Treatment of natural rubber processing wastewater using a combination system of a two-stage up-flow anaerobic sludge blanket and down-flow hanging sponge system

Enhancing Rubber Industry Wastewater Treatment through an Integrated AnMBR and A/O MBR System: Performance, Membrane Fouling Analysis, and Microbial Community Evolution

This study explores the effectiveness of an integrated anaerobic membrane bioreactor (AnMBR) coupled with an anoxic/oxic membrane bioreactor (A/O MBR) for the treatment of natural rubber industry wastewater with high sulfate, ammonia, and complex organic contents. This study was conducted at the lab-scale over a duration of 225 days to thoroughly investigate the efficiency and sustainability of the proposed treatment method. With a hydraulic retention time of 6 days for the total system, COD reductions were over 98%, which reduced the influent from 22,158 ± 2859 mg/L to 118 ± 74 mg/L of the effluent. The system demonstrates average NH3-N, TN, and total phosphorus (TP) removal efficiencies of 72.9 ± 5.7, 72.8 ± 5.6, and 71.3 ± 9.9, respectively. Despite an average whole biological system removal of 50.6%, the anaerobic reactor eliminated 44.9% of the raw WW sulfate. Analyses of membrane fouling revealed that organic fouling was more pronounced in the anaerobic membrane, whereas aerobic membrane fouling displayed varied profiles due to differential microbial and oxidative activities. Key bacterial genera, such as Desulfobacterota in the anaerobic stage and nitrifiers in the aerobic stage, are identified as instrumental in the biological processes. The microbial profile reveals a shift from methanogenesis to sulfide-driven autotrophic denitrification and sulfammox, with evidence of an active denitrification pathway in anaerobic/anoxic conditions. The system showcases its potential for industrial application, underpinning environmental sustainability through improved wastewater management.

Imperative assessment on the current status of rubber wastewater treatment: Research development and future perspectives

The environment has been significantly impacted by the rubber industry through the release of large quantities of wastewater during various industrial processes. Therefore, it is crucial to treat the wastewater from the rubber industry before discharging it into natural water bodies. With the understanding that alarmingly depleting freshwater sources need to be preserved for future generations, this paper reviews the status of the rubber industry and the pollution caused by them, focusing mainly on water pollution. The review pays special attention to the recent advancements in wastewater treatment techniques for rubber industry wastewater categorizing them into pre-treatment, secondary, and tertiary treatment processes while discussing the advantages and disadvantages. Through a comprehensive analysis of existing literature, it was determined that organic content and NH4+ are the most frequently focused water quality parameters, and despite some treatment methods demonstrating superior performance, many of the methods still face limitations and require further research to improve systems to handle high organic loading on the treatment systems and to implement them in industrial scale. The paper also explores the potential of utilizing untreated or treated wastewater and byproducts of wastewater treatment in contributing towards achieving several United Nations sustainable development goals (UN-SDGs); SDG 6, SDG 7, SDG 9, and SDG 12.

Investigate the anaerobic degradation of high-acetone latex wastewater with magnetite supplement

This study evaluated the effects of acetone on the anaerobic degradation of synthetic latex wastewater, which was simulated from the wastewater of the deproteinized natural rubber production process, including latex, acetate, propionate, and acetone as the main carbon sources, at a batch scale in 5 cycles of a total of 60 days. Fe3O4 was applied to accelerate the treatment performance from cycle 3. Acetone was added in concentration ranges of 0%, 0.05%, 0.1%, 0.15%-included latex, and 0.15%-free latex (w/v). In the Fe3O4-free cycles, for latex-added vials, soluble chemical oxygen demand (sCOD) was removed at 43.20%, 43.20%, and 12.65%, corresponding to the input acetone concentrations varying from 0.05% to 0.15%, indicating the interference of acetone for COD reduction. After adding Fe3O4, all flasks reported a significant increase in COD removal efficiency, especially for acetone-only and latex-only vials, from 36.9% to 14.30%-42.95% and 83.20%, respectively. Other highlighted results of COD balance showed that Fe3O4 involvement improved the degradation process of acetate, propionate, acetone, and the other COD parts, including the intermediate products of latex reduction. Besides, during the whole batch process, the order of reduction priority of the carbon sources in the synthetic wastewater was acetate, propionate and acetone. We also found that the acetate concentration appeared to be strongly related to reducing other carbon sources in natural rubber wastewater. Microbial community analysis revealed that protein-degrading bacteria Bacteroidetes vadinHA17 and Proteinniphilum and methylotrophic methanogens might play key roles in treating simulated deproteinized-natural-rubber wastewater.

Development of a post-treatment system using a downflow hanging sponge reactor - an upflow anaerobic reactor for natural rubber processing wastewater treatment

This study aimed to evaluate the nitrogen removal of a post-treatment system for natural rubber processing wastewater (NRPW) under low chemical oxygen demand to total nitrogen (COD/TN) ratios without any supplemental external carbon source. The system including a downflow hanging sponge (DHS) reactor and an upflow anaerobic reactor (UAR) was operated in two phases. In phase 1 (day 0-102), under a nitrogen loading rate (NLR) of 0.23 ± 0.06 kgN m^-3 d^-1 and COD/TN ratio of 0.63 ± 0.47, the DHS-UAR system removed 82.5 ± 11.8% and 83.9 ± 7.6% of TN and ammonium concentrations, respectively. In phase 2 (day 103-229), higher COD/TN ratio of 1.96 ± 0.28 was applied to remove increasing NLRs. At the highest NLR of 0.51 kgN m^-3 d^-1, the system achieved TN and ammonium removal efficiencies of 93.2% and 93.7%, respectively. Nitrogen profiles and the 16S rRNA high-throughput sequencing data suggested that ammonium, a major nitrogen compound in NRPW, was utilized by nitrifying and ammonium assimilation bacteria in DHS, then removed by heterotrophic denitrifying and anammox bacteria in the UAR. The predominance of Acinetobacter detected in both reactors suggested its essential role for the nitrogen conversion.

Full-scale application of a down-flow hanging sponge reactor combined with a primary sedimentation basin for domestic sewage treatment

The down-flow hanging sponge (DHS) reactor is advantageous for sewage treatment since it produces an effluent quality that complies with the standards for reuse and there is little excess sludge. A full-scale DHS module was efficiently employed for the treatment of domestic sewage (200 m³ day^-1) flowing from a primary sedimentation basin (PSB), which was used to reduce the suspended solids loading rate and enhance the oxidation of organics by heterotrophs. The combined PSB-DHS was successfully operated at a total hydraulic retention time of 3.4 h (2.4 h for PSB and 1.0 h for DHS) for the relatively long period of 600 days at sewage temperatures of 10 °C to 32 °C. The PSB-DHS consistently produced an effluent quality with minimum values of chemical oxygen demand, biochemical oxygen demand, and suspended solids of 59 ± 15, 12 ± 3.0, and 15 ± 7 mg L^-1, respectively. The proposed system performed exceptionally well at removing organics and particulate matter over a short hydraulic retention time.

Two-stage anaerobic process benefits removal for azo dye orange II with starch as primary co-substrate

Two-stage anaerobic system (S1: R1 (acidogenic phase) + R2 (methanogenic phase)) and the one-stage control (S0) were established to investigate the effect of phase separation on the removal of an azo dye orange II, i.e., Acid Orange 7 (AO7), with starch as the primary co-substrate. Although final AO7 removal from two systems showed no statistical differences, the first-order rate constants for AO7 removal (k_AO7-) and sulfanilic acid (SA) formation (k_SA) were higher in S1. Kinetic analysis showed that k_AO7- and k_SA in S1 were 2.7-fold and 1.7-fold of those in S0, respectively, indicating the benefit of phase separation to the AO7 reduction. However, this benefit only appeared in the period with influent AO7 concentrations higher than 2.14 mM. Otherwise, this advantage would be hidden due to the longer HRT (5 d) and sufficient electron donor (1.0 g starch L^-1). Within S1, R1 only contributed about 10% of the entire AO7 removal, and k_AO7- in R1 (0.172 h^-1) was much lower than in R2 (0.503 h^-1). The methanogenic phase rather than acidogenic phase was the main contribution to AO7 removal, because the influent of R2 had more available electron donors and suitable pH condition (pH 6.5-7.0) for the bio-reduction process.

Non-aerated single-stage nitrogen removal using a down-flow hanging sponge reactor as post-treatment for nitrogen-rich wastewater treatment

A laboratory-scale experiment is conducted to remove nitrogen from nitrogen-rich wastewater using a down-flow hanging sponge (DHS) reactor. Effluent from an anaerobic-aerobic system for treating synthetic natural rubber wastewater, which still contains high levels of ammonia, was used as nitrogen-rich wastewater. Experimental period was divided into four phases based whether a carbon source was fed to the DHS reactor. The highest nitrogen removal efficiency (59.5 ± 5.4%) was achieved during phase 4, when a sodium acetate solution was fed into bottom section of the DHS reactor. In the DHS reactor, the nitrification occurred in the upper and middle sections. Then, after adding the sodium acetate solution, denitrification occurred. The final chemical oxygen demand, ammonia, and total inorganic nitrogen concentrations in the DHS reactor effluent were 37 ± 24 mg/L, 34 ± 5 mgN/L, and 42 ± 8 mgN/L, respectively. These concentrations were sufficient to meet the effluent standards of the Vietnamese natural rubber industry, which are the strictest in South-East Asia. The dominant bacteria in the sludge retained by the reactor's sponge media were the nitrifying bacteria Nitrosovibrio (0.2%) and Nitrospira (0.2-0.3%), the denitrifying bacteria Hylemonella (1.0-13.7%), Pseudoxanthomonas (1.2-2.1%), and Amaricoccus (2.4-3.5%), and the anammox bacterium Candidatus Brocadia (0.1-0.2%). Significant amounts of the nitrogen-fixing bacterium Xanthobacter (11.2-14.8%) and the rubber-degrading bacterium Gordonia (11.0-28.6%) were also found in the DHS reactor. These bacteria were thus considered to be the key microbes for nitrogen removal in a DHS reactor fed with a carbon source for denitrification.

Characteristics of greenhouse gas emissions from an anaerobic wastewater treatment system in a natural rubber processing factory

Greenhouse gas (GHG) emissions from both open-type and closed anaerobic wastewater treatment systems in a natural rubber processing factory in Vietnam were surveyed. In this factory, wastewater was treated by an open-type anaerobic baffled reactor (OABR) that comprised 60 compartments. A part of the wastewater was fed to a pilot-scale up-flow anaerobic sludge blanket (UASB) reactor to enable a comparison of the process performance and GHG emission characteristics with those of the OABR. In the OABR, 94.4% of the total chemical oxygen demand (COD) and 18.1% of ammonia nitrogen was removed. GHGs emitted from the OABR included both methane and nitrous oxide. The total GHGs emitted from the OABR was 0.153 t-CO₂eq/m³-wastewater. Nitrous oxide accounted for approximately 65% of the total GHGs emitted from the OABR. By contrast, 99.6% of the methane emission and 99.9% of nitrous oxide emission were reduced by application of the UASB. However, the ammonia removal efficiency of the UASB was only 2.2%. Furthermore, Acinetobacter johnsonii, which is known as a heterotrophic ammonia remover, was detected only in the OABR. These results indicated that high nitrous oxide emissions were caused by denitrification in the OABR and that application of the closed anaerobic system could drastically reduce the emissions of both methane and nitrous oxide.

Characterization of downflow hanging sponge reactors with regard to structure, process function, and microbial community compositions

The activated sludge (AS) process has been the most widely used process for wastewater treatment despite it has several limitations for its further application and adoption worldwide, owing to unsustainable properties such as high-energy consumption and the production of large amount of excess sludge. To overcome the drawbacks of the AS process, the downflow hanging sponge (DHS) has been developed as an energy-saving and easy-to-maintain alternative. To date, six types of different sponge configurations have been developed and their performances have been evaluated in practical- to full-scale DHS reactors. A large number of studies have been carried out in order to enhance the performance and expand the application fields of the DHS. Transition of this process to the deployment and diffusion stage from the research and development phase is now ongoing in India and Egypt as well as in Japan. Under this situation, concise and state-of-the art review is important for enhancing DHS research and future applications. Herein, we summarize and present the DHS concerning the history of development, the mechanism of treatment, recent studies on its use in the field of wastewater treatment, and the features of microbial community structure.

High-rate anaerobic treatment system for solid/lipid-rich wastewater using anaerobic baffled reactor with scum recovery

A laboratory scale experiment was conducted to investigate the treatment of solid/lipid-rich wastewater with an anaerobic baffled reactor (ABR) and a down-flow hanging sponge (DHS) reactor. In this study, experimental periods were divided into three phases to explore efficient treatment of solids and lipids in wastewater. In ABR, >90% of the influent chemical oxygen demand (COD) was removed and >70% of the removed COD was converted to methane under steady-state conditions during each phase. During this period, >4.5 kg COD m^-3 d^-1 was achieved on an average in Phases 1 and 3. Biogas contributed to scum formation, and the scum was categorized into lipid-rich and sludge-containing types, which have energy potentials of 53.4 and 212 kcal/kg-wet weight, respectively. Therefore, by recovering solids and lipids, which formed persistent scum, ABR can be applied as a high-rate treatment for solid/lipid-rich wastewater.

Performance evaluation of the pilot scale upflow anaerobic sludge blanket - Downflow hanging sponge system for natural rubber processing wastewater treatment in South Vietnam

A pilot-scale upflow anaerobic sludge blanket (UASB)-downflow hanging sponge system (DHS) combined with an anaerobic baffled reactor (ABR) and a settling tank (ST) was installed in a natural rubber processing factory in South Vietnam and its process performance was evaluated for 267days. The UASB reactor achieved a total removal efficiency of 55.6±16.6% for chemical oxygen demand (COD) and 77.8±10.3% for biochemical oxygen demand (BOD) with an organic loading rate of 1.7±0.6kg-COD·m^-3·day^-1. The final effluent of the proposed system had 140±64mg·L^-1 of total COD, 31±12mg·L^-1 of total BOD, and 58±24mg-N·L^-1 of total nitrogen. The system could significantly reduce 92% of greenhouse gas emissions and 80% of hydraulic retention times compared with current treatment systems.

Development of downflow hanging sponge (DHS) reactor as post treatment of existing combined anaerobic tank treating natural rubber processing wastewater

Conventional aerated tank technology is widely applied for post treatment of natural rubber processing wastewater in Southeast Asia; however, a long hydraulic retention time (HRT) is required and the effluent standards are exceeded. In this study, a downflow hanging sponge (DHS) reactor was installed as post treatment of anaerobic tank effluent in a natural rubber factory in South Vietnam and the process performance was evaluated. The DHS reactor demonstrated removal efficiencies of 64.2 ± 7.5% and 55.3 ± 19.2% for total chemical oxygen demand (COD) and total nitrogen, respectively, with an organic loading rate of 0.97 ± 0.03 kg-COD m^-3 day^-1 and a nitrogen loading rate of 0.57 ± 0.21 kg-N m^-3 day^-1. 16S rRNA gene sequencing analysis of the sludge retained in the DHS also corresponded to the result of reactor performance, and both nitrifying and denitrifying bacteria were detected in the sponge carrier. In addition, anammox bacteria was found in the retained sludge. The DHS reactor reduced the HRT of 30 days to 4.8 h compared with the existing algal tank. This result indicates that the DHS reactor could be an appropriate post treatment for the existing anaerobic tank for natural rubber processing wastewater treatment.