Underground lettuce

Turning a London bunker into a farm

The United Nations expects the world’s population to reach ten billion people by 2050, almost two thirds of whom will live in cities. To be capable of sustainably feeding the growing global population, agriculture has to change. One promising concept is vertical and urban farming. But vertical farming doesn’t necessarily need to mean “high-rise farming”. In London, entrepreneurs have literally turned the concept on its head.

Deep below the metropolis of London, food is growing that could one day supply an entire city.

A busy shopping street in the South West of London. Between a cocktail bar, a restaurant and a large supermarket, nobody would expect to find a farm. But there is one – 33 meters below the city. Located between the Clapham North and Clapham Common subway stations, a farm sited in a former air raid shelter is supplying the neighboring shops with salad stuff, herbs and cress. The facility may go downwards, but it still counts as a vertical farm.

Here, behind thick concrete walls, the ‘fields’ are stacked on top of each other up to four stories high. Metal sheets full of pea sprouts, radish and coriander are piled in neat columns. The LED lamps on the ceiling bathe everything in a pink light. Via ventilation shafts, a filtration and supply air system feeds the underground farm with oxygen. The fans hum softly as they move the air around the room. But why do we need a farm in the middle of the city, especially 33 meters below ground?

Wouldn’t a conventional field be enough? No.

60 harvests in just one year

The vertical fields are far more efficient – in London, six times more efficient than a conventional field. This is mainly because an indoor farm allows you to grow all year round. In conventional fields, this sort of permanent planting would require the intensive use of fertilizers because the vegetables extract their nutrients from the soil. In the British bunker, however, the plants don’t grow in soil. As with most bunker farms, they are cultivated using hydroponics. What at first glance looks like topsoil is actually a carpet made from recycled materials that simply provides stability. The roots of the plants are exposed and are surrounded by water.

Care is taken to ensure that the roots receive sufficient oxygen to prevent them from rotting and the water flows in an almost closed circuit. In this way, it is possible to reduce water consumption by up to 70 percent. All that is added is the nutrients that the plants need for growth. This year-round cultivation is possible because farmers are able to define the optimum environmental conditions. To do this, they use a greenhouse computer to control lighting, temperature and humidity. The light-emitting diodes with their pink light provide the lettuce heads with exactly the same red and blue light waves that they would normally get from the sun. The air supply is regulated by the ventilation system and the farmers can immediately react to any deviation from the ideal value. British leafy vegetables thrive in fairly damp conditions, with a moisture concentration of around 50 to 60 percent and a temperature of about 15 degrees Celsius. This enables the plants to carry out photosynthesis 24 hours a day and obtain the energy they need to grow. The air-raid shelter provides optimal growing conditions and protects the vegetables from the effects of the weather. Storms, floods or drought are the most common reasons for crop failures – but that is not all.

Each of the small plants must be carefully heked and tended.

The best air is underground

As long ago as 2012, the Technical University of Berlin proved in a study that city vegetables were frequently more polluted than conventional ones. The reason for this was identified as cultivation close to busy roads. Particulate matter emitted by vehicles can lead to heavy metal deposits in the crops. In cases where the beds were located less than ten meters from the road, 67 percent of all urban vegetable samples exceeded the EU limit of 0.1 milligrams of lead per kilogram of vegetables. Where the beds were more than ten meters away from the road, the proportion dropped to 38 percent. How is it possible for the air to be so much better just a few meters from the London subway?

In contrast to the conventional vegetable patch, the air-raid shelter is not exposed to the elements. The air is supplied exclusively via a ventilation system. An sophisticated filter system is required to prevent pollutants, particulate matter and heavy metals from entering this ultra-modern farm.

e.FFECTively filtered

Standardized filter systems are often inefficient and do not sufficiently exploit optimization potential. The more accurately filtration systems are tailored to the respective environmental conditions and plant requirements, the more efficient and safer they will be.

The basis for the selection and evaluation of such air filters is the ISO 16890 test standard. This takes into account typical urban and rural particle size distributions of the fractions PM1, PM2,5 and PM10 and even determines the corresponding filtration efficiency of multi-stage filter systems. Diesel soot and other particulate matter occupies a particle size range of one tenth of a micrometer and is therefore best evaluated on the basis of the ePM1 efficiency of a filter system. With e.FFECT, the “electronic Freudenberg Filter Efficiency Calculation Tool”, calculating the perfect filter solution is very easy. Local ambient conditions and specific process requirements are integrated directly into the calculation, thus enabling the optimum design of the system. Effective utilization increases the service life of the filters and reduces energy consumption to a minimum. In this way, filtration makes a decisive contribution to producing food on vertical farms – not just without pesticides, very quickly and close to the consumer, but also in a way that minimizes energy consumption.

Efficient filtration is helping to make the vertical farm concept fit for the future. And it needs to be.

With their concept, the London-based entrepreneurs are countering the effects of the urbanization megatrend on agriculture. More and more people are living in cities. In times of increased environmental pollution, short supply chains are essential. Consequently, food needs to be grown close to where people live. In this case, rather than traveling long distances, freshly harvested vegetables are packaged beneath London’s streets and delivered directly to the supermarket above. Without any supply chain and therefore without any CO2 emissions and losses.