Comparing the efficiency of uaff and uasb with hybrid reactor in treating wood fiber wastewater
Some industrial wastewaters such as pulp and paper mills and chemicals are highly loaded with organic pollutants and can be treated advantageously by means of anaerobic processes. Anaerobic treatment converts the wastewater organic pollutants into a small amount of sludge and a large amount of biogas. Several operational problems have normally been experienced in both suspended growth and biofilm systems, which are widely used for wastewater treatment. More significant problems are long start-up periods, instability in Upflow Anaerobic Fixed Film (UAFF) and granulation problems in Upflow Anaerobic Sludge Blanket (UASB). A hybrid reactor has been conceptualized which addresses these problems but retains the positive aspects of these reactors, such as, high cell concentration, good mixing and tolerance to high loading rates. So, in recent years, studies have focused on hybrid system that is a combination of UASB on bottom and UAFF on top. It retains the advantages of both systems and is also stable and resilient to shock loadings and combines the best features of both suspended bed and fixed film technologies into one unit, with the added benefit of methane production for reuse (Shreekrishnan and Gomes; 2002, Borja et al., 1996). In the lower 30-50 percent of the reactor volume which is the UASB zone, flocculent or granular sludge develops. Most of the organic stabilization occurs in this sludge bed. In the upper 50-70 percent of UAFF section, a cross flow type media is used, which provides an extensive surface area for the fixed film biomass to develop and grow. This media is also effective at intercepting sludge bed solids and raw influent solids, and promoting their flocculation and return to the sludge bed below (ADI Systems Inc.).