This disclosure relates to a process and a system of anaerobic digestion for agricultural biomass waste, livestock waste and industrial wastewater in the presence of anaerobic microorganism, and in particular, relates to the process and system combining the high solid content digestion and the hydro circulation digestion. In this system the material and liquid in the enclosed vessels always flow at one direction, and the system is sealed to prevent other foreign medium going into the system.
Currently, the common anaerobic digestion methods and devices are Complete Stirred Tank Reactor process (CSTR), Anaerobic contact process Reactor, Up-flow Anaerobic Sludge Bed (USAB) and Up-flow Solids Reactor (USR). Those have the following disadvantages: (a). These devices are only suitable for livestock manure and but not to digest crop materials such as stalk or straw due to excessive high carbon & nitrogen ratio in the stalk in comparison with the required carbon & nitrogen ratio by anaerobic digestion; (b). Most of above mentioned devices use internal heating, consequently, such digester gets corrosive easily with bad sealing, and therefore to interfere the growth of aerobic bacteria; (c). Such devices are complicated and a gas storage tank is also required, therefore, these need much large land to install but also with long down time for maintenance; (d). Due to interval feeding and discharging, such devices have to start frequently causing low efficiency; (e). Feedstock generally is fed into the digester from the top, and it is difficult to mix the feedstock well enough inside the digester, therefore, causing caking at top surface of the liquid level; and (f). Higher investment will be needed due to more accessories and high operation cost.
Currently used pneumatic conveying system has some disadvantages: (a) The pneumatic conveying system is merely suitable to transport these materials that are not vulnerable to agglomeration though the system can be used to transport the materials in an enclosed channel; (b) Due to the bad seal, air may be mixed in the system entering the digesters.