投加不同碱性药剂对管网铁释放的影响

针对不同水源切换可能使管网铁释放增加而引起黄水的问题,搭建了管网模拟中试系统,比较了投加3种不同碱性药剂对管网铁释放的影响.结果表明:1投加NaHCO3调节进水碱度,当进水碱度为94~251 mg/L(以CaCO3计)时,增加进水碱度能够有效抑制管网系统的铁释放,并且出水中ρ(TFe)(TFe为总铁)达到GB 5749—2006《生活饮用水卫生标准》(30 mg/L).2p H为7.83~9.01时,采用投加NaOH调节进水p H对管网铁释放无明显抑制作用甚至有所促进;而投加Ca(OH)2调节进水pH虽然能够在一定程度上抑制管网铁释放,但抑制效果有限,不能保证出水中ρ(TFe)达标.3当进水中ρ(SO42-)较低时,试验后期停止投加Na HCO3或Ca(OH)2后,管网系统铁释放能够维持在较低水平;但当进水中ρ(SO42-)较高时,停止投加Na HCO3或Ca(OH)2后,管网铁的释放又会明显升高.

Effects of Different Alkaline Chemical Dosing on Iron Release in Drinking Water Distribution Systems

Abstract: Making use of alternative sources of water (e.g. desalinated water, reclaimed water) and long distance water diversion are possible methods to solve water shortage problems. However, source water switching might cause undesirable water quality changes at consumer taps resulted from destabilization of corrosion scales in existing drinking water distribution systems (DWDS). In the present study, cast iron pipes historically transporting groundwater were harvested from three sites of an existing distribution system of a northern city in China, and pipe-loop simulation distribution systems were established to investigate the effects of different alkaline chemicals on iron release inhibition performance. For better comparison, the sulfate concentration of feed water was manipulated to obtain relatively high iron release. The results showed that:1) The iron release decreased significantly with alkalinity supplementation (through NaHCO₃ addition) in the range of 94-251 mg/L (as CaCO₃) and could ensure the total iron concentration met the GB 5749-2006 Standards for Drinking Water Quality (<0.30 mg/L). 2) When water pH was elevated by addition of NaOH in the range of 7.83-9.01, the iron release was promoted to some extent instead of inhibition; while when the pH was elevated by adding Ca(OH)₂, the iron release decreased obviously, but the total iron concentration was always higher than 0.30 mg/L. 3) Under the condition of low sulfate concentration of feed water, the iron release did not increase when NaHCO₃ and Ca(OH)₂ addition discontinued, but under high sulfate condition, iron release could increase again with the termination of alkalinity and pH adjustments.