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: 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 Reviewer 1: Reviewer 2: Reviewer 3: The thesis will be defended at the doctoral thesis committee at the Academy level, meeting at the Graduate University of Science and Technology - Vietnam Academy of Science and Technology at ………… on………, 20…… The thesis can be found in: - The library of Graduate University of Science and Technology - National Library of Vietnam INTRODUCTION 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 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 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 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 CHAPTER 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 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 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 Control box Wastewater tank I …… … … … … ……… …… … Wastewater supply pump II … … … … … … … 4 Scum breaking pump Circulating pump EGSB reactor Treated wastewater tank 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 – 20 kg CODm-3d-1 on COD removal, biogas generation and the system stability were investigated using the real NRP wastewater 2.2 Results and discussion 1) Development of anaerobic granular sludge On day 27 On day 87 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 days) In particular, when changing from mode (II) to mode (III) with a large increase in OLR (from 11.3 to 17.7 kg CODm-3d-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 CODm-3d-1, was 82.5% Although this efficiency was lower than those at OLRs of 7.7 and 10.8 kg CODm-3d-1, it was also a relatively high COD in effluent Efficiency 100 8000 80 I 6000 II III IV V 60 4000 40 2000 20 COD removal efficiency, % COD, mg/L COD in influent 10000 85 95 105 115 125 135 145 155 Operation time, day Figure 2.8 COD removal efficiency of EGSB reactor during steady operation period OLR (kg CODm-3d-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 at the standard conditions for all study modes was 0.37 L/kg removed COD OLR Amount of biogas 100 I III II IV IV 20 80 15 60 10 40 Generated biogas amount at standard condition, L/day OLR, kg CODm-3day-1 25 20 80 90 100 110 120 130 140 150 160 Operation time, day Figure 2.13 Generated biogas amount in the steady period Generated biogas amount at standard condition, L/day OLR (kg CODm-3d-1): (I) = 7.7; (II) = 11.3; (III) = 17.7; (IV) = 19.0; (V) = 10.8 100 80 60 40 y = 0.371x R² = 0.9174 20 50 100 150 200 Amount of removed COD, g COD/day 250 Figure 2.15 The relationship between the generated biogas amount and the amount of removed COD CHAPTER 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: MgCl26H2O 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) 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 383 µm 328µm 70,6 µm at pH 9,5 at pH 11 Figure 3.3 SEM image of MAP crystal at pH 11 at pH 9,5 Figure 3.4 EDX spectrum of the MAP precipitate In this study, suitable pH for MAP recovery was about 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 10 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 2+ Mg : 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+ : Concentration after MAP Removal efficiency (%) precipitation (mg/L) PO43molar PO43-–P NH4+–N Mg2+ PO43-–P NH4+–N Mg2+ ratio 0.6 : 65.3 185 3.2 53.7 16.7 95.1 0.8 : 34.2 173 3.3 75.7 22.1 96.3 1.0 : 15.6 163 2.8 88.9 26.6 97.4 1.2 : 9.4 159 2.5 93.3 28.4 98.1 1.4 : 9.2 161 3.4 93.5 27.5 97.8 11 Mg2+ : Concentration after MAP Removal efficiency (%) precipitation (mg/L) PO43molar PO43-–P NH4+–N Mg2+ PO43-–P NH4+–N Mg2+ ratio 1.6 : 9.1 174 3.6 93.5 21.6 97.9 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 removal efficiencies Mg2+ : NH4+ Concentration after MAP : PO43- molar precipitation (mg/L) ratio PO43-–P NH4+–N Mg2+ Removal efficiency (%) PO43-–P NH4+–N Mg2+ 0.6 : 1.0 : 1.0 214.0 154.3 8.2 56.5 30.5 96.4 0.8 : 1.0 : 1.0 117.0 138.6 9.6 76.2 37.6 96.8 1.0 : 1.0 : 1.0 36.5 106.5 11.3 92.6 52.0 97.0 1.2 : 1.0 : 1.0 27.4 61.2 13.2 94.4 72.4 97.1 1.4 : 1.0 : 1.0 19.6 42.4 15.6 96.0 80.9 97.1 1.6 : 1.0 : 1.0 15.2 56.4 22.7 96.9 74.6 96.3 1.8 : 1.0 : 1.0 14.3 97.1 28.4 97.1 56.3 95.9 12 The results in Table 3.7 show that the highest N-ammonium removal efficiency of 80.9% was obtained at Mg2+ : NH4+ : PO43molar ratio of 1.4 : 1.0: 1.0 As a result, the optimal Mg2+ : NH4+ : PO43- molar ratio for the simultaneous removal of both Nammonium 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+ : PO43molar 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 (b) (a) Figure 3.12 MAP precipitate (a) and its SEM image (b) 13 CHAPTER 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) Wastewater container Wastewater 10 Wastewater supply pump 3 Wastewater supply pipe Modified SBR Air Effluent I I Effluent tank Air blower Air flowmeter Air diffuser Automatic valve 10 Controller I Oxic zone; II Anoxic zone Figure 4.1 Modified SBR system 2) Research methodology Experimental procedure 14 Two modified sequencing batch reactors (SBRs), R1 and R2, specially configured to consist of both oxic and anoxic zones, and be operated with only a single simultaneous oxic/anoxic phase in each treatment batch were used R1 was operated with a constant aeration, by contrast, R2 was operated with an air flow varied from a lower rate in the early period of the reaction phase to a higher rate in the later period The operating strategy for the reactors was also modified to combine the drawing stage of the treated water from the previous batch and the filling stage for the new batch into the same phase The reactors was operated in a sequential three-step cycle mode (simultaneous drawing and filling; reacting; and setting) as shown in Table 4.1 Table 4.1 Operation mode of the modified SBRs Reactor Time for simultaneous drawing and filling, R1 Time of reaction phase, Air flow 0,4 L/min Air flow 2,0 L/min 145 55 90 10 R2 Setting time, 25 Experimental conditions Study on effects of OLR, ammonium-N loading rate (ANLR) and nitrogen loading rate (NLR) on the performance of R1 and R2 was performed in the OLR and NLR ranges of 0.52 – 1.61 kg CODm-3d-1 and 0.071 – 0.32 kg Nm-3d-1, respectively Study on effect of COD/TN ratio on the performance of the reactors was carried out in the COD/TN ratio range of 3.4 – 6.0 15 4.2 Results and discussion 1) Effect of OLR on the COD removal The results in Figure 4.4 show that both R1 and R2 almost reached steady state after only one week from the startup The average COD removal efficiencies of both R1 and R2 in all phases were quite stable and over 95% There was no significant difference in COD removal efficiency for both R1 and R2 Effluent COD_R1 Removal_R2 Effluent COD_R2 2500 100 2000 80 1500 60 1000 40 II I I 500 III I IV V 20 COD removal , % COD, mg/L Influent COD Removal_R1 0 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 Thời gian vận hành, ngày Figure 4.4 Effect of OLR on COD removal of R1 and R2 Effluent N-amoni_R2 Influent N-amoni 100 300 99 200 98 100 97 I II III IV V 96 Hiệu suất xử lý N-NH4+, % N-NH4+, mg/L effluent N-amoni_R1 400 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 Thời gian vận hành, ngày OLR (kg CODm-3d-1): I = 0.52, II = 0.73, III = 0.90, IV = 1.19, V = 1.61 Figure 4.7 Effect of NLR on ammonium removal of R1 and R2 NLR (kg Nm-3d-1): I = 0.071, II = 0.096, III = 0.16, IV = 0.21, V = 0.31 16 2) Effect of ANLR on the ammonium-N removal The results in Figure 4.7 show that the N-ammonium removal of both R1 and R2 became stable after only one week operation Ammonium removal efficiencies of R1 and R2 were almost the same, averagely over 99% Average effluent ammonium-N concentration was less than mg/L Efluent T-N_R1 Removal_R2 Efluent T-N_R2 500 100 400 80 300 60 200 II I 40 III III IV 100 T-N removal, % TN, mg/L Influent T-N Removal_R1 20 0 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 Operation time, day Figure 4.10 TN removal efficiency of modified SBRs in different phases NLR (kg Nm-3d-1): I = 0.071, II = 0.096, III = 0.16, IV = 0.21, V = 0.31 3) Effect of NLR on the TN removal Figure 4.10 shows that essential time for R1 and R2 to achieve stable TN removal was 30 and 21 days, respectively In the stationary period, the TN removal efficiency of R1 was quite high with an average of 88 - 92% in phases III – V R2 was able to achieve a steady state faster than R1 The removal efficiency of R2 was higher than that of R1, about 97% in phases III and IV, and 94% in phase V At the same NLR, the TN removal efficiency of R2 was always higher than that of R1 The TN concentration in the effluent of R2 was significantly lower than 17 that of R1, always less than 25 mg/L in all three experimental phases III - V, meanwhile, the TN concentration in the effluent of R1 fluctuated within the range of 15 - 50 mg/L 4) Effect of COD/TN ratio on COD removal The results in Figure 4.13 show that no significant differences in the COD removal efficiencies versus COD/TN ratio were observed The COD removal efficiencies of both 3000 100 2500 90 2000 80 COD Influent COD Effluent - R1 COD Effluent - R2 COD removal - R1 COD removal - R2 1500 1000 500 70 60 50 COD removal, % COD, mg/L reactors were similar, with an average of over 95% 40 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 COD/TN ratio Figure 4.13 Effect of COD/TN ratio on COD removal 5) Effect of COD/TN ratio on ammonium-N and TN removal The N-ammonium removal efficiencies of both reactors were over 99%, and N-ammonium concentration in the effluent was below mg/L (Fig 4.14) TN removal efficiencies of both reactors tended to increase when increasing in the COD/TN ratio These results are consistent with expectations, since a low COD/TN ratio leads to a shortage of organic substrates for denitrification, resulting in low TN removal (Figure 4.15) The mean TN removal efficiency 18 ... 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. .. 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. .. 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