Effect of natural biofilm on transport and retention behavior of nanoparticles and microorganisms in limestone sediments: implications for managed aquifer recharge

Author: Amirhosein Ramazanpour Esfahani

Ramazanpour Esfahani, Amirhosein, 2020 Effect of natural biofilm on transport and retention behavior of nanoparticles and microorganisms in limestone sediments: implications for managed aquifer recharge, Flinders University, College of Science and Engineering

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Managed aquifer recharge (MAR) is increasingly becoming a component of water resource management in water stressed arid and semi-arid countries. Surface waters e.g. stormwater or treated wastewaters injected into the aquifer for storage may contain pathogenic bacteria and viruses and engineered nanoparticles, which pose a risk to public health upon subsequent surface reuse. Understanding the behavior of enteric pathogens and engineered nanoparticles in aquifers contributes to the management of this human exposure risk.

In this study, MS2 F-RNA bacteriophage, Escherichia coli (E.coli) and graphene oxide nanoparticles were applied as model virus, bacteria and nanoparticles, respectively. Physically simple and chemically clean sand grains, quartz sediments and limestone sediments were also used as collectors in batch and column studies. RO water with desired pH and ionic strength and treated wastewater obtained from Mount Barker, South Australia were used as aqueous media. Additionally, batch experiments of MS2 inactivation by attachment onto the surfaces of pristine and biofilm-conditioned limestone sediments were conducted at different contact times, initial virus concentrations (103-107 PFU/mL), limestone particle size distributions (0.25-0.5, 0.5-1 and >1 mm), temperatures (4 and 22 °C), agitation status (static and dynamic) and aqueous media (RO water and treated wastewater). The column experiments were conducted in saturated water conditions to mimic the real aquifers. The convection-dispersion equation (CDE) model was used to describe the experimental data of tracer (bromide) transport in sand and limestone columns.

The results of batch studies revealed higher affinity of MS2 to the biofilm-conditioned limestone sediments than the pristine ones. Furthermore, in column experiments of tracer and virus transport, higher biofilm accumulation in sand columns caused higher virus attachment onto the collectors. However, long-term irrigation of limestone columns led to more discharge of virus into the effluents, due to changing the structure of limestone column by causing heterogeneities, due to calcite dissolution. Moreover, the biofilm growth and proliferation increased the physical and biological clogging of porous media, caused decreasing saturated hydraulic conductivity of columns.

GONPs transport and retention was significantly governed by mineralogical features of porous media, in which higher metal oxide/hydroxides enhanced their retention in columns. Moreover, high ionic strength of solution not only decreased the transport of GONPs in all columns, but also changed the shape of retention profiles (RPs) of GONPs from linear, at low ionic strength, to hyper-exponential at high ionic strength. The presence of biofilm in columns also not only increased the attachment of nanoparticles onto the surfaces of collectors, but also led to physical straining in the column.

The co-presence of microorganisms in nanoparticle suspension may have a significant influence on the transport and retention of GONPs. At high ionic strength, no changes were observed in the transport behavior of GONPs, due to the aggregation of microorganisms and nanoparticles. However, at low ionic strength, simultaneous enhanced transport and decreased retention of GONPs were obtained in the columns, due, primarily, to the competition between microorganisms and nanoparticles to occupy surface reactive sites of collectors.

The presence of biofilm onto the surfaces and interpores of columns, at both batch and columns systems, caused higher virus and nanoparticle attachment which can be acted as a biofilter in a real MAR site for prevention of pathogenic and engineered nanoparticles discharge in the groundwater.

Keywords: Managed aquifer recharge, graphene oxide, limestone, biofilm, co-transport.

Subject: Water Management thesis

Thesis type: Doctor of Philosophy
Completed: 2020
School: College of Science and Engineering
Supervisor: Prof. Howard Fallowfield