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

Sample pervious concrete made from byproduct coal-slag coarse aggregate A and conventional rock coarse aggregate B...8Figure 2.1.. LIST OF ABBREVIATIONAAO: Anaerobic – Anoxic – Aerobic A

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 VIETNAM

MAJOR: Environmental Engineering

At very first words, my gratefulness goes to all lecturers, officers and staffs inEnvironmental Engineering Program (MEE), Vietnam Japan University (VJU) andJapan International Cooperation Agency (JICA) for giving me the preciousopportunity 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 andsupervision throughout the time I did the thesis I could not accomplish the thesiswithout your guidance and enthusiasm throughout all progresses, from initial researchidea, reactor setup, experimental analysis and revision of the draft and presentation

And last, I also really appreciate the support and encouragement from myclassmates, friends and family, those who have contributed to my two wonderfulyears 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 microbialattachment, 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 concretemedia, 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 rightsewer 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 concretewas 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 aggregate pervious concrete 18Figure 2.5 Darcy’s Law experiment system for testing permeability of concrete 22

rock-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 withmunicipal 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 runningwith municipal sewage for 30 experimental days 29

Figure 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 31

Figure 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 32

Figure 3.9 Correlation between Turbidity and COD in CS and RA sewers both in15mON/45mOFF and 30mON/30mOFF pump schedules 33

Figure 3.10 COD change in effluent of lab-scaled self-purification sewer, runningwith pump schedule of 15mON/45mOFF simulating dry condition 34

Figure 3.11 COD change in effluent of lab-scaled self-purification sewer, runningwith pump schedule of 30mON/30mOFF simulating wet condition 34

Figure 3.12 Sedimentation flocs settled down on coal-slag concrete (A) and aggregate concrete (B) while sewage flowed through the lab-scaled sewer 37

rock-Figure 3.13 Detached floc from pervious concrete media settled down at the bed ofthe 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-aggregateconcrete sewer, with pump schedule of 15m ON/45m OFF 43

Figure 3.18 TN and ammonia of outflows from coal-slag and rock-aggregateconcrete sewer, with pump schedule of 30m ON/30m OFF 43

Figure 3.19 Correlation between NH4 and TN in CS and RA sewers in both 15/45and 30/30 pump schedules; (1) Portion of TN which was removed by ammonniastripping, (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 48

Figure 3.22 Treatment efficiency for NH4-N of self-purification sewer pipe madefrom CS and RA concretes in dry flow pattern condition 49

Figure 3.23 Treatment efficiency for NH4-N of self-purification sewer pipe madefrom CS and RA concretes in wet flow pattern condition 50

Table 2.2 Experimental sampling schedule of two sewer reactors 17

Table 3.1 Properties of Portland cement pervious concrete from coal-slag and rockaggregate 25

Table 3.2 Composition of coal-slag aggregate in Pha Lai Thermopower Plantanalyzed by X-Ray Fluorescence (XRF) 30

Table 3.3 Correlation of sedimentation and microbial digestions for organic mattersremoval in self-purification sewers 39

Table 3.4 Estimation of flow distance from pump schedules in lab-scaled purification sewer 46

self-Table A.1 Test of heavy metals released from coal slag aggregate 56Table 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 WastewaterWWTP: 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 marketeconomy, 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 Therapid growth of economy and population put a tremendous pressure on the urbandrainage 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 intowns 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 seweragesystem have not been developed or renovated to meet the demand of treatment forthe 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 ofthe sewerage system which could be called drainage system also are the combined type,conveying around 90% of total sewage generated from domestic, industrial and hospitalsources together with rainwater to wastewater treatment plants (WWTP) or directlydischarge into water environment such as lakes, canals or rivers By 2012, only 17wastewater treatment plants being in operation were in charge of sewage treatment inurban areas of Vietnam, with total capacity of 530,000 m3/d (An, 2014) (Table 1.1) Inmajority, the most common wastewater treatment technology is Activated SludgeProcess performed differently in each desired area Among those, ConventionalActivated Sludge (CAS), Anaerobic – Anoxic – Aerobic (AAO) and Sequencing BatchReactor (SBR) are mostly developed and applied in Centralized

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

Table 1.1 Capacity of several wastewater treatment plants in Vietnam

4 Yen So 2012 200,000 120,000 Combined Sequencing Batch

8 Nam 2009 15,000 15,000 Separated Activated Sludge

Vien

2

9 Son Tra 2006 15,900 15,900 Combined Covered Anaerobic

13 Bai Chay 2007 3,500 3,500 Combined Sequencing Batch

Reactor Quang

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

& Trickling Filter

Buon Ma (Anaerobic,

16 Ma 2006 8,125 5,700 Separated

Thuat arbitrary, Thuat

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-sitepretreatment instrument for black water and night-soil before discharging to

3

public sewer, it is reported that only 10% of sewage and 4% of sludge are collectedand treated in WWTP (World Bank, 2013) Moreover, the sewer systems which aremostly combined type are frequently inundated during heavy rainfalls, leaking thepolluted sewage through overflows to public facilities and into surrounding waterbodies Some sewer portions are outdated and have reached dozens of years inoperation without frequent maintenance The drainage system in Vietnam can coveronly 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 beingdesigned 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 appropriateimprovement to meet the growing demand from people and to achieve the sustainableurban development goals, keeping a sound balance between economic growth andenvironmental resource sustainability If viable, obviously there should be moreWWTPs, both centralization and decentralization, being constructed and set inoperation to cover as much treated sewage as possible However, it requires a largefinancial budget, estimated about USD 8.3 billion to provide enough services for 36million urban citizens by 2025 (An, 2014) Besides, the sewer system in Vietnam’surban also requires upgrading and new construction since the current network can onlycover 40 – 50% of sewage generated from households It has no meaning for bothcentralized and decentralized WWTPs being invested if sewage cannot get into thetreatment 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 urbansanitation 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 aneffective and low-cost solution for the situation.

In urban sewerage system, drainage conduits or sewer pipes have a crucial role onconveying rainwater or surface runoff and wastewater from households to WWTP.During its transportation through sewer, the sewage goes through a complex set ofphysical, biological and chemical processes The composition of sewage changes overdifferent sections of pipe Biological process involves the activities of microorganismliving in sewage and on the inner wall of sewer pipe If the retention time is longenough, the quality of water will be improved, as significant part of organic pollutantscan be removed by microbial activities It was reported that the sewer pipe could be apotential 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 conveyingfunction Pomeroy et al., (1972) took the first study on the biological self-purificationcapacity in sewer pipe It was reported that the change in the sewage compositionespecially organic matters occurs throughout the conduit It was estimated that merelyone-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 thedesign 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 insewerage system should be paid more attention

To enhance the in-sewer treatment capacity, the food/biomass in sewer should bereduced, 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 thedensity of microorganisms by providing a rougher surface inward for them to attachand grow (Tanji, Sakai, Miyanaga, & Unno, 2006) Several studies with different kinds

of materials, acting as kinds of microbial media in lab-scaled sewer showed goodresults 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 toboost biofilm attachment in bench-scaled reactors For example,

wet concrete with holes on surface showed a significant removal rate of substratesuch 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, wastewatercould be treated to reduce its pollution load, which in turn can reduce the designscale and operation cost for WWTPs As the sewage has been partly treated to someextent, it is only needed for a decentralized plant to handle the final polishingprocess More decentralized treatment plants could be invested instead of large-scaled centralized sectors Hence, in long-term, the technique could save aconsiderable budget spent for wastewater treatment and associated practices for thesociety especially in developing countries like Vietnam, where financial tariff forsanitation 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 conveyancehave proposed possibilities to use sewer as reactors These studies introduced somespecial materials or specific designs to enhance self-purification The idea of enhancingthe self-purifying potential is to support microorganisms to attach and grow insidesewer by providing a media for them to adhere With the media present, the density ofmicrobial 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 roughsurface for sedimentation and sludge retention A bench-scaled sewer reactor equippedwith circulation pump capable of looping sewage over the pipe to simulate a real sewerline was proposed by Baban & Talinli, (2009), with Raschig rings laid at sewer bed formicrobial attachment On the other hand, Tanji et al., (2006) used different types ofconcretes including conventional Portland concrete, grain concrete, porous concrete(with void content of 88%) and wet concretes as microbial media in a lab-scaled sewerreactor 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 thepipe, 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 ofconveying wastewater containing large solid particles continuously, while lowerdeck placed with sponge media enhanced the microbial density for oxidization oforganic 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 thesewer The sketch of the lab-scaled sewer is illustrated in Fig 1.1 The PVC sewerpipe had a rectangular cross-section, with the media embedded inside made ofpervious concrete or porous concrete, which is a new sustainable constructionmaterial 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 issupplied into the sewer, the concrete media is submerged and organic matters could betrapped inside the concrete’s porous matrix A large portion of particulate organicpollutants would settle down and become susceptible to be digested by microbialcommunities Dissolved oxygen (DO) increases in sewage as the current flows insidethe conduit Moreover, during dry flow, the wastewater level decreases, oxygen gas canhave access to the microbial media, supporting further the oxidization of organicpollutants which trapped inside the pore spaces The treatment phenomenon could be

simulated in a lab-scaled sewer reactor by turning the circulating pump ON andOFF 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 itsspecial characteristic stated by its name The concrete is normally made up from coarseaggregate, Portland cement and water with less or no amount of fine aggregate likeother conventional concretes (Fig 1.2) Therefore, it consists of a large portion of voidcontent internally, typically around 20% Hence, it allows surface water fromprecipitation and runoff to infiltrate through rapidly, from 80 to 720 L/m2/mindepending on aggregate size and mix design, helping to reduce the risk of flooding inurban areas, reduce surface runoff on the ground and peak flow in drainage systems andquickly 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 fromsurface to drains or other water bodies can also be partly treated while infiltratingthrough the pore matrix of this material where biological and chemical processestake 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 desiredbecause of its less compressive strength (3 – 28 MPa) compared to the conventionalPortland 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 mixdesign, size and uniformity of aggregate, admixtures and compaction force A goodpervious concrete batch should be equalized in these main aspects (Marlinghaus,2018) Most mixtures of pervious concrete require 3 parts of coarse aggregate, 1part of Portland cement in volume, and enough water to hydrate the cement Itdepends on the aggregate size to adjust the cement and water amount respectively.For example, fine aggregates require less cement while larger-sized aggregates willneed 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 thepermeability of the concrete after consolidation Though the smaller the rock, moreangular, cleaner and uniform in size it should be to maintain good permeability.Binder material used in pervious concrete is mostly Portland cement, similarly tothat 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, silicafume and polypropylene fiber) to enhance strength, workability, or reduce waterneeded for cement hydration depending on work desires

Mixing and placement of pervious concrete also require carefulness to preventfailure 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 thecement 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 ofnatural aggregates binding by hydrated Portland cement, pervious concrete can also

be made from recycled or waste materials in replacement of conventionalconstituents Some examples of recycled materials used in pervious concrete includeby-products from industrial processes such as coal or steel slag, recycled concreteaggregate (RCA) from construction and demolition waste (CDW) for aggregates,and fly-ash, ground granulated blast furnace slag (GGBFS) or rice husk ash forsubstitution of Portland cement (Sriravindrarajah, Wang, & Ervin, 2012) Hence, avast amount of CDW waste could be recovered lowering the stress load to limitedlandfills and reduction in new natural aggregates exploitation can also be achieved

It turns out to be an environmentally friendly practice, helping to reduce the GHGsemission from those processes while still maintain the design quality for concretecriteria 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 torecycled rock aggregate or by-product aggregates and substituent binder to cementlike fly-ash Due to its rich variability and abundance in sources, pervious concretehas a fairly affordable price compared to conventional concrete while still remain itsdesign requirements for construction quality if combined effectively with rawnatural components.

From the above advantages, pervious concrete could be a potential material asmicrobial media for the modified sewer systems such as long-distance sewerconveying 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 purifyingconduit

1.5 Objectives

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

Objective of the thesis: To assess the self-purification capacity of domestic sewagefor 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 purificationreactors with polluted canal water as the source of sewage I prepared two types ofpervious concrete materials, placed them in the bench scale reactor, and evaluatedthe removal performance of the COD, NH4-N and TN

CHAPTER 2 MATERIALS AND METHODOLOGY

In the second chapter, the experimental reactor setup, operational conditions andanalytical methods are described In details, section 2.1 introduces the sewer reactorwith its main structure and other equipped supplementary units Section 2.2 presentsmore details in how the pervious concrete was made and installed for the modifiedsewer, aiming to be a potential media material for the pretreatment of organicmatters 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 monitorthe change of pollutants in raw municipal sewage inside the modified sewer, whichutilize 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 inthe following section

2.1.1 Reactor setup

Two sewer reactors are designed and set up in Environmental EngineeringLaboratory in VJU, and each consists of two main parts: a lab-scaled rectangularPVC pipe installed with a porous concrete media inward and a set of supplementaryoperational 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 dimensionwas 49/7/5.5 in L/W/H respectively Its bed was completely covered with a 1.5cm-thickpervious concrete, which acts as a porous media There were two types of materialschosen to be coarse-aggregate constituent for the concrete, including coal-slag (CS) androck-aggregate (RA) Each concrete type made from according material was installedfor each sewer reactor, hence the names regarded to two sewers are CS sewer and RAsewer 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 mediaplacement and connection of inflow and outflow pipes, the sewer was coveredcompletely with a transparent lid to make air-tightness condition for monitoring thechange of headspace oxygen gas concentration as well as observing inside

Each reactor was equipped with a recirculation tank (capacity of 1.5L), arecirculation pump, an oxygen gas sensor (Grove-Gas Sensor O2, Seeed Studio), athermometer and other connection pipes, illustrated in the Fig 2.1 and the photo inFig 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 andlog data from sensors A compact LCD screen connected with the board showed alloperational data supporting real-time monitoring for operators Finally, an air pumpconnected with the inflow pipe was utilized to regenerate atmosphere in the sewerheadspace after each experiment, since oxygen was supposed to be consumed forchemical 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

self-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 oftwo sewers equipped with two media materials

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 LiemDistrict, Hanoi which transports domestic wastewater of surrounding residentialareas to Phu Do WWTP (tentative capacity of 84,000 m3/d) was collected asinfluent for the sewer reactors For each batch experiment, new raw sample from thecanal 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 ortwo days prior to the sampling day The sample collection took place at around 8a.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 ofeach reactor accordingly The samples used for experiment and analysis of twosewers were collected on March 23rd, 28th and April 23rd for the 1st pumpingschedule (15mON/45mOFF, 400mL/min), and April 6th, 9th and 13th for the 2ndschedule (60mON/60mOFF, 600mL/min) On other days, the reactors were stilloperated 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

Parameters pH

DO BOD COD NH4 TN (mg/L) (mg/L) (mg/L) (mg/L) (mg/L)

Value

7.3 0.22 116 186 42.2 52.1

± 0.1 ± 0.1 ± 33 ± 94 ± 6.26 ± 8.17

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

is equivalent to retention time in Activated Sludge reactor However, anothersample at 24h of flow was taken to see how much the sewage quality can beimproved or whether the removal rate remains stable

All analytical processes took place in Environmental Engineering Laboratory inVJU 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 analyzedwith Phenate Method (SWMM, Section 4500) and Total Nitrogen was analyzedfollowing 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 concretehas been proven to be a potential material for self-purification sewer constructionwith high porosity and permeability for sewage to infiltrate through, providing porespace 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 perviousconcrete, one was a conventional material used in normal concrete and another was aby-product from industrial process Angular rock gravel exploited at a stream bank inPhu Tho District was chosen as conventional aggregate Coal slag, residue from coal

17

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-scaledreactor Each aggregate type was mixed with Portland cement with ratio of 3:1 involume, the combination was then hydrated by just enough water to produce aworkable 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 sewerreactors 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 howgood it can retain fluid or allow fluid to pass through, porosity and hydraulicconductivity of the concrete were measured Herein, alongside with the mainconcrete blocks installed in the sewer reactors, the concrete paste used to make theblock was also used for making other specific blocks to serve for concreteparameters measurement The concrete block in the reactor was supposed to havethe 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 fordesign and comparison with other construction materials (Dean, Montes, Valavala,

& Haselbach, 2005) Porosity is defined as the volume of void space over the totalvolume of a pervious concrete block stated in percentage % The method applied formeasurement 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 isdetermined by the water amount which infiltrated and replaced air in the matrix after aperiod of 30 minutes in submergence The detail experiment process is described asfollows

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 trappedinto graduate cylinder through a funnel Let the samples sit for 10 minutes and tap themwith rubber mallet 10 times;

(7) Record water amount poured out from the submerged concrete blocks It isassumed 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:

(2) Density of pervious concrete sample:

Pervious concrete is considered a potential emerging construction material to enhancesurface water runoff because of its capability to let water infiltrate rapidly, rangingtypically from 120 to 320 L/m2/min (Sonebi et al., 2016) This ability of the experimentconcrete is assessed via hydraulic conductivity K or permeability (cm/s).

Darcy’s law experiment system in MEE laboratory was utilized to test the permeability

of pervious concrete It applies the theory of potential energy from height differencebetween water source and tested material to see how much effluent flowing through theconcrete column The equipment needed and the experiment procedure are illustrated

as follows (Stapleton, Ph, Antonio, Mihelcic, & Ph, 1994)

(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 Δhh

(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 Δhh;

(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

Q: Flow (cm 3 /s);

K: Hydraulic conductivity constant (specific for each porous material) (cm/s);

A: Area of material block (cm 2 );

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);

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)

CHAPTER 3 RESULTS AND DISCUSSION

3.1 Potential characteristics of pervious concrete as microbial media

3.1.1 Density, porosity and permeability

Several key properties of pervious concretes utilized for the experimental reactorsare illustrated in Table 3.1 Compared to the reference data for other perviousconcretes, the concretes made from conventional rock and coal-slag aggregatesobtained equivalent values in porosity and permeability, though the aggregate sizesused in both concrete were relatively finer (2.0 – 2.8mm) than convention aggregatefor ordinary PCPC (4 – 20mm)

Among the two experimental blocks, coal-slag concrete showed better characteristicsboth in porosity (33%) and hydraulic conductivity (3.93 cm/s) than the concrete madefrom rock-aggregate (21% and 1.28 cm/s respectively) The prior material could letwater infiltrate at a rate almost three times higher than that of the rock concrete Coalslag, at a first glance, presented a much rougher surface when touched by hand, as it isresidue from coal combustion process The material had undergone tremendousmodification in morphology and internal structure at high temperature and pressure inthe blast furnace Hence, there was already interconnected porous matrix inside theslag, which was witnessed under SEM image (Section 3.1.2) However, the strength ordurability of coal-slag concrete seems to be much lower than rock pervious concrete.Though no experiment was conducted to measure the strength of two concretematerials, their durability can be compared through density data (Shohana Iffat, 2015).Coal-slag porous concrete density was about 60% to that of rock porous concrete, andonly 47% when compared to ordinary impervious concrete This drawback on strengthand durability of the concrete, which is crucial in public infrastructure design for long-term usage, could be ameliorated by substituting natural coarse aggregate (NCA) byrecycled coarse aggregate (RCA) at <30%

Table 3.1 Properties of Portland cement pervious concrete from coal-slag and rock aggregate

Density Porosity Permeability Sample

-Note: Pervious concrete made from (*) coal-slag aggregate and (**)

rock-aggregate sized 2.0 – 2.8 mm

With a large void content in their structure, the pervious concretes could bepotential microbial media as well as a good absorber for organic sediment

3.1.2 Morphology and chemical composition

3.1.2.1 Interfacial morphology by SEM

Together with physical properties, morphology of pervious concrete aggregate wasalso evaluated, providing a closer look to its surface structure The sample wastaken from the concrete block, which had been bonded together with cement.Hence, there was also a thin layer of cement paste on the aggregate particles, thoughtheir morphology can still be observed clearly under SEM microscopy

a Sample from coal-slag pervious concrete

Coal-slag aggregate possessed a significant number of interconnected pores Whenwitnessed by eyes, the dark color of the sample also indicated that it might possess

an intense porous surface structure On SEM images, its porous surface can be

observed easily, especially when magnifying to the scale around 5,000 times Thefinest pore sizes can be smaller than 1µm, which even smaller than a single bacterialcell (Fig 3.1).

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

Two states of the material before and after submerging in the sewer reactors withmunicipal wastewater for around 30 days were also monitored with SEM At raw state,the sample still showed a clear morphology with high roughness and high content ofmicro voids However, after contacting with sewage, micro pores were filled with adull sedimental layer though the surface roughness were still maintained