제트 루프 반응기에서 공기탈기법에 의한 폐수 중의 암모니아 제거특성

Abstract

According to development of modern social, Wastewater containing highly concentrated ammonia was made from various field such as industrial process, waste disposal facilities, etc. When the wastewater is discharged into river and sea, it reduces the dissolved oxygen, which can result in eutrophication and algal growth (i.e., Red tide). It is also reduces efficiency of operation in the sewage treatment facilities. For these reasons, a proper treatment of wastewater is essential prior to discharging into water systems. Physiochemical treatment methods and biological methods are applied to dispose of ammonia-containing wastewater. In general, the wastewater containing highly concentrated ammonia was treated by physicochemical treatment methods. Air stripping – in which air is injected after converting ammonium ions of water into ammonia by increasing pH -, one of physicochemical treatment methods, is a common means to remove ammonia from wastewater, because of simple structure, easy operation, and economic. Since the contact between air and wastewater is an important factor, a gas-liquid reactor including packed tower is utilized. A disadvantage of this approach is the high pH necessary for operation generates scale and fouling of the packing matter and pipes. In addition, bubble column and agitated vessel reactors are hindered by the high pressure necessary, low mass transfer, and high operation cost. The jet loop reactor (JLR) was developed as an alternative to the conventional reactor. Researched applications of the JLR include the neutralization of highly concentrated wastewater using CO2 and the crystallization of struvite and the elimination characteristics of total phosphorus. The data revealed the higher air-liquid reaction efficiency of JLR than the conventional reactor. The efficiency was attributed to the ability of the high-speed jet stream generated from the two-fluid nozzle of JLR to increase the turbulence intensity and facilitate the formation of fine bubbles, which expands the air-liquid contact area and increases the mass transfer rate. Other advantages of JLR include its relatively simple structure reasonable costs of installation and operation compared to other reactors. Thus the jet loop reactor applied air stripping will be more efficient then other reactors for removing ammonia. This study aimed to improve the performance of existing jet loop reactor for effectively removing ammonia from wastewater by air stripping. Removal characteristics of ammonia were evaluated with varied pH, liquid circulation flow rate (QL), gas flow rate (QG), and temperature (T) by infecting synthetic wastewater and gas continuously into the JLR at semi-batch scale. As well, this study was examined characteristics of ammonia removal from a synthetic wastewater, when applying varied type of reactors (slanted-type, cylinder-type), the two-fluid venturi-type conventional nozzle (TVCN), the two-fluid venturi-type swirling nozzle (TVSN), and draft tubes (conventional draft tube, swirling draft tube). The result of this study, the cylinder type jet loop reactor applied swirling draft tube and TVSN had the highest efficiency of ammonia removal and overall mass transfer coefficient. And the efficiency of ammonia removal and overall mass transfer coefficient were increased by increasing pH, QL, QG, and T. Especially, overall mass transfer coefficient was significantly incresed in case of increasing QG and T then pH, QL. The highest overall mass transfer coefficient was 0.0056 min-1 in this study on cylinder-type JLR with a TVSN, a gas recirculation preventor, and a swirling draft tube at T = 30 ℃, pH = 11, QL = 25 L min-1, and QG = 35 L min-1. Meanwhile, this study aimed to take basic design data for the jet loop reactor applied air stripping with the highest overall mass transfer coefficient from the semi-batch JLR. For this purpose, reactor analysis was conducted about the JLR. Ammonia concentration was measured in the continuous JLR and then measured results and reactor anlysis results were compared. Result of the study, the JLR was analysed as a mixed flow reactor. And also, predicted ammonia concentration from outflow analysed as a equal-size JLR in series were similar with actual experiment results. Thus in this study, it has been suggested that the design model of the jet loop reactor in series considering operation condition.