Responses of Nitrogen and Phosphorus Removal Performance and Microbial Community to Fe3O4@SiO2 Nanoparticles in a Sequencing Batch Reactor

Stability of aerobic granular sludge for simultaneous nitrogen and Pb(II) removal from inorganic wastewater

ABSTRACTIn this paper, we proposed a strategy for the establishment of an aerobic granular sludge (AGS) system for simultaneous nitrogen and Pb(II) removal from inorganic wastewater. AGS was stored in lead nitrate solution to select functional bacteria resistant to lead poison, and then an AGS system for ammonia nitrogen (180-270 mg/L) and Pb(II) (15-30 mg/L) removal was established based on carbon dosing and a two-stage oxic/anoxic operational mode. After storage for 40 days, the stability of AGS decreased because specific oxygen uptake rate, nitrification rate and abundance of Nitrosomonas decreased to different degrees compared with those before storage. During the first 70 days of the recovery process, AGS in R1 (the blank reactor) and R2 (the control reactor) both experienced a first breakage and then regranulation process. The main properties of AGS in reactors R1 and R2 tended to be stable after days 106 and 117, respectively, but the structure of steady-state AGS in R2 was more compact. The total inorganic nitrogen (TIN) in effluent from R1 and R2 basically remained below 25 mg/L after days 98 and 90, respectively. The Pb(II) concentration in effluent from R2 was always below 0.3 mg/L. On day 140, the relative abundance of Nitrosomonas in R2 (6.17%) was significantly lower than that in R1 (12.15%), whereas the relative abundance of denitrifying bacteria was significantly higher than that in R1 (62.44% and 46.79%). The system removed 1 kg of influent TIN only consuming approximately 1.85 kg of carbon source, demonstrating clear advantages in energy savings.

Cultivation of autotrophic nitrifying granular sludge for simultaneous removal of ammonia nitrogen and Tl(I)

Autotrophic nitrifying granular sludge (ANGS) was cultivated for the simultaneous removal of ammonia nitrogen and Tl(I) from inorganic wastewater. The chemical oxygen demand (COD) in the influent gradually decreased to approximately zero in four parallel sequencing batch reactors (B1: blank controller, B2: 10 mL of added nitrifying bacteria concentrate in each cycle, B3: 1 mg/L Tl(I) added in each cycle and B4: 10 mL of added nitrifying bacteria concentrate and 1 mg/L Tl(I) in each cycle) within 15 days. The main properties, such as the granulation rate and specific oxygen uptake rate (SOUR) of the ANGS in B1, B2, B3 and B4 tended to be stable within 40, 33, 30 and 33 days, the removal efficiencies of Tl(I) were 59.5%-82.9% and 57.1%-88.6% in B3 and B4 after Day 30, the removal efficiencies of ammonia nitrogen in B1, B2, B3 and B4 were usually above 90% after Day 33, and the total inorganic nitrogen (TIN) in the effluent of B1, B2, B3 and B4 gradually stabilized after Day 36, 32, 32 and 36, indicating that mature ANGS was successfully cultivated in B1, B2, B3 and B4 within 40, 33, 33 and 36 days. The nitrogen degradation kinetic parameters of ANGS indicated that B3 had the strongest ability to remove ammonia and nitrite, suggesting that Tl(I) stress was beneficial to ammonia nitrogen removal and nitrite oxidation. The adsorption of Tl(I) can be described by the Freundlich equation, and the addition of external nitrifying bacteria improved the adsorption ability of ANGS.

Fe3O4-Fused Magnetic Air Stone Prepared From Wasted Iron Slag Enhances Denitrification in a Biofilm Reactor by Increasing Electron Transfer Flow

nFe₃O₄ was prepared from waste iron slag and loaded onto air stone (named magnetic air stone or MAS in the following text). The main component of air stone is carborundum. To study the magnetic effects of MAS on denitrification, a biofilm reactor was built, and its microbial community structure and electron transfer in denitrification were analyzed. The results showed that MAS improved the performance of the reactor in both carbon and nitrogen removal compared with air stone (AS) control, and the average removal efficiencies of COD, TN, and NH₄⁺-N increased by 17.15, 16.1, and 11.58%, respectively. High-throughput sequencing revealed that magnetism of MAS had a significant effect on the diversity and richness of microorganisms in the biofilm. The MAS also reduced the inhibition of rotenone, mipalene dihydrochloride (QDH), and sodium azide on the respiratory chain in denitrification and enhanced the accumulation of nitrite, in order to provide sufficient substrate for the following denitrification process. Therefore, the denitrification process is accelerated by the MAS. The results allowed us to deduce the acceleration sites of MAS in the denitrification electron transport chain.

The existence of MAS provides a new rapid method for the denitrifying electron transport process. Even in the presence of respiratory inhibitors of denitrifying enzymes, the electron transfer acceleration provided by MAS still exists objectively. This is the mechanism through which MAS can restore the denitrification process inhibited by respiratory inhibitors to a certain extent.

Responses of nitrogen removal under microplastics versus nanoplastics stress in SBR: Toxicity, microbial community and functional genes

Microplastics (MPs) and nanoplastics (NPs), as emerging pollutants, are frequently detected in wastewater treatment plants. However, studies comparing the effects of MPs versus NPs on nitrogen removal by activated sludge are rarely reported. Here, the responses of nitrogen removal performance, microbial community and functional genes to MPs and NPs in sequencing batch reactors were investigated. Results revealed that MPs (10 and 1000 μg/L) had no effects on nitrogen removal. While upon exposure to NPs, although low concentration (10 μg/L) of NPs showed no remarkable influence on nitrogen removal, high level (1000 μg/L) of NPs decreased NH₄⁺-N removal efficiency by 24.48% and caused accumulation of NO₃^--N and NO₂^--N. These inhibitory probably due to the acute toxicity of NPs to activated sludge, which was reflected by the increasing reactive oxygen species generation and lactate dehydrogenase release. The toxic effects of NPs further declined the relative abundance of nitrifiers (e.g., Nitrospira) and denitrifiers (e.g., Dechloromonas). These negative effects, accompanied by a decrease in abundance of amoA and nxrA genes related to nitrification (30.01% and 65.24% of control) and narG, nirK and nirS genes associated with denitrification (78.59%, 61.39%, and 86.17% of control), directly illustrated the attenuate phenomenon observed in nitrogen removal.

Study on Water Purification Effect and Operation Parameters of Various Units of Wastewater Circulation

The discharge of wastewater from aquaculture ponds causes a certain degree of damage to the environment. It is necessary to continuously improve the treatment efficiency of wastewater treatment devices. The purpose of this study is to obtain an optimal ratio of wastewater circulation devices in order to obtain the best operating parameters and to reduce the discharge of polluted water. We constructed an experimental wastewater circulation device consisting of three units. The primary unit contained modified attapulgite (Al@TCAP-N), volcanic stone, and activated carbon for precipitation. The secondary and tertiary units used biological methods to enhance removal rates of nitrogen and phosphorus. Water quality indicators of total phosphorus (TP), total nitrogen (TN), ammonia (NH3-N), permanganate (CODMn), and total suspended solids (TSS) were detected. Water quality was tested under different matching ratios for three units of different hydraulic retention time (HRT) and load Results showed that the removal rate of TP, TN, NH3-N, and TSS reached 20–60%, 20%, 30–70%, and 10–80%, respectively. The average reduction efficiencies of secondary module chlorella and filler on TP, TN, NH3-N, CODMn, and TSS were 56.88%, 30.09%, 0.43%, 46.15%, and 53.70%, respectively. The best removal rate can be achieved when the matching ratio of each unit becomes 2:1:1 and the hydraulic retention time is maintained within 2 h in the high-concentration load. Finally, the average removal rates of TP, TN, NH3-N, and TSS reached 58.87%, 15.96%, 33.99%, and 28.89%, respectively. The second unit obtained the enhanced removal effect in this wastewater treatment system when adding microorganisms and activated sludge.

Bacterial Community Structure and Dynamic Changes in Different Functional Areas of a Piggery Wastewater Treatment System

Chemicals of emerging concern (CEC) in pig farm breeding wastewater, such as antibiotics, will soon pose a serious threat to public health. It is therefore essential to consider improving the treatment efficiency of piggery wastewater in terms of microorganisms. In order to optimize the overall piggery wastewater treatment system from the perspective of the bacterial community structure and its response to environmental factors, five samples were randomly taken from each area of a piggery’s wastewater treatment system using a random sampling method. The bacterial communities’ composition and their correlation with wastewater quality were then analyzed using Illumina MiSeq high-throughput sequencing. The results showed that the bacterial community composition of each treatment unit was similar. However, differences in abundance were significant, and the bacterial community structure gradually changed with the process. Proteobacteria showed more adaptability to an anaerobic environment than Firmicutes, and the abundance of Tissierella in anaerobic zones was low. The abundance of Clostridial (39.02%) and Bacteroides (20.6%) in the inlet was significantly higher than it was in the aerobic zone and the anoxic zone (p < 0.05). Rhodocyclaceae is a key functional microbial group in a wastewater treatment system, and it is a dominant microbial group in activated sludge. Redundancy analysis (RDA) showed that chemical oxygen demand (COD) had the greatest impact on bacterial community structure. Total phosphorus (TP), total nitrogen (TN), PH and COD contents were significantly negatively correlated with Sphingobacteriia, Betaproteobacteria and Gammaproteobacteria, and significantly positively correlated with Bacteroidia and Clostridia. These results offer basic data and theoretical support for optimizing livestock wastewater treatment systems using bacterial community structures.