# Enhancement of a Spent Irrigation Water Recycling Process: A Case Study in a Food Business
## 4 Conclusions  
This project aimed to enhance the water recycling process in a food company with a view to improve the quality of the spent irrigation water. Water analysis demonstrated that the existing level of filtration was ineffective, as the suspended-solid particle size was considerably smaller than the existing 20 \(\upmu\)m drum filter.  
Three options were considered: reverse osmosis (RO), an alternative drum filtration system, and a membrane filtration system. RO would deliver extremely high-quality water. However, the water required for irrigations needs to retain key nutrients that are likely to be removed during the RO process. Furthermore, the cost of the RO system was deemed prohibitive.  
The proposal to improve the drum filtration to 1 \(\upmu\)m is the cheapest option and delivers a return on investment. However, the results of the water analysis demonstrated that 1 \(\upmu\)m does not remove enough suspended solids and bacteria. This does not allow for the removal of a chemical treatment due to the risk of bacteria still being present in the water.  
A membrane filtration system filtering a nominal 0.45-3 \(\upmu\)m delivers the required level of filtration. The addition of an absolute 0.45 \(\upmu\)m filter after the nominal guarantees that 0.45 \(\upmu\)m filtration is achieved. In addition, an inline UV filter effectively sterilizes any remaining bacteria smaller than 0.45 \(\upmu\)m. This allows for the removal of the existing chemical treatment.  
Facilitating the removal of chemicals from the process, whilst still delivering water that meets the microbiological criteria relating to spent irrigation water, results in the aims of the project being fulfilled. The removal of chemicals provides an overall saving to the business that meets the requirement to provide a return on investment within 24 months. Crucially, removing chemicals from the treatment process also eradicates the effect that chlorine dioxide has on the residue chlorate levels in the grown beansprouts. This means that if the proposed EU maximum residue limits (MRLs) become law, the business would already be compliant. Compliance with these MRLs would potentially give the business acompetitive advantage over other growers if they have not taken similar remedial actions. This could potentially become a unique selling point.  
In conclusion, reducing water use and preserving water quality is particularly important in the food sector. This study shows how different solutions can be applied to optimize water management in food businesses, both improving the quality of the water reused and minimizing the use of fresh water.  
Conceptualization, S.J.; methodology, S.J.; validation, G.G.-G. and S.J.; formal analysis, G.G.-G.; resources, S.J.; data curation, G.G.-G.; writing--original draft preparation, G.G.-G.; writing--review and editing, G.G.-G.; supervision, S.J.; project administration, S.J. All authors have read and agreed to the published version of the manuscript.  
[PERSON] acknowledges the Grant Juan de la Cierva Incorporacion funded by MCIN/AEI/10.13039/501100011033.  
Not applicable.  
We would like to acknowledge staff from the company that participated in the case study as well as from the three anonymized companies who provided data and ideas for the successful completion of this project.  
The authors declare no conflict of interest.