Wet air oxidation of leachate containing emulsified and solubilized hydrocarbons from crude oil-contaminated soil

International Journal of Industrial Chemistry https://doi.org/10.1007/s40090-019-0187-2 RESEARCH Wet air oxidation of leachate containing emulsified and solubilized hydrocarbons from crude oil‑contaminated soil Ganesh Sharma1,2 · Kshitiz Dwivedi1,2 · Amit Bafana1 · Yogesh Pakade1 · Rajesh Biniwale1 Received: 14 September 2018 / Accepted: 4 June 2019 © The Author(s) 2019 Abstract The present research work is focussed on the treatment of leachate generated from crude oil-contaminated soil sites using wet air oxidation as an advanced oxidation process. The factors affecting the wet air oxidation (WAO) process, viz. temperature, pressure and time of treatment were optimized using central composite design and response surface methodology. The significant factors were optimized to maximize % COD removal from the leachate. The linear effects of pressure and temperature (p = 0.000); the square effects of pressure (p = 0.019) and time (p = 0.007) and the interaction effect of temperature–pressure (p = 0.002) were found to be significantly governing the % COD removal. The maximum COD removal of 76% was obtained at temperature = 244 °C, time = 30 min and pressure = 5 bar. Further, the biodegradability index (BOD5/COD) increased from 0.14 ± 0.007 of the untreated leachate to 0.48 ± 0.02 of the wetox-treated leachate. Moreover, the degradation of recalcitrant hydrocarbons in initial leachate by WAO treatment was confirmed using GC–MS analysis. Keywords Crude oil-contaminated soil · Leachate · Recalcitrant hydrocarbons · Wet air oxidation · Response surface methodology · Biodegradability index Introduction Crude oil has been widely used for the production of different products like gasoline, diesel and heavy oil. Crude oil is a complex mixture of aliphatic saturated hydrocarbons, cyclic saturated hydrocarbons, polycyclic aromatics hydrocarbons (PAH) and PAH containing nitrogen and sulphur compounds [1]. PAH are considered toxic, carcinogenic, and mutagenic [2]. Accumulation of long-chain saturated hydrocarbons, viz. nonacosane ( C29H60), hentriacontane (C31H64), and tritriacontane (C33H68) are known to cause severe health problems in human [3] including skin irritation, eye irritation, respiratory irritation, drowsiness or dizziness, and possibly cancer. Worldwide average oil demand for the year 2016 was 96.1 mb/day, and it is estimated to reach up to 97.6 mb/day and 99 mb/day for the year 2017 and 2018 [4]. Increasing global demand for petroleum products leads to * Rajesh Biniwale 1 CSIR-National Environmental Engineering Research Institute (NEERI), Nehru Marg, Nagpur 440020, India 2 Rashtrasant Tukadoji Maharaj Nagpur University (RTMNU), Nagpur 440033, India increase in chances of crude oil spillage due to the transportation of oil, storage tank rupture, and pipeline leakage, thereby causing soil and water pollution [5]. Land treatment unit (LTU) has been reported as a potential bioremediation process for the treatment of crude oil contaminated soil [6]. In order to attain significant bioremediation using LTU the total petroleum hydrocarbon (TPH) concentration of contaminated soil should be below 8%. In addition, for an effective on-site bioremediation, (1) contaminated soil should contain less than 5% TPH; (2) proper irrigation system must be installed to maintain the soil moisture content for proper biodegradation and (3) the depth of the soil should not be more than 18 in. [7]. During the infiltration of water by irrigation and rainfall, water percolates through the contaminated soil and leaches out through LTU [8]. These leachates contain emulsified and solubilized nonbiodegradable and partially degraded eco-toxic hydrocarbons which cause detrimental effects on the groundwater resources [9]. Scott and co-workers investigated the biodegradation of TPH in LTU leachate in California, USA [9]. They also reported a very low biodegradation (12%) of TPH owing to their recalcitrant nature due to the presence of long-chain hydrocarbons (≥ C20) in the leachates. The safe 13 Vol.:(0123456789) International Journal of Industrial Chemistry disposal of leachate generated from LTU is a key issue and certain pretreatment is necessary. In recent years, there has been an increasing interest in the use of advanced oxidation processes (AOPs) for the treatment of recalcitrant organic compounds in wastewater, and crude oil-contaminated soil. These AOP technologies include Fenton, Fenton-like process, ozonation, wet air oxidation, photo-catalysis, etc. Wet air oxidation (WAO) involves the aqueous phase oxidation of organic and some oxidizable inorganic components at elevated temperature 150–325 °C and pressures 5–200 bar [10]. It involves the formation of highly reactive hydroxyl radical which has a high oxidation potential, i.e., E0 = 2.8 V [11]. WAO oxidizes recalcitrant organic component into biodegradable intermediates or mineralizes to carbon dioxide and water [12]. WAO has been widely reported for the treatment of oil sludge, dye degradation, municipal landfill leachate, and degradation of PAH in contaminated soil [13–16]. Jing et al. compared the wet air oxidation of oil sludge in presence of catalyst ( Ni2+) and without catalyst by keeping temperature, pressure and time constant. The oil sludge with an initial COD of 20,000 mg l−1 showed 99.7% and 88.7% COD removal in presence of catalyst and without catalyst, respectively [13]. PAH degradation study was carried out using WAO in presence and absence of free radical promoter by Rivas et al. [17]. Four PAH namely acenaphthene, phenanthrene, anthracene and fluoranthene underwent 80–100% conversion at a temperature of 190 °C, a pressure of 50 bar and reaction time of 80 min while the addition of hydroxyl radical promoter reduced the reaction time up to 60 min and temperature up to 100–150 °C [17]. Some researchers have reported the applicability of WAO for the treatment of landfill leachate. Rivas et al. investigated the differential impact of sulphate radical and hydroxyl radical promoted WAO of landfill leachate with an initial COD of 2700–7000 mg l−1. The temperature of 180–270 °C and pressure of 40–70 bar resulted in 20% COD conversion, while WAO using H 2O 2 provided 35% COD removal, and the addition of oxone resulted in 80% COD conversion [18]. In another study, factorial design methodology was used to optimize catalytic wet air oxidation (CWAO) conditions for the effective COD reduction of landfill leachate with an initial COD of 4920 mg l−1 and biodegradability index of 0.073. The temperature of 200 °C and time of 22 min had shown 78% COD reduction with 250 mg l−1 Cu2+ and 1500 mg l−1 H2O2 loading at oxygen partial pressure of 25 bar [15]. However, to the best of our knowledge, no such study has been conducted previously for the WAO treatment of leachate generated from crude oil contaminated soil sites which further establishes the novelty of the present study. The present research work aims to develop a WAO-based process (...truncated)