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Plant factories of the future

plant factories of the future

Paul Challinor of Jones Food Company describes a new high-care, multi-layer, hydroponic plant production facility in the UK.

Introduction

The global population is increasing exponentially and the demand for food is rising at an unprecedented rate[1]. Vertical farming is a crop production system for the future, which may offer the solution to providing food for the expanding population predicted to increase by a further 3bn by 2050[2].

Vertical farming is a technique for growing plants on a series of levels in a vertical space, where all parameters essential for plant growth, such as light, temperature, water, nutrients and carbon dioxide, are provided at a continuous, optimum level. In theory, this combination of inputs provides the best environment for crop growth, yet it also can create issues with electrical power consumption, labour requirements and the complexities of plant science.

Using controlled environments, crops can be cultivated that may otherwise be unsuited to the UK climate, reducing reliance on overseas supply chains[2]. To meet the increasing demand for high quality herbs, controlled environment agriculture is an alternative to conventional cultivation and can provide a supplement to field production[3].

Another factor in the provision of high quality, fresh produce is the control of microbiological contamination throughout the production process, particularly where the final product is presented in a ready-to-eat format.

Using controlled environments, crops can be cultivated that may otherwise be unsuited to the UK climate, reducing reliance on overseas supply chains.

Designing an intensive plant production system

The Jones Food Company instigated a project to design, build and operate a commercial, high-care, intensive plant production unit. The facility is now up and running, having produced its first harvest of culinary herbs and leafy greens during the Autumn of 2018.

The construction method needed to be both modular and scalable to enable subsequent units to be efficiently assembled in any area where food production is required, including urban spaces.

The production system design incorporates the latest knowledge and research on hydroponics, LED lighting and environmental control systems. Initial water filtration, precision irrigation and recirculation of drainwater (irrigation solution not used by the plants) are key factors in the overall water-use strategy. Additional filtration and the use of ultra-violet light treatments ensure that the water quality is maintained throughout the unit (Figure 1).

Figure 1 Construction of New Water Management Module at the Jones Food Company Unit. All images courtesy http://hollychallinor.co.uk/

The building itself was originally constructed as a cold storage facility (Figure 2) and is very suitable as a controlled, multi-level, growing environment. It is well insulated and twelve metres in height. This has allowed the construction of five main growing racks, each containing seventeen crop production levels. The actual crop production area is, therefore, over 5,000 m2.

The original metal storage racking was removed, strength tested, cleaned and treated with white, anti-microbial paint. This recycled metalwork was then incorporated into the new growing structure, which supports the growing trays and crop produce.

The unit is divided into separate zones for seed sowing, germination, crop growing, harvesting, tray cleaning and despatch. All main areas have independent environmental controls and the unit is sealed to prevent pest ingress from the outside. As a result, the pest and disease risk is lowered and, therefore, there is no need to use pesticides in the unit.

A separate consideration was to automate the crop production and harvesting processes as far as possible, to further reduce the risk of contamination. The use of automation at every stage throughout the production and harvesting processes reduces the requirement for handling of the food products, resulting in a lower microbiological contamination risk. Another positive benefit of this system is less waste product.

The unit layout was designed to allow the operation of an autonomous forklift vehicle from the seeding area into a separate germination chamber and, subsequently, to the growing room and harvesting zone.

A purpose-designed quality management system has also been compiled to match and evolve with specific customer requirements.

Figure 2 Original cold storage facility with racking

LED lighting and cropping

The LED lighting profile uses Current by GE ‘Arize Lynk’ lights (Figure 3), which were firstly tested on a small growing rig. After extensive trials involving many plant types, a balanced light spectrum was selected to allow efficient plant growth and optimum product quality. Important considerations for final selection of the lights included the LED efficiency (conversion of energy to light, rather than heat), spectrum, longevity of the luminaires and ease of installation.

Light is one of the most important environmental factors influencing herb quality, phytonutrient content and growth and development. The recent adoption of light-emitting diodes provides opportunities for targeted regulation of growth and phytonutrient accumulation by herbs to optimise productivity and quality under controlled environments[3].

Figure 3 Current by GE ‘Arize Lynk’ in the Jones Food Company Unit

This facility is currently growing culinary herbs and leafy greens (Figure 4), but the unit is capable of growing most plant types and may be adapted to accommodate larger plants by adjusting the number of growing levels per rack in order to create additional height per growing tray.

Studies growing lettuce under LEDs have demonstrated that growth and nutritional values can be enhanced in indoor plant production facilities[4].

Further plant growth and varietal testing are planned; a range of crop plants may be cultured under the GE LED lights by manipulating the photoperiod.

Figure 4, top right, Basil Growing in Hydroponics

Treatment of growing materials entering the high-care unit

All materials destined to enter the growing and harvesting areas are treated with UV-C light. Both the growing substrate and the cropping trays enter the high-care areas via an enclosed tunnel, which allows 360º exposure to the UV-C light. In addition, all seed is tested before use to monitor microbiological levels and is treated with UV-C in a separate machine, before delivery into the high-care unit. The seed treatment mechanism involves the use of a vibration belt, which causes the seed to somersault, allowing all surfaces of the seed coat to be exposed to the UV-C light.

Potable water is filtered and UV-C treated via a two-stage process, prior to storage in a separate water management building. This provides a clean water supply for all uses inside the facility. Other storage tanks contain concentrated liquid nutrients and diluted nutrient solution is injected into a series of day stock tanks, ready for crop irrigation.

Clean liquid feed, at a known pH level and electrical conductivity (EC), is irrigated into the growing trays, which hold the growing substrate and support the growth of the crops.

Drainwater is captured from each growing rack and returned to the water management area. From the drainwater tank, the liquid feed is transferred back to a clean storage tank, via a separate UV-C treatment unit. This allows a combination of fresh liquid feed and treated drainwater to be irrigated back to the growing crop on a continuous basis.

In terms of labour, all crop operatives complete a sequence of hand washing, use of protective cleanroom suits, hoods and boots, final hand washing and hand sanitising, prior to entering the high-care area. The final step before entering is via a pharmaceutical air-shower unit, to remove any extraneous dust particles (Figure 5).

Figure 5, above, The Air Shower, Showing Access to the High-Care Area.

Intensive hydroponic system

Hydroponics is the culture of plant crops in soilless water- based systems, where nutrients come only from formulated fertiliser[5].

The Jones Food Company irrigation system operates on an ebb and flow principle, where liquid feed is allowed to drain away from the plant trays after flood irrigation. This permits oxygen to reach the root zone in order to maintain root health. It also allows a much reduced usage of water and fertiliser (as all of the drainwater is captured and recirculated back to the crops), compared to traditional farming techniques. The runoff of water, fertiliser and pesticides from traditional overhead and drip irrigation methods is a potential risk to environmental quality in proximity to a glasshouse unit operation[6].

Constant monitoring of nutrient solution pH and EC is essential to maintain nutrient availability for plant uptake, in addition to ensuring that the nutrient balance is maintained at an optimum level.

The nutrient balance of the drainwater is invariably different to the input irrigation solution and other nutrient balance changes occur during the UV-C treatment process. Therefore, it is vitally important to sample nutrient solution on a regular basis and to alter the composition of the nutrient feed stock, based on the analytical laboratory results. It is also essential to sample the background water sources for nutrient content and presence of contaminants, such as heavy metals and pesticides, on a regular basis.

It is possible to exercise precise control over the internal temperature, humidity, carbon dioxide concentration and lighting regime to provide the consistent conditions for plant growth in every twenty-four hour period.

Air filtration

In an indoor plant factory, a forced convection based ventilation and circulation system is used to control the growing environment and maintain climate uniformity[7]. The Jones Food Company environmental control system is specifically designed for growing room and warehouse production of food crops. It is possible to exercise precise control over the internal temperature, humidity, carbon dioxide concentration and lighting regime to provide the consistent conditions for plant growth in every twenty-four hour period.

Outside air is filtered, prior to heating, cooling and onward distribution into the regulated compartment spaces within the building. Independent sensors and controls allow set temperature and humidity levels to be maintained inside the germination, growing, harvesting and despatch chambers. Pure carbon dioxide is added to the airflow and controlled to maintain a safe concentration inside the growing environment.

Many studies have examined the concentrations of airborne bacteria and fungi in different environments, both indoors and outdoors. Bacteria and fungi concentrations of approximately 102 to 106 CFU m−3 and 102 to 103 spores m−3 respectively, are typical[8].

In addition to the treatment of outside air, the internal air volume is also filtered to remove injurious gases, such as ethylene, and to destroy any spores in air that enters the filtration equipment. Wheeler[9] states that in tightly closed space systems, ethylene build-up and management must be considered. The same is true of sealed environments being used to support growing crops in earth.

The air filtration works in parallel with the HVAC (Heating Ventilating and Cooling) air conditioning system (Figure 6).

Fan units fitted along every rack also help to increase airflow along the plant production rows.

Figure 6 , right Exterior Air Treatment HVAC Unit

Microbiological testing

The unit is sampled on a weekly basis to monitor the microbiological levels inside, as well as the effectiveness of the various cleaning regimes in place for operatives, machinery and the fabric of the internal building.

An external pest contractor is used to check the outside of the building and flying insect monitoring apparatus is also used to validate the food safety controls inside the high-care unit.

Phytonutrients

Research has indicated that for most herb species, red light supplemented with blue light significantly increases plant yield[3]. Basil cultivars grown under LEDs, for example, showed increased total phenolic content compared with plants grown under conventional fluorescent light[10]. The antioxidant capacity of assessed basil cultivars was improved when doses of potassium fertiliser were increased in the nutrient solution[11].

A collaborative study on the phytonutrient content of plants raised under LED lights was initiated at Lancaster University in October, 2017. The study is investigating optimisation of phytonutrient and vitamin content of herb and salad leaves grown in an intensive, multi-level hydroponics system.

The results from the research should be directly applicable to the new JFC crop production facility.

Dr Paul Challinor Chief Technical Officer, Jones Food Company Ltd

Email paul@jonesfoodcompany.co.uk

Web maybarnconsultancy.co.uk

References

1. Sarkar, A. and Majumder, M. (2015). Opportunities and Challenges in Sustainability of Vertical Eco-Farming: A Review. Journal of Advanced Agricultural Technologies, 2 (2): 98-105.

2. Stiles, W. and Wootton-Beard, P. (2017). Vertical Farming: A New Future for Food Production ? Farming Connect, Welsh Government.

3. Dou, H., Niu, G, Gu, M, Masabni, J.G. (2017). Effects of Light Quality on Growth and Phytonutrient Accumulation of Herbs under Controlled Environments. Horticulturae, 3: 36.

4. Amoozgar, A, Mohammadi, A, and Sabzalian, M.R. (2017). Impact of Light-Emitting Diode Irradiation on Photosynthesis, Phytochemical Composition and Mineral Element Content of Lettuce cv. Grizzly. Photosynthetica, 55 (1): 85-95.

5. Saha, S., Monroe, A. and Day, M.R. (2016). Growth, Yield, Plant Quality and Nutrition of Basil (Ocimum basilicum L.) Under Soilless Agricultural Systems. Annals of Agricultural Science, 61: 181-186.

6. Gent, P.N. and McAvoy, R.J. (2011). Water and Nutrient Uptake and Use Efficiency with Partial Saturation Ebb and Flow Watering. HortScience, 46(5): 791-798.

7. Zhang, Y., Kacira, M. and An, L. (2016). ACFD Study on Improving Air Flow Uniformity in Indoor Plant Factory System. Biosystems Engineering, 147: 193-205.

8. Prussin, A.J., Garcia, E.B. and Marr, L.C. (2015). Total Virus and Bacteria Concentrations in Indoor and Outdoor Air. Environmental Science and Technology Letters, 2(4): 84–88.

9. Wheeler, R.M. (2014). NASA’s Controlled Environment Agriculture Testing for Space Habitats. 2014 International Conference on Plant Factory (ICPF); 10-12 Nov. 2014; Kyoto; Japan.

10. Bantis, F., Ouzounis, T. and Radoglou, K. (2016). Artificial LED Lighting Enhances Growth Characteristics and Total Phenolic Content of Ocimum basilicum, but Variably Affects Transplant Success. Scientia Horticulturae, 198: 277-283.

11. Salas-Perez, L., Fornari-Reale, T., Preciado-Rangel, P., Garcia-Hernandez, J.L., Sanchez-Chavez, E. and Troyo-Dieguez, E. (2018). Cultivar Variety and Added Potassium Influence the Nutraceutical and Antioxidant Content in Hydroponically Grown Basil (Ocimum basilicum L.). Agronomy, 8: 13.

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