Challenge
In Zwolle, the Netherlands, the bioreactors installed on the trains of a certain rail operator have been scheduled for cleaning. The water flows released from this cleaning process are discharged, but still contain large amounts of undissolved components. The client intends to clean this water flow before discharging it, but the wastewater coming from the collection tank of the purification installation contains a lot of dissolved components. There is also still a high degree of biological activity in this water (concentrations of BOD, COD and ammonium nitrogen compound).

Solution
This investigation aimed to outline the possibilities for purifying and controlling the (waste)water flows from the bioreactors. HMVT was commissioned by Oranjewoud to investigate the composition and degree of sedimentation of a wastewater flow. The sedimentation properties of the wastewater were studied using sedimentation and durability tests at the HMVT test lab in Ede, the Netherlands.

Results
The sedimentation properties of the sludge were found to be good. Already within a short period of 5 minutes, 70% of the volume separates and forms a watery layer on top of the sedimentary sludge layer. This means that the sludge consists of relatively large particles in the water. Based on the properties of the sludge and the additional sedimentation tests on the sludge, we advised mechanical separation using a curved sieve filter or band filter. These filters separate the sludge from the bio containers of the transport water. The sludge was thereby removed from the bio container.