Advanced Treatment Of Decentralized Sewage By Biochar

Today, with urban and rural developing together, the rural water pollution have become increasingly prominent in our country. It has become a major bottleneck in the construction of "beautiful countryside" and "Beautiful China". That forced us to need to invovate the traditional wastewater treatment process, which is used to decentralized sewage. At the same time, the crop residues, animal manure and other waste are widely located in rural areas; they also became one of the main potential sources of agricultural non-point pollution. This study relies on the National Technology Support Program, introduced the "by Waste" concept, combine the advanced treatment of decentralized sewage and disposal of agricultural waste. That is using the agricultural waste for preparing biochar, using the biochar to the water treatment agent for advanced treatment and standard upgrade of decentralized sewage, make the water achieve the quality requirements in the environmental sensitive areas (such as the Three Gorges Reservoir).In this paper, Firstly used tobacco stalks and cow dung to prepare the biochar, studied physicochemical properties and morphology of the tobacco stalk biochar and the cow dung biochar. Then according to static adsorption experiments, selected the biochar which had a better adsorption effect. At last, used the biochar which had been selected to structure the adsorption column and optimized the process conditions of the adsorption column. Hope to provide a technical support to use of biochar and treatment the rural disperse wastewater.The main conclusions as follows:Used tobacco stalks and cow dung to preparation of biomass carbon (TS-500, CD-500), they were alkaline, TS-500 was hard and full particles, CD-500 was loose texture and flocculent. TS-500 and CD-500 contain alkene, aromatics, aliphatic groups and hydroxyl structure, CD-500 also contains aliphatic chain structure. The surface of TS-500 was rough, it has the developed pores, and the internal pore was cleaner. Many projections were attached to the surface of CD-500. Two kinds of biomass carbon pores mainly composed of elements C, N, the content of K element in the pore of TS-500 was higher, the surface protrusions of CD-500 had high Si content, while K, Na, Mg elements are also relatively high, and had a amount of impurity.The adsorption effect of TS-500 to NH4+-N, TP, COD is better than CD-500. The adsorption ability of TS-500 and CD-500 to COD were poor, with increasing dosage of biochar, the trend of adsorbed content of NH4+-N, TP was in the frist increasing and then steady, the trend for COD adsorption capacity is in the first increasing and then reducing.With the Dosage increasing, the unit adsorption volume of both biochar on NH4+-N, TP, COD were decreasing. Considering the removal efficiency and economic administration, the best selection of dosage of biochar is 50g/LWith time increasing, adsorption capacity of TS-500 and CD-500 to NH4+-N, TP, COD was first increasing, and then stable, the fitting effect of the pseudo-first order model and the pseudo-secongd order model for NH4+-N, TP, COD were better, it can be used to describe the NH4+-N, TP, COD adsorption process of TS-500 and CD-500. Intra-particle diffusion model was confirmed that inner diffusion is only part of the adsorption process of CD-500 and TS-500, but not the only factor to control the rate of adsorption. The fitting results of Langmuir and Freudlich show that the NH4+-N, TP, COD adsorption of TS-500 and CD-500 was a molecular monolayer and multi-layer adsorption characteristics presented. There was a complex relationship between the biochar and adsorbate. With temperature increasing, the NH4+-N, TP, COD adsorption capacity was increasing, considering various factors such as the adsorption rate and economy, the optimum reaction temperature is 25 ℃. Increasing the initial concentration, the adsorption amount was increasing, but the removal rate was reducing, The handle concentration of NH4+-N, TP, COD of TS-500 is slightly higher than the CD-500 in the waste water, the preferred range is NH4+-N concentration is less than 20mg/L, TP concentration less than 20mg/L, COD is less than 200mg/L.TS-500 and CD-500 had the similar degree of desorption in NH4+-N. the weak acid leaching nitrogen desorption rate was maximum; for TP desorption, the weak acid adsorbed phosphorus and calcium-binding phosphorus was maximum desorption rate; bothe of two biochar desorption rate of COD was similar.The biochar adsorption column optimization results is that using TS-500 packed, water up flow mode, water rate was 20mL/min and the hydraulic load is 382m3/m2.h. NH4+-N concentration in the effluent achieved the urban sewage treatment plant emission standard level A, TP and COD concentration respectively achieved the level B and level A. All of they had reached the effect of advanced treatment and standard upgrade.