Project overview

Agriculture is the largest user of water globally. Vertical farms – farming on vertically stacked layers – use between 70% and 90% less water (and therefore nutrients and fertilisers), however their holy grail is to operate a closed-loop production system in which all water and nutrient is recycled, known as Zero-Liquid Discharge (ZLD).

GrowUp Farms, in partnership with Salinity Solutions, were awarded a grant by Growing Kent & Medway (GKM) to trial a novel reverse osmosis (RO) technology, called HyBatch™ RO, to establish the proportion of their vertical farm’s wastewater that can be recycled, as a step towards achieving ZLD.

GrowUp uses RO-treated mains water for the irrigation of plants and cleaning of reusable growing trays and other equipment. Water consumption reduction is one of the company’s environmental objectives. By reusing irrigation water over several cycles, GrowUp’s existing production system is already water efficient, however, they identified opportunities to further optimise efficiency.

The trial’s objective was to test the feasibility of recycling four wastewater streams from GrowUp’s production processes, all to a food-safe standard.

Energy efficiency is also of key importance. Improving water efficiency should not come at the expense of energy efficiency, so the impact on energy consumption was also studied.

Trial delivery

The trial took place at GrowUp’s controlled environment production facility (vertical farm) in Sandwich, Kent. Four primary effluent types were identified as candidate alternative water sources for trialling:

  1. Rainwater
  2. Farm irrigation flush down
  3. Tray wash water
  4. Brine from the existing GrowUp RO machine

Tests were also carried out on a combination of the four streams to test combined effectiveness.

Maintaining the highest quality standards in GrowUp’s high-care areas is of critical importance for food safety, so for recycled water to be considered for use in the production and packing areas, it must achieve food safety standards, i.e. be the same or better quality than mains potable water.

Each effluent source treated by Salinity’s HyBatch system was analysed in the following areas:

 -Energy consumption and recovery rates (i.e. the percentage of water ‘cleaned’ from total wastewater input) were measured throughout the trial and comparisons with other technologies made

– Chemical and pathogen content was analysed by an independent laboratory and judged against KPIs

-Microbial tests on the permeate produced were also undertaken by the lab, and the results analysed against a range of KPIs

Technology innovation

Salinity Solutions’ patented technology, HyBatch™ RO, extracts fresh water from wastewater and generates a highly concentrated brine. It’s the most efficient reverse osmosis technology available today, reducing energy consumption by 50% compared to competing technologies, while delivering up to 98% freshwater recovery. Developed over 10 years, first at Aston University and then the University of Birmingham, it’s the world’s first batch reverse osmosis system in the world to be commercially available.

Energy efficient: The system uses >50% less energy than comparative membrane technologies. This is achieved by varying the operational pressure over time, resulting in a much lower average pressure over the course of the treatment process.

Significantly reduced waste volumes: As the concentration levels are so high, the waste volumes are reduced by up to 80% versus comparative processes, significantly reducing waste storage and handling.

Higher recovery: HyBatch™ RO can achieve higher recovery of clean water than competing membrane technologies, while still maintaining higher removal of nutrients (e.g. phosphates and nitrates), viruses, bacteria, microplastics and PFAS contaminants.

Compact footprint: housed in a 20-foot container the system can be rapidly deployed and installed.

Chemical free: Salinity’s rapidly deployed mobile plug-and-play system is chemical-free and can operate alongside nature-based solutions.

Benefits derived

All wastewater streams were demonstrated to recover up to 98% of input volume. Simply put, for every 1 litre of ‘dirty’ water, up to 980ml of ‘cleaned’ water could be extracted. Laboratory tests showed that the Salinity permeate was food safe, in fact it was cleaner than the mains water that Southern Water supply to the area in and around the site.

Furthermore, Specific Energy Consumption (SEC) for processing these streams was 0.99-1.3 kWh/m3, which is 50-72% more energy efficient than modelled comparable desalination technologies.

The trial identified that the HyBatch™ can provide a 38% reduction in mains supply demand – an important benefit in a county that is already facing water shortages.

A high-level cost-benefit analysis identified that installing a Hybatch™ system has the potential, despite the extra energy required, to reduce GrowUp’s water-related operational costs by 32%.

The trial demonstrated a 33% potential reduction in wastewater discharge, which would otherwise have been discharged to the local treatment facility. As well as extracting contaminants from the water, the system also removes valuable nutrients such as phosphate and nitrate which can be captured and reused as fertiliser.

Future potential

HyBatch™ technology can dramatically reduce the water consumption of industries such as agriculture/food and beverage, automotive and textiles. Used in conjunction with waste disposal technologies, such as thermal evaporation, zero liquid discharge (ZLD) is achievable.

As global freshwater scarcity increases, alongside stricter regulations on wastewater discharge, reducing contaminated liquid discharge is more important:

Water Conservation: If every drop of water is treated, purified and reused, it minimises the strain on mains water and reduces water scarcity (a particular problem in Kent).

Environmental preservation: We can significantly reduce the environmental impact of industrial operations by preventing the discharge of pollutants into natural water bodies. This safeguards aquatic ecosystems and protects public health.

Resource recovery: As liquid waste is reduced or eliminated, it allows for the recovery of valuable resources from wastewater, such as nutrients for agriculture, metals, and chemicals, creating a closed-loop system.

Compliance and sustainability: Industries can meet stringent environmental regulations while promoting sustainability, making it a win-win for both businesses and the environment.

Cost reduction: Minimising the amount of liquid waste sent to sewers, allows companies to reuse water for other purposes and saves on water costs. Additionally, replacing existing RO technologies to increase water efficiency reduces both water and energy cost.

Awards and publicity for the trial

Salinity Solutions and GrowUp Farms were awarded ‘Water Efficiency Project of the Year’ in the Water Industry Awards 2024.

The trial was featured on BBC South East, BBC online and in industry publications including The Engineer, Materials World, Aqua Tech, Verticalfarm Daily and the (Don’t) Waste Water podcast.

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