| In the process of treating the wastes of livestock and poultry and producing biogas, large and medium sized biogas project produces large quantity of byproduct-centralized biogas slurry. Biogas slurry is the residual liquid of organic compound by anaerobic fermentation and has high concentration of nutrients, like nitrogen, phosphorus and organic compound. If the biogas slurry is directly discharged, there will be serious environmental pollution; if the treatment of biogas slurry reach the required standards of environmental protection, the cost will be high; if the biogas slurry is directly utilized, there needs to be large area of land for digestion and accommodation。 At present, the biogas slurry disposal methods mostly consists of low-cost cropland application, natural ecological purification, high-cost factory treatment, high additional value oriented treatment and so on. The ideal treatment of biogas slurry is to couple low-consumption disposal with value added utilization, so that the valuable components of biogas slurry could be recycled at a low cost and the pressure of the subsequent treatment process could be relieved.Using the natural porous media to absorb the pollutants is one of the most common methods of low-costly treating wastewater. In view of the powerful ion-exchange adsorbability, adsorbability, diffusivity, and catalytic property of zeolite, with extensive material and in low cost, it is commonly be used as adsorption medium in wastewater treatment. In order to raise the adsorption efficiency of natural zeolite, the physical method(for example, increasing specific surface area) and chemical method (for example, improving cation exchange capacity) are often utilized to modify the natural zeolites. In view of the fact that the adsorption of the nutrients like nitrogen, phosphorus and organic compound in biogas slurry by zeolite has not been reported at home and abroad, the thesis took TRF(Natural zeolite), WLF(Microwave-sodium chloride modified zeolite), CPBF (Cetylpyridinium Bromize modified zeolite), WF(Micro-sized zeolite synthesized from coal fly ash) and YWF(Submicro-sized zeolite synthesized from coal fly ash) as the research objects, studied the isothermal adsorption-desorption characteristics of nitrogen, phosphorus, COD in biogas slurry by five zeolite substrates through isothermal adsorption-desorption experiment and optimized working parameters through filter column experiment; treated the effluent of filter column by Zeolite-strengthened SBR; studied on the agricultural fertilizer efficiency of biogas slurry saturated adsorption zeolite through pot experiment. And then achieve the goal of low-cost recovering nutrients, like nitrogen, phosphorus and COD and promoting the subsequent treatment process of biogas slurry, reaching the required standards of environmental protection, the results showed that:1. The isothermal adsorption characteristics of nitrogen, phc=sphorus and COD by five zeolite substrates were more suitable for Langmuir equation than Freundlich equation. According to Langmuir equation, the order of absorption capacity of anmmonium was YWF (29.155mg/g)>WF (17.637mg/g)>WLF (10.020mg/g)>TRF (8.326mg/g)>CPBF(7.599mg/g); the order of absorption capacity of phosphorus was YWF (3.169mg/g)>WF (2.653mg/g)>CPBF (1.138mg/g)>WLF (0.693mg/g)>TRF (0.611mg/g); the order of absorption capacity of COD was CPBF (37.736mg/g)>YWF (23.256mg/g)>WF (20.121mg/g)> WLF (13.423mg/g)>TRF (12.987mg/g); on the desorption rate of anmmonium and phosphorus, YWF and WF were much smaller than that of the other three materials. The order of desorption rate of COD was TRF>WLF> WF>YWF> CPBF.On the research of absorption kinetics, the absorption of anmmonium, phosphorus and COD by the five zeolites enjoyed the characteristic of "fast absorption, slow balance ". The absorption rate of YWF was obviously higher than that of the other four zeolites.The kinetic model fitting showed that the fitting effect of second-order kinetic model was the best for all the5zeolite materials of the ammonium absorption; the fitting effect of first-order kinetic model was the best for WLF、TRF and WF of phosphorus absorption; the fitting effect of Elovich equation was best for CPBF and YWF. In the COD absorption dynamics model, the fitting effect of first-order kinetic model was the best for TRF, WLF, WF, YWF. From the change of kinetic curve and the apparent rate constant B of first-order kinetic model, it could be concluded that the absorption of COD of biogas slurry was mainly controlled by membrane diffusion which was fast reaction.Both the effect of surface adsorption in original mining area and effect of organic distribu-tion existed in the adsorption of COD of biogas slurry by CPBF, and rapid ad-sorption and slow adsorption also existed at the same time, so CPBF was more suitable for the two-compartment first-order dynamic model.Combined with the results of isothermal adsorption-desorption and adsorption kinetics experiments, it was found out that of the five different zeolites, YWF had better comprehensive adsorption capability of anmmonium, phosphorus and COD in biogas slurry, and was ideal adsorption medium for biogas slurry.(?) of the influential factors on the adsorption capacity, it was found out that of the five zeolite materials, the ammonium absorption quantity of YWF and WF slowly rose along with pH value increased and then it slowly decreased with the further increase of pH value, while the ammonium absorption’ quantity of CPBF、TRF and WLF slowly decreased with the increase of pH value. The phosphorus absorption quantity of YWF and WF was mostly influenced by the change of pH value, while the change of pH value had little effect on the phosphorus absorption quantity of CPBF, TRF and WLF. The COD absorption quantity of YWF and WF decreased with the increased of pH value, that of CPBF, TRF, WLF appeared the tendency of "two low and one high" with the increased of pH value. The ammonium absorption quantity of the five different zeolite materials decreased with the rose of ionic strength, of which the decrease range of the ammonium absorption quantity of WLF was the highest of the five zeolite materials. The influence exerted by ionic strength on the absorption capacity of anmmonium in biogas slurry exceeded that on phosphorus and COD.2. WLF and CPBF were used as adsorption medium to construct mixed modified-zeolite filter column in volume ratio1:1, the research found out that in proper range, there was a negative correlation between the adsorption capacity of NH4+, TP, COD by the modified zeolites filler and inlet velocity of biogas slurry, positive correlation between that and initial concentration of biogas slurry, the strengthening of the biogas slurry influent velocity and influent initial concentration would make the penetrating time of target object decrease. With the increase of the height of filter column, the penetrating time also increase, the unit absorption of NH4+, TP, COD by modified-zeolite would increase too. Therefore, properly increasing the height of filter column and concentration of biogas slurry and reducing the biogas slurry influent velocity could effectively improve the absorption capacity and utilization ratio of the modified-zeolite contents in the filter column, and would make the process more efficiency and economic.In the experiment of the regeneration of saturated filter column, after oscillated in hot water at45°C, then using the mixture of NaCl+Na2SO4(the molar ratio of the solution was5:1, the mass concentration was6g/L) and the mixture NaCl+NaOH(the molar ratio of the solution was7:13, the mass concentration was6g/L) as the regeneration fluid to make continuous chemical removal of the modified-zeolite saturated adsorption of biogas slurry, the absorption capacity of NH4+, TP, COD by the regenerated modified-zeolite reached88.15%,93.30%,84.57%of that of the fresh modified-zeolite. It indicated that modified-zeolite had better reproducibility and the cost of reproducing was acceptable, therefore, the mixed modified-zeolite had great value of application.But for the sake of economic consideration, the regeneration times should be controlled within3.The absorption of COD by zeolite was closely related to the contact time with biogas slurry, and organic matters which were low polarity,small molecular weight and low solubility were difficult to be adsorbed. Therefore, the using of modified-zeolite column to absorb COD biogas slurry was not easy to reach desirable effects. In order to get the desirable effects, it was necessary to supplement the biochemical treatment after the filter column treatment, so that the organic compounds which was difficult to be absorbed in the biogas slurry could be removed.3. Put the zeolite synthesized from coal fly ash whose range of particle size between40μm and60μm into SBR system to form ZFA-SBR system. With the prolongation of acclimation time, the biofilm was formed around the zeolite synthesized from coal fly ash, which created material prerequisite for simultaneous nitrification and denirifica-tion(SND). Compared with SBR, the properties of the activated sludge in ZFA-SBR(SBR added zeolite synthesized from coal fly ash)was improved. During the stable stage, the index of SVI, MLSS in ZFA-SBR was better than that of SBR. During the operation period, compared ZFA-SBR with SBR, the change of pH value was similar while the total value of the former was higher than SBR for0.5to0.7. The nitrogen removal and denitrification efficiency in the ZFA-SBR reactor was relatively high; the degradation rate of COD in the aeration period was also faster.After filtrating by modified-zeolite filter column, the biogas slurry mixed with raw livestock wastewater in order to adjust the BOD5/TN value of filtrate to4, the biodegradability of mixture was improved obviously compared with biogas slurry. Put the mixture into ZFA-SBR system, and then constructed strengthening process of biogas slurry which named "filtration by modified-zeolite filter column-adjusting BOD5/TN value-ZFA-SBR".During the30days period of stable operation of Zeolite-strengthened SBR, the effluent concentration of NH3-N, COD, TP of ZFA-SBR reached at discharge standard of pollatants (?) Lvestook and poultry breeding and realized low consumption standard treatment of biogas slurry. Compared with SBR, it showed better removal rate and resistance to impact load.4. Through pot experiment, the influence on soil-plant system by5kinds of zeolite (?) of biogas slurry nutrients were investigated. It was found out that both A treatment group(5kinds of zeolite materials+chemical fertilizers) and B treatment group(5kinds of zeolites which saturated adsorption of biogas slurry+part of chemical fertilizers) exerted benign effect on soil-plant system.Both AYWF treatment(YWF+chemical fertilizers), AWF treatment(WF+chemical fertilizers) of A treatment group and BYWF treatment(YWF which saturated adsorption of biogas slurry+part of chemical fertilizers), BWF treatment (WF which saturated adsorption of biogas slurry+part of chemical fertilizers) of B treatment group could dramatically raise the pH value of soil. The effect of AYWF in raising pH was the most obvious.Of the influence on Total nitrogen, organic matter and available nitrogen, the maximum were reached by BCPBF treatment (CPBF which saturated adsorption of biogas slurry+part of chemical fertilizers), that were1.09mg/g,13.97mg/g and121.18mg/kg respectively. The maximum total phosphate and available phosphorus of soil were reached by BYWF treatment and AYWF treatment at0.43mg/g and8.02mg/kg respectively. While the minimum were reached by CYWF treatment(only YWF), that were0.33mg/g and4.12mg/kg. Probably because AWF treatment could most effectively improve soil pH value, in turn reduced the fixation of phosphorus in soil and promote occluded phosphate to convert into non occluded phosphate.Of the various processing of the influence on winter wheat, the highest biomass of winter wheat was in AYWF treatment, that was33.48g/pot. The highest yield and1000-grain weight were reached by BYWF treatment and BCPBF treatment, compared with CK1(only using NPK), increased for15.29%and10.29%respectively.The nitrogen, phosphorus uptake and utilization ratios of winter wheat, all reached the highest value in BYWF treatment at668.28,122.31mg/pot and34.06%,12.93% respectively.Within the range of A treatment group, the difference of nitrogen uptake and phosphorous uptake between AYWF treatment and AWF treatment was not obvious(p<0.05), and the difference between BYWF treatment and BWF treatment in B treatment group was also not obvious(p<0.05).The zeolite saturated adsorption of biogas slurry nutrients could partially substitute nitrogen and phosphorus fertilizers, and this would reduce the cost of fertilizers, improve the physicochemical properties of acid purple soil and the biological indexes and nutrient utilization of winter wheat to some extents, and mitigate water environment and atmospheric environment damage caused by the low utilization ratio of fertilizer.In the end, the thesis pointed out that the test systematically studied the adsorption-desorption characteristics and the influential factors of NH3-N, TP, COD in biogas slurry by different zeolites, but in the subsequent research the in situ characterization techniques should be used in order to observe the changes before and after adsorption factually. |
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