestions based on trial and error and can be adjusted.

  Table 1

Jar Number

Mix Fast

Mix Slow

Agitate

1

None

None

None

2

30 min

15 min

None

3

15 min

15 min

None

4

15 min

15 min

5 min

5

None

15 min

5 min

6

None

None

5 min

After agitation and/or stirring, all six jars should be allowed to settle for 1 hour.  Mixing and agitation should be sequenced to insure that all the jars begin settling at the same time.  A possible timing sequence is outlined in Table 2.

 Table 2

Time

Action

0:00

Begin fast mixing of Jar #2.

0:10

Begin agitation of Jar #4.

0:15

Begin fast mixing of Jars #3 and #4, continue fast mixing of Jar #2.

0:25

Begin agitation of Jar #5.

0:30

Begin slow mixing of Jars #2-5.

0:40

Begin agitation of Jar #6.

0:45

Begin settling of all Jars.

1:45

Note settled sludge depth and decant supernatant.

Using a ruler, measure settled sludge depth, and then decant the supernatant from each B-Ker² with a 100-ml pipette and a rubber bulb into each of the six 150-ml beakers.  (To minimize turbulence, do not use the B-Ker²’s built-in sampling ports).  Be sure to label the samples to avoid confusion. 

Measure supernatant Total Suspended Solids using Gooch crucibles in accordance with Standard Methods 19th Edition (1) procedure #2540D.  For comparison, remove another 20-ml aliquot of supernatant from each sample for turbidity measurement. To agitate samples for Jars #3-6, use a 4-liter plastic jug and shake vigorously by hand for the prescribed time.  Use a turbidity meter after performing a linear calibration using primary standards.  Conventional settleometer tests should also be performed on the mixed liquor samples for comparison with the results from Jar #1.  Perform mixed liquor suspended solids and sludge volume index analyses as well.  Record all data on a bench sheet similar to the one attached to this article.

This method demonstrates that a simple jar test procedure can be used to evaluate the brittle structure of activated sludge flocculation.  The de-flocculating and re-flocculating nature of the mixed liquor is a result of such factors as floc size, density (as it relates to sludge age), and presence of filamentous organisms.

Operations personnel can apply their test results to their facility in any number of creative ways.  Samples could be collected at various points in the process for evaluation: in multiple aeration basins, transfer troughs in route to clarifiers, clarifier inlet points, and before and after mixed liquor pumping stations.  Aerobic digesters can be sampled to evaluate fast and/or slow mixing schemes.  Sequence batch reactors could also be examined to determine the benefits of various aeration and mixing combinations prior to effluent decanting.

Operators are encouraged to use this basic procedure as a starting point to develop their own jar testing scheme and to include the results as part of their overall process control strategy.

The procedure outlined in this paper originally appeared in an article titled “Tending the Floc” that was published in the December 2000 issue of Water Environment & Technology Magazine.  The authors graciously edited, revised, re-formatted and modified the information and have granted Phipps & Bird, Inc. permission to publish and distribute it for promotional purposes. This version is made available to the public domain at no cost.

References:

Standard Methods for the Examination of Water and Wastewater, 20th ed.

Eaton et. al. Editors.  American Public Health Association.  Washington, DC.  1998.

About the Authors:

Richard G. Weigand, CET is the Director of the West Virginia Environmental Training Center in Ripley, WV and holds a Class III Wastewater Operators License in WV.  He has a MS Degree in Environmental Science from Rutgers University and has 23 years of plant operations and training experience.

Michael R. Weigand was a lab/computer technician serving a summer internship at the West Virginia Environmental Training Center.  He is currently a Biochemistry major at St. Vincent College in Latrobe, PA.

About Phipps & Bird, Inc.:

Phipps & Bird, founded in Richmond, Virginia in 1925, manufactures equipment for use in water and waste water treatment plant laboratories worldwide. 

Phipps & Bird, Inc.                             Toll-Free:  800/955-7621         Email:      Mail@phippsbird.com  
                1519 Summit Avenue                          Tel:            804/254-2737         Web:        www.phippsbird.com  
            Richmond, Va 23230-4511                  Fax:           804/254-2955

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© 2002  Phipps & Bird, Inc.

EXAMPLE WORKSHEET

Mixed Liquor Data

 

Conventional Settleometer Results

 

 

 

Settled Sludge Volume

 

 

MLSS ______ mg/l

 

 

 

30 min

60 min

 

 

 

Mixed Liquor

 

 

 

SVI ________ mg/l

 

 

 

 

 

 

 

 

50/50

 

 

 

 

 

 

 

 

 

 

 

Jar Number

1

2

3

4

5

6

 

 

 

 

 

 

 

Agitate

min

min

min

min

min

min

 

 

 

 

 

 

 

Fast ___ RPM

min

min

min

min

min

min

 

 

 

 

 

 

 

Slow ___ RPM

min

min

min

min

min

min

 

 

 

 

 

 

 

Settling Depth

mm

mm

mm

mm

mm

mm

 

 

 

 

 

 

 

% Settled Solids Volume

%

%

%

%

%

%

 

 

 

 

 

 

 

Supernatant TSS

mg/l

mg/l

mg/l

mg/l

mg/l

mg/l

 

 

 

 

 

 

 

Turbidity

NTU

NTU

NTU

NTU

NTU

NTU

 


 

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