Summary of Environmental engineering Doctoral thesis: Study on treatment of natural rubber processing wastewater using integrated physicochemical and biological processes

The objective of this study is to develop an energy and nutrients recovering wastewater treatment process combining physicochemical and biological methods for NRP wastewater.

MINISTRY OF EDUCATION

AND TRAINING

VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY

GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY

- Duong Van Nam

STUDY ON TREATMENT OF NATURAL RUBBER PROCESSING WASTEWATER USING INTEGRATED PHYSICOCHEMICAL AND BIOLOGICAL PROCESSES

Major: Environmental Engineering

Code: 9 52 03 20

SUMMARY OF ENVIRONMENTAL ENGINEERING

DOCTORAL THESIS

HA NOI, 2019

The thesis was performed at Graduate University of Science and Technology, Vietnam Academy Science and Technology

Supervisor 1: Dr Phan Do Hung

Supervisor 2: Assoc Prof Dr Nguyen Hoai Chau

at ………… on………, 20……

The thesis can be found in:

- The library of Graduate University of Science and Technology

- National Library of Vietnam

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INTRODUCTION

1 Rationale of the thesis

Vietnam is one of the three leading countries in exploiting and exporting natural rubber in the world Annually, the natural rubber processing (NRP) industry of Vietnam generates over 25 million cubic meters of wastewater This is among the wastewaters having a very high level of pollutants of organic matter, nitrogen, phosphorus and total suspended solids (TSS) Currently, wastewater treatment technologies being applied

in the natural rubber processing industry in Vietnam are mainly the incorporation of a number of the following processes: rubber latex decanting, flotation, UASB (Upflow Anaerobic Sludge Blanket), oxidation ditches, aeration tanks, aerobic biological filtration, algae ponds, and stationary ponds These treatment systems still exhibit many limitations such as inadequate treatment efficiency, especially for organic matter, nitrogen and phosphorous; large print foot and high energy requirement Although the NRP industry is one of five typical industries (textile; NRP; pulp and paper; brewery; and leachate) generating wastewater with high pollutant load, in Vietnam research on treatment of NRP wastewater is still limited So far, study on appropriate technological processes for treating NRP wastewater

in Vietnam with approach to recover nutrients and energy using integrated physicochemical and biological processes has not been conducted

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From the above reasons, this thesis was conducted to study and propose an appropriate technological process for treating the NRP wastewater with the aim to simultaneously solve the following problems: (1) Energy recovery (biogas containing CH4

as fuel); (2) Simultaneous recovery of nitrogen and phosphorus as fertilizer for agriculture; (3) Modifycation of reactors and integration of physicochemical and biological processes to improve the system performance in the simultaneous removal of organic and nutrients substances in NRP wastewater

2 Objectives of the thesis

The objective of this study is to develop an energy and nutrients recovering wastewater treatment process combining physicochemical and biological methods for NRP wastewater

3 Main research content of the thesis

1) Overview of current technologies for treatment of NRP wastewater;

2) Study on removal of organic substances and energy recover from NRP wastewater by Expanded Granular Sludge Bed (EGSB) reactor;

3) Study on simultaneous recovery of nitrogen and phosphorus from NRP wastewater by Magnesium Ammonium Phosphate (MAP) precipitation method;

4) Study on simultaneous removal of organic and nitrogen substances from anaerobically treated NRP wastewater in modified Sequencing Batch Reactors (SBRs);

5) Proposal of an energy and nutrients recovering wastewater treatment process for NRP wastewater

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CHAPTER 1 LITERATURE REVIEW

This chapter presented the following contents: Overview of the natural rubber processing industry; Characteristics of NRP wastewater; The situation of study and treatment of NRP wastewater in domestic and oversea; Wastewater treatment methods related to the thesis; Existing problems in NRP wastewater treatment in Vietnam; and Study orientation of the thesis

The review showed that the study and treatment of NRP wastewater have attracted great attention in past decades in the world and Vietnam as well, and achieved relatively good results However, previous studies have mainly focused on the treatment of organic matter in wastewater without paying attention to the treatment of nitrogen substances, as well as the recovery of energy and nutrients

CHAPTER 2 REMOVAL OF ORGANIC MATTER AND RECOVERY OF ENERGY BY EGSB REACTOR 2.1 Materials and research methodology

1) Materials, chemicals, and equipment

Wastewater: Simulated wastewater (wastewater prepared from coagulation process of natural rubber latex in the laboratory) was used for the start-up period of EGSB reactor Real NRP wastewater was used for further studies

Seed sludge: Anaerobic sludge from an UASB of Sai Gon - Me Linh Brewery was used as seed sludge

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Experimental equipment: An EGSB reactor with a reaction volume of 13.5 L and a height of 155 cm, divided into reaction zone (I) and settling zone (II) as shown in Figure 2.3 was used

1 Control box

2 Wastewater tank

3 Wastewater supply pump

4 Scum breaking pump

5 Circulating pump

6 EGSB reactor

7 Treated wastewater tank

8 Gas measuring device

I Reaction zone

II Setting zone

Figure 2.3 Experimental EGSB system

2) Research methodology

Experimental procedure

Wastewater from the wastewater tank (2) was pumped into the bottom of the EGSB reactor (6), flowed up through the sludge bed in the reaction zone (I), entered the settling zone (II), then flowed into the treated water tank (7) Volume of generated biogas from the reactor was measured by the gas meter (8) Experimental conditions

The EGSB reactor was started up with simulated wastewater (27 days) and real NRP wastewater (60 days) by a gradual increase in organic loading rate (OLR) After the steady state reached, effects of OLR in the range of 7 – 20 kg CODm-3d-1 on COD removal, biogas generation and the system stability were investigated using the real NRP wastewater

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2.2 Results and discussion

1) Development of anaerobic granular sludge

Figure 2.5 Anaerobic granules of EGSB reactor during start-up

period The EGSB reactor start-up was performed for 87 days to form anaerobic granules After 27 days of starting, anaerobic granules appeared, and particles with size of 0.5 - 1.0 mm accounted for 38.5% of activated sludge in the EGSB reactor After 87 days, the amount and size of anaerobic granules in EGSB reactor has increased significantly: at the lower part of the sludge layer, the particles with dimensions of 0.5 - 1.0 mm and 1.0 - 2.0 mm accounted for 45.5% and 35.4%, respectively; in the upper part of the sludge layer, these percentages were 62.6% and 18%, respectively The image of anaerobic granules on days

27 and 87 is shown in Figure 2.5

2) COD removal

COD removal efficiency of the EGSB reactor after start-up period is shown in Figure 2.8 The results show that COD treatment efficiency was quite stable in the experimental modes and tended to decrease in the first days after an increase of OLR, but quickly stabilized in each experimental mode (about 5 days)

In particular, when changing from mode (II) to mode (III) with a

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large increase in OLR (from 11.3 to 17.7 kg CODm-3d-1), COD removal efficiency dropped sharply, then gradually ascended but fairly slowly Sludge concentration in the EGSB reactor at this period was still not high, therefore the effect of OLR was very clear COD removal efficiency in the modes (I), (II), (IV) and (V) are all over 80%, and that at OLR 19 kg CODm-3d-1, was 82.5% Although this efficiency was lower than those at OLRs of 7.7 and 10.8 kg CODm-3d-1, it was also a relatively high

Figure 2.8 COD removal efficiency of EGSB reactor during

steady operation period

OLR (kg CODm -3d -1 ): (I) = 7.7; (II) = 11.3; (III) = 17.7; (IV) = 19.0; (V) = 10.8

3) Biogas generation yield

Figure 2.13 shows that generated biogas amount increased when OLR increased The average generated biogas amount at different OLR modes from (I) to (V) at standard conditions was 33,6, 44.5, 63.9, 76.6, and 44.2 L/day, respectively

The results in Figure 2.15 show that generated biogas amount at standard conditions was directly proportional to the amount of removed COD The average biogas conversion yield

0 20 40 60 80 100

Operation time, day

): (I) = 7.7; (II) = 11.3; (III) = 17.7; (IV) = 19.0; (V) = 10.8

Figure 2.15 The relationship between the generated biogas

amount and the amount of removed COD

y = 0.371x R² = 0.9174

Operation time, day

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CHAPTER 3 RECOVERY OF NUTRIENTS BY MAP

PRECIPITATION 3.1 Materials and research methodology

1) Materials, chemicals and equipment

Wastewater: Wastewater used in this study was the effluent of the EGSB reactor

Chemicals: MgCl26H2O and H3PO4 were used as additional magnesium and phosphate sources

Equipment: A Jar-Test was used for MAP precipitation

2) Research methodology

Experiments: MAP precipitation were performed at different pH values and Mg2+ : NH4+ : PO43- molar ratios of (molar ratios were changed by adding MgCl2 and H3PO4 solutions) After reaction, the reaction solution was let to settle and filtrated to obtain the precipitate P-PO43-, N-NH4+ and Mg2+ in the filtrate was analyzed

to determine treatment efficiency The precipitate was washed, dried, and used to determine MAP amount and composition of Mg,

N, and P elements in the MAP precipitate

Analysis: MAP crystal dimension was determined by SEM images MAP composition was determined through EDX spectrum analysis

3.2 Results and discussion

1) MAP recovery without magnesium addition

NRP wastewater, in addition to ammonium and phosphate, contains significant amounts of magnesium Therefore, increasing wastewater pH to the appropriate value can result in MAP precipitation by reaction (1.3)

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Mg2+ + NH4+ + HPO42- + 6H2O  MgNH4PO46H2O↓+ H+(1.3) The results in Table 3.2 show that phosphate-P removal increased from 15.6% at pH 7.5 to 44.7% at pH 9.5 and tended

to slightly increase as pH continued to increase to 11.5 On the other hand, ammonium-N removal increased from 3.6% at pH 7.5 to a maximum value of 13.1% at pH 9.5, and then gradually decreased to 5.0% as the pH continued to increase to 11

Table 3.2 P, N and Mg removal without magnesium addition

at different pH

pH

Concentration after MAP

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removal efficiency will decrease This result explains why the MAP precipitation optimally occurs at a certain pH range The initial molar ratio of Mg : PO43- in the wastewater was 0.46 : 1.0 (in MAP, it is 1.0 : 1.0), therefore, theoretically, the maximum phosphate-P removal via the MAP precipitation is 46% At pH 9.5, the removal efficiency of P-phosphate is 44.7%, rather high in comparison to theorical value

Figure 3.3 SEM image of MAP crystal

Figure 3.4 EDX spectrum of the MAP precipitate

In this study, suitable pH for MAP recovery was about 9 -

10 At this range, MAP precipitation was clearly observed MAP crystals were easy to settle and could be observed with the naked eyes, and had a large length of 300 - 383 µm The

70,6 µm

383 µm 328µm

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removal efficiencies of phosphate-P and ammonium-N at pH 9.5 were 44.7% and 13.1%, respectively At pH 11, beside MAP crystals with small size, hardly settable fine flocks also appeared (Fig 3.3)

EDX spectrum (Figure 3.4) and data of chemical composition show that: the mass percentages of the P, Mg and

O elements in MAP at pH 9.5 are 14.3%, 10.8% and 54.3%, respectively These percentages are similar to those in pure MAP At pH 11, beside the above main elements, there were many other elements such as C, Na, K and Ca in the MAP precipitate The mass percentages of P, Mg and O elements were 7.4%; 6.0% and 44.2%, respectively, quite lower than those in MAP obtained at pH 9.5

2) MAP recovery with magnesium addition

In NRP wastewater used in this study, the molar ratio of

Mg2+ : NH4+ : PO43- was 0.46 : 3.5 : 1.0, while this ratio in pure MAP is 1.0 : 1.0 : 1.0 Therefore, to improve the recovery of phosphate-P, addition of external magnesium source is required

Table 3.5 Effect of Mg2+: PO43- molar ratio on P and N removal

Mg2+ :

PO4

3-molar

ratio

Concentration after MAP

Concentration after MAP

PO43-–P NH4+–N Mg2+ PO43-–P NH4+–N Mg2+

Table 3.5 show that, removal efficiencies of phosphate-P and ammonium-N reached the best value of 93.3% and 28,4%, respectively, at the Mg2+ : PO43- molar ratio of 1.2 : 1.0

3) MAP recovery with addition of both magnesium and phosphate

MAP recovery efficiency

In order to increase the efficiency of N-ammonium removal and MAP recovery, it is necessary to add external sources of magnesium and phosphate

Table 3.7 Effect of Mg2+ : NH4+ : PO43- molar ratio on P and N

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The results in Table 3.7 show that the highest N-ammonium removal efficiency of 80.9% was obtained at Mg2+ : NH4+ : PO43-molar ratio of 1.4 : 1.0: 1.0 As a result, the optimal Mg2+ : NH4+ : PO43- molar ratio for the simultaneous removal of both N-ammonium and P-phosphate was 1.4 : 1.0 : 1.0

Analyzation of obtained MAP product

MAP sample obtained at pH = 9.5 and Mg2+ : NH4+ : PO43- molar ratio of 1.4 : 1.0 : 1.0 was taken for SEM and EDX analysises to evaluate the crystal size and composition of the MAP product The results show that the precipitate was clear crystals, and had white color mixed with dark brown color and many stains on its surface (Figure 3.12), possibly due to the organic components in wastewater and/or other precipitates formed during the MAP precipitation The mass composition of the P, Mg, O elements was 13.6%, 11.4%, 59.4% respectively This composition is nearly similar to that in pure MAP (12.6%, 9.9% and 65.3%) In addition, the precipitate also contained 11.2% C and other substances

Figure 3.12 MAP precipitate (a) and its SEM image (b)

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CHAPTER 4 SIMULTANEOUS REMOVAL OF

ORGANIC MATTER AND NITROGEN IN MODIFIED

SBRs 4.1 Materials and research methodology

1) Materials, chemicals, and equipment

Wastewater: Wastewater in this study was the effluent of the EGSB reactor

Seed sludge: Activated sludge from an oxic/anoxic biological tank of Hanoi Plastic Company was used as seed sludge

Equipment: Two similar modified SBRs with an effective volume and a working height of 15 liters and 1.34 m, respectively, were used (Figure 4.1)

1 Wastewater container

2 Wastewater supply pump

3 Wastewater supply pipe

I Oxic zone; II Anoxic zone

Figure 4.1 Modified SBR system

9 4 5

I I