Activity of metazoa governs biofilm structure formation and enhances permeate flux during Gravity-Driven Membrane (GDM) filtration

Abstract

The impact of different feed waters in terms of eukaryotic populations and organic carbon content on the biofilm structure formation and permeate flux during Gravity-Driven Membrane (GDM) filtration was investigated in this study. GDM filtration was performed at ultra-low pressure (65 mbar) in dead-end mode without control of the biofilm formation. Different feed waters were tested (River water, pre-treated river water, lake water, and tap water) and varied with regard to their organic substrate content and their predator community. River water was manipulated either by chemically inhibiting all eukaryotes or by filtering out macrozoobenthos (metazoan organisms). The structure of the biofilm was characterized at the meso-and micro-scale using Optical Coherence Tomography (OCT) and Confocal Laser Scanning Microscopy (CLSM), respectively. Based on Total Organic Carbon (TOC) measurements, the river waters provided the highest potential for bacterial growth whereas tap water had the lowest. An increasing content in soluble and particulate organic substrate resulted in increasing biofilm accumulation on membrane surface. However, enhanced biofilm accumulation did not result in lower flux values and permeate flux was mainly influenced by the structure of the biofilm. Metazoan organisms (in particular nematodes and oligochaetes) built-up protective habitats, which resulted in the formation of open and spatially heterogeneous biofilms composed of biomass patches. In the absence of predation by metazoan organisms, a flat and compact biofilm developed. It is concluded that the activity of metazoan organisms in natural river water and its impact on biofilm structure balances the detrimental effect of a high biofilm accumulation, thus allowing for a broader application of GDM filtration. Finally, our results suggest that for surface waters with high particulate organic carbon (POC) content, the use of worms is suitable to enhance POC removal before ultrafiltration units. carbon content on the biofilm structure formation and permeate flux during Gravity-Driven 26 Membrane (GDM) filtration was investigated in this study. GDM filtration was performed at 27 ultra-low pressure (65 mbar) in dead-end mode without control of the biofilm formation. 28 Different feed waters were tested (River water, pre-treated river water, lake water, and tap 29 water) and varied with regard to their organic substrate content and their predator community. 30River water was manipulated either by chemically inhibiting all eukaryotes or by filtering out 31 macrozoobenthos (metazoan organisms). The structure of the biofilm was characterized at the 32 meso-and micro-scale using Optical Coherence Tomography (

The composition and compression of biofilms developed on ultrafiltration membranes determine hydraulic biofilm resistance

“…The detailed characteristics (Total organic carbon, assimilable organic carbon, etc.) of the Chriesbach creek water can be found in Derlon et al (2013). Water and room temperatures were controlled at 20 C. The Hydraulic Retention Time (HRT) was controlled to around 4 h in each water tank.…”

Short-term effects of nutrient enrichment on river biofilm: N–NO3 − uptake rate and response of meiofauna

“…Although their grazing pressure on biofilm microphytobenthos is rather low (Majdi et al, 2012b, c;Mialet et al, 2013), their activity within the biofilm can affect oxygen turnover (Mathieu et al, 2007) and seemingly other key processes such as biofilm detachment and the release of secondary metabolites in the water column (Sabater et al, 2003;Gaudes et al, 2006). Recently, Derlon et al (2013) have shown that, in gravity-driven membrane filtration water depuration systems, the presence of nematodes and oligochaetes increases the heterogeneity and porosity of membrane-associated microbial biofilms, and consequently increases the efficacy of filtration process used to treat organically polluted waters. Riemann & Helmke (2002) report that locomotion of nematodes creates dense micro-burrows from agar plate matrixes.…”

Optical coherence tomography for the in situ three-dimensional visualization and quantification of feed spacer channel fouling in reverse osmosis membrane modules

“…Gao et al proved its potential for visualizing liquid flow patterns in spacer filled feed channels [16]. The effect of (natural) predation on the structure of the fouling layer in gravity driven membrane systems has been shown by Derlon et al [17]. In another study the compaction and detachment of the biofouling layer in a microfiltration unit was investigated [18].…”