WATER AND WASTEWATER
Year:2007 | Volume:17 | Issue:4 (60)|Papers Count:11

Minimizing sludge production in the treatment facility is a reasonable measure to reduce waste in sewage treatment, especially as regards excess biological sludge. In this regard, submerged aerated filters' (SAFs) have recently found increasing applications in treatment facilities. Thanks to their treatment mechanism, they have greatly contributed to reduction of waste production and, thereby, to reduced treatment costs. Biomass growths of both attached and suspended types take place in these filters. However, little attention has been paid to suspended sludge production and to its relationship with the physical properties of the filter. The design and application criterion for these filters is the organic loadings on unit of area or unit of volume of the media used in these filters. In this study, four filters with different physical properties and different specific areas were loaded with synthetic wastewater made of low-fat dry milk powder for five different hydraulic retention times to evaluate excess sludge production rates in submerged aerated filters. It was shown that increasing specific area increased SCOD removal efficiency up to a maximum level in saturated growths after which point the removal efficiency remained unchanging or decreased. The results also revealed that decreased hydraulic retention times increased sludge production rates in all the study columns and that media with higher porosity levels produced less excess sludge despite lower pollutant removal efficiency.

Batch experiments were carried out to study chemical reduction of nitrate by metallic iron (Feo) as a potential technology to remediate nitrate-contaminated water. The effects of different operating conditions such as initial pH of the solution, nitrate concentration, and Feo dosage on both nitrate reduction and removal efficiency were investigated. The results showed that the initial pH of the solution was very effective on nitrate removal which was over 95% within two hours at pH=2. However, nitrate removal decreased with increasing pH. Thus, only 18.2% of nitrate was removed at pH=5. It was also found that the ratio of iron to nitrate was important in nitrate removal, and a ratio of 400g Feo/gNO3- had the best efficiency for nitrate removal. The feasibility of using industrial wastes such as iron filings was also studied and it was found that the wastes could be desirable for nitrate removal.

Arsenic exists in compounds present in the Earth's cru1itin various concentrations. High concentrations of arsenic in drinking water may cause skin and lung cancers or other diseases. Unfortunately, in some urban and rural areas in Kurdistan Province (e.g., Delbaran), arsenic concentrations of above 70 ppb are observed in groundwater resources, which is higher than EPA standards. The objective of this study was to evaluate the effects of using membranes for arsenic removal from drinking water. To study the practical effects of different membranes on arsenic removal, five types of membranes, namely, PVD, TFC-SR, FT30, TFC-ULP, and BW30, were used. Based on the two parameters of effluent flux and arsenic removal efficiency (which was above %95), TFC-SR was selected as the best membrane. Atmospheric pressure, temperature, and pH were the parameters tested for this membrane to obtain an optimum atmospheric pressure of 10 bars and an optimum pH level of 7.57. Results also showed that higher temperatures increased both the effluent flux and arsenic removal.

This study is an independent and a comparative research concerning the accuracy, capability and suitability of three well known packages of ISIS, MIKEI 1 and HEC-RAS as hydraulic river modeling software packages for modeling the flow through bridges. The research project was designed to assess the ability of each software package to model the flow through bridge structures. It was carried out using the data taken From experiments completed by a 22-meter laboratory flume at the University of Birmingham. The flume has a compound cross section containing a main channel and two flood plains on either side. For this study a smooth main channel and a smooth floodplain have been assumed. Two types of bridges are modeled in this research; a multiple opening semi-circular arch bridge and a single opening straight deck bridge. For each bridge, two different simulations were carried out using two different upstream boundaries as low flow and high. flow simulations. According to the results, all three packages were able to model arch and US BPR bridges but in some cases they presented different results. The highest water elevation upstream the bridge (maximum afflux) was the main parameter to be compared to the measured values. ISIS and HEC-RAS (especially HEC-RAS) seem to be more efficient to model arch bridge. However, in some cases, MIKE 11 produced considerably higher results than those of the other two packages. To model USBPR bridge, all three packages produced reasonable results. However, the results by HEC-RAS are the best when the outputs are compared to the experimental data.

Conjunctive use of surface and groundwater resources is a preferred approach in water resources management. Compared to dam construction, groundwater has certain advantages, among which are less costs, less sedimentation and evaporation, fewer water quality problems, and less social and cultural problems. To reduce the major problems associated with the development of large-scale surface impoundment systems, cyclic storage systems can be used as an alternative. A cyclic storage system (CYCS) is an integrated interactive system consisting of two subsystems of surface water storage (reservoir) and groundwater; this system together with artificial recharge is able to satisfy the predefined demands with rather high reliability. In order to optimize these systems, one must consider the hydraulic interactions between all the components, but unfortunately it has been neglected in many studies. In this article, a nonlinear optimization model for design and operation of cyclic storage systems has been developed using the lumped approach. In order to evaluate the model, its results have been compared with the results of a model in which distributed approach had been deployed, and so the efficiency of lumped models to solve the problems of cyclic storage systems has been investigated.

In this study, a conflict resolution methodology for water quality management in a river system is presented. The proposed model maximizes an objective function based on the Nash product which includes different utility functions related to the water quality deviations from the standard limits. Simulation and optimization models are proposed to determine operating policies for river water quality management, based on evaluation of system performance to derive the most appropriate diffusing strategy for different stakeholders. The proposed model includes an integrated GA-based optimization and a water quality simulation model. Sustainability measures of system performance, termed "reliability, resiliency, and vulnerability", are calculated for each water withdrawal sector and combined into a Nash product as an objective function. The model is applied to the Karkheh River system in the southern part of Iran. The utility functions are based on the acceptable risk of the allocated water quality by different sectors, especially by the Environmental Protection Organization. The results of the proposed model show that the waste load allocation policies can significantly reduce the number and duration of deviations from the standard quality limits.

In order to investigate the effects of Boushehr municipal wastewater on the structural diversity and dominance of Gastropods' colonies in intertidal zones, to understand the species of the biological indices, and finally to assess the impacts of the sewage, samples were taken from 7 stations affected by the sewage and from one station without any sewage pollutants (reference station), from March 2002 to February 2003. For the purposes of this study, 1056 benthos were collected, separated, fixed, and then identified. Samples were taken using a 50x50 cm quadrate, a scraper in rocky beds, and a core sampler in sandy beaches to a depth of 5 cm. In this study, 25 species relating to 16 families of gastropods were identified. An important finding was that the species Planaxis sulcatus and Cerithidea cingulata were identified as the biological indices of the polluted areas. The results of this study revealed high pollution in these coasts due to organic materials resulting from the sewage disposal.

Subsidence is a geologically hazardous phenomenon that can be aggravated by human such activities as long term water, oil, and gas extraction from underground resources or other mining activities. Abstractions from aquifers cause the aquifer-maintaining forces to lose their state of equilibrium whereby land starts to settle and ultimately subsides. One of the consequences of exploiting groundwater is the rising of well casings. Actually, it is not the well casings that rise but the ground around them that subsides. Subsiding forces can damage well casings and this can foist repair costs, or the wells might even need to be replaced by new ones. In this paper, finite element methods in two and three dimensional modes as well as ABAQUS software were used to investigate the impacts of subsidence from groundwater exploitation and drawdown on well casings. This investigation was based on data obtained from a real basin. The results obtained through geomechanical simulations using ABAQUS software have shown that the mechanism by which subsidence "bowls" are created cause two forms of rupture in the casings. At the edges of the bowl, surface sediments might slide on soft clay toward the center of the well and cause the casings to bend along their way. Around the center of the bowl something different happens. Considerable compaction of soft clay over time causes the distance between the surface and the bottom of the well to decrease, which results in the buckling of the casings and, in some cases, causes the casings to stick out of the ground.

Flood routing is of special importance from different aspects of river engineering such as flood zoning, flood forecasting, etc. There are two methods employed in river flood routing, hydraulic and hydrological. Hydrological methods are used when the river is at low tide and, hence, cannot be employed to analyze floods caused by the tide. Hydraulic methods must be employed in tidal rivers when the direction of the current reverses at high tide. In this research, MIKE21 modeling software was used for the flood routing of the Zohreh tidal river. The model was calibrated by surveying the river; taking samples from the river bed, measuring sea water level and the velocity of the river flow. Analyzing the sensitivity of the model showed that the coefficient of determination, root mean square error and relative error were 0.95, 0.032, and 0.27, respectively, all indicating the efficacy of the model in simulating different parameters such as velocity, flow rate, and water surface profile. The flood routing results of the tidal currents showed that the hydrograph of the influent and effluent to the reach at high tide (when the current direction is from sea to the river) was similar to the normal flood routing of the river, but at low tide (when the current direction is from the sea to the river) influent and effluent hydrograph would not follow the laws of normal flood routing.