Potential Usage of Sewage Sludge Compost (Scp) in Agricultural Practice : The Reduction of Antibiotics Resistance Genes in Lettuce and Soil Amended with Factory Scp

Excess sludge from wastewater treatment plants (WWTPs), the hotpot of antibiotic resistance genes (ARGs), is widely deposed by composting due to abundant nutrients. However, few studies applied sludge compost products (SCP) as soil amendments because of ARGs and heavy metals in sludge. To explore the potential usage of SCP in agricultural practice, this study fertilized soil with different rates of SCP (2%, 5%, 10%, 15%) and planted vegetables (Lettuce); then, heavy metals, ARGs, and microbes in soil and Lettuce were investigated after Lettuce harvested. Compared to the soil without SCP (S0), SCP additions removed 44.46% - 74.61% of ARGs, increased by 1.92- 2.27 times of Lettuce biomass, and removed 89.62-97.24% of ARGs from Lettuce. Furthermore, the pollution load index (PLI) and contamination factor index (CF) of ARGs analogy to heavy metals (<1) suggested that 5% SCP or less did not aggregate ARGs pollution in soils and Lettuce. Notably, heavy metals of Lettuce in 2% and 5% SCP soil fulfilled the requirement of China national standards, whereas Lettuce Cr and Hg in 10% and 15% SCP soil exceeded the threshold. Thus, SCP addition < 5% may be feasible to enhance Lettuce production and avoid ARGs and heavy metals risk in vegetables