Effects of the substrate depth on purification performance of a hybrid constructed wetland treating domestic sewage.

The depth of substrate in constructed wetlands (CWs) has a significant effect on the construction investment and the purification performance of CWs. In this study, a pilot scale CW system was operated in a domestic sewage treatment plant in Xi'an, China. The experimental systems included three-series CWs systems with substrate depths of 0.1m, 0.3 m and 0.6 m, respectively. Each series was composed of a hydroponic ditch, a horizontal subsurface flow CW and a vertical flow CW. The effluent from the primary clarifier in the sewage treatment plant was intermittently conducted to the wetlands at a flow rate of 0.3 m(3)/d. The hydraulic loading rate of each CWs system was regulated at 0.1 m(3)/m(2).d and the hydraulic retention time was 3 days. Canna indica L. was planted both in the hydroponic ditches and the CWs systems. Results showed that the highest removal efficiency of NH(+)(4)-N and TP was obtained in the hybrid CW with 0.1 m substrate depth. The average removal efficiency for NH(+)(4)-N and TP were 90.6 % and 80.0 %, respectively. The highest average removal efficiency of COD was obtained in hybrid CWs system with 0.6 m substrate depth. Therefore, a simultaneous removal of COD and nutrients can be achieved through the combination of different wetlands using different substrate depths. In addition, the substrate depth presents significant effects on the concentration of DO and root growth characteristics of canna in the system. As a result, the highest concentration of DO (>2 mg/L) and the highest amount of roots production were achieved in the 0.1 m substrate depth horizontal and vertical flow CWs.

[Distribution Characteristics and Ecological Risk Assessment of Phthalate Esters in Surface Sediments of the Songhua River].

This study assesses the spatial distribution characteristics and ecological risk of phthalate esters (PAEs) in the surface sediments of the mainstream and tributaries of the Songhua River, China, using concentrations and composition of six PAEs, which were analyzed using gas chromatography-mass spectrometery (GC-MS). We assess the ∑6PAEs ecological risk using the hazard quotient (HQ) method and environmental risk levels (ERL). The results were as follows. ① It was found that the total concentrations of ∑6PAEs ranged from 6832.5 to 36298.9 ng·g-1 dry weight (average 18388.6 ng·g-1), with the main contributions coming from di-(2-ethylhexyl) phthalate (DEHP) and di-n-butyl phthalate (DBP). The difference between the main stream ∑6PAEs (6832.5-36298.9 ng·g-1, average 18616.9 ng·g-1) and the tributary ∑6PAEs (10367.6-26593.3 ng·g-1, average 18264.1 ng·g-1) was not significant (P >0.05). The mean concentrations of individual PAEs in the tributary stream differed little from that of the main stream. The ∑6PAEs concentration of the Songhua River decreased initially but then increased from the upstream to the downstream. The average ∑6PAEs concentration in natural agricultural areas (18677.5 ng·g-1) was similar to that found in urban industrial areas (18063.7 ng·g-1), and DBP and DEHP contributed 98% of ∑6PAEs. ② The main sources of ∑6PAEs were domestic, agricultural production, and industrial production using plasticizers. ③ The ecological risk assessment indicated that DMP and BBP in the surface sediments of the Songhua River did not pose an ecological risk for aquatic organisms, and that DEP was associated with a low ecological risk, whereas DEHP and DBP posed a high ecological risk for aquatic organisms.

[Nitrogen Removal in Low-C/N Rural Sewage Treatment by Anoxic/Oxic Biofilter Packed with New Types of Fillers].

When low-concentration rural sewage is treated biologically, the effluent total nitrogen (TN) concentration often does not meet the discharge limit because of its low carbon-to-nitrogen ratio (C/N). To solve this problem, a laboratory-scale anoxic/oxic (A/O) biofilter packed with Arundo donax and activated carbon as the anoxic and aerobic column fillers (No. 2) was operated for treatment of simulated rural sewage and advanced nitrogen removal, while an ordinary gravel-packing A/O biofilter (No. 1) was set up as the control group. The results were as follows. When the influent chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), and TN concentrations were (79.47±14.21), (34.49±2.08), and (34.73±3.87) mg·L-1, respectively, the No. 1 and No. 2 reactors achieved removal efficiencies of (88.00±7.00)% and (89.00±10.00)%, (90.00±2.00)% and (97.00±7.00)%, and (37±15)% and (68±7)%, respectively. The results revealed that using Arundo donax and activated carbon new fillers could significantly enhance NH4+-N and TN removal. High-throughput sequencing results indicated that the microorganisms involved in the nitrification process in the No. 1 reactor mainly belong to Proteobacteria, whereas those in the No. 2 reactor belong to Proteobacteria and Nitrospirae. In addition, the main denitrification bacterial phyla in the anoxic column of the No. 1 reactor were Chloroflexi, Proteobacteria, Bacteroidetes, and Planctomycetes, whereas those in the anoxic column of the No. 2 reactor were primarily Bacteroidetes, Proteobacteria, Firmicutes, and Patescibacteria. Quantitative real time polymerase chain reaction (qPCR) results showed that the microbial nitrification (amoA and Nitrospira 16S rDNA), denitrification (narG, nosZ, nirS, and nirK), and anaerobic ammonium oxidation functional genes (ANAMMOX) in the No. 2 reactor were significantly higher than those in the No. 1 reactor. All the genes, except for the narG and nosZ genes, had one to two orders of magnitude of improvement in the No. 2 reactor compared to those in the No. 1 reactor.

[Effect of On-line NaClO Backwashing on Microbial Communities in an Inverted A2O-MBR System].

To study the effect of on-line NaClO backwashing on the microbial community structure of membrane bioreactor (MBR) systems, a reversed A2O-MBR reactor was used to monitor system performance, membrane fouling, and microbial community structure. Measurements were made during the stabilization stage, the on-line pure water backwashing stage, and the on-line NaClO backwashing stage. The results showed that key system performance indicators during NaClO backwashing stage, such as COD, ammonia nitrogen, and TN treatment efficiency, were similar to previous stages. The average membrane fouling rate during the on-line pure water backwashing period was lower than that of the stable stage, while the membrane fouling rate increased during the on-line NaClO backwashing stage, and EPS concentration was the highest and membrane fouling was aggravated. The results of the Chao index, Simpson index, and Shannon index showed that the microbial diversity in the aerobic tank sludge remained almost stable after on-line NaClO backwashing, while the abundance of cake layer sludge increased slightly, but the microbial diversity decreased significantly. Proteobacteria was the main microbial phylum in both the aerobic tank and cake layer sludge, followed by Bacteroidetes. After on-line NaClO backwashing, the relative abundance of Proteobacteria and Bacteroides in the aerobic tank sludge did not change notably, but the composition of filter cake sludge changed significantly. Proteobacteria that possess resistance to chlorine disinfectant increased from 53.4% to 77.8%, while Bacteroides decreased from 33.44% to 14.5%. After on-line NaClO backwashing, the composition of the microbial community in aerobic tank and cake layer was similar. Azospira and Comamonadaceaea also increased significantly after NaClO backwashing. Microbial species that can tolerate NaClO treatment may be the main cause of membrane fouling.

[Effect of Nitrogen on Magnesium Modified Biochar Adsorption to Phosphorus].

The effect of ammonia-nitrogen in water on phosphorus removal by magnesium modified biochar (MBC) was developed to increase the utilization of wetland plants. The crystal structures were measured by X-ray powder diffraction (XRD). MBC was prepared using reed as the biomass feedstock, which was modified with magnesium chloride. The raw biochar (BC) was prepared as a control. The removal of phosphate from solution using four different methods, i.e. MBC, BC, BC, and MgCl2 solutions (BC+Mg2+) and MgCl2 solutions (Mg2+), under different nitrogen to phosphorus molar ratios and initial phosphorus concentrations was investigated in batch experiments. The results demonstrated that the phosphorus removal efficiency of the four treatment methods, which followed the order of MBC>>BC+Mg2+≈Mg2+>BC. NH4+ in the solution, promoted phosphorus removal by MBC. In addition, the larger the ratio of nitrogen to phosphorus and the higher the initial phosphorus concentration, the stronger the phosphorus removal capacity of MBC was. In the three treatments with MBC, BC+Mg2+, and Mg2+, the XRD analysis showed that NH4+ reacted with Mg2+ and PO43- in the solution to form MgNH4PO4·6H2O at N:P=5 or 10, promoting the removal of phosphorus. For recycling purposes, waste biomass from constructed wetlands could be used to produce MBC and treat polluted water rich in ammonium and phosphate. Moreover, the ammonium-nitrogen promotes the phosphate removal by MBC. The results from this study provide a new theoretical basis and data support for the treatment of water eutrophication.

The largest Lyapunov exponent of chaotic dynamical system in scale space and its application.

The largest Lyapunov exponent is an important invariant of detecting and characterizing chaos produced from a dynamical system. We have found analytically that the largest Lyapunov exponent of the small-scale wavelet transform modulus of a dynamical system is the same as the system's largest Lyapunov exponent, both discrete map and continuous chaotic attractor with one or two positive Lyapunov exponents. This property has been used to estimate the largest Lyapunov exponent of chaotic time series with several kinds of strong additive noise.

[Experiment of simultaneous denitrifying phosphorus accumulation].

Denitrifying phosphorus accumulation (DNPA) and the factors affecting it were studied in a SBR with synthetic wastewater. The results showed that the sludge acclimatized under anaerobic/aerobic operation with good phosphorus removal ability, showed DNPA soon when fed nitrate instead of aeration following the anaerobic stage. Anaerobic stage was a vital premise to DNPA. If DNPA sludge was fed with nitrate prior to anaerobic stage, the DNPA would weaken even disappear. When acetate was used as sole carbon resource in the influent and nitrate did not exist in anaerobic, 1 hour of anaerobic time was optimal. NO3- -concentration in the anoxic was one of the factors affecting DNPA. When nitrate concentration was advanced from 5mg/L to 20mg/L, the percentage of DNPA increased from 11.9% to 48.7% under the condition of anaerobic(2h)-anoxic(1h)-aerobic(2h). But when the NO3- -concentration was enhanced upwards of 20mg/L, the efficiency cannot be improved. Induced DNPA did not disappear even though there was aerobic stage following anoxic stage, but the shorter the aerobic stage lasted the higher proportions of phosphorus removal via DNPA to total removal.