The rapid, high increase in production costs and prices of mineral fertilizers leads to a reduction in their use by farmers, while fertilizer manufacturers consider the use of alternative raw materials and reducing the energy consumption of fertilizer production processes. Given these circumstances, special attention is warranted for suspension fertilizers. The manufacturing of suspension fertilizers is simplified and less energy intensive in comparison with solid fertilizers. This is achieved by omitting certain production stages such as granulation, drying, sifting, which usually contribute to more than half of the production costs. This paper presents the production procedure of suspension fertilizers tailored for cabbage cultivation, utilizing alternative raw materials such as sewage sludge ash and poultry litter ash. The final products are thoroughly characterized. The obtained fertilizers were rich in main nutrients (ranging from 23.38% to 30.60% NPK) as along with secondary nutrients and micronutrients. Moreover, they adhere to the stipulated standards concerning heavy metal content as outlined in the European Fertilizer Regulation. A distribution analysis has showed that suspension fertilizers contain nutrients in both liquid and solid phases. This arrangement facilitates their easy availability for plants and subsequent release upon dissolution in soil conditions. To assess process consistency, the production of the most promising fertilizer was upscaled. A preliminary technological and economic analysis was also conducted. The method of producing suspension fertilizers using alternative raw materials is a simple waste management solution offering nutrient recycling with the principles of circular economy. This approach not only encourages nutrient recycling but also curtails reliance on imported raw materials.

Warna and Pengilon Lakes are very close to each other and connected with the sill, a famous tourist destination in the Dieng Plateau Java. Land-use changes are the main problem that affected the lakes. The conversion of forest into an agricultural area had induced erosion and increased the volume of nutrients discharged to the lake due to high use of fertilisers in potatoes farms. In the dry seasons, water from those lakes was pumped to irrigate agricultural land. This study aimed to determine the water quality of Warna and Pengilon Lakes based on physical, chemical parameters, and phytoplankton communities. Water samples were collected from 4 sites at each lake to analyse biological oxygen demand ( BOD), chemical oxygen demand ( COD), ammonia, nitrate, nitrite, and total nitrogen ( TN). Temperature, pH, dissolved oxygen ( DO), turbidity, and conductivity ( EC) were measured in-situ. During this research, turbidity and BOD in Warna and Pengilon Lakes exceeded the Indonesian water quality standard. Based on the STORET method, the water quality of Lake Warna was assessed as highly polluted for all classes. However, based on the pollution index (PI), Lake Warna was slightly to moderately polluted, as well as the saprobic index was in the β-mesosaprobic phase. Based on the species diversity index of phytoplankton, both Warna and Pengilon Lakes were moderately polluted. The long-term monitoring studies are necessary as an early warning sign of water quality degradation. Therefore, they provide insight into the overall ecological condition of the lake and can be used as a basis for developing suitable lake management.