Department of Civil and Environmental Engineering, University of Maine, 5711 Boardman Hall, Orono, Maine 04473.
School of Economics, University of Maine, 5782 Winslow Hall, Orono, Maine 04473.
Biointerphases. 2023 Jul 1;18(4). doi: 10.1116/6.0002796.
This article discusses the challenges and potential solutions for managing wastewater sludge that contains per- and polyfluoroalkyl substances (PFAS), using the experience in Maine as a guide toward addressing the issue nationally. Traditional wastewater treatment, designed to remove excess organic waste and nutrients, does not eliminate persistent toxic pollutants like PFAS, instead partitioning the chemicals between discharged effluent and the remaining solids in sludge. PFAS chemistry, the molecular size, the alkyl chain length, fluorine saturation, the charge of the head group, and the composition of the surrounding matrix influence PFAS partitioning between soil and water. Land application of sludge, incineration, and storage in a landfill are the traditional management options. Land application of Class B sludge on agricultural fields in Maine peaked in the 1990s, totaling over 2 × 106 cu yd over a 40-year period and has contaminated certain food crops and animal forage, posing a threat to the food supply and the environment. Additional Class A EQ (Exceptional Quality) composted sludge was also applied to Maine farmland. The State of Maine banned the land application of wastewater sludge in August 2022. Most sludge was sent to the state-owned Juniper Ridge Landfill, which accepted 94 270 tons of dewatered sludge in 2022, a 14% increase over 2019. Between 2019 and 2022, the sum of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) concentrations in sludge sent to the landfill ranged from 1.2 to 104.9 ng/g dw. In 2022, the landfill generated 71.6 × 106 l of leachate. The concentration of sum of six PFAS in the leachate increased sixfold between 2021 and 2022, reaching 2 441 ng/l. The retention of PFAS within solid-waste landfills and the potential for long-term release of PFAS through liners into groundwater require ongoing monitoring. Thermal treatment, incineration, or pyrolysis can theoretically mineralize PFAS at high temperatures, yet the strong C-F bond and reactivity of fluorine require extreme temperatures for complete mineralization. Future alternatives may include interim options such as preconditioning PFAS with nonpolar solvents prior to immobilization in landfills, removing PFAS from leachate, and interrupting the cycle of PFAS moving from landfill, via leachate, to wastewater treatment, and then back to the landfill via sludge. Long-term solutions may involve destructive technologies such as electron beam irradiation, electrochemical advanced oxidation, or hydrothermal liquefaction. The article highlights the need for innovative and sustainable solutions for managing PFAS-contaminated wastewater sludge.
本文以缅因州的经验为指导，探讨了管理含有全氟和多氟烷基物质 (PFAS) 的废水污泥所面临的挑战和潜在解决方案，以期在全国范围内解决这一问题。传统的废水处理旨在去除多余的有机废物和营养物质，但无法消除 PFAS 等持久性有毒污染物，而是将这些化学物质分配到排放的废水和剩余的污泥固体之间。PFAS 的化学性质、分子大小、烷基链长度、氟饱和度、头基的电荷以及周围基质的组成都会影响 PFAS 在土壤和水中的分配。污泥的土地应用、焚烧和填埋是传统的管理选择。缅因州在农业用地上的 Class B 污泥土地应用在 20 世纪 90 年代达到顶峰，在 40 年的时间里总计超过 2×106 立方码，已经污染了某些食用作物和动物饲料，对食品供应和环境构成了威胁。此外，还将额外的 Class A EQ（特殊质量）堆肥污泥应用于缅因州农田。缅因州于 2022 年 8 月禁止将废水污泥用于土地应用。大多数污泥被送往州属 Juniper Ridge 垃圾填埋场，该垃圾填埋场在 2022 年接收了 94270 吨脱水污泥，比 2019 年增加了 14%。在 2019 年至 2022 年期间，送往垃圾填埋场的污泥中全氟辛烷磺酸 (PFOS) 和全氟辛酸 (PFOA) 的浓度范围为 1.2 至 104.9ng/g dw。2022 年，该垃圾填埋场产生了 7160 万升渗滤液。渗滤液中六种 PFAS 的总和浓度在 2021 年至 2022 年间增加了六倍，达到 2441ng/l。PFAS 在固体废物填埋场中的滞留以及通过衬垫向地下水长期释放 PFAS 的可能性需要持续监测。理论上，高温可以使 PFAS 完全矿化，但强 C-F 键和氟的反应性需要极高的温度才能实现完全矿化。未来的替代方案可能包括使用非极性溶剂对 PFAS 进行预处理，然后将其固定在垃圾填埋场中，从渗滤液中去除 PFAS，以及中断 PFAS 从垃圾填埋场通过渗滤液进入废水处理，然后通过污泥返回垃圾填埋场的循环。长期解决方案可能涉及破坏性技术，例如电子束辐照、电化学高级氧化或水热液化。本文强调了需要为管理受 PFAS 污染的废水污泥寻找创新和可持续的解决方案。
