Study On Characteristics Of Lateral-Flow Biological Aerated Filter (LBAF) For Municipal Wastewater Treatment

Since 1980s, the Biological Aerated Filter (BAF) has got extensive research and use in the field of sewage treatment all over the world. At present , it is a great subject of a sewage treatment technology research field to develop the low consumption , high efficient city sewage treatment tecknology for small-and-medium-sized towns in China. Developing lateral-flow BAF, has offered a new thinking for solving this problem. This study is in drawing traditional BAF operation mechanism and research results of old type lateral flow BAF , based on a redesigned reactor of lateral-flow aerated biological (LBAF). The research contents was focused on the following parts: hydrodynamic bebavior , performance of contamitants removal , influence factors of operation performance , dynamisc model of organic matter removal. To determine the hydrodynamic behavior of lateral flow biological aerated filter (LBAF), pulsed signal experiment was carried out in this study. Experimental results show that the flow pattern of LBAF is close to plug flow, and based upon the flow pattern retention time distribution function was developed. It was also shown in this experiment that flow rate and aeration strength are two key factors that in fluence the reactor flow pattern. The impact on LBAF operation of hydrodynamic behevior includes the waste utility efficiency , volume utilization ratio , nitrogen removal performance. The study found plug flow helps to improve the performance. The LBAF treatment performance trials included 4 main contents: start-up performance, result of treating the municipal sewage, periodic changing of operation performance, backwash characteristic. Because of cation exchanging ability of the media (zeolite) , ammonial removal effciency is quite high in the start-up period. Through the nitrogen equilibrium along the media length , it was detected that zeolite has been releasing ammonia and self-balanced nitrogen supply mechanism i n the media has been set up. The results of operation data analysis shows LBAF got excellent COD , SS removal performance and super ammonia removal ratio. During operation , the average removal ratios of COD, SS, ammonia were 84.6% , 94.6% , 62.7% respectively. During operation , the operation efficiency of LBAF varies periodicly in response to backwash. In a such cycle, the bilfilm amount increase gradually to the saturation, which cause heterotroph increasing excessly , autotroph losting activation simulta-neously. The another phenomenon during the operation cycle is that the COD and ammonia degradation curve along the media length change dramaticly. In general , operation cycle of LBAF is much longer than tranditional BAF. The backwash mode of LBAF adopts the air-water conbined backwash , which the intensity are 5L air/m2.s and 4.5 L water/m2.s, lasting 15 min. In case of 0.85m height of media , backwash water consumption was near 10% of the treating water. It is suggested that backwash water consumption influences investment of LBAF plant and increasing me dia height can availably reduce backwash consumption and air: inflow ratio. The following condition may influence operation performance of LBAF: inflow loading , hydraulic loading (retention time) and temperature. Operation performance decreases with inflow loading increasing , especially nitrogen removal performance, while hydraulic loading can't influence operation performance almost. After temperature is lower than 13 degrees Centigrade, the operation performance of the reactor is obviously reduced. The study on characteristics of LBAF for municipal sewage treatment shows the operation performance of LBAF is comparable with the traditional BAF , while LBAF has longer backwash cycle , lower backwash water consumption and air: inflow ratio. Totally , LBAF accord with the low consumption , high efficient technological requirement.