1. Introduction

1. Introduction

1.1 Engineering Problem

Singapore imports 90% of its food, as a result of land being scarce. With an increasing population, we have little accommodation for agricultural purposes (Swan, 2013). Vegetables grown locally stands at only 7% of the total consumption. High-rise vertical farming has since been a promising solution, as seen in a hydraulic water-driven farm owned by Sky Greens, which yields fresh and delicious vegetables (Sky Greens, 2013). Singapore may be able to sustain our agriculture with such a method. We are, hence, trying to design a vertical garden, with automated lighting and watering systems.

1.2 Engineering Goal

Our goal is to construct a vertical garden. It will be able to use the exact amount of water needed for the plants, to reduce waste of water, as well as save space and land. Overall, it must be able to grow plants efficiently with a minimal use of resources.

The vertical garden will be able to sustain itself with an automatic lighting and watering system. The plants within the housing should be able to grow similarly to those cultivated in soil. The vertical garden will take up significantly less space than typical farms.

1.3 Specific Requirements

Our engineering requirements include the following:
- Must be indoor-oriented
- It is stable and free standing
- Easy to construct with easily obtainable materials and equipment
- Water use is minimal
- Electricity use is minimal

1.4 Alternative solutions

1.4.1  Aquaponics

Aquaponics is a sustainable food production system that consists of conventional aquaculture of breeding aquatic animals and hydroponics, which is a water-based method of cultivating plants. Effluents which are gases and slightly polluted water from the waste of the aquatic animals will accumulate in the water, and increase the toxicity level for the fish. As such, these by-products will be broken down by nitrogen-fixing bacteria, then filtered out by the hydroponics plants. Finally, the clean water will then be recirculated back to the fish and this cycle will repeat itself (Rakocy, Bailey, Shultz & Thoman, 2013).

The advantage is that this system is self-sustainable, and it is an environmentally-friendly method for the hydroponics, which usually uses chemical-based solution for breeding. As the water is constantly being recirculated, water usage is minimal and reuse of water is highly efficient (McCarthy, 2013).

Unfortunately, a major disadvantage would be that it is usually expensive to set up, inclusive of the cost for the tank, tubes and pumps. Water pH level will also have to be monitored closely, as one faulty component can cause the whole system to break down easily. It is also not advised to grow root crops. Leafy vegetables are advised instead. The water needs to be free of toxins such as ammonia and nitrates and have sufficient oxygen levels for aquatic organisms to survive. This would create a complex system that may break down easily (McCarthy, 2013).

1.4.2 Hydroponics

Hydroponics is a method of crop cultivation which uses the method of soilless growth of plants. The nutrients that are normally found in soil are dissolved into water, creating nutrient solutions.  Roots are usually submerged or suspended to be able to absorb the nutrients found in the solution. Since arable land is on the decline, hydroponics is seen as a solution where plants can be cultivated using water which is abundant, hence it is versatile (Turner, 2008).

Hydroponics has several advantages. It has almost no pollution as most of the nutrients are all absorbed by the plants. Normally, agricultural runoff contains fertiliser, containing high amounts of nitrogen and phosphorous. If leaked into water bodies, algae would bloom uncontrollably and use up oxygen rapidly. This would cause the death of aquatic organisms. Hydroponics do not require any herbicides or pesticides, as they are usually grown indoors. Less labour is involved in the up-keeping of such a garden as only the nutrient solutions need to be in check. The growth rates are spruced up as compared to normal soil cultivation, due to the availability of water, oxygen and easily accessed nutrients (Hydroponic Setup, 2010). The water can also be recycled, hence there would be lower water costs.

However, everything has its advantages and disadvantages. It has a high set-up cost as it requires meticulous planning when designing and constructing (Hydroponics Center, 2011). Hydroponic conditions, especially the presence of high humidity, would create a hot bed for salmonella growth (Department of Agriculture, Forestry and Fisheries, 2011). Salmonella can then be transmitted through human consumption and cause food poisoning. Since hydroponics are soilless, diseases are able to spread quicker as they are not contained (Black, 2009). Hydroponics also require many varieties of fertiliser. Finally, hydroponics are unable to cultivate all plants, hence you are limited to certain species only (The Iloveindia website, 2013).
1.4.3 Aeroponics

Aeroponics is a method where plants are grown in a humid environment without the use of any growing medium, making it suitable for indoor gardening or greenhouses (True Aeroponics™, 2013). It stimulates rapid plant growth as the plants will rapidly develop root systems (D’Gardener, 2008).

The plants are suspended in a growing chamber. A pulsed sprayer will release a fine, high pressure mist which consists a mixture of water, nutrients and growth hormones into the enclosed environment of the growing chamber at a time interval and duration for the plants (True Aeroponics™, 2013).

Aeroponics, when compared to the traditional method allow plants to grow faster, as the roots are exposed to more oxygen, and thus obtain higher yields from the plants. It has been proven that it can aid growers to optimize rooting on most plants. When root cutting is performed on the plant grown through aeroponics, the plant will maximize its overall yield. Also, the plants in an aeroponics system are fed more than those planted using the traditional method. Aeroponics is beneficial to the environment in a sense that the water used in aeroponics can be reused. The water loss of an aeroponics system is cut by 99% when compared to the traditional farming methods. When compared to hydroponics, aeroponics offers more control over the root system as the roots aren’t immersed in any liquid (True Aeroponics™, 2013).

If needed, the aeroponics system can be moved around easily. A main drawback of the aeroponics system is that the root chamber, the one containing the dangling roots, attract lots of bacterial growth due to its semi-moist environment, so it has to be cleaned regularly. The entire system depends on the pumps, sprinklers and timers, so if any one of these break down and are not fixed in time, the plants can wither and maybe even die. One must also be proficient in knowledge about plants, such as nutrition amount as there would be no soil to soak up excess nutrition (D’Gardener, 2008). All these may make the system a meticulous one that requires time and effort.
1.4.4 Final Solution

Our best solution would be to incorporate modified passive hydroponics into vertical gardening. By having a vertical garden, one can save up on horizontal space as it requires vertical expansion. By 2050, the human population would increase by 3 billion and an estimated 109 hectares of new land is needed to cultivate sufficient food for the booming population (Despommier, 2004). Added farmland may damage the planet and well-designed vertical gardens can create more arable “land” without much pollution of the environment.

Vertical gardens create harvests of good quality and nutritional value, essential for healthy consumption. Since water from vertical gardens can be collected and recycled, there would be less runoff and lesser chances of water bodies being polluted. They also help to improve air quality, replacing carbon dioxide with oxygen and acting as a natural filter, providing cleaner air (Fitzgerald, 2011). Harvesting would reduce strain as one would not be needed to dig or tile the land, making harvesting a more efficient and easy job with no expensive equipment (Bardot, 2012). This would also mean less fossil fuel used and less carbon emissions.

Vertical gardens can turn abandoned properties and buildings into green production factories. This is due to the fact that plants can be grown indoors under controlled regimes. Being indoors guarantees protection against weather-related devastation such as droughts and floods (Despommier, 2010). It also allows the plants to be grown throughout the year, regardless of seasons.

Passive hydroponics is a method of growing plants without soil, peat moss or bark. Instead, an inert porous medium transports water and fertilizer to the roots by capillary action. Water and fertilizer are held in a reservoir and conducted to the roots as necessary, reducing labor 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. Since routine maintenance is much simplified, passive hydroponics can reduce the labor required to maintain a large collection of plants (Horizen Hydroponics, 2011). We are using sponges instead, as they have water-holding capacities, hence being able to keep the plant watered and growing well.

Hence, vertical gardening with modified passive hydroponics is chosen as the best solution. Its advantages make it a feasible concept due to its versatility.

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