Structural Design of AguaClara Plants, Summer 2011

Lily Siu

Abstract:

Our main objective we wish to accomplish this summer is to analyze the reinforcement configuration and structural strength of the sedimentation and flocculation tank walls. In the previous semester, the structural design team analyzed the structural capabilities of the columns and walls for the Alauca plant using various assumptions and load cases. The previous team analyzed the walls as closely spaced concrete columns. By modeling the walls as columns the flexural support provided by the horizontal reinforcement is unaccounted for, but it allowed for the use of the same tools and procedures that is used for beam analysis. We seek to attempt to validate the previous team’s calculations as well as suggesting methods to analyze the horizontal reinforcement in order to reduce over-designing. This report is meant to augment the Spring 2011 report.

Sedimentation Tank Hydraulics, Summer 2011

Elana Liskovich, Mahina Wang, Jill Freeman, Yiwen Ng

Abstract:

A floc blanket is a dense fluidized blanket of flocs that helps to reduce effluent turbidity in the sedimentation tank by trapping other flocs. The geometry of the sedimentation tank is crucial in determining the extent of floc resuspension by the jet and hence floc blanket formation. To improve tank bottom geometry, nine experiments were conducted, each testing a different tank bottom geometry. The experiments were run in a 1/2 inch wide tank to model a thin slice of the full scale sedimentation tank. The geometry that resulted in the least sludge accumulation and therefore best floc resuspension was two 60 degree inserts leading to a semicircular trench 10 cm in diameter. We also provided initial designs and calculations for a floc weir to maintain the height of the floc blanket. A preliminary experiment was also conducted to evaluate the feasibility of our initial floc weir design.

Sedimentation Tank Hydraulics, Fall 2011

Jill Freeman, Mahina Wang, Saied Khan, Matthew Hurst

Abstract:

A floc blanket is a dense, fluidized bed of particles that forms in the sedimentation tank and helps to reduce effluent turbidity by trapping small flocs and reduces clean water waste through less frequent draining of the sedimentation tank. Floc resuspension is necessary for floc blanket formation so that flocs are recirculated through the tank instead of settling on the tank bottom as sludge. Research was conducted to examine mechanisms for floc resuspension. Parameters important for floc resuspension include energy of the jet stream on its upward flow path, position of the jet as it interacts with solids, and hydrodynamic pressure of the jet compared to hydrostatic pressure of the returning solids. Several geometries were tested with red dye and fully built floc blankets to observe the jet path and velocity profile around the bottom geometry. Best results are achieved through geometries that preserve jet momentum, especially through splitting the jet flow, and geometries that maintain a high jet velocity when contacting solids. Later, quantitative measurements were taken to determine floc blanket performance for various bottom geometries.

Residuals Management, Fall 2011

Patrick Farnham

Abstract:

The Residuals Management sub-team is solving the problem of solids disposal in AguaClara treatment plants. Currently, settled solids from the sedimentation and entrance tanks are drained and routed directly onto the nearby landscape. The newly created stacked rapid sand filtration system will produce backwash water in need of disposal, and spikes of highly turbid influent water bypass the plant by being discharged down the surrounding slope. The research goal is to determine inexpensive and responsible disposal methods for these outflows as well as for precipitate matter removed from the chemical stock tanks. Flow rates and concentrations of all residual flows have been estimated with the help of AguaClara engineers in Honduras, and designs have been created for pipe outlet protection structures which should reduce the erosive power of AguaClara residual flows. The team goal is to identify promising methods and eventually code them into the AguaClara design tool for use in the future and also for possible use in retrofitting current plants.