(Đồ án hcmute) applying biofilm hybrid system (anaerobic aerobic) using coral media and microbe lift ind on automobile wastewater treatment

Topic: Applying biofilm hybrid system Anaerobic – Aerobic using coral media and Microbe-Lift IND on automobile wastewater treatment.. "Applying biofilm hybrid system Anaerobic – Aerobic

MINISTRY OF EDUCATION AND TRAINING

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION

CAPSTONE PROJECT ENVIRONMENTAL ENGINEERING TECHNOLOGY

S K L 0 0 9 9 7 9

APPLYING BIOFILM HYBRID SYSTEM

(ANAEROBIC - AEROBIC) USING CORAL MEDIA AND MICROBE-LIFT IND ON

AUTOMOBILE WASTEWATER

TREATMENT

ADVISOR: Dr NGUYEN MY LINH STUDENT: NGUYEN THI KIM XUYEN NGUYEN PHUOC LOC

STUDENT: NGUYEN PHUOC LOC NGUYEN THI KIM XUYEN SUPERVISOR: NGUYEN MY LINH

TP Hồ Chí Minh, July/2017

MISSION OF GRADUATION THESIS

Nguyen Thi Kim Xuyen 13150181

Major: Environmental Engineering and Technology Class: 13150CLC

Supervisor: Dr Nguyen My Linh

Receive date: 01/2017 Submit date: 7/2017

1 Topic: Applying biofilm hybrid system (Anaerobic – Aerobic) using coral media

and Microbe-Lift IND on automobile wastewater treatment

Fields: Research

2 Content impletemation

- Design a lab-scale model of hybrid (anaerobic – aerobic) using coral media

- Use automobile wastewater in Mercedes-Benz company

- Evaluate the efficiency of nitrogen, phosphorus, COD, removal of the model during the adaptive phase and operated phase

- Evaluate the stability of the model after supplementation with Microbial preparation Microbe-Lift IND

SOCIALIST REPUBLIC OF VIETNAM Independence – Freedom – Happiness

*******

COMMENT OF SUPERVISOR

Name of student: Student ID:

Major:

Topic:

Name of Supervisor:

COMMENT 1 Content impletemation & Amount of work:

2 Advantage:

3 Disadvantage:

4 Defense: Yes/No

5 Evaluate of kind:

6 Score:

HCM City,……/…… /2017

Supervisor

(Sign & write your name)

SOCIALIST REPUBLIC OF VIETNAM Independence – Freedom – Happiness

*******

COMMENT OF REVIEWER

Name of student: Student ID:

Major:

Topic:

Name of Reviewer:

COMMENT 1.Content impletemation & Amount of work:

2 Advantage:

3 Disadvantage:

4 Defense: Yes/No

5 Evaluate of kind:

6 Score:

HCM City, ……/…… /2017

Reviewer

(Sign & write your name)

ACKNOWLEDGEMENTS

This thesis could not have been done without the valuable help from many people First and foremost, we want to thank my supervisor, Dr Nguyen My Linh Thanks for all your patience, understanding, help, advices, planning and encourage-ment throughout the whole period doing thesis graduation Thanks also for giving us the opportunity to be work with you It has been a great inspiration to learn to know your character, both in academic and human terms

We would like to send many thanks to Mr Tran Kiet Huy, for providing me with the best time we have ever had at the Mercedes – Benz company Your experien-

ce, opinion, view, comments and thoughts have been great and useful It was a great pleasure to be part of the laboratory of Mercedes – Benz company We want to spec-ially mention Huy to open me the doors of practical experiences and some questions gave me when we had the pleasure to discuss several times with you We really appre-ciate the high standards you have set for me, which we would never have reached without your help

A special thank goes to the Ms Dong Thi Tu Anh (Dat Hop Company) and Board of Directors of Mercedes – Benz for their unfailing support

We would particularly like to thank All teachers in the Department of High Quality for creating the most favorable conditions for this thesis Moreover, we would like to thank Ms Le Thi Bach Hue for supporting us equipments in laboratory was essential for the success of the thesis

Last but no the least, we should say thanks from the deep of our heart to our beloved family, teachers, friends They never ending love, help, and support in so many ways through all this time Thank you so much

Ho Chi Minh City, 07/2017

Nguyen Phuoc Loc Nguyen Thi Kim Xuyen

ABSTRACT

In this research, automobile wastewater treatment was performed using the Hybrid system (Anaerobic-Aerobic) with coral media The coral media is not only cheap, available but also gives high efficiency of COD, Total Kjeldahl Nitrogen, and total phosphorus removal The results were analyzed daily The Microbe-Lift IND was added in the last stage of the process to enhance the capacity of the whole system

The research was conducted in two phases: adaptive and operative phase During the adaptive phase, operate for 2 weeks to form microfilm on the coral media

At the operated phase with divided into three periods corresponding to the organic loading rate of 0.25; 1 and 2.5 kgCOD/m3d In these stages, the efficiency of COD, TKN, TP treatment is high and stable With a COD removal efficiency of 74.1 ± 6.7%; 80.37 ± 12.2%; 88.1 ± 6.4% and TP were 67.35 ± 8.21%; 66.2 ± 4.3%; 58.2 ± 7.7% and TKN is 66.59 ± 9.7%; 70.81 ± 7.7%; 79.39 ± 6.2% relatively in three different organic loading rates

Keywords: automobile wastewater treatment, coral media, biofilm kinetic,

hybrid system…

TABLE OF CONTENTS

MISSION OF GRADUATION THESIS I COMMENT OF SUPERVISOR II COMMENT OF REVIEWER III ACKNOWLEDGEMENTS IV ABSTRACT V TABLE OF CONTENTS VI LIST OF FIGURES VIII LIST OF TABLES IX LIST OF ABBREVIATIONS X

PREFACE 1

CHAPTER 1 : INTRODUCTION 5

1.1 INTRODUCTIONOFWASTEWATERPRODUCTION 5

1.1.1 INTRODUCE THE AUTOMOBILE INDUSTRY 5

1.1.2 MAIN STAGES OF WASTEWATER GENERATION 6

1.1.3 CURRENT MERCEDES –BENZ AUTOMOBILE WASTEWATER TREATMENT TECHNOLOGY SYSTEM DIAGRAM 9

1.2 INTRODUCTIONTOWASTEWATERTREATMENTTECHNOLOGY 10

1.2.1 MECHANICAL METHOD 10

1.2.2 PHYSICAL AND CHEMICAL METHODS 10

1.2.3 BIOLOGICAL METHOD 10

1.3 THEORETICALBASISOFAEROBICBIOLOGICALPROCESS 10

1.3.1 AEROBIC BIOLOGICAL PROCESS 10

1.3.2 FACTORS AFFECTING AEROBIC BIOLOGICAL PROCESSES 11

1.3.3 SUSPENDED GROWTH PROCESS -ACTIVATED SLUDGE 12

1.3.4 THE GROWTH OF BIOFILM 14

1.4 THEORETICALBASISOFANAEROBICBIOLOGICALPROCESS 17

1.4.1 ANAEROBIC BIOLOGICAL PROCESS 17

1.5 INTRODUCTIONTOHYBRIDTECHNOLOGYANDHYBRID TECHNOLOGYAPPLICATIONINBIOLOGYWASTEWATERTREATMENT ……… 20

1.5.1 A SUMMARY OF HYBRID BIOLOGY 20

1.5.2 THE ANAEROBIC HYBRID SYSTEM COMBINES AEROBIC 21

1.5.2.1 UANF and UAF hybrid systems 21

1.5.2.2 The hybrid system combines anaerobic and aerobic tube 21

1.5.2.3 Anaerobic and aerobic hybrid system – SAA 23

1.5.2.4 Hybrid partition system 24

1.5.2.5 MBR hybrid system combines anaerobic – aerobic 25

1.6 THE REMOVALOFNITROGENANDPHOSPHORUSBYBIOLOGICAL

METHOD 25

1.6.1 MECHANISM OF NITROGEN TREATMENT 25

1.6.2 MECHANISM OF PHOSPHORUS TREATMENT 27

CHAPTER 2 : METHOD OF RESEARCH 29

2.1.STUDYDIAGRAM 29

2.2.MATERIALRESEARCH 30

2.2.1.CAR MANUFACTURING WASTEWATER 30

2.2.2.ACTIVATED SLUDGE AND CORAL MEDIA 31

2.2.3.MICROBIAL PREPARATION 31

2.3.MODEL RESEARCH 33

2.3.1.MODEL DESIGN 33

2.4.SEQUENCE OF EXPERIMENT 34

2.4.1.ADAPTIVE PHASE 34

2.4.2.OPERATIVE PHASE 34

2.5.SAMPLING AND ANALYSIS 35

CHAPTER 3 : RESULTS AND DISCUSSION 37

3.1.ADAPTIVEPHASE 37

3.2.OPERATIVEPHASE 38

3.2.1.THE CHANGE OF MLSS 38

3.2.2.REMOVAL EFFICIENCY OF COD 40

3.2.3.REMOVAL EFFICIENCY OF TP 43

3.2.4.REMOVAL EFFICIENCY OF TKN 45

3.2.5.REMOVAL EFFICIENCY OF BOD5 47

3.2.6.THE CHANGE OF PH 48

3.2.7.EFFECT OF PH TO PHOSPHORUS REMOVAL IN ANAEROBIC 51

3.2.8.EFFICIENCY OF MICROBE-LIFT IND 52

3.2.8.1 The relationship between TP decrease and Microbial preparation Microbe-Lift IND 53

3.2.8.2 The relationship between microbial preparation Microbe-Lift IND and % COD 54

3.2.9.THE CHANGING OF CONCENTRATION IN ALL SAMPLING TAPS 55

CHAPTER 4 : CONCLUSION AND FUTURE WORK 58

4.1.CONCLUSION 58

4.2. FUTURE WORK 58

REFERENCES 60

APPENDIX 62

LIST OF FIGURES

Figure 1.1: The process of producing and assembling cars 7

Figure 1.2: Wastewater generation stages in the production phase 8

Figure 1.3: Mercedes – Benz automobile wastewater treatment technology system diagram 9

Figure 1.4: Biofilm construction 16

Figure 1.5: The stages of anaerobic digestion 18

Figure 1.6: Tubular Hybrid model 21

Figure 1.7: Hybrid model SAA [Y.J Chan et al., 2009] 23

Figure 1.8: Biomedical hybrid model [Y.J Chan et al., 2009] 24

Figure 1.9: Combined MBR model - Aerobic [Y.J Chan et al., 2009] 25

Figure 1.10: Schematic representation of concentration profiles for EBPR under anaerobic - aerobic conditions 28

Figure 2.1: Diagram of research method 29

Figure 2.2: Automobile wastewater 30

Figure 2.3: Coral media 31

Figure 2.4: Microbial preparation Microbe-Lift IND 32

Figure 2.5: Experimental model in drawing 33

Figure 2.6: Experiment model in practicing 33

Figure 2.7: Diagram in Operative phase 35

Figure 3.1: Coral media before and after use for treatment 38

Figure 3.2: Scanning Electron Micrographs of attached microorganism 39

Figure 3.3: The changing of MLSS in second tanks 39

Figure 3.4: Influent and effluent concentrations and removal efficiencies of COD vs time in the whole experiment (three stages) 41

Figure 3.6: The release of phosphorus in three stages 45

Figure 3.7: Influent and effluent concentrations and removal efficiencies of TKN vs time in the whole experiment 46

Figure 3.8: Influent, Anaerobic, Aerobic, Effluent concentrations and removal efficiencies of BOD5 vs time in the whole experiment 47

Figure 3.9: The change of input and output pH 49

Figure 3.10: The change of pH in Anaerobic 50

Figure 3.11: The change of pH in Aerobic 51

Figure 3.12: Relationship between pH and P release 52

Figure 3.13:The relationship between TP decrease and dose of Microbe-Lift IND 53 Figure 3.14: The relationship between %COD and dose of Microbe-Lift IND 54

LIST OF TABLES

Table 1.1: Some major microbial species in the activated sludge population 13

Table 1.2: Mechanism of phosphorus treatment in anaerobic phase and aerobic phase 28

Table 2.1: The composition and characteristics of automobile wastewater 30

Table 2.2: Feature number of microbial preparation 32

Table 2.3: Design parameter 34

Table 2.4: Operating parameter in adaptive phase 34

Table 2.5: Operating parameter in operative phase 35

Table 2.6: Frequency of sampling and analysis wastewater 35

Table 2.7: Methods of analysis sample 36

Table 3.1: Effectiveness of COD treatment in three stages 40

Table 3.2: TP removal efficiencies in three phases 44

Table 3.3: The efficiencies of treating TKN in three stages 45

Table 3.4: BOD5 removal efficiencies in 3 phases 48

Table 3.5: Change of input and output pH 49

Table 3.6: Frequency of preparation added 53

LIST OF ABBREVIATIONS

BOD : Biological Oxygen Demand

BTNMT : Department of Environment and Resource

COD : Chemical Oxygen Demand

RAS : Return Activated sludge

SRT : Sludge Retention Time

SS : Suspended Solid

SVI : Sludge Volume Index

TKN : Total Nitrogen Kjeldahl

TP : Total Phosphorous

PREFACE

Motivation

The automobile industry is one of the industries which have significant role inthe world Today, in Vietnam, the car industry is being built and developed with the strategic objectives to respond promptly modern and in line with consumer trends of today

The automotive has had a major role in the economy The development of this field not only solved the transportation problem, contributed to the development of production and commercial business but also a highly profitable industry by producing products of superior value brought With the advanced development of science and technology, it has helped to increase production capacity and create high – quality vehicles to meet human needs But the industry has caused a lot of harms to the environment and to human health as a result of the toxic substances released from the manufacturing process

Wastewater after the car production process has high phosphorus and COD, therefore, without a suitable treatment process, it may cause environmental pollution

to the surface water The high phosphorus content of the water will cause eutrophication affecting the imbalance in the microbial life, whereas high COD indicates the concentration of toxic chemicals in the water from the processes Production such as the use of chemicals in car dyes, grease from the cleaning process has largely increased the concentration of COD in the wastewater This causes the discharge of water into the environment, causing serious environmental pollution, affecting human life

"Applying biofilm hybrid system (Anaerobic – Aerobic) using coral media and Microbe-lift IND on automobile wastewater treatment” offers a combined processing

technology that report gives the viewer the most objective comment about the processing efficiency when using this method From there, the advantages and disadvantages of the application, and the introduction of a new application in the biological treatment of wastewater

Content

Content 1: An overview of automotive wastewater and hybrid technology

- An overview of the production of automobile wastewater

- Presentation of theoretical foundations of aerobic and anaerobic biological processes, suspended growth, adhesion

- Introduction to Hybrid Technologies

- Presentation of the mechanism of nitrogen and phosphorus treatment by biological method

Content 2: Set up research model at laboratory scale

- Planning and study diagrams

- Manufacturing models at laboratory scale

- Synthesize and collect materials for research: wastewater, growth mud, adhesives and coral media

- Carry out sampling and analysis of wastewater samples and initial sludge samples before starting the model

Content 3: Operate the model at different loads and assess the ability to removal with pollutants

- Adaptive phase: 2 weeks

- Operative phase:

• Period 1 (4 weeks): OLR 0.25 kg/m3.day

• Period 2 (3 weeks): OLR 1 kg/m3.day + Add Microbial preparation Lift IND

Microbe-• Period 3: OLR 2.5 kg/m3.day + Add Microbial preparation Microbe-Lift IND

- Sampling in accordance with planned procedures and analysis of indicators:

pH, COD, BOD5, TKN, TP, MLSS, pH

- Evaluate the ability to treatment efficiency

Content 4: Results and discussion

- Based on the results of the analysis, perform calculations, data efficiency and graphing the results using Excel software

- Present and discuss the results through the graph

Object and scope of the study

❖ Research objects

- Wastewater of the automobile production

- The model is a hybrid that combines anaerobic and aerobic conditions a laboratory scale

- Fixed media used in the tank is coral media

❖ Research scope

- The project is conducted at the laboratory scale with wastewater discharged from the production and assembly process

- The model is placed under normal temperature conditions

- The research process is done at OLR of 0.25 – 2.5 kg/m3.day

- Wastewater flow rate is 40.92 liters/day

- Sample analysis experiments were conducted at the Mercedes – Benz Company Environmental Analysis Laboratory

Research Methods

❖ Document overview

- To collect information, documents and data on subjects and scope of research

on all sources of books, textbooks and scientific journals Analysis and synthesis as the basis for the orientation and implementation of research content

❖ Experimental model

- Design, manufacture and application of models at laboratory scale Operational planning, sample collection and analysis to evaluate the vehicle wastewater treatment efficiency of the research model

❖ Sampling and analysis

- Water samples are taken at locations: aerobic and anaerobic Indicators are analyzed according to methods in Vietnamese Standards (QCVN) in combination with Standard Methods for the Examination of Water and Wastewater (APHA, Eaton

DA, and AWWA)

❖ Practicality

- Technically: the combination of anaerobic and aerobic hybrid technology improves flexibility and high stability, contributing to improved wastewater

treatment efficiency It also improves high load capacity and improves processing efficiency

- Economically: hybrid anaerobic – aerobic technology combined with coral media cost reduced economic costs Compared with using other kind of media such

as bio chip, coir, etc

CHAPTER 1 : INTRODUCTION

1.1 INTRODUCTION OF WASTE WATER PRODUCTION

1.1.1 Introduce the automobile industry

According to Mr Dao Phan Long – Vice Chairman doubles as General Secretary of Vietnam Mechanic Association (VAMI), the development strategy of Vietnam's automobile industry was first approved in 2004 So far, after 20 years, the government continues to set the direction for the development of the automotive industry by 2025 with a vision to 2035 point of view that the automobile industry is

an important motivational sector, accelerating industrialization, and should be uraged to develop with sable, consistent and long – term policies According to the development strategy of the Vietnamese automobile industry to 2025 with a vision to

enco-2035, the industry development orientation is defined with four objectives:

- Firstly, priority is given to the development of trucks and passenger cars for rural, medium and short – haul passenger cars running interprovincial, district, urb-an suitable to the terrain and transport infrastructure, and have a reasonable price, safe and convenient

- Secondly, priority is given to the development of 9 – vehicles, focusing on small passenger cars, small size, low energy consumption, suitable for transport infrastructure and income of the people

- Thirdly, priority should be given to the development of specialized vehicles such as ramps, tanks and special defense – defense equipment, to encourage the production of multi – functional mini – tractors (combining freight with one or more such as land, water pumping, electricity generation, pesticide spraying ) to meet the needs of the people

- Finally, prioritize the development of supporting industries It focuses on approaching and applying technology to make important components and components such as actuators, gearboxes, engines, tires for a few types of vehicles; strengthen cooperation with major automobile manufacturers to select the types of parts and components that Vietnam can produce to ensure a linking role in global production and supply chains, on the basis of which public investment advanced technology, production for export

About the current situation, the total capacity of production and assembly of cars in Vietnam now reaches about 460 thousand cars/year, of which 200 thousand cars/year; trucks and passenger cars reach 215 thousand vehicles/year Vietnam's automobile industry was born late in comparison with other countries in the region, supporting industries and transport infrastructure have not developed synchronously

In addition, the living standard of people is not high enough so the market size is small However, compared with other countries in Southeast Asia, Vietnam's automobile production is behind Thailand and Indonesia respectively 881 thousand vehicles and 1.2 million vehicles In 2014, while the Thai automobile industry down 34%; Indonesia decreased by 2%, the car market in Vietnam continued to achieve an impressive growth of over 35%

1.1.2 Main stages of wastewater generation

❖ Production process - automobile assembly in Vietnam

Often, car manufacturers in Vietnam import components from the parent company and then complete and assemble them in Vietnam

Figure 1.1: The process of producing and assembling cars

❖ Main stages of wastewater generation

Figure 1.2: Wastewater generation stages in the production phase

Most of the stages of production – car assembly are used to water therefore a lot of wastewater is discharged from these stages a lot And from the above steps the main pollutants in the automotive wastewater are including grease, wastewater from the paint process leading to high levels of organic matter in the influent In addition, the phase of powder coating releases high, phosphorus which is about 1000 – 1500 mg/L

1.1.3 Current Mercedes – Benz Automobile Wastewater Treatment Technology System Diagram

Figure 1.3: Mercedes – Benz automobile wastewater treatment technology system

diagram

1.2 INTRODUCTION TO WASTEWATER TREATMENT TECHNOLOGY

1.2.1 Mechanical method

- Technology: garbage clay, settling tank, flotation, centrifuge, filter

- Purpose: this method is usually a preliminary phase, to remove the insoluble impurities contained in the wastewater

- Advantages: the method is relatively simple, low cost, suspended substance efficiency

1.2.2 Physical and chemical methods

- Technology: coagulant using aluminum alum or iron alum combined with polymer coagulation, flotation, ion exchange

- Purpose: this is a method of using chemicals to remove toxins or substances that adversely affect the biochemical cleaning step

- Advantages: most of the contaminants in wastewater can be removed

- Disadvantages: high processing costs

1.2.3 Biological method

- Biological treatment is based on the ability to oxidize dissolved organic and inorganic organic compounds (such as H2S, sulfur, ammonia, etc.) – they use this nutrient source for growth and develop

- Advantages: cheap, a byproduct of the process can be utilized as fertilizer (activated sludge) or energy recovery (methane)

- Wastewater disposed of by biological means will eventually reduce the COD, BOD, Nitrogen, Phosphorus index to the permitted level Therefore, for the treatment

of this wastewater, the biological method is most appropriate This is also the method applied in most countries in the world and in the country today

1.3 THEORETICAL BASIS OF AEROBIC BIOLOGICAL PROCESS

1.3.1 Aerobic biological process

The principle of the method is to use aerobic microorganisms to decompose organic matter in wastewater with adequate dissolved oxygen at appropriate pH, temperature The organic matter decomposition of aerobic microorganisms can be described by diagram: [Nguyen Van Phuoc, 2010]

(CHO)nNS + O2 → CO2 + H2O + NH4+ + H2S + H + Microorganism cell +… Under aerobic conditions NH4 + and H2S are also decomposed by nitrification, sulphatization by autocatalytic microorganisms:

H O H H NO

O

2 3

cells to increase biomass and reproduce Decomposition process: oxidative organisms decompose dissolved organic substances or in small dispersed colloidal particles into water and CO2, or produce other gases Compared to the anaerobic method, aerobic methods have the advantage of having a better understanding of the process Higher processing efficiency and more radical, no secondary pollution such

micro-as chemical methods, physics

In fact, the process of the decomposing organic matter by aerobic means is under oxygen conditions to produce CO2, H2O, NO3- and SO42- As well as anaerobic treatment, when the complex pollutants such as Protein, Starch, Fats will be hydrolyzed by extracellular enzymes to simple substances such as amino acids, fatty acids, organic acids, simple sugars, etc These simple substances generate the cell membrane and continue to decompose or convert into new cell building materials by intracellular respiration The final product is CO2 and H2O Mechanism of aerobic treatment consists of 3 stages: [Eckenfelder and Conon D.J, 1961]

Stage 1 – Oxidation of all organic matter in wastewater to meet the cell's energy needs

3 2

2 2

2

3)

4

334

N O H

Stage 2 (Assimilation process) – Synthesis for cell building

2 7 5 2 2

NH N O H

Stage 3 (Catabolism) – Intracellular Interactions

O H xCO O

NO H

When not enough nutrients, the metabolism of cellular substances begins to occur by autoxidation the cell material

1.3.2 Factors affecting aerobic biological processes

The process of aerobic treatment is affected by the concentration of activated sludge that depends on the sludge volume index The smaller the sludge index, the greater the sludge concentration in the treatment plant or vice versa Oxygen concentration also strongly influences this process When carrying out the process it

is necessary to provide sufficient oxygen continuously so that the dissolved oxygen

in the water from the settling tank II above 2 (mg/L)

Organic loading in aerobic treatment is usually lower, so the concentration of organic wastewater through aerobic tank has a total BOD below 1000 (mg/L) In biofilters, the total BOD below 500 (mg/L) In addition, wastewater should also contain trace elements, micronutrients Normally, trace elements such as K, Na, Mg,

Ca, Mn, Fe, Mo, Ni, Co, Zn, Cu, S, Cl are often enough in wastewater Depending

on the content of organic matter in the wastewater, the required nutrient content is different It is usually necessary to maintain the nutritional elements at an appropriate rate: BOD: N: P = 100: 5: 1 or COD: N: P = 150: 5: 1 If the processing time is 20 days, the ratio fixed: BODtotal: N: P = 200: 5: 1 (MX Moxitrep, 1982) [Nguyen Van Phuoc, 2010]

Activated sludge is capable of absorbing heavy metal salts When the biological activity of mud decreases, the mud will be hard to settle due to the intense growth of the yeast – like bacteria Therefore, the concentration of toxins and heavy metals in wastewater must be within the allowable limits pH and environmental temperatures are factors that mainly influence the biological treatment of wastewater Each different kind of yeast will have a different pH The same type of yeast but obtained from different sources will have different pH values The optimum pH value for most microorganisms is between 6.5 and 8.5 pH below 5 promotes fungal growth

If pH above 9 destroys the proliferative cellular balance, microorganisms die

Each type of glaze will have different temperatures This temperature is not constant but depends on the substrate; pH, yeast concentration, yeast origin Wastewater has an optimum temperature for most microorganisms ranging from 25 – 37oC or 20 – 80oC, or 20 – 40oC (optimal 25 – 35oC), the lowest in winter is 12oC

In addition, the process of aerobic treatment depends on inorganic salts, the amount

of suspended solids flowing into the treatment tank as well as the microbial species and the structure of organic contaminants [Nguyen Van Phuoc, 2010]

1.3.3 Suspended growth process - Activated sludge

In the wastewater, after a period of adaptable, the bacterial cells begin to grow, reproduce and develop on coral media Wastewater always has suspended particles

of suspended solids The bacterial cells will stick to these suspended particles and develop into dirt particles that break down the organic contaminants that are present

in BOD These particles, if blown and stirred, float in water and gradually grow by absorbing many small suspended solids, microorganisms, protozoa and toxins These particles, when they use oxygen or organic substances as nutrients for microorganisms in the water depletion, they will settle to the bottom of the tank or lake to mud This sludge is called activated sludge

Activated sludge is a collection of different microorganisms, mainly bacteria, which binds into cotton granules with the center being suspended solids in water They are brownish yellow, easily settling, and are size of 3 to 150 μm These include microorganisms (about 30 – 40% cotton compositions, if aerobic by gas and stirring short enough, this number is about 30%, long time about 35% and lasting up to

several days can be up to 40%) The microorganisms living here are mainly bacteria,

in addition to yeast, mold, microbes, protozoa, worms, worms, etc

Activated sludge settles down as "old sludge," the activity decreases If activated (in a suitable aeration medium) it will grow back and the activity will be restored

The amounts of bacteria in the activated sludge ranges from 108 to 1012 per 1

mg dry matter Mostly they are Pseudomomonas, Achromobacter, Alkaligenes, Bacillus, Micrococcus, Flavobacterium

Table 1.1: Some major microbial species in the activated sludge population

Pseudomonas Decomposition of hydrocarbon, protein, other

organic compounds and denitrification

Arthrobacter Decomposition of hydrocarbon

Bacillus Decomposition hydrocarbon, protein…

Cytophaga Decomposition of polymer

Zooglea Form polysaccharide, coagulant

Acinetobacter Polyphosphate uptake, denitrification

Nitrosomonas Nitrification

Nitrobacter Nitrification

Sphaerotilus Decomposition of organic carbon

Alkaligenes Decomposition of protein, denitrification Flavobacterium Decomposition of protein

Desulfovibrio Desalting Sulfate, denitrification

[Source: Nguyen Xuan Nghi, 2013]

In activated sludge in primary animal species is also found They play an important role in the mud They participate in the decomposition of organic matter under aerobic conditions, regulating the species and age of the organism in the sludge, keeping the sludge always operating at optimum conditions Protozoa feed on old or dead bacteria, enhance the removal of pathogenic bacteria, thicken the mucous membranes, but also exfoliate the muddy masses, stimulates microbial extracellular enzyme to decompose contaminated organic matter, and rapidly settle sludge

Many organic compounds have a toxic effect on the organism of the activated sludge, affecting their activity, even causing them to die With high concentrations of phenols, formaldehyde and antiseptics as well as plant protection substances, the cytoplasmic can be denatured protein or they can adversely affect the cell wall The metals that affect the life of the bacteria are as follows: Sb, Ag, Cu, Hg, Co, Ni, Pb,

Cr, Zn, Fe

1.3.4 The growth of biofilm

In the wastewater line, there are solid carriers (gills), microorganisms (mainly bacteria) that stick to the surface Among microbes whose species produce polysaccharides that behave like plastics (called biological polymers), they form membranes (biofilm) This film thickens further and in fact it is microbial biomass sticking or fixed on the carrier This membrane is able to oxidize organic matter in water during flow or contact, in addition to the ability to absorb suspended particles

or helminthic eggs, etc

Biofilm is a collection of different species, which have the oxidizing activity

of organic matter in water when exposed to the film This film is 1 – 3mm thick and more The color of the film varies with the composition of the waste water from grey

to dark brown In the process of treating wastewater flowing through biofilter, it is possible to swing the particles of 15 – 30μm film with light yellow or brown color

Biofilms are made up mainly of aerobic bacteria and biological filters that are aerobic water purification plants, but are considered to be an anoxic system In add-ition to the aerobic bacteria, the membrane also has anoxic and anaerobic bacteria Membrane as the aerobic layer, it is easy to see the Bacillus Intermediate classes are

arbitrary bacteria, such as Pseudomonas, Alkaligenes, Flavobacterium, Micrococcus and Bacillus The deep layers inside the membrane are anaerobic, containing

anaerobic desulfurizing bacteria and desulfovibrio nitrate Thus, the organisms in the biofilm of the filter are anoxic individuals

Characteristics of biofilm

In the wastewater line, there are solids that make the base, microorganisms (mainly bacteria) will stick to the surface Among microorganisms are species that produce polysaccharides that behave like plastic, forming the membrane This film grows thicker and is actual a sticky microorganism on the carriers This membrane is able to oxidize organic matter in water during flow or contact, in addition to the ability

to absorb suspended particles or helminth eggs

Thus, the biofilm is a collection of different microorganisms, which oxidize the organic matter in the water when exposed to the film

Biofilm formation

The reason that bacteria attach and make up the biofilm on the surface is because the surface is where the nutrients accumulate It is because all surfaces have negative charges, negative charges will absorb positive ions and dissolved organic carbon Then the positive charged compounds that accumulate together will attract negatively charged compounds Biofilm formation and bioremediation of substances

by biofilm Cells initially adhere to the carrier material by physiological interaction

or by secretion protein off extracellular that form single cell layers This single – celled cell adheres to another cell to form the active biofilm The structure, surface shape and spatial distribution of biomass of this biofilm are influenced by environmental factors such as the hydrodynamics of the effluent

Cells in mature adult cell membranes follow a gradient of substrate concentration leading to horizontal biomass spread of material surface Bio – treatment results in the transport of substances from the effluent stream and biofilm peeling This cycle repeats with different time periods As with any other biofilm process, the diffusion of the biofilm into and out of the biofilm plays a very imp-ortant in the biofilm process As a result, the material must allow the biofilm to form

a smooth, thin, even distribution, which allows the substance and oxygen to penetrate and remove the product

Biological membrane structure

A complete biofilm thickness of 100 μm – 10mm, depending on the lopment conditions and hydraulic mode of the system The biofilm is several hun-dred times thicker than a single bacterium (1 micrometer long) Biofilm is not an amorphous substance or a thick mass of polysaccharides and bacteria, it is orga-nized and structured Even the thickest area of the biofilm also flows through the water Water flows through the mushroom structures of bacterial spheres, thereby providing nutrients to them and removing waste The biofilm is described as a mus-hroom This structure allows the water to flow in the depths of the biofilm and to promote diffusion into the substrate

deve-Obviously, the internal structure of the biofilm is not constitutive rchers say there is constant information exchange between bacteria to ensure that biological membranes are formed precisely (The mutant bacteria can’t communi-cate with one another to produce abnormal biofilms) Biofilms are not always the same, in the form of layers of aerobic bacteria above and several layers of anaerobic bacteria below Because of the flow of water through the agitation, the anaerobic and aerobic bacteria in parallel exist in small niches throughout the biofilm

Resea-Microorganisms in biofilm

At the outermost of the membrane is the aerobic bacterium, which is readily

identified as the bacillus, in the middle have the arbitrary bacteria Alkaligenes, Pseudomonas, Flavobacterium, Micrococus and Bacillus The deep layers within the membrane are anaerobic desulfurizing bacteria and nitrates such as Desulfovibrio

The final part of the membrane is the protozoan and some other organisms Microorganisms in the biofilm oxidize organic matter and use it as a source of nutrients and energy Thus, the organic matter is separated from the water, while the mass of the biofilm increases Dead membranes are washed away with water and taken out of the biofilter [Mr.Michael Ratcliffe et al (2006)]

Figure 1.4: Biofilm construction

Factors affecting the development of biofilm

There are five factors that influence the development of biofilms:

- Environmental conditions of wastewater: pH, temperature, electrons, nutrients

- The degree of the external impedance of the displacement of the mass to the biofilm

- Degree of resistance in biofilm

- Kinetics and coefficients of the rate of change – the metabolism of bacteria inside the biofilm

- The peeling of the biofilm: The growth of the biofilm accumulates bacterial cells, but eventually all the biofilm to lose all the granular components The loss of granular components and the introduction of wastewater is called biofilm peeling Bryers (1984) described four peeling processes of the film: (1) abrasion; (2) erosion; (3) Negativity, and (4) mutually intimate microorganisms – (because microbial

species exist simultaneously in the microbial membrane, for example, protozoa are larger than bacteria can eat the microbial, helminths can eat microorganisms smaller than it)

1.4 THEORETICAL BASIS OF ANAEROBIC BIOLOGICAL PROCESS

1.4.1 Anaerobic biological process

Anaerobic process is the process of biodegradation of waste in which there is

no dissolved oxygen and nitrification The anaerobic process is commonly used to convert biodegradable organic materials into methane and CO2

Nutrients in wastewater for biodegradable bacteria are very complex These include biological polymers such as proteins, carbohydrates and lipids The process

of decomposition of organic compounds includes:

• Group 1: Hydrolytic Bacteria

• Group 2: Fermentative Acidogenic Bacteria

• Group 3: Acetogenic Bacteria

• Group 4: Methanogens

Group 1: Hydrolytic Bacteria

Consortia of anaerobic bacteria break down complex organic molecules (e.g., proteins, cellulose, lignin, lipids) into soluble monomer molecules such as amino acids, glucose, fatty acids, and glycerol The monomers are directly available to the next group of bacteria Hydrolysis of the complex molecules is catalyzed by extracellular enzymes such as cellulases, proteases, and lipases However, the hydrolytic phase is relatively slow and can be limiting in anaerobic digestion of wastes such as raw cellulolytic wastes that contain lignin [Polprasert, 1989; Speece, 1983]

Group 2: Fermentative Acidogenic Bacteria

Acidogenic (i.e., acid – forming) bacteria (e.g., Clostridium) convert sugars, amino acids, and fatty acids to organic acids (e.g., acetic, propionic, formic, lactic, butyric, or succinic acids), alcohols and ketones (e.g., ethanol, methanol, glycerol, acetone), acetate, CO2, and H2 Acetate is the main product of carbohydrate fermentation The products formed vary with the bacterial type as well as with culture conditions (temperature, pH, redox potential)

Group 3: Acetogenic Bacteria

Acetogenic bacteria (acetate and H2 – producing bacteria) such as syntrobacter wolinii and Syntrophomonas wolfei [McInernay et al., 1981] convert fatty acids (e.g., propionic acid, butyric acid) and alcohols into acetate, hydrogen, and carbon dioxide, which are used by the methanogens This group requires low hydrogen tensions for

fatty acid conversion, necessitating a close monitoring of hydrogen concentration Under relatively high H2 partial pressure, acetate formation is reduced and the substrate is converted to propionic acid, butyric acid, and ethanol rather than methane There is a symbiotic relationship between acetogenic bacteria and methanogens Methanogens help achieve the low hydrogen tension required by acetogenic bacteria

Ethanol, propionic acid, and butyric acid are converted to acetic acid by acetogenic bacteria according to the following reactions:

CH3CH2OH (ethanol) + H2O → CH3COOH (acetic acid) + 2H2

CH3CH2COOH (propionic acid) + 2H2O → CH3COOH (acetic acid) + CO2 + 3H2

CH3CH2CH2COOH + 2H2O → 2CH3COOH (acetic acid) + 2H2

Group 4: Methanogens

This is the last stage of anaerobic decomposition, methane – producing bacteria reduce CO2 by hydrogen and decarboxylate acetate to form methane (CH4) Methane bacilli are anaerobic bacteria capable of using only certain substrates They use organic substrates or separate carbon sources such as acetate, H2 Some strains are self – supporting strains that use only carbon dioxide and CO as a carbon source

In general, between 70% and 80% of the methane is made up of acetate – derived organic materials, with the remainder mostly from H2 and CO2

Figure 1.5: The stages of anaerobic digestion

Factors influencing anaerobic process

- Characteristics of wastewater: anaerobic treatment is applied to a variety of wastewater with different levels of pollution Especially suitable for highly polluted wastewater and humid conditions

- Fluctuations in flow and load: as the flow of fluctuations changes, it usually results in a disturbance of the balance of the yeast and methane generation For organic soluble, biodegradable compounds such as sugar or starch, acid – borne reactions can occur more quickly at higher loads and may increase the amount of volatile fatty acids (VFAs) and gases Hydrogen but will reduce the pH Therefore, it

is necessary to regulate the flow of water into the tank to avoid the maximum load and flow conditions

- Substance concentration: the concentration of organic matter and temperature affect the operation of the anaerobic tank Suitable temperature for tank operating from 25 – 35oC COD concentrations greater than 1500 – 2000 mg/L are needed to generate sufficient methane to heat the waste water without the need for an external heat source When COD levels are 1300 mg/L or less, aerobic treatment should be used [Nguyen Van Suc, 2012]

- Temperature: anaerobic digestion can occur at wide temperature fluctuations ranging from 10oC (psychrophilic temperatures) to over 70oC (thermophilic temperatures) [Gabriel Bitton, 2005] Temperature affects the survival, growth and metabolic activity of microorganisms The stronger the metabolic activity, the higher the temperature (within the microbial refractory range) and vice versa

❖ There are three main thermal vibration ranges in anaerobic digestion:

• Psychrophilic temperature: 12 – 18oC

• Mesophilic temperature: 20 – 40oC, optimal 37oC

• Thermophilic temperature: 50 – 65oC, 55oC optimal

Mesophilic and thermophilic systems are the two most suitable processes for anaerobic digestion The thermal systems usually produce more biogas than warm ones

- pH: most methanogen has optimal function at pH 6.7 – 7.4; but optimal at pH 7.0 – 7.2; And this process can fail if pH is near 6 Acid bacteria that produce organic acids tend to reduce the pH of the bioreactor Under normal conditions, this pH reduction is buffered by the bicarbonate produced by methanogens Under adverse environmental conditions, the system's buffer capacity could be affected, eventually stopping methane production

- Toxins (common inhibitors): substances that affect anaerobic digestion are VFAs, pH, free ammonia, and H2S Other factors are salinity, xenobiotics Ammonia

at high concentrations will inhibit methanogenesis There are two ways to overcome ammonia:

• Dilute agent with appropriate amount of wastewater

• Adjust the C/N ratio of the input material

1.5 INTRODUCTION TO HYBRID TECHNOLOGY AND HYBRID

TREATMENT

1.5.1 A summary of hybrid biology

Hybrid biology is a bioremediation model that has a combined presence of different types of bacteria including: suspended – growth bacteria and growth – adhesion bacteria that grow under anaerobic, aerobic conditions or combined anaerobic and aerobic In the 1980s, anaerobic and aerobic hybrid systems began to

be researched and developed Next years, more diverse hybrid technologies have been studied The main objective is to take advantage of the existing system, combine it and use it effectively so that the investment costs are low, the system is reduced, the operation is simplified, and the disadvantages of the single system are overcome Especially increase the processing efficiency, good shock load and prevent the deterioration of the microorganism present

Basically, the hybrid biological systems studied are often combined:

- Combination of suspended growth and adhesion growth on the same anaerobic

or aerobic system, increasing the operating load and processing efficiency due to high density of microorganisms leading to reduced work volume

- Biological and adsorbent combination, use of carriers with large surface area

to participate in adsorption of pollutants by increasing the efficiency of treatment, removal of toxic compounds, biodegradable and nutrients

- Combining biology and membrane filtration thus reducing the volume of work, increasing operating loads, eliminating nutrient and biological residues, and simplifying the process

- Combination of anaerobic, anoxic and aerobic biology in the same treatment system Enzymatic hydrolysis, complex intersecting sequestering occurs simultaneously with aerobic biological responses converted to CO2 and water The reaction goes on at high speed Especially, the denitrification process such as nitrification, nitrate or anammox decomposition occurs in the same treatment syste-

m or removal phosphorus

1.5.2 The anaerobic hybrid system combines aerobic

1.5.2.1 UANF and UAF hybrid systems

Application to thoroughly treat the remaining pollutants and reduce the nitrogen content in wastewater

Applying hybrid technology UANF + UAF technology has the following advantages:

• Easy to operate and maintain

• Small work volume

• Low amount of sludge

• Dehydrated nutrients (Nitrogen, Phosphorus) are very effective

• High organic matter treatment efficiency

• Good shock tolerance

Nguyen Thi Thanh Phuong, Nguyen My Linh (2002) applied hybrid logy combining anaerobic filtering and aerobic filtering of tapioca starch wastewat-

techno-er The study was carried out at a load ranging from 0.5 to 3 kg COD/m3.day wastewater with an average COD of 9000 mg/L; after 6000 mg/L remaining After more than 4 months of operation, the COD efficiency was over 98% The anaerobic filter treats 84 – 90% COD, the aerobic zone thoroughly treated the remaining organic content (8 – 9% COD) Water after COD treatment reduced to 77 – 93 mg/L; Nitrogen decreased by 61.4%

1.5.2.2 The hybrid system combines anaerobic and aerobic tube

Figure 1.6: Tubular Hybrid model

Anaerobic activated sludge process combining anaerobic and aerobic The efficiency of the treatment is evaluated based on the efficiency of nitrogen treatment

Initially sewage enters the inner part of the rotation (the anaerobic part), then enters the activated sludge of the tube by the action of the lift gas Finally, water will come out above the tube The volume ratio of the anaerobic and aerobic zones in the column can be adjusted by varying the diameter of the aerobic tube Change the flow rate of the liquid mixture by varying the height of the tube and the rate at which the gas enters the tube Increasing circulation speeds up the aerobic process As a result, the treatment system is operated with the lowest flow rate to keep the slurry suspended [T.Hano, M.Matsumoto, K.Kuribayashi and Y.Hatate, 1992]

1.5.2.3 Anaerobic and aerobic hybrid system – SAA

SAA Reactor is a combined lift reactor between liquid and sludge anaerobic flow, Inner cylindrical and a cylindrical outer shell The aerobic zone is set inside of the cylinder, the gas being supplied from the bottom of the reactor The anaerobic region is set up in the outer cylinder to limit the transition from the center The inlet flows from the bottom of the bio – reactor and the discharge is recovered in the upper part of the reactor Water leaked with COD is in the range of 1000 – 3300 mg/L treated with SAA system with a treatment efficiency of 85 – 95% [Yi Jing Chan, Mei Fong Chong, Chung Lim Law, DG Hassel, 2009]

Figure 1.7: Hybrid model SAA [Y.J Chan et al., 2009]

1.5.2.4 Hybrid partition system

Figure 1.8: Biomedical hybrid model [Y.J Chan et al., 2009]

The model used to treat wheat starch wastewater with COD values ranges from

1100 to 4500 mg/L To increase the processing efficiency, the coke component is used as carrier; COD removal efficiency can reach 98.7% versus 96% if no coke is used Coke material has a larger specific surface area, which facilitates the adherence

of microorganisms, increases the concentration of biomass resulting in higher amounts of organic matter, the optimum retention time is 12 up to 24 hours

The reactor consists of three anaerobic zones, two compartments and an aerobic zone With a sloping 45° angle, this bulkhead facilitates wastewater upstream and downstream into the reactor The system is divided into three anaerobic zones corresponding to anaerobic digestion of microorganisms Anaerobic regions 1 and 2 are designed for hydrolysis, zone 3 is primarily for methane production The depositional area with major functions is anaerobic and aerobic separation to facilitate anaerobic

The advantage of the model is that it can be applied in small and medium scale

1.5.2.5 MBR hybrid system combines anaerobic – aerobic

Figure 1.9: Combined MBR model - Aerobic [Y.J Chan et al., 2009]

MBR model is designed with MBR layer submerged in aerobic zones Gases dissolved from air diffusers in aerobic zones with MBR layer are used for three purposes:

• Providing oxygen for easy organic decomposition

• Stir in aerobic tanks

• Create disturbances to clean the membrane

The porcelain carrier is designed to avoid congestion at the central tube separating the anaerobic and aerobic zones

Successful systems for the treatment of artificial wastewater have high concentrations of organic matter and ammonia The efficiency of COD treatment is over 99% at the load of 10.08 kg COD/m3.day [Y.J Chan et al., 2009]

1.6 THE REMOVAL OF NITROGEN AND PHOSPHORUS BY

BIOLOGICAL METHOD

1.6.1 Mechanism of nitrogen treatment

Nitrogen in wastewater is found to exist in the form of ammonia and organic nitrogen Nitrogen removal in wastewater occurs in two main mechanisms:

- Biomass synthesis (Nitrogen-Nitrogen Assimilation for cell growth) and removal with sludge

- The process of nitrification (nitrification) and denitrification (denitrification) Ammonia is eliminated mainly in the second mechanism Nitrate is a two steps process in which an aerobic bacterium will oxidize ammonia (NH3 – N to nitrite (NO2

– N)) after Another bacterial species that oxidizes nitrogen – nitrite to nitrogen nitrate

(NO3 – N) In the process of nitrate, an oxidized carbon source uses nitrate/nitrite as

an electron acceptor in the oxidation reaction An anaerobic process that does not require a carbon source to reduce NO2 – N is the anammoanaerobic ammoniumoxidizers process, in which some bacteria are able to oxidize ammonia to reduce nitrite proliferation that produce nitrogen

- Converting ammonia to nitrite:

Nitrosomonas (N.europasa, N.oligocarbogenes) oxidize ammonium to nitrite

Some other microorganisms that oxidize NH4 are Nitosopira, Nitrosococcus and Nitrosolobus

2NH4+ + 3O2 → 2NO2- + 4H+ + 2H2O

- Conversion of nitrite to nitrate:

Nitrobacter (N.agilis, N.winogradski) converts nitrite to nitrate

2NO2- + O2 → 2NO3

-Some factors affect the nitrification process

- Temperature: As the temperature rise, the rate of growth of the microorganism increases

- pH: Self – sustaining microorganisms grow in a pH range of 7.6 – 8.6 pH below 6.2 or pH above 10 virtually completely suppresses microbial activity

- Toxicity: Toxins to self – supporting microorganisms can only have an inhibitory effect or kill them depending on the specific type and concentration A variety of highly synthetic organic compounds for autocatalytic microorganisms are: phenolic compoundds, chlorinated compounds, nitrogen compounds

❖ Denitrification process

The denitrification process is the next step for denitrification to be performed

by heterotrophic strains using nitrate as an electron acceptor in anaerobic conditions The denitrification process involves several stages of converting nitrate to nitrogen gas through intermediates:

NO3 → NO2 → NO → N2O → N2

The denitrification process is carried out by various bacterial strains with different abilities Some strains of bacteria can carry out all the stages of nitrate conversion into nitrogen while others only convert nitrate to nitrite Nitrate and nitrite

are also used as a source of nitrogen for cellular synthesis but ammonia is preferred for direct use when available Many organic substances are simultaneously oxidized during denitrification, for example, acetic acid as a carbon source:

The two most important mechanisms of bio – denitrification are anabolic and catabolized nitrification:

• Assimilation of denitrification

By this mechanism nitrate is converted to nitrite and NH4+ by nisms These include some enzymes that convert NO3 into NH3, which then forms proteins and nucleic acids

microorga-Denitrification is made by many anabolic nitrification enzymes, whose

acti-vity is not affected by oxygen Some microorganisms (Pseudomonas aeruginosa)

have both anabolic nitrification enzyme and catabolized denitrification enzyme which are sensitive to oxygen

• Catabolism of denitrification

Most nitrate reducing microorganisms are heterotrophic, using organic carbon sources in the absence of oxygen to degrade NO3- to N2O oxide nitrogen and N2

nitrogen gas N2 liberation is the dominant product of catabolized nitrification

Anaesthetizing nitrite treatment is carried out in the following order:

NO3 → NO2 → NO → N2O → N2

Microorganisms capable of reducing nitrification are the following varieties:

Pseudomonas, Baccillus, Spirillum, Hyphomicrobium, Agrobacterium, ter They are usually found in waste water

Acinetobac-Nitrogen oxide (N2O) may be having during nitrification in wastewater The result of this is nitrate isn’t release completely

1.6.2 Mechanism of phosphorus treatment

Phosphorus (P) is the nutrient element presenting a relatively large amount in domestic wastewater The components of phosphorus found in wastewater include ortho-phosphates, polyphosphates and organic phosphorus The orthophosphates (PO43-, HPO42-, H2PO4-, H3PO4) are biologically absorbed without further decompo-sition Polyphosphates are very slow hydrolysis in water and transform into ortho-phosphates Phosphorus is one of the contributors to eutrophication in receiving water [Nguyen Van Suc, 2012]

Several mechanisms have been proposed to explain the enhanced uptake of phosphorus by microorganisms in wastewater It has been shown that for biological phosphorous removal to occur in wastewater treatment plants, biomass first needs to pass through an oxygen and nitrate free phase, i.e an anaerobic phase, before enter-

ing a phase where an electron acceptor is present, i.e an anoxic phase where nitrate is present or an aerobic phase where oxygen is present The oxygen and nitrate free phase can be achieved in a separate reactor, the first section of a plug flow reactor or part of a sequence batch reactor cycle Figure 1.10 presents the concentration profiles

of the mean measurable components for EBPR operated under anaerobic – aerobic conditions

Figure 1.10: Schematic representation of concentration profiles for EBPR under

anaerobic - aerobic conditions

When the wastewater enters the anaerobic phase, special organisms, called poly – phosphate accumulating bacteria (PAOs) accumulate carbon sources as an internal polymer called PolyHydroxyAlkanoates (PHAs) The main forms of these PHAs are Poly-𝛽-HydroxyButyrate (PHB) and Poly-𝛽-HydroxyValerate (PHV) The energy to store this polymer is obtained from breakdown of glycogen and hydrolysis

of an energy rich internal phosphorus chain called Poly – Phosphate (Poly – P) Since Poly – P is broken down to ortho – phosphate for energy supply, the phosphate concentration in the anaerobic phase increases The anaerobic phase needs to be followed by an oxygen or nitrate rich phase, i.e an anoxic phase (anoxic P – removal)

or an aerobic phase (aerobic P – removal) During this phase, the stored PHB is consumed, generating energy for growth, for uptake of ortho – phosphate from the liquid phase and generating energy and carbon for replenishment of glycogen and Poly – P pools

Table 1.2: Mechanism of phosphorus treatment in anaerobic phase and aerobic phase

Anaerobic phase Aerobic phase

Poly – P → ENERGY and P release Use PHB as a energy

VFAs + energy → PHB P + energy → Poly – P (P uptake)