Effects Of Nitrogen Contaminated Shallow Groundwater On Nitrogen Metabolic Micro- Organisms And Its Biochemical Remediation

Groundwater contamination is a growing concern in China. Wastewater and solids produced by livestock and poultry breeding are discharged to the environment without any treatment, and seepage from the anaerobic swine logoons is often percolated into groundwater. Meanwhile, treatment of polluted groundwater is difficult and costly. Thus how to effectively remove nitrogen from groundwater is still requires more research.This study investigated the effects of groundwater nitrogen contamination on nitrogen metabolism microorganisms, then analyzed the correlations between them, and designed a Multi-Soil-Layering (MSL) to remove the nitrogen in groundwater by biochemical remediation in groundwater. The main results are as follow:(1) The main nitrogen form in groundwater was NH4+-N, with concentrations ranged from 0.30-463.96 mg/L and showed spatial-temporal heterogeneity. The groundwater was somewhat polluted but the majority of the water samples had NO3--N pollution and NO3--N lower than 10 mg/L. The pH of the water samples ranged from 7-8(alkalescence) and EC ranged from 0.65-2.51 ms/cm. The research area was divided into 3 clusters based on the result of PC A:Cluster Ⅰ was close to No.1 lagoon, Cluster Ⅲ was farther away from the two lagoons and Cluster Ⅲ was close to No.2 lagoon. The concentration of total nitrogen was Cluster Ⅲ> Cluster Ⅱ> Cluster Ⅰ; the carbon nitrogen ratio was Cluster Ⅰ> Cluster Ⅱ> Cluster Ⅲ; the pH was Cluster Ⅱ> Cluster Ⅲ> Cluster Ⅰ and the EC was Cluster Ⅲ> Cluster Ⅰ> Cluster Ⅰ. Water temperature did not show any particular pattern.(2) The main nitrogen metabolism bacteria in this site were ammonia oxidizing bacteria (AOB), nitrite reducing bacteria and nitrous oxide reducing bacteria Among them, the population of oxidizing bacteria> nitrite reducing bacteria> nitrous oxide reducing bacteria. The dominant species was β-Proteobacteria. The numbers of all the bacteria at this site were Cluster Ⅲ> Cluster Ⅱ> Cluster Ⅰ. NH4+N and NO3--N concentrations had positive correlations with all kinds of nitrogen metabolism bacteria to a certain degree. Besides, the number of nitrite reducing bacteria was significantly and positively correlated with total organic carbon (TOC) and EC (P<0.01). The number of nitrous oxide reducing bacteria was also significantly and positively correlated with TOC. We observed that severe nitrogen pollution could lower the microbial diverstity.(3) The soil layers of the traditional MSL were replaced by organic layers that were a mix of saw dust and bran embedded with denitrification incula. Results showed that in the initial running period, almost all the nitrogen in groundwater was removed by strong sorption of the system. But after reached the sorption balance, nitrogen metabolic microbial contributed mainly to nitrogen removal in the polluted groundwater. Molecular biological technique and scanning electron microscope observations indicated that there were nitrogen metabolicmicroorganisms in the system after the initial running period, including cocci and bacillus. The main types of nitrogen metabolic microbial were ammonia oxidizing bacteria, nitrous oxide reductasebacteria and ammonia oxidizing archaea.The dominant microbe in the system was β-Proteobacteria. At the end, the effluent NH4+-N concentration was lower than 5 mg/L and NH4+-N removal ratio was higher than 90%, indicating a good removal ratio of high-concentration ammonia contaminated water. However the effluent NO3--N concentration was still about 80 mg/L, which might be caused by a lack of anaerobic environment that created an unfavorable condition for the key microbe of denitrification nitrite reductase bacteria. The real cause still needs further investigation.