Advanced oxidation processes for pathogen control in wastewater for crop production.

Abstract

The persistence of pathogens in wastewater significantly limits its value for unrestricted crop production. Thus, stringent quality standards have been set to ensure safe water resources for sustainable crop management practices and portable uses. Consequently, there is a pressing need for further treatments in wastewater to ensure safe and unrestricted use for crop production. The present study sought to understand the efficiency of advanced oxidation processes (AOPs) as a post-treatment step for the removal of pathogens contained in municipal secondary effluent to achieve standards for unrestricted crop production that is safe for human consumption. Municipal secondary effluent was subjected to selected AOPs (ozonolysis, UV photolysis, and TiO2-photocatalysis) to reduce pathogens in domestic wastewater and prevent regrowth upon storing the treated effluent. Ozonolysis and TiO2-photocatalysis achieved a 6.4- log reduction in pathogens, while UV-photolysis achieved a 6-log reduction. After four days of storage, ozonolysis-treated (O-TE) samples showed no pathogen regrowth, while TiO2- photocatalysis-treated effluent (Ti-TE) had regrowth of E. coli and Total coliforms at 2.5-log and 2.7-log, respectively. UV-photo lysis-treated effluent (UV-TE) had a regrowth rate of 0.5- log for E. coli and 2.2-log for Total coliforms. Nutrient mineralization dynamics were also examined upon soil irrigation with AOP-treated effluents. Significant reduction in the ammonium-N levels across UV-TE, O-TE, and Ti-TE treatments was noted, which did not translate to notable changes in the nitrate-N levels. P mineralization was relatively slower across UV-TE and O-TE than in the controls (untreated wastewater (RW) and municipal tap water (MTW)); however, total P mineralization was achieved after day 70. Significant reduction of ortho-P in Ti-TE irrigated soils was confirmed, indicating effective phosphorus binding by TiO2. Moreover, the effects of AOP-treated effluents on crop physiological functions with respect to photosynthetic rates and capacity and potential health risks to consumers was also investigated following the irrigation. The study found significant phytotoxicity effects on Swiss chard and lettuce irrigated with AOP-treated effluents, with Ti- TE showing the highest stress levels, followed by O-TE and UV-TE. While no pathogens were detected on the leaves across all the treatments, TiO2 agglomerates were found on crops irrigated with Ti-TE. High TiO2 levels were recorded upon quantification, suggesting potential health risks from consuming crops irrigated with Ti-TE. Overall, Ozonolysis was the most promising method, meeting standards for unrestricted crop production with minimal impact on soil nutrient mineralization and mild phytotoxicity. Additionally, irrigation with O-TE posed no health risks to consumers, as no pathogens were found on the edible parts (crop leaves).