Sewage sludge is considered as a main product obtained from urban liquid effluents that are discharged into sanitation systems of wastewater treatment plants. The aim of this work was to reuse it as compost, after the dehydration process, to replace the amendment applied in agriculture and also to reduce the environmental pollution caused by solid wastes. To justify our biotechnological approach, nutrient characterization of the composted dewatered sewage sludge was carried out and compared to cattle manure. The contents of N, P, K, and the organic matter are 3.67, 5.64, 6.60 g·kg-1 dry matter (DM), and 70%, respectively, in compost and 3.1, 1.6, 3.0 g·kg−1 DM, and 55%, respectively, in manure. Fertilization tests with composted dewatered sewage sludge and cattle manure were performed on Pelargonium inquinans. Monitoring the length of the first internodes showed an improvement of 4.2 mm in the length in compost plants with a development of 22.8 buds and 8.2 flower buds (19.4 buds and 4.4 flower buds developed in manure plants). It appears that the intake of composted dewatered sewage sludge ensures better growth for the studied plant due to its richness in nutrients, which confirms the beneficial effect of composting sewage sludge on plant cultivation.