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A massive use of nitrogen based fertilizers in agriculture is worldwide one of the main causes for nitrate contamination of groundwater. Methods for removing nitrate from aquatic environment through physical and/or chemical processes often turn out to be not applicable because of unaffordable financial resource as well as essential infrastructure lack. On the other hand, biological processes seem to have potentiality to overcome these limitations since they are less expensive and easier to be performed. Accordingly, in the present work, a moving bed biofilm reactor (MBBR) filled with Kaldnes K1 as carrier media was used to remove nitrate from a synthetic groundwater at bench scale. Acetate was used as organic source. Different operational conditions were tested: influent nitrate concentrations of 30, 40, 50 and 60 mg/L; hydraulic retention times of 24, 18, 12 and 8 h; and COD/NO3-N mass ratios of 3.00 and 2.98. Experimental results showed that NO3-N = 60 mg L−1, HRT = 8 h and COD/NO3-N ratio = 2.98 were the optimal operating conditions that allowed achieving a NO3-N removal by 99 % and a COD removal by almost 100 %. Moreover, almost no NO2−-N accumulation and null COD concentration were observed at the optimal operating conditions. An activated carbon filter was placed downstream to remove residual organic compounds prior to disinfection unit, thus avoiding the potential formation of harmful disinfection by-products (e.g. trihalomethanes (THMs)). The MBBR was able to show a rapid recovery whenever the operating conditions were defined as more severe, thus proving that the operating conditions can vary over a wider range. Furthermore, the results showed that the MBBR system can be used effectively as a biological process to remove nitrate from groundwater. [ABSTRACT FROM AUTHOR]

Vortex drop shafts are used in urban drainage systems to connect two sewers located at considerably different elevations. After their introduction in 1947, these were studied with particular reference to subcritical approach flow. Vortex shafts for supercritical approach flow can also be used, but the intake structure may have relatively high cost due to the complex geometry. The present study includes experimental results of a specific investigation on the changes to be made in the supercritical approach channel if a subcritical vortex intake is used. The experimental investigation analyzes the effect of a hydraulic jump on the performance of vortex intake structure to define appropriate technical solutions, essentially consisting in a negative step to be located along the supercritical approach channel. Design criteria are finally presented for the evaluation of the step height and its distance from the vortex intake structure. DOI: 10.1061/(ASCE)HY.1943-7900.0000249 CE Database subject headings: Energy dissipation; Hydraulic jump; Sewers; Shafts; Drop structure; Critical flow; Intake structures. Author keywords: Energy dissipation; Hydraulic jump; Sewer hydraulics; Vortex shaft; Drop structure.

Spurs are river engineering elements used to protect river banks from erosion and to concentrate flow to the river axis. Today, spurs are also employed for promoting environmental conditions along a river bank. These elements are characterized by a large variety of geometrical parameters, of which none is definitely fixed. Based on a preliminary study that identified optimum spur arrangements in a straight river reach the present research project adds to the protection of spurs by riprap. The first two spurs are demonstrated to require a suitable riprap for promoting nearly uniform scour conditions along the entire spur reach. This research investigated the effects of a variety of parameters on spur flow, notably spur length, spur spacing, spur height plus the diameter and the number of riprap rows, along with the main hydraulic and granulometric parameters. Design equations were established based on a large experimental campaign to predict riprap failure in terms of the previous set of variables. The failure modes are described along with a novel failure mechanism. The paper ends with a set of limitations allowing for the application of these results in river engineering. DOI: 10.1061/(ASCE)0733-9429(2008)134:2(135) CE Database subject headings: Bank stabilization; Failures; Groins, structures; Hydraulics; River; Scour.

Manholes often contain small drops for various reasons, the most important being submergence. While this may be appropriate for subcritical flow, its effect was considered doubtful for supercritical flow. This note aims at investigating the effect of a manhole drop on the hydraulics of sewer flow. Based on systematic experimental observations, the flow pattern associated with a manhole drop was established. A distinction was also made between small and intermediate drops. Then, the main wave features were analyzed to result in expressions that contain both the upstream filling ratio and the Froude number of the approach flow. In addition, the discharge capacity was also investigated, and selected photographs show typical drop flow in combined sewer manholes. The result of the present study is evident, based on these observations, and recommendations towards future design of combined sewer manholes are also made. CE Database keywords: Combined sewers; Manholes; Supercritical flow; Shock waves; Hydraulics.

Supercritical flow in a bend manhole for combined sewer systems is considered for a typical relative curvature and deflection angles of 45 degrees and 90 degrees. The typical features of bend flow in a U-shaped channel are determined, including the surface profiles along the inner and the outer bend walls, impact flow at the manhole outlet into the downstream sewer pipe, air entrainment characteristics, and wave development in the downstream sewer. Also, typical velocity distributions along the manhole are presented, and the capacity of the conventional bend structure is determined. To increase the discharge capacity across a bend manhole, the so-called bend cover is introduced. This cover element finished in steel can be removed for maintenance and inspection purposes. It limits the wave height close to the bend outlet to 90% of the sewer diameter and allows air entrainment into the downstream sewer. The performance and capacity of bend flow may significantly be increased, and the novel element may easily be added to existing manholes.

Sideweirs for combined sewers in converging U-shaped channels are analyzed. The results are applicable for storm sewers. Based on extended model observations and a hydraulic approach, the characteristics of sideweir flow are determined. These include the surface profile, the discharge distribution, the end depth ratio, and the energy losses due to lateral outflow. All results are presented in terms of approach conditions, and it is demonstrated that the approach Froude number is the significant flow parameter. For sideweirs with a relatively small weir height, the flow may become unstable and set up a surging phenomenon in the approach pipe. After careful experimentation, the instability was effectively removed with a so-called end plate. This device is positioned at the end wall of the sideweir and is able to stabilize the vorticity interface between the bottom and the surface vortices. The end plate can simply be added to existing designs.