Decoupling of large roof and traffic areas from the sewer network

The Beruf­sgenossen­schaftliche Unfal­lk­linik (BGU) in Frank­furt am Main is one of nine large acute-care hos­pi­tals run by the Beruf­sgenossen­schaft in Ger­many. By sum­mer 2026, two new ward build­ings with 308 beds will be built on the clin­ic cam­pus in the Seck­bach dis­trict. In the course of the upcom­ing con­struc­tion work, a reor­ga­ni­za­tion of the prop­er­ty drainage sys­tem for large parts of the site was also planned. The aim was to chan­nel the pre­cip­i­ta­tion water from around 14,000 m² of roof and traf­fic areas into the ground­wa­ter in a puri­fied form in order to avoid over­load­ing the sew­er system.

Completely new drainage network for 19 hectares

To achieve this goal, the drainage net­work had to be com­plete­ly restruc­tured. The orig­i­nal site area con­nect­ed to the com­bined sew­er was 25 hectares. In the future, around 19 hectares will be drained via infil­tra­tion, with only the runoff from 6 hectares con­tin­u­ing to be dis­charged into the sew­er. New storm and com­bined sew­ers and infil­tra­tion sys­tems were con­struct­ed. It was also nec­es­sary to install a pre­treat­ment sys­tem to clean and remove pol­lu­tants from the stormwa­ter before it is infil­trat­ed into the groundwater.

Cleaning rainwater runoff before infiltration

Spe­cial hydro sys­tems from 3P Tech­nik are used as cen­tral com­po­nents for this pur­pose, which are locat­ed in cus­tom-built spe­cial struc­tures made of rein­forced con­crete from Fin­ger Beton. The fil­ter sys­tem con­sists of eight treat­ment plants arranged in a star shape in con­crete shafts of dimen­sion DN 1500. This arrange­ment around the dis­tri­b­u­tion shaft ensures an even load on the fil­ter sys­tems. The water flows tan­gen­tial­ly into the hydro­dy­nam­ic sep­a­ra­tor, solids set­tle to the bot­tom. In the cen­ter of the fil­ter shaft above each of these are six fil­ter ele­ments, which are flushed in an upflow process. They fil­ter out fine par­ti­cles and bind them adsorp­tive­ly. The large­ly puri­fied water then pass­es through an oil sep­a­ra­tor, from where it is fed into an infil­tra­tion trench. The sludge trap in the low­er part of the plant can be sucked out for clean­ing. The fil­ter ele­ments can be back­washed from above and can be eas­i­ly replaced via the man­hole open­ing if necessary.