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Wastewater from the biodiesel process contains oil and methanol, requiring treatment to reduce chemical oxygen demand (COD) and biological oxygen demand (BOD5). Chemical separation can generate additional waste, so innovative methods like gravity separators are essential. This research uses an inlet diverter and oil collector at the distillation column bottom to treat wastewater effectively. The results show COD and BOD5 values of 210 mg/L and 80 mg/L, respectively, with percentage of removal was ±70 % and ±60 %, respectively, with 96.2 % oil recovery. Gas chromatography (GC) analysis found 2.6 % methanol and minimal impurities. This method effectively separates water-methanol-oil mixtures, making it suitable for biodiesel plants.

Biochar produced from biomass based Empty Fruit Bunches (EFB) pyrolysis presents an alternative energy source. Biomass through the pelletization process will produce bio-pellets with higher density, while microwave pyrolysis achieves better energy efficiency and cost effectiveness. This two-step process will produce a product with a longer combustion duration and higher thermochemical conversion efficiency. This study aims to utilize EFB waste through a two-step process (pelletization and microwave pyrolysis) to produce biochar as an alternative renewable energy approaching commercial standards. EFB bio-pellets with a mass of 80, 100, and 120 g were pyrolyzed in a microwave pyrolysis reactor with the power of 450, 600, and 850 W, and in time variations of 20, 30, and 40 min. The results showed that 850 W power and 80 g mass were the optimal conditions to produce biochar with the highest heating value (26.73 MJ/kg), moisture content (0.48 %) volatile matter content (12.56 %), ash content (22.33 %), and fixed carbon (64.62 %). The SEM-EDX analysis indicated that the biochar product showed an increase in carbon (C) content up to 67.4 %. It is expected that combination of the pelletization process and microwave assisted pyrolysis could become a new alternative for producing biochar that could be commercialized. This research was carried out to address the problem of accumulating EFB in palm oil mills and generating renewable energy from waste.

In Indonesia, the biodiesel industry generates approximately 48–60 tons of solid waste annually using heterogeneous catalysts. The heterogeneous catalyst's reusability is essential to addressing the issue, notably the first reaction. This research develops Amberlyst CM-4 catalyst recycling using continuous methanol washing to be used multiple times in biodiesel production with lauric acid as feedstock. The research involves the esterification, washing, and drying sections connected using self-designed vessels. The Amberlyst CM-4 catalyst was continuously reacted and reused to monitor the biodiesel conversion level. Based on the results, the Scanning Electron Microscope provides the condition of the visible pores on the surface of the fresh and used catalyst. The Fourier Transform Infra-Red results detect both C–H bonds as part of styrene, and CC was obtained from ethane of the fresh and used catalyst that is the nature of Amberlyst CM-4 catalyst. The Brunauer-Emmett-Teller confirms the change in pore surface area for fresh and used catalysts. The results of the lauric acid and biodiesel components in the Gas Chromatography show major components of C12 and C14. The recycling results show that the esterification reaction can be used up to 24th times in experiments obtained at a temperature of 80 °C and a molar ratio of 8:1. However, by the 25th experiment, the conversion was already below 80 %. The determination of the success of biodiesel production in this study is the conversion obtained ≥ 80 %. This refers to the catalyst manufacturer used in the industrial world to reduce biodiesel production costs. Hence, continuous washing of Amberlyst CM-4 catalyst using methanol could be applied in the biodiesel industry.

Pulp quality significantly affects paper products, necessitating a balance between brightness, strength, and environmental sustainability. The bleaching process, which includes delignification and brightening stages, is crucial for achieving high pulp brightness. Current pulp bleaching research emphasizes optimizing processes and developing predictive models for better quality control, yet real-time pulp brightness monitoring remains a challenge. This research developed a MATLAB program to predict pulp brightness and consistency in real-time during bleaching, conducted entirely without incurring any financial costs. Empirical models for predicting pulp consistency at the extraction-oxidative-peroxide (EOP) and D1 stages were created using second-order polynomial equations, incorporating production rate and inlet pressure as variables. Brightness increment correlations were formulated based on temperature, chemical flow rate, residence time, pH, and inlet pressure, with specific models for the preceding chlorine dioxide (DA), EOP, and second chlorine dioxide (D1) stages. Data normalization ensured efficient processing by standardizing parameter scales. Results showed relationships between brightness increment and parameters for each sub-stage such as DA is linear for pH, quadratic for chlorine dioxide (ClO2) flow rate, cubic for temperature and residence time; EOP is linear for hydrogen peroxide (H2O2) flow rate, quadratic for temperature, cubic for inlet pressure, residence time, and pH; D1 is linear for pH, quadratic for ClO2 flow rate and residence time, cubic for inlet pressure and temperature. The coefficient of determination (R2) for the DA, EOP, and D1 sub-stages are 0.85313, 0.86526, and 0.86322, respectively. Parameters with the highest contributions in each stage were identified, such as inlet pressure in the D1 substage yielding the highest brightness gain. This system offers an alternative approach for analyzing pulp quality issues and is adaptable to future mill operational needs.

Palm oil mill effluent (POME) has high levels of contaminants, one of which is Chemical Oxygen Demand (COD) of around 40,000–60,000 mg.L−1. The very high COD levels in POME are harmful in terms of toxicology and aesthetics to the environment. POME treatment by anaerobic digestion can be carried out through the Upflow Anaerobic Sludge Blanket-Hollow Centered Packed Bed (UASB-HCPB) fermentor to produce biogas, while the liquid phase will end up as effluent. However, these effluent not met the quality threshold so further treatment is required. Aerobic process can be address this issue by utilizing microalgae. Chlorella vulgaris is a microalgae that is widely used in wastewater treatment because of its resistance to pollutants and degradation effectiveness. The purpose of this research is to treat the effluent from the UASB-HCPB fermentor by utilizing Chlorella vulgaris in a fed-batch system. The novelty of this research is the utilization of microalgae of Chlorella vulgaris in photobioreactor for treating the effluent from the UASB-HCPB fermentor so that it meets the predetermined quality standards and safe to be discharged into the environment. In this study, the culturing process of Chlorella vulgaris was carried out in photobioreactor with variations of lighting intensity (12:12) and (24:0), with and without aeration. The cultivation process was carried out in the same of the photobioreactor with variation of fed-batch system with effluent addtion of 450 mL.day−1, 900 mL.2 day−1, and 1350 mL.3 day−1 with variation of agitation rate of 10 rpm, 20 rpm, 30 rpm, 50 rpm, and 100 rpm. Based on the experimental results in culturing process, it was found that the aeration and lighting process (24:0) increased the growth of Chlorella vulgaris best with an absorbance of 0.759 with the relationship between optical density and biomass dry weight with a value of (g.mL−1) = 0.008 OD + 0.0017 with R2 = 0.981. The best substrate addition in cultivation process was obtained with the addition of 900 mL.2 day−1 with absorbance 0.758 and specific growth 0.164 day−1. The best COD decomposition efficiency 87.5 % was obtained with the addition of 900 mL.2 day−1. The best agitation of 30 rpm was obtained with absorbance of 0.850 and COD decomposition efficiency of 93.75 % for 12 days cultivation. Total cost estimate offered of 11.1 IDR/L was obtained. This indicates that these conditions are effective for POME effluent treatment applications involving Chlorella vulgaris. The utilization of Chlorella vulgaris optimistically can be applied as a new low cost solution in the integration of sustainable POME treatment in the palm oil industry.

The widespread use of heterogeneous catalysts for biodiesel production has led to the generation of substantial waste. Therefore, it was needed to reduce the solid waste catalyst in the biodiesel industry by exploring the reuse of catalysts. This study focused on the reactivation of used catalysts through the esterification of lauric acid using Amberlyst CM-4 catalyst, with pre-treatments involving methanol washing and HCl reactivation. Gas chromatography was employed to analyze lauric acid and methyl ester while Scanning Electron Microscope provided insights into the pore conditions of the fresh catalyst and used catalyst and Brunauer Emmett Teller provided information into surface area and pore condition. In this study, it was examined how many times the Amberlyst catalyst could be used to catalyze lauric acid to become biodiesel. The limitation of this capability is catalyst conversion above 80 %. The results showed that optimal conditions for biodiesel production were reached at a reaction temperature of 60 °C, a reaction time of 120 minutes, and an agitation rate of 500 rpm, yielding 93.7 % conversion for the used catalyst and 98.5 % for the fresh counterpart. The Amberlyst catalyst can be used up to seven times, because the results still provide a conversion above 80 %. After this catalyst does not provide a conversion above 80 %, then this catalyst is washed with methanol and activated using HCl. The results obtained show that this catalyst can still be used four more times. Hence, the results of this research can be applied to reduce industrial waste and reduce the costs of making biodiesel from fatty acids.