USAB

There are different types of digesters available, some have been proven effective overtime, and others are still being tested. One of the most suitable digesters for tropical conditions is the USAB (upflow anaerobic sludge blanket). In tropical conditions, there are reductions in BOD of 75%-90%. UASB technology is feasible in an urban, developing world context because of its high organic removal efficiency, simplicity, low-cost, low capital and maintenance costs and low land requirements.

Typically, USAB’s have low sludge production and low energy needs. Since nitrogen and phosphorus are not effectively reduced in anaerobic technologies, this primary treatment approach works well with agriculture or aquaculture. However, they are not completely effective at removing all pathogens, the wastewater needs a post treatment option to meet discharge standards, such as composting digested sludge, wetland systems, or stabilization ponds.

The UASB reactor essentially consists of a gas-solids separator (to retain the anaerobic sludge within the reactor), an influent distribution system, and effluent draw-off facilities. It is constructed with entrance pipes delivering influent to the bottom of the unit and a gas solids separator at the top of the reactor to separate the biogas from the liquid phase (water and sludge); overall, this prevents sludge washout.

The hybrid reactor is an improved version of the UASB system and combines the merits of the upflow sludge blanket and the fixed film reactors. The advantages include simplicity of design and operation; it also is more economical than a fixed bed system.