Research On Comparison Of Performance Of Two Media In Biological Aerated Filters

Biological aerated filters (BAFs) are a new kind of biological oxidation process applied widely in wastewater treatment, reclaimed water reuse, and pre-treatment of slightly polluted source water.Biological aerated filter (BAF) is a new kind of biological oxidation wastewater treatment technology from Europe countries and America at the end of 1980s. BAF is a fixed film biological process that can be used for the simultaneous removal of carbonaceous matter, ammonia and suspended solids in a single unit mainly by interception, biological metabolism, adsorption. The BAF has main advantages of high efficiency, small footprint, ease of operation and management, no secondary clarifier, modular construction, and so on. Owing to these advantages, it is an alternative to the traditional activated sludge process which is commonly used in biological wastewater treatment. Nowadays with the rapid development of the BAF systems, they have been selected for many small or large towns for secondary and tertiary treatment of wastewater or reclaimed water reuse purpose throughout the world.The performance of the two BAFs,one containing polyurethane sponge and the other containing biological granular ceramic, both identical in shape and size, in order to determine the suitability of new material as its media was compared. The aim of this study is to determine the suitability of new material as its media and provide reference of media selection for BAF. A series of experiments has been conducted continuously on a pilot scale using synthetic domestic wastewater as feed water with under different conditions. The main research contents are as follows:(1) Start-up of the two BAFs was researched. It took 17 days to reach steady state operation period for the two reactors supported with polyurethane sponge and granular ceramic.(2) Under the different hydraulic loading varied from 5 to 20 L/h, Changes of concentration and removal efficiencies of COD and NH4+-N in two BAFs were discussed. Higher NH4+-N removal in the BAF with polyurethane sponge may be attributed to its higher specific area. COD and NH4+-N removal efficiency increased with increasing media height in both BAF while most of COD and NH4+-N reductions occurred at the media height of 40 cm. (3) Influence of air-water ratio on performance of two BAFs was explored. The results showed that COD and NH4+-N removal efficiency increased with increased air-water ratio. However, their gradient variations on COD and NH4+-N removal in both BAFs are gradually slow. The air-water ratio of 10:1 can meet the requirements of DO in two BAFs. Under the same air-water ratio the performance of new polyurethane sponge BAF was better than biological granular ceramic BAF.(4) Characteristics of operation of the two BAFs and influence of backwashing on filter performances were discussed. The results indicated running time of polyurethane sponge BAF was more than double it of granular ceramic BAF. Influence of backwashing on COD and NH4+-N removal in the two BAFs was less. Value of COD and NH4+-N removal efficiency recovered previous level of backwashing.(5) The kinetics model of BAF decomposing organic matter was probed into and kinetics equation were obtained.(6)The capital cost and maintenance fees of BAFs with biological granular ceramic and polyurethane sponge were calculated. The results showed that the capital cost of the polyurethane sponge BAF and its maintenance fees were a little higher than that of the granular ceramic BAF. In a word, polyurethane sponge is suitable for being used as media in BAFs.