Application of willows (Salix viminalis) and earthworms (Eisenia fetida) in sewage sludge treatment

The aim of the study was to verify the suitability of willows (Salix viminalis) and earthworms (Eisenia fetida) for sewage sludge management. The study was conducted in Tarnów city sewage plant. In April 2004, 81 pots were filled with concentrated sludge, 27 of which acted as controls, another 54 were planted with willows. In May, 20 mature earthworms were introduced to half (27) of the pots with willows. Every month the growth of willows was measured. The density of earthworms, size of willows, and the moisture content, and their chemical properties and structure of the sewage sludge were assessed in November 2004 when: (1) the moisture content of the sludge was lower in the pots with willows (49%) and with willows + earthworms (37%) than in the control (67%); (2) the mass increase of willow was higher by 38% for shoots and 41% for roots, in pots with earthworms; and (3) the introduction of willows and earthworms changed the structure of sludge. Willows and earthworms had no effect on the pH of the sludge, nor on its concentration of nutrients, heavy metals or forms of nitrogen.