Sludges are semi-solid substances that come from various industrial processes, mainly water treatment, waste treatment, and wastewater treatment. Sludge treatment involves all the methods used to reduce or eliminate health risks, extract water from the sludge, and reduce its weight and volume, to decrease the costs of final disposal. Common sludge treatment methods reduce risks to the natural environment while respecting the water cycle. Sludge generated naturally by sewage treatment plants could now be considered a valuable resource, because proper treatment of these sludges and wastewater directly reduces the operating costs of a treatment plant or sewage treatment plant, offering an economic opportunity for some of the biowaste resulting from degradation and settling processes. Various technologies such as thickening, dehydration anaerobic digestion, thermal hydrolysis, co-digestion, and thermal drying are used to transform sludge into valuable energy, the exploitation of which depends on the energy cost in each country. Most countries around the world use part of their energy produced from wastewater treatment plants after the transformation of sewage sludge, whereas in some countries, a portion of this energy produced in large digesters is sold as green energy (Biogas). Other countries prefer to agronomically valorize these sludges after proper and well-managed treatments. Antibiotic is increasingly being considered as a source of valuable by-products and agricultural inputs, such as phosphorus extracted from struvite, which is a mineral that can naturally crystallize in industrial recovery processes through anaerobic degradation. These crystals are sources of phosphorus, magnesium, and nitrogen recovery from residual sludge.