Polyurethane Foams for Domestic Sewage Treatment

Abstract

The aim of the study was to assess the possibility of using polyurethane foams (PUF) as a filling of a foam-sand filter to directly treat domestic sewage with increased content of ammonium nitrogen and low organic carbon to nitrogen ratio (C/N). The study compared performance of two types of flexible foams: new, cylinder-shaped material (Novel Foams, NF) and waste, scrap foams (Waste Foams, WF). The foams serving as a filling of two segments of a foam-sand filter were assessed for their hydrophobic and physical properties and were tested for their cell structure, i.e., cell diameter, cell size distribution, porosity, and specific surface area. The study accounted also for selected application-related properties, such as hydrophobicity, water absorption, apparent density, dimensional stability, amount of adsorbed biomass, and the possibility of regeneration. Cell morphology was compared in reference foams, foams after 14 months of the filter operation, and regenerated foams. The experimental outcomes indicated WF as an innovative type of biomass carrier for treating domestic sewage with low C/N ratio. SEM images showed that immobilization of microorganisms in NF and WF matrices involved the formation of multi-cellular structures attached to the inner surface of the polyurethane and attachment of single bacterial cells to the foam surface. The amount of adsorbed biomass confirmed that the foam-sand filter made up of two upper layers of waste foams (with diameters and pore content of 0.50-1.53 mm and 53.0-63.5% respectively) provided highly favorable conditions for the development of active microorganisms.

Keywords: biofilter; domestic sewage with low C/N ratio; physical properties; polyurethanes; waste foams.

Figure 1

SEM images of the matrix of foam cells in brand new reference NF foams: (a) magnification 50×, (b) magnification 200×.

Figure 2

SEM images of the matrix of foam cells in reference bluish-green waste WF foams: (a) magnification 50×, (b) magnification 200×.

Figure 3

SEM images of the matrix of foam cells in reference yellow-green waste WF foams: (a) magnification 50×, (b) magnification 200×.

Figure 4

SEM images of the matrix of foam cells in reference lilac waste WF foams: (a) magnification 50×, (b) magnification 200×.

Figure 5

SEM images of the matrix of foam cells in reference orange waste WF foams: (a) magnification 50×, (b) magnification 200×.

Figure 6

NF foams before research (at the top) and after 7 months of research (on the bottom).

Figure 7

Excessive accumulation of microorganisms in the second segment of lilac WF foams.

Figure 8

SEM images of accumulated sludge in the matrix of foam cells of new reference NF foams in the upper part of the cylinders (a) on the foam surface (b) and inside the foam; in the lower part of the cylinders (c) on the foam surface (d) and inside the foam.

Figure 9

SEM images of accumulated sludge in the matrix of foam cells of waste reference bluish-green WF foams (a) on the foam surface (b) and inside the foam.

Figure 10

SEM images of accumulated sludge in the matrix of foam cells of waste reference yellow-green WF foams (a) on the foam surface (b) and inside the foam.

Figure 11

SEM images of accumulated sludge in the matrix of foam cells of waste reference lilac WF foams (a) on the foam surface (b) and inside the foam.

Figure 12

SEM images of accumulated sludge in the matrix of foam cells of waste reference orange WF foams (a) on the foam surface (b) and inside the foam.

Figure 13

SEM images of the matrix of foam cells in bluish-green waste WF foams subjected to regeneration; magnification 200×, (a) inside the foam (b) and on the foam surface.

Figure 14

SEM images of the matrix of foam cells in yellow-green waste WF foams subjected to regeneration; magnification 200×, (a) on the foam surface (b) and inside the foam.

Figure 15

SEM images of the matrix of foam cells in orange waste WF foams subjected to regeneration; magnification 200×, (a) inside the foam (b) and on the foam surface.

Figure 16

SEM images of the matrix of foam cells in lilac waste WF foams subjected to regeneration; magnification 200× (the arrows indicate unremoved biomass and pollutants inside the pores and on the surface of the foam skeleton), (a) inside the foam (b) and on the foam surface.