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...

Determining

...

the

...

Cause

...

of

...

Surface

...

Foam

...

Experiments

Experimental Set-Up

...

In

...

an

...

attempt

...

to

...

recreate

...

surface

...

foam

...

in

...

a

...

lab

...

setting,

...

similar

...

to

...

that

...

found

...

in

...

AguaClara

...

Plants

...

in

...

Honduras,

...

we

...

first

...

had

...

to

...

recreate

...

a

...

similar

...

design

...

in

...

the

...

lab.

...

We

...

did

...

so

...

by

...

first

...

having

...

a

...

tank

...

which

...

mixed

...

tap

...

water

...

and

...

clay

...

in

...

order

...

to

...

have

...

a

...

constant

...

turbidity

...

of

...

approximately

...

100

...

NTU.

...

This

...

tank

...

represented

...

the

...

incoming

...

plant

...

water.

...

Water

...

from

...

this

...

tank

...

was

...

then

...

mixed

...

with

...

Natural

...

Organic

...

Matter

...

(NOM)

...

and

...

sent

...

into

...

Tank

...

2

...

which

...

simulated

...

the

...

rapid

...

mix

...

tank

...

and

...

first

...

baffle

...

of

...

the

...

flocculation

...

tank.

...

Once

...

in

...

this

...

tank,

...

the

...

turbidity

...

of

...

the

...

water

...

was

...

once

...

again

...

measured,

...

and

...

alum

...

was

...

dripped

...

onto

...

the

...

surface

...

of

...

the

...

water.

...

The

...

water

...

in

...

the

...

rapid

...

mix

...

side

...

of

...

tank

...

2

...

was

...

mixed

...

with

...

a

...

stirrer

...

before

...

traveling

...

into

...

the

...

first

...

baffle

...

portion

...

of

...

the

...

tank.

...

It

...

was

...

here

...

that

...

the

...

water

...

was

...

able

...

to

...

settle

...

a

...

bit

...

and

...

a

...

webcam

...

took

...

pictures

...

of

...

the

...

surface

...

water

...

every

...

two

...

minutes

...

to

...

determine

...

if

...

surface

...

foam

...

was

...

created.

...

When

...

an

...

aerator

...

was

...

added,

...

it

...

was

...

placed

...

in

...

the

...

first

...

baffle

...

portion

...

of

...

tank

...

2.

...

In

...

order

...

to

...

calculate

...

the

...

energy

...

dissipation

...

rate

...

at

...

the

...

rapid

...

mix

...

due

...

to

...

the

...

tubing,

...

first

...

we

...

calculated

...

the

...

head

...

loss

...

(h)

...

of

...

the

...

tubing

...

using

...

the

...

equation,

...


Latex

\large

$$
h = \left( {{Q \over {ka}}} \right)^2 {1 \over {2g}}
$$

...


 Then we calculated the residence time (θ) 
...
 using,

{
 Latex
}
\large

$$
\theta = {{d_{tube} } \over v}
$${latex}

Where,
...

 Latex
...

\large

$$
v = {Q \over a}
$$
...

 Finally energy dissipation (ε) 
...
 was 
...
 calculated 
...
 using 
...
 the 
...
 following 
...
 equation,

{
 Latex
}
\large

$$
\varepsilon = {{gh} \over \theta }
$${latex}

Where:
...
h= 
...
 the 
...
 head 
...
 loss 
...
 due 
...
 the 
...
 tube,
...

 Q 
...
 = 
...
 is 
...
 the 
...
 flow 
...
 rate 
...
 in 
...
 mL/min
...

 a 
...
 = 
...
 the 
...
 area 
...
 of 
...
 the 
...
 tube
...

 k 
...
 = 
...
 constant 
...
 magnitude 
...
 of 
...
 0.6
...

 g 
...
 = 
...
 gravity
...

 θ 
...
 = 
...
 the 
...
 residence 
...
 time
...

 d
...
tube 
...
 =
...
 the 
...
 length 
...
 of 
...
 energy 
...
 dissipation 
...
 of 
...
 the 
...
 jet, 
...
 which 
...
 was 
...
 estimated 
...
 on 
...
 the 
...
 length 
...
 scale 
...
 of 
...
 the 
...
 diameter 
...
 of 
...
 the 
...
 tubing.
...

 V 
...
 = 
...
 speed 
...
 the 
...
 flow
...

 ε 
...
 = 
...
 energy 
...
 dissipation
...
We 
...
 obtained 
...
 the 
...
 same 
...
 order 
...
 of 
...
 magnitude 
...
 for 
...
 energy 
...
 dissipation 
...
 as 
...
 the 
...
 AguaClara plants.   
 Wiki Markup
 plants.  
\\
{float:right\|border=2px solid black\|width=300px}
!Experimental_Design_SetupAguaClara experiment setup.jpg|width=300px, align=center!
h5. Illustration of Experimental Setup
{float}

Our 
...
 experiment 
...
 included 
...
 the 
...
 following 
...
 parameters: 
...
 Coagulant(Alum) 
...
 dosage, 
...
 concentration 
...
 of 
...
 Natural 
...
 Organic 
...
 Matter 
...
 (NOM), 
...
 location 
...
 of 
...
 alum 
...
 addition, 
...
 aeration 
...
 of 
...
 water 
...
 and 
...
 addition 
...
 of 
...
 a 
...
 surfactant. 
...
 In 
...
 the 
...
 first 
...
 week 
...
 of 
...
 our 
...
 experiment, 
...
 we 
...
 tested 
...
 for 
...
 alum 
...
 dosage 
...
 in 
...
 order 
...
 to 
...
 determine 
...
 whether 
...
 it 
...
 caused 
...
 foam 
...
 formation. 
...
 Alum 
...
 dosages 
...
 of 
...
 35 
...
 mg/L, 
...
 45 
...
 mg/L, 
...
 55 
...
 mg/L 
...
 and 
...
 65 
...
 mg/L 
...
 were 
...
 added 
...
 to 
...
 the 
...
 rapid 
...
 mix 
...
 chamber.
...
The 
...
 following 
...
 week 
...
 the 
...
 group 
...
 used 
...
 Humic 
...
 Acid 
...
 in 
...
 order 
...
 to 
...
 determine 
...
 the 
...
 effects 
...
 of 
...
 NOM 
...
 on 
...
 surface 
...
 foam 
...
 formation. 
...
 Varying 
...
 the 
...
 dosage 
...
 at 
...
 1mg/L, 
...
 2mg/L, 
...
 5 
...
 mg/L 
...
 and 
...
 10 
...
 mg/L, 
...
 Humic 
...
 acid 
...
 was 
...
 mixed 
...
 in 
...
 the 
...
 rapid 
...
 mix 
...
 chamber 
...
 with 
...
 45 
...
 mg/L 
...
 of 
...
 alum.
...
After 
...
 deciding 
...
 to 
...
 add 
...
 an 
...
 aerator, 
...
 we 
...
 kept 
...
 the 
...
 parameters 
...
 the 
...
 same 
...
 as 
...
 in 
...
 the 
...
 NOM 
...
 experiments, 
...
 however 
...
 we 
...
 added 
...
 an 
...
 aerator 
...
 to 
...
 the 
...
 first 
...
 baffle 
...
 portion 
...
 of 
...
 tank 
...
 2.
...
Finally 
...
 to 
...
 study 
...
 the 
...
 effect 
...
 of 
...
 hydraulic 
...
 jump 
...
 on 
...
 bubble 
...
 formations, 
...
 we 
...
 varied 
...
 the 
...
 height 
...
 of 
...
 the 
...
 water 
...
 fall 
...
 at 
...
 12.4cm, 
...
 14cm, 
...
 and 
...
 15.4 
...
 cm. 
...
 We 
...
 used 
...
 these 
...
 heights 
...
 because 
...
 they 
...
 were 
...
 approximately 
...
 equal 
...
 to 
...
 the 
...
 distance 
...
 that 
...
 water 
...
 would 
...
 be 
...
 falling 
...
 in 
...
 the 
...
 LFOM.
...
After 
...
 determining 
...
 both 
...
 the 
...
 cause 
...
 of 
...
 the 
...
 foam 
...
 and 
...
 theoretical 
...
 ways 
...
 to 
...
 prevent 
...
 the 
...
 water 
...
 from 
...
 aerating, 
...
 our 
...
 next 
...
 task 
...
 was 
...
 to 
...
 produce 
...
 designs 
...
 for 
...
 retrofitting 
...
 the 
...
 current 
...
 AguaClara 
...
 plants 
...
 in 
...
 operation.
...
Results 
...
 & 
...
 Discussion
...
Our 
...
 first 
...
 experiment 
...
 sought 
...
 to 
...
 determine 
...
 whether 
...
 overdosing 
...
 alum 
...
 could 
...
 aid 
...
 in 
...
 the 
...
 formation 
...
 of 
...
 surface 
...
 foam. 
...
 After 
...
 dosing 
...
 the 
...
 water 
...
 with 
...
 varying 
...
 alum 
...
 concentrations, 
...
 it 
...
 was 
...
 determined 
...
 through 
...
 observation 
...
 that 
...
 no 
...
 foam 
...
 was formed. 
Although the foam was not formed, this information was crucial to our research. Not only did it minimize the list of potential foam formation factors, it also help build our understanding of foam formation. As a result of foam not forming due to alum addition at the surface of the water, we also were able to rule out alum addition under the water surface as intuitively it was a solution to the form formation.
Our second experiment sought to determine whether or not the addition of Natural Organic Matter (NOM) contributed to the formation of surface foams. At all concentrations of Humic Acid, we again found there was no surface foam formed. Although the NOM did lower the surface tension better enabling bubbles to form, we believe they did not form due to a lack of air bubbles which naturally are found in AguaClara plants. As a result, we modified our experiment to include an aerator to provide them.
In our next experiment, we again varied the concentration of NOM but included an aerator to provide bubbling directly into what would be the first baffle spacing. At concentrations below 2 mg/mL we found that no foam was formed. However at higher concentrations of Humic Acid, we found that large bubbles would rise and then quickly pop in the center of the tank. In the meantime, smaller bubbles would form around the edges of the tank and were slightly more persistent as seen in Figure 2.
 Wiki Markup
{float:left formed. Sample photos are included in Figure 1.
{float:right\|border=2px solid black\|width=300px}
!Figure 1.JPG|width=300px, align=center!
h5. Figure 1: No surface foam formed solely through alum dosing
{float}
Although the foam was not formed, this data was crucial to our research. Not only did it minimize the list of potential foam formation factors, it also help build our understanding of foam formation. As a result of foam not forming due to alum addition at the surface of the water, we also were able to rule out alum addition under the water surface as intuitively it was a solution to the form formation.

Our second experiment sought to determine whether or not the addition of Natural Organic Matter (NOM) contributed to the formation of surface foams. At all concentrations of Humic Acid, we again found there was no surface foam formed. Although the NOM did lower the surface tension better enabling bubbles to form, we believe they did not form due to a lack of air bubbles which naturally are found in AguaClara plants. As a result, we modified our experiment to include an aerator to provide them.

In our next experiment, we again varied the concentration of NOM but included an aerator to provide bubbling directly into what would be the first baffle spacing. At concentrations below 2 mg/mL we found that no foam was formed. However at higher concentrations of Humic Acid, we found that large bubbles would rise and then quickly pop in the center of the tank. In the meantime, smaller bubbles would form around the edges of the tank and were slightly more persistent as seen in Figure 2.
{float:left\|border=2px solid black\|width=300px}
!Figure 2foam.jpg|width=300px, align=center!
h5. Figure 2: Surface foam as a result of Humic Acid Addition
{float}

Bubbles 
...
 form 
...
 when 
...
 water 
...
 molecules 
...
 form 
...
 bonds 
...
 around 
...
 air 
...
 pockets. 
...
 A 
...
 surfactant 
...
 is 
...
 generally 
...
 an 
...
 organic 
...
 molecule 
...
 that 
...
 has 
...
 both 
...
 hydrophobic 
...
 and 
...
 hydrophilic 
...
 ends. 
...
 While 
...
 surfactants 
...
 reduce 
...
 the 
...
 surface 
...
 tension 
...
 of 
...
 water 
...
 they 
...
 also 
...
 form 
...
 micelles 
...
 in 
...
 water 
...
 which 
...
 helps 
...
 to 
...
 stabilize 
...
 air 
...
 bubbles 
...
 and 
...
 prevent 
...
 them 
...
 from 
...
 aggregating. 
...
 The 
...
 concentration 
...
 at 
...
 which 
...
 surfactants 
...
 begin 
...
 to 
...
 form 
...
 micelles 
...
 is 
...
 known 
...
 as 
...
 the 
...
critical 
...
 micelle 
...
 concentration
...
 or 
...
 CMC. 
...
 Although 
...
 the 
...
 addition 
...
 of 
...
 humic 
...
 acid 
...
 did 
...
 reduce 
...
 the 
...
 aggregation 
...
 of 
...
 air 
...
 bubbles 
...
 it 
...
 still 
...
 occurred. 
...
 This 
...
 resulted 
...
 in 
...
 large, 
...
 non 
...
 persistent 
...
 air 
...
 bubbles 
...
 that 
...
 formed 
...
 a 
...
 foam 
...
 at 
...
 the 
...
 surface 
...
 of 
...
 the 
...
 water. 
...
 This 
...
 may 
...
 be 
...
 attributed 
...
 to 
...
 not 
...
 reaching 
...
 the 
...
 CMC, 
...
 however 
...
 using 
...
 higher 
...
 concentrations 
...
 of 
...
 humic 
...
 acid 
...
 would 
...
 not 
...
 accurately 
...
 replicate 
...
 plant 
...
 conditions.
...
Although, 
...
 a 
...
 surface 
...
 foam 
...
 was 
...
 formed 
...
 at 
...
 concentrations 
...
 of 
...
 Humic 
...
 Acid 
...
 greater 
...
 than 
...
 2 
...
 g/mL, 
...
 it 
...
 was 
...
 not 
...
 the 
...
 foam 
...
 that 
...
 is 
...
 found 
...
 in 
...
 AguaClara 
...
 plants. 
...
 The 
...
 foam 
...
 we 
...
 created 
...
 in 
...
 lab 
...
 contained 
...
 large 
...
 non-persisent 
...
 bubbles, 
...
 however 
...
 the 
...
 foam 
...
 we 
...
 sought 
...
 to 
...
 create 
...
 contained 
...
 small 
...
 persistent 
...
 bubbles 
...
 similar 
...
 to 
...
natural 
...
 foams 
...
 found 
...
 in 
...
 rivers 
...
 and 
...
 lakes
...
. 
...
 At 
...
 this 
...
 point 
...
 we 
...
 began 
...
 searching 
...
 for 
...
 a 
...
 stronger 
...
 surfactant 
...
 to 
...
 further 
...
 prevent 
...
 the 
...
 aggregation 
...
 of 
...
 bubbles, 
...
 thus 
...
 replicating 
...
 the 
...
 foam 
...
 found 
...
 in 
...
 Honduran 
...
 AguaClara 
...
 plants.
...
In 
...
 order 
...
 to 
...
 support 
...
 our 
...
 hypothesis, 
...
 we 
...
 added 
...
 soap 
...
 to 
...
 our 
...
 last 
...
 experiment 
...
 with 
...
 Humic 
...
 Acid 
...
 simply 
...
 to 
...
 see 
...
 if 
...
 would 
...
 create 
...
 the 
...
 surface 
...
 foam 
...
 we 
...
 wanted. 
...
 We 
...
 added 
...
 soap 
...
 because 
...
 its 
...
 molecular 
...
 composition 
...
 is 
...
 similar 
...
 to 
...
 that 
...
 of 
...
 fatty 
...
 acid 
...
 surfactants 
...
 found 
...
 in 
...
 nature. 
...
 We 
...
 found 
...
 that 
...
 the 
...
 soap 
...
 caused 
...
 a 
...
 persistent 
...
 foam, 
...
 similar 
...
 to 
...
 that 
...
 found 
...
 in 
...
 AguaClara 
...
 plants 
...
 and 
...
 can 
...
 be 
...
 seen 
...
 in 
...
 Figure 
...
 3 
...
 below.
 Wiki Markup

{float:right\|border=2px solid black\|width=300px}
!Figure 3foamwewant.jpg|width=300px, align=center!
h5. Figure 3: Surface foam after the addition of Dial soap
{float}

In 
...
 our 
...
 bucket 
...
 without 
...
 holes 
...
 experiment, 
...
 we 
...
 found 
...
 that 
...
 at 
...
 heights 
...
 less 
...
 than 
...
 14cm 
...
 we 
...
 can 
...
 prevent 
...
 a 
...
 hydraulic 
...
 jump. 
...
 A 
...
 hydraulic 
...
 jump 
...
 normally 
...
 causes 
...
 a 
...
 significant 
...
 loss 
...
 of 
...
 energy 
...
 and 
...
 the 
...
 production 
...
 of 
...
 turbulence 
...
 often 
...
 resulting 
...
 in 
...
 the 
...
 entrainment 
...
 of 
...
 air. 
...
 This 
...
 experiment 
...
 helps 
...
 us 
...
 determine 
...
 an 
...
 ideal 
...
 height 
...
 for 
...
 our 
...
 cup 
...
 design. 
...
 Although 
...
 we 
...
 have 
...
 eliminated 
...
 this 
...
 cup 
...
 design 
...
 (see 
...
retrofit 
...
 designs 
...
 page 
...
 for 
...
 details
...
), 
...
 if 
...
 we 
...
 were 
...
 to 
...
 continue 
...
 looking 
...
 into 
...
 this 
...
 theory 
...
 it 
...
 would 
...
 be 
...
 beneficial 
...
 to 
...
 start 
...
 by 
...
 testing 
...
 smaller 
...
 hydraulic 
...
 jumps.