A study out of Mississippi State University has focused on the degree to which biosolids found in sewage and diverted from municipal wastewater treatment facilities can serve as a useful resource for agricultural settings in place of traditional and slow-release fertilizers.
The researchers discovered that, across the United States, “about 60% of biosolids are land applied, but in Mississippi almost no biosolids are land-applied.” So agricultural areas within the state of Mississippi became their control setting.
Before the 1950s, wastewater was commonly disposed of in natural waterways (bays, lakes, and rivers), resulting in alarming levels of pollution. By the late 1970s, the Environmental Protection Agency established government regulations for sewage disposal that curtailed the wholesale ruination of wetlands and waterways in this manner. Now, use of rescued biosolids for agricultural applications, including on edible crops, must be done with the USEPA Grade A seal of approval, meaning those biosolids meet all regulatory requirements. All waste matter used for this study was awarded an EQ (excellent quality) rating, meaning they have surpassed all safety requirements and are cleared for most agricultural applications.
To produce the excellent quality biosolids from that diverted from the Clinton, Mississippi, Department of Public Works treatment facility, water was pressed from the sewage sludge. These dewatered solids were then further dried in an enclosed greenhouse until they reached a moisture content below 10% while being constantly turned with an automatic tilling system. The stirring and drying process killed any remaining pathogens and increased the nutrient and organic matter concentration.
Broderick adds, “The continuous-till waste management systems are truly remarkable in that they can be used to turn biohazardous waste into a weed- and disease-free soil amendment of high quality. Our research shows that of the crops we tested, plant performance was very comparable to conventional fertilizers. Utilizing this technology in more municipalities could ultimately lead to better stewardship over and sustainability of limited resources, crops, and soils without sacrificing crop yield or quality.”
To determine the comparative effects of these biosolids on soil and plant size, Broderick and Evans prebedded field rows with four rates of biosolids: 2, 8, 14, and 20 tons/acre. Also, they examined comparison plots using popular commercially available slow-release synthetic fertilizers for growing the same crops and plants during the same period. Those plants were dianthus, petunias, kale, and Swiss chard.
The results of this study were notable. The field plots utilizing EQ biosolids proved to reduce pH levels in the soil and did not alter the chemical nature of those plots. However, biosolids were shown to increase the organic matter and metal content of soils without becoming toxic or excessively sodic. The fields using synthetic fertilizers increased pH levels over time and altered its chemical composition.
Also, plant nutrient levels within crops and plants grown in biosolid-treated plots were shown to increase well above the levels demonstrated within the synthetic fertilized fields.
The researchers were able to demonstrate the usefulness of biosolids in replacing conventional and synthetic fertilizers while supplying needed nutrients and organic matter into the soil. While the appearance of toxicity remains a concern, as there were some signs of it in the larger 20 acres field sizes, repeated applications of biosolids to those land samples are believed to yield an increase in organic matter in the soil, improve soil structure, decrease soil density, and improve water-holding capacity over time.
Their increased adoption into horticultural usage will reduce our reliance on synthetic fertilizers, reduce greenhouse gas emissions, and improve the sustainability of municipal and agricultural ecosystems.
Source: ASHS