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Air in the headspace of sewer laterals can be driven by the flowing sewage as well as air pressure. In this study, the openings on manholes for air flow are approximated as a thin continuous slot at the laterals. In this way, the governing equations can be solved analytically for infinitely long laterals without water flow. For cases with water flow, a numerical solution is developed. It is found that the air flow pattern in a long lateral can be categorized into three zones. The zone closest to the trunk is defined as the "zone of influence," where the air flow in the lateral is dominated by air pressure, and the air pressure and air velocity decay exponentially in the lateral. The second zone is named as "zone of equilibrium" where the air pressure gradient is zero and the air flow is only driven by the drag of water and can be calculated analytically. The air flow zone farthest from the trunk is defined as the "zone of induction" where the air is inducted into the system for mass balance in the system. An explicit fitting expression on the air velocity and water velocity in a long lateral is provided. A graphic solution for air velocity and zone of influence is also developed for a quick estimation on the air movement in sewer laterals. [ABSTRACT FROM AUTHOR]

Current designs of sanitary collection systems normally only consider the transport of wastewater without attention on the air movement in the sewer airspaces. Under anaerobic conditions, hydrogen sulfide (H 2 S) can be generated in the liquid phase in sewer systems. H 2 S is corrosive to concrete and steel structures and odorous or even toxic to human, which can cause corrosion and sewer odor issues. To develop a feasible sewer corrosion and odor control strategy, it is necessary to understand the mechanisms of air flow in sewer systems for developing practical tools to predict and control the air flow. This paper comprehensively reviewed previous efforts on modeling the air flow in sewer systems and provided recommendations on predicting the air flow for engineering applications. The air flow in a single pipe was firstly reviewed followed by the air flow in sewer structures as well as air flow models in sewer networks. Some other considerations such as temperature driven flow, transient water flow, and wind effect were also reviewed. The knowledge gaps were then identified, and recommendations on the further studies were provided. [ABSTRACT FROM AUTHOR]

Hydropower operations can induce significant variation of velocity field upstream of intakes and may lead to fish entrainment into turbines. In this study, the flow fields upstream of a high dam in China under different intake and spillway operation patterns were investigated theoretically using potential flow solution and computational fluid dynamic modeling, and experimentally in a 1:50-scale physical model. Flow fields induced by multiple intakes and by a line sink tends to be the same at about two times of the distance of adjacent operating intake upstream of the intakes. Different operation scenarios were analyzed to improve the general understanding of characteristics of upstream flow and to reduce the risk of fish entrainment. The extent of the risk zone for fish entrainment defined by specified thresholds of velocity and acceleration indicate that smaller water depth over submerged intake means a higher risk of fish entrainment. [ABSTRACT FROM AUTHOR]

Knowledge of the build-up and erosion behaviour of sewer sediment is necessary to facilitate better sediment management strategies. The dynamic behaviours of sediment in specific deep combined sewer overflow (CSO) chambers in Liuzhou, China, were studied through a field investigation in this paper. The results presented show that the chambers suffered from sediment problems of varying severity, and the severity depends on the dry weather flow rate. The sediment layers in chambers reached a certain balance with dry and wet weather flow rate, respectively. It can be classified as irreversible and reversible according to its mobility. The former has a low environmental impact because of its limited mobility and low organic content, and its increasing rate is extremely low year by year, whereas the latter has a highly pollutant content, and is the major cause of sewer odour and CSO pollution. The removal of this layer is seen to be a very important aspect of sewer sediment management. [ABSTRACT FROM AUTHOR]

It is well known that model-building of chlorine decay in real water distribution systems is difficult because chlorine decay is influenced by many factors (e.g., bulk water demand, pipe-wall demand, piping material, flow velocity, and residence time). In this paper, experiments were run to investigate the kinetic model of chlorine decay and the formation model of trihalomethanes (THMs) in pilot-scale water distribution systems. Experimental results show that the rate constants of chlorine decay, including wall decay and bulk decay, increasing with temperature. Moreover, the kinetic model of chlorine decay and the formation model of THMs describe experiment data of pilot-scale water distribution systems. The effect of different piping material on chlorine decay and THMs formation were also investigated. The rate constants of chlorine decay are ranked in order: stainless steel pipe, ductile iron pipe, and last, polyethelene pipe because wall decay is the largest in stainless steel pipe than that in other piping material. Correspondingly, the rate of THMs formation follows the order of stainless steel pipe, ductile iron pipe, and last, polyethelene pipe because of less chlorine in bulk water reacting with the trihalomethane formation potential (THMFP). [ABSTRACT FROM AUTHOR]

Abstract: The rapid economic growth in China has caused ever-increasing pollution and gradual deterioration of surface water quality over the whole territory of China since 1978. Along with it, there have been 130 environmental protection policies publicized and enacted. Unfortunately, even though these contradictory phenomena have coexisted for almost three decades, the cause analysis and the effective evaluation of policy measures are still rare. The Jiaxing region, a lowland located at the Taihu Lake watershed, is a typical representative of this dilemma and was proposed as a case study area for an assessment on the effectiveness of the environmental policy measures mentioned above. The pollutant loads originating from point pollution sources were discharged into rivers at fixed in-stream sites, while pollutant loads from non-point pollution sources in rural areas were assumed to be rushed into rivers by stormwater runoff. The environmental policy measures concerning water quality in the Jiaxing region were specified quantitatively as parameters for estimating the variation of pollutant loads. The base case and other three cases with the effects of policy measures were then simulated by the surface water quality models. The results show that a significant improvement of the surface water quality can be achieved by controlling the non-point pollution in rural areas and the point pollution over the whole area, if the water protection policies are sustainable and executed completely, and if the local government is active in their administrative, supervising and educational responsibilities and the farmers assume voluntary activities on rural pollution control. [Copyright &y& Elsevier]

Abstract: Water permeability of woven geotextile, usually measured in uncompressed state or under compressive stresses, varies significantly under tensile loads. To study the permeability behaviours of woven geotextile in the tensioned state, a series of laboratory experiments were carried out on one type of woven polypropylene geotextile with tensile strength of 20–30 kN/m. The experimental results show that the permittivity of geotextile under tension load in the warp direction first decreases rapidly, then approaches to a value that is 10–25% of the one in the absence of the load. On the contrary, the permittivity increases with the increase of the tension force in the weft direction and no steady value is observed. Since the tension load in the warp direction has obviously influence on the water permeability of geotextile, about 2–3% tensile strain is recommended to be applied on the warp fibres initially for determining a reasonable permittivity in laboratory test. [Copyright &y& Elsevier]

Abstract: Three-dimensional (3D) TiO2 solid microspheres with different morphologies have been synthesized on a large scale by a simple hydrothermal method using titanium tetrachloride (TiCl4) as the titanium source and ammonium fluoride (NH4F) as the etchant. X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM) studies show that the 3D solid microspheres, with an average diameter from hundreds of nanometers to several micrometers, are composed of numerous anatase TiO2 particles. In addition, the morphologies of the as-prepared 3D solid microspheres can be controlled by adjusting the dosage of NH4F and the reaction temperatures. The present study has enlarged the family of 3D solid microspheres, and offers a possible route for the synthesis of other inorganic hierarchical structures. [ABSTRACT FROM AUTHOR]

Modelling air movement in sewer networks is needed in order to address the issues related to sewer odour complaints and sewer corrosions due to hydrogen sulphide in sewers. Most of the existing air flow models can only be applied in small sewer networks or the trunk lines of sewer systems. The purpose of this paper is therefore to propose a theoretical approach to formulate a general governing equation set for modelling steady air movement in large sewer systems. This approach decomposes the sewer system of interest into its basic physical components as pipes and nodes, and builds local topology of each pipe and each node based on geographic information system data as the fundamentals of model formulation. It avoids manually identifying each branch of the sewer system, eliminates the effect of physically closed networks in sewer systems on the governing equations, and considers key sewer components and all known driving forces. The proposed approach was applied to a real sewer system with over 500 pipes. The results show that the proposed model is applicable in modelling air movement in a large sewer system and provides a general idea of sewer gases moving through the system and their emission.

Nanosized titanium dioxides were synthesized by hydrolysis of TiCl(4) followed by calcination at different temperatures ranging from 300 to 1,000 °C. The as-prepared samples were characterized by X-ray diffraction, N(2) adsorption-desorption, and zeta potential analysis. The catalytic activities of the TiO(2) nanoparticles were tested by catalytic ozonation of trace 4-chloronitrobenzene (4-CNB) in water. Moreover, the catalytic ozonation activity of a sample calcined at 400 °C (denoted as T400) was tested in aqueous solution using electron paramagnetic resonance (EPR) spin trapping technique with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin trap. It was found that with increasing calcination temperatures, the average crystallite size and average pore size increased, in contrast the BET surface areas decreased. However, the isoelectric point (IEP) first increased, and then decreased. The ozone adsorption on the catalyst surface played an important role in determining their catalytic activity. Sample T400 with the IEP of 7.0, farthest away from the 4-CNB solution pH value (pH = 5.3), showed the best catalytic activity. The EPR experiments further confirmed that the hydroxyl radicals TiO(2)-catalyzed ozonation followed a radical-type mechanism.