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近年来我国经济的飞速发展,城市生活污水污泥产量连年攀升,随之而来的是污泥处理的压力。一方面,剩余污泥含有重金属、有机污染物和病原微生物等有毒有害物质,如果处理不当,会给环境造成严重污染。另一方面,污泥是一种拥有巨大潜力的生物资源,其有机质含量在50%左右,含有丰富的蛋白质、多糖、腐殖酸和核酸[1]。在传统污水二级生化处理中,进水中近90%的磷和部分的氮最终会转移至污泥中,因此剩余污泥含有丰富的有机质和氮磷养分,若不加以合理利用是一种资源浪费。
污泥固相中营养物质的有效释放是实现污泥有机质和氮磷回收的重要前提。污泥的破解方法有各种物理化学法,如热水解、超声、高压均质法等。碱处理作为一种常用的化学预处理方法,具有操作方便、设备简单、效率高等优点。首选NaOH作为处理试剂,其比Ca(OH)2有更高的增溶效率[2]。碱法常常与其他工艺(如超声[3]、热处理[4]和高压均质法[5]等)联合处理,联合处理对污泥具有更高效的破解能力。微波法在污泥处理中的潜力已得到广泛认可[6],微波产生的热效应和非热效应能高效破解污泥,所以碱联合微波组合工艺拥有巨大潜力。
为了回收利用污泥上清液中丰富的营养物质,可通过磷酸铵镁沉淀法回收氮和磷,其产物鸟粪石可作缓释肥料。但实际应用中受各种因素(例如高离子强度、高碱度和Ca2+干扰)限制[7],且磷酸铵镁沉淀法只能回收PO43--P和NH4+-N等形式的无机盐,上清液中丰富的有机质仍无法利用。硅烷交联剂是一种两性表面活性剂,一个分子中同时拥有烷氧基和有机官能团,烷氧基水解产生的硅烷醇基团能以共价键的形式与无机材料结合,有机官能团与聚合物作用,可显著提高无机/聚合物表面附着力[8]。因此,硅烷交联剂有望解决污泥上清液中有机质无法高值利用的问题。硅烷交联剂成本低、环境友好,被广泛应用于复合材料、纳米材料等表面改性。近年来学者们将其应用于环境领域,Zhou等使用(3-氨基丙基)三乙氧基硅烷有效分离水溶性腐殖酸[9]。甲基三乙酰氧基硅烷(MTAC),常温下为无色透明液体,低温下为白色结晶体,结构式为CH3—Si—(COOCH3)3,其酰氧基相较于其他基团(如甲氧基、乙氧基)更为活泼,分解速度也更快[10]。并且根据美国环境保护署的数据资料显示,MTAC的半数致死浓度(LD50)为2060 mg·kg−1,属于低毒化合物。MTAC与水就能交联,生成具有良好生物相容性的聚硅氧烷和易生物降解的乙酸,且污泥上清液中氮元素的嵌入能够加速聚硅氧烷的水解,从而提高其生物降解性[11]。因此,MTAC的交联聚合反应是一种从污泥上清液中回收有机质和氮磷的有效途径。
本研究采用碱联合微波组合工艺预处理污泥,投加MTAC回收上清液中有机质和氮磷,研究了碱联合微波处理对污泥中有机质及氮磷的释出的影响并优化反应条件,探究了MTAC交联聚合回收污泥上清液营养物质的可行性,利用扫描电镜-能谱(SEM-EDS)、傅里叶红外光谱图(FTIR)、X射线光电子能谱分析(XPS)和热重差示扫描量热法(TG-DSC)对絮凝聚合物进行形态和化学构造分析,旨在探究交联聚合法分离回收有机质和氮磷的机制。
碱联合微波预处理污泥及交联聚合回收上清液中有机质和氮磷
Crosslinking polymerization to recover organic matter and nitrogen/phosphorus from the supernatant of sludge combined alkali-microwave pretreated sludge
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摘要: 从污泥中回收有机组分是实现污泥的妥善处理和资源再利用的理想途径。本研究系统考察了碱联合微波处理下污泥中有机质及氮磷的释放特征,同时使用甲基三乙酰氧基硅烷(methyltriacetoxysilane,MTAC)以絮凝聚合物的形式回收污泥上清液中的营养物质,并探究其内在机制。结果表明,碱联合微波处理能有效加速污泥的溶解和胞内物质释放,最佳处理条件为NaOH剂量1.12 g·L−1污泥、碱处理时间40 min,微波辐射功率640 W、微波辐射时间 120 s。碱联合微波处理比单独碱处理SCOD溶出浓度提高了97.6%,TN和TP分别增加了51.35%和25.13%。MTAC与上清液中营养物质通过交联、絮凝和团聚作用,有效地分离回收了营养物质,其中蛋白质、多糖、TN和TP回收率分别高达44.72%、58.49%、76.90%和48.71%。本研究证实了碱联合微波处理污泥,以MTAC为交联剂进行化学聚合,是一种污泥高效处置和资源回收的简单的替代策略。Abstract: Recovery of high-value products is an ideal option to achieve proper treatment and resource recycling of sludge. In this study, the release behaviors of organic matter and nitrogen/phosphorus during sludge pretreatment by the combined alkali-microwave process were systematically investigated, and methyltriacetoxysilane (MTAC) was used to recover nutrients from sludge supernatant by crosslinking polymerization method. The results showed that combined alkali-microwave could effectively accelerate sludge dissolution and intracellular substance release, and the optimal treatment conditions were observed to be 1.12 g·L−1 NaOH-sludge for 40 min and microwave radiation power 640 W for 120 s. Under the optimal conditions, SCOD concentration in supernatant increased by 97.6%, and TN and TP increased by 51.35% and 25.13%, compared with the alkali treatment alone. MTAC effectively separated and recovered nutrients from the supernatant through chemical cross-linking, flocculation, and agglomeration. The recovery efficiencies of protein, polysaccharide, TN, and TP reached 44.72%, 58.49%, 76.90%, and 48.71%. Our current study demonstrated that combined alkali-microwave pretreatment, followed by chemical polymerization with MTAC as the crosslinking agent, can be a simple and alternative strategy for highly efficient disposal and resource recovery from sewage sludge.
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表 1 污泥的基本理化特性
Table 1. Physicochemical characteristics of the sludge
含水率/%
Moisture
contentpH 总固体/
(g·L−1)
TS挥发性固体/
(g·L−1)
VS溶解性化学需氧量/
(mg·L−1)
SCOD溶解性蛋白质/
(mg·L−1)
SPN溶解性多糖/
(mg·L−1)
SPS总磷/
(mg·L−1)
TP总氮/
(mg·L−1)
TN97.76 ± 0.3 6.80 ± 0.2 22.4 ± 0.6 10.4 ± 0.4 181.75 ± 13.1 84.16 ± 5.3 26.34 ± 2.8 70.44 ± 6.1 2.70 ± 0.1 表 2 絮凝聚合物的BET表面积和孔径分析结果
Table 2. BET surface area and pore size analysis results of flocculated polymer
BET表面积/(m2·g−1)
BET surface area微孔/介孔表面积/( m2·g−1)
Micropore/Mesoporous surface area孔体积/(cm3·g−1)
Pore volume微孔/介孔体积/(cm3·g−1)
Micropore/Mesoporous volume孔径/nm
Pore diameter9.0554 3.9485/5.1068 0.011328 0.001799/0.009529 50.0374 -
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