Takahiro Watari

Development of a BR–UASB–DHS system 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.

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.

Impact of aluminum chloride on process performance and microbial community structure of granular sludge in an upflow anaerobic sludge blanket reactor for natural rubber processing wastewater treatment

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.

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.

Fouling Development in A/O-MBR under Low Organic Loading Condition and Identification of Key Bacteria for Biofilm Formations

Membrane fouling in membrane bioreactors (MBR) remains a major issue and knowledge of microbes associated with biofilm formation might facilitate the control of this phenomenon, Thus, an anoxic/oxic membrane bioreactor (A/O-MBR) was operated under an extremely low organic loading rate (0.002 kg-COD·m−3·day−1) to induce membrane fouling and the major biofilm-forming bacteria were identified. After operation under extremely low organic loading condition, the reactor showed accumulation of total nitrogen and phosphorus along with biofilm development on the membrane surface. Thus, membrane fouling induced by microbial cell lysis was considered to have occurred. Although no major changes were observed in the microbial community structure of the activated sludge in the MBR before and after membrane fouling, uncultured bacteria were specifically increased in the biofilm. Therefore, bacteria belonging to candidate phyla including TM6, OD1 and Gammaproteobacteria could be important biofilm-forming bacteria.

Adsorption of color from dye wastewater effluent of a down-flow hanging sponge reactor on purified coconut fibre

ABSTRACT This study was carried out to evaluate the potential application of agricultural waste coconut (Cocos nucifera) fibre in its purified form for decolorization of dye-containing effluent from a down-flow hanging sponge (DHS) reactor. Batch adsorption experiments were conducted by varying adsorbent dose, solution pH, contact time and temperature. The results showed that the adsorption percentage of colour increased with increasing in adsorbent dosage from 0.1 g to 1.3 g, solution pH from 2 to 10 and contact time from 1 h to 72 h. The adsorption process was sensitive to temperature and the adsorption percentage of colour reached the highest value at 30°C but decreased when temperature increased from 30°C to 60°C. Purified coconut fibre (PCF) had a good adsorption capacity under the optimal conditions of an adsorbent dose of 0.7 g, pH 8, temperature of 30°C and 24 h contact time. The equilibrium data were well fitted to both Langmuir and Freundlich isotherms, and the best fit of equilibrium isotherms was described using the Freundlich isotherm model. The Langmuir maximum adsorption capability of the PCF was found to be 303 (Pt/Co)/g at 30°C. The results of this study indicated the applicability of PCF as post-treatment unit of DHS reactor for removal of colour in the industrial dye effluent. GRAPHICAL ABSTRACT

Process Performance and Microbial Community Structure of an Anaerobic Baffled Reactor for Natural Rubber Processing Wastewater Treatment

Natural rubber processing wastewater contains high concentration of organic compounds mainly acids and ammonia. This wastewater also contains large amount of residual rubber particles. In this study, a laboratory-scale experiment was conducted to evaluate process performance of anaerobic baffled reactor (ABR) treating this wastewater. In addition, microbial community structure in different compartments of ABR was characterized. The highest COD removal efficiency of 92.3 ± 6.3% was observed when operated under organic loading rate of 1.4 ± 0.3 kg-COD·m−3·day−1. Maximum methane gas production of 29.8 NL·day−1 was observed on day 177. Massively parallel next generation sequencing showed the difference of acetogen community could be caused by the difference in pH of these compartments. Acetate utilizing methanogen Methanosaeta was predominantly detected in the 3rd and 4th compartments with abundance of 9.8% to 16.4%. This result indicated that the ABR is considered as a novel applicable treatment system for this wastewater.

Application of DHS-USB System and Ozone in Recirculating Freshwater Aquaria Towards Zero Water Exchange Aquaria

In recirculating aquaria system (RAS), partial water exchange was performed regularly as a part of aquaria maintenance for maintaining water quality and aesthetic beauty. To reduce large consumption of water during maintenance, this study proposed a biological nitrogen removal system consisted of down-flow hanging sponge (DHS) and an up-flow sludge blanket (USB) system with combination of ozone (O3) to simultaneously maintain nitrogen compounds concentration and remove yellow substances that implicate color in aquaria without performing water exchange. The performance of the system was evaluated using on site freshwater aquaria at ambient temperature (20–34 °C). NH3, \( {\text{NO}}_{2}^{ - } \), and \( {\text{NO}}_{3}^{ - } \) concentration detected was 0.10 ± 0.12, 0.03 ± 0.13 and 6.40 ± 7.46 mg N L−1 respectively. Color were maintained at 6 color units at phase 2 and 4 when O3 was applied continuously for 8 h per day. In addition, 16S rRNA gene of microorganisms from the bioreactors were sequenced to identify the microbial communities present. The analysis revealed that ammonia oxidizing archaea (AOA) such as Ca. Nitrososphaera played important role in nitrification and Thauera played important role in denitrification. Fish survived throughout the study despite no water exchange was performed for 425 days. The application of O3 in combination with DHS-USB system appeared to be a promising technology towards less-maintenance aquaria.