The Characteristics of Taiwan Domestic Wastewater Sludge and the Feasibility of Reusing for Growing Edible Crops

The popularity of municipal sewage sewers system leads to producing a massive quantity of domestic wastewater sludge; how to treat and dispose of the sludge is becoming an environmental problem. The sludge is rich in nutrients, and it is often applied to soil as fertilizer or soil conditioner in many developing and developed nations. However, the influence of heavy metals contained in sludge on the crop growth and quality is a major concern when the sludge is reused on farmland for growing edible crops. The objectives of this research are to analyze the municipal sewage sludge for heavy metal contents and their bond fractions, and to conduct crop growth experiments to evaluate the influence on crop growth and quality by applying the sludge as soil additives for growing crop. The experimental sludge samples were collected from Taichung Fu-Tien wastewater treatment plants. The sludge contains Cu, Zn, Ni and Cd with concentrations exceeding the maximum levels legally allowed in Taiwan farmland soil. Most Cu exists in organic bond fraction; Zn is in Fe-Mn oxides bond fraction, Ni is in organic bond fraction, and Cd is in Fe-Mn oxides bond fraction. Three batches of plant growing and harvesting were carried. The crop growth results reveal that the growth of plants grown in the second batch of planting is obviously suppressed, and the extent of influence increases with higher ratios of sludge applied to the soil.