Nutrient and Heavy Metal Levels in Dairy Processing Organic Residues for Potential Recycling to Agricultural Land.

Nutrient and heavy metal levels in dairy processing organic residues for potential recycling to agricultural land S.M. Ashekuzzaman, Patrick Forrestal, Karl Richards, Owen Fenton* Teagasc, Environmental Research Centre, Johnstown Castle, Co. Wexford, Ireland *Corresponding author E-mail: Owen.Fenton@teagasc.ie Wastewater created during the production of butter, cheese, milk powders, cream, and whey powders at milk processing facilities must be treated. This results in the generation of “dairy processing organic residues (DPOR)”, which needs management e.g. approximately 128,636 tonnes were generated in Ireland in 2015. Recovery of nutrients from DPOR through agronomic utilisation provides for a circular economy and should also provide farmers with an organic fertilizer. Present research focuses on the recovery and recycling of agri-nutrients (N, P, K) from DPOR. In particular, this work was aimed to elucidate the physicochemical parameters of DPOR. Results of the analysis of DPOR samples (n=16) (predominantly two types: mixed DPOR after bio-chemical treatment process and lime treated DPOR after De-Areated Fat (DAF) process) from 5 dairy processing plants across Ireland showed that the values of dry matter (DM, in %wt.) and total content of nutrients (kg/tonne DM) were in the range of DM=9.4–19.7, N=37–65, P=18–61, K=3.5–13.6 for mixed DPOR (n=11) and DM=19–30, N=9.1–48.7, P=15–82, K=1.2–6.1 for DAF DPOR (n=5), respectively. The levels of N, P and K in DPOR are generally higher than those typically observed with other commonly used organic fertiliser (e.g. cattle slurry, biosolids), while DPS also showing lower heavy metal levels comparing same. Heavy metals levels in DPOR are significantly lower than those regulated by the European Union in agricultural land due to sludge recycling. An estimated evaluation reflected a higher financial value of DPOR (€13?22 tonne-1) than cattle slurry (~€5.4 tonne-1) considering total content of nutrient levels. Overall, the results indicate that DPOR are enriched in nutrients. The variation in major nutrient contents and other physicochemical composition are highly contrasting across different milk processing plants and DPOR types. Follow on studies will elucidate DPOR fertiliser replacement value and environmental loss of nutrients following DPOR application.