Abstract：
The microbial activities in sewer biofilms are recognized as a major reason for sewer pipe corrosion, malodor, and greenhouse gas emissions. However, conventional methods to control sewer biofilm activities were based on the inhibitory or biocidal effect of chemicals and often required long exposure time or high dosing rates due to the protection of sewer biofilm structure. Therefore, this study attempt to use ferrate (Fe(VI)), a green and high-valent iron, at low dosing rates to damage the sewer biofilm structure so as to enhance sewer biofilm control efficiency. The results showed the biofilm structure started to crush when the Fe(VI) dosage was 15 mg Fe(VI)/L and the damage enhanced with the increasing dosage. The determination of extracellular polymeric substances (EPS) showed that Fe(VI) treatment at 15-45 mgFe/L mainly decreased the content of humic substances (HS) in biofilm EPS. This is because the functional groups, such as C-O, -OH, and C=O, which held the large molecular structure of HS, were the primary target of Fe(VI) treatment as suggested by 2D-Fourier Transform Infrared spectra. As a result, the coiled chain of EPS maintained by HS was turned to extended and dispersed and consequently led to a loosed biofilm structure. The XDLVO analysis suggested that both the microbial interaction energy barrier and secondary energy minimum were increased after Fe(VI) treatment, suggesting that the treated biofilm was less likely to aggregate and easier to be removed by the shear stress caused by high wastewater flow. Moreover, combined Fe(VI) and free nitrous acid (FNA) dosing experiments showed for achieving 90% inactivation, the FNA dosing rate could be reduced by 90% with the exposure time decreasing by 75% at a low Fe(VI) dosing rate and the total cost was substantially decreased. These results suggested that applying low-rate Fe(VI) dosing for sewer biofilm structure destruction is expected to be an economical way to facilitate sewer biofilm control.
摘要：
下水道生物膜中的微生物活动被认为是下水道管道腐蚀的主要原因，恶臭,和温室气体排放。然而,控制下水道生物膜活性的常规方法是基于化学物质的抑制或杀生物作用，并且由于保护下水道生物膜结构，通常需要长暴露时间或高剂量。因此,本研究尝试使用高铁酸盐(Fe(VI))，一种绿色的高价铁,在低给药率下破坏下水道生物膜结构，从而提高下水道生物膜控制效率。结果表明，当Fe（VI）的投加量为15mgFe（VI）/L时，生物膜结构开始破裂，并且随着投加量的增加，损伤程度增强。胞外聚合物（EPS）的测定表明，在15-45mgFe/L的Fe（VI）处理主要降低了生物膜EPS中腐殖质（HS）的含量。这是因为官能团，比如C-O，-哦,C=O，拥有HS的大分子结构，是二维傅里叶变换红外光谱建议的Fe（VI）处理的主要目标。因此,由HS维持的EPS的卷曲链被转变为延伸和分散,并因此导致松散的生物膜结构。XDLVO分析表明，Fe（VI）处理后，微生物相互作用能垒和二次能量最小值均增加，表明处理后的生物膜不太可能聚集，并且更容易被高废水流量引起的剪切应力去除。此外，联合Fe（VI）和游离亚硝酸（FNA）剂量实验显示实现90%失活，在低Fe(VI)给药速率下,FNA给药速率可降低90%,暴露时间可减少75%,且总成本显著降低。这些结果表明，应用低速Fe（VI）剂量破坏下水道生物膜结构有望成为促进下水道生物膜控制的经济途径。
