Valorization of agro-food waste through anaerobic digestion (AD) is gaining prominence as alternative method of waste minimization and renewable energy production. The aim of this study was to identify the key parameters for digester performance subjected to kinetic study and semicontinuous operation. Biochemical methane potential (BMP) tests were conducted in two different operating conditions: without mixing (WM) and continuous mixing (CM). Three different substrates, including food waste (FW), chicken dung (CD), and codigestion of FW and CD (FWCD) were used. Further kinetic evaluation was performed to identify mixing’s effect on kinetic parameters and correlation of the kinetic parameters with digester performance (volatile solid removal (VS%) and specific methane production (SMP)). The four models applied were: modified Gompertz, logistic, first-order, and Monod. It was found that the CM mode revealed higher values of Rm and k as compared to the WM mode, and the trend was consistently observed in the modified Gompertz model. Nonetheless, the logistic model demonstrated good correlation of kinetic parameters with VS% and SMP. In the continuous systems, the optimum OLR was recorded at 4, 5, and 7 g VS/L/d for FW, CD, and FWCD respectively. Therefore, it was deduced that codigestion significantly improved digester performance. Electrical energy generation at the laboratory scale was 0.002, 0.003, and 0.006 kWh for the FW, CD, and FWCD substrates, respectively. Thus, projected electrical energy generation at the on-farm scale was 372 kWh, 382 kWh, and 518 kWh per day, respectively. Hence, the output could be used as a precursor for large-scale digester-system optimization.
Global warming has become a serious issue nowadays as the trend of CO2 emission is increasing by years. In Malaysia, the electricity and energy sector contributed a significant amount to the nation’s CO2 emission due to fossil fuel use. Many research works have been carried out to mitigate this issue, including carbon capture and utilization (CCUS) technology and biological carbon fixation by microalgae. This study makes a preliminary effort to screen native microalgae species in the Malaysian coal-fired power plant’s surrounding towards carbon fixation ability. Three dominant species, including Nannochloropsis sp., Tetraselmis sp., and Isochrysis sp. were identified and tested in the laboratory under ambient and pure CO2 condition to assess their growth and CO2 fixation ability. The results indicate Isochrysis sp. as the superior carbon fixer against other species. In continuation, the optimization study using Response Surface Methodology (RSM) was carried out to optimize the operating conditions of Isochrysis sp. using a customized lab-scale photobioreactor under simulated flue gas exposure. This species was further acclimatized and tested under actual flue gas generated by the power plant. Isochrysis sp. had shown its capability as a carbon fixer with CO2 fixation rate of 0.35 gCO2/L day under actual coal-fired flue gas exposure after cycles of acclimatization phase. This work is the first to demonstrate indigenous microalgae species' ability as a carbon fixer under Malaysian coal-fired flue gas exposure. Thus, the findings shall be useful in exploring the microalgae potential as a biological agent for carbon emission mitigation from power plants more sustainably.
Carbon capture and storage (CCS) through biological approach has attracted much attention as global warming and climate change issue becomes a worldwide agenda. Energy production industry from coal in Malaysia produced 50.661 million metric tons of carbon dioxide in 2012, and the trend showed it will keep increasing year by year. CCS through biological approach can be done by microalgae which are versatile microorganism which perform photosynthesis process that can store CO2 in the biomass form. In this study, microalgae strains were isolated from the native environment nearby a coal-fired power plant, where samples were collected in different canal in which pre-treated flue gases are discharged. The microalgae strains were identified by both morphological and molecular approaches. Result from 18s rRNA gene sequencing showed that the isolated strains is Chlorella sp. with similarity 99% with Chlorella sp. SAG 211-18. The identified strains of microalgae then cultivated with three concentration of CO2 (ambient air, 1% and 5%) and the growth rate showed 0.4017 day -1 , 0.5752 day -1 and 0.4427 day -1respectively. Different concentration of CO2 (ambient air, 1% and 5%) showed that the isolated strains yielded 1.005gL -1 , 1.101gL -1 and 1.035gL -1 respectively. This study also showed that with different concentration of CO2, the sequestration rate is ranging from 1% to 4.3%.Keywords: microalgae, isolation, purification, DNA sequencing Abstrak Pemerangkapan dan penyimpanan karbon (CCS) melalui pendekatan biologi telah menarik minat pengkaji disebabkan masalah pemanasan dan perubahan iklim global. Pada tahun 2012 sahaja, Malaysia telah menghasilkan 50.661 juta ton metrik karbon dioksida hasil daripada penghasilan tenaga yang bersumberkan arang batu, dan tahun demi tahun penghasilan karbon dioksida dijangkakan akan terus meningkat. Pemerangkapan dan penyimpanan karbon melalui pendekatan biologi boleh dilakukan oleh mikroalga yang merupakan mikroorganisma unggul di mana ianya berupaya menjalankan proses fotosintesis dalam menukarkan karbon dioksida ke dalam bentuk biojisim. Dalam kajian ini, mikroalga dipencilkan daripada habitat asal yang merupakan terusan bagi air penyejuk untuk stesen janakuasa arang batu. Mikroalga yang diperoleh, dikenalpasti menggunakan kaedah pengecaman secara morfologi dan molekul. Hasil keputusan pengenal pastian molekul menggunakan kaedah penjujukan genom 18s rRNA mendapati, mikroalga yang berjaya dipencilkan adalah Chlorella sp. yang mempunyai persamaan sehingga 99% dengan Chlorella sp. SAG 211-18. Mikroalga yang telah menjalani proses identifikasi kemudiannya dikultur menggunakan 3 kepekatan karbon dioksida yang berbeza (CO2 pada udara persekitaran, CO2 1% dan CO2 5%) dan hasil menunjukkan kadar pertumbuhan masing-masing adalah 0.4017 hari -1 , 0.5752 hari -1 , dan 0.4427 hari -1 . Pada kepekatan CO2 yang berbeza (CO2 pada udara persekitaran, CO2 1% dan CO2 5%), hasil biojisim yang terkumpul daripada pengkulturan mikroalga masing-masing
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