Reclamation of Phosphorus from Biogas Slurry by Biochar Manufactured from Biogas Residue in Large-scale Hoggery

Author:Yi Man

Supervisor:chen yu cheng


Degree Year:2019





Phosphorus-rich livestock and poultry farms are regarded as“second phosphate mines”.Recovering phosphorus resources in livestock and poultry manure,combining nutrient recycling of phosphorus with environmental pollution control has important theoretical value.With the practical significance,the idea of mining the“second phosphate rock”has also begun to be studied and practiced on a global scale.At present,the phosphorus removal technology of biogas slurry in livestock and poultry farms cannot achieve the synchronization of biogas slurry compliance treatment and phosphorus resource utilization.If the large and medium-sized biogas project biogas slurry is treated,the bio-liquid phosphorus standard treatment can be coupled with the phosphorus resource utilization through engineering and technical measures,and the low-cost recovery of phosphorus can be reduced,and the biogas slurry can be reduced.load.On the other hand,the use of agricultural waste to produce biomass charcoal can not only"treat waste,turn waste into treasure",but also can be us ed as environmental functional materials to improve soil fertility,improve nutrient cycling,improve nutrient utilization,and increase Crop yield.The research intends to use the pyrolysis technology to produce the material charcoal from the biogas resid ue of the livestock and poultry farm,and then use this as a substrate to adsorb and recover the phosphorus in the biogas slurry of the livestock and poultry farm,and finally apply the adsorbed phosphorus-containing recovery product to the soil.As a nutrient resource,Chongqing has entered the agro-ecosystem to make use of it.This innovative idea couples the biogas residue disposal of livestock and poultry farms with biogas slurry treatment,couples pollution control with resource utilization,and couples plantland phosphorus requirements with phosphorus supply from livestock and poultry farms,which has application prospects.At the beginning of the thesis,in view of the unknown potential of phosphorus recovery in pig farms,firstly,based on the establishment of phosphorus accounting method for pig farms,the impact of farm scale on phosphorus flow characteristics,phosphorus nutrient use efficiency and environmental loss pathway was discussed.Then,the biomass charcoal was prepared by low temperature pyrolysis biogas residue,and the adsorption and adsorption mechanism of phosphorus on biogas residue-based biomass carbon were investigated by Ca and Mg modification.The non-adsorption state of small molecule organic acid in biogas slurry was studied aga in.The strengthening effect of phosphorus on the absorbing and utilizing phosphorus;finally,the pot experiment was conducted to investigate the effect of phosphorus recovery products in the biogas slurry on soil-crop.The main findings of the paper are as follows:(1)Based on the material flow analysis method,based on the material flow analysis method,based on the literature summary and NUFER-animal module,the calculation method of phosphorus material flow in pig farms in Chongqing was constructed.By analyzing the flow of phosphorus in pig farms in Chongqing,it is found that the main input of phosphorus flow in pig farms is feed input.The main output is excreta and there is no obvious relationship with the scale of breeding.Phosphorus utilization efficiency of different scale pig farms is low and increases with the increase of pig farm size.There is also a significant difference in the amount of phosphorus loss in pig farms of different scales,and the phosphorus loss per unit of pork product also increases with the increase in scale.Under the premise of the same manure treatment method,there is no significant relationship between the disorderly discharge of phosphorus and leaching and runoff of unit pork products.On the premise of the same scale,the phosphorus loss of pigs treated with manure composting is much higher.Pig farms treated with manure and biogas.(2)Comparing biogas residue-based biomass charcoal(CMZZs)and tobacco stem-based biomass charcoal(CMYGs,reference material in this test),it was found that the calcium-magnesium composite modification did not change the surface chemical functional group.The XRD pattern showed that magnesium oxide[Mg(OH)2,MgO]was present on the surface of the modified biomass carbon,but no calcium oxide[Ca(OH)2,CaO]was found,indicating that the modification effect of magnesium is better than that of calcium.At the temperature of 303 K and pH 9.0,the adsorption of phosphorus by the two biomass carbons was the best,and the theoretical maximum adsorption phosphorus could reach 86.92 and 90.91 mg/g,respectively.(3)The equilibrium adsorption capacity of phosphorus in the two biomass carbons increased first and then gradually increased with the increase of initial phosphorus concentration.The actual maximum adsorption amounts of CMZZs and CMYGs to phosphorus were 81.23 and 84.65 mg/g,respectively.The adsorption conditions were temperature 318 K,pH 9.0,temperature 303 K,and pH 9.0,which were 68.44 times and36.65 times,respectively,before the modification.Isothermal adsorption experiments show that the adsorption of phosphorus by the two biomass carbons is consistent with the Freundlich equation,ie multi-layer adsorption.The adsorption kinetics experiments showed that the adsorption process of phosphorus by the modified two kinds of biomass carbons accorded with the quasi-second-order kinetics equation of chemical adsorption,and reached the adsorption equilibrium in about 200 min.(4)By FTIR and XRD characterization of the materials of biogas residue-based biomass charcoal before and after phosphorus adsorption(CMZZ750,P-CMZZ750),it was found that the adsorption of phosphate by biogas residue-based biochar was caused by surface electrostatic attraction and intragranular adsorption.The result of a combination of compounding and precipitation processes.Phosphorus is mainly present in the form of H2PO4-and HPO42-in the pH range of the test.The initial H2PO4-,HPO42-and protonated MgOH+reacted due to electrostatic interaction.As the reaction proceeded,H2PO4-and HPO42-entered the surface pore or gap of CMZZ750 and further entered the biomass carbon matrix through intragranular diffusion and membrane diffusion.Inside,the particles are recombined and precipitated with MgO to form MgHPO4 and Mg(H2PO4)2 crystals.(5)The occurrence of phosphorus in the biogas slurry of pig farms can be divided into liquid phase phosphorus and solid phase phosphorus,among which liquid phase phosphorus is divided into liquid phase total phosphorus(TP L),liquid phase particulate phosphorus(PP),and dissolved.Reductive phosphorus(RDP),dissolved orthophosphate(Ortho-P),dissolved total phosphorus(TDP);solid phase phosphorus is divided into water soluble phosphorus(H2O-P),sodium bicarbonate bound phosphorus(NaHCO3-P),sodium hydroxide bound phosphorus(NaOH-P),hydrochloric acid bound phosphorus(HCl-P),residual phosphorus(Re-P).The dissolved orthophosphate accounts for only 24.35%of the total phosphorus in the biogas slurry,and the particulate phosphorus(PP+NaOH-P+HCl-P)accounts for 53.72%of the total phosphorus.The experiment found that the biogas residue biochar is mainly used to absorb the dissolved orthophosphate in the biogas slurry,indicating that the particulate phosphorus has a large potential for conversion and utilization in the adsorption and recovery of phosphorus system.Therefore,it is difficult to adsorb and recover by using small molecular organic acids.The particulate phosphorus is converted into orthophosphate which can be adsorbed and utilized by the biogas residue-based biomass charcoal.(6)The organic acid intensification conversion test showed that the three organic acids,tartaric acid,citric acid and acetic acid,can promote the particulate phosphorus(PP)or agglomerate phosphorus(NaOH-P+HCl-P)in the biogas slurry to the soluble orthophosphoric acid.The salt(Ortho-P)is released and its conversion ability is:citric acid>tartaric acid>acetic acid.At a concentration of 5mmol/L,citric acid mainly interacts with the protonic acid effect anion complexing effect,which increases the Ortho-P in the biogas slurry by 174.08%;tartaric acid is mainly a ligand ion,which increases the Ortho-P in the biogas slurry.78.97%;acetic acid mainly promotes the increase of Ortho-P in biogas slurry by 27.79%in molecular form.And tartaric acid and citric acid use chelation and dissolution to promote the release of poorly soluble calcium(magnesium)salt in biogas slurry or phosphorus adsorbed by calcium magnesium oxide and hydrated oxide,and release of phosphorus adsorbed by iron and aluminum.The main mechanism is competitive adsorption.(7)After the biogas slurry of biogas residue-based biochar was adsorbed,the radish pot experiment was carried out by using the recovered product,and it was found that the soil pH,cation exchange amount,soil alkaline nitrogen,available phosphorus and available potassium all increased with the application level of the recovered product.And there is an increasing trend.The total phosphorus and available phosphorus in the seedling stage of the bio-liquid phosphorus recovery product were lower than that of the chemical fertilizer control,but the rosette stage and the fleshy root expansion period were significantly higher than the chemical fertilizer control,indicating that the phosphorus recovery product of the biogas slurry phosphorus was associated with the growth and development of the radish.A slow release effect has occurred.The recovery product treatment increased the vitamin C and total sugar content of the radish,and also reduced the content of the harmful nitrate,and the treatment of the phosphorus replacement fertilizer was 70%.Therefore,the bioreactor-based biochar adsorbs the biogas slurry and the recovered product can not only improve the soil fertility status,but also release the phosphorus during the growth period of the radish,and at the same time improve the quality of the radish.