Comparison of Swine Wastewater Treatment by Microalgae and Heterotrophic Nitrifiers: Focusing on Nitrogen Removal Mechanism Revealed by Microbiological Correlation Analysis

Swine wastewater (SW) poses a great threat to the environment due to its high-nutrient profiles if not properly managed. Advanced biological treatment method is an efficient method to treat SW by screening potent microalgae or bacterial strains. In this study, activated sludge, nine locally isolated heterotrophic nitrification bacteria and one microalgal strain (Chlorella) were used as inoculums in treating a local SW. Their treatment efficiencies were compared, while the nitrogen removal mechanisms and microbiome profile were explored in detail. It was found that certain heterotrophic nitrification strains had a slight advantage in removing chemical oxygen demand and phosphorus from SW, with the highest removal efficiencies of 83.9% and 76.2%, respectively. The removal efficiencies of ammonia nitrogen and total nitrogen in wastewater by microalgae reached 80.9% and 66.0% respectively, which were far higher than all the heterotrophic nitrification strains. Biological assimilation was the main pathway of nitrogen conversion by microalgae and heterotrophic nitrifying bacteria; especially microalgae showed excellent biological assimilation performance. Correlation analysis showed that Comamonas was highly positively correlated with nitrogen assimilation, while Acidovorax was closely correlated with simultaneous nitrification and denitrification. This study gives a comparison of microalgae and heterotrophic nitrifying bacteria on the nitrogen transfer and transformation pathways.

Impact of 17β-Estradiol on Natural Water’s Heterotrophic Nitrifying Bacteria

In this research, bottom water samples were collected from nature water. After cultivating and selecting, bacteria which could use (NH4)2SO4 as the only nitrogen source had been selected. The bacteria in different cultures with different concentration of 17β-estradiol (E2) were cultivated, and every group’s concentration of N-NH4 +, N-NO3 - and OD600 were measured. The result shows that compare with the control group, in which no E2 was added, the growth of heterotrophic nitrifying bacteria had been promoted when the concentration of E2 was in range of 1-100 ng/L. In addition, heterotrophic nitrifying bacteria’s growing speed has a positive correlation between the E2’s concentration. However, low concentration of E2 (like 0.1 ng/L), could inhibit the growth of heterotrophic nitrifying bacteria. Considering the impact of E2 on heterotrophic nitrifying bacteria, it is necessary to intensify the detection to E2 in the future.

Ammonium removal efficiency of biochar-based heterotrophic nitrifying bacteria immobilization body in water solution

In order to explore the performance of biochar-based microbial immobilization body in ammonium removal from water and potential mechanisms, a strain of heterotrophic nitrifying bacteria (HNB) was isolated from activated sludge, and the biochemical and molecular biological identification of HNB was carried out. Moreover, HNO₃-, Mg²⁺-, NaOH_-, and NaOH+Mg²⁺-modified rice husk-derived biochars were prepared. Then all the five kinds of biochars, including the original biochar, were used as carriers of HNB to remove NH₄⁺_-N from water. Results showed that HNB was classified as <i>Pseudomonas</i>, and the 72-h NH₄⁺_-N removal ratio of the free bacteria reached 80.24%. Compared with biochar itself, biochar-based HNB immobilization body showed a much stronger ability to remove NH₄⁺_-N, especially for NaOH_- and NaOH+Mg²⁺-modified biochars. At the initial NH₄⁺_-N concentration of 100 mg/L and biochar addition dose of 10 g/L, NH₄⁺_-N removal ratio of NaOH_- and NaOH+Mg²⁺-modified biochar-based HNB immobilization bodies reached 57.78% and 58.35% after 5 h, and reached 88.66% and 90.93% after 48 h respectively, which were obviously higher than the original, HNO_3- and Mg²⁺-modified biochar-based HNB immobilization bodies. The phenomenon resulted from significantly higher bacteria adsorption ability of NaOH_- and NaOH+Mg²⁺-modified biochars, which reached 773.75 and 941.17 nmol P/g biochar, respectively.