-
磷(P)对生命活动有重要的作用,但是磷资源正被污染,而且磷是有限且不可再生的资源[1],因此磷的回收至关重要。从城市污水厂中回收磷有助于磷资源的持续再生和生态平衡[2],而当前广泛应用的从城市污水中回收磷的方法是结晶法[3],它是通过添加额外的试剂形成不溶性磷酸盐。国际上常用的结晶法是鸟粪石法[4],但其产品价值低;而且此方法多适用于传统强化生物除磷工艺(EBPR),需对富磷污泥提取后回收磷,因此回收效率不理想(10%—50%) [5-7]。研究人员在污水处理厂的污泥中发现了蓝铁矿污泥,并且占了大部分Fe-P结合物[8-10];又因为蓝铁矿(Fe3(PO4)2 •8H2O)稳定易获得(Ksp = 10−36)和经济价值可观[11-13],因此在磷回收方面受到研究人员的广泛关注。
现有的以蓝铁矿的形式回收磷的研究中,一种是从污泥中回收:周健[14]在pH值为7.00—7.40、ORP(氧化还原电位)为−450—−400 mV、铁磷离子物质的量比2.5∶1的条件下对人工培养剩余污泥的磷回收率约90%,纯度为43.32%;Li 等[15]在pH值为5.00—5.80、ORP为−105 mV的条件下对厌氧消化污泥的磷回收率为90%左右,纯度为55.70%;程翔[16]在pH为6.00—9.00、ORP为−420 mV、铁磷离子物质的量比3∶1的条件下对化粪池的磷回收率在96%左右。这些研究中,回收得到的产物中除蓝铁矿外还有污泥,对后续的蓝铁矿分离纯化不利;另一方面,从污泥中进行提取磷再在上清液中进行磷回收,增加了磷损失,会导致回收效率降低[17]。另一种是从污水中回收:Priambodo等[18]在pH为5.00—6.00、铁磷离子物质的量比2.5∶1的条件下对TFT-LCD含磷废水进行了磷回收,磷回收率为93%,纯度为63%。这种方式虽然避免了与污泥分离困难的问题,但所得纯度不高,会使得其与其他沉淀固相难分离。
鉴于目前鸟粪石磷回收工艺存在污水处理流程长、污泥量大、回收效率不理想,本课题组采用生物膜法(好氧/厌氧交替运行模式)直接在主流工艺中富集磷酸盐,且富磷溶液的磷浓度已经达到179.5 mg·L−1[19-20],并将得到的富磷溶液进行蓝铁矿法磷回收。此工艺系统不仅避免了从污泥中回收磷的磷损失和与污泥难分离问题,还避免了在现有研究集中的厌氧消化、发酵过程中的pH(<5.00)与蓝铁矿生成的pH(6.00—9.00)不同(Fe(Ⅱ)-P会溶解)的问题[17]。由于蓝铁矿在自然条件下的形成需要较高浓度的磷铁元素、还原性环境和较丰富的有机质及适中的pH条件(6.00—9.00)[21],并且干扰因素如SS、Ca2+、Mg2+、NH4+、S2-、Al3+ [22-23]在本实验用水中的浓度几乎为0,因此本研究以生物膜法高倍富集的磷溶液为对象,通过探讨pH、ORP、铁磷离子物质的量比对蓝铁矿的磷回收率、纯度的影响,并对回收产物进行XRD、SEM-EDS定性表征,确定以蓝铁矿的形式回收生物膜法富集的磷溶液中的磷的最优反应条件,为建立新型磷回收工艺提供技术依据。
蓝铁矿法回收生物膜富集的城市污水中的磷
Vivianite crystallization method to recover phosphorus in municipal sewage enriched by biofilm method
-
摘要: 磷资源因具有不可再生性和污染性,需要进行磷回收。目前污水处理厂使用的传统磷回收方法多是鸟粪石法,但存在利用价值低、磷回收率不高等缺点。本课题组提出了一种新的磷回收工艺系统,即在生物膜法高倍富集城市污水中的磷的基础上,通过蓝铁矿的形式回收磷,具有经济价值高、磷回收率高等优势。本实验研究主要通过探讨蓝铁矿法回收富磷溶液的过程中获得高磷回收率和蓝铁矿纯度的反应条件,并进行X-射线衍射仪(XRD)、扫描电子显微镜—能谱(SEM-EDS)定性表征最优条件下的蓝铁矿。结果表明,最优反应条件是pH值为7.00—7.50、氧化还原电位(ORP)降到−100 mV左右、铁磷离子物质的量物质的量比为3∶1,此时蓝铁矿法的磷回收率约为95.00%,蓝铁矿纯度为88.35%,蓝铁矿为沉淀回收物中主要晶相且晶型较好。Abstract: Phosphorus resources need to be recycled due to their non-renewability and pollution. At present, the traditional phosphorus recovery method used in sewage treatment plants is mostly struvite method, but there are disadvantages such as low utilization value and low phosphorus recovery rate. Our research group proposed a new phosphorus recovery process system, which is based on the high enrichment of phosphorus in urban sewage by the biofilm method, and recovers phosphorus in the form of vivianite, which has high economic value and phosphorus recovery rate. Higher advantage. This experimental study mainly explores the reaction conditions for obtaining high phosphorus recovery rate and vivianite purity in the process of recovering phosphorus-rich solution by vivianite crystallization, and performs XRD and SEM-EDS to qualitatively characterize vivianite under optimal conditions. The results show that the optimal reaction conditions are pH 7.00—7.50, ORP drops to about −100 mV, and iron-phosphorus ion molar ratio of 3∶1. At this time, the phosphorus recovery rate of the vivianite crystallization is about 95.00%, the purity of vivianite is 88.35% and vivianite is the main crystal phase in the recovered precipitate and has a good crystal form.
-
Key words:
- phosphorus recovery /
- vivianite /
- phosphorus-rich solution /
- crystallization
-
表 1 Hupfer提取法
Table 1. Hupfer extraction method
磷组分
Phosphorus components提取剂Extractant 浓度/(mol·L−1)
Concentration提取时间/min
Extraction duration固液比(mL∶gDS)
Solid-to-liquid Ratiolabile-P 去离子水 — 20 60∶1 MCO3-P 醋酸 0.10 80 60∶1 Fe-P,Al-P,Org-P NaOH 1.00 1080 60∶1 Ca-P HCl 0.50 1080 60∶1 Residual-P HNO3 14.4 60 60∶1 表 2 实验方案表
Table 2. Experimental protocol table
影响因素
Influencing factor富磷溶液磷浓度/(mg·L−1)
Phosphorus concentration in phosphorus-rich solutionpH ORP/mV 铁磷离子物质的量比
Molar ratio of iron and phosphorus ionspH 86.5 6.00、6.50、7.00、7.50、8.00、8.50、9.00 −250— −100 3∶1 ORP 80.2 实验的最佳pH 加抗坏血酸和曝N2① 3∶1 铁磷离子物质的量比 86.8 实验的最佳pH ORP实验的最佳ORP 1.5∶1、2∶1、2.5∶1 、3∶1、3.5∶1、4∶1 注:①由于本实验用水的COD很低,很难维持金属还原菌的生长,使得无法通过金属还原菌维持反应时的还原环境。因此,本实验拟采用加抗坏血酸和曝N2两种物化手段使溶液ORP降低,保持还原环境。
Note: ① Because the COD of the water in this experiment is very low, it is difficult to maintain the growth of metal reducing bacteria, which makes it impossible to maintain the reduction environment during the reaction by metal reducing bacteria.Therefore, two physical and chemical means-adding ascorbic acid and blowing N2 gas, were adopted in this experiment to reduce the ORP of the solution and maintain the reduction environment. -
[1] SUN D Q, HALE L, KAR G, et al. Phosphorus recovery and reuse by pyrolysis: Applications for agriculture and environment [J]. Chemosphere, 2018, 194: 682-691. doi: 10.1016/j.chemosphere.2017.12.035 [2] MAYER B K, BAKER L A, BOYER T H, et al. Total value of phosphorus recovery [J]. Environmental Science & Technology, 2016, 50(13): 6606-6620. [3] HUANG H M, LIU J H, DING L. Recovery of phosphate and ammonia nitrogen from the anaerobic digestion supernatant of activated sludge by chemical precipitation [J]. Journal of Cleaner Production, 2015, 102: 437-446. doi: 10.1016/j.jclepro.2015.04.117 [4] 李子阳, 陆东亮, 华天予, 等. 蓝藻发酵液中氮磷回收及其作为反硝化碳源研究 [J]. 环境化学, 2020, 39(12): 3562-3573. LI Z Y, LU D L, HUA T Y, et al. Recovery of nitrogen and phosphorus from fermentation liquid of cyanobacteria and its application as a carbon source for denitrification [J]. Environmental Chemistry, 2020, 39(12): 3562-3573(in Chinese).
[5] HAO X D, WANG C C, van LOOSDRECHT M C M, et al. Looking beyond struvite for P-recovery [J]. Environmental Science & Technology, 2013, 47(10): 4965-4966. [6] HUANG H M, ZHANG D D, LI J, et al. Phosphate recovery from swine wastewater using plant ash in chemical crystallization [J]. Journal of Cleaner Production, 2017, 168: 338-345. doi: 10.1016/j.jclepro.2017.09.042 [7] LIN L, LI R H, LI Y, et al. Recovery of organic carbon and phosphorus from wastewater by Fe-enhanced primary sedimentation and sludge fermentation [J]. Process Biochemistry, 2017, 54: 135-139. doi: 10.1016/j.procbio.2016.12.016 [8] POFFET M S, KÄSER K, JENNY T A. Thermal runaway of dried sewage sludge granules in storage tanks [J]. Chimia International Journal for Chemistry, 2008, 62(1): 29-34. [9] RASMUSSEN H, NIELSEN P H. Iron reduction in activated sludge measured with different extraction techniques [J]. Water Research, 1996, 30(3): 551-558. doi: 10.1016/0043-1354(95)00203-0 [10] CABEZA R, STEINGROBE B, RÖMER W, et al. Effectiveness of recycled P products as P fertilizers, as evaluated in pot experiments [J]. Nutrient Cycling in Agroecosystems, 2011, 91(2): 173-184. doi: 10.1007/s10705-011-9454-0 [11] JOHNSTON A E, RICHARDS I R. Effectiveness of different precipitated phosphates as phosphorus sources for plants [J]. Soil Use and Management, 2003, 19(1): 45-49. doi: 10.1111/j.1475-2743.2003.tb00278.x [12] LI Y C, GENG G W, HAO J H, et al. Optimized synthesis of LiFePO4 composites via rheological phase assisted method from FePO4 with acetic acid as dispersant [J]. Electrochimica Acta, 2015, 186: 157-164. doi: 10.1016/j.electacta.2015.10.121 [13] RAO S R, VARADARAJU U V. Hydrothermal synthesis of LiFePO4 nanorods composed of nanoparticles from vivianite precursor and its electrochemical performance for lithium ion battery applications [J]. Bulletin of Materials Science, 2015, 38(5): 1385-1388. doi: 10.1007/s12034-015-1025-6 [14] 周健. 从厌氧消化污泥中回收磷—蓝铁矿形成机制初探[D]. 北京: 北京建筑大学, 2018: 103. ZHOU J. Recovery of phosphorus from anaerobic digested sludge-a preliminary study on the formation mechanism of vivianite[D]. Beijing: Beijing University of Civil Engineering and Architecture, 2018: 103(in Chinese).
[15] LI R H, LI X Y. Recovery of phosphorus and volatile fatty acids from wastewater and food waste with an iron-flocculation sequencing batch reactor and acidogenic co-fermentation [J]. Bioresource Technology, 2017, 245: 615-624. doi: 10.1016/j.biortech.2017.08.199 [16] 程翔. 类水滑石吸附和蓝铁石沉淀回收污水中磷的研究[D]. 哈尔滨: 哈尔滨工业大学, 2010: 141. CHENG X. Phosphorus recovery from sewage water by layered double hydroxides as an adsorbent and by vivianite precipitation[D]. Harbin: Harbin Institute of Technology, 2010: 141(in Chinese).
[17] WU Y, LUO J Y, ZHANG Q, et al. Potentials and challenges of phosphorus recovery as vivianite from wastewater: A review [J]. Chemosphere, 2019, 226: 246-258. doi: 10.1016/j.chemosphere.2019.03.138 [18] PRIAMBODO R, SHIH Y J, HUANG Y H. Phosphorus recovery as ferrous phosphate (vivianite) from wastewater produced in manufacture of thin film transistor-liquid crystal displays (TFT-LCD) by a fluidized bed crystallizer (FBC) [J]. RSC Advances, 2017, 7(65): 40819-40828. doi: 10.1039/C7RA06308C [19] ZHANG H, BI Z, PAN Y, et al. Enhanced phosphorus storage in suspended biofilm by increasing dissolved oxygen [J]. Science of the Total Environment, 2020, 722: 137876. doi: 10.1016/j.scitotenv.2020.137876 [20] CORDELL D, DRANGERT J O, WHITE S. The story of phosphorus: Global food security and food for thought [J]. Global Environmental Change, 2009, 19(2): 292-305. doi: 10.1016/j.gloenvcha.2008.10.009 [21] 郝晓地, 周健, 王崇臣, 等. 污水磷回收新产物: 蓝铁矿 [J]. 环境科学学报, 2018, 38(11): 4223-4234. HAO X D, ZHOU J, WANG C C, et al. New product of phosphorus recovery—Vivianite [J]. Acta Scientiae Circumstantiae, 2018, 38(11): 4223-4234(in Chinese).
[22] 郝晓地, 周健, 王崇臣. 探究污泥厌氧消化系统中蓝铁矿生成的干扰因子 [J]. 中国给水排水, 2018, 34(23): 1-7. HAO X D, ZHOU J, WANG C C. Determination of interference factors of vivianite formation in anaerobic digestion of excess sludge [J]. China Water & Wastewater, 2018, 34(23): 1-7(in Chinese).
[23] ROTHE M, KLEEBERG A, HUPFER M. The occurrence, identification and environmental relevance of vivianite in waterlogged soils and aquatic sediments [J]. Earth-Science Reviews, 2016, 158: 51-64. doi: 10.1016/j.earscirev.2016.04.008 [24] WILFERT P, DUGULAN A I, GOUBITZ K, et al. Vivianite as the main phosphate mineral in digested sewage sludge and its role for phosphate recovery [J]. Water Research, 2018, 144: 312-321. doi: 10.1016/j.watres.2018.07.020 [25] FROSSARD E, BAUER J P, LOTHE F. Evidence of vivianite in FeSO4-flocculated sludges [J]. Water Research, 1997, 31(10): 2449-2454. doi: 10.1016/S0043-1354(97)00101-2 [26] KOPELIOVICH D. Pourbaix diagrams [EB/OL]. [2012-5-31]. http:// www. substech. com/dokuwiki/doku. php?id=pourbaix_diagrams. [27] DOYLE J D, PARSONS S A. Struvite formation, control and recovery [J]. Water Research, 2002, 36(16): 3925-3940. doi: 10.1016/S0043-1354(02)00126-4 [28] REGY S, MANGIN D, KLEIN J P, et al. Phosphate recovery by stuvite precipitation in a stirred reactor [EB/OL]. [2009-10–9]. http://www. nhm. ac. uk/ research-curation/ research/ projects / phosphate-recovery/LagepReport. pdf , 2001. [29] 马晓迅, 夏素兰, 曾庆荣. 化工原理[M]. 北京: 化学工业出版社, 2010:456. MA X X, XIA S L, ZENG Q R. Principles of chemical engineering [M]. Beijing: Chemical Industry Press, 2010(in Chinese):456(in Chinese).