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The superior traffic control system can promote the efficiency of mainstream expressway. As the effective method to smooth traffic system, the variable speed limits (VSL) strategies are discussed in an expressway traffic network. The dynamic OD estimation model is used to produce the real traffic information, which is loaded to the traffic network. Then, the prediction information of traffic variables and the VSL strategy are introduced to macro hierarchical control traffic flow model. A solution algorithm is further developed to find the optimal parameters of VSL by minimizing the total travel time and delay. The simulation results show that the proposed strategy perfects well, the traffic congestion is effectively alleviated, and the traffic efficiency of the road section is significantly improved. This framework can be adopted by transit managers for traffic efficiency.

The urban expressway network is the main part of the urban traffic network carrying most of the city’s traffic pressure for its continuity and rapidity, but the control method of the traffic flow was too simple to other control methods in application in addition to the ramp control and the fixed speed control. In this paper, the theory of variable speed limit (VSL) was used to develop an optimal control model based on the improved traffic flow simulation model according to the characteristics of urban expressway traffic flow. The objective of the proposed model is to minimize the delay and maximize the traffic flow. It can adjust the traffic flow on the network in space time so that the whole network is in a state of equilibrium which not only is conducive to the control of the local traffic congestion and avoids the spread of congestion but also improves the traffic safety. The SPSA-based solution algorithm was proposed by taking into account the needs of real-time online applications. It can not only ensure the accuracy of the solution but also meet the requirements of the simulation time. The simulation results show that the variable speed limit can be optimized in moderate demand, and the proposed model and algorithm are effective and feasible in this paper. The conclusions are useful to help the traffic management department to formulate reasonable traffic control strategies.

Inductively coupled plasma mass spectrometry (ICP-MS) has been developed as an accurate and sensitive technique for multi-elemental or isotopic analysis. There are many circumstances in which the i...

With the rapid urbanization during the past three decades in China, the urban expressway network has arisen with large numbers in many cities. However, the traffic conditions are becoming worse and worse. One of the main reasons is that the connected sections of main road and expressway do not have a coordination by the intersection signal and variable speed limits (VSL) on expressway. In this paper, a new cooperation optimization model of VSL on urban expressway and the intersection signal timing are proposed based on the mesoscopic traffic flow model. Its objective is to minimize the total delay and the number of parking. Its essence is adjusting traffic flow on the network in space-time so that the whole network can be in a state of equilibrium. It is effective to the control of local traffic congestion and can avoid the spread of congestion, thus improving traffic safety. Additionally, the optimal VSL strategy is proposed. And then a solution algorithm based on the simultaneous perturbation stochastic approximation (SPSA) is designed for the proposed model. In the end, a practical example of Yanshan overpass in Ji’nan elevated expressway is used to validate the effectiveness of the proposed method. The simulation results are satisfactory. The conclusions are very useful for traffic management department to implement reasonable traffic control strategy.

A mechanism for carbamazepine (CBZ) sorption by mangrove plant residue-derived biochars pyrolyzed at 200-700 °C (referred as MPR200-MPR700) was elucidated in this study. The experimental results demonstrated that the dominant sorption mechanism of biochars for CBZ was evolved from partition to adsorption with increasing pyrolysis temperature. The CBZ concentration-dependent contributions of partition and adsorption were controlled by the relative noncarbonized and carbonized fractions of biochars. The partition medium changed from a polymeric aliphatic fraction (mangrove plant residue [MPR]200-MPR400) to a more condensed aromatic phase (MPR500-MPR600), which made the partition less favorable. Meanwhile, the adsorption was selectively regulated by polarity (MPR200-MPR300) and porosity (MPR400-MPR700) for different biochars. A pragmatic model including the sorbent aromaticity index (H/C) was put forward to predict CBZ sorption to MPR200-MPR700 and other carbonaceous materials reported in the literature. The findings can be helpful in understanding CBZ-biochar interactions and developing effective sorbents (such as biochars) for pollutant sequestration.

Oxidation of Cr(III) by birnessite (δ-MnO

The vegetation deterioration and pollution expansion from non-ferrous metal tailings pond have been found in many countries leading to water soil erosion and human health risk. Conventional ecological remediation technologies of mine tailings such as capping were costly and elusive. This study provided an economic and effective model as an alternative by substrate amelioration and vegetation restoration. A field experiment was carried out on a silver tailings pond in southwest China. Tailings substrate was ameliorated by adding organic matter (decomposed chicken manure, DCM), structural conditioner (polyacrylamide, PAM), water-retaining agent (acrylic acid-bentonite water-retaining agent, AAB), and heavy metal immobilizer (biofuel ash, BFA), which were optimized by laboratory experiment. Native heavy metal hyperaccumulator, Bidens pilosa, was colonized. Vegetation coverage and plant height of Bidens pilosa reached about 80% and over 30 cm respectively after 3 months, and the turbidity of tailings leaching solution decreased by 60%. The practice showed that the proportion of available heavy metals in tailings substrate was significantly lower than that in the soil surrounding mining area. Immobilization didn't have stabilization effect on Cd, Zn, and Pb, and As was only 0.002%, phytoremediation had stabilization effect of Cd, Zn, As, and Pb were 2.5-3.5%, 1-2%, 0.25-0.5%, and 0.25-0.75%. Phytoremediation was more effective significantly in controlling heavy metal pollution risk of tailings than immobilization. These results provided a new ecological remediation OSA-NHC model, meaning a combination of optimal substrate amelioration and native hyperaccumulator colonization, which could achieve vegetation restoration and augment heavy metal pollution control in non-ferrous metal tailings pond.

A novel fully passive permeable reactive barrier (PRB) with oxygen-releasing compound (ORC) and clinoptilolite was proposed for the removal of ammonium-nitrogen from groundwater. The PRB involves a combination of oxygen release, biological nitrification, ion exchange, and bioregeneration. A pilot-scale performance comparison experiment was carried out employing three parallel columns to assess the proposed PRB. The results showed that the PRB achieved nearly complete NH 4 + - N depletion (>99%). NH 4 + - N of 5.23–10.88 mg/L was removed, and NO 2 − - N of NO 3 − - N of 2.03–19.67 mg/L were generated. Ion exchange and biological nitrification both contributed to NH 4 + - N removal, and the latter played a dominant role under the condition of sufficient oxygen. Biological nitrification favored a delay in sorption saturation and a release of exchange sites. The ORC could sufficiently, efficiently supply oxygen for approximately 120 pore volumes. The clinoptilolite ensured a robust NH 4 + - N removal in case of temporary insufficient biological activities. No external alkalinity sources had to be supplied and no inhibition of aerobic metabolism occurred. The ceramicite had a negligible effect on the biomass growth. Based on the research findings, a full-scale continuous wall PRB was installed in Shenyang, China in 2012.

In situ remediation of ammonium-contaminated groundwater is possible through a zeolite permeable reactive barrier (PRB); however, zeolite's finite sorption capacity limits the long-term field application of PRBs. In this paper, a pilot-scale PRB was designed to achieve sustainable use of zeolite in removing ammonium (NH(4)(+)-N) through sequential nitrification, adsorption, and denitrification. An oxygen-releasing compound was added to ensure aerobic conditions in the upper layers of the PRB where NH(4)(+)-N was microbially oxidized to nitrate. Any remaining NH(4)(+)-N was removed abiotically in the zeolite layer. Under lower redox conditions, nitrate formed during nitrification was removed by denitrifying bacteria colonizing the zeolite. During the long-term operation (328 days), more than 90% of NH(4)(+)-N was consistently removed, and approximately 40% of the influent NH(4)(+)-N was oxidized to nitrate. As much as 60% of the nitrate formed in the PRB was reduced in the zeolite layer after 300 days of operation. Removal of NH(4)(+)-N from groundwater using a zeolite PRB through bacterial nitrification and abiotic adsorption is a promising approach. The zeolite PRB has the advantage of achieving sustainable use of zeolite and immediate NH(4)(+)-N removal.

Nitrogen as ammonium (NH4+-N) is one of the most common nitrogen contaminants in groundwater; this is particularly true in the industrial and agricultural regions of northern China, where rapid population growth and economic development have stressed public water supplies and reduced groundwater quality. In this study, we report the performance of a zeolite permeable reactive barrier (PRB) designed to remove ammonium from contaminated river water that infiltrates to a groundwater aquifer that serves as a drinking water supply for the city of Shenyang. Groundwater monitoring data obtained over 5 months of operation indicate that ammonium concentrations in the groundwater decreased from 2–10 mg/L to

A new composite adsorbent, zeolite-supported microscale zero-valent iron (Z-mZVI) was evaluated as a potential adsorbent for the removal of Cd

In order to remediate ammonium contaminated groundwater, an innovative multimedia permeable reactive barrier (M-PRB) was proposed, which consisted of sequential columns combining oxygen releasing compound (ORC), zeolite, spongy iron and pine bark in the laboratory scale. Results showed that both ammonium and nitrate could be reduced to levels below the regulatory discharge limits through ion exchange and microbial degradation (nitrification and denitrification) in different compartments of the M-PRB system. The concentration of dissolved oxygen (DO) increased from 2 to above 20 mg/L after the simulated groundwater flowed through the oxygen releasing column packed with ORC, demonstrating that ORC could supply sufficient oxygen for subsequent microbial nitrification. Ammonium was efficiently removed from about 10 to below 0.5 mg N/L in the aerobic reaction column which was filled with biological zeolite. After 54 operating days, more than 70% ammonium could be removed by microbial nitrification in the aerobic reaction column, indicating that the combined use of ion exchange and nitrification by biological zeolite could ensure high and sustainable ammonium removal efficiency. To avoid the second pollution of nitrate produced by the former nitrification, spongy iron and pine bark were used to remove oxygen and supply organic carbon for heterotrophic denitrification in the oxygen removal column and anaerobic reaction column separately. The concentration of nitrate decreased from 14 to below 5 mg N/L through spongy iron-based chemical reduction and microbial denitrification.

A novel sequential permeable reactive barrier (multibarrier), composed of oxygen-releasing compound (ORC)/clinoptilolite/spongy iron zones in series, was proposed for ammonium-nitrogen-contaminated groundwater remediation. Column experiments were performed to: (1) evaluate the overall NH4 +–N removal performance of the proposed multibarrier, (2) investigate nitrogen transformation in the three zones, (3) determine the reaction front progress, and (4) explore cleanup mechanisms for inorganic nitrogens. The results showed that NH4 +–N percent removal by the multibarrier increased up to 90.43 % after 21 pore volumes (PVs) at the influent dissolved oxygen of 0.68∼2.45 mg/L and pH of 6.76∼7.42. NH4 +–N of 4.06∼10.49 mg/L was depleted and NO x −–N (i.e., NO3 −–N + NO2 −–N) of 4.26∼9.63 mg/L was formed before 98 PVs in the ORC zone. NH4 +–N of ≤4.76 mg/L was eliminated in the clinoptilolite zone. NO x −–N of 10.44∼12.80 mg/L was lost before 21 PVs in the spongy iron zone. The clinoptilolite zone length should be reduced to 30 cm. Microbial nitrification played a dominant role in NH4 +–N removal in the ORC zone. Ion exchange was majorly responsible for NH4 +–N elimination in the clinoptilolite zone. Chemical reduction and hydrogenotrophic denitrification both contributed to NO x −–N transformation, but the chemical reduction capacity decreased after 21 PVs in the spongy iron.