Coagulation of turbidity and organic matter from leafy-vegetable wash-water using chitosan to improve water disinfectant stability

- Chitosan effectively reduced particulate matter but not dissolved matter.
- Filtration increased aerobic psychrotrophic counts and total coliforms reduction.
- Disinfectant decay in wash water was slightly reduced after chitosan coagulation.
- Coagulation did not reduce chlorination by-products (trihalomethanes) in wash water.

The use of chitosan for coagulation of artificial fresh-cut lettuce wash-water, made from butterhead lettuce and tap water, was assessed for reducing particulate and dissolved matter in order to improve the physicochemical quality, as such lowering the disinfectant demand and allowing longer reuse of postharvest wash-water. Chitosan was used to coagulate industrial leafy-vegetable wash-water from a processing company. Lowering the pH improved the reduction efficiency. Although the turbidity reduction was very high (>90%), virtually no dissolved organic matter was removed. Rapid sand filtration subsequent to coagulation resulted in more than 2 log reduction of aerobic psychrotrophic counts and total coliforms. Coagulation lowered the disinfectant demand (of free chlorine and peracetic acid) to some degree but had no positive impact on the trihalomethanes formation. As such, coagulation does not seem to be a viable option to lower the disinfection by-products, the disinfectant dose or the water use by itself. However, due to the efficient particle reduction by chitosan coagulation it shows potential to be used as a pretreatment for a subsequent biological treatment in a more developed water treatment system to allow water reuse in the fresh produce companies.