Long-Term Biosolids Application on Land: Beneficial Recycling of Nutrients or Eutrophication of Agroecosystems?

Abstract

The impact of repeated application of alkaline biosolids (sewage sludge) products over more than a decade on soil concentrations of nutrients and trace metals, and potential for uptake of these elements by crops was investigated by analyzing soils from farm fields near Oklahoma City. Total, extractable (by the Modified Morgan test), and water-soluble elements, including macronutrients and trace metals, were measured in biosolids-amended soils and, for comparison, in soils that had received little or no biosolids. Soil testing showed that the biosolids-amended soils had higher pH and contained greater concentrations of organic carbon, N, S, P, and Ca than the control soils. Soil extractable P concentrations in the biosolids-amended soils averaged at least 10 times the recommended upper limit for agricultural soils, with P in the amended soils more labile and soluble than the P in control soils. Several trace elements (most notably Zn, Cu, and Mo) had higher total and extractable concentrations in the amended soils compared to the controls. A radish plant assay revealed greater phytoavailability of Zn, P, Mo, and S (but not Cu) in the amended soils. The excess extractable and soluble P in these biosolids-amended soils has created a long-term source of slow-release P that may contribute to the eutrophication of adjacent surface waters and contamination of groundwater. While the beneficial effects of increased soil organic carbon on measures of “soil health” have been emphasized in past studies of long-term biosolids application, the present study reveals that these benefits may be offset by negative impacts on soils, crops, and the environment from excessive nutrient loading.

Evaluating the effectiveness of sulfidated nano zerovalent iron and sludge co-application for reducing metal mobility in contaminated soil

“…Some studies have determined that Zn may be more biologically available and mobile in soils treated with sludge 28 . McBride 29 also showed that adding biosolids to soil can increase the fraction of bioavailable Zn. This mobility has been observed to increase with time after sewage sludge addition to the soil since it can form soluble chelates with humified and non-humidified forms of organic matter 28 .…”

Phosphorus Recovery from Whole Digestate through Electrochemical Leaching and Precipitation

“…The P solids recovered from the EPRC can be comparable to phosphate rock, making it suitable to be a feedstock for conventional wet phosphoric acid processes or as solid P fertilizers for tropical acid soils. , Recent studies found that long-term application of biosolids (whole digestate after dewatering) on land could result in an excessive P concentration in surface soils, contributing to nonpoint source P contamination and eutrophication in aquatic environments. , Thus, the P products containing consistent P contents (28.42–33.51% as P 2 O 5 ) will enable more accurate P resource management. In addition, the P production rate, heavy metal contents, and the distribution of P products in the ENRC are controllable, making it a versatile technology that will be applicable to other P-abundant solid wastes such as livestock manure.…”

Systematic Review and Meta-Analysis on the Use of LCA to Assess the Environmental Impacts of the Composting Process

“…Padeyanda et al [56] found a very high EP value for Composting (Not Specified), more than 7 kg PO 4 3− eq/t of food waste, due to the high NH 3 emission during the composting process. The eutrophication category is more affected by excess nutrients derived from nitrogen and phosphorus, that in high concentrations in organic waste to be composted, can affect the ecosystem with eutrophication [88]. Another aspect that can increase the EP results is considering the high concentration of nutrients from the wastewater generated on composting piles and often leachate into the soil [33].…”