Research Of The Cellulose Carriers With Pretreatment And Their Enhanced Nitrogen Removal In MBR

Adding carbon source is the reliable method for removing nitrogen from the low C/N ratio sewage. Methanol, ethanol, acetic acid and others being the external carbon sources are often added, whereas they are generally high-cost, high-energy and high operating requirements. Fortunately, it has been noticed that lignocelluloses such as agricultural wastes support a sustainable slow release of carbon source, to become the most potential solid carbon sources. But new solid carbon sources such as straw and other agricultural wastes are difficult for large-scale application because of their low utilization and denitrification rate, also the high organic concentration in the effluent. Given this, three kinds of lignocellulosic agricultural wastes including retinervus luffae fructus, corncob, rice straw through ultrasound, microwave radiation, alkali pretreatment were made as cellulose carriers. In this study, carbon release capacity, denitrification capacity, denitrification rules of these cellulose carriers were compared, then applied in MBR to evaluate their promotion for removing nitrogen.According to this study, some conclusions can be drawn as follows:(1) Compared carbon release capacity, denitrification capacity and denitrification rules of retinervus luffae fructus, corncob, straw through ultrasound, microwave radiation, alkali pretreatment, results showed that alkali treatment promote higher carbon release capacity. The carbon release quantity (COD release quantity) of these cellulose carriers improved from 136-178mg/g to 250-323mg/g, and denitrification potential (DP) improved from 112.04-157.94mg/g to 233.82-250.69mg/g after 2% NaOH treatment for 24h. Analysis of the component, scanning electron microscopy and infrared spectroscopy of the cellulose carriers showed that the alkali treatment removed the nonbiodegradable lignin effectively, while increased the contents of cellulose, enhanced the accessibility for enzyme. Otherwise, cellulose carriers could be used as preferential solid carbon sources.(2) Traditional MBR removed TN limitedly. The average TN removal efficiencies were 26.81% for control MBR,36.05% for polypropylene carriers addition,72.96% for alcohol 0.4g/(L·d) addition, respectively. It indicated that carbon source was the critical factor for removing nitrogen in MBR. When the dosage was 1.42g/d, the average TN removal efficiencies were 63.46% for the alkali-straw addition MBR, and the average TN effluent lower than the discharge standard for municipal sewage treatment plant (GB18918-2002) concentration of class A standard control (15mg/L). The kinetic model of simultaneous nitrification and denitrification (SND) was established, and NO3--N saturation coefficient of the alkali-straw addition MBR was 0.21, which was much lower than the control MBR, and similar to the single-stage denitrification.(3) Appropriate straw dosage would not increase COD concentration in the effluent, but also promoted the dehydrogenase activity of sludge. The dehydrogenase activity of the alkali-straw addition MBR were 144.60mgTF/(L·H), much higher than 78.17mgTF/(L·H) of the control MBR. After 110 consecutive days of operation without excluding sludge, the MLSS of the alkali-straw addition MBR rose from 7865mg/L to 9466mg/L, and no blockage, no decline of the membrane flux or any other adverse reactions were found.