Green Building Done It Right

“One green trend attracting attention this year is technology that uses plants to purify the air and soil. Products are reaching the market which reduce toxic substances that can create photochemical smog with greenery on building walls. Progress is also being made in the use of special grasses to inexpensively break down any oil residue remaining in the soil on the sites of former gas stations.

Sakata Seed’s SunPatiens plants blossom with a number of orange variations. Their strong ability to break down NO2 makes them useful for soil remediation.

Daiwa House Industry this spring is about to release a system that utilizes wall-side greenery to clean the surrounding air. Soil embedded when greening the walls plays a role akin to the filter in an air purifier. These walls can reduce the amount of nitrogen dioxide (NO2) — a harmful component of air that the plants take in — by a fifth, and PM2.5 — tiny particulate matter that can cause serious health problems — by half.

This is how it works. First, polluted air is drawn in by a fan and is passed through the soil from the ventilation layer on the side surface, allowing the PM2.5 particles to be absorbed into minute gaps in the soil. NO2 dissolves into water in the dirt, transforming into a substance known as nitrate-nitrogen. This is absorbed by plants that make up the wall greenery and used during photosynthesis. Nitrate-nitrogen is also reduced by the action of microbes in the soil and returned to the atmosphere as harmless nitrogen.

When it comes to soil used in wall greenery, varieties with more spaces are lighter and thus easier to install, and also offer the benefit of plant roots being able to breathe better. However, the PM2.5 also readily passes through such soil, which decreases the purification functionality. According to Daiwa House officials, the company was able to engineer a balance in the soil to realize both wall-side greenery and the ability to capture toxic substances.

Typical wall greenery consists of small potted plants arranged vertically, but Daiwa House’s system utilizes an arrangement in which soil is embedded in large containers. One serious issue is the cost to power the fans that pull in the air. One square meter of wall-side greenery can purify 100 cu. meters of air per hour. However, leaving the fans running 12 hours a day would run up an electric bill of about 5,000 yen ($42) per square meter per year.

In the future, the company is considering introducing the system in combination with solar generation to reduce power costs. It plans to sell the system to distribution facilities and parking garages of commercial institutions that want to show the public their concern for the environment. Because wall-side greenery can also be factored into afforestation ratios, it enables efficient use of space. To hold down running costs, the homebuilder also envisions endowing some of the wall-side greenery with an atmospheric purification function. Demand could also be anticipated in the future from China, where air pollution is serious.

Oil-eating grasses

S.T. Corp. has developed a system that efficiently picks out an extract from residual matter left behind when thinning Sakhalin firs in Hokkaido that is effective at removing NO2 and the like. Timber components contained in this extract mix with NO2 in the air and the molecules form a large particle, the weight of which causes it to fall, thereby rendering the NO2 harmless. The company plans to begin selling an air purifier for automobiles using this Sakhalin fir extract from 2013.

Meanwhile, it has been established that certain plants that thrive in the intense heat of summer have an unexpected “environmental cleansing” function. These are SunPatiens, developed by Sakata Seed. Compared with typical bedding plants, SunPatiens absorb and break down five to eight times as much NO2 and three to four times as much formaldehyde. Such substances are drawn into the plant through pores in the leaves and are broken down into nitrogen and other elements in the course of photosynthesis.

SunPatiens are vigorous growers — 20cm seedlings planted in bare earth in May can grow to heights of 80cm to a meter by August under ideal conditions. It is thought that high photosynthesis reaction efficiency is linked to the plants’ cleansing power. SunPatiens are one of Sakata Seed’s leading products, with 27 million units shipped in 2014. Executive officer Takaaki Miura said, “Our main focus in product development is plants that are pleasing to the eye and easy to grow, but we also give attention to the environmental purification capability.”

Cleaning dirty dirt

A technology known as phytoremediation, which uses plants to reduce soil pollution, is also being commercialized. Sumitomo Forestry and JX Holdings have developed a method of extracting oil from former sites of gas stations by planting special grasses there. Grasses that can withstand dryness and oil can secrete nutrients such as proteins and amino acids into the earth, encouraging the propagation of microbes with the ability to break down oil. In this way, oil decomposes into harmless low-molecular-weight compounds.

One big advantage of this approach is the low cost — just a tenth as much as using heavy equipment to remove and replace the soil, and a third to a half as much as using soil remediation chemicals.

However, it takes two to three years for the oil concentration to decline enough to satisfy JX’s in-house standards, and there are other limitations such as the oil being broken down to depths of only about 1 meter in the soil. nevertheless, JX is forging ahead, and has introduced the method in nine locations so far. Sumitomo Forestry has received inquiries about it from gas station operators.”

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