Treated Greywater Reuse for Hydroponic Lettuce Production in a Green Wall System: Quantitative Health Risk Assessment

The scarcity and pollution of freshwater are extremely crucial issues today, and the expansion of water reuse has been considered as an option to reduce its impact. This study aims to assess the efficiency of an integrated greywater treatment system and hydroponic lettuce production as a part of a green wall structure, and to evaluate the health risk associated with the production and consumption of lettuce through a quantitative microbial risk assessment (QMRA) and a chemical health risk assessment. The study was conducted based on the unique configuration of a source separation system; an on-site greywater treatment system; a green wall structure as a polishing step; and hydroponic lettuce production in the green wall structure. The final effluent from the system was used to grow three lettuce varieties by adding urine as a nutrient solution. Both water samples and plant biomass were collected and tested for Escherichia coli (E. coli) and heavy metals contamination. The system has gained a cumulative 5.1 log(10) reduction of E. coli in the final effluent and no E. coli found in the plant biomass. The estimated annual infection risk for Cryptosporidium, Campylobacter, and Norovirus was 10(-6)-10(-8), 10(-8)-10(-10), and 10(-10)-10(-11) respectively. These results indicate that the system attained the health-based targets, 10(-6) disability adjusted life years (DALYs) per person per year. Similarly, the health risk index (HRI) and targeted hazard quotient (THQ) results did not exceed the permissible level, thus the chemical health risk concern was insignificant.