In general, there are two ways to design an UASB reactor
If input COD: 5,000 - 15,000 mg/l or more, the design method should be used based on Organic Loading rate, (OLR) If input COD < 5000 mg/l, the design method should be calculated based on velocity.
Some H2S gas can pass the GSL separator and accumulate above the water level in the top of the reactor. This will be oxidized to sulphate by oxygen in the air to form Sulphuric Acid that will in turn cause corrosion of both concrete and steel. Below the water level: Calcium Oxide, (CaO), in concrete can be dissolve with by Carbon Dioxide, (CO2), in the liquid in low pH conditions. To avoid these problems, the material used to construct the UASB reactor should be corrosion resistant, such as stainless steel or plastics, or be provided with proper surface coatings, (e.g. coated concrete rather than coated steel, plastic covered with impregnated hardwood for the settler, plastic fortified plywood, etc).
Operation
Operation criteria: The optimum pH range is from 6.6 to 7.6 The wastewater temperatures should not be < p =" 350"> 20oC) and sometimes the start-up can take up to 3 – 4 months. In start-up process, hydraulic loading must be Ј 50% of the design hydraulic loading.
The start-up of the UASB reactor can be considered to be complete once a satisfactory performance of the system has been reached at its design load.
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