A Comparative Study of Soil and Other Adsorbents on Decolorizing Livestock Wastewater.
Xin Chen1, Kuniaki Sato1, Toshiyuki Wakatsuki2, and Masunaga Tsugiyuki1. (1) Faculty of Life and Environmental Science, Shimane University, 5-542 shoohokudai, Matsue, Japan, (2) Faculty of Agriculture, Kinki University, Japan, 2-3-22 Tomio, Kinki University, Nara, 631-8505, Japan
High concentration of pigments in livestock wastewater not only caused visual pollution but also associated with many health hazards. Adsorption is one of the techniques that have been successfully employed for effective color removal. To investigate soil's sorption and decomposition capacity of pigments in livestock wastewater, three soil samples were compared with activated carbons (AC), zeolite, wood charcoal and bamboo charcoal in their respectively sorption and decomposition rates. In adsorption experiment, different amount of adsorbents were put in centrifuge tubes and added with 30ml livestock wastewater. After shaking for one hour, treated water was centrifuged and filtered, then measured with spectrophotometer at a wavelength of 406nm. Preliminary data showed that Andisol was a quite competitive adsorption material and adsorption rate can reach 59.9% and 66.6% respectively with an adsorbency of 2.85 and 1.91 at 10 grams. The adsorption rates of AC differed a lot as the original source and activation process were different and was strongly infected by their surface area, volume and pore size distribution. In decomposition experiment, eight columns with soil or zeolite, mixed with 10% of AC or charcoal, were applied with livestock wastewater at an adsorbency of 1.91 for 2 days and saturated with wastewater at an adsorbency of 2.85 for 5 days, then put into incubation machine at 30 oC for three days, one week or two weeks. After that, the columns were put into circular application again. Results showed that sandy soil, when mixed with 10% of AC, showed almost the same adsorption and decomposition rate of Andisol plus 10% AC. Red soil got clogged easily due to its high clay content. The increase of incubation time from one week to two weeks could enhance Andisol, zeolite and charcoal's decomposition rate by 48.9%, 37.9% and 21.5% respectively after 3 circles incubation, but had little influence on AC as they seemed to have their own effective decomposition capacity (EDC), which could be achieved within short time and was closely connected with their own characteristics. Continuous column (100ml) experiment showed decolorization of livestock wastewater by Andisol system could be sustainable with appropriate hydraulic retention time (HRT) and pigment concentration. At a HRT of 2 days and adsorbency of 1.91, Andisol could keep decolorization rate from 61.5-71.8% with an average of 63.4% and Andisol mixed with 15% AC from 60.5-75.18% with an average of 68.0% for 25 days continuous application. Air-sending also greatly enhanced Andisol's decolorization rate by around 20% and the decolorization could keep 100% for one week with air-sending rate of 1L min-1 system-1 under the same condition. Key words: decolorization, livestock wastewater, pigments, soil