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\begin_layout Title
Observing the effect of natural organic matter on kaolinite and aluminum
 sulfate flocs within a model AguaClara plant
\end_layout

\begin_layout Author
Alexandra Cheng, Roxanne Li, Ying Zhang
\end_layout

\begin_layout Address
School of Civil and Environmental Engineering, Cornell University, Hollister
 Hall, Ithaca NY, 14853 USA
\end_layout

\begin_layout Abstract
The effect of natural organic matter in an AguaClara plant was observed
 and analyzed.
 Modeling humic acid as natural organic matter and kaolinite as non-natural
 organic matter with aluminum sulfate as the coagulant, it was found that
 water purification was moderately improved in a low turbidity environment
 at higher humic acid concentrations, while lower concentrations yielded
 more scattered results.
 Additionally, it was found that humic-alum flocs did not create a floc
 blanket but managed to yield comparable results to kaolin-alum flocs that
 did create a floc blanket in a trial with raw water of 25 NTU.
 It is expected that at higher tubidities, humic acid would not follow this
 trend but instead would match the more traditional notion that higher humic
 acid concentrations yield less successful sedimentation processes.
\end_layout

\begin_layout Section
Introduction
\end_layout

\begin_layout Standard
Previous research has revealed that kaolinite-aluminum sulfate flocs can
 induce floc roll up in AguaClara plants and are a failure mechanism in
 plate settlers, but realistic raw water conditions also include natural
 organic matter (NOM).
 Natural organic matter can be best recognized as a key contributor of color
 and odor in raw water.
 Its by-products can be harmful to humans and also impede upon the purification
 process (Qin et al., 2005).
 Increased concentrations of natural organic matter have been shown to decrease
 floc strength and significantly worsen sedimentation success, which makes
 it all the more pertinent to reconsider AguaClara's plate settler design
 to include NOM (Zhong et al., 2011).
 The presence of NOM creates a physical and chemical change in flocs, as
 flocs coated in NOM have less successful further floc formation, decreasing
 the likelihood of a strong floc blanket (Wilkinson and Reinhardt, 2005).
 NOM flocs also tend to be less dense, which could result in intensified
 floc roll up in AguaClara plate settlers.
 Understanding the floc roll up response to NOM and NOM-kaolin-alum flocs
 will allow continued assessment of the ideal spacing between plate settlers.
 The objectives of this paper were to determine how much NOM, if any at
 all, the current model AguaClara plant could purify, and then to offer
 background data for further design improvements and adjustments to the
 plate settlers.
\end_layout

\begin_layout Section
Materials and methods
\end_layout

\begin_layout Subsection
Chemical choices and concentrations
\end_layout

\begin_layout Standard
Humic acid was used as a model for natural organic matter, while kaolin
 represented suspended non-organic matter in raw water.
 Aluminum sulfate (alum) was used as the coagulant because it is the choice
 coagulant of many actual AguaClara plants; however, it has been observed
 that alum has a lower success rate (in comparison to other coagulants such
 as ferric chloride) in the purification of NOM (Zhong et al., 2011).
 Due to this fact, alum plant dosage was set at 150 mg/L to compensate for
 its lower efficiency and to ensure that the coagulant dosage would not
 become a limiting factor in flocculation and sedimentation.
\end_layout

\begin_layout Subsection
Apparatus
\end_layout

\begin_layout Standard
Process control software controlled the experiment.
 10 g/L clay solution was added into a raw water reservoir until the desired
 turbidity was achieved, while humic acid of the chosen plant dosage was
 added at a constant rate of 4.3 mL/min.
 150 mg/L alum plant concentration solution was then added to raw water
 at a rate of 3.9 mL/min, after which the water flowed into a coiled tube
 flocculator.
 After going through the flocculater, the water flowed into a sedimentation
 column and formed a floc blanket.
 Once the floc blanket had been solidly formed, the tube settler and floc
 blanket turbidities were measured.
 In this model, the tube settler mimicked the plate settlers in an actual
 plant.
 Turbidity data was recorded every second.
 The tube settler pump velocity was set at the lower velocity of 3.785 mL/min
 because at a higher velocity, the quarter-inch diameter tube settler could
 easily draw up the less dense humic flocs.
\end_layout

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\begin_inset Caption

\begin_layout Plain Layout
Plate settler spacing team model AguaClara system
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\end_inset


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\end_inset


\end_layout

\begin_layout Subsection
Humic-alum floc experiment
\end_layout

\begin_layout Standard
To test for the worst case scenario, the humic acid plant concentration
 was set at 40 mg/L (an amount unrealistic to find in actual raw water)
 and the turbidity was kept at 0 NTU; without kaolin, the flocs created
 were essentially those most difficult for the current plant to handle.
 Also, if no floc blanket formed, it could be concluded that it is not possible
 to purify humic acid/NOM alone through traditional sedimentation processes.
\end_layout

\begin_layout Subsection
Humic-kaolin-alum floc experiment
\end_layout

\begin_layout Standard
Raw water turbidity was maintained at 25 NTU with varying humic acid plant
 concentrations of 2.5 mg/L, 5 mg/L, and 10 mg/L.
 The reason for choosing to vary humic acid dosage rather than turbidity
 was due to the fact that the chosen situation was theoretically more difficult
 for the current system to handle.
 Having a higher turbidity would make the humic acid less prominent and
 more closely mimicked conditions in which the system has succeeded.
 It was expected to find that lower humic acid plant concentrations would
 yield better tube settler performance than higher humic acid plant concentratio
ns because having fewer less dense flocs would decrease the possibility
 of inadvertant floc roll up.
\end_layout

\begin_layout Section
Results and discussion
\end_layout

\begin_layout Subsection
Purification of humic-alum flocs
\end_layout

\begin_layout Standard
The high humic acid plant dosage of 40 mg/L created large, low density,
 highly colored flocs which did not create a floc blanket.
 Tube settler performance was consistently negative, and the average turbidity
 difference between floc blanket effluent and tube settler effluent was
 -11.59% (Equation 
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reference "eq:Percentages"

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).
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	filename 0NTU 40NOM, TubeSettlerFlocBlanket effluent turbidities.emf
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\begin_inset Caption

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Floc blanket and tube settler effluent turbidities
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Sedimentation tank during turbidity measurement
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\begin_inset Caption

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AguaClara model response to 0 NTU, 40 mg/L humic acid plant dosage
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\end_layout

\begin_layout Standard

\size footnotesize
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\begin_inset Formula 
\begin{equation}
PercentageDifference=\frac{FlocBlanketTurbidity-TubeSettlerEffluentTurbidity}{FlocBlanketTurbidity}\label{eq:Percentages}
\end{equation}

\end_inset


\end_layout

\begin_layout Standard
From this experiment, it was determined that any floc blanket that might
 form in an experiment containing humic acid would be a result of other
 substances, like kaolin.
 Additionally, it was discovered that tube settler performance, although
 negative, was not as poor as expected because high concentrations of humic
 acid yield very large flocs which were unable to be drawn up by the quarter-inc
h diameter tube settler.
\end_layout

\begin_layout Subsection
Effect of humic acid on kaolin-alum flocs
\end_layout

\begin_layout Standard
All trials yielded floc blankets which grew progressively less colored as
 the humic acid plant dosage decreased.
 
\end_layout

\begin_layout Standard
The average turbidity difference between floc blanket effluent and tube
 settler effluent was -20.07% for 10 mg/L humic acid plant dosage, -17.17%
 for 5 mg/L humic acid plant dosage, -34.79% for 2.5 mg/L humic acid plant
 dosage, and -24.62% for 0 mg/L humic acid plant dosage (Equation 
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reference "eq:Percentages"

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).
 The trial with raw water at 25 NTU and a humic acid plant dosage at 10
 mg/L was the only trial in which the tube settler was successful for any
 period of time, which indicates floc roll up in all experiments.
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10 mg/L humic acid plant dosage
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5 mg/L humic acid plant dosage
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2.5 mg/L humic acid plant dosage
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No natural organic matter
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\end_layout

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\begin_inset Caption

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Floc blanket and tube settler effluent turbidities at 25 NTU with varying
 humic acid plant dosages
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Percent removal of turbidity: average difference between floc blanket and
 tube settler effluent
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\end_layout

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\begin_layout Standard
Although it was expected that lower humic acid plant dosage would yield
 better tube settler performance, the low turbidity environment created
 a floc blanket with a low enough amount of 
\begin_inset Quotes eld
\end_inset

fill
\begin_inset Quotes erd
\end_inset

 that smaller flocs could escape with ease.
 When humic acid plant dosage was at the higher concentrations of 10 mg/L
 and 5 mg/L, flocs were less dense but also larger, essentially creating
 a more dense floc blanket because they were trapped in the blanket.
 At the low humic acid concentration of 2.5 mg/L, the flocs became smaller
 and because the floc blanket created at 25 NTU was fairly porous, flocs
 escaped the blanket and were drawn up by the tube settler, yielding poor
 tube settler performance.
 The trial with no humic acid attests to the porous floc blanket theory;
 the current AguaClara plant has been proven to purify raw water with only
 kaolin fairly successfully, and the negative tube settler results in that
 run demonstrate a weak floc blanket that makes the size of flocs very critical.
 The results of the runs including NOM seem to counter traditional notions
 about the negative effect humic acid has on fractal size and the sedimentation
 process, but it can be inferred that these properties hold true in cases
 where the turbidity is high enough to create a floc blanket that allows
 little floc escape.
\end_layout

\begin_layout Section
Conclusions
\end_layout

\begin_layout Standard
The effect of humic acid in an AguaClara plant is highly dependent upon
 the conditions.
 Humic acid does not create a floc blanket on its own with aluminum sulfate,
 which puts great emphasis on turbidity levels because the kaolin is the
 key factor in fabricating a floc blanket.
 It was found that at low turbidities, a higher humic acid concentration
 actually improved the sedimentation process because the large flocs created
 more fill in the floc blanket, while a lower humic acid concentration created
 small flocs that could easily escape the floc blanket and impede upon the
 sedimentation process.
 It is predicted that humic acid would behave in an opposite manner at higher
 turbidities and may also be purified out of raw water more easily with
 different coagulants such as ferric chloride or polyaluminum chloride.
\end_layout

\begin_layout Description

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Acknowledgements
\end_layout

\begin_layout Standard
The assistance and support of Karen Swetland and Monroe Weber-Shirk is greatly
 appreciated.
\end_layout

\begin_layout Bibliography
\labelwidthstring References
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key "key-1"

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Qin, J.J., Oo, M.H., Kekre, K.A., Knops, F., Miller, P., 2005.
 Impact of coagulation pH on enhanced removal of natural organic matter
 in treatment of reservoir water.
 Separation and Purification Technology 49 (3), 295-298.
\end_layout

\begin_layout Bibliography
\labelwidthstring References
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key "key-2"

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Wilkinson, K.J., Reinhardt, A., 2005.
 Contrasting roles of natural organic matter on colloidal stabilization
 and ﬂocculation in freshwaters.
 In: Droppo, I.G., Leppard, G.G., Liss, S.N., Milligan, T.G.
 (Eds.), Flocculation in Natural and Engineered Environmental Systems.
 CRC Press, Boca Raton.
\end_layout

\begin_layout Bibliography
\labelwidthstring References
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key "key-1"

\end_inset

Zhong, R., Zhang, X., Xiao, F., Li, X., Cai, Z., 2011.
 Effects of humic acid on physical and hydrodynamic properties of kaolin
 flocs by particle image velocimetry.
 Water Research 45, 3981-3990.
\end_layout

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