The Characteristics Of Corrosion And Water Quality Along The Reclaimed Water Cast Iron Pipeline In The Simulation System

Wastewater reuse is an important way to alleviate the shortage of fresh water resource. However, the corrosion of pipe material often leads to the water quality degradation of the effluent. Four CDC reactors were set up to model the reclaimed water cast iron pipeline and the reclaimed water from Wastewater Treatment and Reuse Plant(WTRP) located in Xi’an was usedin this experiment. The characteristics of water quality and corrosion were analyzed based on collecting and measuring the water samples and corrosion samples in the simulation system during different corrosion periods. The main results were as follows:First of all, the iron concentration in the reclaimed water increased along the pipeline in the simulation system and ferrous iron contributed a small share in total iron; NH4+-N/NO2--N in the reclaimed water along the pipe decreased and the NO3--Nalong the pipe raised, which showed that the nitrification happened in conveying the reclaimed water; PO43--P in the reclaimed water reduced along the pipeline; the number of heterotrophic bacteria along the pipe increased. On the other side, the concentration of total alkalinity, total hardness, Cl- and SO42- in the simulate system were stable along the pipeline, which had little effect on the cast iron corrosion; total chlorine and residual chlorine decreased along the pipeline, p H and the concentration of dissolved oxygen along the pipe kept increased.Secondly, the microscopic morphology and structure of corrosion products changed obviously with time. The dense particle layer, particle/ filaments layer and the characteristics of multi-layer hierarchical structure were found during the corrosion process; Fe(about 50%) and O(about 30%) in the corrosion products were the main component which had different content during different corrosion phase and more than 85% of all elements. Different iron oxide type including α-Fe OOH/ γ-Fe2O3/ Fe CO3 and β-Fe OOH appeared in the corrosion products in the reclaimed water cast iron pipeline and material types changed obviously with time while little change along the pipeline, however, the crystal morphology was poor. The corrosion rate of cast iron decreased with time, the severe corrosion occurred at the initial segment while the weak corrosion occurred at the end segment.In short, the corrosion of cast iron pipe had a significant effect on iron of water quality in the simulation system while the reclaimed water quality had little influence on corrosion of cast iron pipe. The characteristics of corrosion products were similar along the pipeline and the severe corrosion occurred at the initial segment of pipe.