Abstract

Since the limit of resources has been realized, preventing from waste of resources became an important issue. Sludge is a source of nutrients and organic materials and has the capability of use as a fertilizer but unfortunately disposal of the sludge is the most current approach in WWTPs including Montreal WWTP. At the Jean. R. Marcotte waste water treatment plant, the sludge is incinerated and sent for disposal. In this study an attempt has been made to solve this issue by recycling the sludge.
The mentioned sludge has high concentrations of cadmium, copper, cobalt and selenium and therefore a treatment process is needed to pass Quebec regulations before use as fertilizer. Among all treatment methods, leaching was selected in this research. Leaching has high efficiency for heavy metal removal but nutrient loss is also its disadvantage. In this thesis, preserving nutrients and removing heavy metals are performed at the same time.
To meet the mentioned goals, a new leaching agent is proposed, K2HPO4, and its effects and removal efficiency on the sludge was investigated. The correlation of heavy metal removal and preserved nutrient concentration with time and pH is shown.
Based on the result, the removal efficiencies of cadmium, copper, cobalt and selenium are respectively 80%, 44%, 70% and 93%. Also the remaining concentrations of primary nutrients in the biosolids including nitrogen, phosphorus and potassium are respectively 17%, 17% and 25%.
To conclude, using dipotassium phosphate as a leaching agent is an effective method to remove heavy metals and increase primary macro nutrients at the same time. The efficiency of this method has indirect correlation with pH and direct correlation with time and considering the product properties, its price is acceptable.