Wasserman Marlee, Moretti Alessandro, Goi Daniele, Mainardis Matia
Polytechnic Department of Engineering and Architecture (DPIA), University of Udine, Via del Cotonificio 108, 33100 Udine, Italy.
Polytechnic Department of Engineering and Architecture (DPIA), University of Udine, Via del Cotonificio 108, 33100 Udine, Italy.
Sci Total Environ. 2025 Feb 15;965:178634. doi: 10.1016/j.scitotenv.2025.178634. Epub 2025 Jan 31.
Sewage sludge is the main by-product of wastewater treatment plants, requiring significant environmental and economic burdens for its management and disposal. Recently, solar drying processes, often performed through solar greenhouses, received interest due to their limited energy requirement and renewable energy exploitation. The dried sludge shows significant volume and mass reductions, reducing transportation and disposal costs. However, its physicochemical and microbiological characteristics must be properly assessed, especially if agricultural reuse is the final sludge destination, due to the possible accumulation of (micro)pollutants in the soil. This review depicts the state-of-the-art solar drying processes of sewage sludge, with a focus on the technological aspects and the sludge quality. The review discusses greenhouse-specific features, sludge composition (organic matter, pathogens, heavy metals and emerging pollutants) and drying conditions (seasonality, ventilation, sludge mixing and thickness, and drying speed). The economic aspects connected to sludge solar drying are presented. The limitations of this technology are discussed as well, including the limited applicability to wet sludge and the environmental issues connected to greenhouse structure degradation. A wider application of sludge solar drying is recommended to increase the sustainability of small and medium wastewater treatment plants, especially in areas with high amounts of solar radiation and dry weather conditions, while thermal drying still appears preferable for large plants. More agronomic studies must be conducted to assess the possible pollutant accumulation in crops, and alternative uses of the dried sludge (e.g., energy recovery through incineration, pyrolysis or gasification; utilization in construction materials) should be explored, also using life cycle assessment.
污水污泥是污水处理厂的主要副产品，其管理和处置需要巨大的环境和经济负担。最近，通常通过日光温室进行的太阳能干燥工艺因其能源需求有限和可再生能源利用而受到关注。干燥后的污泥体积和质量显著减少，降低了运输和处置成本。然而，必须对其物理化学和微生物特性进行适当评估，特别是如果污泥最终用于农业回用，因为（微）污染物可能会在土壤中积累。本文综述了污水污泥太阳能干燥的最新工艺，重点关注技术方面和污泥质量。综述讨论了温室的特定特征、污泥成分（有机物、病原体、重金属和新兴污染物）以及干燥条件（季节性、通风、污泥混合与厚度以及干燥速度）。还介绍了与污泥太阳能干燥相关的经济方面。本文也讨论了该技术的局限性，包括对湿污泥的适用性有限以及与温室结构降解相关的环境问题。建议更广泛地应用污泥太阳能干燥，以提高中小型污水处理厂的可持续性，特别是在太阳辐射量大且天气干燥的地区，而对于大型工厂来说，热干燥似乎仍然更可取。必须开展更多的农艺研究，以评估作物中可能的污染物积累情况，还应探索干燥污泥的其他用途（例如，通过焚烧、热解或气化回收能源；用于建筑材料），同时也应采用生命周期评估。
