Effect of sewage sludge on urban soils and growth of lawn grass mixtures

Abstract

The aim of this study was to evaluate the influence of municipal sewage sludge on urban environment, especially on accumulation of heavy metals (Cr, Ni, Pb and Zn) in soil and in the aboveground parts of lawn grasses mixtures. Eko and Roadside. The experiment was established along four main streets of Białystok (Poland) and three doses of sewage sludge were used: 0 (control), 7.5 and 15 kg/m².

At the end of the first vegetation season heavy metal content in studied soils did not excess acceptable level for urban soils defined in the regulation of the Polish Ministry of the Environment. Among studied heavy metals zinc concentration was the highest both in soils (even >200 mg/kg D.M.) and in grass dry matter (even >60 mg/kg D.M.). Among study heavy metals in soil, chromium concentration was the lowest (from about 2 to 9 mg/kg D.M.). The nickel concentration was relatively similar independently of sewage sludge dose (about 40-47 mg/kg D.M. Concentration of lead in soil in studied locations was in a broad range independently of sludge dose (from about 20-29 at Hetmańska and Raginisa Streets to about 90 mg/kg D.M. in soil at Popiełuszki Street fertilized with the highest dose of sewage sludge. Content of Cr in the soil was significantly correlated with the content of Zn (r = 0.8), and with Ni content (r = 0.9).

The biomass of grass mixtures increased with increasing of sewage sludge dose and depended strongly on the location. Heavy metal content in studied above ground parts of grasses was was slightly increasing with dose of sewage sludge

Soil pH both in KCl and H₂O after sewage sludge application were in the range of 6.9 to 8.0 and independent of sewage sludge dose. Such pH was unfavorable for root uptake of heavy metals.