Using Treated Wastewater Sludge to Improve Soil and Growth characteristics of Rain-fed Wheat under Semi-Arid Conditions

Sludge is an increasingly growing concern in Lebanon given the absence of proper treatment and disposal methods. As a solution, this two-years study proposes the valorization of sludge as an organic amendment on soil cultivated with rainfed wheat (Triticum icaversea) and itsimpact on soil properties, microbial activity, wheat yield and grain quality. Baseline characterization of sewage sludge collected from secondary treatment plant (SS) and tertiary treatment plant (TS) in Bekaa, Lebanon, showed that both sludge types can be classified as suitable for restricted agricultural use (Class B), which cannot be used on soils to grow fruits or vegetables that are eaten raw as per the Lebanese guidelines for sludge use. Post-harvest analysis of the amended soils revealed a significant enhancement in organic matter (OM), organic carbon (OC), soil moisture, wheat yield and grain quality in both seasons SS and TS amended soils compared to the control. All the tested heavy metals were much lower than the allowable limits for agricultural soils, except for zinc (Zn).  Wheat biomass and grain quality assessment revealed a significant increase of 30% in grain yield in both treated soils (SS: 74 g/m², TS: 81 g/m²) compared to the control (46 g/m²). Notably, TS treatment exhibited the highest protein content (14.5%) and ash (1.9%) in the first season, while both SS and TS treatments showed a significant increase in grain moisture in the second season. Soil microbial analysis were not consistent in the two seasons, but showed a potential risk of total coliforms contamination with SS application in the second season. This research provides valuable insights into the positive effects of sewage sludge application on soil fertility, microbial communities, and wheat grain quality. The findings emphasize the potential benefits of sewage sludge in sustainable agriculture, underscored by numerical improvements in various parameters. Although promising soil quality improvement and yield increase were observed in this study, further research is still needed to assess the potential soil microbial contamination and heavy metal accumulation over the long term.