Study On The Technology Of N,P Recovery And Cu(?),Zn(?) Removal From Swine Wastewater And Food Safety Of Hydroponic Water

In recent years,the rapid development of the intensive aquaculture had led to the increasingly serious pollution of ammonia nitrogen?NH₄⁺-N?,total phosphorus?TP?and heavy metals in swine wastewater?SW?.Based on solving the pollution of swine wastewater,this dissertation focused on the mechanism and effect of anaerobic digestion of swine manure?SM?on morphology and content of N,P,Cu???,and Zn???in SW,and development of low-cost,high-efficiency,environment friendly treatment technology for the recovery of N,P,and removal of Cu???and Zn???from SW,which provided a scientific foundation for maximizing the utilization of SM and reducing the environmental pollution caused by intensive SW and constructing a more civilized ecological environment.The detail contents of the study are showed as follows:1.After anaerobic digestion of SM at 37?,the cumulative yield of methane was 1.06,24 times higher than that at 20?and 55?,which was due to the lower microbial activity and the inhibition of NH₄⁺-N at high temperature during anaerobic digestion of SM.The methane yield also increased significantly with the increase of VS ratio.The degradation and utilization of organic nitrogen containing substances by acidogenic bacteria and methanogens during anaerobic digestion of SM resulted in significant increase of NH₄⁺-N concentration in SW.With the increase of VS ratio,NH₄⁺-N concentration in the SW also significantly increased.The concentration of total phosphorus?TP?and water soluble phosphorus?WSP?in the SW decreased significantly after anaerobic digestion,which was mainly attributed to the degradation of the phosphorus-containing organic matter in the SM,phosphate precipitation and adsorption precipitation.With the increase of VS ratio,the decreasing rate of TP and WEP in the SW gradually increased.After anaerobic digestion process,the concentration of Cu???and Zn???in SW significantly increased,which was attributed to the degradation and release of organic bound metals and sulphide metals by microorganisms.2.Due to the increase specific surface of SW molecule,high shear force,and temperature difference between SW and circulating heating tube,the NH₄⁺-N removal rate from SW remarkably increased with increase of temperature,spraying frequency and rate by using a spraying system.The order of influencing conditions of ammonia removal by spraying technology was as follows:spraying frequency>spraying rate>temperature>pH.Considering the cost and discharge standard,the optimum parameters for NH₄⁺-N removal from SW using spraying system were alkaline condition,0.24 m³/h of continuous spraying,and 45?circulating water.The removal rate of NH₄⁺-N was 88.35%under optimal condition for 8 h treatment,which met national discharge standards?<80 mg/L?.Over 85%recovery rate for NH₄⁺-N could be obtained by this spraying technology.The cost of NH₄⁺-N removal from SW to the national discharge standard for livestock wastewater was about$8.82/m³.3.The NH₄⁺-N,TP,Cu???,and Zn???removal from SW were investigated by using the technology of stripping coupled struvite precipitation.The removal rate of NH₄⁺-N,TP,Cu???,and Zn???significantly increased as increase of MgO dosage because of the synergistic action of ammonia stripping,struvite precipitation,and coagulation/flocculation.Considering the processing cost and national discharge standard for SW,0.75 g/L MgO dosage was recommended using the combining technology for nutrient removal from SW.88.03%NH₄⁺-N and 96.07%TP could be recovered from SW by adsorption of phosphoric acid and precipitation of magnesium ammonium phosphate?MAP?.The cost of SW treatment costed$4.94/kg NH₄⁺-N_removed,which was lower than cost of other technologies for removal of NH₄⁺-N and TP from SW.4.A cost-efficient bentonite-zeolite?BZ?adsorbent for heavy metal?HM?removal from SW was developed using bentonite and aluminate as materials.The gasification of rice husk could effectively improve the specific surface area and pore volume during preparation of adsorbents.Taking Cu???and Zn???as model metal by batch experiment,the optimal pH for adsorption of BZ was pH 5.0.The pseudo-first order kinetic and Langmuir isotherm model of BZ was the optimal model for Cu???and Zn???.The maximal adsorption capacity value?q_m?were 16.39and 12.72 mg/g for Cu???and Zn???,respectively.The adsorption affinity order of BZ in the binary solution was Cu???>Zn???.NH₄⁺-N concentration over 500 mg/L significantly affected the adsorption capacity of BZ?P<0.05?.The adsorption capacity of BZ was higher than that of artificial zeolite?AZ?and bentonite in SW,which indicated the feasibility of Cu???and Zn???removal from SW using BZ.5.After SW was treated with adsorption-stripping,the removal rates of NH₄⁺-N,TP,and Cu???in SW was 43.48%,90.54%,and 96.78%,respectively,which met the growth requirement of Chlorella.vulgaris.The acidification of SW could significantly improve the nutrient utilization efficiency and promote the growth rate of C.vulgaris due to the hydrolysis of macromolecular substances into smaller molecules usable by microalgae.By combining adsorption?Part I?,stripping?Part II?and cultivation?Part III?,the highest removal rates of NH₄⁺-N,TP,COD and total organic carbon?TOC?from SW were 80.50,96.90,72.91,and 84.17%,respectively,and the OD₆₈₀ value was 1.129?1.48 times of control?at pH 6.0.6.The tolerance values of water spinach to Cu???,Zn???,TP,and NH₄⁺-N were obtained to be 0.5,2.0,150,and 300 mg/L in wastewater-fertilizer integrated system.The water spinach could be cultivated in the undiluted SW treated by anaerobic digestion,stripping and sedimentation.The fresh stem production of water spinach in undiluted SW increased by 38.93%compared to control group,and the nutrients of water spinach including chlorophyll a,chlorophyll b,carotene,and sugar were also higher than the control group.The content of Pb???,Hg???,As???,and Cd???in vegetable stems is lower than national safety standard for agricultural products.After 20 d hydroponic culture,the removal rates of NH₄⁺-N,TP,Cu???,and Zn???from SW were up to 87.91,92.38,64.29,and 49.53%,respectively,which met the national discharge standard of livestock wastewater in China.