Stability of co-existing ZnO and TiO2 nanomaterials in natural water: Aggregation and sedimentation mechanisms.

The use of diverse engineered nanomaterials (ENMs) potentially leads to the coexistence of multiple ENMs in the natural environment. The fate such as colloidal stability, transport, and transformation of individual ENMs are dedicated to the coexistence of other types of ENMs in the environment. Here, we for the first time investigated the sedimentation behaviors of two most widely used ENMs (i.e. ZnO and TiO2 nanomaterials, nZnO and nTiO2) copresented in the natural water of China. Sedimentation rates (Vs), homo-aggregation (khom, crit) and hetero-aggregation (khet, crit) rate of nZnO and nTiO2 were calculated based on Von Smoluchowski-Stokes equation and the sedimentation mechanisms were systematically analyzed. The results showed that the coexistence of like negative charge nZnO and nTiO2 effectively enhanced the stability of either ENM by competing hetero-aggregation with natural colloids (NCs) and reducing to form homo-aggregates by the hindrance effect on particle collision. In the natural water, homo-aggregation, hetero-aggregation between ENMs and NCs, as well as the hetero-aggregation between nZnO and nTiO2 were the main aggregation and sedimentation mechanisms. The coexistence of nZnO and nTiO2 made Vs of nZnO decreased by 30.7-49.1% and Vs of nTiO2 decreased by a factor of 42.4%. Value of khet.crit between nZnO and NCs was 0.084-0.132 L mg-1 day-1, was 0.038 L mg-1 day-1 between nTiO2 and NCs, and was 0.011-0.014 L mg-1 day-1 between nZnO and nTiO2.

[Physiological responses of tubificidae to heavy metal chromium stress].

Tubificidae is now used in the wastewater treatment systems to successfully minimize the sludge production, which has been proved an effective, economical and sustainable technology. But the excess sludge inevitably contains a variety of heavy metals, especially the sludge from industrial wastewater treatment plant. In order to apply tubificidae to these systems, Chromium was selected as pollutant object and the physiological responses of tubificidae to Chromium were studied in this paper. Acute toxicity was analyzed and Median lethal concentrations (LC50) were determined over 96 h periods for Cr. Results indicated that 24 h LC50 and 96 h LC50 were 7.94 mg x L(-1) and 0.49 mg x L(-1), respectively. The duration f tubificidae in Cr solution decreased with increasing Cr concentration. Under the Cr stress, a highest respiration rate was obtained when the concentration of Cr(VI), temperature, pH and DO was 2.50 mg x L(-1), 26 degrees C, 6.0 and 6.0 mg x L(-1), respectively. The order of these factors was the concerntration of Cr(VI), temperature, DO and pH. The respiration experiments demonstrated that low concentration (< 2.50 mg x L(-1)) of Cr could promote the respiration rate of tubificidaes. On the other hand, when the concentration of Cr was 8.00 mg x L(-1), it could remarkably inhibit the respiratory rates of tubificidae.

[Effect of simulated heavy metal leaching solution of electroplating sludge on the bioactivity of Acidithiobacillus ferrooxidans].

An Acidithiobacillus ferrooxidans strain WZ-1 was isolated from the tannery sludge in Wenzhou, Zhejiang Province in China. The cell of WZ-1 strain is Gram negative and rod-shaped, its 16S rDNA sequence is closely related to that of Acidithiobacillus ferrooxidans ATCC23270 with 99% similarity. These results reveal that WZ-1 is a strain of Acidithiobacillus ferrooxidans. The effects of Ni2+, Cr3+, Cu2+, Zn2+ and 5 kinds of simulated leaching solutions of electroplating sludge on the bioactivity of Fe2+ oxidation and apparent respiratory rate of WZ-1 were investigated. The results showed that Ni2+ and Cr3+ did not have any influence on the bioactivity of WZ-1 at concentrations of 5.0 g x L(-1) and 0.1 g x L(-1), respectively. WZ-1 showed tolerance to high levels of Ni2+, Zn2+ (about 30.0 g x L(-1)), but it had lower tolerance to Cr3+ and Cu2+ (0.1 g x L(-1) Cr3+ and 2.5 g x L(-1) Cu2+). Different kinds of simulated leaching solution of electroplating sludge had significant differences in terms of their effects on the bioactivity of WZ-1 with a sequence of Cu/Ni/Cr/Zn > Cu/Ni/Zn > Cu/Cr/Zn > Cu/Ni/Cr > Ni/Cr/Zn.

[Effect of mixed carbon sources in the granulation process of EBPR system].

Activated sludge highly enriched of phosphorus accumulating organisms (PAOs) were seeded, and cultivated with mixed carbon sources of different propionate to acetate ratios, to obtain granule-based enhanced biological phosphorus removal (EBPR) system. The results showed that the granule growth rate was obviously increased as the proportion of propionate in the mixed carbon sources increased. After operating for 90 d, the volume average particle diameters of the mature granules were 550.64 microm, 599.41 microm, 642.38 microm, 680.99 microm and 745.08 microm, and the sludge volume indexes (SVI) of the mature granules were 30 mL x g(-1), 40 mL x g(-1), 50 mL x g(-1), 60 mL x g(-1) and 75 mL x g(-1), in the treatment of 0%, 25%, 50%, 75% and 100% propionate in mixed carbon sources, respectively. The phosphorus (P) removal performances of granule-based EBPR system cultivated with different carbon sources showed significant differences under the same P-loading. It was about 0.78 mg x g(-1), 2.29 mg x g(-1), 2.96 mg x g(-1), 3.23 mg x g(-1) and 3.77 mg x g(-1) of net P removed in the treatment of 0%, 25%, 50%, 75% and 100% propionate in mixed carbon sources, respectively, which resulted in the phosphorus removal efficiencies were 31.5%, 56.5%, 77.4%, 85.9% and 97.0%, respectively.

Impact of Cr(VI) on P removal performance in enhanced biological phosphorus removal (EBPR) system based on the anaerobic and aerobic metabolism.

Influence of Cr(VI) on P removal in enhanced biological phosphorus removal (EBPR) system was investigated with respect to the composition of poly-phosphate-accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs), the transformation of poly-ß-hydroxyalkanoates (PHA) and glycogen, enzymes' activities, and the intracellular Cr. Whether EBPR system could revive after Cr(VI) shock was also explored. Results showed P removal performance was completely inhibited by Cr(VI) with the concentration more than 5 mg L(-1). PAOs were more sensitive to Cr(VI) than GAOs and the other bacteria were. PHA consumption, glycogen synthesis and adenylate kinase's activity had been inhibited by 5 mg L(-1) Cr(VI). Both adenylate kinase's activity and P removal efficiency were negatively correlated with the intracellular Cr. Recovery experiments revealed that P removal performance with 5 mg L(-1) Cr(VI) shock could revive after a 2-day recovery treatment, while systems with high level Cr(VI) (20 and 60 mg L(-1)) shock could not.

[Effects of composite substrates on the phosphorus removal in granule-based EBPR system and its optimization experiment].

Based on the mature granular sludge, effects of composite substrates [m(C)/m(N)/m (P)] on the process of phosphorus removal in granule-based EBPR system was conducted by the optimal mixed-carbon sources ratio. Results showed that it was observed with the expanded filamentous bulking to granular sludge in the system of R2 [m(C)/m(N)/m (P) = 400:10:5], R3 [m(C)/m(N)/m (P) = 600: 10:10] and R5 [m(C)/m(N)/m (P) = 400:20:15]. The presence of large amount of granular fragments led to the poor performance of R6 [m(C)/m(N)/m (P) =600:20:5], and it returned back after the particulate debris was removed off the system. The particle size of R3, R8 [m(C)/m(N)/m (P) = 400:30:10] and R9 [m(C)/m(N)/m (P) = 600:30:15)] gradually decreased from 0.8 mm to 0.3 mm, and other systems were similar to the initial size. More than 95 percent of the COD was consumed in the anaerobic stage in R1 [m(C)/m(N)/m (P) = 200:10:15], R4 [m(C)/m(N)/m (P) = 200:20:10] and R7 [m(C)/m(N)/m (P) = 200:30:5], and the phosphorus release/uptake rates fluctuated within the range of 60-100 mg x (g x h)(-1), 60-80 mg x (g x h)(-1) and 40-60 mg x (g x h)(-1), respectively. However, the COD consumption was mainly occurred in aerobic stage in other systems, and the phosphorus release/uptake rates gradually declined, even decreased to 0 mg x (g x h)(-1). Phosphate removal rate of each system was (from R1 system to R9 system) 83.5%, 52.8%, 7.1%, 96.7%, 19.7%, 72.2%, 79.7%, 28.1% and 48.7%, respectively. Finally, we also found that the optimal composite substrate condition for the granule-based EBPR system was the ratio of the m(C)/ m(N)/m (P) = 200:20: 15.

[Growth kinetics of aquatic worms feeding on activated sludge].

The growth kinetics of aquatic worms was investigated from juvenile to decline phase for 18 weeks by cultivating with activated sludge in batch test. Results showed that the growth of aquatic worms well fit Gauss function for cultivating 18 weeks. The maximum specific growth rate, growth yield of aquatic worms and sludge reduction rate was 0.41 d(-1), 0.32 and 25.5%, respectively. When the concentration of substrate and dissolved oxygen change from low to high, the relationship between the specific growth rate with dissolved oxygen, and substrate concentration meet the Monod equation. Compared with the dissolved oxygen, the substrate concentration had greater effect on the specific growth rate of aquatic worms, and aquatic worms can live in the environment with low dissolved oxygen. Furthermore, the breath test showed the oxygen uptake rate of aquatic worms was almost 6.39, 10.10, 11.31 and 5.74 mg x (L x g x h)(-1) from juvenile to decline phase, the dissolved oxygen demand of the rapid growth and mature stage was higher than juvenile and decline phase.

[Removal of high concentration NH4(+) -N by nanochem zeolite ion exchange technology].

This paper assesses the potential of NanoChem zeolite for ammonia removal from synthetic solution and actual landfill leachate. The data from experiments in batch study were applied to Langmuir isotherm. The saturated amount of NH4(+) -N adsorbed per unit weight of NanoChem zeolite was about 364 mg x g(-1), which yield significantly 3-30 times higher ammonium adsorption capacity than nature zeolite and Microporous molecular sieves. The results of batch study showed that the contact time needed at least 20 h in order to attain exchange equilibrium; the ammonia removal capacity of NanoChem zeolite increased with the increase of initial ammonia concentration, while the ammonia removal rate decreased with the increase of initial ammonia concentration; the pH had an effect on ammonia removal efficiency as it can influence both the character of the exchanging ions and the NanoChem zeolite itself; regeneration made little change on ammonia removal efficiency, repeatability was good. In column study, the NanoChem zeolite was used for high ammonia nitrogen removal such as actual landfill leachate and the ammonia nitrogen was removed 100%.

[Effects of C/P on the competition between PAOs and GAOs and PHAs metabolism in EBPR system].

Based on accumulating enrich phosphorus accumulating organisms (PAOs) in activated sludge and by fluorescence in situ hybridization (FISH) technique, the effects of C/P (25: 1, 20: 1, 15: 1 and 10: 1) on flora changes and polyhydroxyalkanoates (PHAs) metabolism in enhanced biological phosphorus removal (EBPR) system were systematically studied. The results show that after 10 days treatment (acetate as carbon source), the systems with C/P of 25: 1, 20: 1 and 15: 1 have good phosphate removal rate (> 88%); while for C/P of 10: 1 system, the phosphate removal rate was 0%. FISH results showed that the content of PAOs decreased from( 76.42 +/- 1.24) % to (10.40 +/- 0.97) % with C/P decreasing from 25: 1 to 10: 1, while glycogen accumulating organisms (GAOs) increased from (16.36 +/- 3.41)% to (34.25 +/- 2.59)%. In various C/P systems in the anaerobic, the production kinetic coefficients of PHB and PHV were K25: 1 > K20: 1 > K15: 1 > K10: 1 and K15: 1 > K20: 1 > K25: 1 > K10: 1, respectively. The PHB production in the proportion of PHAs decreased from 85% to 24%, while PHV increased from 15% to 76% with C/P decreasing from 25: 1 to 10: 1. For various C/P systems in the aerobic phase, their consumption kinetic coefficients of both PHB and PHV were K:20: 1 > K25: 1 > K15: 1 > K10: 1. PHB (the proportion of PHAs is 71% -75%) was the main consumption component in C/P of the 25: 1, 20: 1 and 15: 1 systems; while PHV(the proportion of PHAs is 71%) was the main consumption component in C/P of 10: 1 system. It is suggested that an increases of GAOs and decreases of PAOs in the EBPR system lead to the decreasing of PHB production and consumption, and to the increasing of PHV.

[Full-scale experiments of municipal sewage treated by symbiotic system consisting of tubifex and microbes].

A symbiotic system consisting of tubifex and microbe was formed when tubifex was incubated in the biological contact oxidation process,the tubifex attached to the outer layer of the carriers. When the density of tubifex was about 31.3 g/L, a recycling food chain between corpse of tubifex and excrement and wastewater and microbe and sludge was formed and it could reach balance. The large scale control experimental system for treating 20,000 m3 x d(-1) municipal sewage was carried out for a long time. The result showed that tubifex could improve water quality in the effluent. When the concentration in the influent of COD,NH4+ -N,TP and SS were 130-459, 14.21-27.46, 1.60-6.93, 60-466 mg x L(-1), respectively,the removal rates of COD and SS can be improved by 8.7% and 13.6%. However, tubifex can also increase the concentration of NH4+ -N in the system,but a proper operation can make the effluent concentration of NH4+ -N below 5 mg x L(-1) stably. The symbiotic system consisting of tubifex and microbe has very good phosphorus removal efficiency. The reactor has a high toleration to loading shock and it could keep the effluent quality stable.

[Experimental research on separate structure jet aerator].

A new type of jet aerator (separate structure jet aerator) was designed and developed, and an idea of separate design was put forth. This type of jet aerator was mainly applied to the treatment of small-scale wastewater and industrial wastewater of high density treatment projects. The experimental set-up was built to investigate the influences of the structural parameters (R1, R2 and R3) on the gas suction flowrate. The experimental results are listed as follows: the gas suction flowrate fluctuates with the changes of R2, and the optimal R2 is relevant to the length of the mixing tube; R3 does not contribute a lot to the suction performance, but choosing a suitable R3 can help to make further use of the gas suction potential of the jet aerator while keeping the other parameters unchanged; R1 has a great impact on the suction performance, and the optimal R1 can be found out in the transitional region. The experiments also prove that it is feasible to apply CFD to designing jet aerator, since its gas suction flowrate is high (reaching 900 approximately 1100 L/min) and it shows prominent performance in agitating liquid.