The Many Uses of Tea Waste

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By Peter Keen

By definition, tea “waste” has little, if any, economic value. It’s a throwaway: dust, bits and pieces of twigs, damaged fragments of leaf, floor sweepings, stalks, and leftover detritus that doesn’t meet the standards or processes that result in it becoming part of the packaged end product.

The term is misleading. Tea waste has many properties that can be turned into a commercial asset. Waste isn’t necessarily inert. The innovations exploit the chemical and molecular richness of the tea bush and its leaf. Waste retains polythenols, antioxidants, catechins, flavanols, cellulose, amino acid, nonsoluble proteins, caffeine, fiber, sugars, lignin, zinc, and tannic acid that make tea so rich in flavors, textures, and nutrients. The waste is easily processed to extract, mix, and shape these to create value instead of burning or burying it.

Nutrients

The caffeine nutrient in the waste has a broad market with substantial export potential. It is extracted for use in many products, including cosmetics, fertilizers, instant teas, medical, and nutritional supplements. Tea waste makes a high protein cattle feed after removal of the tannic acid that interferes with protein metabolization. This can be done cheaply. The high fiber count makes it suitable for ruminants. It tastes pretty awful, but is improved by adding molasses.

The caffeine is also the base for poultry and pig feed. Some Japanese specialty farmers market their pork as green tea fed. In Korea and China, tea waste is a not-infrequent part of pigs’ diets. The distinctive contribution of tea is that its fat-soluble nutrients are not flushed out of the body but retained so that they affect flavor-building. A 2014 study of waste-fed young goats reported that it produced higher-quality meat, with lower “coarse” fat.

Another report points to waste being a superior ingredient for manufacturing supplements, with black tea waste matching cultivated green leaf in meeting quality and functional requirements, at a far lower price.

Adsorption

Adsorption is one of the growing areas of opportunity for tea waste. It is the collecting of molecules by a substance that retains them on its surface. They don’t enter its interior (that is absorption). The difference is like spilling ice cream on your wrist (adsorption: it stays there and can be wiped off and your skin is unaffected) versus eating it (it’s absorbed in your stomach and can’t be recovered or reconstituted.)

The need for adsorption reflects the widespread environmental damage caused by waste created in manufacturing across the globe. It’s the base for removing stuff that runs off into fields and waterways, accumulates in the soil, and is non-degradable.

Here are a few examples.

Mixed with clay, tea waste forms adsorptive membranes for removing toxic effluents from ponds that are generated as a factory byproduct.

Black tea waste powder is an effective dye adsorbent. Dyes are a core ingredient in textiles, printing, papermaking, and cosmetics. The 2% that are directly fed into water resources are concentrated, health hazards, and seriously toxic. Try oolong waste: one study recorded a 98% efficiency in removing methylene blue dye by using it. By and large, waste made in processing any type of tea will do the job. It will match more complex and expensive techniques, such as catalytic oxidation and membrane separation. At a lower cost.

Activated tea waste charcoal adsorbs lead, antibiotics, and heavy metals such as zinc, at a lower cost. This is a form of carbon processed to increase the surface area available for adsorption of other compounds or stimulation of chemical reactions. This micro-porosity can make a single gram of carbon provide 30,000 square feet of surface.

Activated carbon has largely been made from charcoal. This is complex and relatively expensive to produce. Biomass tea waste is growing as an effective substitute. Lightly treated with sulfuric acid it offers a widely available and highly environmental-friendly resource. It also has added properties that enable broader water purification, through advanced technologies like nanoparticles and capacitative deionization.

Fertilizer

Tea waste is packed with the compounds that make for a superior fertilizer: nitrogen, potassium and phosphorus. Case reports include horse stable manure when mixed with quarry sandstone dust, substrate for mushroom growing, vermicomposting — worm activation — compost for foliar (direct leaf) spraying and soil drenching that improve the plant’s access to nutrients and speed up toxin degradation, and specialty fertilizers with high levels of a particular ingredient, such as methane, ash, or potassium.

Finlay, the massive and now bankrupt Indian tea garden firm operates a biogas plant that takes black and green tea spent leaf as input from its farms and discharges it into a slurry lagoon to be used as a soil fertilizer for timber locations, new field clearing and tea plantations. The digester can hold 7,000 metric tons of organic tea waste.

Energy

Tea dust and stalks and all the other little bits of waste can be easily processed and turned into liquids and bricks as biomass fuel, bio-char, and bio-oil. The waste is decomposed using fluidized bed pyrolysis, a thermal decomposition process that occurs in the absence of oxygen. Tea waste pyrolysizes at high temperatures of 500-700°C and through gasification to produce bio-oil and biochar. The char can be converted into briquettes or mixed with biomass. This provides a highly efficient solid fuel for use in ovens and boilers across many industries – including tea. The techniques can be fine-tuned to optimize the yield of char, liquid, and gas.

The cellulose in tea waste is the same as that of timber. The high levels of this plus sugar, starch, and pectin are encouraging the use of fuel briquettes to replace wood fuel for ovens. The waste is even able to generate battery-power electric charges via vermicomposting.

The use of tea waste to make a fuel for tea making illustrates the circular economy, a framework for reducing waste through recycling, packaging, safety procedures, process, and production innovation to end the linear sequence in production and consumption of take-make-dispose.

Energy management is a major immediate target of opportunity for the circular economy. Electricity and fossil fuels comprise a large proportion of operating costs. There are many examples of crop waste being turned into biofuel. In Kenya, one small organization collects sugarcane waste from outside a factory where it has piled up for decades, dries and mills it before pressure compacting it into briquettes. These are smokeless and generate 50% more energy than equivalent sizes of logs.

Mokomboki Tea Factory in Kenya initiated a program that shows the scale of direct energy savings by replacing firewood with briquettes made of biomass waste. Its energy expenses fell from $542,000 to $295,000. It has entirely eliminated the use of timber.

The market

How much tea waste is generated is partly a matter of definition. India’s Tea Board regulators have somewhat arbitrarily set a figure of 2% of factory production volume — “made tea” — being waste. It has imposed a cumbersome tea waste-licensing process, with expensive testing, and renewal costs, and restricted exports. In late 2019, North Eastern Tea Association, which represents growers in Assam and West Bengals, centers for domestic tea waste trade, petitioned for the actual waste to be declared, which ranges from less than 1% to over 3%. They thanked the tea board for permitting exports: “This can be a game changer for the tea industry.”

There had been earlier game change initiatives. In 2012, the board had announced the introduction of a tea waste e-auction service, with a site for registration and links to six auction centers. Ironically, the registration page is still up on the web but there is an entire absence of any references as to what happened to the now vanished venture.

The total volumes of waste produced globally is completely unclear. Figures generally lack sourcing references and may or may not include spent tea waste, the waste at the end of the bush to cup chain. Pakistan produces 100 billion tea bags, with thousand metric tons of waste. These do not share the value-creation opportunities, since they are largely depleted of nutrients.

How much waste is there that can be used? The simplest answer is “lots and lots.”

An opportunity not to be wasted

Tea waste is an opportunity to create products that have many uses in many potential markets. Given the immense financial pressures tea growers face in every major region, turning waste into income is a step forward on the business innovation front. The trick is to make use of what is already in place, without adding heavy investment and risks. Tourism has been one of the initiatives Indian and Sri Lankan gardens have taken, turning old houses into guest lodges and offering tours and field education. It’s a natural extension of the core business. Though its future looks very iffy as the Covid pandemic has brought travel and tourism to a near halt, the logic is sound: waste not, want not and use what you have on hand.

Tea waste is best thought of in these terms: an innovation opportunity that is a natural extension of the core.