Search

In this study, a two-stage down-flow hanging sponge (TSDHS) reactor was used as biotrickling filter for biogas desulfurization by utilizing the anaerobic digester supernatant (ADS) of sewage sludge of an activated sludge process (ASP). The reactor comprises a closed-type first-stage down-flow hanging sponge (1st DHS) and an open-type second-stage down-flow hanging sponge (2nd DHS) reactors. In the 1st DHS, hydrogen sulfide in biogas was dissolved into the ADS, and then it was oxidized into elemental sulfur and sulfate by microbe using dissolved oxygen and nitrite in the ADS. More than 99.9 % of hydrogen sulfide was removed within 400 s of empty bed residence time, and >50 % of removed hydrogen sulfide was oxidized into elemental sulfur and accumulated at the surface of the sponge carrier in the 1st DHS. The 1st DHS effluent was fed into the 2nd DHS for nitrogen removal via nitrification and sulfur-based denitrification with the recirculation of the 2nd DHS effluent under nonaeration condition. In the 2nd DHS, 36.8 % of ammonia and 5.3 % of total inorganic nitrogen were removed. Sulfurimonas and Halothiobacillus were increased and contributed to the sulfur-based denitrification as well as the accumulation of elemental sulfur in the 1st DHS, respectively. In the 2nd DHS, Nitrosococcus, Nitrobacter, and Sulfuritalea were considered as the contributors of nitrogen removal via nitrification and sulfur-based denitrification. Further, this study shows that a TSDHS reactor can achieve not only desulfurization of biogas in the 1st DHS but also a 3.5 %-15 % reduction of the ammonia load in the 2nd DHS by effective utilization of the ADS during sewage treatment, assuming that the ADS is returned to the ASP., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Current pretreatment methods for wastewater from natural rubber (NR) factories either have low rubber recovery efficiency or are costly to operate. A wastewater treatment system was developed that combines a pretreatment canal (PTC) seeded with rubber, an anaerobic baffled reactor (ABR), and a down-flow hanging sponge (DHS) reactor. The PTC is simple to implement and contributes to not only rubber recovery but also organic matter removal in the ABR and nitrogen removal in the DHS reactor. In experiments, the PTC recovered 16.6% of residual rubber through coagulation. The ABR increased the chemical oxygen demand removal efficiency and methane recovery compared with other anaerobic reactors treating raw NR wastewater. The DHS reactor removed 30.7% of total inorganic nitrogen (TIN) by nitrification, anaerobic ammonia oxidation and denitrification. Feeding the bottom stage of the DHS reactor with sodium acetate solution increased the TIN removal efficiency to 87.8%. The water quality of the final effluent achieved the Vietnamese standards for the NR industry. Microbial community analysis was performed to identify the dominant microorganisms and mechanisms in the PTC, ABR, and DHS reactor., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

In this study, a laboratory scale experiment for the treatment of synthetic molasses wastewater using a combination of an anaerobic baffled reactor (ABR) and a two-stage down-flow hanging sponge (TSDHS) reactor (ABR-TSDHS system) was conducted. The TSDHS comprised a closed-type first-stage down-flow hanging sponge (first DHS) for desulfurization and an open-type second-stage DHS (second DHS) for post-treatment of effluent from the ABR and first DHS. Effluent from the second DHS was sprinkled on top of the first DHS, whereas biogas produced from the ABR was supplied to its bottom. A chemical oxygen demand (COD) removal efficiency of 88.3% was found for the ABR-TSDHS system during the final treatment phase. The ABR achieved a maximum organic loading rate (OLR) of 3.70 kg COD/(m 3 day). Most of the organic matter was degraded in the first compartment of the ABR, with methane-producing archaea as its main consumer. The biogas generated by the ABR contained high concentrations of hydrogen sulfide (up to 4,500 ppm). In the TSDHS, the first DHS achieved 87.3% hydrogen sulfide removal via dissolution into sprinkled effluent water. Dissolved sulfide in the first DHS effluent was oxidized to sulfate in the second DHS in the absence of aeration. In addition, 85.0% of the ammonia and 57.7% of the total nitrogen were removed in the second DHS via biological reactions, including sulfur-based autotrophic denitrification. Therefore, the ABR-TSDHS system can be applied to not only molasses wastewater treatment but also the desulfurization of the produced biogas.

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., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

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-CO 2 eq/m 3 -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.

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., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

A novel gas-scrubbing bioreactor based on a downflow hanging sponge (DHS) reactor was developed as a new volatile organic compound (VOC) treatment system. In this study, the effects of varying the space velocity and gas/liquid ratio were investigated to assess the effectiveness of using toluene gas as a model VOC. Under optimal conditions, the toluene removal rate was greater than 80%, and the maximum elimination capacity was observed at approximately 13 g-C m -3  h -1 . The DHS reactor demonstrated slight pressure loss (20 Pa) and a high concentration of suspended solids (up to 30,000 mg/L-sponge). Cloning analysis of the 16S rRNA and functional genes of toluene degradation pathways (tmoA, todC, tbmD, xylA, and bssA) revealed that the clones belonging to the toluene-degrading bacterium Pseudomonas putida constituted the predominant species detected at the bottom of the DHS reactor. The toluene-degrading bacteria Pseudoxanthomonas spadix and Pseudomonas sp. were also detected by tmoA- and todC-targeted cloning analyses, respectively. These results demonstrate the potential for the industrial application of this novel DHS reactor for toluene gas treatment.

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., (Copyright © 2017. Published by Elsevier Ltd.)

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.

Natural rubber processing wastewater contains high concentrations of organic compounds, nitrogen, and other contaminants. In this study, a treatment system composed of a baffled reactor (BR), an upflow anaerobic sludge blanket (UASB) reactor, and a downflow hanging sponge (DHS) reactor was used to treat natural rubber processing wastewater in Vietnam. The BR showed good total suspended solids (TSS) removal of 47.6%, as well as acidification of wastewater. The UASB reactor achieved a high chemical oxygen demand (COD) removal efficiency of 92.7 ± 2.3% and energy recovery in the form of methane with an organic loading rate of 12.2 ± 6.6 kg-COD m -3  day -1 . The DHS reactor showed high performance in residual organic matter removal from UASB effluent. In total, the system achieved high-level total COD removal of 98.6% ± 1.2% and TSS removal of 98.0% ± 1.4%. Massive parallel 16S rRNA gene sequencing of the retained sludge in the UASB reactor showed the predominant microbial phyla to be Bacteroidetes, Firmicutes, Proteobacteria, WWE1, and Euryarchaeota. Uncultured bacteria belonging to the phylum Bacteroidetes and Phylum WWE1 were predominant in the UASB reactor. This microbial assemblage utilizes the organic compounds contained in natural rubber processing wastewater. In addition, the methane-producing archaea Methanosaeta sp. and Methanolinea sp. were detected.

In this study, granular sludge formation was carried out using an aluminum chloride supplement in an upflow anaerobic sludge blanket (UASB) reactor treating natural rubber processing wastewater. Results show that during the first 75 days after the start-up of the UASB reactor with an organic loading rate (OLR) of 2.65 kg-COD·m(-3)·day(-1), it performed stably with a removal of 90% of the total chemical oxygen demand (COD) and sludge still remained in small dispersed flocs. However, after aluminum chloride was added at a concentration of 300 mg·L(-1) and the OLR range was increased up to 5.32 kg-COD·m(-3)·day(-1), the total COD removal efficiency rose to 96.5 ± 2.6%, with a methane recovery rate of 84.9 ± 13.4%, and the flocs began to form granules. Massively parallel 16S rRNA gene sequencing of the sludge retained in the UASB reactor showed that total sequence reads of Methanosaeta sp. and Methanosarcina sp., reported to be the key organisms for granulation, increased after 311 days of operation. This indicates that the microbial community structure of the retained sludge in the UASB reactor at the end of the experiment gave a good account of itself in not only COD removal, but also granule formation.