CONVERSION OF SLUDGE FROM A WASTEWATER TREATMENT PLANT TO A FERTILIZER

Preventing wastage of resources is an important priority for sustainability. Sludge from a wastewater treatment plant (WWTP) is such a resource that it often wasted. It is a source of nutrients and organic materials that can be used as a fertilizer. At a waste water treatment plant in Montreal, the sludge is currently incinerated and sent for disposal. Alternatives to the practice are thus desirable. Elevated concentrations of cadmium, copper, cobalt and selenium are found in the sludge and therefore a treatment process is required before use as a fertilizer according to the Province of Quebec regulations. Leaching was selected as there is potential for heavy metal removal. However, nutrient loss must be minimized to preserve its use as a fertilizer. To meet these goals, a new leaching agent (K2HPO4) was proposed, and investigated for heavy metal removal efficiency on the sludge. A correlation of heavy metal removal and preserved nutrient concentration with time and pH was found. Removal efficiencies of cadmium, copper, cobalt and selenium of 80%, 44%, 70% and 93%, respectively were determined. In addition, concentrations of nitrogen, phosphorus and potassium of 17%, 17% and 25%, respectively, resulted in the treated sludge. In conclusion, the use of dipotassium phosphate is an effective leaching method to remove heavy metals and simultaneously increase the primary macro nutrients at an acceptable cost.