Elsevier

Journal of Environmental Management

Volume 169, 15 March 2016, Pages 145-154
Journal of Environmental Management

Research article
Application of controlled nutrient release to permeable reactive barriers

https://doi.org/10.1016/j.jenvman.2015.12.002Get rights and content

Highlights

  • Timeframes of nutrient release from two controlled release fertilisers is examined.

  • Increasing temperature shortened timeframes of controlled nutrient release.

  • Activated carbon rapidly depleted nutrients from nutrient amended zeolites.

  • Increasing flow velocity was shown to alter nutrient release rates.

  • Nutrient release was shown to be unchanged in the presence of petroleum hydrocarbons.

Abstract

The application of controlled release nutrient (CRN) materials to permeable reactive barriers to promote biodegradation of petroleum hydrocarbons in groundwater was investigated. The longevity of release, influence of flow velocity and petroleum hydrocarbon concentration on nutrient release was assessed using soluble and ion exchange CRN materials; namely Polyon™ and Zeopro™. Both CRN materials, assessed at 4 °C and 23 °C, demonstrated continuing release of nitrogen, phosphorus and potassium (N–P–K) at 3500 bed volumes passing, with longer timeframes of N–P–K release at 4 °C. Zeopro™–activated carbon mixtures demonstrated depletion of N–P–K prior to 3500 bed volumes passing. Increased flow velocity was shown to lower nutrient concentrations in Polyon™ flow cells while nutrient release from Zeopro™ was largely unchanged. The presence of petroleum hydrocarbons, at 1.08 mmol/L and 3.25 mmol/L toluene, were not shown to alter nutrient release from Polyon™ and Zeopro™ across 14 days. These findings suggest that Polyon™ and Zeopro™ may be suitable CRN materials for application to PRBs in low nutrient environments.

Introduction

Global extraction and transport of crude oil has resulted in the terrestrial environment being exposed to approximately 25,000 tonnes of crude oil every year as a result of damaged pipelines and storage vessels (McDonald and Knox, 2014). Permeable Reactive Barriers (PRBs) offer the potential to capture petroleum hydrocarbon contaminants in groundwater, minimising the transport of spills to uncontaminated terrestrial environments (Mumford et al., 2015). PRBs stand to significantly reduce remediation costs where soil remediation operations such as ‘dig and haul’ can influence petroleum hydrocarbon mobilisation through subsurface disturbance (Snape et al., 2001, Filler et al., 2006). Snape et al. (2001) and Ferguson et al. (2003) also emphasise the importance of coupling soil and groundwater remediation infrastructure to prevent contaminant migration in low organic, free-draining Antarctic soils.

The effectiveness of petroleum hydrocarbon adsorption materials such as granular activated carbon (GAC) in PRBs has been well reported (Karanfil and Kilduff, 1999, Arora et al., 2011, Mumford et al., 2015). However, in the absence of biodegradation, the finite adsorption capacity of GAC presents issues associated with breakthrough, regeneration and disposal as a hazardous material. The adsorption potential of GAC is also regulated by the hydraulic conductivity of a PRB which can be influenced by biomass growth and particle breakup with exposure to freeze–thaw cycling (Seki et al., 2006, Mumford et al., 2014). At contaminated sites in cold regions such as Antarctica, low nutrient groundwater has been shown to hinder microbial growth and biodegradation (Ferguson et al., 2003, Walworth et al., 2007). Simultaneous adsorption and biodegradation of petroleum hydrocarbons on GAC has been observed (Mason et al., 2000), suggesting the advantages of biofilms to the longevity of adsorption and degradation of heavy, long chained petroleum hydrocarbons (Mumford et al., 2015). Controlled release nutrient (CRN) materials are therefore important for the sustained delivery of essential nutrients to particle-attached biofilms in PRBs (Freidman et al., submitted for publication).

Mumford et al., 2013, Mumford et al., 2014, Mumford et al., 2015 report the first application of soluble and nutrient-amended zeolite CRN materials to promote biodegradation in a sequenced PRB at Casey Station, Antarctica. Total petroleum hydrocarbon concentrations, degradation indices and microbial analyses support the application of CRN materials to promote biodegradation within PRBs (Mumford et al., 2015). Due to logistical constraints associated with accessing contaminated sites in cold regions, the timeframes over which CRN materials will deliver essential nutrients will dictate the longevity and contribution of biodegradation to PRB performance.

In this study, timeframes of nitrogen, phosphorus and potassium (N–P–K) release from a polymer-coated and nutrient-amended zeolite CRN material under cold and temperate flow conditions were assessed. Cold flow conditions refers to water temperatures less than 5 °C that are characteristic of polar and alpine regions, while temperate flow conditions denote mild water temperatures in the range 15 °C–25 °C. This study compliments previous works that examine the influence of freeze–thaw cycling on nutrient release under batch conditions (Freidman et al., submitted for publication). While these batch tests are theoretically sufficient to predict nutrient release timeframes, in practice this understanding is not directly applicable to dynamic and fluctuating systems of flow through PRB media. Fluctuations within PRBs were also examined through the influence of changing flow velocity and petroleum hydrocarbon concentration on the rates of nutrient release. These findings will have significant implications for PRB design and longevity of biodegradation at contaminated sites in low nutrient environments.

Section snippets

Materials

A polymer-coated soluble fertiliser, Polyon™, and a nutrient-amended zeolite, Zeopro™, were examined in this study (Table 1). Similar to previous works, Zeopro™–GAC mixtures were also investigated (Freidman et al., submitted for publication). Additional CRN material information can also be found in previous works (Freidman et al., submitted for publication). All materials were sterilised with ethylene oxide prior to the commencement of flow cell experiments (Steritech).

Flow cell design

Flow cells were

Longevity of nutrient release

The pH in Polyon™ flow cells at 4 °C and 23 °C increased from 5.38 to 5.67 and 5.52 to 6.16 across 3500 BV passing, respectively (Table 2). The EC decreased from 1200 to 340 μS/cm at 4 °C and from 2800 to 490 μS/cm at 23 °C across 3500 BV passing (Table 2). These EC results suggest that nutrient concentrations through the Polyon™ bed decreased across 3500 BV passing, and that the concentration of individual nutrient constituents in solution varied overtime; as reflected by increasing pH values.

Discussion

An increase in temperature commonly results in increased nutrient release from polymer-coated fertilisers (Husby, 2000, Jacobs, 2005, Du et al., 2006, Adams et al., 2013). In this study and others, Polyon™ clearly demonstrates faster release of N–P–K at 23 °C compared to 4 °C (Adams et al., 2013). Differential release between N–P–K at 4 °C, specifically total NH3 > NO3 > K+ > PO43−, is consistent with previous findings (Husby, 2000, Jacobs, 2005, Adams et al., 2013). For example, Adams et al.

Conclusion

The longevity of nutrient release, influence of flow velocity and effect of petroleum hydrocarbon concentrations on nutrient release were examined to inform the application of CRN materials to PRBs at petroleum hydrocarbon contaminated sites subject to low nutrient groundwater. The longevity of N–P–K release from Polyon™ and Zeopro™ was shown to be extended at 4 °C. In the presence of GAC, however, accelerated depletion of N–P–K from Zeopro™ was observed. Dilution of nutrient concentrations in

Acknowledgements

The authors gratefully acknowledge the financial support of Australian Antarctic Science Project 4029 and The Particulate Fluids Processing Centre. We extend our thanks to Dr Simon Crawford of the Melbourne Advanced Microscopy Facility, The University of Melbourne for his assistance with particle imaging. Sally Gras is supported by The ARC Dairy Innovation Hub (IH120100005).

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