Pretreatment Of Pig Biogas Slurry And Degradation Of COD By Photosynthetic Bacteria

In recent years,the mode of modern pig farm is gradually intensive development,and the traditional direct return mode of biogas slurry is no longer applicable.Although the nitrogen and phosphorus in biogas slurry can be absorbed and utilized by crops,it still contains a large number of persistent pollutants,such as antibiotics and other harmful substances,which could lead to toxic effects on plants if it is directly used in farmland.If it is discharged directly,it will aggravate environmental pollution and cause the waste of nutrient resources.Therefore the reasonable and efficient treatment and resource utilization of biogas slurry are the key.Nutrients in biogas slurry can be recovered and effectively retained by integrating a variety of treatment methods,and then rationally applied to farmland on the premise of preventing pollution and damage to soil and water.The premise of the biogas slurry containing high concentration of organic matter used in farmland is that it should be fully ferment.Only after being fermentation,the fertilizer efficiency is increased,the nutrients in it can be more easily absorbed and utilized by crops.In addition,a large number of hyphae can have an inhibitory effect on diseases and insect pests after fermentation.Fermentation microorganisms need suitable carbon and nitrogen ratio to maintain their normal life activities.However,high concentration of organic matter can cause the clogging of the soil,wihch can lead to the decline of soil permeability,water permeability decline,harden,salinization,degradation of soil quality,crop roots to burn even seedlings,etc.,and finally cause death and production.Therefore,it is eager necessary to take measures to reduce the high concentration of organic matter content in the biogas slurry.In this paper,the pig biogas slurry was prtreated by the physical three-stage sedimentation method to remove a large number of total suspended substance(TSS)in the first phase,so as to reduce the turbidity of biogas slurry.In the meanwhile,a part of chemical oxygen demand(COD)was removed.Besides,the biogas slurry still contained a large number of dissolved and free substances,which were difficult to remove through natural settlement.Then different flocculants and other chemical agents were used to treat the biogas slurry,and the influence of different dosage on turbidity and COD of the biogas slurry were investigated.Subsequently,the treatment effect of microorganisms on pre-treated biogas slurry was studied.The domesticated photosynthetic bacteria were further used to remove pollutants in biogas slurry,and their action conditions were optimized to improve the degradation efficiency.The main conclusions were as follows:1.The pretreatment process of pig biogas slurry included three-stage sedimentation and chemical flocculation.After the pig biogas slurry was fully been mixed,the three-stage settlement was carried out.After the system reached stability,the turbidity and chroma were reduced.The primary sedimentation had 60% particles settling.The content of TSS reached 42.5 mg/L after the third stage deposition,and the removal rate of TSS reached 96.7% after 3 h of total deposition.Then the pretreatment effects of different sources of polyaluminum chloride(PAC),anion/cationic polyacrylamide(APAM/CPAM),polyferric sulfate(PFS)and COD deoxidizing agent were compared on biogas slurry.The results showed that PFS can significantly improve the turbidity of biogas slurry,and the precipitate produced was stable and dense.At the concentration of 800 mg/L,the degradation rate of COD reached 44.5%.In addition,the effect and economy were better than other agents,and it was more suitable for large-scale application.2.The effects of Photosynthetic Bacteria(PSB),EM bacteria,Bacillus subtilis,Bacillus licheniformis,Bacillus subtilis natto,Rhodotorula glutinis and Pichia pastoris were screened and compared on the pretreatment of biogas slurry.The results showed that PSB had the most research value,due to high COD removal rate.The COD degradation rate reached up to 25.0% after inoculation for 7 days.3.In order to improve the treatment effect of PSB on COD in pig biogas slurry,the influencing factors,such as initial concentration of biogas slurry,pretreatment method,inoculation amount,p H and illumination intensity were optimized.After being treated with chemical flocculant PFS,PSB could grow normally in biogas slurry.But the higher dilution of biogas slurry limited the proliferation of bacteria.When the inoculation amount achieved 20%,the COD degradation rate increased to 37.6%.The neutral and weak alkaline conditions were more suitable for the growth of PSB.When the p H of biogas slurry reached 7.0,the COD degradation rate reached 36.1%,and the COD degradation rate attained 34.5% at 8000 Lux.In summary,from the comprehensive results of pretreatment and the effect of PSB,we could draw the following conclusion,a triple subsidence and PFS flocculants in preprocessing could be used to pretreat the pig biogas slurry contained a large amount of impurity.Then,choosing the domesticated PSB to treat the biogas slurry under the optimized conditions.This process not only could achieve the purification of biogas slurry,but also get a relatively low cost,save time and manpower.In addition,PSB recovery can be further explored for resource utilization.