Development And Application Of A Porous Carrier Used In Biofilm Reactors

Although biofilm process is widely applied in municipal and industrial wastewater treatment, there are still some problems related to the process such as high initial investment and long start-up time. A porous biofilm supporter called perilite was first developed, which was cheap and rich in China. Then, the property of the carrier was investigated. Finally, the application of the carrier was researched. The main conclusions were gained as follows:(1) Roasting is the most important step and the factors influencing the quality of the carrier are roasting temperature and duration. Lower density carrier with coarse and porous surface can be developed under the condition of proper temperature and time.(2) Biofilm thickness, structure and activity were mainly influenced by package ratio and turbulent intensity in MBBR (moving bed biofilm reactor) with carrier of outer surface to be utilized. Biofilm thickness decreased and activity increased when package ratio was enhanced among 10%, 20% and 30% at the same turbulent intensity. The detachment in this MBBR was a continuous process, which was controlled by the collision of the carriers. Because of high detachment rate biofilm was thin (<400 μm) in this experiment, which favored diffusion of DO and other substrates. However granular sludge was formed in reactor with 5% package ratio when high COD loading rate and short HRT were executed.(3) The patchy biofilm dominated in Batch MBBR when XEG-5 carrier was used. At the same time the carrier wrapped in the sludge was frequently washed out from the reactor with the wasted sludge. So it seemed that small carrier was not fit for MBBR.(4) The mechanism of the biofilm detachment in MBBR was abrasion caused by the collision between carriers. The detachment rate from abrasion could be described by combination of collision frequency with energy required to produce a new surface as crystal formation. The relationship between the specific detachment rate r and thepackage ratio n and energy input G for a MBBR reactor filled with carriers of the average diameter d can be expressed as: r = η ·nd³G^3/2. The result of experiment showed that specific detachment rate was approximately consistent with the prediction in theory. So the detachment rate in MBBR could be controlled by change of package ratio and energy input in practical operation.(5) Hybrid biofilter with porous carrier united the characters of activated sludge and biofilter, which could make use of both advantages. No clog was found during 220 days operation and COD removal efficiency was above 80% under the organic loading of 4kgCOD/m³Â·d.