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Personally, one of life’s great pleasures is walking into Zarraffa’s Coffee at Hope Island most mornings and getting that immediate lift that the aroma of coffee gives. As a plumber, one of the more problematic issues we face is when a building has a problem with sewer gases or sewer odour. I was not surprised when I came across research that showed that the leftover coffee grounds could eliminate that offensive odour that is sewer gases. 

Sewer odour is hydrogen sulphide and has a characteristic rotten egg smell which can be detected at very low levels, well below those known to cause health effects. 

The sewer odour smell can cause worry, anxiety and resentment as it overwhelms the sense of smell. Repeated odour events may culminate in real symptoms such as headache, fatigue and nausea. Although these are not direct health effects, they are undesirable. It is unlikely the odour will affect your health as humans smell it at shallow levels, as hydrogen sulphide is denser than air and tends to pool on the ground or the floor, especially inside a building. In addition, any absorbed hydrogen sulphide does not accumulate in the body as it is rapidly metabolised in the liver and excreted in the urine. 

The problems with sewer odour inside buildings are often related to the drainage system’s venting, which requires filters. Over the years at Whywait Plumbing, we have tried many different filter systems and non-return valves with varying degrees of success in controlling sewer odour. 

New research to develop a novel, eco-friendly filter to remove toxic gases from the air has found that a material made from used coffee grounds can sop up hydrogen sulphide gas. CCNY Chemical Engineering develops and tests materials that scrub toxic gases like hydrogen sulphide from the air in industrial facilities and pollution control plants. Similar to the grains of charcoal packed into water filter cartridges, the CCNY filters use a form of charcoal called activated carbon. 

The manufacturers of activated carbon producers already use materials like coal, wood, peat, fruit pits, and coconut shells to make filters. CCNY concluded that our modern coffee culture could supply an abundant source of eco-friendly organic waste. An added advantage is that coffee grounds also have a special ingredient that boosts their smell-fighting power. The stimulant that gives coffee its energy jolt, caffeine, also contains nitrogen. Nitrogen dramatically increases the carbon’s ability to clean hydrogen sulphide from the air through adsorption. 

Manufacturers traditionally have treated the carbon with nitrogen-rich chemicals such as ammonia, melamine, or even urea, the primary nitrogen-containing substance in urine. All of these treatments significantly increase the cost of adsorbents. Instead, CCNY carbonised coffee grounds turn them into charcoal by activation that fills the carbon with scores of minute holes about 10-30 angstroms in diameter and roughly equivalent to 10-30 hydrogen atom widths across. These densely packed pores are blanketed with nitrogen, perfect for capturing hydrogen sulphide molecules passing through. 

Trials are continuing on the filters with positive results so remember, next time you have a coffee, the grounds that made it can be developed into an environmentally sustainable green filter that can control the most nauseating odour of all – sewer odour.