About 1.2 m3 of sludge generates from every 10 m3 of wastewater whose iron mass fraction is more than 2%. 
This sludge is composed of iron hydroxide and also a kind of iron-containing resource. 
Few people have focused on finding a good way to dispose this sludge. Generally the sludge is disposed as solid waste,
which means cost of sludge disposal, loss of iron resource and risk of secondary pollution.