Evaluation of the performance of lab-scaled self-purification sewer system for municipal wastewater treatment in Vietnam

LIST OF ABBREVIATION AAO: Anaerobic – Anoxic – Aerobic ASTM: American Society for Testing and Materials CAS: Conventional Activated Sludge CS: Coal Slag EDS: Electron Dispersion Spectrom

VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

LUONG HUU TRUNG

EVALUATION OF THE PERFORMANCE

OF LAB-SCALED SELF-PURIFICATION SEWER SYSTEM FOR MUNICIPAL WASTEWATER TREATMENT IN

VIETNAM

MASTER'S THESIS ENVIRONMENTAL ENGINEERING

Hanoi, 2019

VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

LUONG HUU TRUNG

EVALUATION OF THE PERFORMANCE

OF LAB-SCALED SELF-PURIFICATION SEWER SYSTEM FOR MUNICIPAL WASTEWATER TREATMENT IN

ACKNOWLEDGEMENT

At very first words, my gratefulness goes to all lecturers, officers and staffs in Environmental Engineering Program (MEE), Vietnam Japan University (VJU) and Japan International Cooperation Agency (JICA) for giving me the precious opportunity to study and train under this disciplinary academic environment, where I could improve myself unexpectedly and access to a broader career future

In advance, I would like to spend the most gratitude toward my supervisors, Assoc Prof Hiroyasu Satoh and Prof Dr Jun Nakajima, for their intense support and supervision throughout the time I did the thesis I could not accomplish the thesis without your guidance and enthusiasm throughout all progresses, from initial research idea, reactor setup, experimental analysis and revision of the draft and presentation And last, I also really appreciate the support and encouragement from my classmates, friends and family, those who have contributed to my two wonderful years in VJU, turning it into something priceless and unforgettable in my youth

TABLE OF CONTENT

ACKNOWLEDGEMENT i

TABLE OF CONTENT ii

LIST OF FIGURES iv

LIST OF TABLES vii

LIST OF ABBREVIATION viii

CHAPTER 1 INTRODUCTION TO SELF-PURIFICATION SEWER FOR MUNICIPAL WASTEWATER TREATEMENT IN VIETNAM 1

1.1 Wastewater treatment and management in urban areas of Vietnam 1

1.2 Introduction to a new approach: In-sewer self-purification technique 4

1.3 Modified sewer for enhancing the self-purification capacity of sewage 6

1.4 Pervious concrete as potential material for self-purification sewer 8

1.4.1 Introduction to pervious concrete 8

1.4.2 Constituent and mix design 9

1.4.3 Sustainable construction material 10

1.4.4 Potential usage for self-purification sewer construction 10

1.5 Objectives 11

CHAPTER 2 MATERIALS AND METHODOLOGY 12

2.1 Lab-scaled self-purification sewer reactor 12

2.1.1 Reactor setup 12

2.1.2 Reactor operation 14

2.1.3 Sampling and analytical methods 15

2.2 Microbial media for the modified self-purification sewer 17

2.2.1 Pervious concrete as a potential material for self-purification sewer

17

2.2.2 Physicochemical characteristics of pervious concrete made from conventional and waste aggregates 19

CHAPTER 3 RESULTS AND DISCUSSION 24

3.1 Potential characteristics of pervious concrete as microbial media 24

3.1.1 Density, porosity and permeability 24

3.1.2 Morphology and chemical composition 25

3.2 Pollution transformation regimes in self-purification sewer 33

3.2.1 Sedimentation and oxidization of organic matters 33

3.2.2 Ammonia stripping due to high pH 40

3.3 Estimation of sewer treatment capacity 45

3.3.1 Removal efficiency of organic matters (COD) 46

3.3.2 Removal efficiency of Ammonia (NH4-N) and total nitrogen (T-N)

49

CONCLUSION 51

REFERENCES 53

APPENDIX 56

LIST OF FIGURES

Figure 1.1 Sample modified sewer equipped with porous media for microbial attachment, with an impervious outer wall to prevent leakage of sewage 7Figure 1.2 Sample pervious concrete made from byproduct coal-slag coarse aggregate (A) and conventional rock coarse aggregate (B) 8Figure 2.1 Flow diagram of PVC sewer reactor installed with pervious concrete media, oxygen gas sensor, recirculation tank and pump 13 Figure 2.2 Self-purification sewer reactors with equipment and porous concrete inward Left sewer is coated with pervious concrete made from industrial by-product (coal-slag) while conventional rock-aggregate pervious concrete is used in the right sewer 14Figure 2.3 My Dinh Canal in Nguyen Co Thach Street, My Dinh, Nam Tu Liem 15Figure 2.4 Pervious concrete media for the PVC sewer reactor (A) Pervious concrete was placed inside in the bed of the sewer for evenly distribution of sewage and more esthetical look (B) Hardened coal-slag pervious concrete; (C) Hardened rock-aggregate pervious concrete 18Figure 2.5 Darcy’s Law experiment system for testing permeability of concrete 22

Figure 3.1 Surface structure of raw coal-slag aggregate, before submerged in the CS sewer for operation, observed under two scales of 1/1000 and 1/5000 with SEM 26 Figure 3.2 Comparison of coal-slag surface structure before and after running with municipal sewage for 30 experimental days 27Figure 3.3 Surface structure of raw rock aggregate, before submerged in the RA sewer for operation, observed under two scales of 1/1000 and 1/5000 with SEM 28

Figure 3.4 Comparison of rock-aggregate surface structure before and after running with municipal sewage for 30 experimental days 29Figure 3.5 Chemical composition of raw coal-slag aggregate 31Figure 3.6 Chemical composition of coal-slag aggregate submerged in sewage inside

CS reactor for 30 experimental days 31Figure 3.7 Chemical composition of raw conventional rock aggregate 32Figure 3.8 Chemical composition of rock aggregate submerged in sewage inside RA reactor for 30 experimental days 32Figure 3.9 Correlation between Turbidity and COD in CS and RA sewers both in 15mON/45mOFF and 30mON/30mOFF pump schedules 33Figure 3.10 COD change in effluent of lab-scaled self-purification sewer, running with pump schedule of 15mON/45mOFF simulating dry condition 34Figure 3.11 COD change in effluent of lab-scaled self-purification sewer, running with pump schedule of 30mON/30mOFF simulating wet condition 34Figure 3.12 Sedimentation flocs settled down on coal-slag concrete (A) and rock-aggregate concrete (B) while sewage flowed through the lab-scaled sewer 37Figure 3.13 Detached floc from pervious concrete media settled down at the bed of the recirculation tank in coal-slag sewer reactor 37Figure 3.14 Oxygen concentration monitored in headspace of coal-slag sewer reactor

by Oxygen sensor (Experimental date: April 9th, 2019) 38Figure 3.15 Ammonia in effluent of coal-slag and rock-agregate concrete sewer, with schedule of 15m ON/45m OFF 40Figure 3.16 Ammonia in effluent of coal-slag and rock-agregate concrete sewer, with schedule of 30m ON/30m OFF 41

Figure 3.17 TN and ammonia of outflows from coal-slag and rock-aggregate concrete sewer, with pump schedule of 15m ON/45m OFF 43Figure 3.18 TN and ammonia of outflows from coal-slag and rock-aggregate concrete sewer, with pump schedule of 30m ON/30m OFF 43Figure 3.19 Correlation between NH4 and TN in CS and RA sewers in both 15/45 and 30/30 pump schedules; (1) Portion of TN which was removed by ammonnia stripping, (2) Portion of particulate nitrogen (P-N), (3) Remained ammonia 44Figure 3.20 Treatment efficiency for COD of self-purification sewer pipe made from

CS and RA concretes in dry flow pattern condition 47Figure 3.21 Treatment efficiency for COD of self-purification sewer pipe made from

CS and RA concretes in wet flow pattern condition 48Figure 3.22 Treatment efficiency for NH4-N of self-purification sewer pipe made from CS and RA concretes in dry flow pattern condition 49Figure 3.23 Treatment efficiency for NH4-N of self-purification sewer pipe made from CS and RA concretes in wet flow pattern condition 50

LIST OF TABLES

Table 1.1 Capacity of several wastewater treatment plants in Vietnam (Source: NGOenvironment.com; Hanoi Department of Construction, 2015) 2Table 2.1 General wastewater quality of My Dinh Canal in Nguyen Co Thach Street 16 Table 2.2 Experimental sampling schedule of two sewer reactors 17Table 3.1 Properties of Portland cement pervious concrete from coal-slag and rock aggregate 25 Table 3.2 Composition of coal-slag aggregate in Pha Lai Thermopower Plant analyzed by X-Ray Fluorescence (XRF) 30Table 3.3 Correlation of sedimentation and microbial digestions for organic matters removal in self-purification sewers 39Table 3.4 Estimation of flow distance from pump schedules in lab-scaled self-purification sewer 46Table A.1 Test of heavy metals released from coal slag aggregate 56 Table A.2 Maximum permissible concentration for domestic wastewater parameters discharged from households 56

LIST OF ABBREVIATION

AAO: Anaerobic – Anoxic – Aerobic

ASTM: American Society for Testing and Materials

CAS: Conventional Activated Sludge

CS: Coal Slag

EDS: Electron Dispersion Spectrometry

ICOP: Intermittent Contact Oxygen Process

MWW: Municipal Waste Water

OD: Oxidation Ditch

PCPC: Portland Cement Pervious Concrete

PN: Particulate Nitrogen

PPD: Physical Pollutants Deposition

RA: Rock Aggregate

RCA: Recycle Concrete Aggregate

SBR: Sequencing Batch Reactor

SEM: Scanning Electron Microscopy

SWMM: Standard Methods for The Examination of Water and Wastewater WWTP: Wastewater Treatment Plant

CHAPTER 1 INTRODUCTION TO SELF-PURIFICATION SEWER FOR MUNICIPAL WASTEWATER TREATEMENT IN VIETNAM

1.1 Wastewater treatment and management in urban areas of Vietnam

In recent decades, after the renovation in 1986 to create a socialist-oriented market economy, Vietnam has been rocketing in both economy and urbanization The growth

in these aspects also lead to many other problems in the environment nationwide Being a developing country with emerging economy and young human resource, Vietnam is now facing many opportunities and challenges at the same time The rapid growth of economy and population put a tremendous pressure on the urban drainage and sewerage systems which have been constructed decades ago By 2018, the total population of Vietnam is estimated to be 94 million, and 35.5% lives in towns or big cities, generating a huge amount of wastewater that needs to be treated in a daily basic (VWSA, 2018) However, the existing drainage and sewerage system have not been developed or renovated to meet the demand of treatment for the current municipal sewage load

According to World Bank in 2013, most of domestic wastewater from residential areas is pretreated by septic tank before being discharged to public sewer drains Majority of the sewerage system which could be called drainage system also are the combined type, conveying around 90% of total sewage generated from domestic, industrial and hospital sources together with rainwater to wastewater treatment plants (WWTP) or directly discharge into water environment such as lakes, canals or rivers

By 2012, only 17 wastewater treatment plants being in operation were in charge of sewage treatment in urban areas of Vietnam, with total capacity of 530,000 m3/d (An, 2014) (Table 1.1) In majority, the most common wastewater treatment technology is Activated Sludge Process performed differently in each desired area Among those, Conventional Activated Sludge (CAS), Anaerobic – Anoxic – Aerobic (AAO) and Sequencing Batch Reactor (SBR) are mostly developed and applied in Centralized

WWTPs It was estimated only 23.2% of sewage was collected and treated in treatment facilities, the rest of wastewater and sludge were semi-treated in septic tanks before overflowing to public combined sewer system and then discharged to the environment causing serious water pollution in urban areas of Vietnam (NGO International, n.d.)

Table 1.1 Capacity of several wastewater treatment plants in Vietnam

No City WWTP Establish

year

Capacity (m 3 /d)

Sewage collection type

Treatment technology

2009 42,000 7,000 Combined Anerobic – Anoxic

6

Binh Hung Hoa

2008 30,000 30,000 Combined Aerobic &

11 Phu Loc 2006 36,430 36,430 Combined Covered Anaerobic

Lagoon

12

Ngu Hanh Son

2006 11,629 11,629 Combined Covered Anaerobic

15 Da Lat Da Lat 2006 7,400 6,000 Separated

2-shells sedimentation tank

& Trickling Filter

Lake chains (Anaerobic, arbitrary, completed lagoons)

17 Bac

Giang

Bac Giang 2010 10,000 8,000 Combined Oxidation Ditch

(Source: NGOenvironment.com; Hanoi Department of Construction, 2015)

Even though several efforts have been initiated and practiced by the Government to address the problems related to water environment, urban sanitation is still now facing serious issues comprising sewage collection, treatment and management Though 94% of citizens have access to toilet, and 90% of households equip septic tanks as on-site pretreatment instrument for black water and night-soil before discharging to

public sewer, it is reported that only 10% of sewage and 4% of sludge are collected and treated in WWTP (World Bank, 2013) Moreover, the sewer systems which are mostly combined type are frequently inundated during heavy rainfalls, leaking the polluted sewage through overflows to public facilities and into surrounding water bodies Some sewer portions are outdated and have reached dozens of years in operation without frequent maintenance The drainage system in Vietnam can cover only from 40 – 50% of sewage as reported in the water sector review done by ADB

in 2009, ranging from 70% in urban areas to around 20% in sub-urban or rural areas (Pham & Kuyama, 2013) Though there have been more WWT facilities being designed and constructed recently, with an increase to 41 sectors with total capacity

of around 950,000 m3/d in 2018, this number is still relatively limited to keep track

of the total sewage generated by the society

The current wastewater management in Vietnam needs urgent and appropriate improvement to meet the growing demand from people and to achieve the sustainable urban development goals, keeping a sound balance between economic growth and environmental resource sustainability If viable, obviously there should be more WWTPs, both centralization and decentralization, being constructed and set in operation to cover as much treated sewage as possible However, it requires a large financial budget, estimated about USD 8.3 billion to provide enough services for 36 million urban citizens by 2025 (An, 2014) Besides, the sewer system in Vietnam’s urban also requires upgrading and new construction since the current network can only cover 40 – 50% of sewage generated from households It has no meaning for both centralized and decentralized WWTPs being invested if sewage cannot get into the treatment sectors via the drainage conduit Building more wastewater sewer pipes, especially separated pipelines, is a must to address urban sanitation in Vietnam

1.2 Introduction to a new approach: In-sewer self-purification technique

As described in the previous section, it is required to define the issues in urban sanitation in Vietnam as well as to find proper solutions to improve the water

environmental quality across the country In short-term, it is preferable to state an effective and low-cost solution for the situation

In urban sewerage system, drainage conduits or sewer pipes have a crucial role on conveying rainwater or surface runoff and wastewater from households to WWTP During its transportation through sewer, the sewage goes through a complex set of physical, biological and chemical processes The composition of sewage changes over different sections of pipe Biological process involves the activities of microorganism living in sewage and on the inner wall of sewer pipe If the retention time is long enough, the quality of water will be improved, as significant part of organic pollutants can be removed by microbial activities It was reported that the sewer pipe could be a potential bio-reactor which can partly treat domestic sewage along its way to WWTP Several researchers have interest in this ability of sewer besides its main conveying function Pomeroy et al., (1972) took the first study on the biological self-purification capacity in sewer pipe It was reported that the change

in the sewage composition especially organic matters occurs throughout the conduit

It was estimated that merely one-third of COD could be removed in an actual gravity sewer (Huisman et al., 2004) This self-purifying nature of sewage inside sewer can significantly impact on the design and operation of WWTP at the dead-end of the drainage system (Nielsen et al., 1992) These results proved that the potential of sewer network as a pretreatment unit in sewerage system should be paid more attention

To enhance the in-sewer treatment capacity, the food/biomass in sewer should be reduced, as the food source in sewage is considerably higher than microbial community (Warith, Kennedy, & Reitsma, 1998) An idea to lower the ratio is to increase the density of microorganisms by providing a rougher surface inward for them to attach and grow (Tanji, Sakai, Miyanaga, & Unno, 2006) Several studies with different kinds of materials, acting as kinds of microbial media in lab-scaled sewer showed good results on improvement of self-purification rate for both organic matter and nitrogen Porous ceramic, Raschig ring or different kinds of concretes have been applied so far to boost biofilm attachment in bench-scaled reactors For example,

wet concrete with holes on surface showed a significant removal rate of substrate such as DO: 460, TOC: 480, NH4-N: 87 mg/m2/h (Tanji et al., 2006)

If self-purification sewer could be applied in the situation of Vietnam, wastewater could be treated to reduce its pollution load, which in turn can reduce the design scale and operation cost for WWTPs As the sewage has been partly treated to some extent,

it is only needed for a decentralized plant to handle the final polishing process More decentralized treatment plants could be invested instead of large-scaled centralized sectors Hence, in long-term, the technique could save a considerable budget spent for wastewater treatment and associated practices for the society especially in developing countries like Vietnam, where financial tariff for sanitation is still a problem

1.3 Modified sewer for enhancing the self-purification capacity of sewage

Several researchers have studied on the self-purification of sewage during conveyance have proposed possibilities to use sewer as reactors These studies introduced some special materials or specific designs to enhance self-purification The idea of enhancing the self-purifying potential is to support microorganisms to attach and grow inside sewer by providing a media for them to adhere With the media present, the density of microbial community can increase over time At most basic, Shi, et al., (2018) utilized a 32m long work-scaled sewer with the inner wall being polished providing a rough surface for sedimentation and sludge retention A bench-scaled sewer reactor equipped with circulation pump capable of looping sewage over the pipe to simulate a real sewer line was proposed by Baban & Talinli, (2009), with Raschig rings laid at sewer bed for microbial attachment On the other hand, Tanji et al., (2006) used different types of concretes including conventional Portland concrete, grain concrete, porous concrete (with void content of 88%) and wet concretes as microbial media in a lab-scaled sewer reactor Porous media was also employed in a research conducted by Marjaka et al., (2003); fabricated porous ceramic with 71.5%

of void was investigated in this case Though these modified sewers may seem ideal

to boost the microbial activities in the pipe, they might interfere with the sewage

transportation function Another modified purifying pipe designed by Shoji et al., (2015) and developed by Sekisui Chemical Co LTD could help secure both self-purification and transportation capacity of sewage The sewer was innovated with 2-deck structure in which the upper deck with smooth surface was in charge of conveying wastewater containing large solid particles continuously, while lower deck placed with sponge media enhanced the microbial density for oxidization of organic pollutants

In this study, I utilized a lab-scaled sewer reactor made by transparent PVC plastic, with a modified porous media block laying at the bed, to evaluate the self-purification capacity of sewage after certain time running in circulation through the sewer The sketch of the lab-scaled sewer is illustrated in Fig 1.1 The PVC sewer pipe had a rectangular cross-section, with the media embedded inside made of pervious concrete

or porous concrete, which is a new sustainable construction material in replacement

of ordinary Portland cement concrete for storm water runoff in urban areas The detail

of the material is described further in the next section

Figure 1.1 Sample modified sewer equipped with porous media for microbial attachment, with an impervious outer wall to prevent leakage of sewage

The treatment concept could be described as follows During peak flow, the sewage

is supplied into the sewer, the concrete media is submerged and organic matters could

be trapped inside the concrete’s porous matrix A large portion of particulate organic pollutants would settle down and become susceptible to be digested by microbial communities Dissolved oxygen (DO) increases in sewage as the current flows inside the conduit Moreover, during dry flow, the wastewater level decreases, oxygen gas can have access to the microbial media, supporting further the oxidization of organic pollutants which trapped inside the pore spaces The treatment phenomenon could be

simulated in a lab-scaled sewer reactor by turning the circulating pump ON and OFF intermittently, which is called the Intermittent Contact Oxidation Process (ICOP) (Sotelo et al., 2019)

1.4 Pervious concrete as potential material for self-purification sewer

1.4.1 Introduction to pervious concrete

Pervious concrete or high-porous concrete is an emerging construction material for its special characteristic stated by its name The concrete is normally made up from coarse aggregate, Portland cement and water with less or no amount of fine aggregate like other conventional concretes (Fig 1.2) Therefore, it consists of a large portion of void content internally, typically around 20% Hence, it allows surface water from precipitation and runoff to infiltrate through rapidly, from 80 to 720 L/m2/min depending on aggregate size and mix design, helping to reduce the risk of flooding in urban areas, reduce surface runoff on the ground and peak flow in drainage systems and quickly recharge the groundwater aquifer (Sonebi, Bassuoni, & Yahia, 2016)

Figure 1.2 Sample pervious concrete made from byproduct coal-slag coarse

aggregate (A) and conventional rock coarse aggregate (B)

The first 30 minutes of rainwater which transfers highest load of pollution from surface to drains or other water bodies can also be partly treated while infiltrating through the pore matrix of this material where biological and chemical processes take place in the pedosphere (Sabnis, Obla, & Sabnis, 2012) For these specialties, pervious concrete has been applied in several public facilities such as pavement, parking lot, sport court, playground and low-traffic road, etc where inundation must

be unwanted For heavy-traffic construction, pervious concrete is not desired because

of its less compressive strength (3 – 28 MPa) compared to the conventional Portland cement concrete (15 – 30 MPa) (Mishra, 2014)

1.4.2 Constituent and mix design

Porosity, permeability and durability of pervious concrete are influenced by the mix design, size and uniformity of aggregate, admixtures and compaction force A good pervious concrete batch should be equalized in these main aspects (Marlinghaus, 2018) Most mixtures of pervious concrete require 3 parts of coarse aggregate, 1 part

of Portland cement in volume, and enough water to hydrate the cement It depends

on the aggregate size to adjust the cement and water amount respectively For example, fine aggregates require less cement while larger-sized aggregates will need more cement to adhere together Coarse aggregate generally ranges from 2.4 mm to

20 mm in size, both for grading or uniform aggregate (Sonebi et al., 2016) Smaller aggregate yields a better workability for the mixture, but lowers the permeability of the concrete after consolidation Though the smaller the rock, more angular, cleaner and uniform in size it should be to maintain good permeability Binder material used

in pervious concrete is mostly Portland cement, similarly to that of conventional concrete Other mix designs can include some optional portions of admixture such as water reducer or superplasticizer (E.g Fly ash or slag, silica fume and polypropylene fiber) to enhance strength, workability, or reduce water needed for cement hydration depending on work desires

Mixing and placement of pervious concrete also require carefulness to prevent failure such as binder bleeding or surface crumble Mix ratio of coarse aggregate, cement and water is crucial to achieve a successful and workable concrete mixture The blend should form in a stiff block when we squeeze them with hands, and the cement paste shines and sticks evenly onto our gloves Several trial batches should be practiced before making the final product (Marlinghaus, 2018)

1.4.3 Sustainable construction material

Besides Portland cement pervious concrete (PCPC), which mostly composes of natural aggregates binding by hydrated Portland cement, pervious concrete can also

be made from recycled or waste materials in replacement of conventional constituents Some examples of recycled materials used in pervious concrete include by-products from industrial processes such as coal or steel slag, recycled concrete aggregate (RCA) from construction and demolition waste (CDW) for aggregates, and fly-ash, ground granulated blast furnace slag (GGBFS) or rice husk ash for substitution of Portland cement (Sriravindrarajah, Wang, & Ervin, 2012) Hence, a vast amount of CDW waste could be recovered lowering the stress load to limited landfills and reduction in new natural aggregates exploitation can also be achieved It turns out to

be an environmentally friendly practice, helping to reduce the GHGs emission from those processes while still maintain the design quality for concrete criteria if we can find a proper mix ratio between natural and recycled aggregates (Guilherme C Cordeiro et al., 2015)

1.4.4 Potential usage for self-purification sewer construction

Being an emerging construction material in urban areas to reduce surface water runoff, pervious concrete possesses unique characteristics such as high interconnected porous structure and high fluid pertaining rate Hence, the concrete could provide a sufficiently rough surface for microbial attachment and therefore is expected to enhance the self-treatment capacity of sewage biologically Besides, the constituents utilized in manufacturing pervious concrete are flexible in sources, ranging from raw

natural materials such as newly exploited rock aggregate and Portland cement to recycled rock aggregate or by-product aggregates and substituent binder to cement like fly-ash Due to its rich variability and abundance in sources, pervious concrete has a fairly affordable price compared to conventional concrete while still remain its design requirements for construction quality if combined effectively with raw natural components

From the above advantages, pervious concrete could be a potential material as microbial media for the modified sewer systems such as long-distance sewer conveying sewage from residential areas to centralized wastewater treatment plants

or open canal for polluted wet weather overflow from combined sewer These scaled infrastructures are easier for workers to access for maintenance and removal

large-of sludge which accumulates quickly over a short time in this in-sewer purifying conduit

1.5 Objectives

With high potential in treatment capacity and application stated in the four previous sections, it could be commendable to introduce the self-purification sewer using by-product pervious concrete as media inward to the case of water sanitation and sewerage system in Vietnam The treatment performance will be evaluated via lab-scaled sewer system Hereby, this study is conducted to investigate the in-sewer treatment capacity of modified self-purification sewer The specific objective of the study is described as follows

Objective of the thesis: To assess the self-purification capacity of domestic sewage for organic pollutants using pervious concretes as microbial attached media in terms

of removal efficiency of organic pollutants and nitrogen

To achieve the above objective, I operated a bench scale in-sewer purification reactors with polluted canal water as the source of sewage I prepared two types of pervious concrete materials, placed them in the bench scale reactor, and evaluated the removal performance of the COD, NH4-N and TN

CHAPTER 2 MATERIALS AND METHODOLOGY

In the second chapter, the experimental reactor setup, operational conditions and analytical methods are described In details, section 2.1 introduces the sewer reactor with its main structure and other equipped supplementary units Section 2.2 presents more details in how the pervious concrete was made and installed for the modified sewer, aiming to be a potential media material for the pretreatment of organic matters along the channel The last section will describe analytical methods applied to measure characteristics of the modified concrete

2.1 Lab-scaled self-purification sewer reactor

The modified self-purification sewer reactor is set up with the purpose to monitor the change of pollutants in raw municipal sewage inside the modified sewer, which utilize the design of former sewer reactor from Mino-Sato Laboratory (Sotelo et al., 2019) The main proportion and additional equipment of the reactor are described in the following section

2.1.1 Reactor setup

Two sewer reactors are designed and set up in Environmental Engineering Laboratory

in VJU, and each consists of two main parts: a lab-scaled rectangular PVC pipe installed with a porous concrete media inward and a set of supplementary operational equipment

The main sewer made of transparent PVC had an outer dimension of 50cm length (L), 8.2cm width (W) and 6.5cm height (H), and thickness of 0.5cm The inner dimension was 49/7/5.5 in L/W/H respectively Its bed was completely covered with a 1.5cm-thick pervious concrete, which acts as a porous media There were two types of materials chosen to be coarse-aggregate constituent for the concrete, including coal-slag (CS) and rock-aggregate (RA) Each concrete type made from according material was installed for each sewer reactor, hence the names regarded to two sewers are CS sewer and RA sewer respectively Details about these pervious concrete media are

described further in the session 2.2 The installation of concrete inward the reactors was to ensure the even distribution of sewage and prevent shortcut flow After media placement and connection of inflow and outflow pipes, the sewer was covered completely with a transparent lid to make air-tightness condition for monitoring the change of headspace oxygen gas concentration as well as observing inside

Each reactor was equipped with a recirculation tank (capacity of 1.5L), a recirculation pump, an oxygen gas sensor (Grove-Gas Sensor O2, Seeed Studio), a thermometer and other connection pipes, illustrated in the Fig 2.1 and the photo in Fig 2.2 All equipment was connected and controlled by an Arduino UNO board, which acted as

a micro-computer with a crucial function to operate the pump and log data from sensors A compact LCD screen connected with the board showed all operational data supporting real-time monitoring for operators Finally, an air pump connected with the inflow pipe was utilized to regenerate atmosphere in the sewer headspace after each experiment, since oxygen was supposed to be consumed for chemical and biological reactions occurred inside the system

Figure 2.1 Flow diagram of PVC sewer reactor installed with pervious concrete

media, oxygen gas sensor, recirculation tank and pump

Figure 2.2 Self-purification sewer reactors with equipment and porous concrete inward Left sewer is coated with pervious concrete made from industrial by-product (coal-slag) while conventional rock-aggregate pervious concrete is used in the right sewer

2.1.2 Reactor operation

Batch experiments were conducted to evaluate the treatment performance of purification sewers equipped with two different pervious concretes The two sewer reactors were operated using the same influent, pumping schedule and under the same temperature The purpose was to monitor and compare the pollutant removal rate of two sewers equipped with two media materials

self-1.5L of raw sewage was filled in the recirculation tank of each reactor before experiment right after sampling Sewage was then recirculated through the sewer with two pumping schedules: (1) 15minsON/45minsOFF with Q of 400mL/min and (2) 30minsON/30minsOFF with Q of 600mL/min to simulate dry and wet condition flow patterns respectively

2.1.3 Sampling and analytical methods

Raw sewage from an open canal on Nguyen Co Thach Street, Nam Tu Liem District, Hanoi which transports domestic wastewater of surrounding residential areas to Phu

Do WWTP (tentative capacity of 84,000 m3/d) was collected as influent for the sewer reactors For each batch experiment, new raw sample from the canal was taken accordingly; therefore, the inlet quality of each batch was different as the deviation shown in Table 2.1

Sampling process was taken under nice weather when there was no rain in one or two days prior to the sampling day The sample collection took place at around 8 a.m in the morning when pollutant load was considered at highest level of the day (SHOJI

et al., 2015), then 1.5L of raw sewage was filled in the recirculation tank of each reactor accordingly The samples used for experiment and analysis of two sewers were collected on March 23rd, 28th and April 23rd for the 1st pumping schedule (15mON/45mOFF, 400mL/min), and April 6th, 9th and 13th for the 2nd schedule (60mON/60mOFF, 600mL/min) On other days, the reactors were still operated to maintain the continuous environment without experimental analysis

Figure 2.3 My Dinh Canal in Nguyen Co Thach Street, My Dinh, Nam Tu Liem

Several samples have been collected to test the raw water quality of the canal, which

is described in the Table 2.1

Table 2.1 General wastewater quality of My Dinh Canal in Nguyen Co Thach Street

(mg/L)

BOD (mg/L)

COD (mg/L)

NH4 (mg/L)

TN (mg/L)

During batch experiments, the effluent from two reactors were collected at 0, 1, 3, 5,

7, 9 and 24h of flowtime to measure the change of water quality over different lengths

of the purifying pipes Oxygen gas concentration in sewer headspace was also monitored by the Grove sensor and recorded every second Sample name was assigned regarding to the sampling time (E.g CS-1 is the sample taken after 1h of recirculation from the coal-slag pervious concrete sewer, and similarly RA-1 is the sample from rock-aggregate sewer with the same flowtime) It is estimated that the time a portion of wastewater requires to reach WWTP ranges around 7 to 9h, which

is equivalent to retention time in Activated Sludge reactor However, another sample

at 24h of flow was taken to see how much the sewage quality can be improved or whether the removal rate remains stable

All analytical processes took place in Environmental Engineering Laboratory in VJU Water parameters monitored includes pH, Turbidity, COD, NH4 and T-N Mettler Toledo Seven Compact pH meter was utilized for measuring of pH Turbidity was measured with HANNAH portable turbidity meter, model HI98703 COD in sewage was analyzed following Standard Method 5220D Closed Reflux, Colorimetric method (SMWW, Section 5220) Ammonia-Nitrogen was analyzed with Phenate Method (SWMM, Section 4500) and Total Nitrogen was analyzed following Analytical methods for wastewater examination (ASTM D8083)

Table 2.2 Experimental sampling schedule of two sewer reactors

2.2 Microbial media for the modified self-purification sewer

2.2.1 Pervious concrete as a potential material for self-purification sewer

From several advantages reviewed in the literature in session 1.4, pervious concrete has been proven to be a potential material for self-purification sewer construction with high porosity and permeability for sewage to infiltrate through, providing pore space and rough surface for microorganism to grow, which can enhance the self-purification capacity of domestic sewage

Two coarse aggregates were chosen as main constituent for the experimental pervious concrete, one was a conventional material used in normal concrete and another was a by-product from industrial process Angular rock gravel exploited at a stream bank

in Phu Tho District was chosen as conventional aggregate Coal slag, residue from coal combustion in Pha Lai thermopower plant, was reused as waste or by-product aggregate for the pervious concrete Both of these two materials were then sorted by

sieves into size ranges of 2.0 – 2.8, 2.8 – 4.0, 4.0 – 5.6 mm Aggregates sized 2.0 – 2.8 mm were chosen for the experiment since concrete made from this small-medium aggregate produces a better workability and be more suitable in size for a lab-scaled reactor Each aggregate type was mixed with Portland cement with ratio of 3:1 in volume, the combination was then hydrated by just enough water to produce a workable mixture ready to be placed inside the sewer (Fig 2.4A)

Figure 2.4 Pervious concrete media for the PVC sewer reactor (A) Pervious concrete was placed inside in the bed of the sewer for evenly distribution of sewage and more esthetical look (B) Hardened coal-slag pervious concrete; (C) Hardened rock-aggregate pervious concrete

Several methods to evaluate the properties of experimental concretes used for sewer reactors are described in session 2.2.2

2.2.2 Physicochemical characteristics of pervious concrete made from

conventional and waste aggregates

To quantify how much the porous space the pervious concrete possesses, and how good it can retain fluid or allow fluid to pass through, porosity and hydraulic conductivity of the concrete were measured Herein, alongside with the main concrete blocks installed in the sewer reactors, the concrete paste used to make the block was also used for making other specific blocks to serve for concrete parameters measurement The concrete block in the reactor was supposed to have the same property as the concrete block for the measurement of these parameters

2.2.2.1 Density and porosity

Porosity and density are considered crucial parameters for pervious concrete, needed for design and comparison with other construction materials (Dean, Montes, Valavala,

& Haselbach, 2005) Porosity is defined as the volume of void space over the total volume of a pervious concrete block stated in percentage % The method applied for measurement in this experiment follows the idea of water displacement method (Montes, et al., 2005) but in a simplified version The porous space inside concrete block is determined by the water amount which infiltrated and replaced air in the matrix after a period of 30 minutes in submergence The detail experiment process is described as follows

Apparatus

(1) Cylindrical plastic moulds, used for keeping pervious concrete sample;

(2) Ruler, used for measuring diameter and height of concrete specimen;

(3) Balance with accuracy to the nearest of 0.1g;

(4) Oven, capable for rising temperature more than 100oC;

(5) Water bath;

(6) Graduate cylinder, with accuracy to the nearest 0.5ml;

Procedure

(1) Dry the specimens stored in cylindrical moulds completely in the oven for 24h

at 105oC;

(2) Weigh the samples with balance, record the dry weight (Wdry);

(3) Measure the diameter (D) and height (H) of each sample, record it for Total Volume (Vtotal);

(4) Submerge the samples into water bath, filled with tap water at room temperature (~20oC) for at least 30 minutes;

(5) Rotate and tap the samples 10 times around its circumference with a rubber mallet to let air escape from the core completely;

(6) Take out concrete samples, rotate them upside down to pore all water trapped into graduate cylinder through a funnel Let the samples sit for 10 minutes and tap them with rubber mallet 10 times;

(7) Record water amount poured out from the submerged concrete blocks It is assumed that the water volume (mL) is equivalent to the void space volume (Vvoid) (cm3);

(8) Calculate the porosity of the concrete sample by the equation below;

Calculation

(1) Total volume of concrete sample:

(1) Run the water at a fixed rate, and wait until h1 and h2 are stabilized;

(2) Measure the effluent discharged from concrete column according to that Δh (h1 – h2);

(3) Increase the h1 of the higher water column compared to h2 of the lower concrete column, wait 3-5 minutes for the system to be stable;

(4) Measure the effluent discharge again according to the new Δh;

(5) Repeat the procedure from step (3) to record the change of effluent volume; (6) The Q and Delta h in the Darcy’s equation has a linear correlation, from that

we could estimate the KA/L, then hydraulic conductivity constant (K) of material could be calculated

The experiment procedure is illustrated by the Fig 2.5

Figure 2.5 Darcy’s Law experiment system for testing permeability of concrete

L: Thickness of material block (cm);

h1: elevation of higher elevation where water starts to fall down (cm);

h2: elevation of lower elevation where water reaches (cm);

2.2.2.3 SEM and EDS

Coarse aggregate, the main proportion consisted in pervious concrete, has been shown to have critical role in the concrete characteristics For instance, interconnected porous matrix in pervious concrete is determined mostly by the coarse aggregate type rather than its size (Ćosić, Korat, Ducman, & Netinger, 2015) The material types such as conventional and by-product aggregates used in the research were also measured to evaluate their potential as an adsorbent and porous media for microorganism to grow in later phase of sewer pipe’s lifespan

Two types of concrete aggregate including coal slag and rock angular aggregate, sized 2.0 – 2.8mm, were tested for surface structure and composition both at raw state and after running with sewage for around 20 experimental days by Scanning Electron Microscopy (SEM) JOEL modeled JSM-IT100, integrated with the Electron Dispersion Spectrometry (EDS) JOEL modeled JED-2300 in Nanotechnology Laboratory, Vietnam Japan University (VJU)