An Environmentally Sound Method for Disposal of Both Ash and Sludge Wastes by Mixing with Soil: A Case Study of Bangkok Plain

This study reported the test done on ash-sludge mixture foramendment of soil in pot experiments. Ash-sludge mixture ratiostudies revealed that 1:5 fly ash-sludge mixture and 1:10 bottom ash-sludge mixture were the optimum mixture ratio thatminimized toxic element and provided sufficient nutrients. Experiments indicated that ash-sludge mixtures is more suitablefor amendment of acid soil than neutral soil which can increasesoil pH and reduce available heavy metal toxicity. The maximumheavy metal adsorption occurred in a pH range of 4 to 6 for allsoil studied. The finding also revealed that fly ash applicationseemed more effective than bottom ash, due to its higher loadingrate and metal contents. Heavy metal toxicity was monitored usingseed germination test. Marigold and tomato seeds were the two crops selected for this test. Seed germination test result showsthat percentage of seed germination increased in pot experimentswith sludge only and ash-sludge mixtures. In addition, higherpercentages of seed germination were observed to vary with longer incubation time (1–8 weeks). After week 12 of the incubation period, percentage of seed germination began to decline, as a result of reduced soil pH and release of toxic heavy metals.