【作者】 徐杰；

【导师】 黄群星；

【作者基本信息】 浙江大学 ， 工程热物理， 2021， 硕士

【摘要】 磷是一种不可替代的营养元素,主要存在于自然界中的磷矿石中。由于磷在自然界中单向流动,磷矿成为一种不可再生资源。污水处理厂的污泥中含有十分丰富的磷资源,同时污泥中也存在重金属和致病菌等有毒有害物质,因此合理处理处置污泥以及资源化利用污泥是目前研究中的热点问题。热处置方法是污泥处置的常用方法。热处置在改变污泥原有物化特性的同时也会对污泥中磷形态产生影响,而磷形态是影响磷的生物有效性以及后续产物回收利用的基本因素。添加剂也是热处置过程中影响磷形态的因素之一。本文采用城市污水污泥作为原料,分别收集污泥经过热解和水热炭化两种热处置方式后的固相产物,研究了CaCl₂对两种热处置方式过程中污泥中磷形态和生物有效性的影响,并得到了以下结论:（1）污泥中80%以上的磷经过热解和水热炭化反应后转移到污泥热解炭和污泥水热炭中,热解炭和水热炭中总磷（TP）浓度上升。无机磷是污泥中磷的主要存在形式,污泥中部分有机磷（OP）经过热解和水热炭化后进一步转化为无机磷（IP）,因此热解炭和水热炭中的IP含量上升,OP含量降低。（2）污泥中的非磷灰石无机磷（NAIP）经过热解和水热炭化后向磷灰石无机磷（AP）转化,AP含量增加。污泥中的含磷化合物在热解和水热炭化过程中均质化混合并释放,由于（PO₄）^3-与Ca²⁺的亲和性强于Al³⁺和Fe³⁺,因此（PO₄）^3-更多的与Ca²⁺相结合,造成部分Fe-P和Al-P向Ca-P的转化,导致固相产物中AP浓度上升,NAIP浓度下降。在水热炭化中CaCl₂的引入会加剧这一转化,并在其质量分数达到20%时呈现最佳转化效果。但是在热解过程中,CaCl₂的加入在加剧这一转化的同时会造成污泥热解炭中AP和IP含量的降低。（3）在水热炭化反应温度为200℃的条件下,当CaCl₂质量占样品总质量的20%时,水热炭中AP浓度和占IP百分比例达到最大,水热炭中可溶性磷在2%柠檬酸溶液（CA）中的溶解度也达到最大,此时污泥水热炭中磷的生物有效性最佳。在热解温度为600℃,不加CaCl₂的条件下,热解炭中AP和IP含量均达到最大,热解炭中可溶性磷在2%CA和中性柠檬酸铵溶液（NAC）中溶解度也达到最大,此时污泥热解炭中磷的生物有效性最佳。（4）经过热解和水热炭化后,污泥热解炭和污泥水热炭的生物有效性得到提升,并且污泥热解炭和污泥水热炭中的重金属含量符合国家B级污泥产物标准,故此条件下得到的两种焦炭具备直接土地利用的潜力。综上所述,热解和水热炭化使污泥中的磷富集到固相产物中,并且对污泥中磷的生物有效性有积极的影响。CaCl₂对热解和水热炭化过程中污泥中的磷含量、形态及生物有效性的影响不同。更多还原

【Abstract】 Phosphorus is an irreplaceable nutrient element,which mainly exists in phosphate rocks in nature.Phosphorus becomes a non-renewable resource due to its unidirectional fluidity.The sewage sludge from sewage treatment plants contains abundant phosphorus resources,and there are also toxic and harmful substances such as heavy metals and pathogenic bacteria in the sewage sludge.Therefore,the rational treatment and disposal of sludge and the resource utilization of sludge are hot issues in the current research.The thermal treatment method is a common method for sludge disposal.Thermal treatment not only changes the original physical and chemical properties of sludge,but also affects the form of phosphorus in the sludge,and the form of phosphorus is a basic factor that affects the bioavailability of phosphorus and subsequent product recycling.Additives are also one of the factors that affect the phosphorus form in the thermal treatment process In this research,municipal sewage sludge was used as raw material to collect the solid phase products of pyrolysis and hydrothermal carbonization of the sludge.The effects of CaCl₂on the phosphorus content and form in the sludge during the two thermal treatment methods were studied,and the following conclusions were drawn:（1）After pyrolysis and hydrothermal carbonization of sludge,more than 80%of P in sludge is enriched in pyrochar and hydrochar,in which the concentration of total phosphorus（TP）increases.Phosphorus in sludge mainly exists in the form of inorganic phosphorus（IP）.Pyrolysis and hydrothermal carbonization make part of organic phosphorus（OP）further transform into inorganic phosphorus（IP）.Therefore,IP content in pyrochar and hydrochar increases while OP content decreases.（2）Pyrolysis and hydrothermal carbonization results in the conversion of non-apatite inorganic phosphorus（NAIP）to apatite inorganic phosphorus（AP）,and the content of AP increases.Phosphorus-containing compounds in sludge are homogenized and mixed and released during pyrolysis and hydrothermal carbonization.Since（PO₄）^3-has a stronger affinity with Ca²⁺than Al³⁺and Fe³⁺,more（PO₄）^3-is combined with Ca²⁺,resulting in the transformation of part of Fe-P and Al-P to Ca-P,resulting in the increase of AP concentration in solid products and the decrease of NAIP concentration.In the hydrothermal carbonization,the introduction of CaCl₂ will intensify the transformation,and the best conversion effect will be achieved when the mass fraction of CaCl₂ reaches 20%.However,during the pyrolysis process,the addition of CaCl₂ will not only aggravate the transformation,but also reduce the content of AP and IP in the sludge pyrolysis charcoal.（3）Under the condition that the reaction temperature of hydrothermal carbonization is 200℃,when the mass of CaCl₂ accounts for 20%of the total mass of the sample,the AP concentration and the percentage of IP in the hydrochar reach the maximum.The soluble phosphorus in the hydrothermal carbon is in 2%citric acid（CA）solution The solubility in sludge is also maximized,and the bioavailability of phosphorus in the hydrochar is the best.When the pyrolysis temperature is 600℃and CaCl₂ is not added,the contents of AP and IP in the pyrochar reach the maximum,and the solubility of the soluble phosphorus in the pyrolysis carbon in the 2%CA and neutral ammonium citrate（NAC）solution also reaches the maximum.At this time,the bioavailability of phosphorus in pyrochar is the best.（4）After pyrolysis and hydrothermal carbonization,the bioavailability of phosphorus in pyrochar and hydrochar is improved,and the heavy metal content in pyrochar and hydrochar meets the national standard of B-class sludge product.Therefore,the two kinds of char derived under these conditions have the potential of direct land application.In conclusion,pyrolysis and hydrothermal carbonization will enrich phosphorus of sewage sludge in solid phase products of sludge and have a positive effect on the bioavailability of them.CaCl₂has different effects on the content,form and bioavailability of phosphorus in the sludge during the two thermal treatment methods.更多还原