Harvest Time is Here! -- Biosolids' Unspoken Role in Improving Our Declining Soil Health -- A Literature Review to Enhance Communication Tools for Biosolids Managers

As utilities increasingly focus on implementing a circular economy, wastewater treatment plants' (WWTPs) byproducts are no longer viewed as waste, but valuable resources. Biosolids are a nutrient-rich recovery product that can be used as soil amendment, promoting sustainable agriculture, enhancing soil health, and ensuring the recycling of nutrients. Utilities aim to produce high quality biosolids and promote its beneficial use as they also undertake the crucial task of educating and informing farmers along with the general public on potential misconceptions regarding environmental and public health risks associated with biosolids land application. This scenario presents a great opportunity to partner with the farming community and establish open communication channels to overcome the often negative stigma associated with biosolids. Such partnership must include science-based information supported with data obtained from current research to respond to public concerns. Understanding the stakeholder concerns also helps identify future research needs, such as which crop types and soil classes to focus on, what parameters are of higher concern to stakeholders, and how to balance the priorities of different stakeholders. To help strengthening the communications, there is a crucial need to compile and interpret current scientific research on this topic and help utilities with their message based on scientific data. The beneficial impact of biosolids on soil health can be overshadowed by the increasing research on contaminants of emerging concern that is expected to be regulated. While there is a rapidly growing body of research on the treatment, fate and transport of potential contaminants in biosolids, measuring the impact of the biosolids application in agricultural settings requires long time frames. Additionally, the lack of a standardized framework for evaluating the soil health and reporting results and the variability based on region, types of crops studied, type of biosolids applied, and the parameters measured can make interpretation challenging. For farmers, the most important asset to provide nutritious crops and to generate high yields is the soil they are tending. Unfortunately, soil erosion, compaction, heavy use of synthetic fertilizers and pesticides have been the culprits of declining soil quality on the farmlands. In the United States alone, soil erosion costs the US $8 billion each year and reduces the agricultural food production by 33.7 million metric tons per year (Martina Sartori, 2019). Soil health can be improved if certain management practices are routinely incorporated into agricultural management such as minimal tillage, cover crops, reduced use of synthetic fertilizers and pesticides. There is a growing interest in finding ways to improve soil health first and foremost rather than focusing solely on increasing yields through chemical inputs. US Department of Agriculture's Natural Resource Conservation Service has been implementing best practices in this area, working with the farmers to improve not only soil health but also water quality in areas where farmland makes up much of the land in the watersheds. (USDA, 2024). The authors believe that biosolids can be an important part of the conversation seeking to improve and reverse the ongoing condition of degrading soils. Despite the growing concerns regarding contaminants of emerging concern in biosolids, on-going research will take time to come to a definitive and realistic conclusion. Until then, 'all-or-nothing' approach for land application will mean the reduced or eliminated use of a valuable resource to implement a better soil health practice. The authors have run a data query on SCOPUS, which is a Science Direct service for analyzing only peer-reviewed journals and cited research. The research on biosolids and soil has been going on since 1980s (Figure 1 and 2) but not until recently that we see the soil health aspect and term incorporated in it (Figure 3). Now that 'how and why' of soil ecosystem functionality is better understood, further actions can be implemented. Initial literature review efforts have already shown that the biosolids application increases soil carbon, microbiology, aggregate stability and decreases bulk density of soil (Ippolito James A., 2021) (Bolan N.S., 2013) (Villa Y., 2021) (Ippolito J.A., 2024). Nutrient management and recycling are also heavily researched as biosolids can act as a slow-release fertilizer, replacing the conventional, synthetic fertilizers that doesn't contribute to improving soil health. There is also research and discussion taking place across the soil community as to which parameters really are indicative of soil health and trying to establish a framework for the farmers to make evaluation easier and comparable across the sites (Bagnall D.K., 2023) (Liptzin D., 2022) (Rieke E.L., 2022). With this paper, the authors' goal is to complete thorough literature research on biosolids impact on soil health parameters in agricultural settings. We aim to detail the following as it pertains to the agricultural application of biosolids to the practical extent possible to provide water and wastewater utilities with a comprehensive literature review: - A map of the US showing where research has been undertaken. - A table summarizing and comparing research methodologies (crops, trial settings, biosolid types). - A summary of the findings and trends (soil health parameters measured, emerging contaminants of concern, timeframes, etc.). - Funding sources to support research. - Potential future research areas. - Contributions of research to existing biosolids management strategies At the end of this literature research, the authors will summarize previously completed research efforts and up-to-date results which will serve as an important tool to utilities as they develop and implement communication plans that support a sustainable management of biosolids programs. The literature research will also help utilities in their efforts to measure their contribution to soil health in their land application sites. The authors will evaluate the past soil test results from their current application sites, and identify control sites that can be sampled to make comparisons. Based on the initial findings, soil parameters and sites will be determined for the next steps of the localized research effort. The results will inform the communication tools with the farmers as well as the public.