PENGGUNAAN BIOFILTER ANAEROB UNTUK MENURUNKAN KADAR PENCEMAR ORGANIK PADA LIMBAH CAIR INDUSTRI TAHU

Limbah cair industri tahu mengandung zat organik yang tinggi seperti BOD5 dan COD sehingga perlu adanya pengolahan sebelum dibuang ke lingkungan. Salah satu alternatif pengolahan yaitu menggunakan sistem biofilter anaerob. Penelitian ini bersifat eksperimental yang bertujuan untuk mengetahui penurunan kadar BOD5 dan COD pada limbah cair industri tahu menggunakan sistem biofilter anaerob. Reaktor yang digunakan terdiri dari 2 buah reaktor dan terbuat dari kaca dengan ketebalan 10 mm. Reaktor pertama bervolume 0,081 m3 yang diisi dengan media batu kerikil setinggi 70 cm dan reaktor kedua bervolume 0,059 m3 diisi dengan media bioball rambutan setinggi 45 cm. Limbah cair industri tahu dialirkan ke dalam reaktor biofilter anaerob secara kontinyu dengan arah aliran down flow. Parameter yang diukur yaitu kadar BOD5 dan COD pada inlet maupun outlet reaktor biofilter anaerob. Reaktor 1 bermedia batu kerikil mampu menyisihkan kadar BOD5 dengan penyisihan tertinggi terjadi pada waktu operasi hari ke-4 yaitu sebesar 943,8 mg/L dan penyisihan kadar COD tertinggi pada waktu operasi hari ke-4 yaitu sebesar 1931,2 mg/L. Sedangkan pada reaktor 2 bermedia bioball rambutan mampu menyisihkan kadar BOD5 dengan penyisihan tertinggi terjadi pada waktu operasi hari ke-4 yaitu sebesar 936,7 mg/L dan penyisihan kadar COD tertinggi pada waktu operasi hari ke-4 yaitu sebesar 1856,6 mg/L. Kata Kunci : batu kerikil, bioball rambutan, biofilter anaerob, limbah tahu. Tofu industrial liquid waste contains high organic matter such as BOD5 and COD so it needs processing before being discharged into the environment. One of alternative processing is using an anaerobic biofilter system. This study is experimental which aims to determine the decrease of BOD5 and COD levels in tofu wastewater using anaerobic biofilter system. The reactor consist is 2 reactors and is made of glass with a thickness of 10 mm. The first reactor with a volume of 0.081 m3 was filled with 70 cm of gravel media and a second reactor with a volume of 0.059 m3 filled with 45 cm of rambutan bioball media. Tofu industrial liquid waste is flowed into the anaerobic biofilter reactor continuously with down flow direction. Parameters measured were BOD5 and COD levels at the anaerobic biofilter reactor inlet and outlet. The highest removal of BOD5 levels in reactor 1 with gravel media occurred on the 4th day of operation with a allowance of 943.8 mg/L and the highest removal of COD levels at the 4th day of operation was 1931.2 mg/L. Whereas the highest removal of BOD5 levels in reactor 2 with rambutan bioball media occurred on the 4th day of operation with a allowance of 936.7 mg/L and the highest removal of COD levels at the 4th day of operation with a allowance of 1856.6 mg/L. Keywords: anaerobic biofilter, gravel stone, rambutan bioball, tofu waste.

Vapor-phase oxidation of propylene glycol-methanol mixture to methyl lactate on CeO2/Al2O3 catalyst

The vapor-phase oxidation of mixtures of propylene glycol with methanol and ethanol to methyl and ethyl lactate, respectively, on supported CeO2/Al2O3 catalyst with 10 wt.% CeO2 content was studied. The steel flow reactor with a fixed catalyst bed (4 cm3) was used. 20 wt.% solution of propylene glycol in alcohol was fed to the reactor inlet by Waters 950 pump at LHSV= 0.5-0.8 h-1. Reaction temperature and pressure were varied in the interval of 190-250 0C and 1.3-1.8 bars respectively. Compressed air was given to the reactor inlet at the molar ratio of propylene glycol/O2 = 1. The reaction products were analyzed using gas chromatography (Agilent 7820A) and 3C NMR (Bruker Avance 400) methods. Studied oxidation of propylene glycol in the presence of methanol describes by total reaction CH3CHOHCH2OH +O2 + СН3OH = CH3CHOHCOOСН3 +2H2O At first, hydroxyacetone is formed that is further oxidized to pyruvic aldehyde, which attaches alcohol to form hemiacetal. Then, hemiacetal of methyl glyoxal rearranges into methyl lactate by Cannizzaro. At 220 0C and load on a catalyst of < 2 mmol PG/gcat/h, the selectivity towards methyl lactate reaches 70 wt.% at 100 % propylene glycol conversion. The main by-products are formed as the result of acetaldehyde transformation. Acetaldehyde could be formed at hydroxyacetone aldol decondensation. In the presence of ethanol, the formation of a significant amount of acetaldehyde and its aldol condensation products as well as the formation of diethoxyethane are observed. Therefore, ethyl lactate selectivity at 100 % propylene glycol conversion does not exceed 45 %. Supported CeO2/SiO2 contact was tested in this oxidation reaction also. However, CeO2/SiO2 provides the low, up to 25%, selectivity towards methyl lactate at full propylene glycol conversion. It was shown that at the same conditions methyl lactate is formed with higher selectivity then ethyl lactate. The high methyl lactate yield up to 70 wt.% could be obtained via vapor-phase oxidation of 20% mixture of propylene glycol with methanol by air oxygen on supported CeO2/Al2O3 catalyst at 210 - 220°С and at time contact of 3-4 seconds.

Flow-Excited Acoustic Resonance Vibration Mitigation of Reactor Inlet Piping by a Perforated Annulus

Piping vibration had been observed in one of our refinery’s reactor inlet piping for several decades. Vibration levels in inlet piping for reactor ‘D’ and ‘E’ were highest, relative to those in reactor ‘A’, ‘B’, and ‘C’. To cope with the vibration, design changes to small-bore branch connections had been implemented to reduce susceptibility to the vibration. A recent increase in production demand made the vibration levels more evident and a production constraint was imposed after an MOV gas seal failure. Analysis identified the root-cause as flow-excited acoustic resonance of (almost) coaxial closed side branches in the flow path. The selected vibration mitigation solution involved installing a perforated annulus in the main line, in front of the mouth of the (almost) coaxial closed side branch acoustic resonator. Before fabricating and installing the perforated annulus, it was decided to evaluate its expected performance by means of computational fluid dynamics (CFD) and structural stress finite element analysis (FEA). This paper gives an account of the selection of the perforated annulus as the preferred vibration mitigation solution and its evaluation by means of high-performance computing CFD and FEA. The CFD and FEA analysis showed that the perforated annulus would perform as intended and mitigate the piping vibration. The perforated annulus was fabricated and installed in the inlet piping for reactor ‘D’. Piping vibration was observed to be mitigated, even when flowing above the design rate. The perforated annulus vibration mitigation solution was replicated in the inlet piping for reactor ‘E’. The production constraint has since been lifted.

Radiative Transport and Hydrodynamic Modeling of Microalgae Photosynthesis in Bio-Flow Reactors

A simplified two-phase flow PCH (physicochemical hydrodynamics) model is developed for modelling and simulation of microalgae growth in bio-flow reactor. The model considers carbon balance through coupled gas-phase and liquid-phase transport equations. The transport model accounts for interfacial transport of CO2 from gas bubble/slug to liquid, and microalgae photosynthesis reactions. A simplified photosynthesis reaction is adopted in the model, which assumes a pseudo-first order reaction for glucose pathway. The reaction rate is calculated assuming that it is proportional to the solar absorption rate by microalgae in the liquid. The reaction model also includes a simplified photoinhibition sub-model which assumes that the rate of photoinhibition is proportional to the square-root of solar irradiation reaching the algae cell. The Beer-Lambert law is used to calculate the radiative transfer of solar flux in seeded microalgae liquid flow. Analytical solution was obtained for single-channel bio-flow reactor. Decrease of the CO2 concentration in gas bubble/slug and in liquid flow is assumed to be the result of the microalgae growth in bio-flow reactor. Two efficiency parameters are defined: CO2 conversion efficiency and photosynthesis efficiency. The conversion efficiency is calculated based on the decrease of CO2 between the bio-flow reactor inlet and exit. The photosynthesis efficiency is based upon the heating value of microalgae yield versus solar irradiation. The rate of microalgae yield is calculated by multiplying the mass stoichiometric coefficient of photosynthesis reaction to CO2 consumption rate. Model analysis provided some insight of the microalgae formation in bio-flow reactor as interpreted from the PCH-coupled photosynthesis model that includes a dimensionless number as a potential scaling parameter for gas-phase only CO2 supply operation; photosynthesis efficiency increases with increasing CO2 molar concentration (i.e., number of moles per unit volume) at the reactor inlet for both gas-phase and liquid-phase only CO2 supply; an optimal irradiation flux for maximum photosynthesis efficiency — a factor to consider should artificial light source be used for harvesting algae.

(Solar) Mixed Reforming of Methane: Potential and Limits in Utilizing CO2 as Feedstock for Syngas Production—A Thermodynamic Analysis

The reforming of natural gas with steam and CO2 is commonly referred to as mixed reforming and considered a promising route to utilize CO2 in the production of synthetic fuels and base chemicals such as methanol. In the present study, the mixed reforming reaction is assessed regarding its potential to effectively utilize CO2 in such processes based on simple thermodynamic models. Requirements for the mixed reforming reactions based on process considerations are defined. These are the avoidance of carbon formation in the reactor, high conversion of the valuable inlet streams CH4 and CO2 as well as a suitable syngas composition for subsequent synthesis. The syngas composition is evaluated based on the module M = ( z H 2 − z CO 2 ) / ( z CO 2 + z CO ) , which should assume a value close to 2. A large number of different configurations regarding CO2/H2O/CH4 at the reactor inlet, operating pressure and outlet temperature are simulated and evaluated according to the defined requirements. The results show that the actual potential of the mixed reforming reaction to utilize CO2 as feedstock for fuels and methanol is limited to approximately 0.35 CO2/CH4, which is significantly lower than suggested in literature. At 900 °C and 7 bar at the reactor outlet, which is seen suitable for solar reforming, a ratio of H2O/CH4 of 1.4 can be set and the resulting value of M is 1.92 (CO2/CO/H2 = 0.07/0.4/1).

Analysis of Loss-of-Flow Accidents in Pre-Cooler and Inter-Cooler of HTR-10GT

Closed Brayton cycle (CBC) coupled with High Temperature Gas-cooled Reactor (HTGR) has potential application due to its compact configuration, high power generation efficiency and inherent safety. It is also one of the major power conversion methods for Generation IV advanced nuclear power systems. The typical CBC has several helium-water heat exchangers, including pre-cooler and inter-cooler. These helium-water heat exchangers have important influence on the performance of power conversion system, especially in loss-of-flow accidents (LOFAs). A system model including the reactor and the energy conversion system was established in this paper. The 10MW High Temperature Gas-cooled reactor-test Module helium Gas Turbine (HTR-10GT) was taken as the example to show the consequences of LOFAs. The results showed that LOFAs led to the rising of water temperature out of heat exchangers. With the reduction of water flow rate, the maximum water temperature would increase sharply, and the water temperature in pre-cooler was higher than that in inter-cooler. At low water flow rate, the water temperature would exceed the boiling point. LOFAs also made the rising of helium temperature. It had impacts on the performance of helium compressors. The elevated inlet temperature of helium compressors changed the corrected speed and corrected flow rate, therefore caused the deterioration of compressor’s performance. Furthermore, the LOFAs caused the reactor inlet temperature increasing. In low water flow rate, it would make the reactor inlet temperature beyond the temperature limitation of reactor pressure vessel and influence the safety of reactor. And the LOFAs also reduced the output work of cycle. This paper provides insights of features of CBC in LOFAs and will be helpful to the design and safety operation of closed Brayton cycle coupled with HTGR.

Nuclear Heat Supply Fluctuation Tests by Non-Nuclear Heating With HTTR

The nuclear heat utilization systems connected to high-temperature gas-cooled reactors (HTGRs) will be designed on the basis of non-nuclear-grade standards in terms of easier entry for the chemical plant companies and the construction economics of the systems. Therefore, it is necessary that the reactor operations can be continued even if abnormal events occur in the systems. The Japan Atomic Energy Agency has developed a calculation code to evaluate the absorption of thermal-load fluctuations by the reactors when the reactor operations are continued after such events, and has improved the code based on the high-temperature engineering test reactor (HTTR) operating data. However, there were insufficient data on the transient temperature behavior of the metallic components and the graphite core support structures corresponding to the fluctuation of the reactor inlet coolant temperature for further improvement of the code. Thus, nuclear heat supply fluctuation tests with the HTTR were carried out in non-nuclear heating operation to focus on the thermal effect. In the tests, the coolant helium gas temperature was heated to 120°C by the compression heat of the gas circulators in the HTTR, and a sufficiently large fluctuation of 17°C for the reactor inlet coolant was achieved by devising a new test procedure under the ideal condition without the effect of the nuclear power. Then, the temperature responses of the metallic components and the graphite core support structures were investigated. The test results adequately showed as predicted that the temperature responses of the metallic components are faster than those of the graphite blocks, and the mechanism of the thermal-load fluctuation absorption by the metallic components was clarified.

Thermal Mixing Behavior in the Annulus of Co-Axial Double-Walled Piping in HTGR

The future HTGR has been designed in JAEA. The HTGR uses the helium gas as the coolant in primary cooling system. The reactor has many merging points of the higher-temperature helium gas and the lower-temperature helium gas in the cooling system. Previously, the reactor inlet coolant temperature was controlled lower than the specific one in the HTTR constructed in JAEA. It was confirmed that this event was caused by the lack of mixing of helium gas thermally at the measurement point of the reactor inlet coolant temperature. From this operational experience, it is needed to clear the thermal mixing characteristics of the helium gas at the annulus of the co-axial double-walled piping in HTGR from the viewpoint of the appropriate temperature control in future HTGR. In this paper, thermal-hydraulic analysis on the helium gas at the annular flow path of the co-axial double pipe with T-junction was conducted to clarify the thermal mixing behavior of the helium gas. It is shown that the thermal mixing behavior is not so much affected by the flow rate helium gases. Moreover it is difficult to mix the helium gas with the smaller height of the annular flow path. This is caused by smaller contact area of higher- and lower-temperature helium gas and the lack of helium gas flow in radial direction. It is confirmed that it is difficult to mix the higher- and the lower-temperature helium gas in the annular flow path of the co-axial double-walled piping by using the hydraulic behavior, and it is necessary to arrange the mixing promotor in the annular flow path in order to mix the higher- and the lower-temperature helium gas.