THE ENVIRONMENTAL AND ECONOMIC SUSTAINABILITY OF SEWAGE SLUDGE TREATMENT: EVIDENCE FROM THE LITERATURE

Abstract

Wastewater sludges are the product resulting from the purification treatments applied to wastewater. These sludges, derived from sewage and industrial effluent treatment processes, may have potential beneficial uses, but they pose significant challenges due to their complex chemical composition and possible contaminations. This study aims to explore in detail various aspects related to wastewater sludges, with a primary focus on environmental and economic issues. This review consists of three parts: i) a narrative review of sludge treatment technologies; ii) a review of Life Cycle Assessment (LCA) studies published between 2010 and 2020; and iii) a review of Life Cycle Costing (LCC) studies published between 2004 and 2022. Based on the literature review, some indications can be drawn. One of the primary advantages of wastewater sludges is their potential use in agriculture as a fertilizer. These sludges contain essential nutrients such as phosphorus and nitrogen, which are valuable for plant growth. However, this approach can entail environmental risks if the sludges contain contaminants such as heavy metals, organic pollutants, or pathogens. Therefore, it is essential to carefully assess the composition of the sludges before considering their application in agriculture to prevent potential harm to the environment and human health. Furthermore, wastewater sludges can undergo various treatment methods, each with specific environmental and economic impacts. The use of methodologies such as Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) is crucial for comprehensively evaluating these treatment options. LCA provides a detailed analysis of the environmental impacts associated with each treatment method. On the other hand, LCC examines the costs associated with these processes. A review of scientific literature reveals several noteworthy trends and significant findings related to wastewater sludge management. For instance, anaerobic digestion emerges as a beneficial pre-treatment method, as it not only reduces the volume of sludge but also produces biogas, a renewable energy source. This method is advantageous in terms of both environmental and economic impacts. Another treatment option is land spreading on agricultural fields, which is economically advantageous due to reduced disposal costs. However, it raises environmental concerns, particularly regarding potential soil and groundwater contamination. Therefore, careful consideration of environmental safeguards is necessary when implementing this approach. Co-incineration of sludges with other waste streams appears to be a promising solution, yielding positive results from both environmental and economic perspectives. It not only reduces the volume of sludge but also harnesses the energy content of the sludge for power generation. This approach contributes to resource recovery and waste-to-energy efforts. Composting is another option that falls within the average range for environmental impacts and is often cost-effective. It involves the biological decomposition of sludges into stable organic matter, which can be used as soil conditioner or fertilizer. However, its feasibility depends on the local conditions and on the availability of appropriate infrastructure. On the other hand, landfill disposal results the most cost-effective short-term option for sludge management. However, it raises serious environmental concerns, as it can contribute to soil and groundwater pollution, release greenhouse gases, and occupy valuable land resources. The extent of these impacts can vary significantly depending on the disposal site, the treatment of the sludge before landfilling, and the implementation of mitigation measures. It is important to emphasize that the results of LCA and LCC studies can vary considerably depending on local conditions, the technology used, and the composition of the sludges. Therefore, conducting specific assessments for each case and carefully considering the trade-offs between environmental and economic impacts is essential. In conclusion, the management of wastewater sludges is a complex challenge that requires a holistic approach. LCA and LCC methodologies provide valuable tools for evaluating treatment and disposal options comprehensively, enabling better decision-making based on specific local circumstances. Ongoing research in this field is crucial for developing increasingly sustainable and efficient solutions for wastewater sludge management. By considering the delicate balance between environmental protection and economic feasibility, we can work towards a more sustainable and responsible approach to managing wastewater sludges, reducing their environmental impact, and maximizing their potential benefits.