# Enhancement of a Spent Irrigation Water Recycling Process: A Case Study in a Food Business
## 3 Results
### Analysis of Potential Solutions  
Based on the results reported above, the three companies that were approached initially were requested to provide suggested solutions and associated quotations. Company 1 suggested that, to implement an RO-based system, a minimum of GBP 1,000,000 would be required. No quotation was submitted, as it was clear that this was not a viable option in terms of ROI. Upon reflection, more research should have been conducted on the estimated costs involved with RO technology before this was considered. Company 2 supplied a proposal to supply and fit a membrane filtration system, delivering nominal filtration from 3 to 0.45 \(\upmu\)m. A subsequent in-line filter would also be installed in order to deliver absolute filtration to 0.45 \(\upmu\)m. Two UV sterilization systems would also be added to facilitate the sterilization of any bacteria smaller than 0.45 \(\upmu\)m. The total cost for this proposal was GBP 90,000. Company 3 supplied a proposal to supply and fit a triplex drum filtration system delivering a nominal 5 \(\upmu\)m filtration. This would include two duty units, and a third unit to come on line when one of the first two is on auto backwash. Their capacity is 34 m\({}^{3}\)/h per unit. There was a secondary recommendation to fit a subsequent centrifugal \begin{table}
\begin{tabular}{c c c} \hline  & **Number** & **Volume** \\ \hline Mean & 0.591 & 31.67 \\ Median & 0.510 & 27.33 \\ Mode & 0.404 & 80.67 \\
95\% confidence limits & 0.591–0.592 & 31.65–31.69 \\ SD & 0.55 & 19.2 \\ d\({}_{10}\) & 0.415 & 11.62 \\ d\({}_{50}\) & 0.510 & 27.33 \\ d\({}_{90}\) & 0.789 & 58.38 \\ \hline \end{tabular}
\end{table} 
Table 1: Statistical data of the tests. All values in \(\upmu\)m.  
Figure 3: Particle diameter in relation to cumulative volume. cartridge system required to deliver nominal 1 \(\upmu\)m. This would include two duty units with a capacity of 34 m\({}^{3}\)/h per unit. The total cost of this proposal was GBP 29,000. Upon analysis of the proposals, both the membrane and the drum proposal deliver improved water filtration to a higher grade than the existing 20 \(\upmu\)m. In order to fulfil the aim of removing chemical treatment from the water, it was key to understand the level of filtration required to remove bacteria and pathogens to a level where the water could be deemed \"potable\". Filtration to 1 \(\upmu\)m is a vast improvement on the existing process in terms of particle removal. However, this filtration would not yet remove the majority of the bacteria from the water. It has been claimed that filters with an absolute minimum rating of 0.48 \(\upmu\)m are required to strain out the smallest bacteria [32]. Furthermore, it was calculated that this filtration would only remove 83% of the suspended solids. Based on this, the proposal from Company 3 to install a 5 \(\upmu\)m drum filter with an additional nominal 1 \(\upmu\)m unit would not allow the removal of the chemical treatment. Therefore, the proposal by Company 2 to install a membrane filtration system with nominal filtration to 0.45 \(\upmu\)m, with a subsequent in-line filter and UV sterilisation system, seemed to be the ideal solution and was selected. A scheme of this system is shown in Figure 4. It should be noted that, with the new system, fresh water and wastewater flows could be reduced to virtually zero. For the membrane filtration system, the vessel diameter is 1.2 m, and the filtration flow range is 28-68 m\({}^{3}\)/h. The addition of an absolute \"safeguard\" filter following the primary filtration system would ensure that absolute filtration of 0.45 \(\upmu\)m is achieved. This secondary filtration system allows for flow rates of 50 m\({}^{3}\)/h. The downside of this is the use of filter cartridges, which are consumable items that require a certain amount of ongoing replacement, adding additional overhead back into the business. This system houses 11 cartridges. MF membranes are efficient at removing bacteria and fine inorganic particles, but they do not remove colloids and all viruses [33; 34].