REMEDIATION OF ACID SOILS BY USING ALKALINE BIOSOLIDS

Alkaline biosolids may be suitable as a liming amendment for acid soil s, The efficacy of two alkaline biosolids, lime-stabilized sewage slud ge (LS) and N-Viro Soil (NV), for remediating soil acidity and Al toxi city in strongly acid soils were evaluated, For comparison, soils were also treated with unlimed anaerobically digested sewage sludge (SS) a nd agricultural lime (L). Three acid soils were amended with LS, NV, S S, and L and incubated at 25 degrees C. Soil solution was extracted at 1, 30, 90, and 180 d incubation and analyzed for pH, electrical condu ctivity (EC), dissolved organic carbon (DOC), Al, Mn, Ca, Mg, Na, K, F , Cl, PO4, NO3, and SO4, In general, soil pH increased linearly with a mendment rate for all soils and all amendments, The magnitude of incre ase in soil pH after 6 mo for the four amendments followed the order L similar or equal to NV>LS>>SS. All amendments decreased soluble Al, b ut lime-containing amendments (LS, NV, and L) decreased soluble Al bel ow detection limits (<0.4 mmol L(-1)). The largest decreases in exchan geable Al were associated with lime-containing amendments, Lime-contai ning amendments reduced soluble Mn but unlimed sewage sludge had no ef fect on soil solution Mn. Soluble Al speciation using MINTEQA2 showed that all rates of lime-containing amendments (LS, NV, and L) decreased Al3+ activity to nontoxic levels (<10 mmol L(-1)). Saturation indices indicated sewage sludge amendments may have resulted in precipitation of Al as alunite [KAl3(OH)(6)(SO4)(2) . H2O]. Although SS decreased p hytoavailable Al, alkaline biosolids caused greater reductions in pote ntially phytotoxic Al than nonalkaline biosolids (SS).