管道特征对给水管网中锰释放的影响

Influence of pipe characteristics on manganese release in drinking water distribution system

针对南方某市历年来与锰相关的多次黄水问题,在当地黄水多发区域挖取10年管龄的旧PE管和20年管龄的镀锌钢管,搭建中试装置,开展了管网中锰释放行为的中试研究,并以新PE管做对比,探讨了微生物对管网内锰的氧化沉积的影响。实验结果表明,在进水锰浓度很低时,镀锌钢管与旧PE管的管壁沉积物中均会出现锰的释放。镀锌钢管中释放的锰主要为溶解性锰,释放量大;而旧PE管中释放的锰主要为不溶态的锰,且释放量小。同时,镀锌钢管管道浸泡结果表明,随着余氯浓度的提高,镀锌钢管中溶解锰的释放会显著降低,但即使余氯浓度高达15 mg·L^(-1)仍会有25.3μg·L-1的溶解锰的释放。新旧PE管的对比实验表明,当提高进水Mn(Ⅱ)浓度时,旧PE管中Mn(Ⅱ)在6.67 h内的氧化量低于新PE管,这可能是旧PE管生物膜中的锰还原菌含量较多导致的。

To understand the mechanism of manganese related red water frequently occurred in a city of South China, a pilot setup was built with in-service PE （10 years old） and galvanized steel pipes （20 years old） har- vested from areas with red water complaints. The manganese release behavior in the two kinds of pipes was inves- tigated. With new PE pipe as experimental control, the effect of microorganism on the oxidation/deposition of Mn （Ⅱ） was explored. Results showed that significant manganese release happened in both old PE and galvanized pipes when the feed water manganese concentration was low. The manganese release from galvanized pipe was higher than that from PE pipe, and the released manganese was mainly in dissolved form. While the manganese release from PE pipe was mainly in particulate form. Stagnant immersion experiment indicated that free chlorine could greatly inhibit dissolved manganese release from galvanized pipe, but even with chlorine concentration of 15 mg·L-1 （as C12）, 25.3μg· L-1 of dissolved manganese release was observed. Compared with relatively new PE pipe, the oxidation rate of Mn（ Ⅱ ） was slower in old PE pipe, which might be attributed to the relative- ly higher manganese-reducing microorganisms in old PE pipes.