22    PERFORMANCE OF A HYBRID ANAEROBIC PROCESS
George V. Crawford, Project Manager
Gore & Storrie Ltd.
Toronto, Canada M4G 3C2
Gerald H. Teletzke, President
GS Processes Inc.
Scottsdale, Arizona 85258
This paper describes the process development, full scale design and performance of a 2,500 mVday
capacity hybrid anaerobic treatment process located at the Lakeview Water Pollution Control Plant in
Mississauga, Ontario. The municipal treatment plant serves a residential population of 350,000 and
an industrial fraction that includes a major corn starch processing facility. This hybrid anaerobic
process treats the byproduct liquors from a sludge thermal conditioning process at the plant. Decant
tanks and vacuum filters are employed to dewater the conditioned sludges. The vacuum filtrate is
returned to the decant tanks. The byproduct liquors being treated by the anaerobic process are the
overflows from the decant tanks.
Prior to 1975, the plant sludges were anaerobically digested. Thermal conditioning was not
employed. The sludge thermal conditioning facility was commissioned in 1975, and until 1985 the
byproduct liquors were returned to the step aeration activated sludge plant for treatment. The liquors
are high in COD and BOD averaging 14,000 mg/L and 7,000 mg/L, respectively. The byproduct
liquors constitute over 20% of the total plant organic load. In 1985, a full scale hybrid anaerobic
process was put into operation to treat the byproduct liquors and thereby reduce the plant organic
load.
The design of the hybrid anaerobic process followed six years of laboratory and pilot scale process
development and study. The studies tested a variety of anaerobic processes and configurations including sludge blanket, fluidized bed, filter and hybrid reactors. Upflow and downflow filters were
studied. Random and modular type filter medias were investigated. The most suitable design for
thermal conditioning liquor treatment was found to be a unique hybrid configuration combining
anaerobic suspended growth and fixed film filter technology. The HYAN process HYbrid ANaerobic
design was adopted and implemented.
PROCESS DEVELOPMENT
Sludge thermal conditioning liquors (TCL) are generated at many municipal and industrial waste
treatment facilities as a byproduct of sludge dewatering operations. As part of the thermal conditioning process, biological cells in the sludge are lyzed and oxidized. A significant portion of the particulate solids matter is converted to dissolved solids. After the conditioned solids have been separated
from the liquid by settling and dewatering, the liquid phase contains high concentrations (10,000 to
20,000 mg/L) of COD. This liquid stream must undergo treatment before it can be discharged to any
receiving stream.
Because of the nature of the waste, and because of its obvious potential for anaerobic treatment,
the Region of Peel and the Ontario Ministry of the Environment commissioned Gore & Storrie
Limited in 1978 to conduct a laboratory scale investigation into the potential for anaerobic treatment
of the TCL generated at Lakeview. Subsequent studies and design effort by the firm led to the
development of the HYAN anaerobic hybrid reactor system.
Some early research by others on the treatment of sludge thermal conditioning liquors considered
the use of the anaerobic filter as proposed by Young and McCarty [1]. Such works considered the
treatability of TCL in anaerobic filters but did not explore the longer term effects of solids accumulation, solids inventory control, short circuiting and cleaning.
During 1978 and 1979 Gore & Storrie conducted a laboratory scale treatability study of the Lake-
view TCL using five anaerobic filters operating in parallel [2,3]. BOD removals of 70 to 95% and
COD removals of 60 to 75% were achieved at various loadings up to 24 kg COD/mVday. The study
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