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The aim of our research work is the realization of anaerobic digestion by using the organic sludge of the urban wastewater treatment plant as a substrate. The biodegradable nature of the wastewater sludge allowed flammable biogas to be recovered after 24 hours of digestion and biogas production reached almost 5 liters for an initial concentration of 70 g / L The rate of reduction in COD (chemical demand in oxygen) of the sludge was estimated at 87.3% . For the good functioning of the digestion one must control the following parameters: type of substrate, pH of the medium, the organic load expressed in COD or BOD, the temperature. Once the operation is conducted we must follow the VFA / CAT (Volatile Fatty Acid/ Complete Alcalimetric Title) parameter which shows if the process will continue or will be stopped. And finally, the C / N ratio gives us an indication if there is more carbon in the medium, this will indicate that the residence time is going to be very long in the reactor and if nitrogen is abundant in the organic matter it is will produce in the digestion medium ammonia which inhibits the degradation process and stops it in the acidogenic phase and the production of biogas. The use of anaerobic digestion can be an interesting solution to dispose of energy from organic waste, while effectively participating in the remediation of these effluents. This renewable energy, inexpensive, non-polluting can replace conventional and nonrenewable fossil fuels. Keys words: Organic matter, biogas, anaerobic digestion, sludge. 8 International conference on Research in Engineering, Science and Technology Paris, France November2-4, 2018 193 Introduction The new sources of energy will have to have as main characteristic a near zero balance in CO2 . Among them, the pathways of bioenergy production from waste are particularly interesting. A first, relatively old pathway is related to the production of methane by anaerobic digestion. A second possibility, much more recent and innovative, is the production of hydrogen by microbial ecosystems. The use of renewable energies such as biogas has become a necessity and is an integral part of the current strategy to mobilize all available resources (Demayer 1982). Methanation or anaerobic digestion is a series of operations of biological degradation of organic matter by a microbial flora that occur in the absence of oxygen. Products resulting from degradation can be classified into two categories, biogas and digestate. Biogas is a mixture of methane (CH4), carbon dioxide (CO2) and water vapor (H2O). Methane is the main constituent of natural gas. The digestate is the liquid residue containing the non-degraded materials. The process of anaerobic digestion is carried out in four stages (Gautron. P. 1990). These are the steps (Fig. 1.): Fig. 1.Anaerobic digestion steps [4]. Experiments are conducted on sludge from a wastewater treatment plant by. 8 International conference on Research in Engineering, Science and Technology Paris, France November2-4, 2018 194 Methods Our study includes laboratory experiments on the anaerobic digestion of organic waste. For this, a specific material for handling is necessary to know : A digester of 1 liter equipped with a sampling ; A water bath to set the temperature at 37 ° C. A system for measuring the volume of gas produced (measurement of volume by the method of displaced liquids) [5]. The parameters monitored are: pH measurement, temperature measurement, volume of biogas produced and chemical oxygen demand (COD). The anaerobic is must be controlled very rigorously in the digester before the launch of the waste digestion reaction. The experiments are conducted with a residence time of 20 to 30 days. Substrate of choice: Sludge of wastewater treatment plant. A wastewater treatment plant is a set of facilities and processes where wastewater is directed to eliminate the various pollutants. We will be particularly interested in a natural lagoon type, used as a sludge producer in our study. It is the most used biological treatment for medium-sized stations (more than 2000 equivalent inhabitants). The sludge is taken from the settling pond n°3. The physicochemical characteristics are given s on average of the samples taken during one year (see TABLE I.). TABLE I. Composition of the Wastewater Sludge Parameters Composition

Recovery of the sludge of a wastewater treatment plant by anaerobic digestion and biogas production