Advanced treatment process for hot spring wastewater containing arsenic

无机砷化合物通常在溶液中观察到AsO_2^-和AsO_4^<3->，这些氧阴离子通常是水溶性的。砷不形成不溶性氢氧化物，可通过共沉淀法去除。污水污泥相互作用过程中，砷在污泥沉降池中积累的最重要机制是与污染废水中含水氧化铁的吸附和共沉淀。水合氧化铁是一种较好的除砷混凝剂。含水氧化铁是一种有效的混凝剂，即使进水砷含量很高（1.5mg/1）。当进水砷高污染（1.5mg/1）时，铝化合物并没有将排放废水中的砷浓度降低到排放废水限值的0.1mg/1。污水处理过程中产生的污泥体积不受混凝剂种类的影响，而受混凝剂用量的影响。20 mg/1的含水氧化铁对氧化沟中活性污泥的活性没有影响。在改性氧化沟工艺中，随着混凝剂（含水氧化铁）投加量的增加，废水中铁的浓度有所提高。为了达到相同的除砷效果，投加在化学沉淀池中的混凝剂浓度必须低于投加在氧化沟中的混凝剂浓度。

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.