Adsorption Effect Of Biochar And Its Modified Materials On Phosphorus In Effluent From Septic Tanks

In recent years,the construction of small towns and villages has accelerated.With the increase in residents’ income,the eutrophication of surrounding lakes and reservoirs has also increased.Various localities have actively responded to the requirements of the state and local "toilet revolution",banning dry toilets in villages and towns in order to improve sanitary conditions,and septic tanks have become one of the first choices for rural households in the construction of supporting treatment facilities.Septic tanks need to be cleaned regularly to ensure the treatment effect,and the collection,treatment and resource utilization of manure wastewater in the cleaning process has become an urgent problem to be solved.In this paper,aiming at the key nutritional control index total phosphorus in the eutrophication process,corn straw and rice straw derived from agricultural waste are selected as raw materials to prepare modified biochar,and the adsorption characteristics of modified biochar to phosphorus and the adsorption of practical applications are explored effect.According to kinetics and thermodynamics theories,the simulation research is carried out to clarify the important influencing factors of the adsorption process and determine the appropriate dosage and operating conditions accordingly.In addition,XRD,XPS,SEM,Fourier transform infrared spectroscopy and other microscopic methods are used to characterize the morphology of the biochar surface before and after adsorption,the adsorption products,and the chemical bonds and functional groups of the main elements to explore the adsorption mechanism.Finally,the adsorption effect of the manure separation liquid collected from the actual septic tank in Chongqing,the preliminary design of the treatment process and the preliminary estimation of the operating cost,and the provision of certain research support for the resource-based treatment and disposal of decentralized rural manure were carried out.The surface pores of the straw biochar after metal impregnation and drying are increased,and there are no obvious fragmented sections.It can be observed that many particles are loaded on the surface of the biochar,forming irregular concave and convex structures,and there are certain amorphous crystals.Structure,but the metal filling causes some of the original pores to collapse.Pickling is beneficial to the loading of metals on the surface of biochar to a certain extent.The original straw biochar is mainly composed of C,N,O,K and other elements,and also contains a small amount of S,Si and other elements.From the comparison before and after the modification,the C content decreased slightly after modification,and the corresponding metal cation content increased,accounting for 1%～1.5% of the total element ratio,respectively 3.2～4.0,6.5～6.9,2.5～before loading.2.8 times.From the point of view of molecular composition,modified biochar is mainly composed of organic matter(saturated bond),mineralized inorganic matter,and metal salt loaded on the surface and pores.Unmodified biochar has very poor crystallinity.After modification,the metal is attached to the surface of biochar in the form of a mixture of metal oxides and unoxidized metal salts(chlorides).Calcium-modified biochar has a geometric crystal structure that can be observed.The magnesium-modified biochar has higher crystallinity.The results of the research on the characteristics of corn and rice straw biochar and its modified biochar show that:(1)The modification method and the loading amount of the modifier mainly affect the adsorption capacity of the biochar,and the biomass source under the same preparation conditions is not affected.Significantly.(2)The proportion of CH and CC in the carbon groups of the modified biochar has decreased,while the proportion of oxygen-containing groups such as CO has increased.Under the modified condition of 100 ℃,no C=O etc.Obvious changes in saturated oxygen-containing functional groups.(3)Unmodified biochar and magnesium-modified biochar have obvious precipitation of phosphate within 1,2 hours,and there is still continuous precipitation within 24 hours.(4)In addition to the preparation method,pH and temperature have an important influence on the adsorption effect of biochar.Ferric chloride modified biochar has better adsorption effect under acidic conditions,while the adsorption capacity of calcium chloride modified biochar is lower.Increase with the increase of pH.(5)Magnesium chloride does not generate corresponding oxides under non-high temperature(100°C)conditions.After modification,magnesium chloride still exists on the surface of biochar.Under non-strong alkali environments(pH < 12),it appears as phosphate precipitation,but It shows a good adsorption effect in a strong alkaline environment.(6)The addition of carbonate shows the same rule as the effect of pH change after addition,while sulfate ions basically have no effect on the adsorption capacity of calcium-modified biochar,and have a certain catalytic effect on the adsorption of iron-modified biochar.(7)Phosphorus on the surface of calcium and iron modified biochar after adsorption under alkaline conditions mainly exists in the form of metal phosphate precipitation.(8)Modified biochar adopts the Freundich and Langmuir isotherm adsorption equations to fit well.The Langmuir isotherm adsorption equation is slightly better than the former.The adsorption of phosphate by the modified biochar belongs to monolayer adsorption.(9)The kinetic adsorption of phosphorus on modified biochar conforms to the quasi-order II equation,and the fitting R2 is above 0.95.The adsorption process is affected by the process of external liquid film diffusion,surface adsorption and intra-particle diffusion.In the actual septic tank manure separation liquid adsorption experiment,it was found that:(1)Two forms of phosphate crystal products were mainly produced after adsorption.The surface of the two kinds of biochar is relatively smooth before adsorption.After the adsorption of calcium modified biochar,the surface is mainly amorphous polyhedral phosphate crystals,while after the adsorption of iron modified biochar,needleshaped phosphate crystals are formed(2)The adsorption rate of calcium chloride and ferric chloride modified biochar on simulated and actual septic tank cleaning wastewater can reach more than 90%,and the effluent TP is less than 0.5 mg/L,and the phosphorus removal effect is better.(3)The actual kinetic test found that each modified biochar material can reach adsorption saturation within 10 minutes,and the adsorption efficiency is high.Produce a large amount of agricultural waste that needs to be treated into biochar material with strong phosphate adsorption effect,and apply it to the integrated integrated mobile processing equipment,making full use of its adsorption capacity to enrich and recycle the front of the three-format manure tank The concept that the phosphorus element in the separated liquid produced by the two-grid manure cleaning is used in place of chemical fertilizers after treatment is in line with the core idea of harmony between modern people and the ecological environment,and has great development and application prospects.