The biochemical response of willow plants (Salix viminalis L.) to the use of sewage sludge from various sizes of wastewater treatment plant.

Sewage sludge production is increasing, as is the importance of its safe and sustainable disposal. The study examine the impact of fertilizing poor quality soil with sewage sludge from three sizes of wastewater treatment plants (WTP) (small, medium and large) located in Central Poland, applied in two doses (3 and 9tons per hectare), on biomass yield and selected biochemical parameters in willow plants. The WTPs were selected based on the size criterion given in Polish regulations. Three variables were analyzed in the leaves and roots of willow cuttings after twenty weeks of cultivation: the degree of oxidative reaction, assessed as thiobarbituric-acid-reactive substances (TBARS) content; catalase activity (CAT, EC 1.11.1.6), reflecting the efficiency of the antioxidative response; and changes in the concentration of proline, one of the major cellular osmoprotectants. For plants growing in poor-quality soil, sewage sludge administration results in a large increase of willow biomass by creating good conditions for plant growth associated with protection against oxidative damage, efficient functioning of the antioxidant system and maintenance of the osmotic balance between the soil environment and plant roots. The greatest increase was 204% of control in the case of 9tha-1 sludge from the medium WTP. Biomass production correlated with the applied sludge dose. After sewage sludge application lipid peroxides were reduced in leaves (81%) and roots (69%), CAT activity was enhanced (to 855% in leaves) and proline level was increased in root tissues. The application of sewage sludge originating from small WTPs offers the best conditions than larger WTPs: sludge from large WTPs may cause oxidative damage and exceed the possibilities of plants to counteract stress factors, especially when used in high doses.