CONVERSION OF SLUDGE FROM A WASTEWATER TREATMENT PLANT TO A FERTILIZER

Abstract

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.