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The new alchemy of human waste

At the black solider fly larvae plant in Durban, Sun Kim from the Bill & Melinda Gates Foundation takes a closer look at sludge produced from harvested larvae and, below right, oil produced from harvested larvae.

At the black solider fly larvae plant in Durban, Sun Kim from the Bill & Melinda Gates Foundation takes a closer look at sludge produced from harvested larvae and, below right, oil produced from harvested larvae.

Published Nov 15, 2017


Dr Sudhir Pillay, research manager for Sanitation at the Water Research Commission in Pretoria, explains the link.

First question: Is there actually gold in toilet waste?

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According to Paul Westerhoff and co-workers from Arizona State University, there is actually gold and other precious metal contained with human sewage flushed down the toilet.

In a study they conducted and published in the scientific publication Environmental Science & Technology in 2015, they estimated that for a community of 1 million people, the metals contained in the sludge generated from the wastewater treatment process had a value of around $13 million.

Further, a model they used to determine the relative potential for economic value from the sludge showed that there are 13 lucrative elements, including silver, copper and gold, with an estimated value around $280/ton of sludge.

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While this scientific study showed that there are actually precious metals contained in toilet-derived waste, there is some way to go before we reorientate our engineering processes to extract these resources.

Making Gold from Faecal Waste: Changing Our Mindset: From Wastewater to Resource Recovery Facilities

In August, the author attended the 2nd International Resource Recovery Conference held at Columbia University, New York.

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The three-day conference aimed to showcase the latest developments in resource recovery from sewerage-derived and faecal sludge waste.

(Note: sewerage waste is that which is moved through sewers, and can be from domestic sources, including clothes washing and toilet use, and/or industrial sources, for example, manufacturing. Faecal sludge refers to waste that collects in on-site pit-type systems, and includes septic tanks.)

The conference was not only focused on technology, there was also a focus on the monetisation, financing and policy-making required to drive resource recovery in the form of energy and commercially valuable chemicals. 

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What was telling about the conference was “waste” was not a word used to describe their engineering systems - these systems were called resource recovery facilities.

A New Approach to Harvesting Valuable Commodities from Toilet Waste

Attending the conference was a young engineer, Dr Shashwat Vajpeyi, co-funder and chief executive of a biotech start-up named Carbocycle, the technology of which was developed through his postgraduate research at the Chandran laboratory at Columbia University and with funding support from the Bill & Melinda Gates Foundation.

In conventional wastewater treatment processes, sludge produced from the wastewater treatment process is often treated anaerobically - meaning in the absence of oxygen - through specialised micro-organisms which thrive when there is no oxygen.

Through a cascade of reactions involving a host of micro-organisms, methane gas is ultimately produced.

The methane produced from the anaerobic process can then be used for heating or could be converted into electrical energy. 

What Shashwat and his team have shown is that they do not have to convert all the carbon source in the waste to methane - they actually engineer their systems to produce organic acids, and instead of taking this and further degrading ultimately into methane, they feed it to oil-producing yeasts.

The oils produced are similar in composition to common vegetable oils, including palm oil, which are used in many manufacturing processes, including cosmetics and soaps.

This process is not confined only to wastewater processes, but to other so-called “waste industries” that have a lot of organics contained within them.

In so doing, Shashwat and his team aim to establish a new industry based on converting readily-available organic “wastes” into usable chemicals, thereby creating new material supply chains within cities. To see more of the patented system, see this video:

In Ghana, the Columbia University team led by Professor Kartik Chandran partnered with a local university, Kwame Nkrumah University of Science and Technology, to adapt the process to make biodiesel from toilet waste.

A pilot plant, guided by Columbia University laboratory research, was established in Kumasi and was fed with pit latrine waste. 

Like the rest of sub-Saharan Africa, full-sewered systems are not common in Ghana. Instead, pit toilets are used - these technologies usually rely on a hole in ground in which the faecal-origin waste collects and eventually needs to be emptied.

This can be a costly process to the household and for service providers who empty these toilets as part of their business, as profits are linked to affordability of their service to consumers and the cost of disposing the waste in an environmentally safe manner. 

A common challenge in the developing world is that this waste often ends up being disposed into the environment.

What Professor Chandran’s team aimed to do was to show that through innovative eng ineering processes, toilet waste can be converted into valuable products with the further promise of off-setting costs into the sanitation supply chain.

This has the potential to reduce the cost of services to customers requiring emptying services and incentivising pit-emptying businesses to bring the collected waste to these resource recovery facilities.

Similar strategies are being explored elsewhere around the world (see

In South Africa, a novel treatment system for the treatment of the sludges collected from dry toilets was recently commissioned in Durban.

The sludge processing plant, located south of Durban, was built through a grant awarded to Khanyisa Projects by the Bill & Melinda Gates Foundation and using a novel black soldier fly larvae technology developed by Agriprotein and managed through its business offshoot Biocycle, which is based near Cape Town.

The black soldier fly technology is an industrial biology technology in which Black Solider Flies, which have limited lifespan of up to eight days, lay eggs which develop into larvae.

The larvae eat waste products - this was mostly confined to food wastes but has now been applied to human faecal waste - to reduce its volume.

These larvae gain significant weight in a few days and the flies, unlike household flies, are not considered a pest, nor do they spread diseases.

These larvae can be further processed into protein feeds and oils. In Durban, the harvested larvae are being collected after composting with a combination of food and faecal-origin waste for further processing into a branded product called “MagOil” ( (Fig.1).

The pilot aims to demonstrate circular economy principles where products are reused and recycled while providing sanitation services, and is a platform to showcase the technology to potential partners who may be interested in new supply chains for their products.

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