Study On Organic Wastewater Deep Treatment Using Biological Aerated Filter(BAF)

As the backbone of domestic economy, textile industry need to consume vast water resource and produce a mass of organic wastewater. Dyeing wastewater is difficult to be deep treated by general method due to its complicated degradable component. Therefore, it is no doubt that to research the new equipment for dying wastewater deep treatment, corresponding technology and its basic theory have important industrial and academic significance.In this dissertation, the biological aerated filter (BAF) with two kinds of filter and two parts has been constituted. The first part of the BAF at bottom is packed by the granular ceramics as the substrate for microorganism growing, which is not adsorbent but is cheaper and has large surface area and used to partially replace the expensive activated carbon. The second part of the BAF at top is packed by activated carbon for ensuring to remove some undegradable organic materials and obtain effective organic removal ratio. The effect of treatment conditions on organic removal ratio has been studied in detail; the operation characteristics of the BAF have been examined; the kinetics and mechanism of organic removal have also been discussed; cellulose material based ion exchangers have been prepared for pretreatment of dying wastewater containing heavy metal ions and their adsorption properties have been investigated. The main results obtained are as follows:1．The effect of treatment conditions, such as the ratio of air/water, HRT, temperature, influent concentration and pH value, on the removal ratio was studied in detail. It is shown that the organic materials can be most effectively removed at air/water ratio 3, hydraulic load 0．52 m³/(m²Â·h), HRT 1, temperature 25℃～30℃; the removal ratio of NH₄⁺-N, COD_cr, SS, turbidity and color are above 89%, 50%, 80%, 80% and 75% respectively, and their effluent concentration are below 1．2 mg/L, 50 mg/L, 10 mg/L, 5 NTU and 40 times, respectively, and can meet the reuse requirement. 2．The effect of temperature, DO, pH and the ratio of CODcr/N on simultaneous nitrification-denitrification (SND) and its mechanism were studied. The results indicate that the mechanism of SND in the BAF was unique structural feature and operation mode of the BAF; it is practicable that effluent concentration of NH₄⁺-N can meet the reuse requirement with the above character; the property of shortcut nitrification-denitrification obviously occurred in BAF. It is shown that the SND action is most effective, the removal ratio of TN reaches the highest at temperature 20～28℃, DO 0．8～1．5 mg/L, pH 7．2～8 and C/N 6．9～9．2 and the average removal ratios of TN at these conditions are 63．4%, 66．9%, 65．3% and 67．2%, respectively.3．The relation between operation characteristics and filter height of the BAF was investigated. The removal of NH₄⁺-N, COD_cr, SS, turbidity and color mainly concentrated on the beginning part of about 60cm. Thus the BAF height of 100cm used can make effluent meet the requirement of the wastewater reuse.4．The operation period and backwash process were examined. It is shown that backwash strength and duration are two important factors which significantly affect the regeneration of the BAF. In order to ensure the turbidity of the effluent to meet the requirement of the wastewater reuse, the backwash method and the corresponding fittest backwash parameters are firstly air scour with strength of 13 L /(m²Â·s) and duration of 2 min, secondly simultaneously air and water scour with duration of 3 min, strength of 11 L/(m²Â·s) and 3L/(m²Â·s), respectively, and then water scour with strength of 3L/(m²Â·s) and duration of 5 min. It was deduced that the biggest head loss is 100 cm and the backwash period is 5 d based on the turbidity of effluent less than 5 NTU.5．The kinetics and mechanism of organic-removal were discussed. Two main results are obtained as follows: (1) The relationship between the removal ratio of CODcr andthe filter height is deduced and the equation obtained is as follows:(?);and the parameters of the equation are calculated and thus the general equation at experimental conditions used is as follows:(?);(2) The kinetics equation was deduced as follows: , the parameters of theequation are calculated and thus the general kinetic equation at experimentalconditions used is as follows: (?). From theequation above, the ratio of undegradable matter is more than 10%. With ourexperimental conditions, the value of (?) tends to be 1 and the dye is difficult tobe hydrolyzed.6．It is reported that natural cellulose is unable to be oxidized by TEMPO-NaOCl-NaBr system. In this work, natural cellulose was modified by treating with less than 20 wt% NaOH solution for improving its accessibility. The alkaline celluloses obtained were oxidized by TEMPO-NaOCl-NaBr system and the factors which influence the selective oxidation reaction rate have been investigated, the structure of the oxidized products has been characterized by FTIR, NMR and WAXD methods, and their adsorption properties for Cu²⁺ and Cd²⁺ in aqueous salt solutions were examined. The results show that after the alkaline treatment, the primary hydroxyl at C₆ position of natural cellulose can be selectively oxidized to carboxyl group, the higher NaOH concentration and the longer alkaline treatment time, the largerer the oxidation rate. The adsorption capacity is significantly enhanced by introducing carboxyl groups into the cellulose macromolecular chains. The greater the carboxyl content, the higher the value of the adsorption capacity. However, since the oxidized cellulose prepared from cellulose treated with 25 wt% NaOH solution, having carboxyl content of 14．98%, was partially soluble in aqueous solutions, the dissolution of this sample resulted in reduced metal-adsorption efficiency. The metal-adsorption of the oxidized celluloses followed the Langmuir adsorption isotherm mode. Compared with the oxidized cellulose having carboxyl content of 5．12 wt% from cellulose treated with 25 wt% NaOH solution, the oxidized cellulose having carboxyl content of 5．12 wt% from cellulose treated with 15 wt% NaOH solution has a bit weaker metal-adsorption capacity, but has higher polymer of degree and weaker solubility, and can be practically used to remove the heavy metal ion in dyeing wastewater.