Study On Production Of Biological Activated Carbon From Orange Peel And Landfill Leachate Subsequent Treatment Techlonogy

Orange peel is a typical agricultural waste rich in cellulose and hemicelluloses', which has the unique natural pores which cause its features such as high surface area and high porosity compared with other agricultural wastes. Based on the analysis of the characteristics of orange peel, it was considered that these natural pores of orange peel were conducive to format activated carbon with developed mesopores in this paper. These natural pores of orange peel also facilitate active agent entering into material interior and activate reaction can occur under mild conditions, then activated carbon with developed pores and rich surface function groups should be gained. Based on the property of preserved function groups of the activated carbon from orange peel, it was considered that natural organic function groups of the activated carbon from orange peel had excellent compatibility to the microbes, which was conducive to growth of microorganism and formation of biological activated carbon (BAC). So, the technological process and parameters of preparing biological activated carbon from orange peel were researched in this paper. To treat the refractory landfill leachate biochemical effluent, the naturalization, culture and immobilization process of biological activated carbon were explored. The technology of Ozone/biological activated carbon (O3-BAC) for orange peel for subsequent treating landfill leachate biochemical effluent was built. The research results were as follows:①Activated carbon with compatibility to the microbes from orange peel was prepared with one-step activation method by parameters such as impregnation ratio, impregnation time, heating temperature and heating preservation time. The experiment showed that the prepared orange peel carbon, under the conditions of impregnation ratio of 3:1, impregnation time of 36h, heating temperature of 550℃and heat preservation time of 1h, had iodine number of 1523.1mg/g, methylene blue adsorption of 262.5mg/g. The carbon had BET specific surface area of 1477m2/g, mesoporous pore volume of 1.440 cm3/g, total pore volume of 2.090 m3/g, with very concentrative pore distribution of average pore diameter 3.87nm, belongs to activated carbon of well-developed mesoporous pores. Surface functional groups of the activated carbon were further examined by infrared spectroscopy (FT-IR), which indicated that orange peel activated carbon prepared under these conditions contained hydrophilic functional groups of hydroxyl, carbonyl and lactone. XRD spectrum showed that it had very obvious turbostratic graphitizing tendency with little crystallite diameter and thickness, which indicated a higher reactivity of the activated carbon.②According to analyzing adsorption characteristics of activated carbon from the orange peel, it was found that it had the chracteristics of typeⅠadsorption isotherm. Static absorption experiment indicated that activated carbon from orange peel had a good adsorption performance to leachate biochemical effluent, and the removal rate of UV254 and TOC were 63.0% and 59.7%, respectively. The adsorption process was tracked by three-dimensional fluorescence spectrum; and it was found that the activated carbon had high adsorption ability to organic matters such as humic-like. Further research showed that pseudo-second kinetic model could be used to describe the adsorption processes of orange peel activated carbon adsorbing leachate biochemical effluent with the adsorption activation energy is 12.72 kJ·mol-1. In this study, the correlation of Freundlich model was better than that of the Langmuir model and 1/n of Freundlich model was 0.3078~0.3147. Theoretical limit of adsorption of orange peel activated carbon is about 12.0 mg/g.③The start-up characteristics and operating effciencies for using self-made activated carbon from orange peel and activated carbon from market as supporter of biological activated carbon were compared in this paper. The research results indicated that sludge was naturalized based on SBR process operation mode and operated by dynamic immobilizing biofilm and static biofilm immobilizing mode, then rapid biofilm immobilizing and start-up of biological activated carbon reactor could be achieved. Naturalized sludge was made up microbial solution of 500mg/L; biological activated carbon reactor was circular operated with flow quantity of 400～560 mL/min with water upward-flow and controlling the sludge mass of biological activated carbon reactor in according to volume concentration of 2～4g/L. The research found that biological activated carbon reactor could be steady colonized biofilm in one or two days. Microorganisms immobilizing can be completed within one day for the BAC system from orange peel, which is faster than that of BAC from market. It was found that organic removal rate of Self-made BAC from orange peel can steadily be over 70% and 5%~10% higher than that of BAC from market. It was found that fulvic-like fluorescence intensity of leachate biochemical effluent decreased 80.0% ~ 88.0% and high-excitation wavelength tryptophan-like fluorescence intensity decreased more than 50.0% through the BAC system from orange peel by tracking three-dimensional fluorescence spectroscopy, which was significantly better than BAC system from market of 60.0%~70.0% and 33.0%, respectively.④With the increasingly stringent discharge standard of landfill leachate, the wastewater treating technology based on ozone-biological activated carbon (O3-BAC) from orange peel was built with the purpose of meeting the discharge standard. By tracking the charge processof molecular weigh (MW) of organic matter in leachate biochemical effluent, it was found that the organic matter of MW>100k Da in the effluent decreased from 25% of raw wastewater to approximately 12%, while the organic matter of MW<1k Da in the effluent increased from 7% to 30% or more when ozone dosing was 10.0mg/L. Moreover, the wastewater B/C increased from 0.186 to 0.313. Further research showed, when COD concentration of leachate biochemical effluent that entering the O3-BAC wastewater treating system was below 700mg/L and NH3-N concentration was below 100 mg/L with hydraulic loading of 4.62m3/m2·d, O3-BAC system effluent can meet the discharge standard (GB16889-2008) with COD below 100mg/L and NH3-N below 10mg/L.⑤The performance along the flow direction and kinetic characteristics of BAC system were preliminary explored. It was found that microorganism was firmly adhered by activated carbon with good bio-compatibility from orange peel. Microbial biomass of BAC from orange peel was up to 429.9 nmolP/g Carbon and obvious high than it of BAC from market. Moreover, microbial activity of BAC from orange peel was more 10% than it of BAC from market. The overall trend of microbial distribution gradually decreased along the flow direction, so organic matter was mainly removed at inlet carbon layer of BAC system. More than 50% organic matters were removed within inlet 90cm carbon layer, accounting for more than 80% of the total removal rate. A first order kinetic equation can be used to describe the degradation laws of organic matters, the reaction rate constants decrease along the water flow direction. There is a good correlation between the reaction rate constant and microbial activity of BAC fron orange peel, with the correlation R2 of 0.9596, while the correlation R2 between reaction rate constant and microbial biomass is just 0.2044.