The Study On The Treatment Of Landfill Leachate By Using An External Circulating Fluidized Bed

Since the 21st century, industrial and domestic waste production in city is increasing year by year with the rapid development of urbanization process, which makes an outstanding problem of dealing with landfill leachate. Leachate is a kind of high concentration organic waste water, containing kinds of pollutants, the water quality is variable, and it has a poor biodegradability. If not controlled properly, it will easily result in water, soil and air pollution. This paper reviewed the sources, hazards and treatment technologies of leachate. And then, an external circulating fluidized bed was designed to deal with the landfill leachate during the research, which combined aerobic/anaerobic biological treatment and fluidized bed technology.At first, hydraulic characteristics of external fluidized bed were studied, to get preliminary operation conditions. The factors of carrier quantity, air inflow and water inflow on the bed pressure drop and gas holdup were studied. The results showed that the bed pressure drop increased with carrier quantity increasing, decreased with air inflow increasing, increased initially with water inflow and kept stable afterwards. The gas holdup in the main bed increased with air inflow increasing, increased initially with carrier quantity and decreased afterwards. When carrier quantity was 10%, air inflow was 80 L/h, the volumetric oxygen mass transfer coefficient in the reactor was 10.2 h-1.The influencing factors on the starting of external circulating fluidized bed reactor were also studied. The results showed that when the carrier filling rate was 5-10%, the aeration rate was 80 L/h, hydraulic retention time (HRT) was 8 h, about 80% removal rate of chemical oxygen demand (COD) was achieved, and the thickness of the carrier biofilm was calculated at 135 μm. When the carbon nitrogen ratio (C/N) of influent was larger than 12 or lower than 6, sludge bulking was observed because of the numerous filamentous bacteria, the optimal C/N ratio should be controlled at 8-10 during the starting.At last, the process parameters on the effects of the treatment of landfill leachate during the runtime of the external circulating fluidized bed were studied. The results showed that:the removal rate of ammonia nitrogen in the main bed increased with the aeration rate and kept stable afterwards, the effluent COD removal rate increased firstly and then decreased as the increase in the aeration rate. With HRT going up, the ammonia nitrogen removal rate increased, and the effluent COD concentration reduced gradually. Moreover, the ammonia nitrogen decomposition rate was inhibited when influent pH was too large or too small. The optimum operating conditions were achieved after experiments that aeration rate was 80L/h, HRT was 8 h, pH was 7.5.At the same time, the load capacity of the reactor on the organic loading was tested, when the influent COD concentration increased from 4000 to 6000 mg/L suddenly, the reactor could make a response and adjustment in 4 days, and recovered the degradation effect of 90% COD removal rate. At the end of the research, COD and ammonia nitrogen removal rate reached 90.5% and 80.4% respectively under optimal and stable operation conditions.