Ferrous is one of the groundwater contaminants that negatively impacts health and the environment. The allowed ferrous content is < 1 ppm in water for daily use. Removal of Fe in groundwater by adsorption using low-cost bio-sorbent from rice husk has been conducted. The process was carried out in continuous mode using two types of rice husk-sourced adsorbents, one was only carbonated at 400 C and another was followed by a physical activation at 650 C. To study the effects of physical activation on the surface characteristics, both types of biosorbents were characterized by Scanning Electron Microscope and Fourier-transform infrared spectroscopy. The concentration of artificial sample before and after adsorption was evaluated using the Atomic Absorption Spectroscopy. From the results, the adsorption using physically activated sorbent had greater removal efficiency of 74.02% compared to that of without activation treatment, which was only 65.70%. In addition, the concentration of ferrous was successfully reduced to 1,029 and 0.779 ppm from the initial concentration of 3 ppm for the process using the adsorbent without and with activation, respectively. It can be concluded that the physically activated rice husk has the potential to be used for adsorption of Ferrous in continuous column.

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The increasing types of people needs along with the times have resulted in the need for energy increasing so that the supply of energy, especially energy that cannot be renewed (unrenewable energy) is decreasing. Currently, almost 80% of the world's energy needs are met by fossil fuels. In fact, the use of fossil fuels can cause global warming. To reduce dependence on fossil fuels as an energy source, it is necessary to search for energy sources that can be used as alternative fuels that are environmentally friendly. Indonesia is an agricultural country that is overgrown with plantation crops that produce various kinds of waste such as rubber seeds which contain oil. This plant produces a lot of wasted seeds that are not useful. Therefore, researchers want to research the oil from rubber seeds to be a biodiesel product and in order to get high quality results. This study regulates several independent variables, namely the alcoholysis temperatures: 650C, 700C and 750C and the alcohol volume: 200 ml, 250 ml and 300 ml. The process is carried out by extraction using the alkolysis method. The best yield yielded 60.5%, with the best yield of biodiesel from alcoholysis obtained at a volume of 250 ml of ethanol and a temperature of 75oC with a density of 09 kg/m3 and a viscosity of 3,285 mm2/s (cSt), fulfilling the requirements of SNI 7182:2015. Based on the results of GC analysis, the main fatty acid components in the sample were at peak 1, namely saturated fatty acids in the form of palmitic acid at 44,28% and peak 4, namely unsaturated fatty acids in the form of oleic acid at 31.99%.

This study examines the composite quality of PP and HDPE plastic waste materials using Microfiber Oil palm empty fruit bunches (OPEFB) as filler, the fiber used is 90 µm. The ratio of matrix: filler used is 60:40 and 70:30 for each type of PP and HDPE polymer. The method used is a melt blending screw extruder, where plastic and fiber materials are dissolved with a compatibilizer and then melt blended in an extruder by providing temperatures of 160 and 170 oC. Tensile tests showed the strength of the PP composite with a filler ratio of 60:40 and 70:30, respectively, of 313.25 N and 336.35 N, while the HDPE composite with a filler ratio of 60:40 and 70:30, respectively are 392.93 N and 187.90 N. The maximum force required to break HDPE composites reaches 21.10 Mpa while for PP composites it reaches 18.56 Mpa. From the morphology of the PP and HDPE composite samples, the overall surface structure of HDPE looks regular with a width from 1 to 13.5 mm. The PP composite shows a uniform and regularly arranged surface structure and the bond between the fibers and the filler looks more compatible but the surface pores are rougher. Heat resistance can be seen from the melting point of PP composites which can reach 163.81oC while HDPE composites only reach 134.21oC.

Rice husk has been converted into activated carbon for the adsorbent to remove the heavy metal from the aqueous solution. This study aimed to convert rice husk to activated carbon (AC) for use in the adsorption of Fe ions in a fixed-bed column. Rice husk was first pyrolyzed in an atmosphere of nitrogen gas at 400 oC, then a chemical activation method using sodium hydroxide. The rice husk activated carbon (RH-AC) was characterized using Fourier transform infrared (FTIR) and Scanning electron microscope (SEM) to identify the functional group and microstructure of carbon. The performance of the carbon was tested on the Fe removal from an aqueous solution in a continuous column. The adsorption process was carried out using Fe solution with an initial concentration of 3 mg/L as an artificial sample. The amount of carbon is 25, and 50 g were filled in an adsorber column with a diameter of 5.4 cm and height of 40 cm. SEM images revealed that the activated carbons shown with well-developed pore sizes and pore structure were produced after the chemical activation.  The FTIR absorption bands observed in the RH-AC sample confirmed the presence of hydroxyl (-OH), carbonyl, and carboxylic (-COOH) groups of RH-AC adsorbent. The highest Fe removal efficiencies were 91.9% on chemically activated carbon and column mass 50 g at 400 minutes. The overall study revealed the potential value of chemically activated RH-AC as a possible commercial adsorbent in a continuous column wastewater treatment strategy.