Treatment of Filamentous Bulking
with Hydrogen Peroxide
P. J. KELLER, Research Chemist
E. I. du Pont de Nemours & Co.
Wilmington, Delaware
C. A. COLE, Assistant Professor
Pennsylvania State University
Harrisburg, Pennsylvania
INTRODUCTION
An activated sludge plant is usually considered to be bulked when the mixed liquor
suspended solids (MLSS) settle slowly. Bulking can have several causes (I), one of which is
filamentous bacteria. Bulked sludges cause two problems, suspended solids losses to the
effluent and reduced MLSS. Both of these conditions lead to poor effluent quality.
The growth of filamentous organisms can have several causes, including a high
carbohydrate content in the feed, low nutrient supply, improper solids loading and shock
loads.
Several types of treatments of filamentous bulking have been used. These include
wasting sludge, increasing or decreasing the air supply, by-passing or diluting the waste to
change loading, addition of flocculating chemicals and chlorination of return sludge (2).
These treatments have had sporadic success records and where they have worked
seriously degraded effluent quality. The need for good operation at all times will not allow
poor plant performance during bulking incidents.
EXPERIMENTAL PROCEDURES
The H202 was added at a point where good mixing and efficient contact with the sludge
could be obtained. The point of addition varied with each plant as a point of convenience
was chosen. Sludge volume indices were used as an indication of the settleability of the
mixed liquor suspended solids.
Demonstrations have been made on both conventional step aeration and completely
mixed activated sludge units for domestic and industrial waste waters.
The experimental results cover tests at the EPA-DC pilot plant units (100,000 gpd) and
municipal and industrial waste treatment demonstrations. Results ofthe initial laboratory
experiments and the EPA-DC pilot plant studies were presented in a previous paper (3).
EPA-DC CONVENTIONAL UNIT
At the EPA-DC pilot plant an activated sludge process was operated as step aeration
with a high sludge retention time and it produced good effluents. However, adjustment to
the process to reduce sludge retention time and produce an effluent to be used for further
nitrification studies permitted establishment of Sphaerotilus organisms. Process variations
such as wasting sludge and changing loading failed to reduce the SVI over a period of
several months. Chlorination was avoided to protect the subsequent nitrifying activated
sludge. H202 was added to the recycle sludge at a dose of 20 mg/1 influent flow and 40 mg/1
of recycle flow for two days. This was increased to 40 mg/1 influent flow for an additional 12
days.
The actual SVI reduced from 300^400 to less than 200 within two days and then
eventually to 50-60 as can be seen in Figure 1.
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