BIOLOGICALLY-EXTENDED
PHYSICOCHEMICAL TREATMENT
WALTER J. WEBER, Jr.*, LOUIS D. FRIEDMAN** and RALPH BLOOM, Jr.**
Professor of Environmental and Water Resources Engineering, Dept. of
Civil Engineering, The University of Michigan, Ann Arbor, Michigan 48104, USA
**Research Chemist and Program Manager, respectively, Chemical Research and
Development Center, F.M.C. Corporation, Princeton, New Jersey, USA
The technologic and economic benefits of direct treatment of municipal and industrial
wastewaters by physicochemical processes - specifically coagulation and adsorption —
have been demonstrated and detailed (Rizzo and Schade, 1969; Weber et al., 1970, 1971;
Hager and Reilly, 1970; Bishop et al, 1971). Weber et al (1970, 1971) have further
demonstrated the advantages of expanded-bed adsorbers for this application.
Among several benefits noted for expanded-bed adsorbers is the duration over which
effective operation may be maintained without significant increases in head loss, coupled
with an apparent extension of the operational capacity of the carbon. Indeed, Weber et
al. (1970, 1971) observed that activated carbon could function efficiently for markedly
longer periods in expanded-bed operation than predicted by saturation data obtained
from measurements of adsorption isotherms or from sorption capacities obtained in
packed-bed adsorption systems; they suggested that the observed enhancement in
effective capacity was attributable to bacterial activity on the surfaces of the carbon. This
activity can be tolerated, indeed encouraged, in expanded-bed adsorbers, whereas
conventional packed-bed adsorbers are normally subject to fouling as a consequence of
biologic growth.
Weber et al. (1970, 1971) found that sorption capacities in excess of 60
weight-percent (wt-%) as organic matter and 90 wt-% as COD could be obtained in
expanded beds of activated carbon in which biologic growth was allowed to develop.
Because expanded beds require little maintenance, extended periods of undisturbed
operation facilitate the development and continuous growth of bacteria on the carbon
surfaces. These bacteria utilize the organic material adsorbed on the carbon as a food
source, at the same time acting to renew the surface for continued adsorption.
The capacities attained in the pilot studies by Weber et al, (1970, 1971) were not
reported as ultimate capacities, for at the time the capacities were measured, the systems
were still producing effluent of essentially the same quality as when the carbon was fresh.
The longest continuous experiment with a single batch of carbon was limited by
requirements of the pilot program to four months. It was of interest for design of the
present investigation, therefore, to obtain some better indication of the extent to which
the apparent in situ regeneration by biologic activity could increase the effective
operating life of active carbon. This information is highly significant relative to the
economics of physicochemical treatment, for regeneration of carbon by conventional
thermal means incurs one of the highest single Operating costs for the adsorption process.
It was also of interest for this study to determine whether there were differences in
operational capacities relating to whether the adsorbers were maintained in aerobic or
anaerobic state. One manner in which biologic activity can be enhanced in an
expanded-bed adsorber is by addition of air or oxygen, a treatment which could cause
air-binding of a packed-bed adsorber. Weber et al (1970, 1971) noted that maintenance
of aerobic conditions in solution phase in expanded-bed adsorbers enhances effluent
quality by preventing H 2 S generation. It was not immediately obvious, however, whether
641
PHYSICOCHEMICAL TREATMENT
WALTER J. WEBER, Jr.*, LOUIS D. FRIEDMAN** and RALPH BLOOM, Jr.**
Professor of Environmental and Water Resources Engineering, Dept. of
Civil Engineering, The University of Michigan, Ann Arbor, Michigan 48104, USA
**Research Chemist and Program Manager, respectively, Chemical Research and
Development Center, F.M.C. Corporation, Princeton, New Jersey, USA
The technologic and economic benefits of direct treatment of municipal and industrial
wastewaters by physicochemical processes - specifically coagulation and adsorption —
have been demonstrated and detailed (Rizzo and Schade, 1969; Weber et al., 1970, 1971;
Hager and Reilly, 1970; Bishop et al, 1971). Weber et al (1970, 1971) have further
demonstrated the advantages of expanded-bed adsorbers for this application.
Among several benefits noted for expanded-bed adsorbers is the duration over which
effective operation may be maintained without significant increases in head loss, coupled
with an apparent extension of the operational capacity of the carbon. Indeed, Weber et
al. (1970, 1971) observed that activated carbon could function efficiently for markedly
longer periods in expanded-bed operation than predicted by saturation data obtained
from measurements of adsorption isotherms or from sorption capacities obtained in
packed-bed adsorption systems; they suggested that the observed enhancement in
effective capacity was attributable to bacterial activity on the surfaces of the carbon. This
activity can be tolerated, indeed encouraged, in expanded-bed adsorbers, whereas
conventional packed-bed adsorbers are normally subject to fouling as a consequence of
biologic growth.
Weber et al. (1970, 1971) found that sorption capacities in excess of 60
weight-percent (wt-%) as organic matter and 90 wt-% as COD could be obtained in
expanded beds of activated carbon in which biologic growth was allowed to develop.
Because expanded beds require little maintenance, extended periods of undisturbed
operation facilitate the development and continuous growth of bacteria on the carbon
surfaces. These bacteria utilize the organic material adsorbed on the carbon as a food
source, at the same time acting to renew the surface for continued adsorption.
The capacities attained in the pilot studies by Weber et al, (1970, 1971) were not
reported as ultimate capacities, for at the time the capacities were measured, the systems
were still producing effluent of essentially the same quality as when the carbon was fresh.
The longest continuous experiment with a single batch of carbon was limited by
requirements of the pilot program to four months. It was of interest for design of the
present investigation, therefore, to obtain some better indication of the extent to which
the apparent in situ regeneration by biologic activity could increase the effective
operating life of active carbon. This information is highly significant relative to the
economics of physicochemical treatment, for regeneration of carbon by conventional
thermal means incurs one of the highest single Operating costs for the adsorption process.
It was also of interest for this study to determine whether there were differences in
operational capacities relating to whether the adsorbers were maintained in aerobic or
anaerobic state. One manner in which biologic activity can be enhanced in an
expanded-bed adsorber is by addition of air or oxygen, a treatment which could cause
air-binding of a packed-bed adsorber. Weber et al (1970, 1971) noted that maintenance
of aerobic conditions in solution phase in expanded-bed adsorbers enhances effluent
quality by preventing H 2 S generation. It was not immediately obvious, however, whether
641