340
N.I. Galil and Y. Levinsky
Schwartz-Mittelman and Galil (2000) focused on the clarification of the
biological mechanisms involved in bioflocculation disturbances caused by the
exposure of suspended biomass to phenol shock loading. Contact experiments
were performed by exposing activated sludge biomass under nongrowth and
growth conditions to various concentrations of phenol. Severe damages to the
settling of biosolids could be observed, especially under growth conditions. The
following mechanisms were found to be relevant to these disturbances: (1)
cellular lysis resulted in the creation of a fraction of small particles «0.45 /lm),
which could be considered as mostly cellular debris, due to their sizes and
especially to their lack of oxygen uptake; (2) lower hydrophobicity of biosolids
surfaces could be a result of the amphiphatic properties exerted by the phenol
molecule, as well as by the cellular components released to the aqueous phase by
lysis and by membranal damage; (3) the exposure to phenol caused the unbinding
of exocellular biopolymers from biosolids surfaces to the aqueous solution,
creating conditions of poor settleability resulting from: (a) bioflocs characterized
by low density; (b) dispersion of small biofloc fragments; (c) dispersion of single
cells; (4) phenol loading was found able to lower the cellular ATP concentrations
and this inhibition of the cellular biokinetics could also be a factor impairing the
boflocculation process.
4.4 Powdered-Activated Carbon (PAC) - Activated Sludge
Powdered activated carbon (PAC) addition to activated sludge is suggested in
many cases as a modification being able, potentially, to improve the process,
especially in the case of concentrated industrial wastewater containing refractory,
toxic, and hazardous compounds. The modification has been investigated by Flynn
(1975), Robertaccio (1976), Speccia and Gianeto (1984), Benedek et al. (1985),
and Garcia-Orozoco et al. (1986). The benefits of PAC in removing toxic
adsordable compounds, such as phenols, have been described by Ferguson et al.
(1976), Nayar and Sylvester (1979), and Sundstorm et al. (1979). The
enhancement of activated sludge by PAC addition in the treatment of oil refinery
wastewater was reported by De John and Adams (1975), Stenstrom and Grieves
(1977), Grieves et al. (1983), and Guarino et al. (1987).
Galil and Rebhun (1988) reported that in PAC-activated sludge treating
concentrated wastewater of an integrated oil refinery, 40% of the organics were
removed by stripping. The organic matter not removed by stripping could be
classified into three categories: (1) adsorbed on PAC, most of them phenols; (2)
removed by biodegradation; (3) residual in the effluent, most of them
nonbiodegradable;
The study indicated that the adsorption of hazardous phenolic compounds on
PAC enabled an improvement in the kinetics of biodegradation. No improvement
in settling characteristics ofML VSS could be achieved by PAC addition.
N.I. Galil and Y. Levinsky
Schwartz-Mittelman and Galil (2000) focused on the clarification of the
biological mechanisms involved in bioflocculation disturbances caused by the
exposure of suspended biomass to phenol shock loading. Contact experiments
were performed by exposing activated sludge biomass under nongrowth and
growth conditions to various concentrations of phenol. Severe damages to the
settling of biosolids could be observed, especially under growth conditions. The
following mechanisms were found to be relevant to these disturbances: (1)
cellular lysis resulted in the creation of a fraction of small particles «0.45 /lm),
which could be considered as mostly cellular debris, due to their sizes and
especially to their lack of oxygen uptake; (2) lower hydrophobicity of biosolids
surfaces could be a result of the amphiphatic properties exerted by the phenol
molecule, as well as by the cellular components released to the aqueous phase by
lysis and by membranal damage; (3) the exposure to phenol caused the unbinding
of exocellular biopolymers from biosolids surfaces to the aqueous solution,
creating conditions of poor settleability resulting from: (a) bioflocs characterized
by low density; (b) dispersion of small biofloc fragments; (c) dispersion of single
cells; (4) phenol loading was found able to lower the cellular ATP concentrations
and this inhibition of the cellular biokinetics could also be a factor impairing the
boflocculation process.
4.4 Powdered-Activated Carbon (PAC) - Activated Sludge
Powdered activated carbon (PAC) addition to activated sludge is suggested in
many cases as a modification being able, potentially, to improve the process,
especially in the case of concentrated industrial wastewater containing refractory,
toxic, and hazardous compounds. The modification has been investigated by Flynn
(1975), Robertaccio (1976), Speccia and Gianeto (1984), Benedek et al. (1985),
and Garcia-Orozoco et al. (1986). The benefits of PAC in removing toxic
adsordable compounds, such as phenols, have been described by Ferguson et al.
(1976), Nayar and Sylvester (1979), and Sundstorm et al. (1979). The
enhancement of activated sludge by PAC addition in the treatment of oil refinery
wastewater was reported by De John and Adams (1975), Stenstrom and Grieves
(1977), Grieves et al. (1983), and Guarino et al. (1987).
Galil and Rebhun (1988) reported that in PAC-activated sludge treating
concentrated wastewater of an integrated oil refinery, 40% of the organics were
removed by stripping. The organic matter not removed by stripping could be
classified into three categories: (1) adsorbed on PAC, most of them phenols; (2)
removed by biodegradation; (3) residual in the effluent, most of them
nonbiodegradable;
The study indicated that the adsorption of hazardous phenolic compounds on
PAC enabled an improvement in the kinetics of biodegradation. No improvement
in settling characteristics ofML VSS could be achieved by PAC addition.