Expert System for the Control of Effluent TN Exceedance of AAO

Process

Xingguan Ma

, Zhiyi Wang, Hongyu Shi and Li Zhang

School of Municipal and Environmental Engineering, Shenyang University of Architecture, Shenyang, Liaoning 110168, China

Keywords: AAO, Process, Nitrification System, Denitrification System, TN Exceedance, NH4+-N Exceedance, Expert

System.

Abstract: Based on the mechanism of microbial denitrification and the principle of wastewater treatment process control,

an expert system is built for the purpose of dealing with the exceeding of TN standard, and the data

information collected from the equipment of the wastewater treatment plant is combined with intelligent

diagnostic means to make a technical analysis of the factors triggering the exceeding of TN standard in

accordance with the wastewater treatment logic. According to the structure characteristics of the activated

sludge AAO process, the causes of TN exceedance are analyzed step by step and the system is adjusted with

the predetermined response strategy to achieve effective control of TN exceedance in the effluent, taking a

wastewater treatment plant in Liaoning Province as an example to make a detailed diagnosis and provide a

solution.

1 INTRODUCTION

Most wastewater treatment plants suffer from

effluentNH4+-N The problem of excess TN in the

effluent, especially in winter, TN，NH4+-N exceeds

the standard is more frequent, and if the process is not

adjusted in time, the light effluent NH4+-N If the

process is not adjusted in time, the effluent will

exceed the standard of TN and other indicators, and

the biochemical system will "collapse". As the

wastewater treatment process using biochemical

treatment process, the treatment effect is affected by

a number of factors, including influent factors,

organic load, process section operation and many

other elements, and in the treatment process by its

impact and complexity and uncertainty. Most

wastewater treatment plants in the management of the

lack of high-level professional and technical

personnel, wastewater treatment plant technicians

rely on years of work experience to operate, the lack

of scientific and quantitative basis, in the current

context of intelligent water (Ma, 2018) In the current

context of smart water, the establishment of a system

with alarm, diagnosis and other functions to assist

professionals in the efficient management of

wastewater treatment plants is necessary, when faced

with the deterioration of the effluent quality, the

system can be independent according to the impact

factors to investigate, through the adjustment of

process parameters to better maintain the efficient

operation of wastewater treatment plants. The so-

called expert system is a class of intelligent computer

programs with expertise and experience in a certain

field. The purpose of this paper is to combine mature

theoretical research and engineering experience

methods in the field of wastewater treatment with

wastewater treatment process control theories,

technologies and methods to achieve intelligent

control of the system by simulating human "brain

thinking" in an unpredictable environment. The

system has the advantages of The advantages of the

system are: the system can simulate the human brain

to a certain extent, so that it has the ability to self-

decision; it can monitor the whole process of

wastewater treatment process, so as to achieve the

best control under certain performance indicators, and

can provide operational guidance (Chen, 2016). To a

certain extent, it can reduce the influence of the

influent factors and environmental f actors that cause

the exceedance of the effluent index; it can also

diagnose and analyze the influencing factors that

trigger the effluent index, and quickly issue

corresponding instructions to the process section

according to the corresponding influencing factor

strategy until the effluent quality no longer

deteriorates and meets the standard. AAO process as

the traditional activated sludge method of

Ma, X., Wang, Z., Shi, H. and Zhang, L.

Expert System for the Control of Efﬂuent TN Excedance of AAO Process.

DOI: 10.5220/0012149800003562

In Proceedings of the 1st International Conference on Data Processing, Control and Simulation (ICDPCS 2023), pages 79-88

ISBN: 978-989-758-675-0

 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

denitrification and phosphorus removal process to

COD removal, denitrification, phosphorus removal

three integrated functions of sewage treatment

process, and is not easy to trigger sludge expansion,

production and management difficulties; especially

suitable for large and medium-sized urban sewage

treatment projects, C, N, P elements are removed in

the biochemical pond, the disadvantage is that the

process is subject to the biochemical system within

the system of substrate competition and sludge age

contradiction and other issues It is difficult to further

improve the efficiency of nitrogen removal, and the

TN effluent often exceeds the standard in the actual

operation process.

2 ANALYSIS OF THE CAUSES OF

EXCESS TN IN AAO PROCESS

Most wastewater treatment plants facing exceedance

of effluent TN can be divided into two situations: one

is caused by effluentNH4+-N TN exceedance caused

by the exceedance of the effluent standard, and one is

the TN exceedance caused by the exceedance of the

effluentNO3 -N exceeds the standard caused by the

TN effluent exceeds the standard. The common

reasons for exceedance of effluent standard in

wastewater treatment plants are: (1) exceedance of

effluent standard due to the impact of subsequent

treatment effect caused by influent factors, and (2)

exceedance of effluent quality caused by

abnormalities in the wastewater process section. For

the AAO process, there are many factors affecting the

denitrification efficiency, for example, the

abnormalities caused by the influent include water

quantity and quality. The abnormalities caused by the

process section include DO, pH, sludge concentration

MLSS, sludge age SRT, etc. The above factors can be

divided into direct factors and indirect factors. Direct

factors are the data obtained directly through sensors,

such as water quantity, DO, pH, MLSS, etc.; indirect

factors are the indicators obtained by transferring the

data obtained from the functional sensors of the

building to the central control room and calculating

them with the computer, such as sludge load F/M,

sludge age SRT, etc. The following is a detailed

summary of the influencing factors that cause TN

exceedance.

2.1 Sludge Load (F/M)

In the activated sludge AAO process, theNH4 + -N

removal rate was negatively correlated with F/M, and

low F/M facilitated the system toNH4 + -N removal

and higher nitrogen removal efficiency. Some studies

have demonstrated that (WU, 2017), nitrogen

removal is best when the sludge load F/M is between

0.14 and 0.22gBOD5-gMLSS-1-d.-1The reasons for

this are: nitrifying bacteria, as strictly autotrophic

bacteria with good oxidative energy, require few

sources of energy in oxidizing elemental nitrogen,

oxidize elemental nitrogen more slowly, and the long

retention time of effluent in low F/M operation is

conducive toNH4+-N andNO2--N are fully oxidized

(WU, 2017).

2.2 Hydraulic Retention Time (HRT)

During the nitrification reaction, the oxidation of

nitrogen elements is slow and requires a long

residence time for full oxidationNH4+-N andNO2--N.

Relevant experiments have proved that as the

hydraulic residence time increases, theNH4+-N The

removal effect becomes better and better (Chen,

2017). If the HRT is too short, the nitrifying bacteria

in the aeration tank will be lost with the water flow

when they do not fully grow upto play a role, and the

nitrification reaction will not be sufficient and the

denitrification efficiency will not be high.

2.3 Mixture Reflux Ratio (R)

It has been shown that the mixed liquor reflux ratio

hasNH4 + -N The effect on the removal rate of TN is

not obvious, but the effect on the removal rate of TN

is large. If the ratio is too large, it will cause the

mixture containing some DO to flow back to the

anoxic tank and the denitrification will be inhibited.

The mixture reflux ratio is too small, which will lead

to the anoxic tank in 𝑁𝑂3 − insufficient, and the

denitrification is not complete, thus resulting in poor

TN removal (Lv, 2016). This results in poorTN

removal.

2.4 Dissolved Oxygen (DO)

It has been shown that the DO gradually increases at

the first and end of the aerobic tank, and the

nitrification rate is accelerated, and the effluentNH4

+ -N decreases. The effect of denitrification is not

affected due to the internal reflux effect and to ensure

that the DO of the anoxic tank is <0.5 mg/L. In

addition, maintaining a certain level of dissolved

oxygen is beneficial to sludge settling, avoiding the

growth of filamentous bacteria due to low DO, which

leads to sludge expansion and thus affects the sludge

settling performance(Chang, 2016). In addition,

ICDPCS 2023 - The International Conference on Data Processing, Control and Simulation

maintaining a certain amount of dissolved oxygen is

beneficial to sludge settling, avoiding the growth of

filamentous bacteria due to low DO, which can lead

to sludge expansion and thus affect the sludge settling

performance.

2.5 Carbon Source (C/N)

Carbon source is one of the important factors

affecting denitrification. In the process of

denitrification reaction, denitrifying bacteria need to

consume organic matter in wastewater as electron

donor for denitrification reaction, so it needs to meet

the denitrification system C/N morethan 4. If the

above requirements are not met, carbon source needs

to be added to the wastewater to ensure that

denitrification is carried out smoothly.

2.6 Sludge Age (SRT)

Sludge age reflects the growth state, growth

conditions and generation time of activated sludge in

the biochemical tank. Studies have shown that for

AAO process, the age of nitrifying bacteria sludge

should not be <15d. The reason for longer nitrifying

bacteria sludge age is that nitrifying bacteria

reproduce slowly and have long generation time, if a

longer sludge age of nitrifying bacteria is not

guaranteed, nitrifying bacteria cannot function and

denitrification is not effective.

2.7 Temperature

In northern wastewater treatment plants, exceedances

of effluent TN standards tend to occur frequently in

winter. Low temperature is an important factor to

limit the growth of microorganisms. The suitable

growth temperature range of nitrifying bacteria is

20~40℃, and the suitable growth temperature range

of denitrifying bacteria is 20~40℃. When the

temperature is lower than 15℃, the efficiency of

biological denitrification will be significantly reduced,

and the growth rate of nitrifying bacteria will be

reduced by 10% for every 1℃ (Xu, 2017).

2.8 pH and Alkalinity

The suitable pH for microbial growth is 6.5~8.5, and

the pH of incoming wastewater from most wastewater

plants is generally alkaline. Nitrification in aerobic

tank will lower the pH and alkalinity of the system. If

the nitrification system in aerobic tank drops to pH

<7.0, the nitrification process will be hindered and

alkalinity must be replenished to maintain the pH

stability of the treatment process.

3 THE ESTABLISHMENT OF

EXPERT SYSTEM FOR THE

CONTROL OF TOTAL

NITROGEN EXCEEDANCE

With the development of big data, artificial

intelligence and the gradual improvement of

intelligent control technology, the field of wastewater

treatment already has the conditions and ability to

realize expert system control. The system is supported

by mature scientific theories, through monitoring,

collecting and storing process data, sieving and

analyzing each factor on the basis of known theories

and in line with logical thinking, diagnosing process

abnormalities, adjusting the process in time, and

containing the risk of effluent exceedance in the early

stage of budding, while also improving the quality

and efficiency of wastewater treatment. The

following will be the introduction of the TN

exceedance expert system combined with the causes

of TN exceedance andthe characteristics of AAO

process.

In this paper, the diagnostic process idea is as

follows. In order to establish the logical relationship

between the abnormal condition of effluent TN and

the cause (or influence factor) of the failure,

intermediate nodes need to be introduced, which

include influent water quality parameters, process

section operating parameters, and design standard

values (design standard range). The influent water

quality parameters reflect whether the effluent

exceeds the standard because the influent

concentration is too large leading to an increase in

system load: the process section operation parameters

reflect the operation status of the wastewater

treatment plant, such as whether the effluent is not

completely nitrification of the aerobic pond because

the DO is too low,resulting inNH4+-N exceeds the

standard; the design standard value reflects the design

specifications and standards of the indicators during

the construction of the wastewater treatment plant.

For this reason, firstly, according to the information

obtained from the inlet,outlet and process section

operating conditions along the actual measurement

data, determine whether the effluent water quality

concentration is greater than the design effluent

standard, and if it is greater than that, determine the

effluent TN exceeds the standard, then it is necessary

to check the corresponding triggering factors

Expert System for the Control of Efﬂuent TN Excedance of AAO Process

according to the TN effluent exceeds the standard,

check the process parameters affecting the effluent

TN in the process section and conduct diagnostic

analysis, and finally propose a fault diagnosis in line

with the logic of wastewater treatment thinking The

system combines the principle of microbial

denitrification with the principle of microbial

nitrogen removal. The system combines the principle

of microbial denitrification and a large amount of

practical engineering experience to classify the

problem of excess TN in the effluent of a wastewater

plant into two different types of problems:

denitrification system failure and nitrification system

failure.

3.1 Abnormal Denitrification System of

the Aeration Tank

Abnormal data: effluent TN> 15mg/L, effluentNO3--

N ＞ 10mg/L, theNH4+-N < 5mg/L. If the effluent

TN> 15mg/L, you should pay attention to the aerobic

tank effluent.NO3--N If it is > 10mg/L, it means the

effluent is caused by poor denitrification.NO3--N

exceeds the standard, also can be observed by

observing the end of the anoxic tankNO3--N

concentration value is higher than that at the end of

the aerobic tankNO3--N concentration value; the first

section of the anoxic tankNO3--N concentration is

close to the end of the anoxic tankNO3--N The

concentration valueof the first section of the anoxic

tank is close to the concentration value of the end of

the anoxic tank.

The diagnosis process is as follows: The first

stage is mainly for the sudden water intake factors to

be investigated, using intelligent meters at the water

intake for pH, CODNH4+-N TN, toxic substances

and other incoming water indicators for 24 hours

monitoring, if found that the incoming water

monitoring of a certain indicator or a number of

indicators appear abnormal, or the incoming water

has an obvious irritatingsmell, color appears

abnormal color, such as green, yellow and other

phenomena are required to alarm in a timely manner,

but also with the help of microscopic technology to

determine the type, abundance and number of

microorganisms to check the impact of incoming

water factors. At this time the system issued a signal

feedback to the lifting pump, should be taken to

reduce the inlet water operation strategy, and the high

concentration of wastewater into the accident pool or

regulating pool, through all possible measures, in

appropriate circumstances in a timely manner to

reduce the impact of the system on the hydraulic

impact load, such as increasing the denitrification

pool required carbon source and chemical phosphorus

removal drug dosing, increase the amount of

dewatering of sludge dosing, extend the treatment

equipment For example, when the plant's influent

waterNH4+-N concentration is 1.5 times of the design

value, it will increase the influentNH4+-N For

example, when the plant's influent concentration is

1.5 times the design value, it will increase the influent

load.NH4+-N concentration to reduce theNH4+-N

load. As far as possible to eliminate the influent

factors caused by the impact on the effluent water

quality decline. At the same time need to cooperate

with the environmental protection department team

pollution sources to investigate, from the source to

solve the sewage treatment plant sewage exceeds the

standard problem.

If there is no abnormality at the end of the first

phase, the second phase will becarried out, mainly for

DO, temperature, pH, C/N, to check. The system first

identifies the DO value or oxidation reduction

potential (ORP) of the anoxic tank, and needs to check

whether the DO of the anoxic tank is 0.2~0.5 mg/L,

or whether the ORP of the anoxic tank is in the range

of -50mV~50mV. If the DO value of the anoxic tank

is > 0.5 mg/L, and the DO content at the end of the

aerobic tank is > 3 mg/L, it is determined that the

anoxic tank is caused by Aerobic pool end aeration

caused by excessive, then the mixture reflux liquid

will carry part of the DO back to the anoxic pool,

destroy the front anoxic section denitrification

reaction, so set the aerobic pool end DO critical value,

this critical value just will not make the anoxic pool

DO higher than 0.5mg / L, the system will be

temporarily defined as 2 ~ 3mg / L aerobic pool DO

(critical value). If the end of the aerobic pool DO>

critical value, it means that the aerobic pool is over-

aerated or the internal reflux is too large to cause the

anoxic pool denitrification is not good, the system to

obtain DO value feedback to the aeration system, at

this time, the aeration system to adjust the aeration of

the blower, the internal reflux is too large need to

recalculate the internal reflux ratio, and feedback

tocontrol the internal reflux pump system for flow

adjustment. If there is no abnormality in DO of anoxic

pool, further judge whether pH of anoxic pool is

abnormal, according to the mechanism of

denitrification reaction, denitrification produces

alkalinity, which will increase pH of anoxic pool,

generally speaking, no measures are needed to

increase pH of anoxic pool, it is enough to ensure pH

7.0~8.5 of aerobic pool nitrification system. If the pH

of the anoxic tank is abnormally high and the pH

cannot be controlled to about 7.3 for a long time, then

you can consider to add some acid to the anoxic tank,

ICDPCS 2023 - The International Conference on Data Processing, Control and Simulation

you can add a large amount at once, and add it several

times in a day to control the pH of the wastewater at

about 7.3 for about one to two hours, which can also

restore the system as soon as possible. If the pH of the

anoxic tank is not abnormal, then further judge

whether the water temperature is lower than the

design value, if yes, it means that the denitrification is

not good due to the low water temperature, so we

should increase the SRT or increase the sludge return

flow to reduce the influence of low temperature on

denitrification, or add steam heating device to keepthe

water temperature constant. If the water temperature

is not abnormal, then the system needs to determine

whether the C/N value of the system is less than the

design value (C/N4 to meet the denitrification

requirements (Chen, 2019; Yang. 2019). The actual

operation of the wastewater treatment plant generally

C/N>4 to meet the nitrogen removal requirements. If

C/N, it means that the denitrification caused by low

C/N is not good, and the control system needs to

choose a suitable feeding position to add external

high-quality carbon source in order to improve the

denitrification capacity of the system and other

comprehensive measures to control and restore the

system in a normal state.

3.2 The Nitrification System of the

Aeration Tank Is Abnormal

Abnormal data: effluent TN> 15mg/L, effluentNH

N ＞ 5mg/L, effluentNO

-N < 10mg/L. If the

effluent TN> 15mg/L, then pay attention to the

aerobic tank effluentNH

-N is > 5 mg/L.

If yes, it means that the poor nitrification causes the

effluentNH

-N exceeds the standard. When the index

exceeds the standard, the system will immediately

send an alarm to the central control room.

The diagnostic process is as follows: the first

stage is basically the same as the first stage of the

denitrification system of the aeration tank.

If there is no abnormality at the end of the first

phase, the second phase will be carried out, mainly for

DO, temperature, pH, C/N, mud age SRT and sludge

load F/M. The system first judge the DO value of

aerobic pool, through the DO analyzer online data

Water inlet and outlet、Biochemical

system Online monitoring information

and measured delay monito

ring data

Inflow water quality

concentration

＞Design

influent concentration

Troubleshooting

Procedures for

Water Inflow Factors

Poor denitrification

Effluent nitrate

nitrogen

＜10mg/L

Effluent ammonia

nitrogen

Troubleshooting

procedure for

connecting to

nitrification

system

Do not need to take any

action, and do value can be

appropriately reduced to

reduce energy consumption

on the basis of ensuring that

other effluent quality reaches

the standard

No operation is taken

to maintain the status

quo, and the internal

circulation return flow

is controlled

reasonably

It mainly analyzes a

series of non

subjective factors,

such as whether the

water temperature is

too low and whether

the machinery in the

biochemical tank is

faulty, otherwise,

human intervention

Control the

internal reflux

pump to the

anoxic tank

＜0.5mg

Reduce DO of aerobic tank and

prevent DO at the end of aerobic

tank from flowing back to anoxic

tank

1. Select an appropriate

location to add external

high-quality carbon sources

2. Internal carbon source

(exceeding the primary

sedimentation tank in whole

or in part; reducing the

amount of carbon source put

into the biochemical tank)

Caused by large internal loop flow

Excessive DO in aerobic tank

Caused by

insufficient C/N

Effluent ammonia

nitrogen

＜5mg

Nitrate nitrogen at

the end of anoxic

tank 1-3mg/L

Anoxic tank

＜0.5mg/L

C/N

＜4

Identify other symptoms

of poor denitrification

caused by sludge floating

in secondary

sedimentation tank

Troubleshooting

procedure for direct

access to denitrification

system

Troubleshooting

Procedures for

Denitrification

System

Figure 1: Flow Chart for Abnormal Diagnosis of Denitrification System.

Expert System for the Control of Efﬂuent TN Excedance of AAO Process

obtained DO value todetermine whether the aerobic

pool DO between 2 ~ 3 mg/L, a large number of

experimental results prove that when the aerobic pool

DO value of at least ≥ 2 mg/L to meet the aerobic pool

in the nitrifyingbacteria growth conditions (Zhang,

2015). If the DO of aerobic pool is <2 mg/L, it means

that the aeration of aerobic pool is too low caused

byNH

-N exceeds the standard, at this time the

system feeds back the monitoring data to the aeration

system and initiates the instruction to adjust the

aeration of the blower to increase the DO at the end

of the aerobic tank. If the DO is normal, indicates that

the effluentNH

-N is not caused by DO abnormality,

need to further check whether the alkalinity of the

effluent from the secondary sedimentation tank is <20

mg/L, if so, need to check whether the pH of the

influent water is less than the design value, if so, it is

determined that the wastewater plant is subject to pH

shock, at this time, take lime neutralization for

treatment. If the influent pH is not abnormal, the

aerobic tank pH curve needs to be observed.

According to the mechanism of nitrification process,

oxidation of 1 mg ofNH

-N needs to consume 7.14 mg

of alkalinity (Zhang, 2012), if there is a continuous

Figure 2: Abnormal Diagnosis Flow Chart of Nitrification System.

Water inlet and outlet、Biochemical system Online

monitoring information and measured delay monito

ring data

Inflow water quality

concentration

＜Design

influent concentration

Troubleshooting

Procedures for

Water Inflow Factors

Poor nitrification

Effluent nitrate

nitrogen

＜1mg/L

Effluent ammonia

nitrogen

＜5mg/L

Inlet water

C/N

＜ 4

Whether PH has

been decreasing

Effluent nitrate

nitrogen

＞ 10mg/L

Calculate the

required carbon

source, select a

reasonable

carbon source

agent and add it

to the aerobic

tank, supplement

the carbon

source or when

the influent COD

is relatively high,

the influent can

pass the primary

sedimentation

tank and enter

the aeration tank

Aerobic tank

＜ 2mg/L

Inadequate DO in

aerobic tank

Increase DO

content at

the end of

aerobic tank

¡Ý 2mg/L or

reduce water

inflow

Caused by

insufficient C/N

Inlet water F/M is

within the design

rangeCaused by

abnormal

sludge load

abnormal

normal

Determine the

level of sludge

load, and

adopt different

methods to

adjust sludge

load

according to

different

problems

Considering

nitrogen and

phosphorus

removal,

recalculate the

sludge age

and regulate

the discharge

of excess

sludge

It mainly analyzes

whether the water

temperature is too

low, whether the

machinery in the

biochemical tank

is faulty and a

series of non

subjective factors,

or manual

intervention

Inflow PH exceeds

the design range

Alkalinity of

aerobic effluent

Calculate the

required

alkalinity, select

reasonable

alkalinity agents

and add them to

the aerobic tank

to supplement

alkalinity to

ensure smooth

nitrification

Caused by

insufficient

alkalinity

Mai ntai n

the status

quo

Access to

denitrification

troubleshooting

procedure

DO end of

aerobic tank is

1-2mg/L

Insufficient DO

at the end of

aerobic tank

No operation is

required, and the

DO value can be

appropriately

reduced to reduce

energy

consumption on the

basis of ensuring

that other effluent

quality meets the

standard

Properly

increase DO

content in

aerobic tank

Identify the phenomenon

of poor nitrification

Troubleshooting Procedures

for Direct Access to

Nitrification System

ICDPCS 2023 - The International Conference on Data Processing, Control and Simulation

decrease of pH curve, it can be judged that the system

is caused by insufficient alkalinity, and alkalinity

accounting should be carried out to determine the

amount of chemical dosing. If the pH is in the normal

range, then determine whether the water temperature

caused by the water dischargeNH

-N When the water

temperature is lower than 15℃, the temperature

becomes an important reason to limit the nitrification

rate of nitrifying bacteria. At this time, the

nitrification efficiency can be improved by increasing

the sludge reflux ratio, appropriately increasing the

aerationand extending the SRT, or installing

additional steam heating devices to keep the water

temperature constant. In addition, the influent

waterNH

-N concentration is too high resulting

inNH

-N The removal rate is severely reduced

(YANG, 2017). The system needs to identify the

frontend influentNH

-N analyzer monitoring data

whether it exceeds 1.5 times of the design flow value,

if yes, it means the system is subject toNH

-N shock

caused the discharge waterNH

-N exceeds the

standard, at this time, see the first stage of the

diagnostic process. If the inlet waterNH

-N

concentration is less thanor equal to the design water

volume, indicating that the system waterNH

-N

exceeds the standard is not caused byNH

-N If there

is no abnormality above, the system needs to

determine the C/N, mud age SRT, sludge load F/M of

the system through online and offline data, and check

the C/N to determine whether the inflow of sewage

C/N is too large, so that the proportion of nitrifying

bacteria in microorganisms is reduced. In this case,

we can increase the residence time of primary

sedimentation tank to reduce the C/N value; check

whether the mud age of nitrifying bacteria is ≥ 15 d,

and need to extend the SRT; check whether the sludge

load is within the design range. For the sludge load

F/M and sludge age SRT, as the above F/M and SRT

influencing factors are introduced, additional carbon

source, change the water intake method to multi-point

water intake method, beyond the primary

sedimentation tank directly into the biochemical tank

and other measures can be taken to change the F/M

and SRT (Liu, 2016). As described above, the F/M

and SRT can be changed by adding a carbon source,

changing the influent to a multipoint influent, and

going beyond the primary settling tank directly into

the biochemical tank.c

If each of the above impact

factors is within the normal range, it is indicated by

amalfunction of the equipment, it is possible that

the treatment structure has a short flow

phenomenon, the system triggers an alarm and

requires manual intervention to overhaul the faulty

equipment.

4 CASE APPLICATION

ANALYSIS

The treatment scale of a city wastewater treatment

plant in Liaoning Province is 10×104 m3 /d, and the

treatment process uses AAO process + amplitude flow

secondary sedimentation tank + contact disinfection

tank. This wastewater plant has been found since

December 2019~January 2020 that the effluent TN,

NH4+-N often exceeded the Class I A standard of the

Discharge Standard for Pollutants from Urban

Wastewater Treatment Plants (GB18918-2002).

Taking this plant as an example, the effluent TN, the

NH4+-N exceeded the standard problem for

troubleshooting analysis, diagnosis, and regulation.

This paper introduces the system to guide the plant for

the effluent TN, theNH4+-N The problem of excess

effluent is carried out, and the specific guidance

process is as follows.

The monitoring platform monitors the water TN,

theNH4+-N exceeds the standard, the platform

immediately issues an alarm and reports to the person

in charge. The system determines that the TN

exceedance isNH4+-N exceeds the standard, and

solving theNH4+-N exceeds the standard is to solve the

problem of exceeding the TN，NH4+-N The excee-

dance is often due to abnormalities in the nitrification

system.

The diagnostic process is as follows: in the first

stage, the intake factors were first checked and the

monitoring data for two months, December 2019 and

January 2020, were retrieved. The data are shown in

Table 1.

Table 1: Actual Incoming and Outgoing Water Quality in December and January 2019.

Water quality

parameters

COD

(mg/L)





-N

(mg/L)

TN (mg/L) TP (mg/L) SS (mg/L) pH (mg/L)

Temperature

(℃)

Water inlet range 150~310 31~48 38~53 2.5~5.2 105~155 6.3~8.9 12~15

Effluent range 31~63 13~28 21~36 0.2~0.6 8~23 6.7~9.1 -

Effluent standard value

＜50 ＜5（8）＜15 ＜0.5 ＜10

- -

Expert System for the Control of Efﬂuent TN Excedance of AAO Process

The conclusions of the influent factors are as

follows: the influent COD fluctuates less, the effluent

is more stable, and occasionally does not meet the

standard; the influent TN, theNH4+-N fluctuations

are small, but the effluent does not meet the standard;

influent TP, SS fluctuations, the effluent is more

stable and basically meets the discharge standard.

The results of microscopic examination were as

follows: the mixture contained caseworms of the

genus Caspius, Trachomorpha, bell worms, cover

ciliates, etiolated ciliates, etc. The protozoa were

slightly reduced compared to normal.

The first stage of investigation concluded that

the influent water was not abnormal,and the influent

water quality was within the design range and not

affected by the influent shock load. The results of the

microscopic examination indicate that the activated

sludge is in a state of too low load. For the problem of

too low load, additional carbon source can be adopted,

adjusting the influent mode to multi-point influent

mode and improving the sludge load of the

biochemical tank beyond the primary sedimentation

tank directly into the biochemical tank. In the second

stage, first of all, DO, through DO analyzer to monitor

the anoxic pool first and last two ends DO is 0.24

mg/L ~ 0.35 mg/L, aerobic pool DO first and last DO

is 1.7 ~ 3.6 mg/L, then it means that DO is not the

cause ofNH4+-N The system was measured, and the

water temperature was basically around 13℃, so it

was suspected that the low water temperature caused

the exceedance. In the case of determining that the pH

of the inlet water is notcaused byNH4+-N The pH

value at the end of the aerobic tank is 6.9, and the

alkalinity of the water from the secondary

sedimentation tank is 35 mg/L. Therefore, the pH

value is also not a factor causing theNH4+-N

Therefore, the pH value is not a factor for exceeding

the standard. The design sludge load value of the

wastewater treatment plant is 0.09 kgBOD5

/(kgMLSS-d), but the actual detected sludge load is

0.035 kgBOD5 /(kgMLSS-d), which indicates that

the sludge load is too low, which is consistent with the

diagnosis of the first stage. It is proved that too low

sludge load willput nitrifying bacteria at a

disadvantage in the competition with heterotrophic

bacteria (organic matter degrading bacteria), reducing

nitrification rate and denitrification efficiency[3].

Then the MLSS value was investigated and the MLSS

value of 4500 mg/L was collected by the sludge

concentration meter. After inspection, it was found

that the MLSS increased because the sludge discharge

volume became smaller due to the sludge pump not

being maintained for a long time, and the increased

MLSS value also had an effect on the F/M value.

Through the comprehensive analysis of the

system; due to the biochemical system F/M is too low

and the discharge of sludge is too low, there are also

suspicions of low water temperature caused by the

effluentNH4+-N exceeded the standard. For the low

F/M, it is possible to add carbon source, adjust the

water intake to multi-point water intake, and increase

the sludge load of the biochemical tank beyond the

primary sedimentation tank directly into the

biochemical tank; for the sludge discharge, without

affecting the actual capacity of the dewatering process

of the wastewater plant, increase the sludge discharge

as much as possible until the sludge concentration of

the aerobic tank is controlled at 3500 mg/L. For the

low water temperature, it is possible to increase the

external reflux ratio, appropriately increase the

aeration, and extend the SRT. It should be noted that

the above operation is best to choose only one

operation for each adjustment to avoid multifaceted

regulation, resulting in confusion, so the following

regulation scheme needs to be taken in conjunction

Figure 3:

Changes

in effluent TN andNH

-N changes.

ICDPCS 2023 - The International Conference on Data Processing, Control and Simulation

with the results of diagnostic analysis, and the

following process can be taken to adjust the MLSS:

carry out maintenance, recalculate the sludge

discharge volume, and resume normal discharge to

ensure the sludge concentration MLSS is about 3500

mg/L. F/ M: when the influent COD is large, you can

improve F/M by going beyond the primary

sedimentation tank directly into the biochemical tank;

when the influent COD is low, you need to

supplement the carbon source organic matter to

improve F/M. Water temperature: you can increase

the aeration without affecting the denitrification

reaction of the anoxic tank. These three measures in

turn, each measure and other effectiveness after the

next step. As shown in Figure 3, take the above

operation, after a period of time, the end of the

secondary sedimentation tank effluent TN, theNH4+-

N The concentration gradually decreases, and after

keeping the state for 8 hours, if the effluent quality

does not exceed the standard again, the problem can

be considered solved.

5 CONCLUSION

This paper combines the theory of microbial

denitrification principle and wastewatertreatment

process control theory to make a diagnosis and

analysis process for TN exceedance. The system takes

the data information collected from the monitoring

platformof the wastewater treatment plant as a

decision support platform and uses intelligent

diagnosis methods and technologies to diagnose and

analyze the triggering factors that cause TN

exceedance, such as whether the DO, MLSS is too

low, F/M is within the design range and a series of

other factors. The system can identify the root cause

of the problem and analyze it. The system can identify

the root cause of the problem and make adjustments

to the operation of the process section independently.

In case the TN exceeds the standard in the AAO

process, the system will issue an early warning

prompt at the first time, and then the system will start

to identify that the effluent is caused by a certain

nitrogen component exceeding the standard, for

example, the effluent exceeds the standard and then

the TN exceeds the standard.NH4+-N Then the

system starts to identify the excess of TN caused by a

certain nitrogen component in the effluent, such as the

excess of TN caused by the excess of effluent, and

then conducts a special diagnosis and analysis of the

nitrification system to solve the problem of excess TN

caused by the inlet water factor or improper operation

of the process section. With the introduction of the

process control system, the causes of TN exceedance

can be analyzed step by step according to the steps set

up in the system, and the existing methods and means

can be used to tap the advantages of the AAO process

to adjust the system, so that the aeration tank can

recover itself under the assistance and guidance of the

system and ensure the stable discharge of effluent to

meet the standard.

ACKNOWLEDGMENTS

The first author, Xingguan Ma (1972- ), M, PhD,

Professor, is mainly interested in the research of water

pollution control theory and technology. Tel:

13050200371; E-mail: hj_mxg@sjzu.edu.cn.

[Corresponding author] Corresponding author,

Xingguan Ma, M., Ph.D., Professor, whose main

research interests are in water pollution control theory

and technology. e-mail: shihongyu0371@163.com

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ICDPCS 2023 - The International Conference on Data Processing, Control and Simulation