<p>Sewage sludge generated from wastewater treatment plants (WWTPs) is rich in nutrients. Use of this resource in agricultural purposes offers a sustainable solution of disposal in line with waste management, effective use of resources, and nutrient closed-loop systems. However, sludge-based fertilizers contain harmful heavy metals (HMs) and various medicines which pose a threat to the environment. This study examined the key compositions of sludge-based organomineral fertilizers and their effectiveness on growth and productivity of spring barley. Standard methods were applied for compositional analyses. In addition, experimental trials were set up to understand the effectiveness of organomineral fertilizers on barley seedlings. Results revealed that sludge-based fertilizers from case WWTP contain a good level of nutrients, and low levels of harmful HMs and medicines, indicating the quality of sludge is of high quality to use as fertilizers. Sludge-based fertilizers have a positive impact on growth and productivity of barley seedlings, and these are maximized when the seedlings are treated with sludge-struvite organomineral fertilizer. However, the performance of sludge-based organomineral fertilizers depends on the type of mixing recipes. As such, further research on mixing recipes, extensive field trials, risk and a detailed sustainability analysis are needed to understand the long-term impact of this resource.</p>