Veolia Water Technologies & Solutions

MNF underdrain

Pour-in-place concrete floor for filters

The MNF high-density concrete underdrain system is a single, poured-in-place concrete floor supported by polystyrene forms, incorporating air/water backwash nozzles. The system can be incorporated in most filtration applications including single media or multimedia for potable water treatment, advanced wastewater treatment, and various industrial filtration systems. MNF underdrains are ideal for many retrofit applications since few restrictions exist regarding filter size or orientation.

Features & Benefits

MNF Underdrain Features & Benefits

MNF filter underdrain systems are not only less expensive to own and maintain, but they also cost less to install since the rebar and concrete are obtained locally, minimizing shipping and handling costs. 

Other key advantages of the MNF Underdrain System: 

  • high-impact, molded polystyrene forms and nozzle adapters designed to withstand rigors of installation without deflecting or breaking 
  • easy installation with single-pour concrete 
  • simple installation of air-water distribution nozzles and nozzle adapters, with no adhesive required for each nozzles 
  • nozzle size selected for specified filter media 
  • thorough air-water media washing, due to 4.8 nozzles per square foot 
  • highest nozzle density on the market 
  • structural rigidity for the life of the system because MNF underdrain uses stainless steel all-thread rods to tie the underdrain slab into the base concrete floor 
  • NSF certified 

Structural Designs

The five different standard structural designs will ensure applied loads, during backwashing or filtration, can be met: HD-1200, HD-1400, HD-1600, HD-1900, and HD-2100. Each is designed in accordance with ACI-318 code, with pressure ratings from 1200 PSF to 2100 PSF in both upflow direction (backwash) and downflow direction (filtration). The MNF underdrain® is NSF 61 approved.


  • Drinking water
  • Process water
  • Wastewater

How it Works

How The MNF underdrain Drain Works

Veolia’ MNF underdrain high-density concrete underdrain system is a single, poured-in-place concrete floor providing superior structural strength and simple installation, even in retrofit applications. 

The key component of the MNF underdrain system is a high-impact, molded polystyrene form. When concrete is poured into the form, it becomes a permanent part of the filter underdrain without deflecting. Each form includes nozzle adapters into which the distribution nozzles are threaded after the concrete is installed. Disposable, threaded plugs are included to prevent concrete from entering the nozzle adapters. Even the posts which support the monolithic floor are formed in the same single pour of concrete. 

MNF underdrain incorporates air scour without use of precast underdrain components. Once the concrete is cured, the plugs are easily removed, and the polypropylene nozzles are installed. 

A finished MNF underdrain installation is not only strong, but it’s also less likely to suffer installation-related problems leading to media leakage or other operational difficulties.

Monoflor Diagram