Development of an appropriate treatment system for natural rubber industrial wastewater treatment

igh removal efficiency in this study could be related to long HRT. Many of researches reported that application of anaerobic treatment process to natural rubber processing wastewater [7]. The UASB reactor is most promising system for this wastewater; some laboratory scale UASB reactor achieved high organic removal efficiency together with high methane recovery rate [9] [42]. However, the pilot scale UASB reactor could be operated at low OLR condition due to influent containing high sulfate or residual natural rubber particulars [24][43]. Tanikawa et al. (2016) reported that the pilot scale UASB reactor treating natural rubber processing wastewater containing high sulfate performed 95.7 ± 1.3% of total COD removal efficiency with OLR of 0.8 kg-COD·m-3·day-1 in Thailand [24]. Also, the pilot scale UASB reactor treating natural rubber discharged from RSS manufacturing process performed 55.6 ± 16.6% for total COD removal efficiency and 77.8 ± 10.3% for BOD with OLR of 1.7 kg-COD·m-3·day-1 [43]. There are several limitations for application of UASB reactor to this wastewater and the UASB reactor was operated at low OLR. Thus, ABR which have different compartments could be a strong point for its application in treatment of natural rubber processing wastewater. The composition of biogas produced from ABR during phase 2 was 73.7 ± 5.1% of (A)20,000 P1 P2 P3 18,000 16,000 14,000 12,000 10,000 100 80 60 8,000 6,000 40 4,000 20 2,000 0 0 0 50 100 150 200 250 Time course (day) Inf. Eff. Removal effeciecny (B) 600 P1 P2 P3 500 100 400 80 300 60 200 40 100 20 0 0 0 50 100 150 200 250 Time course (day) Inf. Eff. Removal effeciecny Figure 3.10 Time course of (A) Total COD and (B) TSS concentrations through phase 1 to phase 3 methane, 23.8 ± 5.5% of carbon dioxide and 2.5 ± 2.4% of nitrogen. The maximum methane gas production of 29.8 NL·day-1 was observed on day 177. The methane recovery ratio based on removed total COD was 52.4 ± 33.6% during phase 2. The ABR performed good TSS removal of 91.0 ± 0.6% during phase 2. The accumulated natural rubber particulars were never removed from the ABR. These results suggested that the ABR trapped suspend solids from natural rubber processing wastewater and degraded it to soluble organics. The total COD, TSS and TN of effluent were 311 ± 218 mg·L-1, 27 ± 12 mg·L-1 and 460 ± 44 mg-N·L-1, respectively during phase 2. This result shows most of the organic compounds were removed in ABR. This result indicated that the ABR is considered as a novel applicable treatment system for this wastewater. However, it requires further post-treatment to achieve the industrial standards. After increasing OLR up to 2.1 ± 0.1 kg-COD·m-3·day-1, the process performance of ABR was deteriorated. The influent and effluent COD of ABR were 7,890 ± 680 mg-COD·L-1 and 1,840 ± 1,520 mg-COD·L-1, respectively during phase. At the end of experiment, the foam was observed on the water surface of the reactor. In addition, the COD removal efficiency and methane recovery ratio of ABR were significantly decreased to 50% and 20%, respectively. Therefore, the optimal OLR for this wastewater should be approximately 1.5 kg-COD·m-3·day-1 in this study. Figure 3.10 Time course of (A) Total COD and (B) TSS concentrations through phase 1 to phase 3 3.3.2 Determinates profiles inside the ABR The soluble COD, acetate and propionate concentrations in each ABR comportments on day 103 and day 199 were shown in Figure 3.11. The VFA concentration also decreased longitudinally down the reactor. The highest VFA concentration was found in the first compartment. Almost 80% of soluble COD were acetate and propionate in the compartments 1 to 3. The VFA values demonstrated that hydrolysis and acidogensis were the main biochemical activities occurring in the first few compartments. On the other hands, the soluble COD and acetate was removed in the compartment 3 to 5. In fact, most of biogas was produced from these compartments. Therefore, methanogen could be dominant in these compartments and its produced biogas. This result indicated that in an ABR different microorganisms develop in different compartments resulting in phase separation. After high OLR operation, acidification of wastewater occurred compartments 1 to 5. The highest soluble COD was observed 5th compartment. Watari et al. (2016) reported the concentrations of acetate and propionate were increased in the ABR treating natural rubber processing wastewater [9]. The soluble COD and VFA removal were observed in the 5th to 6th compartment in this day. At the compartment 7 to 8, acidification of wastewater was observed, again and acetate was accumulated in compartment 9 to 10. previous study reported that accumulation of acetate could be caused a foaming [44]. Thus, this acetate accumulation caused low COD removal efficiency and a forming in the ABR during high OLR operation. Figure 3.11 Soluble COD, acetate and propionate concentrations in ABR on (A) 103 day and (B) 199 day Development concept of a pilot scale UASB-DHS system experiment for treatment of natural rubber processing wastewater Process performance Table 3.3 lists the process performance of the treatment system during phases 1-4. The temperature was 29.6 ± 1.1˚C and the total COD and BOD removal efficiencies were 93.8 ± 3.7% and 93.3 ± 7.4%, respectively, during the entire experimental period (Figure 3.13). The ABR was installed to remove residual natural rubber particles from the influent. In this study, a part of the existing full-scale ABR was diverted as the pre- treatment of the pilot scale UASB reactor. Previous studies have reported that remaining rubber particles adversely affected the anaerobic biological treatment [6][7][9]. The RSS wastewater contained a total COD of 3,470 ± 760 mg·L-1, soluble COD of 3,210 ± 850 mg·L-1, total BOD of 2,650 ± 950 mg·L-1, and soluble BOD of 2,550 ± 860 mg·L-1. The concentrations of organics in RSS wastewater gradually increased with increasing natural rubber sheet production. The ABR achieved a 31.6 ± 15.6% of total COD and 40.5 ± 16.0% of soluble COD removal efficiency during the entire experiment. Similarly, total BOD and soluble BOD removal efficiencies of the ABR were 45.1 ± 14.5% and 50.7 ± 14.3%, respectively. The total COD and total BOD concentration of the ABR effluent were 2,540 ± 710 mg·L-1 and 1,600 ± 620 mg·L-1, respectively. In addition, TSS in the ABR influent and effluent were 200 ± 58 mg·L-1 and 166 ± 65 mg·L-1, resulting in a TSS removal efficiency of 18.7 ± 41.1%. These results indicate that ABR roughly removed organic compounds in the RSS wastewater. The UASB reactor achieved most of the organic removal and methane recovery in the system. During phase 1, the UASB reactor had a low total COD removal efficiency of 18.6 ± 17.0% likely due to the large amount of washed out sludge caused by the low settleability of seed sludge and high biogas production of 370 ± 250 L·day-1. However, soluble COD removal efficiency increased from 23.4 ± 15.4% to 63.3 ± 21.4% in phase 2. During phase 3, the UASB reactor demonstrated total COD and BOD removal efficiencies of 55.5 ± 16.1% and 77.8 ± 10.3% with OLR of 1.7 ± 0.6 kg-COD·m-3·day-1. The efficiencies were lower than our previous laboratory scale experiments and other anaerobic treatment systems treating natural rubber processing wastewater [8][7][9]. On the other hand, the UASB reactor achieved high soluble COD and BOD removal efficiencies of 70.2 ± 19.6% and 76.3 ± 7.5% during phase 3. During phase 4, OLR of the UASB reactor increased to 3.0 kg-COD·m-3·day-1. The total COD and soluble COD removal efficiencies of UASB decreased to 33.9 ± 19.4% and 57.4 ± 12.2% in phase 4. In addition, TSS of the UASB effluent significantly increased to 245 ± 70 mg·L-1. In summary, high OLR operation of the UASB reactor led to the retained sludge wash out and the performance of the UASB reactor deteriorated. In addition, the accumulation of natural rubber particular was frequently occurred in the supply pipe (Figure 3.12) and required further modification for remove natural rubber particulars. The composition of the biogas was 6.8 ± 10.1% nitrogen, 68.7 ± 10.9% methane, and 24.5 ± 5.5% carbon dioxide during phase 1, and 1.3 ± 0.7% nitrogen, 77.4 ± 1.9% methane, and 21.3 ± 1.7% carbon dioxide during phase 3. The average methane gas production of the UASB reactor in phases 1–4 was 250 ± 160 L·day-1, 202 ± 117 L·day-1, 323 ± 198 L·day-1, and 357 ± 234 L·day-1, respectively. Moreover, methane recovery ratio based on removed total COD were 32.7 ± 86.4%, 41.5 ± 29.3%, and 64.3 ± 71.6% for phase 1, phase 3, and phase 4, respectively (Table 3.4). During phase 2, a large amount of sludge wash-out was observed in the UASB reactor. Therefore, methane recovery ratio could not be calculated in this phase. Such low methane recovery rates in the other phases can be attributed to the large number of natural rubber particles accumulated in the UASB reactor. Thus, further modifications to the system are required to remove residual natural rubber particles by adding processes, such as chemical precipitation. A settling tank was installed for trapping washed out sludge and residual rubber particles from the UASB reactor. During phases 2 and 3, the ST efficiently removed total COD (76.0 ± 7.7% and 47.2 ± 18.1%, respectively). In addition, TSS removal efficiencies were 95.7 ± 1.8% and 60.4 ± 14.9% in phases 2 and 3, respectively. Therefore, the ST could be protected from the unexpected sludge washed out from the UASB reactor. The residual natural rubber particles floated to the surface of ST were removed once per month (data not shown). Thus, the UASB reactor should be equipped with an ‘excess sludge and rubber particle removal system’ in addition to a ST for treating natural rubber processing wastewater that contains a large amount of residual natural rubber particles. In addition, some soluble organic removal was observed in the ST during phase 3 and 4. The DHS reactor can serve as an effective post-treatment system for residual organic particles and TSS removal. In this study, the DHS reactor removed 83.5 ± 10.0% of total COD, 82.6 ± 11.2% of total BOD, and 73.5 ± 20.0% of TSS during the entire experiment. These organic removal efficiencies were higher than the post- treatment DHS reactor treating the ABR effluent [9]. DO level of the DHS effluent was only 0.5 ± 0.3 mg·L-1 in phase 1. After the effluent was recirculated to DHS, DO increased to 0.9 ± 0.5 mg·L-1 in the DHS effluent. BOD of the DHS effluent also increased to 30 ± 16 mg·L-1 in phase 2. Okubo et al. (2016) reported that the effluent recirculation improved the DO levels in the system, however, DO was consumed very quickly to degrade high concentration organics in the upper part of the reactor [45]. During phase 3, the organics concentration in the DHS effluent was 140 ± 64 mg·L-1 for total COD and 31 ± 12 mg·L-1 for total BOD, indicating that most of the biodegradable organic compounds were removed from the system. Thus, the DHS reactor can be used as an effective post-treatment process for treating this wastewater. Figure 3.12 Accumulation of rubber particular in feed pipe and photo of wastewaters. Table 3.3 Summary of the process parameters of the system during entire experimental period. Figure 3.13 Time course of (A) Total COD removal efficiency and organic loading rate of UASB reactor, (B) Total BOD removal efficiency. Table 3.4 Biogas production and compositions of the UASB reactor. 3.4.2 Nitrogen removal and greenhouse gas emissions Table 3.5 lists the concentrations of TN, ammonia, nitrate, and nitrite in the treatment system. The TN in the ABR influent and effluent were 184 ± 93 mg-N·L-1 and 155 ± 72 mg-N·L-1, respectively. On the other hand, ammonia concentrations of the ABR influent and effluent were 122 ± 49 mg-N·L-1 and 151 ± 70 mg-N·L-1, indicating that ammonia could be produced from organic nitrogen by anaerobic digestion. In addition, small amounts of nitrate detected in the ABR effluent suggested the occurrence of nitrification in ABR. According to Tanikawa et al. (2016a) [24] , ammonia was oxidized to nitrate at the surface of ABR and nitrous oxide was emitted to the atmosphere. In fact, 213 ppm of nitrous oxide was detected in the biogas collected from ABR on day 190 of this study. Nitrate reduction in the UASB reactor indicated the possibility of denitrification of wastewater in the UASB reactor. The concentrations of nitrous oxide in the biogas produced in UASB were 213 ppm, 72 ppm and 614 ppm on day 42, day 190 and day 264, respectively. The nitrous oxide production ratio from 1 m3 of treated RSS wastewater was 4.737 × 10-6 m3·m-3-w.w during phase 3. The maximum nitrous oxide concentration of 614 ppm was observed on day 264. The production rate equivalent to carbon dioxide for 1 m3 of treated RSS wastewater for nitrous oxide in this UASB reactor was calculated as 2.77 × 10-5 t-CO2 eq·m-3-w.w during phase 3. The DHS reactor was installed for the nitrification of wastewater as well as residual organics removal in this system. During phase 1, the DHS reactor demonstrated low TN and ammonia removal efficiencies of 38.8 ± 16.0% and 19.3 ± 5.8% (Figure 3.14). A small amount of nitrate production was also observed in the DHS reactor. However, TN and ammonia reduction suggested that nitrification occurred in the reactor and nitrification products were immediately utilized by denitrifying bacteria in the DHS reactor. Araki et al. (1999) and Machdar et al. (2000) reported that the inner section of the DHS sponge carrier is anaerobic [21][18]. Therefore, denitrification would be occurred to some degree in the DHS reactor. In addition, the low BOD concentration in the DHS effluent suggested that autotrophic bacteria could be in abundance in that reactor. Several studies reported the coexistence of anaerobic ammonia-oxidizing bacteria and heterotrophs in the DHS reactor [74-76]. During phase 2 through phase 4, the DHS effluent was recirculated back as DHS influent in order to enhance TN removal efficiency. The TN removal efficiency of the DHS reactor was increased to 52.9 ± 5.1% during phase 2. Ikeda et al. (2013) demonstrated that advantage of effluent recirculation up to 2.0 in the DHS reactor treating industrial wastewater containing a high concentration of organic and ammonia for enhancing denitrification [47]. The nitrification ratio (based on ammonia oxidization) of the DHS reactor also increased to 0.42 ± 0.03 kg-N·m-3·day- 1 during phase 4. This nitrification rate was greater than the same sponge-type DHS reactor treating sewage and natural rubber processing wastewater in other studies [19][48]. During phase 4, the TN removal efficiency of the DHS reactor was decreased to 35.9± 10.7% due to high nitrogen loading rate operation of 0.68 ± 0.22 kg-N·m-3·day-1. Nitrous oxide emissions from the DHS reactor were evaluated by a small closed cylinder with a sponge carrier that retained sludge. The biogas from the DHS reactor contained 99.2 % of nitrogen, 0.8% of carbon dioxide and 85.4 ppm of nitrous oxide on 190. The amount of the biogas from the DHS reactor was under the detection limit. Kampschreur et al. (2009) reported that low DO and low COD/N ratio were the most important operational parameters leading to nitrous oxide emissions [35]. Thus, the DHS reactor could emit nitrous oxide from nitrification and/or denitrification processes. Kampschreur et al. (2008) also reported that 0.6% of the nitrogen load was emitted as nitrous oxide in full-scale nitrifying and denitrifying sewage treatment plants [38]. According to this nitrous oxide emission ratio (0.6% of the nitrogen load), nitrous oxide emissions from the DHS reactor were calculated as 0.00026 t-CO2 eq·m-3 - w.w. during phase 3 [38]. Therefore, nitrous oxide emissions from the DHS reactor are an important parameter to consider when designing full- scale treatment systems. In total, the TN removal efficiency was 33.6 ± 17.7%, 51.3 ± 34.0%, 68.3 ± 15.1%, and 57.9 ± 7.0% in phases 1 to 4, respectively. However, ammonia and TN remained in the final effluent. Therefore, a system modification such as the addition of a denitrification tank or autotrophic nitrogen removal process is required. The emission ratios for 1 m3 of RSS wastewater treatment for ABR, UASB, and DHS were calculated as 0.0129 t-CO2eq·m-3, 0.0045 t-CO2eq·m-3 and 0.00026 t-CO2eq·m- 3, respectively. The UASB reactor can recover biogas as energy, thus GHGs emission ratio from the proposed system can be reduced to 0.013 t-CO2eq·m-3, corresponding to a 92% reduction of GHGs emissions compared with the existing open-type anaerobic treatment systems. However, pre-treatment ABR emitted most of the GHGs emissions in this study. Therefore, the development of effective closed type pretreatment systems is needed for further reductions in GHGs emissions. Table 3.5 Nitrogen concentrations (mg-N·L-1) in the proposed system. Phase Parameter Unit Influent ABT eff. UASB eff. ST eff. DHS eff. Phase 1 TN mg-N·L-1 150 ± 80 127±65 125±65 152±49 123±46 (R=0) Ammonia mg-N·L-1 118±16 88 ± 30 113 ± 41 88 ± 17 77 ± 29 Nitrate mg-N·L-1 1.8 ± 2.8 1.6 ± 2.0 1.0 ± 1.8 0.1±0.2 2.1±2.1 Nitrite mg-N·L-1 N.D N.D N.D. N.D N.D Phase 2 TN mg-N·L-1 143±19 120±22 126±61 84 ± 38 53 ± 39 (R=1) Ammonia mg-N·L-1 64 ± 36 69±58 99±48 60 ± 16 29±33 Nitrate mg-N·L-1 N.D N.D. N.D. N.D. N.D. Nitrite mg-N·L-1 N.D N.D. N.D. N.D. N.D. Phase 3 TN mg-N·L-1 202±54 156±50 175±54 165±63 58±24 (R=4) Ammonia mg-N·L-1 109±17 176±31 172 ± 29 153 ± 21 49±22 Nitrate mg-N·L-1 N.D. 4.0 ± 7.5 0.7 ± 0.6 0.9 ± 0.3 4.1±4.0 Nitrite mg-N·L-1 N.D. N.D. N.D. N.D. N.D Phase 4 TN mg-N·L-1 273±117 224±53 252±54 197±38 128±36 (R=4) Ammonia mg-N·L-1 171 ± 52 232 ± 44 224 ± 4.3 227 ± 17 133 ± 4.8 Nitrate mg-N·L-1 1.5 ± 1.4 0.3 ± 0.4 0.5 ± 0.6 0.2 ± 0.5 0.2 ± 0.5 Nitrite mg-N·L-1 N.D. N.D. N.D. N.D 0.1 ± 0.3 R: Recirculation ratio, N.D.: Not detected Figure 3.14 (A) Total nitrogen and (B) ammonia removal efficiency of total system and DHS reactor during phase 1 to phase 4. 3.4.3 Performance comparison of ABR-UASB-DHS system and existing treatment system The characteristics of natural rubber processing wastewater is different in the local factory and producing countries (Table 3.6). This difference composition of wastewater related to which acids used for the coagulation process of latex. Acetic acid, formic acid and sulfuric acid are normally used in the coagulation process in natural rubber factory [49]. The most natural rubber produced countries Thailand and Malaysia have been used sulfuric acid because of high oxidizing activity and low reagent costs. Therefore, wastewater in these countries did not contain a large number of residual rubber particles due to high oxidizing power of sulfuric acid, but it still had a large impact on aquatic environments. On the other hands, acetic acid and/or formic acid have been typically used for the coagulation process in Vietnamese local natural rubber processing factory, because they have a lower impact on the environment compared to sulfuric acid. However, the natural rubber processing wastewater from the Vietnamese factories contains a large quantity of residual rubber particles and these particles have a negative effect on the wastewater treatment processes reactor due to the accumulation of floating particles [7][9]. From this difference of wastewater composition, the wastewater treatment process is different between Vietnam and other natural rubber processing countries. Table 3.6 Characteristics of natural rubber processing wastewater in Thailand, Malaysia and Vietnam. Acetate and propionate are main organic compounds in the natural rubber processing wastewater in Vietnam. This organic compound is easy to covert to methane by acetate utilizing methanogen. Therefore, the natural rubber processing wastewater in Vietnam could be easy to degrade. However, the natural rubber particulars are remained in the wastewater and post-treatment for removing this particular to introduce wastewater treatment process is required. Nguyen (1999) firstly applied an UASB reactor for treating natural rubber processing wastewater in Vietnam [6]. Nevertheless, large amount of rubber particulars accumulated in the UASB column and the its process performance deteriorated. The high biodegradability of natural rubber processing wastewater in Vietnam after removed natural rubber particulars was reported by Watari et al. (2016) [9] and Thanh et al. (2016) [42]. The laboratory scale UASB reactor performed high methane recovery ratio of 93.3% calculated based on removed total COD [9]. Thus, the efficient process performance of natural rubber processing wastewater treatment process is necessary to develop effective rubber particular process. The natural rubber processing wastewater in Thailand and Malaysia contains sulfide acid. The sulfate-rich wastewater creates the onset of toxic H2S gas production in the wastewater holding ponds and wastewater treatment process. H2S gas production was carried out by the SRB, which could proliferate in wastewater containing sulfate and other sulfur compounds under aerobic composition. The activated sludge process and oxidation ditch process, could be carried out, the energy cost for air delivery systems has always discouraged the continual operation. In many cases, the systems were left an-aerated and turned to be aerobic pound which again cause H2S emission. Therefore, closed system such as anaerobic digester is an attractive treatment system. Tanikawa et al. (2017) designed two-stage UASB reactors that effectively utilized SRB by effluent recirculation and demonstrated COD removal efficiency of 95.7±1.3% at an OLR of 0.8 kg ·m-3·day-1 [15]. Previous studies on the process performance of existing treatment systems for natural rubber processing wastewater are summarized in Table 3.7. The combined ABR (HRT=3.4 day) - UASB (HRT=1.8 day) - ST (HRT=0.6 day) - DHS (HRT=0.5 day) system removed 94.8 ± 2.1% of total COD, 98.0 ± 0.9% of total BOD, 71.8 ± 22.6% of TSS, and 68.3 ± 15.1% of TN during phase 3. A combination of anaerobic and aerobic lagoons has also been widely used in Thailand, Vietnam, and Malaysia because of its low operational cost and easy maintenance [14][7][15]. Oxidation ditches were used for the treatment of the natural rubber processing wastewater due to their highly efficiency in removing nitrogen [14][7]. Tanikawa et al. (2017) reported that the process performance of full-scale DAF–anaerobic lagoon–anoxic lagoon–aerated tank system achieved the removal efficiencies of 89% for TSS, 98% for total COD, 91% for TN in South Vietnam [15]. Thus, the ABR-UASB-ST-DHS system developed in this study demonstrated similar removal efficiencies to existing treatment systems. Moreover, our system could reduce approximately 80% of HRT similar to the existing systems (e.g. existing anaerobic – aerobic lagoon need 1 month for treatment) [7]. The final effluent of our system met the required Vietnamese national technical regulation on effluent of the natural rubber processing industry-B except for the ammonia content (QCVN01: 2015/BTNMT, pH: 6-9, Total BOD: < 50 mg·L-1, Total COD: < 200 mg·L-1. TSS: < 100 mg·L-1, TN: < 60 mg-N·L-1, Ammonia: < 40 mg-N·L-1). Several current treatment systems exceed the effluent regulations in Vietnam [7]. Thus, an effective nitrogen removal process is required in both the proposed and existing systems. However, the pilot scale ABR-UASB-ST-DHS system demonstrated high potential for the treatment of natural rubber processing wastewater in Vietnam. Furthermore, the full-scale UASB-DHS system that will be developed based on the results obtained in the pilot scale system in this study and in previous studies will likely achieve a high process performance and energy recovery potential in the form of methane. 83 Table 3.7 Process performance of the existing treatment system for treating natural rubber processing wastewater. HRT Influent concenration (mg·L-1) Effluent concentration (mg·L-1) Removal effciency (%) System Country Wastewater days pH TCOD TBOD TSS TN Ammonia pH TCOD TBOD TSS TN Ammonia TCOD TBOD TSS TN Reference Decantation - UASB - aeration Vietnam CL + SVR - 9.2 18,885 10,780 900 611 342 6.8 123 57 70 35.3 30.8 99 99 92 94 Nguyen and Luong (2012) tank - settling and filiter Decantation - oxidation ditch - Vietnam CL - 9.1 26,914 8,750 740 766 361 8.4 567 50 74 160 137 98 99 90 79 Nguyen and Luong (2012) settling and filiter Decantation -oxidation ditch - Vietnam CL - 8.55 19,029 7,830 2,220 813 302 8.2 466 70 300 40.6 34.5 98 99 86 95 Nguyen and Luong (2012) settling and filiter Decantation -oxidation ditch - Vietnam CL + SVR - 8.23 14,466 9,200 850 450 350 7.4 107 92 60 65 47 99 99 93 86 Nguyen and Luong (2012) settling and filiter Decantation - flotation - oxidiation ditich - settling and Vietnam CL + SVR - 9.42 26,436 13,820 1,690 651 285 8.1 120 85 60 74.9 33 99.5 99 96 88 Nguyen and Luong (2012) filiter Decantation - flotation - UASB - aeration tank - settling and Vietnam CL - 8.09 13,981 7,590 468 972 686 7.9 127 61 39 129 30.3 99 99 92 87 Nguyen and Luong (2012) filiter Decantation -oxidation ditch - Vietnam CL + SVR - 8.59 11,935 8,780 1,164 1,306 1,043 6.6 130 60 94 67 50 99 99 92 95 Nguyen and Luong (2012) settling and filiter Dissolved air flotation - anaerobic lagoon - anoxic Vietnam CL + SVR - 5.37 5,610 - 867 372 341 7.8 136 - 98 33 13 98 - 89 91 Syutsubo et al. (2015) lagoon - aerated tank Dissolved air flotation - lagoon Vietnam CL + SVR - 6.34 5,350 - 357 394 154 7.8 128 - 70 41 27 98 - 80 90 Syutsubo et al. (2015) - aeration tank - aerated tank ABR - DHS Vietnam RSS 42 5.5 3,700 3,450 200 220 108 8.1 102 35 27 57 20 97 99 87 74 Watari et al. (2016b) ABR - Algal Tank Vietnam RSS 14.2 5.5 3,700 3,450 200 220 108 8.1 222 92 126 97 77 94 97 37 56 Watari et al. (2016b) ABR - UASB -DHS Vietnam RSS 2.0 5.3 8,430 - 1,470 420 200 7.6 120 - 36 220 100 99 - 98 48 Watari et al. (2016a) UASB Vietnam RSS 0.8 7.1 1,450 - 279 - - 7.4 102 - 72 - - 96 - 74 - Thanh et al. (2016) UASB Thailand CL 4 1.95 3,350 1,855 340 661 271 - - - - - - 60 - - - Boonsawang et al., (2008) UASB - UASB - DHS Thailand CL 11.5 5.5 9,710 8,670 1,780 1,370 - - - - - - - 96 - - - Tanikawa et al. (2016) Oxidation Ditch Process Malaysia CL - 7.16 2,675 1,871 3,645 231 17 7.1 56 22 1,313 36 0 98 99 64 84 Ibrahim et al. (1980) Stablilisation pond Malysia CL - - - - - - - - - - - - - 93 90 - - Madhu et al. (2007) ABR-UASB-ST-DHS Vietnam RSS 6.3 5.5 3,940 3,320 170 200 110 7.7 140 36 46 53 53 95 98 72 67 This study (during phase 3) Note: ABR: anaerobic baffled reactor, CL: Concentrated latex, DHS: down flow hanging sponge, RSS: Ribbed smoked sheet, ST: settling tank, SVR: standard Vietnamese rubber, UASB: upflow anaerobic sludge Design guideline for full scale UASB-DHS system for natural rubber processing wastewater in Vietnam From this research, the UASB-DHS system could be appropriate treatment system for natural rubber processing wastewater in Vietnam. In order to design full scale UASB – DHS system, some key factor (scale and cost) was calculated in the following section. A large-scale natural rubber processing factory surveyed (Section 3.1) is selected for designing the proposed treatment system. The factory daily produced 200 ton of latex and 30 ton of cup lump, respectively. The factory discharged 1,000 m3·day-1. The characteristic of wastewater used for this designing was showed in Table 3.8. Table 3.8 Water quality of natural rubber processing wastewater for simulation. Content Unit Concentration pH 5.6 Total COD mg-COD·L-1 6,430 Soluble COD mg-COD·L-1 6,020 TSS mg·L-1 650 VSS mg·L-1 250 TN mg·L-1 420 Acetate mg-COD·L-1 810 Propionate mg-COD·L-1 760 Design parameter for natural rubber processing wastewater Pre-treatment process for UASB reactor Previous study reported that the UASB reactor operated without any pre-treatment process was accumulated large amount of natural rubber particulars in the UASB column and finally the reactor was broken [6]. In addition, our pilot scale experiment happened large amount of sludge washed-out due to the wastewater containing large amount of rubber particulars. Therefore, pre-treatment process for UASB reactor treating this wastewater is necessary. Current local natural rubber processing factories have been widely used anaerobic lagoon and can be modified to baffled reactor with easy modification. Thus, modified anaerobic lagoon would be recommended to pre-treatment system for UASB reactor in this wastewater. In addition, pre-treatment anaerobic lagoon should be covered and collected biogas to reduce GHG emission. If the factory didn't have any wastewater treatment facility, DAF system would be recommended. The design parameter of pre-treatment anaerobic lagoon is (Design factor) Flow rate: 1,000 m3·day-1 Influent COD: 6,500 mg-COD·L-1 According to survey of OAS (in 3.1.1), large amount of solid COD was removed until compartment 5. Therefore, the volume of pre-treatment anaerobic lagoon was calculated by using HRT of first 5 compartments. Volume of one compartment = 6.3 m3 Volume of 5 compartments = 6.3 m3 × 5 = 31.5 m3 Flow rate of OAS: 110 m3·day-1 HRT of OAS until compartment 5: 31.5 m3 / 110 m3·day-1 = 8.65 hours From this calculation, number of compartments and HRT of pre-treatment ABR are 5 compartments. The pre-treatment ABR can be designed as follows Volume of ABR : 1,000 m3·day-1 / 8.65 hours = 2,780 m3 Number of compartments: 5 Volume of each compartment: 560 m3 The calculation of single compartment is w × l × h = 560 m3 (single compartment) w: wide (m) l: length (m) h: height (m) The upflow speed can be calculated by 83 m3/hour (flow rate) / l × w = 0.5 m·hour-1 The bottom area is l × w = 166 m2 The size of bottom area can be calculated by l= w = √116 = 13 m Height of ABR is h = 560 / 166 = 3.4 m In summary, the design of pre-treatment ABR was Wide: 13m, length: 13 m, depth: 3.4 m Number of compartments: 5 The pre-treatment ABR recommended to cover to collect biogas. UASB reactor The UASB reactor for treating natural rubber processing wastewater could be recommended to operate with OLR of 1.5 ~3.0 kg-COD·m-3·day-1 from this pilot scale experiment (3.4). Previous study mentioned the optimal upflow speed in UASB reactor was 0.5 m·hour-1 (van lier et al., 2015). Using this parameter, the UASB reactor for full scale treatment might be. (Design factor) · Influent of UASB reactor: 5,000 mg-COD·L-1 · Flow rate of UASB reactor: 1,000 m3·day-1 · HRT of UASB reactor: 24 hours · Upflow speed in UASB reactor: 0.5 m·hour-1 The calculation of UASB reactor is W × L × H = 1,000 m3 W: wide (m) L: Length (m) H: Hight (m) The bottom area can be calculated by W × L = 83 m3·hour-1/ 0.5 m·hour-1 = 166 m2 W and L can be calculated by W = L = √ 166 m2 = 13 m Hight of UASB reactor was H = 1,000 m3 / 166 m2 = 6m In summary, the design of UASB reactor was Wide = Length = 13 m, Hight = 6 m The UASB reactor should equipped GSS. DHS reactor According to the laboratory scale and pilot scale experiment, the HRT of DHS reactor was designed 4 hours together with effluent recirculation. The sponge volume of the DHS reactor can be calculated by following equation. V = Q/HRT = 250 m3 V: sponge volume (m3) Q: Flow rate (m3·day-1) HRT: hydridic retention time (hours) The sponge volume of 250 m3 DHS reactor will be more than 500 m3 of total volume. The expected height of DHS rector is more than 5 m, thus it could be considered to install several DHS reactors. Calculation of Energy consumption and generation for operation of UASB-DHS system Energy consumption of UASB-DHS system Tandukar et al. (2007) demonstrated that UASB-DHS system was cost effective compared with activated sludge process [22]. In addition, Tanikawa et al. (2016) reported that two stage UASB- DHS system treating natural rubber latex wastewater in Thailand can be reduced 95% of energy consumption [24]. The strong point of UASB-DHS system is electricity only required for pumping wastewater to UASB reactor. Therefore, electricity consumption can be calculated as below. The speciation of centrifugal pump is Flow rate: 1,000 m3·day-1 Lifting height: 6 m The centrifugal pump (GE-4M, Kawamoto pump) was selected for this calculation. The electricity consumption of this pump was estimated 7.5 kWh. In addition, pump for DHS recirculation is used. Therefore, the electricity consumption of this UASB- DHS system is 15.0 kWh. Energy production of UASB-DHS system The UASB reactor could be recovered energy in form as the methane. The energy recovery from UASB reactor was calculated flow as; Influent COD: 6,000 mg-COD·L-1 Influent flow rate: 1,000 m3·day-1 Estimated methane recovery ratio (based on influent total COD): 60% Estimated methane production (L-CH4·day-1) = 6,000 (mg-COD·L-1) × 1,000 (m3·day-1) × 60% / 2.857 (g-COD·L-CH4-1) = 1,260 (m3-CH4·day-1). The manual for installation of biomass plant published by Ministry of Environment, Japan mentioned gas power generation unit is 1.8 kWh· m3-CH4. The power generation from UASB reactor can be calculated flow as; The power generation from UASB reactor (kWh) = Methane gas production (1,260 m3-CH4·day-1) × (1.8 kWh·m3-CH4-1) = 2,268 (KWh·day-1). Compared with the electricity consumption and electricity generation, the UASB reactor could be generated approximately 2,000 KWh·day-1. This generated electricity is enough for operating a factory. Conclusions The water quality and greenhouse gas emission from the existing treatment system treating natural rubber processing wastewater in Vietnam was surveyed. The effluent from existing treatment was exceed the discharge standard. In addition, open-type anaerobic system emitted not only methane, but also nitrous oxide had high GWP. The final effluent of existing process was Total COD of 730 mg·L-1, TSS of 200 mg·L-1 and TN of 60 mg-N·L-1, respectively. The emission rates (flux) from 1 m3 of treated RSS wastewater for methane, nitrous oxide, and total GHGs by open-type anaerobic system were calculated as 0.054 t- CO2eq·m-3, 0.099 t- CO2eq·m-3, and 0.153 t-CO2eq·m-3, respectively. Laboratory scale UASB-DHS system and ABR system was demonstrated treatment of natural rubber processing wastewater. Both systems performed good process performance and were capable for treating natural rubber processing wastewater. The laboratory scale UASB reactor performed high-level total COD removal at 92.7 ± 2.3% with an OLR of 12.2 ± 6.2 kg-COD m−3 day−1 and 93.3 ± 19.3% methane recovery, corresponding to the influent and effluent COD concentration of 7,010 ± 1,430 mg-COD·L-1 and 530 ± 220 mg-COD·L-1, respectively. The laboratory scale ABR performed good process performance of 92.3 ± 0.3% COD removal efficiency with OLR of 1.4 ± 0.3 kg-COD·m-3·day-1 without pretreatment corresponding to the influent and effluent COD concentration of 3,420 ± 660 mg-COD·L-1 and 311 ± 218 mg-COD·L-1, respectively. Pilot scale UASB-DHS system was operated in an actual natural rubber processing factory. The system generated same effluent quality compared with current treatment system. Approximately 80% of hydraulic retention times can be reduced. The system could be significantly reduced GHGes emission. The proposed system could be an appropriate treatment system for treating natural rubber processing wastewater in Vietnam. The system achieved high organic removal efficiency together with energy recovery form as methane. The existing treatment system and proposed system need more effective nitrogen process for achieve the discharge standard. Recommendation for future study · In this research, energy-recovery type wastewater treatment system UASB-DHS system was applied to natural rubber processing wastewater in Vietnam. The key point for application of UASB reactor in natural rubber processing wastewater was combined with efficient pretreatment process. ABR system was used in this study, however, accumulation of natural rubber particular in the UASB column is always happed and leaded sludge washed-out. Therefore, effective pre-treatment process is need to researched. Moreover, the production process of natural rubber should be considered like acid and ammonia addition. · Our research and present researches often exceed discharge standard of ammonia and nitrogen contents. Effective nitrogen removal process should be researched for achieve the discharged standard. Moreover, autotrophic denitrification processes such anammox process would be applied to this wastewater in order to reduce operational cost for wastewater treatment. · This study investigated that current anaerobic treatment system emitted large amount of GHGes. Therefore, further study for emission principle and reduction methods should be studied. PUBLICATION LIST 1. D. Tanikawa, K. Syutsubo, T. Watari, Y. Miyaoka, M. Hatamoto, S. Iijima, M. Fukuda, N. B. Nguyen, T. Yamaguchi (2016), “Greenhouse gas emissions from open-type anaerobic wastewater treatment system in natural rubber processing factory”, Journal of Cleaner Production, Vol. 119, pp. 32–37 2. P. T. Tran, T. Watari, Y. Hirakata, T. T. Nguyen, M. Hatamoto, D. Tanikawa, K. Syutsubo, M. T. Nguyen, M. Fukuda, L. H. Nguyen, T. 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