Abstract
Thiourea is used in agriculture and industry as a metal scavenger, synthetic intermediate, and nitrification inhibitor. However, in wastewater, it can inhibit the nitrification process and induce the collapse of the nitrification system. In such a case, ammonia-oxidizing bacteria (AOB) lose their ability to remove ammonia. We investigated the nitrification system of a 60,000-t/d municipal sewage treatment plant in Nanjing, which collapsed after receiving 5–15 ppm (5–15 mg/L) thiourea. Ammonia nitrogen removal quickly recovered to more than 95% after inoculation with 10 t high-efficiency nitrification sludge, which was collected from a kitchen waste treatment plant. A heterotrophic nitrification strain was isolated from the inoculated sludge and identified as wild Pseudomonas by 16S rDNA sequencing and named “BT1.” Based on thiourea tolerance tests, BT1 can tolerate a thiourea content of more than 500 ppm. For comparison, the in situ process was imitated by the simulation system, and the wastewater shocked by 10 ppm thiourea could still meet the emission standard after adding 1% (V/V) BT1. High-throughput sequencing analysis was applied to study microbial succession during thiourea shock loading. The results showed that Hydrogenophaga and Thiobacillus grew with the growth of BT1. Pseudomonas BT1 was used for a 6,000-t/d printed circuit board (PCB) wastewater treatment system, the nitrification system returned to normal in 15 days, and the degradation rate stabilized at more than 95%.
Highlights
Thiourea is widely used in various industries [1, 19, 22], for example, as a metal scavenger in the metallurgical industry and in printed metal board manufacturing [17, 23]) and as a synthetic intermediate in the pharmaceutical and resin industries [10, 16]
Thiourea inhibits nitrification,it is a specific nitrification inhibitor because its C=S structure can covalently bond with copper in the active center of ammonia-oxidizing bacteria (AOB), causing them to lose their ammonia oxidation ability [30, 31]
Physiological and biochemical analyses of Pseudomonas BT1 showed that the pure strain could rapidly proliferate and maintain ammonia oxidation activity at thiourea concentrations of 10–500 ppm
Summary
Thiourea is widely used in various industries [1, 19, 22], for example, as a metal scavenger in the metallurgical industry and in printed metal board manufacturing [17, 23]) and as a synthetic intermediate in the pharmaceutical and resin industries [10, 16]. If the nitrification system of a sewage treatment plant is severely impacted, the addition of AOB, including autotrophic nitrifying bacteria (ANB) and heterotrophic nitrifying bacteria (HNB), can facilitate the restoration of nitrogen removal, helping the system recover rapidly [14, 38, 39], and this approach has been widely accepted [33, 35]. Most studies on HNB have focused on reducing the C/N ratio, denitrification, and low-temperature ammonia oxidation [13], [21], [32],the specificity of HNB in engineering applications is low In this sense, HNB can be used to protect specific ANB from toxicity, which is important to restore the nitrification efficiency of sewage treatment plants. Due to the limitations of the AOB that have been discovered, a strain of bacteria with low producing cost and high specificity is urgent and important for sewage treatment systems to restore ammonia nitrogen removal after the collapse
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