Sanitary Waste : New project aims to turn diapers into biochar

Scottish circular economy start-up Carbogenics is already using pyrolysis to turn difficult-to-recycle organic waste such as coffee cups and cardboard into patent-pending product CreChar, an additive for anaerobic digestion plants that is intended to stabilise the digestion process and thus increase production efficiency. Now the ambitious team is turning to another topic: non-degradable materials such as diapers and sanitary items clogging up sewage systems. Carbogenics CEO Ed Craig tells Waste Management World about the project, which is funded by a Smart:Scotland grant from Scottish Enterprise.

What is the problem with sanitary items, diapers and wet wipes in wastewater facilities?

At the moment, non-degradable materials such as wet wipes, nappies and sanitary items are “screened” – filtered out – as they arrive at wastewater treatment works via the sewage system. They are then taken away for costly and unsustainable landfilling. This means they are a source of methane emissions, a greenhouse gas that is 25 times more potent than carbon dioxide.

How much of this kind of waste ends up in landfills?

We estimate that every citizen causes 1 kg (wet weight) of screening waste per year.

What solution does Carbogenics offer? What is new about it and how does it work?

This new way of dealing with wastewater screenings involves putting them through a high-temperature low-oxygen process known as pyrolysis, to produce a patent-pending biochar called FilaChar®. This will then be added back into the wastewater treatment process to absorb contaminants and stimulate microorganisms to efficiently remove wastewater contaminants.

The hope is that by preventing the screenings from going to landfill and adding biochar to boost biological wastewater cleaning, treatment plants will require less energy to operate, which in turn will help reduce their carbon footprints. Moreover, spent biochar can be used to enhance the quality of biosolids, an organic fertiliser that many treatment plants produce, and which is applied to soils where it sequesters carbon for centuries.

Do the functional carbons only “clean” wastewater and sludge, or do they also dissolve the material those sanitary products are made of?

FilaChar is not able or intended to break down sanitary products that are clogging the sewers. Our solution is to make good use of these wastes after they are removed from the inlet of a wastewater treatment plant. Once the FilaChar is added to the WWT (wastewater treatment) process, we believe it will help break down complex organic matter but not any plastics. Our production process will convert the sanitary products fully into FilaChar. However, if the screening waste mixture contains materials that are not carbon-based like metals, stone and glass, then these have to be disposed of separately.

How much of the carbons is needed to work effectively?

Optimisation of properties and dosage of our FilaChar product is the goal of our current project. We hope to move to full-scale trials next year.

How did you come up with the idea?

The co-founder of Carbogenics, Jan Mumme, worked in wastewater treatment at the beginning of his career and was aware of the screening waste as a problem of this sector. With the rise of biochar production in recent years and the global search for solutions that make WWT more efficient and climate-friendly, he saw an opportunity in developing FilaChar.

Carbogenics already uses pyrolysis to turn waste paper into a patent-pending product called CreChar®. This additive helps improve the anaerobic digestion of food and farming waste, producing biogas and liquid fertiliser, which in turn helps reduce climate change emissions and remove CO2 from the atmosphere.

The work we are doing with Scottish Water is an extension of our core business, and shows the potential multiple applications for our product. We saw an opportunity to progress the project via a £100,000 Smart:Scotland grant from Scottish Enterprise, a funding pot aimed at supporting highly ambitious research and development projects by small and medium-sized enterprises. The funding will cover costs, including the employment of a full-time experienced project engineer to carry out trials at locations such as Scottish Water’s Waste Water Development Centre in Bo’ness.

Would it also be possible to use the functional carbons to treat separately collected sanitary products/diapers?

Potentially, yes.

The functional carbons are already used in AD. How do they help improve the performance of a digester?

Our biochar-based AD enhancer CreChar helps stabilise the digestion process, and creates better growth conditions for the microorganisms that produce the biogas. This results in higher-quality gas and fertiliser, and increased production efficiency.

CreChar is in the form of little carbon flakes that can be mixed in with the regular feedstock of an anaerobic digestion plant. Adding it is easy. It is supplied in digestible bags so plant staff don’t come into contact with it and no extra equipment is needed on site.

The plants that have used CreChar have been reporting greater stability and efficiency of the biogas production process, and increased biogas yields. Robert Kennedy, founder and CEO of Strathendrick Biogas in Stirlingshire, participated in an industrial-scale trial with CreChar during lockdown and was delighted with the results. He’s getting the same high output with reduced feedstock input, and digestate disposal has also significantly reduced.

Robert’s site uses a variety of feedstocks, including distillery wastes, farm wastes and energy crops. To underline the robustness of the product, further full-scale testing is underway at other farm sites in the UK using different feedstocks.

For the WWT sector the main benefit of using CreChar is to enhance the anaerobic degradation of sewage sludge. In small-scale trials we have shown a 15% uplift in biomethane production from sewage sludge. We believe that CreChar helps to overcome biological problems caused by the inhibitory effect of various substances such as H2S and antibiotics through both adsorption and strengthening microbial processes. This means that water utilities can produce more renewable energy from their WWT sites and reduce their output of sludge or biosolids. Dewatering of the final sludge will also return less chemical oxygen demand (COD) to the WWT plant.

About Carbogenics

Carbogenics is a spin-out from the University of Edinburgh. Last year it recruited experienced sustainability leader Ed Craig as chief executive. The business, which was founded in 2016, plans to consolidate its production process in Scotland, demonstrating the advantage of a regional supply chain that currently involves materials being sent between various sites in the UK and Europe.