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Birnessite-type manganese oxide is multifunction material that has been used in various application and the characteristic depends heavily upon its preparation method. In this study, birnessite-type manganese oxide was synthesized using the reaction between KMnO4 (oxidant) and two different reducing agents i.e., citric acid and oxalic acid via a solvent-free method. The characterization of the birnessite was carried out using X-Ray Diffraction (XRD), Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDX), and Surface Area Analyzer (SAA). Birnessite from this variation of reducing agents showed different levels of crystallinity, diverse morphology, crystal size, and surface area. The birnessite-type was then applied as a catalyst for the degradation of Palm Oil Mill Effluent (POME) with hydrogen peroxide (H2O2) as an oxidant to reduce the concentrations of Chemical Oxygen Demand (COD). The maximum reduction in COD concentration was obtained using the catalyst concentration of 400 and 800 mg/L for reducing agent of as-synthesized catalyst citric acid and oxalic acid. Birnessite-type manganese oxide shows potential as a catalyst in the degradation of POME with citric acid as reducing agents showed better degradation in reducing COD values.

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Dumai is one of the coastal waters of Indonesia that has the potential for the biodiversity of microorganisms including anoxygenic photosynthetic bacteria (APB). Anoxygenic photosynthetic bacteria are bacteria that carry out decomposition activities even though oxygen levels in water and sediment are very little or even absent. This study aims to determine anoxygenic photosynthetic bacteria from aquatic and sedimentary ecosystems in the coastal waters of Dumai, Indonesia. This research was conducted by an experimental method using modified mineral media. The APB was isolated from six different places in sequence, namely Dumai sea station, river prayer room, harbor, shrimp pond area, fish auction place, and, Purnama tour. All bacteria obtained were then characterized by their morphological and physiological characteristics. The isolation results showed that 15 different bacterial isolates were obtained after being determined based on Bergey’s Manual of Determinative Bacteriology. All isolates contained different pigments such as carotenoids, xanthophylls, and, chlorophylls. Thus, further utilization of APB bacteria can be carried out in various microbiological applications such as bioremediation, aquaculture, biofuel, food, and medicines.

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The pristine cryptomelane (OMS-2) and Fe-OMS-2 (1%, 5%, and 10%) have been successfully synthesized by a one-step sol-gel method and characterized by XRD, SEM, BET surface area and AAS. The incorporation of Fe (III) within the structure of OMS-2 leads to an increase in surface area, pore-volume, and catalytic activity for the degradation of methylene blue (MB) and a decrease in the content of K+ and average of pore diameter. The catalytic test indicated that the catalytic activity of Fe-OMS-2 1% is considerably higher that of pure OMS-2. The highest degradation of MB is 93.5% achieved using Fe-OMS-2 1% after 120 minutes of degradation time, the initial concentration of MB of 20 ppm, the catalyst concentration of 0.125 mg and the H2O2 volume of 15 mL. The enhanced catalytic activities of Fe-OMS-2 compared to pristine OMS-2 for catalytic degradation of MB are associated with an increase in surface area, pore-volume, and smaller particle size. The results from catalytic studies imply that the metal doping is an effective strategy to enhance the catalytic activities of OMS-2 for degradation of MB.

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