Internship Report

October 2014 - January 2015

At

Environmental Dynamics International. Inc

Student: Can Cui

Program: Modeling of Partial ly Mixed Zone

Supervisor: Tim Canter

January 19 2015

1

Acknowledgement

It was a great opportunity for me to do a three-month internship at Environmental

Dynamics International (EDI). First of all, I would like to thank Mr. Tim Canter, the

Global Product Manager of Lagoon Solutions at EDI, for giving me the opportunity. For

me, it was a unique experience at the last stage of my graduation study. I was able to

apply what I have learned in courses and obtain invaluable hand-on experiences in

biological wastewater treatment modeling. My abilities of problem solving,

communicating, independent learning and attention to details also improved greatly.

I would also like to thank Dr. Chris Bye at EnviroSim Associates Ltd., Dr. Zhiqiang Hu

and Dr. Enos Charles Inniss at University of Missouri-Columbia, for providing technical

support during my internship.

2

Summary

The internship was concentrated to tackle ammonia rebound issue in a lagoon

system when temperature starts to rise from January to late May. The system consists of

two lagoons, IDEAL™ followed by a polishing lagoon. The IDEAL™ (Intermittently

Decanted Extended Aeration Lagoon), is a fully aerated lagoon and operated like

extended SBR system. The first part of the polishing lagoon, also known as partially

mixed (PM) zone, receives effluent water and MLSS from upstream IDEAL lagoon and

is hired for solids separation and sludge storage. After further solids removal in quiescent

zone, the final clean water is discharged out of the treatment system.

The internship was a step-by-step process. The accuracy of data can never be overstated

so I first reviewed the sample storage, preservation and measurement and provided my

suggestions to increase the data reliability. With all the proceeding preparation and data

at hand, I started to build a model for PM zone to analyze the rebound of ammonia. Two

approaches were proposed. One is mathematical approach and the other is BioWin

simulation approach. Results from both approaches indicate that the system is very

complicated and more data of PM zone and temperature and other parameters were

needed for better modeling.

3

Contents  

1. Modification of current sample storage, preservation and measurement methods ......... 4  

2. Model building ................................................................................................................ 7  

2.1 Introduction ........................................................................................................................ 7  

2.2 Conceptual model .............................................................................................................. 9  

2.3 Nitrification in PM zone ................................................................................................... 10  

2.4 Basic calculation of PM zone .......................................................................................... 11  

3. BioWin simulation approach ........................................................................................ 13  

3.1 Introduction ...................................................................................................................... 13  

3.2 Parameters of simulation ................................................................................................. 16  

3.3 Simulation results and discussion .................................................................................... 18  

4. Mathematical approach ................................................................................................. 20  

4.1 Mass balance of ammonium in PM zone ......................................................................... 20  

4.2 Total biomass accumulated in PM zone .......................................................................... 21  

4.3 Ammonia released to water from settled biomass ........................................................... 21  

4.4 Nitrification in water column ........................................................................................... 21  

4.5 Challenges about mathematical model ............................................................................ 22  

5. Conclusion .................................................................................................................... 22  

5.1 Possible explanations of ammonia rebound .................................................................... 22  

5.2 Additional parameters ..................................................................................................... 24  

4

1. Modification of current sample storage, preservation and

measurement methods

The first step of the internship is to scrutinize the sample storage, preservation and

analysis methods, which the company hired, and compare the methods with standard

methods to ensure reliability.

Appropriate storage and preservation are vital for obtaining reliable data. For

wastewater samples, the nature of sample changes with high temperature and exposure to

air. Microbiological activities also affect the nitrate-nitrite-ammonia content if the

samples are not well stored. However, I found some activities of sample storage,

preservation and measurement are improper and need to be corrected in the future. They

are summarized as followed.

1) The samples should be stored at low temperature and insulated from air

during transportation.

To minimize the volatilization or biodegradation of samples before analysis,

water samples should be kept at 4 °C in refrigerator or in ice water mixture for

transportation from the treatment plant to the lab, especially in summer, when

temperature is high and bacteria are very active. Besides the temperature, water samples

should also be isolated to prevent bacteria contamination. The operator didn’t keep the

samples at low temperature and isolate the samples, so it might cause some adverse effect

on the measurement.

2) The samples should be refrigerated as soon as possible if they are not

analyzed immediately.

5

After arriving in lab, the samples should be refrigerated as soon as possible if not

analyzed immediately because at high temperature the bacteria will biodegrade the

nitrogen and cause error to the results. The action that the operator left the water samples

at room temperature should be avoided in the future.

3) The samples should be stored by containers of the same material (all

plastic or glass).

When taking samples, the operator sometimes use containers of different material.

It is unknown whether different material causes difference in the results, but to increase

the accuracy to a max extend, I suggest the operator use the same material.

4) The samples need to be filtrated before analysis.

Before analyzing the ammonia concentration, the water samples should be

filtrated with 0.45µm pore size membrane filter to remove the solids. If the membrane

filter is not available, filter paper (fine pores) can serve as an alternative. Filtration is

necessary because turbidity may interfere with the final results. Thus fine solids should

be removed for future measurement.

5) The samples should be analyzed within 24 hours after reaching lab or

preserved at 4°C up to 7 days for ammonia measurement.

For ammonia measurement, Standard Methods suggests measurement carried out

as soon as possible. If samples can be analyzed within 24 hours of collection, the lab

operator can store the samples at 4 °C and unacidified. However, if preservation is

required or necessary, the operator can preserve samples by adding sulfuric acid to the

samples to pH <2 and storing at 4 °C up to 7 days. Burke et al’s research indicates that

after 7 days of preservation (acidification by sulfuric acid and stored at 4 °C), it is

6

impossible to obtain reliable results. The third party lab used 25% (percentage by volume)

of sulfuric acid for preservation more than 7 days. This should be avoided in the future to

get more accurate results.

Table 1 shows container, sample size, and preservation suggestions from the

Standard Methods.

Table 1: Nitrogen species guidance for sample size, container type, and preservation method

6) Duplicate or triplicate water samples should be obtained from lagoon and

duplicate or triplicate measurements should be carried out for each sample.

While sample storage and preservation are crucial for data accuracy, the

measurement is of same importance. Duplicate or triplicate samples and measurements

help to eliminate the chance of unexpected disturbance and calculate the standard

deviation. If the results deviate from each other too much, the lab operator may consider

repeating the measurement or changing new samples until the results are reasonable. The

7

sample and measurement are only taken once during the operator’s sampling and

measurement. This should be corrected in the future.

In conclusion, to ensure reliable results, I recommend the operator strictly follow

the requirements and avoid contamination and deterioration of samples. After samples

reach the lab, the lab operator should take the measurement as soon as possible or

preserve at 4 °C up to 7 days. The samples and measurement should be taken duplicate or

triplicate for statistical analysis.

With all the preparation work completed, a model of PM zone is built for further

analysis of rebound. In the following paragraphs, the model will be presented in three

aspects: considerations of model building, BioWin simulation model and mathematical

model.

2. Model building

2.1 Introduction

The lagoon process for municipal wastewater treatment has been used in the

United States for over 40 years with merits of low cost, easy maintenance and high-

efficiency to remove COD. The drawbacks are obvious too: lagoons have limited ability

to remove nutrients and in cold weather conditions effluent water quality deteriorated. As

the requirement of effluent water quality proposed by US E.P.A (United States

Environmental Protection Agency) is more and more stringent, especially the nitrogen

concentration, upgrade of lagoon technology becomes necessary.

The IDEAL™ (Intermittently Decanted Extended Aeration Lagoon) Solution

proposed by EDI is an innovative approach to provide full nitrogen removal under low

temperature condition. The IDEAL is a fully aerated lagoon and the treatment mode is

8

like extended SBR system. After 4-hour operation in IDEAL lagoon, clean effluent water

is discharged to partially mixed (PM) zone. In the case of Miner, MO the sludge is

wasted through the decanters to a downstream polishing lagoon, which consists of a PM

zone followed by a quiescent zone. The PM zone receives effluent water and MLSS from

upstream IDEAL lagoon and is hired for solids separation and sludge storage. After

further solids removal in quiescent zone, the final clean water is discharged out of the

treatment system.

Figure 1. Plan view of IDEAL and polishing lagoon

The performance of IDEAL is stable and highly efficient even during severe cold

winter. However ammonia rebound was observed from late April to early May 2014

when temperature rose. Effluent ammonia from IDEAL is below the method detection

limit (0.05 mg/L), so it is believed that excess ammonia is from PM zone where large

quantity of sludge is stored.

In order to find out where excess ammonia comes from and to better understand

the biological activities in PM zone, a conceptual model is developed. In this chapter, the

model will be presented as well as analysis of nitrification activities in PM zone so that

based on the discussion of model and biological activities we can come up with possible

9

mechanisms for ammonia rebound. The calculation of PM zone is covered at the end of

the chapter in preparation for discussion of BioWin and mathematical approaches.

2.2 Conceptual model

A conceptual model of the PM zone is presented in figure 2. This model shows a

sludge deposit dividing into three layers based on oxygen distribution. Dissolved oxygen

(DO) in water is saturated due to aeration from bottom and partial agitation makes the

oxygen in water gradually penetrate into the sludge deposit. So from layer one to three,

they can be viewed as in aerobic, anoxic and anaerobic conditions. Layer one, the aerobic

layer, because of ample oxygen around, has nitrifying bacteria attaching to the surface

and conducting nitrification. Layer three, completely isolated from oxygen, undergoes

anaerobic fermentation and thus releases ammonia. Layer two, in anoxic condition, have

both biological activities.

Besides autotrophic bacteria, heterotrophic bacteria also contribute to the changes

of nitrogen concentration through assimilating ammonia for growth but ammonia

removed by assimilation is much less than nitrification and is assumed negligible in

consideration of nitrogen changes.

The MLSS concentration in the PM zone is 150 mg/L. As nitrifying bacteria

comprise a very small portion of biomass, it is reasonable to assume no nitrification and

weak biomass decay are occurring in the water column.

When it comes to biological activities, temperature should always be emphasized

for their crucial effect. During the sampling period, December 2013 to June 2014,

temperature range was between 13°C and 2.3°C in the IDEAL reactor. Low temperature

10

will inhibit the activities of nitrification and decay so in the model it will be set as the

limiting variable to affect ammonia concentration.

Figure 2. Conceptual model of PM zone

2.3 Nitrification in PM zone

Nitrifying bacteria are autotrophic microorganisms that obtain their energy from

the oxidation of reduced nitrogen. Two types of bacteria are involved in nitrification,

ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB). They are very

sensitive to low temperature and low oxygen. Research has shown that oxygen

concentration below 2.0 mg/L begin to have a strong negative effect on nitrifying bacteria

and those below 0.5 mg/L have an even stronger negative effect. Low temperature also

greatly inhibits the activity of nitrifying bacteria and causes some loss of the population.

Once temperatures begin to increase, the population should begin to recover.

The growth of nitrifying bacteria can be expressed by the Monod equation (1):

(1)

where,

µ is the specific growth rate of the microorganisms;

µmax is the maximum specific growth rate of the microorganisms;

11

S is the concentration of the limiting substrate for growth;

Ks is the half-saturation coefficient, the value of S when µ/µmax = 0.5.

Equation 1 explicitly shows that when S is small, µ is linearly proportional to S.

In the PM zone, ammonia is the limiting substrate for growth of AOB and NOB.

2.4 Basic calculation of PM zone

For partially mixed (PM) zone, there is no sludge accumulation at the bottom

because of benthal aeration. Sludge is mainly accumulated on the inlet side. Assume

sludge accumulate on levee and occupy all the space above the levee as illustrated in

Figure 3.

Figure 3. Side view of PM zone

1) Volume of PM zone (Figure 4):

VPM zone = [(150 ft) × (350 ft) × (25 ft) × (1/3) – (90 ft) × (290 ft) × (15 ft) × (1/3)] – [(150

ft) × (120 ft) × (17 ft) × (1/3) – (90 ft) × (90 ft) × (13 ft) × (1/3)]

= 307000 ft3 – 66900 ft3

= 240100 ft3

12

Figure 4. Calculation of volume of PM zone

2) Assume sludge all accumulate on the inlet side(Figure 5):

Volume of sludge deposit:

Vsludge deposit = (150 ft) × (30 ft) × (25 ft) × (1/3) + (90 ft) × (25 ft) × (0.5) × (30 ft) × (1/3)

= 37500 ft3 + 11250 ft3

= 48750 ft3

Figure 5. Calculation of volume of sludge deposit

3) Volume of water:

Vwater = VPM zone – Vsludge deposit

= 240100 ft3 –48750 ft3

= 191350 ft3

13

3. BioWin simulation approach

3.1 Introduction

Since the biological activities in PM zone are very complicated, I used BioWin

software for simulation of the PM zone. In BioWin, lagoon is not a primary treatment

process so we need to combine other primary processes to simulate the lagoon treatment.

The following chart (figure 6) is a lagoon process developed by EnviroSim. The

water column and sediments stand for water phase and sludge phase in a lagoon

respectively. The Water Column, an aerated reactor in BioWin, simulates the biological

activities under aerated condition in lagoon water phase. While the Sediments, an

anaerobic digester in BioWin, undergoes anaerobic digestion of the sludge, just like the

same process at the bottom of a real lagoon. The point clarifier is used to retain solids and

itself has no volume. Because of internal agitation in real lagoon, some solids will go

back and forth between water phase and settled sludge phase. These solids will finally

settle down at the bottom thus no obvious solids loss occurs in real lagoon. The point

clarifier in the flow-chart functions to retain solids in Sediments and prevent solids loss.

Although I proposed three layers of the sludge deposit in the conceptual model, to

make it easier to adjust the parameters in simulation, I decide to adopt this model and not

to add Sediments configuration, which may have a more accurate simulation of the

sludge deposit.

So the goal of BioWin simulation is through adjusting the parameters of

temperature, DO, AOB and NOB concentration and their kinetics of growing to get the

effluent ammonia concentration pattern similar to the one monitoring by the company.

14

Figure 6. Flow chart of BioWin simulation

Each configuration in the BioWin simulation is explicitly presented in following

paragraphs.

1) Influent: the influent in this simulation system is effluent from IDEAL lagoon.

The N-species concentration from IDEAL effluent is unknown. To simulate the influent

to PM lagoon, I use the final effluent concentration. Random grab samples form the

IDEAL near the decanter at the time of decant returned ammonia-nitrogen concentrations

of <0.05 ppm. So it is reasonable to assume influent ammonia to PM zone is zero. As for

nitrate, nitrite and total COD, the total average concentration of final effluent is used.

Influent water quality parameter:

Flow: 849 m3/d

Total COD: 19 mg/L

TSS: 1400 mg/L

VSS: 980 mg/L (70% of TSS)

Ammonium: 0 mg/L

Nitrate: 8.39 mg/L

Nitrite: 0.76 mg/L

15

TKN: 98 mg/L (10% of VSS)

2) Water column: used to simulate water portion in PM zone. The volume of water

column is as calculated before. The water column configuration is a bioreactor and will

conduct COD removal and nitrification.

Volume of Water Column: 191350 ft3 = 5418 m3

HRT = V/F = 5418/849 d = 6.4 d

3) Sediments: used to simulate sludge deposit in PM zone. The volume is calculated

before. Sediments configuration is an anaerobic digester and will release ammonia

through decay process.

The volume of sediment equals to the volume of sludge deposit

Volume: 48750 ft3 = 1380 m3

TSS concentration of sediment: 100 g/L = 105 g/ m3 = 100 kg/ m3

Mass of sludge deposit: (1380 m3) × (100 kg/ m3) = 1.38 ×105 kg

4) Point clarifier: point clarifier is an ideal reactor. It has no volume and is employed to

retain solids which go back and forth between water column and sediments, just like what

happens in real lagoon. Otherwise, solids will be eventually washed out from sediments.

In the conceptual model, sludge deposit is divided to three layers. The reason why

only anaerobic sludge layer is modeled in BioWin simulation is for simplicity of

modeling. The aerobic layer contacting with water is incorporated into water column to

carry out nitrification in simulation. Anoxic layer is assimilated in both water column and

anaerobic digester. The current model with two reactors is easy and simple for adjusting

parameters and analyzing the results.

16

3.2 Parameters of simulation

In BioWin simulation, all biological activities rely heavily on temperature. The

influence of temperature is reflected by the Arrhenius coefficient Θ. Besides temperature,

the value of each parameter is also significant for simulation. So it is necessary to explore

the effect of each parameter on effluent ammonia.

First of all, a simulation is processed with default settings and these results will be

saved for control and contrast. Then each of the parameter of interest is changed while

keeping others the same.

1) Hydrolysis rate value

Figure 7. The effect of hydrolysis rate on effluent ammonia (2.1 is default number)

The simulation results show that hydrolysis rate has no effect on effluent

ammonia in BioWin simulation.

2) Arrhenius coefficient of hydrolysis rate

17

Figure 8. Effect of Arrhenius coefficient on effluent ammonia in BioWin simulation

(1.029 is default number)

As seen from the figure, when Arrhenius coefficient of hydrolysis rate increases,

effluent ammonia decreases.

3) AOB growth rate

Figure 9. Effect of AOB growth rate on effluent ammonia (0.9 is default number)

As shown in figure, when AOB growth rate increases, effluent ammonia

decreases.

4) NOB growth rate

Figure 10. Effect of AOB growth rate on effluent ammonia (0.7 is default number)

18

The above figure shows that effluent ammonia in simulation decreases when

AOB growth rate increases.

5) Arrhenius coefficient of AOB and NOB

Figure 11. Effect of Arrhenius coefficient of AOB and NOB on effluent ammonia (1.072

is default number)

The above figure shows that when Arrhenius coefficient of AOB and NOB

decreases, effluent ammonia decreases.

3.3 Simulation results and discussion

Simulation results from BioWin differ from each other greatly with different

parameters setting. The result that fits the pattern of data set from Minor project is shown

below.

Figure 12: BioWin simulation results for variable parameters

19

Although the pattern is similar, the peak value of effluent ammonia from

simulation is up to 30 mg/L, which is much higher than practical data. The time of peak

showing is postponed in simulation. What is more, instead of back to normal in Minor

project, the effluent ammonia starts to increase again from late May.

Here are the possible reasons:

1) More data is needed for better modeling

First of all, PM zone temperature is absent. The temperature at hand is air

temperature and water temperature in IDEAL. Compared to air temperature, water

temperature has smaller range. And because aeration in IDEAL lagoon is much higher

than in PM zone, the temperature in PM zone should be lower than IDEAL lagoon

temperature. At present this set of data is absent.

Secondly, sludge deposit temperature is also needed. Sludge deposit in PM zone

undergoes anaerobic digestion. The energy released from sludge deposit will be trapped

in sludge so the temperature of sludge deposit should be higher than ambient water. We

may want to consider measuring the sludge temperature in the future.

Thirdly, effluent water from IDEAL lagoon is not monitored on a regular basis. I

suggest taking effluent water from IDEAL lagoon and track the water quality for quality

control. The data will also be useful for better modeling of PM zone.

2) Limitation of Biowin software

Finally, it is still not clear whether the hydraulic disturbance inside the PM zone

has a significant contribution to excess ammonium. Monitoring the suspended solids (SS)

concentration near the sludge deposit may be advisable when temperature starts to rise in

late March. If there is significantly increase in SS near sludge deposit, it is likely that

20

excess ammonium come from solids. However, in BioWin, there is no specific

configuration for lagoon. The model showed above is convenient to simulate the

biological activity but not hydraulics. The limitation may be a key factor in BioWin

simulation.

4. Mathematical approach

4.1 Mass balance of ammonium in PM zone

Due to the limitation of BioWin software, I also proposed mathematical approach

to simulate the nitrogen activities. The fundamental idea of mathematical approach is to

set up an ammonia mass balance (equation 2) in PM zone. By calculating and comparing

the amount of ammonia released from sludge and oxidized by AOB and NOB, we can

find how the ammonia rebound is related to temperature or other factors we didn’t

recognize before.

Mass balance equation:

Accumulation = Influent + Reaction - Effluent (2)

Influent: ammonia coming into PM zone is assumed to be zero because ammonia

in effluent water from IDEAL lagoon is below detection limit so it is reasonable to

assume influent ammonium to PM zone is zero.

Reaction: releasing from sludge deposit and nitrification will both affect

ammonia concentration. Each of these reactions will be articulated in the following

paragraphs.

Effluent: effluent ammonia is a term to be calculated.

Accumulation: assume no ammonia is retained in PM zone and all ammonia in

water is discharged out of the system. So accumulation is zero.

21

Thus a simplified mass balance equation is:

Reaction - Effluent = 0 (3)

4.2 Total biomass accumulated in PM zone

Mass of sludge deposit (sludge already settled in PM zone)

M = 1.38 ×105 kg

Total biomass coming into PM lagoon

MLSS to PM lagoon: 1400 mg/L = 1.4 g/L = 1.4 kg/m3

Average flow rate: 0.2 MGD = 757 m3/d

So biomass discharging rate to PM lagoon: 1060 kg/d

Thus total biomass accumulated in PM lagoon is M = (1.38 ×105 + 1060t) kg,

where t is operation time with a unit of day

4.3 Ammonia released to water from settled biomass

Assume the rate of ammonia releasing to water from sludge deposit is rN. This

number should be obtained from experiment with sludge from PM zone. Once get this

number, the ammonium released can be calculated as:

MNH4-N = M﹒rN (4)

4.4 Nitrification in water column

Nitrification is expressed by the equation:

OHHNOONH 2324 22 ++→+ +−+ (5)

For nitrification the reaction rate (first order) will be in the range 0.01-0.3 (1/day).

A typical value of 0.05 (1/day) and a temperature coefficient of 1.088 are suggested.

22

From proceeding discussion, it is assumed that aerobic sludge layer comprise 10

percent of total sludge mass. And empirical composition of nitrifying bacteria in biomass

is 8 percent. So highest nitrification is achieved when both of the population and

nitrification rate of nitrifying bacteria reach maximum.

Highest nitrification= M×10%×8%×0.3

4.5 Challenges about mathematical model

At this point, the releasing rate of ammonia from sludge to water needs to be

identified. To increase the accuracy of the rate, I suggest taking sludge from different

layer and measure at different temperature conditions.

In this mathematical model, I initially assume that no ammonia is accumulated in

PM zone. However, this may not be the case in IDEAL operation, especially during the

ammonia rebound period. Thus in next sampling cycle, I recommend taking more water

samples for ammonia measurement in PM zone.

5. Conclusion

5.1 Possible explanations of ammonia rebound

Combining all the discussion above, I proposed two possible explanations for the

period of Dec 2013 to early April during which time the ammonia concentration in PM

zone is low. One explanation is that: decay of biomass and releasing of ammonia takes

place year round. The decay coefficient is temperature dependent, so when temperature

varies, the amount of ammonia released will also vary. The reason why ammonia

concentration in effluent water is observed below 0.05 mg/L from Dec 2013 to early

April is that the released ammonia acts as a substrate for AOB and NOB so that nitrifying

23

bacteria growing in aerobic and anoxic sludge layer take up the released ammonia and

keep the ammonia concentration low.

During the coldest period, January to March, the rate of releasing ammonia to

water was minimized due to thermal dynamics decreased with temperature. The decline

in substrate leads to decrease in the population of nitrifying bacteria. At the same time,

nitrification rate also decreased, or even ceased, because of low temperature inhibition.

So the balance between ammonium released to water and oxidized is used to maintain the

low concentration of ammonium in water.

As for ammonia releasing to water phase, it is believed that because of long

Solids Retention Time (SRT) and long-time settling at bottom without agitation, large

quantities of ammonia are released but most of them are trapped inside the sludge deposit.

The trapped ammonia is slowly released from sludge deposit to water column.

In terms of the sudden increase of ammonia, there are two explanations for it: one

is that: starting from early April, the rising temperature greatly increases the amount of

ammonia released to water. However at this point, nitrifying bacteria have not recovered

from inhibition. They need time to grow on the substrate-ammonia. Then, in this lag

period, ammonia is built up and rebound is observed. But after some time of growing,

according to equation 1, nitrifying bacteria finally catch up to oxidize excess ammonia.

Another cause of increase of ammonia could be internal hydraulics disturbance of

the sludge deposit due to enormous diurnal temperature change, which moves more

solids to the water column. The enormous diurnal temperature change greatly affects the

density of water. Surface water, due to contact with air, has temperature changing faster

than bottom water. From afternoon, when ambient temperature starts to cool down, water

24

of top layer cools down faster than bottom water. Then the colder surface water sinks to

bottom and causes hydraulic disturbance inside PM zone. The ammonia associated with

solids is released to water phase. While solids get removed at the end of PM zone or in

quiescent zone ammonia stays in water and causes ammonia concentration in water to

increase.

5.2 Additional parameters

After the modeling and calculation work, I realized that the lagoon system is

much more complicated than original expected. The data we have right now is not

enough to support the analysis. Thus we need additional parameters to effectively model

the system, and here are what those parameters:

1) Temperature of water and sludge in PM zone.

The temperature we have is ambient temperature and temperature of water in IDEAL

but they are improper to represent the temperature of water and sludge in PM zone.

While it is easy to understand that ambient temperature cannot represent the water

temperature, the discrepancy of operation condition between IDEAL and PM zone

indicates that the temperature in water is slightly different. The temperature of sludge

deposit at the inlet of PM zone is also different from that of water. Therefore, it is

necessary to monitor the temperature of water and sludge in PM zone.

2) Ammonia concentration of effluent water from IDEAL.

Even though the system proves stable and excellent performance during most of the

time and IDEAL is a high-efficiency reactor, without the ammonia concentration of

the effluent water from IDEAL, we are still not fully convinced that excess ammonia

25

only from PM zone. This possibility might be very small but I still recommend

monitor the effluent ammonia from IDEAL.

3) Ammonia concentration of water around sludge deposit in PM zone.

If the ammonia coming into PM zone is zero, the excess ammonia is from sludge

deposit. Through the change of ammonia concentration of the water around sludge

deposit, we can clearly see the trend of ammonia concentration change with

temperature. I suggest measure the concentration under different temperature

conditions.

4) Suspended Solids (SS) concentration near sludge deposit in PM zone from

March to June when temperature starts to increase.

This data can help identify whether the internal hydraulic disturbance is a key factor

to cause ammonia rebound. If it is the case, BioWin simulation may not be suitable.