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磷是一种日益匮乏的稀缺资源,以现有磷矿开采技术,可被经济开采出来的磷矿资源实际上只能使用约50年时间[1]。此外,全球开采的磷矿石中约80%用于农业生产,其中仅有40%被农作物吸收利用,大量磷流失进入水体中,导致水体富营养化[2]。通过技术手段从污水中回收磷,既能够解决磷污染问题,又能够实现磷资源的可持续利用,具有较高的环境效益和经济效益。
鸟粪石(MgNH4PO4·6H2O, MAP)结晶成粒法是目前普遍认可的一种磷回收方法,其工艺操作简单,可以有效去除废水中氮磷污染物,且可将回收的鸟粪石作为优质缓释肥[3],应用于农业生产或其他领域,因此,受到国内外研究人员的广泛关注。吴健等[4]采用中试流化床反应器回收污泥液中的磷(50~65 mg·L−1),处理规模为2 m3·d−1,磷回收率可达85%,鸟粪石颗粒平均粒径为0.74 mm,其纯度为98.23%。岛根县污水厂[5]采用流化床回收污泥厌氧消化上清液中的磷(100~110 mg·L−1),磷去除率可达90%,鸟粪石粒径为0.5~1.0 mm,每日可回收500~550 kg鸟粪石用作农业肥料。MAVINIC等[6]用中试反应器处理污水厂污泥厌氧上清液中的磷,磷去除率可达90%以上。虽然鸟粪石结晶成粒技术已在国外实现工程化应用[7-10],但往往集中在鸟粪石结晶的工艺变量(pH、构晶离子比、过饱和度、外来离子等)的影响方面,缺乏对产品质量(粒径、纯度、形貌、共沉淀物、有机物分析、重金属含量)的系统研究。而国内对鸟粪石结晶研究仍集中在实验室研究,工程应用较少。
本研究利用较大规模中试流化床反应器(处理规模为25 m3·d−1)对强化污泥厌氧释磷后的上清液进行了回收,对不同培养时间下的鸟粪石结晶成粒进行了研究,并对颗粒品质(粒径、纯度、共沉淀物分析、有机物含量、重金属含量)进行了系统分析,且对过程进行了经济分析,为回收的鸟粪石作为缓释肥提供技术支持。
中试鸟粪石流化床反应器回收污泥强化厌氧释磷上清液中的磷及产品分析
P-recovery as struvite from the enhanced anaerobic phosphorus release supernatant in a pilot-scale fluidized bed reactor and characterization of the product
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摘要: 为了探究鸟粪石结晶成粒技术在实际工程中的应用效果及回收的鸟粪石产品作为缓释肥的可能性,利用大规模中试鸟粪石流化床反应器(25 m3·d−1)处理天津市某污泥厂污泥强化厌氧释磷上清液,探究不同培养时间下鸟粪石结晶成粒情况并系统分析收获的鸟粪石颗粒品质。结果表明,在反应周期内,磷回收率达到95%,鸟粪石颗粒平均粒径随反应时间逐渐增大,由最初的0.340 mm增至0.563 mm,纯度均在90%左右,颗粒形貌呈不规则短柱状。采用visual Minteq3软件模拟、X射线衍射光谱(EDX)分析和拉曼光谱等手段进行分析发现,鸟粪石颗粒含有无定形磷酸钙(ACP, Ca3(PO4)2·xH2O)、碳酸钙(CaCO3)及少量有机物等杂质沉淀。回收的鸟粪石颗粒中Pb、As、Cr等重金属含量均低于现行国家化肥控制标准(GB/T 23349-2009)限值,Hg和Cd均未检出。因此,该中试工艺中的鸟粪石有较好的回收利用价值。经济分析结果表明,鸟粪石结晶成粒技术回收每吨污泥厌氧消化上清液中磷的成本为0.46元。
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关键词:
- 鸟粪石 /
- 中试流化床反应器 /
- 污泥强化厌氧释磷上清液 /
- 颗粒品质表征 /
- 共沉淀物
Abstract: In order to explore the application of struvite crystallization technology in actual engineering and the possibility of recycled struvite as a slow release fertilizer, a large pilot-scale struvite fluidized bed reactor (25 m3·d−1) was used to recover phosphorus from the enhanced anaerobic phosphorus release supernatants derived from a sludge treatment plant in Tianjin. Struvite crystallization at different reaction times was investigated and the quality of harvested struvite pellet was systematically analyzed. The results indicate that the recovery efficiency of$ {\rm{PO}}_{\rm{4}}^{{\rm{3 - }}}$ -P was around 95%. The average crystal size of struvite increased from 0.340 mm to 0.563 mm with the increase of reaction time. The purity of struvite reached 90% and it particle morphology was irregular column. Analysis by Raman spectroscopy, energy dispersive X-ray (EDX) and software visual Minteq3 showed that some impure precipitates of calcite, amorphous calcium phosphate (ACP, Ca3(PO4)2·xH2O) and little organic compounds occurred in struvite. The contents of heavy metals such as Pb、As、Cr were below the limits of heavy metal contents regulated by the current fertilizer control standards in China (GB/T 23349-2009). Mercury (Hg) and cadmium (Cd) were not detected. Therefore, the harvested struvite had good recovery and application value. Economic analysis indicates that the cost of struvite crystallization technology for phosphorus recovery is 0.46 yuan·t−1 anaerobic digestion supernatant. -
表 1 不同反应时间下MAP粒径和纯度
Table 1. Crystal size and the purity of MAP at different reaction time
反应时间/h 平均粒径/mm 最大粒径/mm 纯度/% 6 0.340 1.4~2.36 89.3 12 0.449 1.4~2.36 89.7 18 0.453 1.4~2.36 90.4 24 0.486 1.4~2.36 90.2 30 0.538 1.4~2.36 90.1 36 0.563 1.4~2.36 90.3 表 2 鸟粪石EDX定量分析
Table 2. Quantitative analysis of MAP by EDX
元素 重量百分比/% 原子百分比/% C 7.23 11.58 O 47.25 56.79 N 1.86 2.56 Mg 13.92 11.01 P 26.91 16.71 Ca 2.83 1.36 总量 100 100 表 3 肥料中重金属限值与MAP颗粒重金属对比
Table 3. Comparison of heavy metals content in struvite and heavy metal limits in fertilizer
元素 产物值/% 肥料标准限值/% Pb 0.004 3 0.020 0 Hg — 0.000 5 Cr 0.004 2 0.050 0 As 0.000 9 0.001 2 Cd — 0.001 0 注:“—”表示未检出。 表 4 中试药剂费用分析
Table 4. Analysis of reagent costs in pilot scale test
项目 市场价/
(元·t−1)每吨上清液药剂
投加量/kg上清液处理
费用/(元·t−1)NH4Cl 1 200 0.52 −0.62 ${\rm{MgC} }{ {\rm{l} }_{ {\rm{2} } } }{\rm{\cdot6} }{ {\rm{H} }_{\rm{2} } }{\rm{O} }$ 800 0.39 −0.31 NaOH 2 500 0.15 −0.37 鸟粪石 1 760 0.48 +0.84 总计 −0.46 注:“+”表示收益;“−”表示投入。 -
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