Reuse of paper mill sludge for hydroseeding and food crop applications

Abstract

Study objectives included defining the capability of pulp and paper mill sludge to replace the cellulosic component used in hydroseeding applications while determining the ideal application rate on an incline plane along with consideration into the uptake of heavy metals into the plant material. Sludge with embedded seed at loadings of 5 to 25% on soil was shown to speed up germination, but after 3 weeks post application with mixtures containing 5 to 75% sludge provided the densest coverage. Transfer of heavy metals was below regulatory levels in all samples. Greenhouse trials with lettuce (Lactuca sativa), carrots (Daucus carrota), and strawberries (Fragaria × ananassa) were used to evaluate sludge’s nutrient availability and bioaccumulation to determine if it can also be utilized alone or in combination with Promix to promote plant growth. Lettuce flourished within the first three weeks post-transplant, increasing speedof germination, while carrot and strawberry samples did not see increased speed of germination with sludge addition. Strawberries however showed the potential to grow in up to 50% sludge while carrots and lettuce succeeded in up to 25% sludge. Bioaccumulation factors of key nutrients in lettuce and carrot samples were < 1 apart from magnesium, sodium, boron, and zinc.