journal critique mike
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USE OF FLOATING BEAD FILTERS TO RECONDITION CIRCULATING WATERS
IN WARMWATER AQUACULTURE PRODUCTION SYSTEM
Ronald F. Malone;Lance E. Beecher
Published in Journal of Aquacultural Engineering © / 2000
A CRITIQUE
Submitted to
AILEEN D. NIEVEA, Ph.D.
For
RES298 COM / RESEARCH SEMINARSchool of Graduate Studies
Mapua Institute of Technology
On
05 OCTOBER 2010
By
NAPOLEON MICHAEL B. ORIGENES
MSST - 1989131132
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2. Theory of Operation
It is clear that the author works on the function of floating bead filters and
states vividly the process involved. The author describes the advantages of such
use of the FBF in the production system so as mentioning its involvement in the
simplification of the most important water reconditioning performance.
CLARIFICATION PERFORMANCE
Clarification is the process of removing suspended solids from water .
Specifically, the study did not nebtion specific amount of physical straining it can
provide. Its only a belief that bioabsorption, the capture of particles by the
bacterial biofilter is the dominant removal process for such fine particles, that’s why
clarification efficiency is rarely an issue for a recirculating bioclarifier application,
allowing focus on another important water reconditioning process, biofiltration.
BIOFILTRATION PERFORMANCE
Biofiltration depends on the formation of a filter bead through the attachment and
growth of beneficial bacteria that extracts and dissolves chemicals from the water
and convert them to biomass or harmless dissolved compounds. The study clearly
states the importance of the process involved whereas conversions of toxic
components of water into relatively safe form. The study of the bacteria which are
responsible to these conversions are only limited to the toxic nitrogen forms,
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ammonia and nitrate. The study does not affirm if any other harmful variety of
toxic forms other than nitrogen passes through the biofiltration process.
not exclusively specified or identified but it is quite clear that the authors generally
worked on only one hypothesis during the entire duration of the study, which is:
The presence of oil in the sediments will affect the partitioning of PCB during land
biotreatment of impacted sediment . Proving this hypothesis, however, is not
straightforward or simple since it entails a lot of required routine tasks which would
include, at least for this particular study, mechanism by which the presence oil
affects the PCB partitioning and/or degradation, coming up with an appropriate
equilibrium partitioning model in the presence of a third phase (oil phase), and
predicting equilibrium partitioning in the presence of oil phase using these models.
Further, it was postulated that, as a consequence of PCB oil-phase
partitioning, biotreatment would lead to higher PCB concentrations in the oily
matter and thus increased PCB partitioning to the aqueous phase if the degradation
of oily matter proceeded faster compared to PCBs. This postulate appeared in the
abstract although it can also appear as a conclusion.
3. Experimental approach
3.1 Experimental set-up and data gathering
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The data used by the authors were based on the study of Alcoa (1995). This
long-term field study of the biodegradation of PCB-contaminated sediments and
sludge in pilot-scale engineered land-treatment units (LTUs) in Massena, N. Y.
made use of three of the four LTUs (labeled LTU1, LTU2 and LTU4) in the facility. A
schematic of the cross-section of the 1.2-m wide and 9.1-m long pilot-scale LTUs is
shown in Figure 1.
The sediments originated from on-site settling and treatment lagoons with
varying levels of PCBs, polycyclic aromatic hydrocarbons (PAHs), oil, cyanide,
fluoride and heavy metals (Alcoa 1995); Smith et al. 1999).
Figure 1. Schematic of pilot-scale land biotreatment unit.
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The design of the pilot-scale land treatment seems to be a very good
approximation of what the full-scale biotreatment facility would look like. In
addition, the processes (partitioning, degradation, etc.) and effects of other
components that may be present, which were not quantified in this research, in the
pilot scale could well represent the processes that would be occurring in the full
scale facility.
For experimental purposes, it is quite rational to premix lagoon sediments
and mix them with sand to homogeneity by repeated tilling and shoveling.
However, there was no indicated means to determine the degree of homogeneity
the sand-sediment mixture attained. While it is true that mixing the sediment with
sand would increase the porosity of the treatment zone matrix (to promote aerobic
condition for microbial degradation), some degrees of heterogeneity (uneven
distribution of sand in sediment or of sediment in sand) would greatly affect the
sampling. It should be noted that sand adsorbs neither the aqueous phase nor
organic carbons (oil included). A sample taken from a specific point could not have
represented the entire system. Average of the values from multiple sampling (i.e.
sampling from different points), however, could lessen the uncertainty. Even the
basis or reason for the choice of sediment-to-clean sand amendment ratio (1:11 for
LTU1, 1:14 for LTU2, and 1:1 for LTU4) was not clearly established.
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3.2 Conceptual models for equilibrium partitioning
The following were three conceptual models evaluated to compare the
predicted and the measured PCB partitioning between sediments-phase and
aqueous phase:
3.2.1 Model 1
PCB distributes between two phases: aqueous phase and organic-carbon
phase in the sediment . In this case, the PCB partitioning to the aqueous phase was
calculated with the following equation:
W OC OC S C K f C = (1)
where KOC values were estimated using the following equations by Chiou et al.
(1983) and Oliver (1985), respectively:
log KOC = 0.904 log KOW – 0.543 (2a)
log KOC = 0.41 log KOW + 3.42 (2c)
These equations had been developed on experimental measurements of PCB
partitioning between sediments and water. Equation 2a was derived from on
investigation of the sorption relationships for PCBs and chlorinated benzenes on
various soils and sediments and the equation was proposed for compounds with log
KOW ranging from 2.11 to 5.62 (R2 = 0.96) (Chiou et al. 1983). Equation 2c was
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based on PCB determination in suspended sediments from Lake Ontario (Oliver
1985).
The incorporation of the equations 2a and 2c are justified only on the basis
that the model assumes partitioning only between the aqueous phase and the
sediment phase containing the organic carbon. These are similar systems utilized
to come up with equations.
3.2.2 Model 2
PCB partitions or distributes among three phases: organic-carbon phase in
the sediment , the oil , and the aqueous phase. It was assumed that the oil had
characteristics similar to Fyrquel 220 (f OC = 0.75), a hydraulic fluid used at the site
where sediment samples were taken. Luthy et al. (1997) investigated the
dissolution of PCB congeners from Arochlor 1242 and mixture of Arochlor 1242 with
Fyrquel 220 and found an equilibrium partitioning consistent with Raoult’s law of
liquid solubilities:
iiiiS X C γ = (3)
It was reported that the apparent the average activity coefficients of prominent
congeners for which corresponding solubility existed (Luthy et al. 1997). Equations
1 and 2a were used to calculate sediment-water partitioning while equation 3 was
used to calculate oil-water partitioning.
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It should be noted that the distribution or partitioning of PCB in the three
phases at equilibrium were not clearly presented. Material balances could make this
possible. It can be suggested that maybe, in a separate paper, a thermodynamic
model for the liquid-liquid-equilibrium involving the PCB distributed into the three
different phases. In addition, it would help if the distribution of the PCB were
presented in a ternary diagram.
3.2.3 Model 3
This model assumes that the PCBs distribute into aqueous phase and oil-
phase, which means that the PCBs in the sediment-phase is solely associated with
the oil in it. This model also uses the same activity coefficients specified in model
2.
At this particular point it would be expected that Models 2 and 3 would be
useful in explaining the effect of oil in the partitioning of PCB in impacted sediment
during land biotreatment.
3.3 Relative rate of oil and PCB degradation
Based on a two-box modeling approach, the effects of differential rates of oil
degradation were analyzed to determine the fraction of fast- and slow-degrading oil
components and their respective degradation constants (Ghosh 1998):
( ) t k t k t s f e f feC
C −− −+= 10
(4)
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and PCB on equilibrium partitioning relationships during the time course of land
biotreatment operations.
After evaluating the constants from the fitted model for oil and PCB
degradation, profiles of the PCB homologs within the sediment carbon, the oil, and
the aqueous phase were simulated and compared with the measured concentrations
in the corresponding phases. The simplified relative model used for the partitioning
of PCB from the oil to the aqueous phase is given in equation 5, and equation 6
results when equation 5 is combined with equation 4.
( )
( ) t k
oil
oil
o
ioil
t k
i
i
o
i s
oil
iS
it
oil s
i s
e f MW
C
e f MW
C
t C
C X
,
,
1
1
)(,
,
,
−
−
−
−
≅= (5)
( )
( )
t k k
ooil
o
i s
oil i
ioil iiiw
i soil seC
C
f MW
f MW S t C
)(,
,,,
1
1)(
−
−
−≅ γ (6)
These equations would suggest that the mole fraction of PCB in the oil phase is
small; further, they predict the concentration of PCBs in the aqueous phase will
increase if the slow rate constant for oil is greater than the slow rate constant for
PCB degradation. The aqueous concentration would be constrained by the limits of
pure-phase PCB solubilities, partitioning onto sediment organic carbon, and the
general recalcitrance of heavier oil compounds.
The effect of the presence of oil could only be partly explained by kinetics as
described in this paper. However, a better understanding of the process or pre-
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4.2 Organic carbon in sediment and changes during land biotreatment
It is evident in Figures 3(a-c) that there was a significant reduction in oil
levels during the active phase of remediation; further, the oil continued to deplete
even after the passive treatment phase. Nearly half of the carbon associated with
the sediment was also degraded in the first two years. The increase in biomass by
year 5 or 6 was attributed by the author to the introduction of biomass when
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healthy vegetation on the topsoil geotextile was established. Another possible
reason to explain the decrease in organic-carbon to sediment ratio is the
degradation of oil, which is part of the organic carbons.
4.3 Prediction of equilibrium partitioning of PCB
As expected, Model 2 (sediment-oil-water) and Model 3 (oil-water) gave
close predictions of the observed (or measured) concentration of PCB homologs in
the aqueous phase. These are indistinguishable in Figure 4, which shows this
agreement. The graphical presentation (aqueous PCB concentration vs PCB
homolog) already speaks for the agreement between the model and the
experimental values; thus, no further statistical proof would be necessary. And,
while it is true, as suggested by the author, that the oil-water model (Model 3) is
adequate in itself for describing total aqueous-phase PCB partitioning in LTU
systems, an extensive study involving other initial oil-to-PCB ratios and effect of the
type of organic carbon (other than oil) in the impacted sediment be considered.
Further, Ghosh et al. (2000b) suggested that rather than the widely used f OC-KOC
relationships, oil measurements be combined with bulk PCB measurements to
provide far better predictions of sediment-water PCB partitioning for systems
similar to this.
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4.4 Change in oil and effect on PCB partitioning
Used as a model for determining the rates of in oil and PCB degradation
(changes in PCB and oil concentration), equation 4 predicted, and closely
approached, the actual rate of degradation as measured. From this tow-box model,
the parameters were evaluated. Like in the previous part, the graphical
presentation in Figure 5 is probably the best possible way to report the data. As in
any other modeling studies, a parity plot may also be presented to show how the
predicted values agree with the measured values.
There is a discussion on the constants determined for different PCB
homologs; however, this is not presented.
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Figure 6 shows the same results as Figure 5, only that the data for LTU4
were removed.
4.5 Prediction of changing PCB equilibrium with degradation of PCB and oily matter
Although presented for the di- and tetra- PCB homologs only, Figures (7a-b)
could very well suggest that the models described previously couldt not predict the
effects of changing PCB equilibrium on degradation of PCb and oily matter. Other
models should be proposed. As suggested, the models could be derived based on a
combination of equilibrium and mass transfer principles.
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5. Conclusions
Most conclusions are solely based on the objectives and findings in this study
and, therefore, are sound. However, the way one conclusion was presented in the
abstract was quite confusing: As a consequence of PCB oil-phase partitioning,
biotreatment would lead to higher PCB concentrations in the oily matter and thus
increased PCB partitioning to the aqueous phase if the degradation of oily matter
proceeded faster compared to PCBs. This appeared in the abstract as postulate and
could be mistaken as a conclusion.
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6. Nomenclature:
CS hydrophobic organic compounds (HOCs) concentration on the solid, mg/kg
Cs,io PCB homolog concentration in sediment at t = 0
CW aqueous concentration, mg/L
CWi aqueous concentration of component i at equilibrium, mg/L
C0 initial oil concentration at t = 0
f fraction of fast-degrading oil
f OC fraction of organic carbon
kf fast fraction rate constant, y-1
ks slow fraction rate constant, y-1
ks,oil slow pool rate constant for oil
KOC organic-carbon-normalized partition coefficient, L/kg
KOW octanol-water partition coefficient
MW molecular weight of homolog or oil
S compound solubility
Si subcooled liquid solubility of pure component i in water
Xi mole fraction of component i in the organic liquid
γ I activity coefficient of component i in the organic liquid
7. References (from the paper)
All the references used here are the actual references used by this paper. The
original paper follows this page.
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