Comparative study of soils and other adsorbents for decolorizing sewage and livestock wastewater.

To investigate a soil's decolorization capacity for wastewater treatment, three types of soil (an Andisol, a sandy soil and a red soil) were compared with activated carbon and charcoal in their respective adsorption and recovery capacities. Sandy soil and red soil showed negative decolorization rates for sewage plant effluent. When 10 g of Andisol was applied to decolorize 30 mL of sewage plant effluent or livestock wastewater diluted fivefold and 20-fold, its decolorization rates reached 51.8%, 59.9% and 66.6%, respectively. The decolorization capacity of activated carbon and charcoal varied greatly because of their different original sources and production processes. An analysis of pore size distribution of activated carbons and charcoal showed that their decolorization capacity was positively related to their respective outside pore surface area and total mesopore volume. The result of a recovery experiment showed that activated carbon had a quick desorption for the adsorbed colored substances, which was hardly influenced when incubation time was increased from 7 days to 14 days. In contrast, the recovery rates for Andisol, zeolite and charcoal could be enhanced by increasing the incubation time from 7 days to 14 days or by decreasing the concentration of colored substances. During the continuous operation of Andisol-based decolorization systems, a column (100 cm3) filled with Andisol (84 g) and activated carbon (6 g) maintained a decolorization rate of more than 60% for 20 days for 20-fold diluted livestock wastewater with an absorbance of 0.8 at a wavelength of 406 nm at a hydraulic loading rate of 50 mL soil 100 cm−3 day−1.