77    TWO STAGE UASB TREATMENT OF INDUSTRIAL
WASTEWATER WITH INTERNAL CIRCULATION (IC)
Andre de Vegt, Mangager of Technology
Paques, Inc.
Exton, Pennsylvania 19341
Peter Yspeert, Process Specialist
Paques B.V.
Balk, The Netherlands
INTRODUCTION
For years, UASB treatment has been an effective method for treatment of industrial wastewater.
The Upflow Anaerobic Sludge Blanket (UASB) process has now been reconfigured into a two stage
reactor system. The result of a two stage reactor configuration is an anaerobic reactor capable of
volumetric loading rates substantially greater than conventional UASB reactors. A key to the design is
the internal circulation inherent with the design, hence the reactor is called IC (Internal Circulation).
In this paper, the design principles and functioning of the IC reactor are described. Results .from
years of full scale operation are presented.
A requirement for efficient purification of industrial wastewater is a treatment system with high
capacities. In practice this means that an industrial reactor should be able to handle both high organic
and hydraulic loading rates. The parameters determining the treatment capacity of an anaerobic
reactor can be classified in microbial and physical factors, as shown in Table I.
Microbial aspects mainly depend on physiological parameters, such as temperature, pH and alkalinity, nutrients and inhibitory compounds. In the past, a lot of research has been conducted in order
to determine the influence of these physiological factors. Optimal values and tolerance ranges are now
well known and understood for most wastewaters. The potential activity of methanogenic biomass
appears to be much higher than the sludge loading rates (or food to mass ratios, F/M) generally
applied in full scale reactors (F/M <0.5 kgCOD/kgVS.d).
Whereas the conversion rates in aerobic systems are limited by such things as the transfer of oxygen,
anaerobic processes have no such limitations and the maximum treatment capacity is in fact only
limited by the physical aspects of the applied reactor design: 1) biomass retention capacity and 2)
biomass/wastewater contact.
Biomass Retention
The treatment capacity of the current conventional UASB systems is restricted by the limited
biomass retention ability within the reactor. For low concentrated wastewaters (COD < 2500 mg/L)
the applicable volumetric loading rate (VLR) is limited to 8-10 kgCOD/m3-d so that wash-out of
biomass solids due to the high liquid upflow velocity can be avoided. At this VLR, the corresponding
hydraulic retention time (HRT) is approximately 4-5 h. As a result, relatively large, space consuming
reactors are required for treatment of low strength effluents. For higher concentrated wastewaters
(COD > 2500 mg/L), the volumetric loading rate is usually restricted to 12-20 kgCOD/m3-d; in this
case to avoid wash-out of biomass, due to turbulence caused by elevated biogas production rates.
Table I.
Factors Defining Reactor Treatment Capacity
Microbial Factors
Physical Factors
- Biomass activity
- Biomass growth
- Biomass retention capacity
- Biomass/wastewater contact
49th Purdue Industrial Waste Conference Proceedings, 1994 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
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