The present study develops a multi-step methodology for identification and quantification of microplastics and micro-bioplastics (together called in the current work micro-(bio)plastics) in sludge. In previous studies, different methods for the extraction of microplastics were devised for traditional plastics, while the current research tested the methodology on starch-based micro-bioplastics of 0.1–2 mm size. Compostable bioplastics are expected to enter the anaerobic or aerobic biological treatments that lead to end-products applicable in agriculture; some critical conditions of treatments (e.g. low temperature and moisture) can slow down the degradation process and be responsible for the presence of microplastics in the end-product. The methodology consists of an initial oxidation step, with hydrogen peroxide 35% concentrated to clear the sludge and remove the organic fraction, followed by a combination of flotation with sodium chloride and observation of the residues under a fluorescence microscope using a green filter. The workflow revealed an efficacy of removal from 94% to 100% and from 92% to 96% for plastic fragments, 0.5–2 mm and 0.1–0.5 mm size, respectively. The methodology was then applied to samples of food waste pulp harvested after a shredding pre-treatment in an anaerobic digestion (AD) plant in Italy, where polyethylene, starch-based Mater-Bi® and cellophane microplastics were recovered in amounts of 9 ± 1.3/10 g <2 mm and 4.8 ± 1.2/10 g ⩾2 mm. The study highlights the need to lower the threshold size for the quantification of plastics in organic fertilizers, which is currently set by legislations at 2 mm, by improving the background knowledge about the fate of the micro-(bio)plastics in biological treatments for the organic waste.

本研究开发了一种多步骤的方法，用于对污泥中的微塑料和微生物塑料（在当前工作中统称为微（生物）塑料）进行识别和定量。在先前的研究中，为传统塑料设计了不同的提取微塑料的方法，而当前的研究测试了尺寸为0.1–2 mm的淀粉基微生物塑料的方法。预计可堆肥生物塑料将进入厌氧或好氧生物处理方法，从而产生适用于农业的最终产品；处理的某些关键条件（例如低温和潮湿）可能会减慢降解过程，并导致最终产品中存在微塑料。该方法包括一个初始的氧化步骤，用35％的过氧化氢浓缩以清除污泥并除去有机部分，然后将其与氯化钠一起浮选，并在荧光显微镜下使用绿色滤光片观察残留物。工作流程显示，对于大小为0.5–2 mm和0.1–0.5 mm的塑料碎片，去除效率分别为94％至100％和92％至96％。然后将该方法应用于在意大利的厌氧消化（AD）工厂进行切碎预处理后收获的食物垃圾纸浆样品，该样品中回收的聚乙烯，基于淀粉的Mater-Bi®和玻璃纸微塑料的量为9±1.3 / 10 g <2毫米和4.8±1.2 / 10 g⩾2毫米。这项研究强调了降低有机肥料中塑料定量阈值的必要性，目前该法规已将阈值设置为2毫米，