基于氮磷固定化回用的畜禽沼液农田配施重金属污染风险阻控研究

At present, in China, the farmland use of livestock and poultry biogas manure is a common phenomenon in large-scale livestock and poultry farms. However, as the nutrient imbalance and high concentration of heavy metal in livestock and poultry biogas manure, its long-term farmland use could cause a certain risk of heavy metal pollution, and high nitrogen and phosphorus load aggravated the pollution trend.. To solve these problems, the project used natural zeolite as raw materials, to optimize the magnesium salt modified zeolite with the characteristics of nitrogen and phosphorus adsorption performance, magnesium ions targeted supply, seed induced crystallization and alkaline automatic control function, when it was used for the treatment of livestock and poultry biogas slurry, its nitrogen and phosphorus could be fixed through the synergy of zeolite adsorption and struvite precipitation. In addition to good slow-release fertilizer function，the recycled ammonium saturated zeolite carrying struvite composite material could be used for immobilization of heavy metal in soil. Through the laboratory and in situ test, the immobilized recovery mechanism of nitrogen and phosphorus by magnesium salt modified zeolite- struvite precipitation coupling technology and the long-term stability of heavy metal in contaminated soil were deeply studied. Related research results are very important for both the resource reuse of nitrogen phosphorus in livestock and poultry biogas slurry and soil heavy metals pollution in situ repairation, and has very wide application prospects.

畜禽沼肥农田回用是当前我国规模化畜禽养殖场普遍采用的一种模式，但是，由于畜禽沼肥养分不平衡，重金属浓度较高，其长期土地利用存在一定的重金属污染风险，且氮磷负荷过高更是加剧了这一污染趋势。本项目针对上述问题，拟以养猪场沼液为研究对象，研究构建集氮磷吸附性能、镁离子靶向供给、晶种作用和碱性自调控功能于一体的镁盐改性沸石，其用于畜禽沼液处理时，可通过沸石吸附与鸟粪石生成的协同作用，实现对沼液中氮磷的高效固定回收；其回收所得的鸟粪石-铵饱和沸石复合缓释肥产品，除了具有良好的缓释肥功能外，同时能对畜禽粪便农田利用中的重金属污染风险进行有效阻控。项目通过实验室和现场试验，深入探讨镁盐改性沸石-鸟粪石沉淀耦合技术固定化回收氮磷机制及其回收产品在重金属污染土壤修复中的长效稳定性能及机理。有关研究成果对畜禽沼液氮磷的资源化回用和重金属污染土壤的原位修复具有重要的实际意义，有着十分广阔的推广应用前景。

以氧化镁改性沸石复合材料（NZ-MgO）为吸附剂，实现对废水中磷酸盐和氨氮的高效固定回收，并进一步将回收的负载有鸟粪石的天然沸石（NZ-MAP）应用于土壤中重金属污染阻控。.（1）NZ-MgO材料的最优制备条件：Mg2+/沸石质量比为20%，OH-/Mg2+摩尔比为2.0，焙烧温度为400 ℃，焙烧时间为5 h。.（2）NZ-MgO对水中氮磷的回收性能研究表明， NZ-MgO对沼液中磷酸盐和氨氮的吸附量分别达119.2 mg·g-1和48.5 mg·g-1；吸附过程符合准二级动力学模型；吸附行为符合Langmuir等温吸附模型； Ca2+的存在对NZ-MgO回收溶液中氨氮会产生明显抑制作用；共存有机酸中，柠檬酸对NZ-MgO回收溶液中磷酸盐和氨氮的影响最大，腐殖酸次之，乙酸最小； NZ-MgO材料对溶液中磷酸盐和氨氮的回收机制主要有物理吸附、离子交换、静电吸附和化学沉淀这四种，其中以鸟粪石化学沉淀为主。.（3）NZ-MAP对水中重金属的吸附实验表明， NZ-MAP的最佳投加量分别为0.4 g·L-1和0.2 g·L-1时，对Pb2+和Cd2+最大吸附量分别为749.74 mg·g-1和249.35 mg·g-1；NZ-MAP对Pb2+和Cd2+的吸附过程符合准二级动力学模型，吸附行为符合Langmuir等温吸附模型。NZ-MAP对溶液中Pb2+和Cd2+的吸附量随pH的增大呈先增加后趋于平衡的趋势；共存重金属离子对NZ-MAP去除溶液中Pb2+和Cd2+的影响从大到小排列依次是Al3+>Zn2+>Cu2+>Ni2+； NZ-MAP对溶液中Pb2+和Cd2+去除主要是分别通过生成Pb10(PO4)6(OH)2沉淀和Cd5(PO4)3(OH)沉淀的方式。.（4）NZ-MAP对土壤中重金属的稳定性能研究表明，随钝化时间和钝化剂投加量的增加，土壤中重金属中Pb和Cd的有效态含量呈明显下降趋势，且NZ-MAP材料钝化效果要明显优于天然沸石；当NZ-MAP钝化剂投加量为10%时，污染土壤中Pb2+和Cd2+的可交换态含量分别降低了87.90%和24.71%，残渣态分别增加了7.10倍和5.52倍； NZ-MAP钝化剂对重金属污染土壤的酸缓冲能力有一定的提升作用；NZ-MAP材料的施加对土壤微生物组成和丰度水平产生一定影响。.有关研究成果对畜禽沼液的农田安全回用具有重要意义。