Abstract:
The changes of manganese and iron in soil were studied in Phetchaburi municipal wastewater treatment system by grass filtration. This system has been treated cyclically, 7 days per cycle; 5 days submergence at 15-centimetres depth and 2 days for drainage, period of 12 weeks. Seven plots of 5 x 100 meters size each, with 1:1,000 slope, having 3:1 mixture of paddy soil and coarse sand, as plant medium were used. The plants were Cyperus corymbosus Rottb., Leptochloa fusca L.Kunth, Cynodon dactylon (L.) Pers. Vetiveria zizanioides (L.) Nash ex Small (Srilanka), VEtiveria zizanioides (L.) Nash ex Small (Indonesia) and Cynodon plectostachyus and control plot, having no plant. In open system, PVC pipes (6.35 x 15 cm.) were pushed into soil at 5 distance with 3 replications for each plot. In close system, soil had contained in 150 ml. plastic box and saturated with wastewater at the same distance as 20, 40, 60, 80 and 100 meters. Soil samples; PVC pipes. Plastic box and soil had collected at 0, 4, 8 and 12 weeks of experiment for manganese and iron analysis. The five forms of manganese and iron studies were the water-soluble, the 1 N KC1 extractable, the Morgan's solution extractable, the exchangeable and the solid phase in soil.The results found that, (1) Manganese and iron had same tendency in the experiment; (2) Variety of plants were highly significantly effected changes all forms of manganese and iron and all of sampling periods of this study. Cyperus corymbosus Rottb., and Cynodon plectostacyus had the highest significant on uptake manganese and iron; (3) Distance has significant effected on some of manganese and iron forms quantities at 80 and 100 meters; (4) manganese and iron in soil in anaerobic condition, its had non available form of Mn (II) and FE (II) and lower content in water soluble and exchangeable form. Manganese and iron toxicity from wastewater in this system were not effected to plants, especially changes of these micronutrient elements.