12    SUSPENDED SOLIDS REMOVAL FROM THE EFFLUENT OF
A FIXED-FILM ANAEROBIC REACTOR
Karel Kapoun, Senior Environmental Engineer
Badger Engineers, Inc.
Cambridge, Massachusetts 02142
Frederic C. Blanc, Professor
James C. O'Shaughnessy, Professor
Department of Civil Engineering
Northeastern University
Boston, Massachusetts 02115
INTRODUCTION
The purpose of this investigation was to evaluate Dissolved Air Flotation as a method for removal
of suspended solids from the effluent stream of a randomly packed fixed-film anaerobic reactor
(Celrobic). The test work reported here include 5 months operation with and without addition of
organic flocculent. All the experimental work was performed at the Celanese Chemical Company
plant located in Pampa, Texas, an integrated chemical production facility that includes one of the
world's largest acetic acid plants.
Feed to the Celrobic reactor is the process wastewater from the entire facility. The organic contaminants are primarily volatile fatty acids and, to a lesser degree, lower alcohols, ketones, esters, and
aldehydes.
The Celrobic reactor effluent contains some soluble organic contaminants which are refractory to
the bacterial degradation and suspended solids which are predominantly anaerobic bacteria washed
out from the reactor packing with some inorganic solids.
Because of its ability to remove both settleable and floatable solids, the Dissolved Air Flotation
(DAF) system was selected for pilot plant testing.
BACKGROUND OF DISSOLVED AIR FLOTATION TESTS
The DAF unit used as a feed the effluent stream from the full size randomly packed anaerobic
reactor (Celrobic System) [1).
The Celrobic reactor has a volume of approximately 1.5 million gallons. The reactor feed rate
during the testing period fluctuated between 400 gpm and 600 gpm while the COD removal efficiency
was maintained at approximately 80%. The average COD concentration in the reactor feed has been
reported as 16.7 grams/liter. Net sludge production in the Celrobic reactor has been determined to be
0.038 lb/lb of COD removed. This represents daily sludge production of between 2,440 and 3,660 lb/
day. Since the Celrobic reactor effluent contains approximately 400 mg/L TSS, the daily sludge
removal due to the suspended solids in the reactor effluent is less than the solids production. This
leaves some of the biomass (suspended solids) to accumulate in the reactor. The biomass is normally
attached to the randomly packed media and must be periodically removed.
The pilot DAF system (13.5 ft2 rectangular unit) was manufactured by Komline-Sanderson [2]. The
DAF aeration system is based on partial recycle of the treated effluent via a pressurized and aerated
retention tank. The float removal is effected through a timer-operated, countercurrent float skimmer.
In addition the DAF pilot plant was equipped with a flocculation tank with a "picket-fence," variable-
speed flocculator and chemical dosing equipment.
DAF TESTING PROCEDURES
Initially, the DAF unit was tested without chemicals while the Celrobic reactor was operated in the
normal steady-state condition producing low TSS effluent. The later part of the testing included high
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