海洋环境腐蚀与生物污损重点实验室知识库

   微生物腐蚀（MIC）是影响海洋工程设施服役安全的重要因素，制约开发和利用海洋资源的脚步。硝酸盐作为我国近海海域的典型污染物，能够通过影响微生物的生长代谢进而影响金属材料的腐蚀过程。此外，在海上石油开采的回注水系统中也常采用添加硝酸盐的方式抑制腐蚀性微生物硫酸盐还原菌（sulfate reducing bacteria，SRB）的生长，进而抑制腐蚀，但其有效性饱受争议。本研究选取海水中分布广泛的典型腐蚀性微生物硫酸盐还原菌（脱硫弧菌：Desulfovibrio vulgaris）与硝酸盐还原菌（铜绿假单胞菌：Pseudomonas aeruginosa）为研究对象，以EH40钢和纯铜为实验材料，探究硝酸盐的添加对混合菌作用下典型金属材料腐蚀的影响。主要的研究结果如下：

（1）揭示了硝酸盐对D. vulgaris与P. aeruginosa共同作用下EH40钢腐蚀的促进作用。硝酸盐促进了混合菌作用下EH40钢的腐蚀，且腐蚀促进具有浓度依赖性，不同体系的腐蚀速率大小关系为：5 > 0.5≈50 > 0 g/L NaNO₃，这些差异与硝酸盐对细菌的生长调节密切相关。D. vulgaris与P. aeruginosa均通过胞外电子传递（EET）促进EH40钢的腐蚀。低浓度的硝酸盐（0.5和5g/L）促进了P. aeruginosa的生长，由于其生长速度快、对有机电子供体的消耗快，易于形成碳饥饿环境使得混合菌的EET腐蚀活性得以发挥、促进腐蚀。高浓度的硝酸盐（50 g/L）使得溶液渗透压提高、细菌数量与活性降低，腐蚀促进作用减弱。

（2）探究了硝酸盐与有机电子供体对D. vulgaris与P. aeruginosa共同作用下EH40钢腐蚀的耦合影响。有机电子供体匮乏在未添加与添加硝酸盐的环境下，对D.vulgaris与P.aeruginosa共同作用下EH40钢腐蚀的影响不同。未添加硝酸盐时，有机电子匮乏促使细菌体型变长且扭成螺旋状，更加利于EET腐蚀促进的进行，使得腐蚀速率为全营养状态下的2倍。硝酸盐存在下（5 g/L NaNO₃）有机电子供体匮乏抑制了混合菌的生长，使得试样表面混合菌数量明显减少，利用Fe⁰的速率降低，腐蚀促进作用减弱，为营养状态下的1/2。

（3）探究了在不同腐蚀机制参与下，硝酸盐的添加对D. vulgaris与P. aeruginosa共同作用下纯铜腐蚀的影响。硝酸盐的添加抑制了混合菌作用下纯铜的腐蚀，且呈现一定的浓度依赖性，14天时不同体系中铜的腐蚀速率大小关系为：0≈0.5 > 5 > 50 g/L NaNO₃，这与两种细菌对铜的不同腐蚀机制有关。D. vulgaris对铜的腐蚀机制为代谢产物腐蚀，P. aeruginosa对铜的腐蚀机制为EET-MIC。硝酸盐的添加促进了P. aeruginosa的生长抑制了D. vulgaris的生长，D. vulgaris代谢产生的HS^-减少，导致混合菌抵御铜毒害作用的能力减弱、生物膜变薄、附着细菌数量减少，进而抑制了其对铜的腐蚀作用。

   本文通过研究发现，硝酸盐、材料性质、有机电子供体等多种因素都能影响D. vulgaris与P. aeruginosa共同作用下EH40钢的腐蚀，硝酸盐对腐蚀影响的实际作用需根据具体体系具体分析。

Microbiologically influenced corrosion (MIC) is an important factor affecting the service life of offshore engineering facilities, which restricts the development and utilization of marine resources. Nitrate, a typical offshore pollutant, can affect the corrosion by affecting the metabolism of microorganisms. In addition, in produced water reinjection (PWRI) systems for offshore oil production, nitrate is often added to inhibit the growth of sulfate reducing bacteria (SRB), so as to inhibit corrosion, but its effectiveness is controversial. In this study, nitrate was added at different concentrations into different systems with Desulfovibrio vulgaris and Pseudomonas aeruginosa, which were typical strains of SRB and nitrate reducing bacteria (NRB) and commonly found in seawater. The EH40 steel and pure copper were used as experimental materials, the main results are as follows:

(1) Nitrate could accelerate the corrosion of EH40 steel through the action of D. vulgaris and P. aeruginosa, and it was related to the concentration. The corrosion rate of EH40 steel in different systems at 7 days was: 5 > 0.5≈50 > 0 g/L NaNO₃, which was related to the microorganisms. D. vulgaris and P. aeruginosa could accelerate the corrosion of EH40 steel through the mechanism of extracellular electron transfer (EET). Low concentrations of nitrate (0.5 and 5 g/L) promote the growth of P. aeruginosa. Due to its fast growth, nutrients were depleted. And it was easy to form a carbon starvation environment so that the EET corrosion activity of mixed bacteria could be exerted and promoted corrosion. The high concentration of nitrate (50 g/L) increased the solution osmotic pressure and reduced the number of bacteria, so the corrosion weight loss was decreased.

(2) The effect of nitrate and organic electron donor on the corrosion of EH40 steel under the action of D. vulgaris and P. aeruginosa was investigated. In the systems without/with nitrate added, the lack of organic electron donors had different corrosion results of EH40 steel under the action of D. vulgaris and P. aeruginosa. Without nitrate added, the lack of organic electrons caused the shape of bacteria became longer and twisted into a spiral shape, and accelerated corrosion through the EET mechanism. The corrosion rate was twice that of the total nutrition. When 5 g/L NaNO₃ was added, the organic electron donor deficiency inhibited the growth of mixed bacteria, and the number of mixed bacteria on the surface of the coupon was reduced. The utilization of Fe⁰ by mixed bacteria was decreased, and inhibited the corrosion. The corrosion weight loss was only 1/2 of that under total nutrition.

(3) Explored the effect of nitrate on the corrosion of pure copper under the action of D. vulgaris and P. aeruginosa with different corrosion mechanisms. The addition of nitrate inhibited the corrosion of pure copper under the action of mixed bacteria, and it was related to the concentration. The corrosion rate of copper in different systems was: 0≈0.5 > 5 > 50 g/L NaNO₃ at days14, which was related to the different corrosion mechanisms of copper by two bacteria. The corrosion mechanism of D. vulgaris to copper is metabolite corrosion (M-MIC), and the corrosion mechanism of P. aeruginosa to copper is EET-MIC. The addition of nitrate promoted the growth of P. aeruginosa and inhibited the growth of D. vulgaris. The reduction of HS^- had led to a weaken ability of mixed bacteria to resist copper toxic effects. The biofilm became thinner, and the number of bacteria attached to the surface of copper decreased. So, the corrosion of mixed bacteria to copper was inhibited.

In this paper, it was found that nitrate, material properties, organic electron donors and other factors could affect the corrosion of EH40 steel under the joint action of D. vulgaris and P. aeruginosa. The actual effect of nitrate on corrosion needed to be analyzed according to the specific system.