Synthetic zeolites as amendments for sewage sludge-based compost

The effects of incorporating a synthetic zeolite (Zeolite P) in a range of concentrations (0.1-1.0 w:w) into an experimental horticultural compost, de rived from sewage sludge, have been investigated. The impact of zeolite tre atment on time-related changes of the labile zinc, copper, iron and mangane se pools within the compost was compared to lime incorporation (5% w:w) and to a proprietary unamended peat-based compost. Addition of 0.5% and 1.0% z eolite significantly reduced labile zinc over a 90 day period. The highest zeolite treatment was more effective than liming; 0.5% zeolite was as effec tive as lime. Plant growth trials measuring transfer of metals to ryegrass (Lolium perenne L. cv Elka) in successive harvests demonstrated that both 1 .0% zeolite and 5% lime treatment caused significant reduction in total met al transfer from soil-plant over a 116 day growth period. It is concluded t hat the use of synthetic zeolite as an amendment for compost of this type s ignificantly reduces potential for soil metal mobility and soil-plant trans fer. (C) 2000 Elsevier Science Ltd. All rights reserved.