Influence of sewage sludge from iasi water treatment station on soybean yield quantity and quality and soil chemical characteristics

The fermented sewage sludge from Iaşi Municipal Treatment Station, by its chemical and biological characteristics can be used as fertilizer on most of soils, except the salted soils, due to high content of soluble salts (1.0 g/100 g dry sewage sludge) and amendment measures, necessary in these cases. The use of fermented sewage sludge in soybean crop, at a rate of 40 t/ha, resulted in getting mean yield increases of 50 % (813 kg). Heavy metals content from fermented sewage sludge at the Iaşi Municipal Treatment Station was higher at zinc (3620 ppm) and copper (53 ppm), requiring the limitation of sewage sludge rate to 20-30 t/ha. The concentration of heavy metals in seeds obtained from soybean treated with 40 t/ha sewage sludge was higher (compared to untreated control) with 5.3 ppm at Fe, 0.92 ppm at Cu and with 0.01-0.07 at Zn, Mn and Ni. The other analysed heavy metals (Cr, Pb, Cd, Co, As, Hg) were not found in soybean seeds, treated with 40 t/ha sewage sludge. The concentration of heavy metals registered in soybean seeds, fertilized with 40 t/ha sewage sludge, has shown that these values did not exceed maximum allowable concentration established by Directive of EC no. 466/2001