Effects of sewage sludge on biodiesel production in energy crops

The search for new alternatives to traditional fossil fuels, which have been used for a long time, continues due to the fact that the damage they cause to the natural environment is now directly affecting human life and the significant increase in their costs as their quantities decrease. However, the most important alternatives are solar, wind, etc. Since only electrical energy can be produced from renewable sources, existing technologies must either be completely renewed or significantly revised in order to use the energy produced from these sources. However, biodiesel production has a very important place in the process of complete transition to renewable energies, as it is directly compatible with existing technologies that work with conventional fossil fuels. Oils produced from various plants are used in biodiesel production. However, studies explaining the relationships between the growing conditions of these plants and their biodiesel yield are quite limited. The main purpose of this study is to grow the Ricinus communis L. (castor bean) plant, which has a high potential to be used in biodiesel production, in sewage sludge (SS), one of the most important organic solid wastes of today, to examine the effects of this application on biodiesel yield and to propose an alternative disposal method for sewage sludge, which has become one of the most important solid wastes in recent years due to its large formation amounts. In the study, domestic wastewater treatment sludge was tested in potted and soil cultivation at different rates in order to examine the effects of SS on the growth, seed and oil production and therefore biodiesel production of Ricinus communis L., an inedible oilseed plant belonging to the Euphorbiaceae family. While the effects of SS addition on Ricinus communis L. plant growth were examined in potted experiments, the effects of sewage sludge on seed quantity, oil yield and biodiesel production of Ricinus communis L. plant were examined in soil trials. To examine the effects of sewage sludge addition on the growth of Ricinus communis L. plant, growing medium mixtures were prepared by adding sewage sludge to soil and commercial peat at varying rates (12.5%, 25% and 50%; v/v%). SS was dried by solar drying before being used in mixtures. In the field study SS was applied to the soil at two different rates (25, 50 tons/ha) in a garden located in Karasu District of Sakarya Province (Türkiye), and the effects of this application on the growth and seed yield of Ricinus communis L. (castor bean) plant were examined. The garden has a silty-sandy soil texture (44.7% silt, 38.9% sand, 16.4% clay). The SS that used was taken from the Karasu biological domestic wastewater treatment plant and dried by solar drying (90% DW). After the Ricinus communis L. seeds were germinated in the viols (15 cm), they were planted in 5 replicates in each application ccording to the randomized plots trial plan and their growth was monitored for two years. In the experiments examining the effects of sewage sludge on plant growth, the seeds were planted in 5-liter pots filled with growing medium mixtures and allowed to germinate and grow there. The height and stem diameter of the plants in soil trials and potted applications were measured at the end of the first and second growing years. The seeds of the Ricinus communis L. (Castor Bean) plant, which was grown for two years in soil experiments, were harvested every year. Seeds were dried after harvest and weighed individually to determine the amount of seed removed from each treatment. Oil extraction from seeds was carried out by automatic squeezing. It has been observed that the addition of sewage sludge increases the macro and micro nutrient content of the growing media. In the growing media using soil, the highest micronutrient content was measured in the application using 50% SS (Zn: 16.32 mg/kg, Cu: 7.32 mg/kg, Mn: 4.92 mg/kg), and similarly, among the growing media using peat, the highest plant nutrient element content was determined in the application containing 50% SS (Zn :45.94 mg/kg, Cu: 9.12 mg/kg, Mn: 5.92 mg/kg). The addition of sewage sludge also increased the macro plant nutrient content of the growing media. The highest nitrogen content was measured as 0.64% in growing media prepared with a mixture of soil and sewage sludge, and 2.08% in growing media containing peat, in applications containing 50% SS. The highest phosphorus content in growing media prepared using soil was determined as 122 mg/kg. In growing media using peat, the highest phosphorus value was obtained from the application using the most sewage sludge. The highest potassium value was measured in the growing medium prepared using 50% peat and 50% SS. The heights of the plants grown in pots for two years were measured at the end of the first and second year. The highest plant height measured in the first year was 0.96 m, while the highest plant height measured in the second year was 1.4 m. At the end of both growth years, the application in which the highest plant heights were measured was the application consisting of a mixture of 50% peat and 50% SS. The lowest plant heights were measured in the application containing 87.5% soil and 12.5% SS, as 0.62 m and 1.05 m in the first and second years, respectively. The plant height values obtained in all growing environments using SS were above the plant height values at the end of the first and second year of the plants used for control purposes and grown in pots filled with 100% soil (1.year: 0.49 m, 2.year: 0.62 m) and peat (1st year: 0.56 m, 2nd year: 0.79 m). The positive effects of SS on the growth of Ricinus communis L. were clearly seen in the plant stem diameter results. In pot experiments, the highest stem diameter value measured at the end of the first year was 1.7 cm in the application containing the highest amount of SS, containing 50% peat and 50% SS, while the highest stem diameter value at the end of the second year was determined in this application with 2.3 cm. The lowest stem diameter value measured in pot experiments was found at the end of the first growing year in the control application (0.4 cm) using 100% soil. In the field experiments, SS was applied to the soil at two different rates (SSW1:25, SSW2:50 tons/ha) in a garden located in Karasu District of Sakarya Province (Türkiye), and the effects of this application on the growth and seed yield of Ricinus communis L. (castor bean) plant were examined. The garden has a silty-sandy soil texture (44.7% silt, 38.9% sand, 16.4% clay). The results obtained showed that the addition of SS improved the chemical properties of the soil that affect plant growth potential with its high content of macro and micro nutrients. Total nitrogen, potassium and phosphorus values obtained in both applications using SS were found to be higher than the values in the soil without treatment sludge, which is the control application. According to the results of field trails obtained, the highest plant height, 3.29 m, was seen in the application using the highest amount of SS. The average height of Ricinus communis L. plants grown in soil without SS as a control application was found to be 2.32 m. The highest stem diameter, 4.1 cm, was observed in the application using the highest amount of SS. The seed amount of the plant at the end of the first year was low. The amount of seeds obtained per plant from SSW2, SSW1 and control applications were 0.58 kg, 0.23 kg and 0.15 kg, respectively. The oil content of the seeds was examined and it was seen that the highest oil content was obtained in the SSW2 application with 45.82%. The seed oil content in the SSW1 treatment was 44.98% and the oil content in the control treatment was 44.12%. The results of the study are evaluated as a whole, it can be said that the application of sewage sludge significantly improves the chemical properties and plant growth potential of the soil.