technical features
Treatment Mechanism
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The units are designed to remove suspended solids and floatables, sediments and oil from waste/stormwater and to prevent re-entrain ment of these contaminants. VersaTrap devices remove pollutants by directing the flow tangentially into a cylindrical chamber (treatment chamber), creating a vortex, and then passing downwards into the cylindrical screen or basket. Vortex separators have no moving parts and are designed to operate under high flow conditions. Generally, no external power is required for operation of the unit as the influent and underflows may be conveyed by gravity through the vortex separator depending on the available hydraulic head. Suspended pollutants are captured in the perforated stainless steel basket or screen, and clean effluent exits to the outlet through the external chamber. In the case of the VTW, a system of nested baskets is used, with screen aperture size progressively decreasing. Suspended solids and sediments are concentrated in the centre of the base of the basket, whilst floarables and oil are collected at the water surface in the treatment chamber. Emptying by vacuum eduction or removable basket removes accumulated sediments, suspended solids and floatable poll utants .
Experimental Setup Graphical representations of the models are presented in Figure 1. Each model basically consists of two cylindrical chambers with d iameters of 300 and 500 mm, screen size of 2500 mm fo r VTG, two screen sizes of 2500 and 30 00 mm for VTW, in/outlet pipes with same diameters of 50 mm for VTW and 150 mm for VTG. The models were fitted in a pipe system as depicted in Figure 2. A centrifugal pump was used to pump water from the rank to the model, returning to the reservoir downstream. The flow rate was adjusted using a valve immediately downstream from the pump. Pollutants were introduced through a tee junction upstream of the inlet. Mano meters connected upstream and downstream of the model were used to measure the head p ressure and flow level, from which the velocity head was calculated.
Manometer
Downstream Pipe
Upstream Pipe
Water Tank p
va1••
Pllmp
Figure 2. Schematic diagram of experimental setup.
M T F (0.4 Lis) is defined as the flow at which the vo rtex establishes in the treat ment chamber. DTF (0.6 Lis) is l. 5*MTF, considered to represent the mean flow rate. DPF (1 .25 Lis) is 2*DTF, and allows for peak fl ows of approximately double the average fl ow. DDPF (2.5 Lis) is considered to be the ultimate flow capacity of the device, being double the anticipated normal peak flow. This safety factor of 2 allows for potential exceptional events and/or blockages. By using energy equatio n (1), the Head loss of the model was calculated. The corresponding Head loss of the trap model was determined at the four different screen conditions namely; clean si ngle screen, clean double screens, 50% blocked single screen and 50% blocked double screens, replicating potential conditions in the field. 2
2
~+A+z =~+h+z +HL 2g pg I 2g pg 2
(])
Versatrap Type W
Where P 1 is the pressure head at the inlet pipe, P2 is the pressure head at the outlet pipe, VJ is the velocity head at the inlet pipe, V2 is the velocity head at the outlet pipe, zl is the elevation level at the inlet pipe, z2 is the elevation level at the outlet pipe and HL is the total head loss (energy loss).
Hydraulic characteristics including velocity head and pressure head were determined at the fo llowing flow rates; M inimum Treatment Flow (MTF), Design Treatment Flow (DTF), Design Peak Flow (DPF) and D o uble Design Peak Flow (DDPF). The
VT type G has a built-i n bypass facility; therefore the hyd raulic testing procedures of VT type G were more extensive than VT type W. The hydraulic tests involved the
Hydraulic testing procedure
68
DECEMBER 2007
Water
Versatrap Type G
Journal of the Australian Water Association
determination of treatment flows and the correspo nding H ead losses with single basket at 0%, 25%, 50 %, 75 % and 100% blocked screen conditions. This was done to represent typical screen conditions in the field. In the 100% blocked screen condition, water will not enter the basket in the treatment chamber but passes over the built-in weirs directly to the outlet of the exit chamber via the annulus between inner and outer cylinders. T he method of hydraulic testing of the VTG for each screen condition was to establish both a Design Treatment Flow (DTF) and Design Peak Flow (D PF). DTF is the maximum treatment flow with zero bypass flow. DPF is 5 x DTF - the maximum pipeline flow that the d evice is designed to carry (i.e. 20 Lis in the case of the model).
Pollutant removal efficiency testing procedure
Versatrap Type W Three different categories of pollutant samples were prepared and tested for VT type W with 50% d ouble blocked basket conditions to determine Pollutant Removal Effi ciency (PRE) . The pollutant categories such as suspended solids; sediments and oil were collected to represent the actual pollutant types that the wastewater carries. The PRE tests were done at Design Treatment Flow (0 .6 Lis), Design Peak Flow (1.25 Lis) and the Double D esign Peak Flow (2 .5 Lis). The PRE was determined by comparing the amount of pollutants being recovered from the