Evaluation of Biosolids for Use in Biodegradable Transplant Containers
Sustainability practices are leading to the development and use of alternative products in the floriculture and wastewater industries, such as the use of biodegradable containers instead of plastic containers. The objective of this research was to evaluate the efficacy of using digested biosolids from a regional wastewater treatment plant as an ingredient in creating a biodegradable transplant biocontainer. The biosolids were tested for metals limits as specified by the U.S. EPA Part 503 Rule, and met the requirements for Class B. Multiple mixes of biosolids, fibers, starch, polymer, and natural glue were developed to provide overall pot stability and structural strength. Engineering tests, such as tensile strength, pH, and saturated paste tests, were conducted on the different mixes to determine the optimum strength that could be produced.
The top-performing biosolids mixes were used to make 10.2 cm (four-inch) pots that were compared in various ways to the market leaders, Peat Pots and standard plastic pots. A two-part mold was created on a 3D printer, which would allow for positive pressure to be used in forming the BioPots. Mixes were transferred to the lower half of the mold, the upper part was then plunged and fastened into the lower half, and then the mold with its mix was placed in an oven to dry. Laboratory germination bioassays were performed to test for the presence of phytotoxic compounds. Construction of BioPots for the lab-scale studies was tedious. Different methods (e.g., negative pressure systems) need to be investigated for use in producing the BioPots commercially.
Most of the BioPots survived the resiliency study. Leachate quality from the biocontainers was no worse than from the plastic containers. Some discoloration was observed on the biocontainers, but it was not due to algal/fungal growth. Growth of soybeans, marigolds, and romaine in the biocontainers was significantly better (e.g., increased height, leaf sizes, and weight) than in the plastic containers.