Tofu waste liquid contains high levels of organic impurities, such as protein and amino acids. These organic compounds cause the tofu industrial wastewater to contain high biological oxygen demand (BOD), chemical oxygen demand (COD), pH and total suspended solid (TSS) which can pollute the environment. In general, the liquid waste from the tofu factory is discharged directly into rivers through sewers and rivers. Most of the tofu wastewater contains various kinds of pollutants which may be produced in the form of organic pollutants (foul smelling), inorganic pollutants (spicy and colored), so they are dangerous to the surrounding environment and need to be treated. One alternative to tofu liquid waste treatment is electrocoagulation. The electrocoagulation method has the potential to purify tofu wastewater and reduce the content of BOD, COD, TSS and neutralize pH without the addition of certain chemical coagulants. The purpose of this study was to obtain the characteristics and levels of pollutants contained in tofu industrial wastewater before and after processing, and to determine the effectiveness of the electrocoagulation method with various variations in voltage and reaction time. The electrocoagulation tub is attached with a cable connected to the power supply, then connected to a current source with a variable voltage (8; 10; 12 V) and a variable reaction time (30; 60; 90; 120; 150 minutes). The optimum conditions were obtained at a voltage variation of 12 volts and a reaction time of 150 minutes, with a percentage increase in pH of 72.33% to 5.98, a decrease in COD of 28.57% to 10 mg/L, a decrease in BOD5 of 46.87% to 2, 29 mg/L, and TSS from 11.47% to 21.6 mg/L.

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Tray dryer is one type of plate-shaped dryer, which is often used to dry materials in the form of solid or paste, therefore the tool is very suitable for drying or converting hydrogel to silica. The working principle of the dryer is to transfer heat around the environment of the material to be dried by means of heat transfer by convection and conduction. Weight reduction due to water loss due to evaporation when drying process is done. In this research, the silica to be dried was made from bagasse using a number of additional ingredients namely hydrochloric acid and sodium hydroxide with various variations. Tool performance is determined based on the amount of thermal efficiency obtained where thermal efficiency is a percentage of the amount of heat flowing during the drying process. In addition, the rate and time of drying will also affect the quality of the product. research steps include; tool design using the functional approach method to find out the functions of the unit of equipment used and structural approach to get the dimensions of the tool Silica gel produced from the drying process is analyzed using X-Ray Difraction (XRD) and Fourier Transform Infra Red (FTIR) which aims to characterize the crystal structure and detect functional groups. Based on the analysis results obtained silica gel has a functional group of Si-OH and amorphous crystal structure, so it is categorized as meeting the standards of JIS-0701. Calculation results obtained optimal conditions achieved at the time and speed of drying 360 minutes, 0.019 kg / hour m2 with a silica gel moisture content of 0.81% and thermal efficiency of 86.4%.

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