The Covid-19 pandemic showed many global city dwellers a future in which we might all breathe more freely. Across the world, as populations were subject to stay-at-home orders and road transport activity dipped, city-dwellers enjoyed clear skies; and a respite from road traffic produced pollutants such as nitrogen dioxides, carbon monoxides and the dangerous vehicle particulates PM 2.5s: tiny specks of pollution which, once inhaled, lodge in the lungs and can cause a variety of health problems.

Those traffic-borne emissions prompted the World health Organisation, in 2019, to characterise air pollution as the number one environmental health risk globally, the cause of an estimated 7.1 million premature deaths per year.

One solution to cities’ pollution problem is air purifiers and, as populations demand clearer air yet policies to reduce car-borne pollution lag behind, air purifiers are big business. Indeed market size is expected to reach USD 22.80 billion by 2028 and is expected to expand ten percent a year from 2021 to 2028.

The problem with standard electric air purifiers however is similar to air conditioners, in that they can compound the problem in themselves requiring power to run, which, in most global contexts, produces additional carbon pollution. Trees, of course, are excellent natural air purifiers but demands for land in cities make it difficult to plant the number of trees necessary to drastically improve air quality.

One answer to this problem also comes from nature, in one young German horticulturist’s design for an air filter that’s based on air-cleansing abilities of common-or-garden moss.

Green City Solutions was founded in 2014 by 29-year-old Peter Sänger, who brought together a team of experts in fields ranging from horticulture to mechanical engineering to design a novel bio-tech filter, the City Tree. “I felt the solution to air pollution can only emerge in combination with nature,” he says, of concentrating his research efforts on moss. “After all, nature has millions of years of experience in air purification.”

Moss is well adapted to the task of filtering polluted air, possessing the ability to bind fine dust and metabolise it. It can filter soot and particulates from the air breathed by 7,000 people every hour. In addition, mosses cool surrounding air by evaporating water on their leaf surface. The problem is that mosses can barely survive in cities due to their need for water and shade. So Green City Solutions solved this problem by connecting a range of species of mosses (with different filtering abilities) to low-energy water and nutrient provision based on unique Internet of Things technology, which measures the plants’ requirements and surrounding pollution levels in real time.

Independent field studies have shown that up to 82 percent of the fine dust in city air can be filtered directly by the City Trees, which the company has installed in cities across Germany, and in London and Paris. Each moss tower has the carbon dioxide absorbing capability of 275 trees.

Positioning is key; as Sänger notes: “Not all places where people live are polluted, and people aren’t everywhere there is pollution. Where the two meet, that’s where we place the trees.” Sänger would like to see his devices installed in the world’s most vehicle-polluted cities within the next decade.

The company is now developing moss-based air filters that are also suitable for consumers to use in their homes or that function – in an extra boon – as attractive greenery for vertical facades.

Author: James Gavin, The India Story Agency for Sacred Groves
Images Credit: Green City Solutions; Peter Sänger and Peter Puhlmann for Green City Solutions; Nate Bell

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For fish, rivers are high-speed traffic lanes in the same way that motorways are for humans. The Ruhr in west Germany, for example, is such a highway, leading fish to spawning and feeding grounds as well as summer or winter resting places in small lakes and tributaries. On those motorways, however, fish, just like humans, also have to deal with narrow lanes, road works or complete closures. And any such obstacle can have serious consequences for species diversity.

“Fish need unobstructed water ways as they depend on different conditions in different life stages,” says Svenja Storm, a fishing biologist at the regional fishing association of Westphalia/Lippe. “Where an adult fish finds the optimal food for itself, there does not have to be a suitable place for the positioning of spawn or the growth of the young fish. In fact, all fish species migrate in the course of their life in order to optimize their food intake, to avoid unfavourable conditions such as water bodies falling dry to increase the reproductive success.”

One man currently trying to solve this problem is Markus Kühlmann. The 53-year-old engineer has spent the last nine years transforming the 219-kilometre-long Ruhr into the aquatic superhighway it once was. At Baldeney weir near Essen, Kühlmann, together with a team of engineers, biologists, ecologists and hydraulic engineers, developed a system that is unique to the world: a continuously running elevator which transports the fish to the top of the weir.

Part of the impetus for the project, which cost a cool US $8 million, were regulations published by the European Union and the German Environment Agency which require all water bodies in Germany to be in “good condition” again by 2027. Within this regulation was the provision for every German river to be passable for fish.

There being the political will to get Kühlmann’s project off the ground, there was an immediate problem. This location in the Ruhr was not spacious enough for a traditional fish ladder (a series of pools where one is a little higher than the next to allow fish to climb the distance step by step).

Looking for an alternative, Kühlmann found novel fish elevator designs in France, Australia and the United States: “But they did not cover enough height or were created only for certain species,” he says. “We had to come up with something completely new.” He teamed up with engineers from southern Germany as well the Karlsruhe Institute of Technology to first develop a computer simulation.

The way the eventual elevator design works is simple: there’s a tube with a flexible chamber; when the chamber is at the bottom, the fish enter, get transported nine meters upwards and exit the chamber again to continue their journey. To prevent fish from queuing in front of a closed door at the bottom while the lift is at the top, the system consists of two tubes with alternating elevators. Kühlmann and his team developed specific algorithms and underwater sonars to detect when the chamber is full or if a particularly large fish – possibly a predator – is waiting in the elevator and preventing other fish from entering. (The large fish is then transported separately.) “A second software is fed with environmental data that influence the migration activity of the animals, such as season, water temperature or moon phase. That way, the operating intervals of the elevator automatically adjust,” Kühlmann explains.

After years of development, the fish elevator started operating in August 2020 and has been running round the clock since then.

Officials from other cities such as Augsburg are looking to adopt the high-tech elevator model, although Kühlmann admits the price tag of what’s currently a bespoke build will inhibit roll-out of replicas of the Baldeney fish ladder across the globe. That said, Kühlmann hopes his insights will help other regions to think more radically about how they can help migratory fish get from A to B.

Author: Florian Sturm, The India Story Agency for Sacred Groves
Images Credit: Florian Sturm

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