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 for amendment of soil in pot experiments. Ash-sludge mixture ratio studies revealed that 1:5 fly ash-sludge mixture and 1:10 bottom ash-sludge mixture were the optimum mixture ratio that minimized toxic element and provided sufficient nutrients. Experiments indicated that ash-sludge mixtures is more suitable for amendment of acid soil than neutral soil which can increase soil pH and reduce available heavy metal toxicity. The maximum heavy metal adsorption occurred in a pH range of 4 to 6 for all soil studied. The finding also revealed that fly ash application seemed more effective than bottom ash, due to its higher loading rate and metal contents. Heavy metal toxicity was monitored using seed germination test. Marigold and tomato seeds were the two crops selected for this test. Seed germination test result shows that percentage of seed germination increased in pot experiments with sludge only and ash-sludge mixtures. In addition, higher percentages 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.