Yanchen Liu

Study of operational conditions of simultaneous nitrification and denitrification in a Carrousel oxidation ditch for domestic wastewater treatment.

The study on the operational conditions of simultaneous nitrification and denitrification (SND) in the channel of oxidation ditch (OD) without the need for a special anoxic tank was carried out based on lab-scale and pilot-scale experiments using real domestic wastewater. The influence of sludge loading and component proportion in influent, temperature, hydraulic retention time (HRT), dissolved oxygen (DO) and operational mode on SND was investigated. The result indicated that the optimal DO (ODO) of SND occurrence was confirmed majorly by the sludge loading of influent and temperature, the high TCOD/NH(3)-N and short HRT can enhance the occurrence of SND. A new operational mode was proposed that achieved a higher removal efficiency of 60-70% for total nitrogen by SND with HRT of 4-6h, and the concentrations of NH(3)-N and TN in effluent are less than 5 and 15 mg/L, respectively.

Aggregation behavior of engineered nanoparticles and their impact on activated sludge in wastewater treatment

The ever-increasing daily use of engineered nanoparticles will lead to heightened levels of these materials in the environment. These nanomaterials will eventually go into the wastewater treatment plant (WWTP), therefore, resulting into a pressing need for information on their aggregation behavior and kinetics in the wastewater aqueous matrix. In this work, we dispersed two different metal oxide nanoparticles (ZnO and TiO2) into the influent of two different WWTPs. Through the time-resolved dynamic light scattering analysis and transmission electron microscopy, the metal oxide nanoparticles (NPs) were quite stably existed in the wastewater matrix with aggregates of diameter 300-400 nm after 4.5h or more suspension. We confirmed that the dissolved organic matters (DOMs) attributed to the stability of nanoparticles. No propensity of NPs to aggregate were observed in the presence of both monovalent and divalent electrolytes even at high concentrations up to 0.15 M in NaCl or 0.025 M in CaCl2, indicating that the destabilization of nanoparticles in the complicated wastewater matrix was not achieved by the compression of electrical double layer, therefore, their aggregation kinetics cannot be simply predicted by the classic Derjaguin-Landau-Verwey-Overbeek theory of colloidal stability. However, obvious aggregation of nanoparticles in the Al2(SO4)3 solution system was observed with the likely mechanism of bridging of the metal oxide nanoparticles and aggregates due to the formation of hydrous alumina (Al(OH)3·H2O) in the Al2(SO4)3 solution. In the wastewater matrix, we used the noninvasive measurement technology to detect the O2 flux of activated sludge before and after treatment with 1, 10 and 100 mg L(-1) NPs. The results confirmed that both ZnO and TiO2 NPs showed an adverse impact on the O2 uptake of activated sludge when the exposure time extended to 4.5 h.

Inhibition of chemical dose in biological phosphorus and nitrogen removal in simultaneous chemical precipitation for phosphorus removal

A study on the influence of chemical dosing on biological phosphorus and nitrogen removal was carried out through batch experimental tests by lab-scale and a full-scale wastewater treatment plant (employing a typical anaerobic-anoxic-oxic treatment). Results indicated that the inhibition of aluminum salt on biological phosphorus release and uptake processes is significant, as well as the inhibition of aluminum salt on Ammonia-Oxidizing Bacteria (AOB) is dominantly observed in the nitrification process and is recoverability. The inhibition of iron salt in biological phosphorus and nitrogen removal is weak, and only the inhibition of iron salt on phosphorus release at anaerobic periods emerge under large dosing. Evidence shows persistent inhibition from the accumulation of chemical doses in sludge mass. Intermittent chemical dosing proves recommendable for simultaneous chemical phosphorus removal.

Ultrasonic Treatment Enhanced Ammonia-Oxidizing Bacterial (AOB) Activity for Nitritation Process

Oxidation of ammonia to nitrite rather than nitrate is critical for nitritation process for wastewater treatment. We proposed a promising approach by using controlled ultrasonic treatment to enhance the activity of ammonia-oxidizing bacteria (AOB) and suppress that of nitrite-oxidizing bacteria (NOB). Batch activity assays indicated that when ultrasound was applied, AOB activity reached a peak level and then declined but NOB activity deteriorated continuously as the power intensity of ultrasound increased. Kinetic analysis of relative microbial activity versus ultrasonic energy density was performed to investigate the effect of operational factors (power, sludge concentration, and aeration) on AOB and NOB activities and the test parameters were selected for reactor tests. Laboratory sequential batch reactor (SBR) was further used to test the ultrasonic stimulus with 8 h per day operational cycle and synthetic waste urine as influent. With specific ultrasonic energy density of 0.09 kJ/mg VSS and continuously fed influent containing above 200 mg NH3-N/L, high AOB reproductive activity was achieved and nearly complete conversion of ammonia-N to nitrite was maintained. Microbial structure analysis confirmed that the treatment changed community of AOB, NOB, and heterotrophs. Known AOB Nitrosomonas genus remained at similar level in the biomass while typical NOB Nitrospira genus disappeared in the SBR under ultrasonic treatment and after the treatment was off for 30 days.

Response to shock load of engineered nanoparticles in an activated sludge treatment system: Insight into microbial community succession.

The environmental impacts of the use of engineered nanoparticles (NPs) remain unclear and have attracted increasing concern worldwide. Considering that NPs eventually end up in wastewater treatment systems, the potential impact of ZnO and TiO2 NPs on the activated sludge was investigated using laboratory-scale sequencing batch reactors (SBRs). Short-term (24 h) exposure to 1, 10 and 100 mg/L shock loads of NPs reduced the oxygen uptake rate of the activated sludge by 3.55%-12.51% compared with the controls. In our experiment, the toxicities of TiO2 NPs were higher than those of ZnO NPs as reflected in the inhibition of oxygen utilization in the activated sludge. However, both the short-term (24 h) and long-term (21 days) exposure to ZnO and TiO2 NPs did not adversely affect the pollutant removal of the SBRs. Furthermore, the polymerase chain reaction-denaturing gel gradient electrophoresis revealed that the microbial community did not significantly vary after the short-term exposure (24 h) to 1, 10 and 100 mg/L shock loads of NPs; however, the cluster analysis in our experiment revealed that the slight difference caused by the NPs largely depended on exposure time rather than on NP type and NP concentration. The long-term exposure (13 days) to 10 mg/L shock load of ZnO or TiO2 NPs caused no substantial microbial community shifts in the activated sludge. The microbial diversity also showed no significant change when exposed to NPs as revealed by the Shannon-Wiener index.

Use of low frequency and density ultrasound to stimulate partial nitrification and simultaneous nitrification and denitrification.

Low frequency and density ultrasound has attracted considerable attention in enhancing wastewater treatment performance, particularly in the removal of nitrogen. In the present study, two sequencing batch reactors were operated to confirm the effects of ultrasound at the frequency of 40 kHz and density of 0.027 W/mL on partial nitrification and simultaneous nitrification and denitrification (SND). At the optimal irradiation time of 2.0 h, the obtained nitrite accumulation ratio and SND efficiency at full aerobic were 73.9% and 72.8%, respectively. Nitrite accumulation was the result of increased NH4(+)-N removal and improved ammonia oxidizing bacteria (AOB) activity with simultaneous inhibition of nitrite oxidizing bacteria (NOB) activity. Ultrasonic treatment could provide suitable conditions in temperature and pH for AOB growth, and destroy the NOB community structure. Moreover, organic matters were released and offered an additional carbon source for denitrification apart from the negative effects on sludge properties.

Distribution and population structure characteristics of microorganisms in urban sewage system

The sewage system functions as an important public infrastructure. The survived microbial population inside the sewage system plays an important role in the biochemical process during wastewater transportation within the system. The study aims to investigate the microbial communities spatial distribution inside manholes and sewage pipes by using the massive parallel 454 pyrosequencing combined with denaturing gradient gel electrophoresis of V1–V3 regions of 16S rRNA. The microbial structure, distribution characteristic, taxonomic composition analysis, and compositional overlaps of the microbial community both were conducted. The result indicated that the changes in microbial diversity exhibited a consistent trend with average dehydrogenase activity. Proteobacteria, Firmicutes, and Anaerolineae were the dominant bacteria in the sewage system. The microbial community exhibited distinguishing characteristics in comparison with fecal, surface water, and wastewater treatment process. Parachlamydia acanthamoebae, Zymophilus paucivorans, and uncultured Epsilon proteobacterium were mainly found at the upper position of the manhole, while Microbacterium sp. was mainly found at the lower position. Longilinea, Georgenia, and Desulforhabdus were mainly observed in the sewage pipe. The microbial bacteria that survived in the anaerobic environment (i.e., sulfate reduction bacteria groups) exhibited a significant positive relationship with anaerobic crucial environmental factors in the redundancy analysis.

Reusable DNA-functionalized-graphene for ultrasensitive mercury (II) detection and removal

Mercury is a bioaccumulative and highly toxic heavy metal. Thus, the removal and detection of Hg2+ from the environment is a major challenge. This paper reports a novel bio-nanomaterial for the simultaneous determination and removal of Hg2+ with the use of rGO-Fe3O4 functionalized with Hg2+-specific thymine oligonucleotide (T-DNA). T-DNA interacts with Hg2+ and changes from having a random coil into a hairpin structure, thereby increasing the fluorescence of SYBR Green I. Such fluorescence turn-on process allows the detection of Hg2+ in the concentration range of 1-20ng/mL, with a detection limit of 0.82ng/mL. Removal is achieved by exploiting the T-Hg2+-T base pairs and the large surface area of graphene; these bio-nanocomposites exhibit excellent removal efficiency (over 80%) and rapid separation from the aqueous solution. Moreover, bio-nanomaterials can be regenerated after a simple treatment. The proposed method also demonstrates the evident practicability of the simultaneous detection and removal of Hg2+ in lake water samples.

Study on a discrete-time dynamic control model to enhance nitrogen removal with fluctuation of influent in oxidation ditches

The aim of study was proposed a new control model feasible on-line implemented by Programmable Logic Controller (PLC) to enhance nitrogen removal against the fluctuation of influent in Carrousel oxidation ditch. The discrete-time control model was established by confirmation model of operational conditions based on a expert access, which was obtained by a simulation using Activated Sludge Model 2-D (ASM2-D) and Computation Fluid Dynamics (CFD), and discrete-time control model to switch between different operational stages. A full-scale example is provided to demonstrate the feasibility of the proposed operation and the procedure of the control design. The effluent quality was substantially improved, to the extent that it met the new wastewater discharge standards of NH(3)-N<5mg/L and TN<15 mg/L enacted in China throughout a one-day period with fluctuation of influent.

Study on enhanced denitrification using particulate organic matter in membrane bioreactor by mechanism modeling.

Particulate organic matter (POM) in wastewater is a potential denitrification carbon source, while the optimal operational mode using denitrification mechanism with POM is still unclear in wastewater treatment plants. In this work, we investigated the denitrification rates (DNRs) in a full-scale membrane bioreactor (MBR) coupled with two-stage pre-anoxic (pre-AN), and then evaluated the POM denitrification efficiency using mechanism modeling. The results indicate that POM related fraction accounted for the majority of the obtained specific DNR of 1.39±0.46mgNg(-1) MLVSS h(-1) in the second pre-AN without available soluble carbon source. The modeling approaches with calibration and validation procedures estimated a high residual POM concentration of 0.17g COD g(-1) MLVSS in the activated sludge, which provided specific DNR of 1.14mgNg(-1) MLVSS h(-1). High POM retention time in the reactor was the result of high solid retention time used in the MBR. In particular, post-AN of high biomass concentration could provide the highest POM denitrification efficiency in MBR. The MBR process combined with additional sludge reduction technology could further enhance denitrification by POM.