High-performance modular screens for Combined Sewer Overflows (CSO)

The Challenge

Even when Com­bined Sew­er Over­flows (CSO’s) and Storm Sew­er Over­flows (SSO’s) are equipped with scum boards or lamel­la baf­fles, con­sid­er­able quan­ti­ties of float­a­bles and sus­pend­ed solids still reach the receiv­ing water­course. San­i­tary arti­cles, toi­let paper and syn­thet­ics are left caught on the riv­er bank after heavy rain; these waters become  bio­log­i­cal­ly and hydrauli­cal­ly “stressed”.

The Way

All pol­lut­ed dis­charges into receiv­ing waters have to be treat­ed. Float­a­bles and sus­pend­ed solids can be screened out. This should be done con­tin­u­ous­ly and care­ful­ly to pre­vent the screen­ings from break­ing up and slip­ping through the screen struc­ture. 

The Solution

The Stein­hardt^® Hydro­Screen Fine Bar Screen Type FSRF is a flat bar screen. It is installed hor­i­zon­tal­ly on the over­flow wall with­in com­bined sew­er­age sys­tems. The spill flow ris­es up through the bars retain­ing the debris with­in the foul flow. All fine bar screens Mod­el FSRF are made of stain­less steel and are typ­i­cal­ly hydrauli­cal­ly dri­ven, there-fore not requir­ing explo­sion pro­tec­tion. The con­trol cab­i­net can be in any cho­sen posi­tion above ground. 

The Hydro­Screen Fine Bar Screen Type FSRF is mod­u­lar in design and can be installed through small open­ings (min. Ø 600) and assem­bled in the struc­ture. The dri­ve mod­ule is 1.30 m long and incor­po­rates a hydraulic ram. Up to 4 slave units can be con­nect­ed to the dri­ve unit to increase the screen­ing rate to suit the appli­ca­tion. To pre­vent screen­ings being car­ried over the whole length of the screen, each mod­ule has rest zones. The screen­ings are released there assist­ed by the under flow and are car­ried away by the sew­er flow.  

The min­i­mum screen width starts at 40 cm and can be extend­ed in 10 cm wide steps up to 1.30 m width. The screen height, includ­ing the hydraulic dri­ve, is less than 40 cm when assem­bled. It is installed hor­i­zon­tal­ly, per­mit­ting the whole screen to be uti­lized to screen the flow at all times, thus min­imis­ing the veloc­i­ty through the bars. 

The stan­dard bar spac­ing is 4 and 6 mm which ensures the high­est pos­si­ble degree of clean­ing by cor­re­spond­ing flow rate. In order to trap as much dis­solved mat­ter as pos­si­ble, the flow veloc­i­ty between the screen bars is lim­it­ed to ≤ 1.4 m/s. 

The spac­ing between the bars is auto­mat­i­cal­ly raked when the spill com­mences and con­tin­ues until the spill event fin­ish­es main­tain­ing the screen­ing capac­i­ty. 

Hydro­Screen Fine Bar Screen Type FSRF is designed for a max. impound­ing head of 2x over­flow height. If high­er over­flow heights are expect­ed, e.g. in emer­gency sit­u­a­tions, the screen should be reinforced.

Range of Application 

• before com­bined inflows into receiv­ing waters
• before storm water inflows into receiv­ing waters
• before soil fil­ter systems
• before earth and reten­tion basins 
• before per­co­la­tions
• before dif­fi­cult-to-clean basins

The Advantages

• robust stain­less steel construction
• mod­u­lar in construction
• retro­fit through small aper­tures possible
• high clean­ing efficiency
• head loss approx. ≤10 cm
• veloc­i­ty between screen bars lim­it­ed to  ≤ 1.4 m/s
• effec­tive per­for­mance approx. 500 l x s^-1 x m^-2
• bio oil
• screen­ings release zone every 65 cm
• stain­less steel construction
• no re-adjust­ment