From sewage to sustenance

James Bezzina's studies in physical chemistry in the Australian city of Wollongong, where agriculture is the driving force behind the economy, inspired him to apply to the Grantham Centre for Sustainable Futures.

The Grantham Centre is an organisation that is devoted to funding PhDs that deal with issues surrounding the sustainability of food and food sources.

As a Grantham Scholar and a member of the Separations and Nuclear Chemical Engineering Research group, his research focuses on the remediation of sewage in order to generate a viable phosphate and nitrogen source as well as a potentially profitable source of heavy metals.

Declining natural reserves of phosphate

Fertiliser provides two major macronutrients for crop growth: phosphate and nitrogen. While the nitrogen can be sourced from the ample volume found in air, the main source of phosphate for fertilisers is phosphate rock.

The reserves of phosphate rock have been predicted to last no longer than 370 years with current consumption levels, while this does seem like a long time, other sources predict less than 100 years which is a worrying position.

Could sewage fill the gap?

Enter sewage: a source of material that itself is a rich source of phosphate and nitrogen. Is sewage, (arguably) the most unavoidable waste stream, a potential gold mine, literally?

There is much potential value buried within the landfill deposits left behind after sewage treatment; be this from phosphate and nitrogen, or strangely enough the heavy metal content. With declining natural reserves should we not be looking at circulating what we can from where ever we can?

Sewage sludge is currently used wildly throughout agriculture and forestry, however much of the sludge is discarded untreated by either landfill or relieved to the ocean. No matter the disposal method, untreated sewage can contain concentrations of heavy metals that have the potential to harm fragile ecosystems.

Removal of harmful heavy metals

With the strict guidelines on metal concentrations of sewage sludge allowable for the use as an agricultural fertiliser, and even still with limitations of use on particular crops, removal of the metallic fraction from this rich phosphate and nitrogen source would allow for a much broader application.

One method of this separation is the treatment of sewage sludge as a raw mining material. This method has the added benefit of refinement of the metals retained within sludges as a raw material.

This recovery is more lucrative than you might think, with the estimated annual economic value of heavy metals (such as silver, gold, copper, zinc, etc) from sewage from a community of 1 million people is US $8 million. Without even taking into account the sustainability aspect of this, it has the potential for economic viability.

Towards a sustainable resource

James' project is the transformation of sewage to sustenance. With the aid of mining techniques he's attempting to take what is usually a waste and convert it into a sustainable resource. With the focus on and need for a recycling of waste becoming essential, utilisation of sewage must be seriously considered.

He hopes that by the end of his time as a PhD student, sewage is seen as a resource more than a waste.