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2020年我国城市生活垃圾清运量已高达2.35×108 t,其中餐厨垃圾约占生活垃圾总量的60%以上[1]。餐厨垃圾具有高有机质、高含水率、易腐败变质等特点,其资源化利用是我国全面推进垃圾分类的关键技术堵点[1]。根据国务院办公厅发布的《“无废城市”建设试点工作方案》[2],我国鼓励固体废物的充分资源化利用,并明确要求促进餐厨垃圾资源化,拓宽产品出路。如好氧堆肥和厌氧消化等生物转化方法,可通过较长的腐殖质化周期 (30~60 d) 将餐厨垃圾转化为相对稳定的腐殖质物质 (肥料) 或沼气 (60%~70% CH4,30%~40% CO2) 等产品[3]。然而,餐厨垃圾的高含水率、C/N不平衡、腐殖化过程营养元素流失严重等特性[4]制约了其好氧堆肥的发展。餐厨垃圾的高蛋白特性使其在厌氧消化过程中极易遭遇氨抑制,容易造成厌氧消化的失稳[5]。近年来,研究者一直在寻求餐厨垃圾的资源化利用新途径,如提取生物降解塑料技术、生物柴油技术等[6]。其中,将餐厨垃圾制成水凝胶是一种具有前景的资源化利用新方式。
水凝胶是一种亲水性、不溶性交联聚合物,具有较高的溶胀能力,可在三维网状网络中吸收大量的水溶液[7],广泛用于农业、园艺和水处理等领域[8]。餐厨垃圾含有丰富的-COOH、-OH、C=C等特征官能团,可通过聚合反应转化为具有三维网络结构的水凝胶。淀粉基、纤维素基、木质素基和多糖基等水凝胶具有良好的生物相容性和生物可降解性,因此相关研究备受关注[8-10]。如以木屑为原料,尿素作为氮源,采用过硫酸钾和N,N'-亚甲基双丙烯酰胺分别作为引发剂和交联剂,可通过接枝共聚法制备出最大含水率210 g·g−1的吸水性水凝胶缓释氮肥[11]。以米饭粉末为底物、N,N'-亚甲基双丙烯酰胺为交联剂、过硫酸盐为引发剂、丙烯酸为单体,同样可合成具有优越吸水性能 (102.6 g·g−1) 和缓释性能的凝胶基缓释氮肥[12]。作为底物制备水凝胶时,采用混合餐厨垃圾比单独的剩余米饭更具有吸引力,因为其具有更丰富的特征官能团。
本研究以混合餐厨垃圾为底物,引入热/过硫酸盐系统对餐厨垃圾浆液进行预处理,以预处理后的浆液合成餐厨垃圾凝胶基缓释氮肥。拟探究单体、引发剂、交联剂和调控剂投加量对水凝胶样品吸水率的影响,以确定最优的聚合交联工艺参数,对生成的水凝胶进行了微观表征,并对水凝胶的膨胀行为能力和pH释放行为开展研究。通过餐厨垃圾水凝胶与牡蛎壳粉复配制备出凝胶基缓释氮肥,并对其缓释氮的能力和在土壤中的保水性能进行综合评价。
热活化过硫酸盐预处理的餐厨垃圾凝胶基缓释氮肥制备及性能
Preparation and properties of gel-based slow-release urea fertilizers synthesized from food waste by pretreatment of thermal activated persulfate
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摘要: 水凝胶转化是一种有前景的餐厨垃圾资源化新方式。采用热活化过硫酸盐对餐厨垃圾浆液进行预处理,并通过聚合交联制备出餐厨垃圾水凝胶 (food waste hydrogel,FWH) 。探究了各试剂投加量对FWH吸水性能的影响,表征了水凝胶的物理化学性质。通过FWH与牡蛎壳粉复配制备出凝胶基缓释氮肥,并以淋洗实验、保水性能实验和种子发芽实验评价其作为缓释氮肥的效果。结果表明,过硫酸钾/热处理系统可在1 h内实现餐厨垃圾浆液的高效水解。FWH样品具有良好的热稳定性,展示出疏松多孔的微观结构,且-OH、-C=O 等含氧官能团以络合反应的形式参与到FWH的合成过程中。在最佳合成条件下,最大吸水率可达351.4 g·g−1,高共价阳离子会显著降低FWH的吸水率。复配后的凝胶基缓释氮肥不仅解决了FWH的酸化劣性,还具有较好的缓释氮肥和保水能力,施用后小白菜种子发芽率增加了17%。本研究结果可为餐厨垃圾资源化利用提供参考。Abstract: One promising method for recycle food waste is to convert it to hydrogel. The food waste slurry was pretreated by persulfate/heat system, and food waste hydrogel (FWH) was synthesized by polymerization and crosslinking. Variables including concentrations on the water absorption of FWH were investigated. The physical and chemical properties of FWHs were characterized. Gel-based slow-release nitrogen fertilizer (FWH-OSP) was prepared by compounding FWH with oyster shell powder, and its slow-release nitrogen fertilizer performance was evaluated by leaching test, water retention test, and seed germination test. The results showed that the KPS/heat treatment system can achieve efficient hydrolysis of food waste slurry within 1 h. FWH had good thermal stability and it’s surface possessed a great number of ravines and microporous structures. Oxygen-containing functional groups such as -OH and -C=O participate in the synthesis of FWH in the form of surface complexation reaction. Under the optimized conditions, the water absorption of FWH can reach 351.4 g·g−1. The high covalent cations significantly reduced the water absorption of hydrogels in salt solution. Compared with the pure urea (54.9 %), the FWH-OSP had a lower leaching loss of N (18.5%). FWH-OSP not only solved the acidification of FWH, but also had excellent properties for retention water and slow-release nitrogen. The result of this study could provide a new idea for the resource utilization of food waste.
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Key words:
- food waste /
- hydrogel /
- water absorption /
- slow-release nitrogen fertilizer
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表 1 FWH-2的膨胀动力学参数
Table 1. The obtained swelling kinetic parameters of FWH-2
溶液类型 Kis Q∞ R2 蒸馏水 0.8250 558.8522 0.9425 0.1 mol·L−1 NaCl 0.3384 155.8906 0.9312 0.1 mol·L−1 CaCl2 0.2038 88.5754 0.8875 0.1 mol·L−1 AlCl3 0.1443 48.9463 0.9493 表 2 尿素和FWH-OSP对小白菜种子发芽率的影响
Table 2. Effects of urea and FWH-OSP on germination percentage of Chinese cabbage seeds %
肥料投加量 尿素 FWH-OSP 0 60 2.0$ \pm $ 60 2.0$ \pm $ 3 69 3.0$ \pm $ 86 6.0$ \pm $ 6 35 1.0$ \pm $ 47 5.0$ \pm $ 10 6 2.0$ \pm $ 5 2.0$ \pm $ -
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