A Comprehensive Adsorption Study of 1-Hydroxy-2-Naphthoic Acid using Cost Effective
Engineered Materials
Muhammad Aurang Zeb
1
, Ghulam Murtaza
1
, Muhammad Aamer Hussain
1
, Khadija Tul Kubra
2
,
Ralph Muvhiiwa
3,4
, Lueta-Ann De Kock
3
, Francis Hassard
3
,
4,*
1. Institute of Soil and Environmental Sciences, University of Agriculture Faisalabad, Punjab,
Pakistan.
2. Government College University Faisalabad, Punjab, Pakistan.
3. Nanotechnology and Water Sustainability (NanoWS) Research Unit, University of South Africa,
College of Science Engineering and Technology (CSET), UNISA Science Campus, 1710
Roodepoort, Johannesburg, South Africa.
4. Cranfield University, College Way, Bedford, MK43 0AL, UK.
*Corresponding author: Francis Hassard (
francis.hassard@cranfield.ac.uk)
Abstract
The naphthoic acids are challenging and costly to remove from water and soil. 1-Hydroxy-2-
Naphthoic acid (HNA) is a phenanthrene decomposition product from petroleum-contaminated
environments during the aerobic decomposition of polyaromatic hydrocarbons. The
hydrogeological mobility of hydrocarbon breakdown products represent a pollution risk (e.g. for
drinking water sources). Adsorption to biochar produced from agricultural by-products is a useful
strategy to remediate contaminated wastewaters. Here, we examine the controls on the HNA
adsorption to the adsorbents magnetite, clay minerals, biochar and magnetite enriched
companion materials, namely the influence of contact time, contaminant concentration and
ionization effects at different pH. The adsorption of HNA was investigated using low-cost and
readily available adsorbents: i) wheat straw biochar, ii) rice husk biochar, iii) sugarcane biochar,
iv) zeolite, v) montmorillonite, vi) magnetite and their enriched magnetic companions. Magnetite
Environmental Technology & Innovation, Volume 19, August 2020, Article number 100881
DOI:10.1016/j.eti.2020.100881
Published by [Elsevier. This is the Author Accepted Manuscript issued with: Creative Commons Attribution Non-Commercial No Derivatives License (CC:BY:NC:ND 4.0).
The final published version (version of record) is available online at DOI:10.1016/j.eti.2020.100881. Please refer to any applicable publisher terms of use.
enriched biochar exhibited greater adsorption rates compared with their nonmagnetic analogs
for HNA. The maximum adsorption capacity of the magnetite enriched compounds (initial water
concentration of 0.32 mmol HNA.L
-1
) was 0.45 mmol.HNA.g
-1
of enriched zeolite. The magnetite
enriched biochar and conventional biochar showed similar adsorption kinetics although
magnetite enrichment improved the efficacy of adsorption. The adsorption fitted the pseudo-
second order model in all cases, suggesting the dominant mechanism of adsorption was
chemisorption. The magnetite enrichment reduced intra-particle diffusion, possibly due to fouling
or blocking of pores within the particles, as evidenced by the decrease in diffusion rate
constants. Overall, HNA adsorption improved after magnetic enrichment due to magnetite
competing with inhibition sites on the biochar carriers. These findings translate into equivalence
between magnetite and magnetic biochars, suggesting cheaper alternative materials could be
synthesized in situ with the biochar acting as both an adsorbent and carrier, increasing the
prospect of designer biochars for targeted pollutant removal. This approach has the potential to
be used for wastewater treatment or for application as a soil additive for remediation of runoff
from contaminated soils.
Keywords: Enriched adsorbents; zeolite; organic pollutants; biochar; 1-Hydroxy-2-Naphthoic
Acid;
poly aromatic hydrocarbons.
1. Introduction
Inappropriate treatment or disposal of hydrocarbon waste can lead to contamination due to
leaching and transport of organic pollutants into the soil matrix (Mao et al., 2015). Organic
pollutants come from a variety of sources including wastewaters which are derived from food,
leather and textile industries and the petrochemical industry amongst others (Hassard et al.,
2015). Petroleum hydrocarbons (PH) are widely found pollutants in soil and contaminated water
due to their ubiquity and frequency of use (Qadir et al., 2008). Elevated PH concentrations in
industrial wastewater effluents have been reported from low income scenarios (e.g. southern
Punjab) and this polluted water is frequently released to the environment without sufficient
treatment. Wastewaters containing PH are also used for agricultural irrigation creating a
pathway for contamination of soil (Feenstra et al., 2000) and accumulation within crops, soil and
surface water. The accumulation of the PH pollutants within the tissues or on the surfaces of
crops could also promote a human health exposure pathway (Raschid-Sally et al., 2005; Rattan
et al., 2005). The PH are mostly hydrophobic in nature, they are preferentially adsorbed to soil
particles, and they can persist within soils for many years. Clean-up of these contaminated soils
and treatment of run off wastewater is critical to mitigate environmental human health exposure
(Baedecker et al., 1993, Cozzarelli et al., 1994 Das and Mukherjee, 2007). Clearly additional
research is required into novel technologies which can remove PH and their breakdown
products.
The breakdown products of PH are of particular concern as they are predominately polar
chemicals, which are readily water soluble, have high hydrogeological mobility and therefore
elevated pollution potential for groundwater. 1-Hydroxy-2-Naphthoic acid (HNA) is the first
phenanthrene decomposition product in petroleum-contaminated soils during the aerobic
decomposition of polyaromatic hydrocarbons (PAH) and is a widely used surrogate for PAH and
other breakdown products of PH (Hanna and Carteret, 2007; Carney et al. 2008). HNA is not
just a useful surrogate, it is in itself a compound which needs to be treated to reduce the toxicity
of wastewaters. For example, HNA irritates the human respiratory system, causes inflammation
of the eyes and skin and can disrupt normal gut function in humans and animals. Several
studies have shown HNA as a potent inhibitor of intracellular communication and highlighted a
possible role of this compound as a mutagen (Samanta et al., 1999). Quantitative risk estimates
for exposure to HNA are not well defined, however oral exposure is considered one route due to
consumption of contaminated crops or water. The acute oral Lethal Dose 50 (LD
50
) of HNA in
rats was 823-1040 mg.kg
-1
body weight. The no observed effect level (NOEL) for HNA is
considered to be much lower 12-60 mg.kg
-1
body weight per day (European Chemicals Agency,
2019) suggesting removal of HNA from drinking water and soils through treatment is necessary,
particularly in areas prone to high levels of contamination.
Currently, wastewater treatment rely on biological or chemical oxidation processes such as
aerobic or anaerobic bio-treatment, ozone or advanced oxidation processes (Rolph et al., 2018).
These processes are costly are require significant operation and maintenance investment. A
promising route for cost effective remediation of PH breakdown products is
adsorption to natural
or engineered adsorbents (Chen et al., 2011). Natural adsorbents are cheaper and more readily
available than conventional industrial adsorbents such as granular activated carbon (GAC) and
would not require costly regeneration to be effective as additional material can be produced in
situ as required. A diverse range of organic and inorganic contaminants (include PH and HNA)
can be removed using adsorbents such as magnetite and biochar (Cundy et al., 2008; Lu et al.,
2010). Biochar in particular is considered multifunctional and useful for removal of PH
breakdown products from wastewater. Concentration of the pollutant and phase separation
(usually water to solid) could facilitate a safe disposal route, for example incineration (Singh et
al., 2018). Identifying a suitable material which does not create secondary pollution concerns
has proved challenging (Hanna and Carteret, 2007). Recent work has shown the propensity of
‘designer’ or enriched natural materials (where surface area, surface charge or porosity is
altered) to target the specific removal of contaminants for removal of organic pollutants such as
pesticides or PH (Busquets et al., 2014; Rolph et al., 2018; Rolph et al., 2019). Other natural
materials such as the minerals magnetite (Fe
3
O
4
), zeolite and montmorillonite which have high
surface area and ion exchange capacity to remove a wide range of pollutants / ions from
solution (Rashed, 2013). Biochar and iron oxides are readily used separately for the adsorption
of organic pollutants however, their interaction effect requires further study under controlled
conditions. Our hypothesis was that magnetite enrichment of biochar and clay minerals would
enhance the adsorption properties (number and availability of active sites) of natural biochar
adsorbents towards HNA for the remediation of contaminated waters. Studies were done to
assess the removal of HNA under a variety of adsorption conditions and kinetic modeling was
undertaken to assess the dynamic removal rate and permit comparison between materials and
suggest the dominant mechanism(s) of adsorption.
2. Materials and Methods
2.1. Chemicals
1-Hydroxy-2-naphthoic acid, sodium hydroxide (NaOH) both with a purity ≥97 % and hydrochloric
acid (HCl) were obtained from Sigma-Aldrich (Islamabad, Pakistan). Two types of clay minerals
(natural zeolite and montmorillonite), three types of biochars (wheat straw, sugarcane and rice
husk biochars) and one iron oxide (magnetite) were used for investigating the sorption of organic
pollutants from water. Biochar produced by pyrolysis at 350 ⁰C were obtained from NARC
(Islamabad, Pakistan). Magnetite and natural zeolite were obtained from Meiqi Industry and Trade
Co., Ltd (Gongyi City, China) both having a purity of ≥99 percent and particle sizes of 53 and 150
