Advanced treatment process for hot spring wastewater containing arsenic

无机砷化合物通常以AsO_2~-和AsO_4~(-3-)的形式存在于溶液中，这些含氧阴离子是典型的水溶性阴离子。砷不会形成不溶的氢氧化物，可以通过共沉淀系统去除。在废水-污泥相互作用过程中，污泥沉淀池中砷的积累最重要的机制是吸附和共沉淀污染废水中的水合氧化铁。水合氧化铁是一种比铝化合物更适合于除砷的混凝剂。即使进水砷污染较高(1.5 mg/l)，水合氧化铁仍是一种有效的混凝剂。当进水砷污染较高(1.5 mg/l)时，铝化合物不能使出水砷浓度降至排放限值的0.1 mg/l。废水处理过程中产生的污泥量不受混凝剂种类的影响，而受混凝剂投加量的影响。20 mg/l的水合氧化铁不影响氧化沟内活性污泥的活性。随着改良氧化沟工艺中混凝剂(水合氧化铁)投加量的增加，废水中铁的浓度也随之增加。投加到化学沉淀池的混凝剂浓度需要低于投加到氧化沟的投加量，才能达到相同的除砷效果。

Inorganic arsenic compounds are commonly observed in solution as AsO_2^- and AsO_4^<3-> and these oxo-anions are typically water soluble. Arsenic does not form an insoluble hydroxide and can be removed by coprecipitation system. The most important mechanism for the accumulation of arsenic in sludge settling tank during wastewater-sludge interaction is adsorption on and coprecipitation with hydrous iron oxides in contaminated wastewater. Hydrous iron oxides is a suitable coagulant for the removal of arsenic than aluminum compounds. Hydrous iron oxides were a effective coagulant even if the influent were highly contaminated with arsenic (1.5mg/1). The aluminum compounds did not reduce the arsenic concentration of the discharged wastewater to 0.1mg/1 of the limitation level of discharged wastewater when the influent was highly contaminated with arsenic (1.5mg/1). Amount of sludge volumes which were produced during the wastewater treatment process was not effected by the species of coagulants but by the amounts of coagulants. The activity of activated sludge in oxidation ditch was not affected by 20 mg/1 of hydrous iron oxides. The concentration of iron in the discharged wastewater was increased with increasing the amount of coagulant (hydrous iron oxides) added to the modified oxidation ditch process. The concentration of coagulant added to the chemical sedimentation tank needed lower than that added to the oxidation ditch to attain the same arsenic removal efficiency.