TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Process: In treating the sludge, the liquid fraction comprises alkalinity, and the ammonium salt solution is acidic and has an increased concentration of ammonia and decreased alkalinity relative to the liquid fraction. The process comprises producing a flake, granule or pellet comprising the solids fraction and the ammonium salt solution. The process further comprises a step of drying the flake, granule or pellet by way of flowing air over the pellets at a temperature of 90 degrees C or less or 80 degrees C or less. The flake, granule or pellet is combined with compost, where the compost comprises fibers separated from the sludge prior to step (a). Step (a) comprises one or more of physical or mechanical dewatering and thermal drying. The process as well comprises a step of concentrating the ammonium salt solution before combining it with the solids fraction. Step (b) comprises extracting ammonia gas from the liquid fraction. Also, step (b) comprises one or more of (i) steam based ammonia stripping of the liquid fraction; (ii) applying heat and a vacuum to the liquid fraction; and (iii) a combination of subsurface aeration and airflow across the liquid surface in multiple stages. Step (b) comprises a step of mixing an acid, for example one or more of sulfuric, acetic or citric acid, with the extracted ammonia gas. In step (c), the solids are combined with the ammonium salt solution in a dryer or pelletizing machine. The sludge is produced in an anaerobic digester. The process also comprises producing a liquid stream with reduced ammonia concentration in step (b) and returning this liquid stream to the anaerobic digester or to an activated sludge wastewater treatment plant. Making the fertilizer pellet further comprises drying the pellet by way of a flow of air at 90 degrees C or less. Preferred Process: In the process, the fibers are used in a plant growing medium, where at least some of the solid or liquids are added to the plant growing medium, and where at least some of the solids or liquids are converted into a granule or flake form. In removing ammonia from the liquid, the flow rate of the surface flow is greater than the flow rate of the bubbles. Preferred Apparatus: The apparatus for treating sludge further comprises an air flow drier to receive and dry the pellets. The ammonia recovery system comprises one or more of (i) a steam based ammonia stripper, and (ii) a vacuum induced ammonia gas extractor. The ammonia recovery system further comprises an ammonium salt solution concentrator. The apparatus also comprises an anaerobic digester to produce the sludge. EXAMPLE - No suitable example given.