Hydroponics

From Wikipedia, the free encyclopedia

NASA researcher checking hydroponic onions with Bibb lettuce to his left and radishes to the right

Hydroponics is a subset of hydroculture and is a method of growing plants using mineral nutrient solutions, in water, without soil. Terrestrial plants may be grown with their roots in the mineral nutrient solution only or in an inert medium, such as perlite or gravel.

History

The earliest published work on growing terrestrial plants without soil was the 1627 book Sylva Sylvarum by Francis Bacon, printed a year after his death. Water culture became a popular research technique after that. In 1699, John Woodward published his water culture experiments with spearmint. He found that plants in less-pure water sources grew better than plants in distilled water.
By 1842, a list of nine elements believed to be essential to plant growth had been compiled, and the discoveries of the German botanists Julius von Sachs and Wilhelm Knop, in the years 1859-65, resulted in a development of the technique of soilless cultivation.^[1] Growth of terrestrial plants without soil in mineral nutrient solutions was called solution culture. It quickly became a standard research and teaching technique and is still widely used today. Solution culture is now considered a type of hydroponics where there is no inert medium.

In 1929, William Frederick Gericke of the University of California at Berkeley began publicly promoting that solution culture be used for agricultural crop production.^[2][3] He first termed it aquaculture but later found that aquaculture was already applied to culture of aquatic organisms. Gericke created a sensation by growing tomato vines twenty-five feet high in his back yard in mineral nutrient solutions rather than soil.^[4] By analogy with the ancient Greek term for agriculture, γεωπονικά (geoponica),^[5] the science of cultivating the earth, Gericke coined the term hydroponics in 1937 (although he asserts that the term was suggested by W. A. Setchell, of the University of California) for the culture of plants in water (from Ancient Greek ὕδωρ, water,^[5] and πόνος, labour ^[5]).^[1]

Reports of Gericke's work and his claims that hydroponics would revolutionize plant agriculture prompted a huge number of requests for further information. Gericke had been denied use of the University's greenhouses for his experiments due to the administration's skepticism, and when the University tried to compel him to release his preliminary nutrient recipes developed at home he requested greenhouse space and time to improve them using appropriate research facilities. While he was eventually provided greenhouse space, the University assigned Hoagland and Arnon to re-develop Gericke's formula and show it held no benefit over soil grown plant yields, a view held by Hoagland. In 1940, he published the book, Complete Guide to Soil less Gardening, after leaving his academic position in a climate that was politically unfavorable.

Two other plant nutritionists at the University of California were asked to research Gericke's claims. Dennis R. Hoagland^[6] and Daniel I. Arnon^[7] wrote a classic 1938 agricultural bulletin, The Water Culture Method for Growing Plants Without Soil,.^[8] Hoagland and Arnon claimed that hydroponic crop yields were no better than crop yields with good-quality soils. Crop yields were ultimately limited by factors other than mineral nutrients, especially light. This research, however, overlooked the fact that hydroponics has other advantages including the fact that the roots of the plant have constant access to oxygen and that the plants have access to as much or as little water as they need. This is important as one of the most common errors when growing is over- and under- watering; and hydroponics prevents this from occurring as large amounts of water can be made available to the plant and any water not used, drained away, recirculated, or actively aerated, eliminating anoxic conditions, which drown root systems in soil. In soil, a grower needs to be very experienced to know exactly how much water to feed the plant. Too much and the plant will not be able to access oxygen; too little and the plant will lose the ability to transport nutrients, which are typically moved into the roots while in solution. These two researchers developed several formulas for mineral nutrient solutions, known as Hoagland solution. Modified Hoagland solutions are still used today.

One of the earliest successes of hydroponics occurred on Wake Island, a rocky atoll in the Pacific Ocean used as a refuelling stop for Pan American Airlines. Hydroponics was used there in the 1930s to grow vegetables for the passengers. Hydroponics was a necessity on Wake Island because there was no soil, and it was prohibitively expensive to airlift in fresh vegetables.

In the 1960s, Allen Cooper of England developed the Nutrient film technique. The Land Pavilion at Walt Disney World's EPCOT Center opened in 1982 and prominently features a variety of hydroponic techniques. In recent decades, NASA has done extensive hydroponic research for their Controlled Ecological Life Support System or CELSS. Hydroponics intended to take place on Mars are using LED lighting to grow in different color spectrum with much less heat.

Origin

Soilless culture

Gericke originally defined hydroponics as crop growth in mineral nutrient solutions. Hydroponics is a subset of soilless culture. Many types of soilless culture do not use the mineral nutrient solutions required for hydroponics.

Plants that are not traditionally grown in a climate would be possible to grow using a controlled environment system like hydroponics. NASA has also looked to utilize hydroponics in the space program. Ray Wheeler,a plant physiologist at Kennedy Space Center’s Space Life Science Lab, believes that hydroponics will create advances within space travel. He terms this as a bioregenerative life support system.^[9]

Techniques

The two main types of hydroponics are solution culture and medium culture. Solution culture does not use a solid medium for the roots, just the nutrient solution. The three main types of solution cultures are static solution culture, continuous-flow solution culture and aeroponics. The medium culture method has a solid medium for the roots and is named for the type of medium, e.g., sand culture, gravel culture, or rockwool culture.

There are two main variations for each medium, sub-irrigation and top irrigation^[specify]. For all techniques, most hydroponic reservoirs are now built of plastic, but other materials have been used including concrete, glass, metal, vegetable solids, and wood. The containers should exclude light to prevent algae growth in the nutrient solution.

Static solution culture

In static solution culture, plants are grown in containers of nutrient solution, such as glass Mason jars (typically, in-home applications), plastic buckets, tubs, or tanks. The solution is usually gently aerated but may be un-aerated. If un-aerated, the solution level is kept low enough that enough roots are above the solution so they get adequate oxygen. A hole is cut in the lid of the reservoir for each plant. There can be one to many plants per reservoir. Reservoir size can be increased as plant size increases. A home made system can be constructed from plastic food containers or glass canning jars with aeration provided by an aquarium pump, aquarium airline tubing and aquarium valves. Clear containers are covered with aluminium foil, butcher paper, black plastic, or other material to exclude light, thus helping to eliminate the formation of algae. The nutrient solution is changed either on a schedule, such as once per week, or when the concentration drops below a certain level as determined with an electrical conductivity meter. Whenever the solution is depleted below a certain level, either water or fresh nutrient solution is added. A Mariotte's bottle, or a float valve, can be used to automatically maintain the solution level. In raft solution culture, plants are placed in a sheet of buoyant plastic that is floated on the surface of the nutrient solution. That way, the solution level never drops below the roots.

Continuous-flow solution culture

In continuous-flow solution culture, the nutrient solution constantly flows past the roots. It is much easier to automate than the static solution culture because sampling and adjustments to the temperature and nutrient concentrations can be made in a large storage tank that has potential to serve thousands of plants. A popular variation is the nutrient film technique or NFT, whereby a very shallow stream of water containing all the dissolved nutrients required for plant growth is recirculated past the bare roots of plants in a watertight thick root mat, which develops in the bottom of the channel and has an upper surface that, although moist, is in the air. Subsequent to this, an abundant supply of oxygen is provided to the roots of the plants. A properly designed NFT system is based on using the right channel slope, the right flow rate, and the right channel length. The main advantage of the NFT system over other forms of hydroponics is that the plant roots are exposed to adequate supplies of water, oxygen, and nutrients. In all other forms of production, there is a conflict between the supply of these requirements, since excessive or deficient amounts of one results in an imbalance of one or both of the others. NFT, because of its design, provides a system where all three requirements for healthy plant growth can be met at the same time, provided that the simple concept of NFT is always remembered and practised. The result of these advantages is that higher yields of high-quality produce are obtained over an extended period of cropping. A downside of NFT is that it has very little buffering against interruptions in the flow, e.g., power outages. But, overall, it is probably one of the more productive techniques.

The same design characteristics apply to all conventional NFT systems. While slopes along channels of 1:100 have been recommended, in practice it is difficult to build a base for channels that is sufficiently true to enable nutrient films to flow without ponding in locally depressed areas. As a consequence, it is recommended that slopes of 1:30 to 1:40 are used. This allows for minor irregularities in the surface, but, even with these slopes, ponding and water logging may occur. The slope may be provided by the floor, or benches or racks may hold the channels and provide the required slope. Both methods are used and depend on local requirements, often determined by the site and crop requirements.

As a general guide, flow rates for each gully should be 1 liter per minute. At planting, rates may be half this and the upper limit of 2 L/min appears about the maximum. Flow rates beyond these extremes are often associated with nutritional problems. Depressed growth rates of many crops have been observed when channels exceed 12 metres in length. On rapidly growing crops, tests have indicated that, while oxygen levels remain adequate, nitrogen may be depleted over the length of the gully. As a consequence, channel length should not exceed 10–15 metres. In situations where this is not possible, the reductions in growth can be eliminated by placing another nutrient feed halfway along the gully and reducing flow rates to 1 L/min through each outlet.

Aeroponics

Aeroponics is a system wherein roots are continuously or discontinuously kept in an environment saturated with fine drops (a mist or aerosol) of nutrient solution. The method requires no substrate and entails growing plants with their roots suspended in a deep air or growth chamber with the roots periodically wetted with a fine mist of atomized nutrients. Excellent aeration is the main advantage of aeroponics.
Aeroponic techniques have proven to be commercially successful for propagation, seed germination, seed potato production, tomato production, leaf crops, and micro-greens.^[10] Since inventor Richard Stoner commercialized aeroponic technology in 1983, aeroponics has been implemented as an alternative to water intensive hydroponic systems worldwide.^[11] The limitation of hydroponics is the fact that 1 kg of water can only hold 8 mg of air, no matter whether aerators are utilized or not.

Another distinct advantage of aeroponics over hydroponics is that any species of plants can be grown in a true aeroponic system because the micro environment of an aeroponic can be finely controlled. The limitation of hydroponics is that only certain species of plants can survive for so long in water before they become waterlogged. The advantage of aeroponics is that suspended aeroponic plants receive 100% of the available oxygen and carbon dioxide to the roots zone, stems, and leaves,^[12] thus accelerating biomass growth and reducing rooting times. NASA research has shown that aeroponically grown plants have an 80% increase in dry weight biomass (essential minerals) compared to hydroponically grown plants. Aeroponics used 65% less water than hydroponics. NASA also concluded that aeroponically grown plants requires ¼ the nutrient input compared to hydroponics. Unlike hydroponically grown plants, aeroponically grown plants will not suffer transplant shock when transplanted to soil, and offers growers the ability to reduce the spread of disease and pathogens. Aeroponics is also widely used in laboratory studies of plant physiology and plant pathology. Aeroponic techniques have been given special attention from NASA since a mist is easier to handle than a liquid in a zero gravity environment.

Passive sub-irrigation

Passive sub-irrigation, also known as passive hydroponics or semi-hydroponics, is a method wherein plants are grown in an inert porous medium that transports water and fertilizer to the roots by capillary action from a separate reservoir as necessary, reducing labour and providing a constant supply of water to the roots. In the simplest method, the pot sits in a shallow solution of fertilizer and water or on a capillary mat saturated with nutrient solution. The various hydroponic media available, such as expanded clay and coconut husk, contain more air space than more traditional potting mixes, delivering increased oxygen to the roots, which is important in epiphytic plants such as orchids and bromeliads, whose roots are exposed to the air in nature. Additional advantages of passive hydroponics are the reduction of root rot and the additional ambient humidity provided through evaporations.

Ebb and flow or flood and drain sub-irrigation

In its simplest form, there is a tray above a reservoir of nutrient solution. Either the tray is filled with growing medium (clay granules being the most common) and planted directly or pots of medium stand in the tray. At regular intervals, a simple timer causes a pump to fill the upper tray with nutrient solution, after which the solution drains back down into the reservoir. This keeps the medium regularly flushed with nutrients and air. Once the upper tray fills past the drain stop, it begins recirculating the water until the timer turns the pump off, and the water in the upper tray drains back into the reservoirs.^[13]

Run to waste

In a run-to-waste system, nutrient and water solution is periodically applied to the medium surface. This may be done in its simplest form, by manually applying a nutrient-and-water solution one or more times per day in a container of inert growing media, such as rockwool, perlite, vermiculite, coco fibre, or sand. In a slightly more complex system, it is automated with a delivery pump, a timer and irrigation tubing to deliver nutrient solution with a delivery frequency that is governed by the key parameters of plant size, plant growing stage, climate, substrate, and substrate conductivity, pH, and water content.

In a commercial setting, watering frequency is multi factorial and governed by computers or PLCs.

Commercial hydroponics production of large plants like tomatoes, cucumber, and peppers use one form or another of run-to-waste hydroponics.

In environmentally responsible uses, the nutrient rich waste is collected and processed through an on site filtration system to be used many times, making the system very productive.^[14]

The majority of bonsai are now grown in soil-free substrates (typically consisting of akadama, grit, diatomaceous earth and other inorganic components) and have their water and nutrients provided in a run-to-waste form.

Deep water culture

The hydroponic method of plant production by means of suspending the plant roots in a solution of nutrient-rich, oxygenated water. Traditional methods favor the use of plastic buckets and large containers with the plant contained in a net pot suspended from the centre of the lid and the roots suspended in the nutrient solution. The solution is oxygen saturated by an air pump combined with porous stones. With this method, the plants grow much faster because of the high amount of oxygen that the roots receive.^[15]

Top-fed deep water culture

Top-fed deep water culture is a technique involving delivering highly oxygenated nutrient solution direct to the root zone of plants. While deep water culture involves the plant roots hanging down into a reservoir of nutrient solution, in top-fed deep water culture the solution is pumped from the reservoir up to the roots (top feeding). The water is released over the plant's roots and then runs back into the reservoir below in a constantly recirculating system. As with deep water culture, there is an airstone in the reservoir that pumps air into the water via a hose from outside the reservoir. The airstone helps add oxygen to the water. Both the airstone and the water pump run 24 hours a day.

The biggest advantage of top-fed deep water culture over standard deep water culture is increased growth during the first few weeks. With deep water culture, there is a time when the roots have not reached the water yet. With top-fed deep water culture, the roots get easy access to water from the beginning and will grow to the reservoir below much more quickly than with a deep water culture system. Once the roots have reached the reservoir below, there is not a huge advantage with top-fed deep water culture over standard deep water culture. However, due to the quicker growth in the beginning, grow time can be reduced by a few weeks.^[16]

Fogponics

Fogponics is an advanced form of aeroponics which uses water in a vaporised form to transfer nutrients and oxygen to enclosed suspended plant roots. Using the same general idea behind aeroponics except fogponics uses a 5-10 micron mist within the rooting chamber and as use for a foliar feeding mechanism.

Rotary

A rotary hydroponic garden is a style of commercial hydroponics created within a circular frame which rotates continuously during the entire growth cycle of whatever plant is being grown.

While system specifics vary, systems typically rotate once per hour, giving a plant 24 full turns within the circle each 24-hour period. Within the center of each rotary hydroponic garden is a high intensity grow light, designed to simulate sunlight, often with the assistance of a mechanized timer.

Each day, as the plants rotate, they are periodically watered with a hydroponic growth solution to provide all nutrients necessary for robust growth. Due to the plants continuous fight against gravity, plants typically mature much more quickly than when grown in soil or other traditional hydroponic growing systems. Due to the small foot print a rotary hydroponic system has, it allows for more plant material to be grown per sq foot of floor space than other traditional hydroponic systems.

Substrates

One of the most obvious decisions hydroponic farmers have to make is which medium they should use. Different media are appropriate for different growing techniques.

Expanded clay aggregate

Expanded clay pebbles.

Baked clay pellets, are suitable for hydroponic systems in which all nutrients are carefully controlled in water solution. The clay pellets are inert, pH neutral and do not contain any nutrient value.

The clay is formed into round pellets and fired in rotary kilns at 1,200 °C (2,190 °F). This causes the clay to expand, like popcorn, and become porous. It is light in weight, and does not compact over time. The shape of an individual pellet can be irregular or uniform depending on brand and manufacturing process. The manufacturers consider expanded clay to be an ecologically sustainable and re-usable growing medium because of its ability to be cleaned and sterilized, typically by washing in solutions of white vinegar, chlorine bleach, or hydrogen peroxide (H
2O
2), and rinsing completely.

Another view is that clay pebbles are best not re-used even when they are cleaned, due to root growth that may enter the medium. Breaking open a clay pebble after a crop has been grown will reveal this growth.

Growstones

Growstones, made from glass waste, have both more air and water retention space than perlite and peat. This aggregate holds more water than parboiled rice hulls.^[17] Growstones by volume consists of .5 to 5% Calcium carbonate.^[18] for a standard 5.1 kg bag of Growstones that's 25.8 to 258 grams of calcium carbonate. The remainder is Soda-lime glass. ^[18]

Coir

Coco peat, also known as coir or coco, is the leftover material after the fibres have been removed from the outermost shell (bolster) of the coconut. Coir is a 100% natural grow and flowering medium. Coconut coir is colonized with trichoderma fungi, which protects roots and stimulates root growth. It is extremely difficult to over-water coir due to its perfect air-to-water ratio; plant roots thrive in this environment. Coir has a high cation exchange, meaning it can store unused minerals to be released to the plant as and when it requires it. Coir is available in many forms; most common is coco peat, which has the appearance and texture of soil but contains no mineral content.

Rice husks

Parboiled rice husks (PBH) are an agricultural byproduct that would otherwise have little use. They decay over time, and allow drainage,^[19] and even retain less water than growstones.^[17] A study showed that rice husks did not affect the effects of plant growth regulators.^[19]

Perlite

Perlite is a volcanic rock that has been superheated into very lightweight expanded glass pebbles. It is used loose or in plastic sleeves immersed in the water. It is also used in potting soil mixes to decrease soil density. Perlite has similar properties and uses to vermiculite but, in general, holds more air and less water. If not contained, it can float if flood and drain feeding is used. It is a fusion of granite, obsidian, pumice and basalt. This volcanic rock is naturally fused at high temperatures undergoing what is called "Fusionic Metamorphosis".

Vermiculite

Like perlite, vermiculite is a mineral that has been superheated until it has expanded into light pebbles. Vermiculite holds more water than perlite and has a natural "wicking" property that can draw water and nutrients in a passive hydroponic system. If too much water and not enough air surrounds the plants roots, it is possible to gradually lower the medium's water-retention capability by mixing in increasing quantities of perlite.

Pumice

Like perlite, pumice is a lightweight, mined volcanic rock that finds application in hydroponics.

Sand

Sand is cheap and easily available. However, it is heavy, does not hold water very well, and it must be sterilized between uses.

Gravel

The same type that is used in aquariums, though any small gravel can be used, provided it is washed first. Indeed, plants growing in a typical traditional gravel filter bed, with water circulated using electric powerhead pumps, are in effect being grown using gravel hydroponics. Gravel is inexpensive, easy to keep clean, drains well and will not become waterlogged. However, it is also heavy, and, if the system does not provide continuous water, the plant roots may dry out.

Wood fibre

Wood fibre, produced from steam friction of wood, is a very efficient organic substrate for hydroponics. It has the advantage that it keeps its structure for a very long time. Wood fibre has been shown to reduce the effects of "plant growth regulators."^[19]

Rock wool

Rock wool (mineral wool) is the most widely used medium in hydroponics. Rock wool is an inert substrate suitable for both run-to-waste and recirculating systems. Rock wool is made from molten rock, basalt or 'slag' that is spun into bundles of single filament fibres, and bonded into a medium capable of capillary action, and is, in effect, protected from most common microbiological degradation. Rock wool has many advantages and some disadvantages. The latter being the possible skin irritancy (mechanical) whilst handling (1:1000). Flushing with cold water usually brings relief.
Advantages include its proven efficiency and effectiveness as a commercial hydroponic substrate. Most of the rock wool sold to date is a non-hazardous, non-carcinogenic material, falling under Note Q of the European Union Classification Packaging and Labeling Regulation (CLP).^{[citation needed]}

Sheep wool

Wool from shearing sheep is a little-used yet promising renewable growing medium. In a study comparing wool with peat slabs, coconut fibre slabs, perlite and rockwool slabs to grow cucumber plants, sheep wool had a greater air capacity of 70%, which decreased with use to a comparable 43%, and water capacity that increased from 23% to 44% with use. Using sheep wool resulted in the greatest yield out of the tested substrates, while application of a biostimulator consisting of humic acid, lactic acid and Bacillus subtilis improved yields in all substrates.^[20]

Brick shards

Brick shards have similar properties to gravel. They have the added disadvantages of possibly altering the pH and requiring extra cleaning before reuse.

Polystyrene packing peanuts

Polystyrene packing peanuts are inexpensive, readily available, and have excellent drainage. However, they can be too lightweight for some uses. They are used mainly in closed-tube systems.
Note that polystyrene peanuts must be used; biodegradable packing peanuts will decompose into a sludge. Plants may absorb styrene and pass it to their consumers; this is a possible health risk.^{[citation needed]}

Nutrient solutions

Plant nutrients used in hydroponics are dissolved in the water and are mostly in inorganic and ionic form. Primary among the dissolved cations (positively charged ions) are Ca²⁺ (calcium), Mg2+
(magnesium), and K+ (potassium); the major nutrient anions in nutrient solutions are NO−
3 (nitrate), SO2−
4 (sulfate), and H
2PO−
4 (dihydrogen phosphate).

Numerous 'recipes' for hydroponic solutions are available. Many use different combinations of chemicals to reach similar total final compositions. Commonly used chemicals for the macronutrients include potassium nitrate, calcium nitrate, potassium phosphate, and magnesium sulfate. Various micronutrients are typically added to hydroponic solutions to supply essential elements; among them are Fe (iron), Mn (manganese), Cu (copper), Zn (zinc), B (boron), Cl (chlorine), and Ni (nickel). Chelating agents are sometimes used to keep Fe soluble, and humic acids can be added to increase nutrient uptake.^[21] Many variations of the nutrient solutions used by Arnon and Hoagland (see above) have been styled 'modified Hoagland solutions' and are widely used. Variation of different mixes throughout the plant life-cycle, further optimizes its nutritional value.^[22] Plants will change the composition of the nutrient solutions upon contact by depleting specific nutrients more rapidly than others, removing water from the solution, and altering the pH by excretion of either acidity or alkalinity.^[23] Care is required not to allow salt concentrations to become too high, nutrients to become too depleted, or pH to wander far from the desired value.

Although pre-mixed concentrated nutrient solutions are generally purchased from commercial nutrient manufacturers by hydroponic hobbyists and small commercial growers, several tools exists to help anyone prepare their own solutions without extensive knowledge about chemistry. The free and open source tools HydroBuddy^[24] and HydroCal^[25] have been created by professional chemists to help any hydroponics grower prepare their own nutrient solutions. The first program is available for Windows, Mac and Linux while the second one can be used through a simple Java interface. Both programs allow for basic nutrient solution preparation although HydroBuddy provides added functionality to use and save custom substances, save formulations and predict electrical conductivity values.According to Kumar and Cho (2014) the hydroponics waste nutrient solution can be reused for growing commercially important crops and reuse of waste nutrient solution may control point source pollution.^[26]

The well-oxygenated and enlightened environment promotes the development of algae. It is therefore necessary to wrap the tank with black film obscuring all light.

Organic hydroponics uses the solution containing microorganisms. In organic hydroponics, organic fertilizer can be added in the hydroponic solution because microorganisms degrade organic fertilizer into inorganic nutrients. In contrast, conventional hydroponics cannot use organic fertilizer because organic compounds in the hydroponic solution show phytotoxic effects.

Commercial

Some commercial installations use no pesticides or herbicides, preferring integrated pest management techniques. There is often a price premium willingly paid by consumers for produce that is labelled "organic". Some states in the USA require soil as an essential to obtain organic certification. There are also overlapping and somewhat contradictory rules established by the US Federal Government, so some food grown with hydroponics can be certified organic. Most hydroponically grown produce cannot be sold as organic due to the fact that they do not use soil as a growing medium.

Hydroponics also saves water; it uses as little as ¹⁄₂₀ the amount as a regular farm to produce the same amount of food. The water table can be impacted by the water use and run-off of chemicals from farms, but hydroponics may minimize impact as well as having the advantage that water use and water returns are easier to measure. This can save the farmer money by allowing reduced water use and the ability to measure consequences to the land around a farm.

To increase plant growth, lighting systems such as metal-halide lamp for growing stage only or high-pressure sodium for growing/flowering/blooming stage are used to lengthen the day or to supplement natural sunshine if it is scarce. Metal halide emits more light in the blue spectrum, making it ideal for plant growth but is harmful to unprotected skin and can cause skin cancer. High-pressure sodium emits more light in the red spectrum, meaning that it is best suited for supplementing natural sunshine and can be used throughout the growing cycle. However, these lighting systems require large amounts of electricity to operate, making efficiency and safety very critical.

The environment in a hydroponics greenhouse is tightly controlled for maximum efficiency, and this new mindset is called soil-less/controlled-environment agriculture (CEA). With this growers can make ultra-premium foods anywhere in the world, regardless of temperature and growing seasons. Growers monitor the temperature, humidity, and pH level constantly.

Hydroponics have been used to enhance vegetables to provide more nutritional value. A hydroponic farmer in Virginia has developed a calcium and potassium enriched head of lettuce, scheduled to be widely available in April 2007. Grocers in test markets have said that the lettuce sells "very well", and the farmers claim that their hydroponic lettuce uses 90% less water than traditional soil farming.^[27]

Advancements

With pest problems reduced, and nutrients constantly fed to the roots, productivity in hydroponics is high, although plant growth can be limited by the low levels of carbon dioxide in the atmosphere, or limited light exposure. To increase yield further, some sealed greenhouses inject carbon dioxide into their environment to help growth (CO
2 enrichment), add lights to lengthen the day, or control vegetative growth, etc.

Green chemistry

From Wikipedia, the free encyclopedia

Green chemistry, also called sustainable chemistry, is a philosophy of chemical research and engineering that encourages the design of products and processes that minimize the use and generation of hazardous substances.^[1] Whereas environmental chemistry is the chemistry of the natural environment, and of pollutant chemicals in nature, green chemistry seeks to reduce the negative impact of chemistry on the environment by preventing pollution at its source and using fewer natural resources.

As a chemical philosophy, green chemistry applies to organic chemistry, inorganic chemistry, biochemistry, analytical chemistry, physical chemistry and even chemical engineering. While green chemistry seems to focus on industrial applications, it does apply to any chemistry choice. Click chemistry is often cited as a style of chemical synthesis that is consistent with the goals of green chemistry. The focus is on minimizing the hazard and maximizing the efficiency of any chemical choice.

In 2005 Ryōji Noyori identified three key developments in green chemistry: use of supercritical carbon dioxide as green solvent, aqueous hydrogen peroxide for clean oxidations and the use of hydrogen in asymmetric synthesis.^[2] Examples of applied green chemistry are supercritical water oxidation, on water reactions, and dry media reactions.

Bioengineering is also seen as a promising technique for achieving green chemistry goals. A number of important process chemicals can be synthesized in engineered organisms, such as shikimate, a Tamiflu precursor which is fermented by Roche in bacteria.

The term green chemistry was coined by Paul Anastas in 1991.^[3] However, it has been suggested^[4] that the concept was originated by Trevor Kletz in his 1978 paper in Chemistry and Industry where he proposed that chemists should seek alternative processes to those involving more dangerous substances and conditions.^[5] The "Zero Effluent Lab Manual" was developed by Thomas Hellman Morton when he was on the faculty at Brown University in the 1970s. The Manual is still available on-line via links at the Hendrix College Green Chemistry site. Also in Chemistry and Industry the solvent free green chemistry version of “The Hajos-Parrish Cyclisation” has been highlighted in 1996 by Professors Andrew B. Holmes and G. Richard Stephenson.^[6]

Principles

Paul Anastas, then of the United States Environmental Protection Agency, and John C. Warner developed 12 principles of green chemistry,^[7] which help to explain what the definition means in practice. The principles cover such concepts as:

• the design of processes to maximize the amount of raw material that ends up in the product;
• the use of safe, environment-benign substances, including solvents, whenever possible;
• the design of energy efficient processes;
• the best form of waste disposal: not to create it in the first place.

The 12 principles are:

1. It is better to prevent waste than to treat or clean up waste after it is formed.
2. Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.
3. Wherever practicable, synthetic methodologies should be designed to use and generate substances that possess little or no toxicity to human health and the environment.
4. Chemical products should be designed to preserve efficacy of function while reducing toxicity.
5. The use of auxiliary substances (e.g. solvents, separation agents, etc.) should be made unnecessary wherever possible and innocuous when used.
6. Energy requirements should be recognized for their environmental and economic impacts and should be minimized. Synthetic methods should be conducted at ambient temperature and pressure.
7. A raw material or feedstock should be renewable rather than depleting wherever technically and economically practicable.
8. Reduce derivatives – Unnecessary derivatization (blocking group, protection/deprotection, temporary modification) should be avoided whenever possible.
9. Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.
10. Chemical products should be designed so that at the end of their function they do not persist in the environment and break down into innocuous degradation products.
11. Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances.
12. Substances and the form of a substance used in a chemical process should be chosen to minimize potential for chemical accidents, including releases, explosions, and fires.

Trends

Attempts are being made not only to quantify the greenness of a chemical process but also to factor in other variables such as chemical yield, the price of reaction components, safety in handling chemicals, hardware demands, energy profile and ease of product workup and purification. In one quantitative study,^[8] the reduction of nitrobenzene to aniline receives 64 points out of 100 marking it as an acceptable synthesis overall whereas a synthesis of an amide using HMDS is only described as adequate with a combined 32 points.

Green chemistry is increasingly seen as a powerful tool that researchers must use to evaluate the environmental impact of nanotechnology.^[9] As nanomaterials are developed, the environmental and human health impacts of both the products themselves and the processes to make them must be considered to ensure their long-term economic viability.

Examples

In the statement for the 2005 Nobel Prize for Chemistry for "the development of the metathesis method in organic synthesis," the Nobel Prize Committee states, "this represents a great step forward for 'green chemistry', reducing potentially hazardous waste through smarter production. Metathesis is an example of how important basic science has been applied for the benefit of man, society and the environment."^[10] The concept of green pharmacy was developed recently based on similar principles.^[11]

Hydrazine

Addressing principle #2 is the Peroxide Process for producing hydrazine without cogenerating salt. Hydrazine is traditionally produced by the Olin Raschig process from sodium hypochlorite (the active ingredient in many bleaches) and ammonia. The net reaction produces one equivalent of sodium chloride for every equivalent of the targeted product hydrazine:^[12]

NaOCl + 2 NH₃ → H₂N-NH₂ + NaCl + H₂O

In the greener Peroxide process hydrogen peroxide is employed as the oxidant, the side product being water. The net conversion follows:

2 NH₃ + H₂O₂ → H₂N-NH₂ + 2 H₂O

Addressing principle #4, this process does not require auxiliary extracting solvents. Methyl ethyl ketone is used as a carrier for the hydrazine, the intermediate ketazide phase separates from the reaction mixture, facilitating workup without the need of an extracting solvent.

1,3-Propanediol

Addressing principle #7 is a green route to 1,3-propanediol, which is traditionally generated from petrochemical precursors. It can be produced from renewable precursors via the bioseparation of 1,3-propanediol using a genetically modified strain of E. coli.^[13] This diol is used to make new polyesters for the manufacture of carpets.

Carbon dioxide as blowing agent

In 1996, Dow Chemical won the 1996 Greener Reaction Conditions award for their 100% carbon dioxide blowing agent for polystyrene foam production. Polystyrene foam is a common material used in packing and food transportation. Seven hundred million pounds are produced each year in the United States alone. Traditionally, CFC and other ozone-depleting chemicals were used in the production process of the foam sheets, presenting a serious environmental hazard. Flammable, explosive, and, in some cases toxic hydrocarbons have also been used as CFC replacements, but they present their own problems. Dow Chemical discovered that supercritical carbon dioxide works equally as well as a blowing agent, without the need for hazardous substances, allowing the polystyrene to be more easily recycled. The CO₂ used in the process is reused from other industries, so the net carbon released from the process is zero.

Lactide

Lactide

In 2002, Cargill Dow (now NatureWorks) won the Greener Reaction Conditions Award for their improved method for polymerization of polylactic acid . Unfortunately, lactide-base polymers do not perform well and the project was discontinued by Dow soon after the award. Lactic acid is produced by fermenting corn and converted to lactide, the cyclic dimer ester of lactic acid using an efficient, tin-catalyzed cyclization. The L,L-lactide enantiomer is isolated by distillation and polymerized in the melt to make a crystallizable polymer, which has some applications including textiles and apparel, cutlery, and food packaging. Wal-Mart has announced that it is using/will use PLA for its produce packaging. The NatureWorks PLA process substitutes renewable materials for petroleum feedstocks, doesn't require the use of hazardous organic solvents typical in other PLA processes, and results in a high-quality polymer that is recyclable and compostable.

Carpet tile backings

In 2003 Shaw Industries selected a combination of polyolefin resins as the base polymer of choice for EcoWorx due to the low toxicity of its feedstocks, superior adhesion properties, dimensional stability, and its ability to be recycled. The EcoWorx compound also had to be designed to be compatible with nylon carpet fiber. Although EcoWorx may be recovered from any fiber type, nylon-6 provides a significant advantage. Polyolefins are compatible with known nylon-6 depolymerization methods. PVC interferes with those processes. Nylon-6 chemistry is well-known and not addressed in first-generation production. From its inception, EcoWorx met all of the design criteria necessary to satisfy the needs of the marketplace from a performance, health, and environmental standpoint. Research indicated that separation of the fiber and backing through elutriation, grinding, and air separation proved to be the best way to recover the face and backing components, but an infrastructure for returning postconsumer EcoWorx to the elutriation process was necessary. Research also indicated that the postconsumer carpet tile had a positive economic value at the end of its useful life. EcoWorx is recognized by MBDC as a certified cradle-to-cradle design.

Trans and cis fatty acids

Transesterification of fats

In 2005, Archer Daniels Midland (ADM) and Novozymes won the Greener Synthetic Pathways Award for their enzyme interesterification process. In response to the U.S. Food and Drug Administration (FDA) mandated labeling of trans-fats on nutritional information by January 1, 2006, Novozymes and ADM worked together to develop a clean, enzymatic process for the interesterification of oils and fats by interchanging saturated and unsaturated fatty acids. The result is commercially viable products without trans-fats. In addition to the human health benefits of eliminating trans-fats, the process has reduced the use of toxic chemicals and water, prevents vast amounts of byproducts, and reduces the amount of fats and oils wasted.

Bio-succinic acid

In 2011, the Outstanding Green Chemistry Accomplishments by a Small Business Award went to BioAmber Inc. for integrated production and downstream applications of bio-based succinic acid.
Succinic acid is a platform chemical that is an important starting material in the formulations of everyday products. Traditionally, succinic acid is produced from petroleum-based feedstocks. BioAmber has developed process and technology that produces succinic acid from the fermentation of renewable feedstocks at a lower cost and lower energy expenditure than the petroleum equivalent while sequestering CO₂ rather than emitting it.^[14]

Laboratory chemicals

Several laboratory chemicals are controversial from the perspective of Green chemistry. The Massachusetts Institute of Technology has created the [2] to help identify alternatives. Ethidium bromide, xylene, mercury, and formaldehyde have been identified as "worst offenders" which have alternatives.^[15] Solvents in particular make a large contribution to the environmental impact of chemical manufacturing and there is a growing focus on introducing Greener solvents into the earliest stage of development of these processes: laboratory-scale reaction and purification methods. In the Pharmaceutical Industry, both GSK^[16][17] and Pfizer^[18] have published Solvent Selection Guides for their Drug Discovery chemists.

Legislation

Europe

In 2007, Europe put into place the Registration, Evaluation, Authorisation, and Restriction of Chemicals (REACH) program, which requires companies to provide data showing that their products are safe. This regulation (1907/2006) ensures not only the assessment of the chemicals' hazards as well as risks during their uses but also includes measures for banning or restricting/authorising uses of specific substances. ECHA, the EU Chemicals Agency in Helsinki, is implementing the regulation whereas the enforcement lies with the EU member states. The US Toxic Substances Control Act, passed in 1976, in principle has similar provisions but is not comparable to REACH as to its regulatory effectiveness.

On September 29, 2008 California approved two laws which encourage green chemistry, launching the California Green Chemistry Initiative. The law requires California's Department of Toxic Substances Control to prioritize "chemicals of concern", and puts the burden of testing on the agency rather than industry. The laws were criticized by Paul Anastas, who stated that the laws did not go far enough in encouraging research, education, and industry incentives.^[19] The law called for regulations to be in place by January 1, 2011, but universal opposition to the previously proposed regulations rendered that date impossible. Mid October 2012 is the new target date for new draft regulations to be in place to implement the law.^[20]

United States

Passed in 1990, the Pollution Prevention Act helped create new approaches for dealing with pollution by preventing problems before they happen.

It has been stated that long-standing weaknesses in the U.S. chemical management program, notably the Toxic Substances Control Act (TSCA) of 1976, discounts the hazardous properties of chemicals relative to their function, price, and performance.^[21] The report concludes that these market conditions represent a key barrier to the scientific, technical, and commercial success of green chemistry in the U.S., and that fundamental policy changes are needed to correct these weaknesses.^[22]

Education

Many institutions offer courses^[23] and degrees on Green Chemistry. Examples from across the globe are Denmark's Technical University,^[24] and several in the US, e.g. at the Universities of Massachusetts-Boston,^[25] Michigan,^[26] and Oregon.^[27] A masters level course in Green Technology, has been introduced by the Institute of Chemical Technology, India. In the UK at the University of York^[28] University of Leicester, Department of Chemistry and MRes in Green Chemistry at Imperial College London. In Spain different universities like the Universidad de Jaume I^[29] or the Universidad de Navarra,^[30] offer Green Chemistry master courses. There are also websites focusing on green chemistry, such as the Michigan Green Chemistry Clearinghouse at www.migreenchemistry.org.

Apart from its Green Chemistry Master courses the Zurich University of Applied Sciences ZHAW presents an exposition and web page "Making chemistry green" for a broader public, illustrating the 12 principles.^[31]

Scientific journals specialized in green chemistry

• Green Chemistry (RSC)
• ChemSusChem (Wiley)
• ACS Sustainable Chemistry & Engineering (ACS)

Controversy

Following historical analyses of the green chemistry development, there have been green chemistry advocates who see it as an innovative way of thinking. On the other hand, there have been chemists who have argued that green chemistry is no more than a public relations label. In fact, a lot of chemists use the term "green chemistry" independently from the green chemistry paradigm, as proposed by Anastas and Warner. This explains the uncertainty of the scientific status of green chemistry.^[32]

Awards

Many scientific societies have created awards to encourage research in green chemistry.

• Australia’s Green Chemistry Challenge Awards overseen by The Royal Australian Chemical Institute (RACI).
• The Canadian Green Chemistry Medal.^[33]
• In Italy, Green Chemistry activities center around an inter-university consortium known as INCA.^[34]
• In Japan, The Green & Sustainable Chemistry Network oversees the GSC awards program.^[35]
• In the United Kingdom, the Green Chemical Technology Awards are given by Crystal Faraday.^[36]
• In the US, the Presidential Green Chemistry Challenge Awards recognize individuals and businesses.^[37][38]

Environmental engineering science

From Wikipedia, the free encyclopedia

Students in Environmental Engineering Science typically combine scientific studies of the biosphere with mathematical, analytical and design tools found in the engineering fields

Environmental engineering science (EES) is a multidisciplinary field of engineering science that combines the biological, chemical and physical sciences with the field of engineering. This major traditionally requires the student to take many basic engineering classes in fields such as thermodynamics, advanced math, computer modeling and simulation as well as technical classes in subjects such as statics, mechanics, hydrology, and fluid dynamics. As the student progresses, the upper division elective classes define a specific field of study for the student with a choice in a wide range of science, technology and engineering related classes.^[1]

Difference with related fields

Graduates of Environmental Engineering Science can go on to work on the technical aspects of designing a Living Roof like the one pictured here at the California Academy of the Sciences

As a recently created program, environmental engineering science has not yet been incorporated into the terminology found among environmentally focused professionals . It should be noted in the few engineering colleges that offer this major, the curriculum shares more classes in common with environmental engineering than it does with environmental science. Typically, EES students follow a similar course curriculum with environmental engineers until their fields diverge during the last year of college. While, a majority of the environmental engineering students must take classes designed to connect their knowledge of the environment to modern building materials and construction methods. This is meant to steer the environmental engineer into a field where they will more than likely assist in building treatment facilities, preparing environmental impact assessments or helping to mitigate air pollution from specific point sources.

Meanwhile, the environmental engineering science student will choose a direction for their career. From the wide range of electives they have to choose from, these students can move into a wide range of fields in anything from the design of nuclear storage facilities, bacterial bioreactors or environmental policies. With this in mind, it is important to note that these students combine the practical design background of an engineer with the detailed theory found in many of the biological and physical sciences. In other words, these students have the capabilities to imagine, design and build ideas from many interconnected disciplines concerned with the healthy fate of our environment.

Description at universities

UC Berkeley

The College of Engineering at UC Berkeley defines Environmental Engineering Science as follows^[1]

This is a multidisciplinary field requiring an integration of physical, chemical and biological principles with engineering analysis for environmental protection and restoration. The program incorporates courses from many departments on campus to create a discipline that is rigorously based in science and engineering, while addressing a wide variety of environmental issues. Although an environmental engineering option exists within the civil engineering major, the engineering science curriculum provides a more broadly based foundation in the sciences than is possible in civil engineering. This major prepares the student for a career or graduate study in many environmental areas.

Massachusetts Institute of Technology

At MIT, the major is described in their curriculum and says^[2]

The Bachelor of Science in Environmental Engineering Science emphasizes the fundamental physical, chemical, and biological processes necessary for understanding the interactions between man and the environment. Issues considered include the provision of clean and reliable water supplies, flood forecasting and protection, development of renewable and nonrenewable energy sources, causes and implications of climate change, and the impact of human activities on natural cycles. Both programs provide awareness of the sociopolitical context in which civil and environmental engineering problems are solved. Premedical students may satisfy medical school entrance requirements while earning the accredited degree in environmental engineering science with proper planning of their program.

Wet labs are required as part of the lower division curriculum

Lower division coursework

Lower division coursework in this field requires the student to take several laboratory-based classes in calculus-based physics, chemistry, biology, programming and analysis. This is intended to give the student background information in order to introduce them to the engineering fields as well as prepare them for more technical information in their upper division coursework.

Upper division coursework

Students learn to integrate their advanced knowledge of math and statistics with software such to perform analysis of physical systems like the Finite Element Analysis shown above

The upper division classes in Environmental Engineering Science prepares the student for work in the fields of engineering and science with coursework in (but not limited to) the following subjects^[1]

• Fluid mechanics
• Mechanics of materials
• Thermodynamics
• Environmental engineering
• Advanced math and statistics
• Geology
• Physical, organic and atmospheric chemistry
• Biochemistry
• Microbiology
• Ecology

Electives

Process engineering

On this track, students are introduced to the fundamental reaction mechanisms in the field of chemical and biochemical engineering. See also Process engineering

• 

  Designing a better catalyst for use with biofuels
• 

  Considering a cleaner process for coal gasification
• 

  Using more waste heat from power plants with better heat exchangers

Resource engineering

For this track, students are encouraged to take classes introducing them to various ways to conserve natural resources. This can include but is not limited to classes in water chemistry, sanitation, combustion, air pollution and radioactive waste management.

• 

  Using design knowledge to make better wastewater treatment facilities
• 

  Designing a safe way to store nuclear waste
• 

  Design ways to effectively deal with industrial waste

Geoengineering

This gives the student an in-depth look at geoengineering.

• 

  Figuring out what to do with emissions in a large scale
• 

  Sequestering carbon from the atmosphere
• 

  Figuring out what to do with rising levels of greenhouse gases in the atmosphere

Ecology

Prepares the students for using their engineering and scientific know how to solve the interactions between plants, animals and the biosphere.

• 

  How to alter certain biologic interactions in order to optimize the survival of the system
• 
• 

  Examining how the harvesting of kelp effects the sea otter population

Biology

Gives the environmental engineering science student a more advanced knowledge of microbial, molecular and cell biology. Classes can include cell biology, virology, microbial and plant biology

• 

  Understanding the way in which viruses function in order to safely sanitize water supplies
• 

  Understanding the metabolism of bacteria in order to see how their proliferation effects the climate
• 

  Using the biological design of chloroplasts to design a more effective way of turning solar energy into future sources of power

Policy

Gives the students a more rigorous look at ways improve our environment through political means. This is done by introducing students to both qualitative and quantitative tools in classes such as economics, sociology, political science as well as energy and resources.

• 

  Studying politics in an effort to understand and influence environmental policy
• 

  Learning about economics to determine the financial burden it might take to implement an "environmentally friendly" technology
• 

  Observing groups and learning the way that "greener" ideas might get passed between people

Post graduation work

The multidisciplinary approach in Environmental Engineering Science gives the student expertise in a wide variety of technical fields related to their own personal interest. While many graduates choose to use this major to go to graduate school,^[1] students who choose to work often go into the fields of civil and environmental engineering, biotechnology, and research. However, the less technical math, programming and writing background gives the students opportunities to pursue IT work and technical writing.