Treatment of Pb ion contaminated wastewater using hazardous parthenium (P. hysterophorus L.) weed

 
• 1/n

  Freundlich model constants related to intensity of adsorption

 
• B

  Constant related to adsorption energy E in mol² kJ⁻²

 
• E

  Free energy of adsorption in kJ mol⁻¹

 
• e

  Polanyi potential

 
• q

  Metal uptake capacity in mg g⁻¹

 
• R

  Gas constant in kJ mol⁻¹ K⁻¹

 
• T

  Temperature in K

 
• V

  Volume of the solution in L

 
• W

  Mass of biosorbent in g

 
• C_e

  Equilibrium metal ion concentration in solution mg L⁻¹

 
• C_o

  Initial metal ion concentration in mg L⁻¹

 
• C_a

  Equilibrium metal ion concentration adsorbed on adsorbent in mg L⁻¹

 
• G

  Gibbs free energy in kJ mol⁻¹

 
• H

  Enthalpy in J mol⁻¹

 
• K^’

  First-order Lagergren kinetics rate constant of biosorption in min⁻¹

 
• K^”

  Pseudo-second-order rate constant of biosorption in mg g⁻¹ min⁻¹

 
• K_d

  Distribution coefficient

 
• K_F

  Freundlich model constants related to adsorption capacity

 
• K_L

  Langmuir biosorption constant in L mg⁻¹ relating the free energy of biosorption

 
• K_p

  Intra-particle diffusion rate constant in mg g⁻¹ min^−1/2

 
• q_e

  Equilibrium metal uptake capacity in mg g⁻¹

 
• q_m

  Monolayer biosorption capacity of the biosorbent in mg g⁻¹

 
• R_L

  Dimensionless constant separation factor

 
• S

  Entropy in kJ mol⁻¹

In the last two decades, there is a continuously growing interest of researchers in developing new techniques and materials for removal of hazardous pollutants from wastewater. Among the water pollutants, heavy metals, in particular, Pb is more dangerous due to its toxic nature to human being (Mishra & Patel 2009). This Pb ion contamination is mainly originated from various industrial activities, fuel refining and use, metallurgy, pigmenting, etc. (Volesky & Holan 1995). The presence of Pb ion in the human body can cause anemia, gastrointestinal, cardiovascular, nervous, and memory diseases mainly in children and pregnant women. The maximum permissible limit of Pb ion concentration in drinking water set by the European community and the World Health Organization (WHO) is 0.05 mg L⁻¹ (Gupta & Rastogi 2008).

The conventional methods used for treating Pb ion contaminated wastewater includes physical processes, such as UV radiation, filtration and membrane process, etc. The chemical processes, namely chlorine, ozone, iodine treatment, etc. and physicochemical processes, such as ion exchange, chemical coagulation and precipitation, etc. have been used (Gupta & Ali 2004). Although these techniques have their advantages, they also have different disadvantages, such as inefficient removal of metal ion, the requirement of expensive chemicals, not practicable and sometimes cause secondary pollution. Another physicochemical process, adsorption process is one of the efficient methods studied extensively (Ghaedi et al. 2016; Mazaheri et al. 2016). But high adsorbents price and the requirement of adsorbent regeneration step make this process inadequate.

In recent years, the living and nonliving biomass of biological materials have received considerable attention due to their binding ability of heavy metal ions (Jianlong et al. 2001). Literature survey reveals that biosorption process was studied extensively for removal or recovery of heavy metal ions from wastewater using several biological materials as an adsorbent. The range of biomass as biosorbent is wide including husk, bark, leaves, aquatic plants, algae, animal bone, fungi, bacteria, yeast, etc. (Gupta & Ali 2004; Asfaram et al. 2016). The significant advantages of biosorption process over other conventional treatment techniques include inexpensive materials, derived from renewable sources, easy availability, high removal efficiency of pollutants, no requirement of adsorbent regeneration, and possibility of metal recovery.

The biomass of parthenium (P. hysterophorus L.), a native of Mexico and now widely spread in Australia, China, Pacific Islands, India, and the subcontinent, has recently drawn the attention of researchers due to its hazardous nature and harmful effect on human beings. Prolonged exposure of parthenium (P. hysterophorus L.) weed may cause several health issues in people, such as asthma, eczema, hay fever, black spots, blisters around eyes, and burning. This species is amply available and has no economical use. Only a few studies found reporting the utilization of parthenium were, as a biosorbent for Cr (VI) ion sorption (Venugopal & Mohanty 2011), Cd (II) ion sorption in aqueous solution (Ajmal et al. 2006). The weed was also studied in the production of biofuels (Singh et al. 2015).

In this study, the waste biomass of parthenium (P. hysterophorus L.) weed was investigated as biosorbent for Pb ion sorption in aqueous solution. First, the biosorbent was developed from waste biomass of parthenium (P. hysterophorus L.) and their physicochemical characteristics such as bulk density, porosity, Brunauer–Emmett–Teller (BET) surface area, particle size, moisture content, point of zero charge, Fourier transform infrared spectroscopy (FTIR) transmittance spectra, field-emission scanning electron microscopy and energy-dispersive X-ray (FESEM-EDX) spectra were analyzed. Next, the batch biosorption experiments were conducted to evaluate the effect of contact time, initial Pb ion concentration, adsorbent dose, pH, agitation speed and temperature on Pb ion uptake. Then, the Pb ion sorption kinetic studies were carried out by fitting the biosorption experimental data with the pseudo-first-order kinetic model, pseudo-second-order model, and Weber–Morris model. Finally, the equilibrium data were tested with three isotherm models (viz. Langmuir, Freundlich, and Dubinin–Radushkevich (D-R)) and the thermodynamics parameters, such as Gibbs free energy (G), enthalpy (H), and entropy (S) were evaluated.

Parthenium (P. hysterophorus L.) weed was collected from inside IIT Guwahati campus. The adhering impurities and dust were removed from plants surface by cleaning it with tap water. Then, those were dried naturally in sunlight for one week, then in hot air oven (Sonuu Instruments, India) at 70 °C (343 K) for 24 h. Next, the dried weeds were ground into fine powder in mixer grinder (Bajaj, mixer grinder, India). Powdered biosorbent was sieved through 120 BSS mesh screen (particle size: 125 μm) (Multi Science, India) and then the powdered biosorbent was stored in zipping lock plastic bags for further applications.

A synthetic wastewater stock solution of 1,000 mg L⁻¹ Pb ion concentration was made in the laboratory by dissolving 1.606 g of lead nitrate (minimum purity 99.5%, Merck, Germany) in approximately 250 mL of deionized water. 10 mL of 0.1 M HNO₃ (Merck, Germany) was added and diluted to 1,000 mL with deionized water. This stock solution was used after further dilution with deionized water; the required solutions concentrations were ranging between 20 and 200 mg L⁻¹. All the chemicals and reagents used in these studies were of analytical grade and used without any further purification.

The physicochemical properties of biosorbent parthenium (P. hysterophorus L.) such as bulk density, porosity, BET surface area (Coulter, SA3100, Germany) were measured. Also, the particle size (Mastersizer, APA 2000, UK), moisture contain and point of zero charge (Beckman Coulter, Delsa^Tm Nano C, Germany) were analyzed. The bulk density of developed biosorbent was measured as 0.42 g cm⁻³, porosity as 45%, BET surface area as 20.79 m² g⁻¹, particle size as <125 μm, moisture content as 68% and point of zero charge as 5.6. The pH value of the biosorbent dispersed solution was measured using Eutech Instruments, pH700, India. The FTIR transmittance spectra (Shimadzu, IR Affinity-1, Japan) of both native as well as Pb ion loaded biosorbent were analyzed using KBr (Merck KGaA, Germany) matrix. The elemental composition of native, as well as Pb ion, adsorbed biosorbent were analyzed by FESEM-EDX (Zeiss, Sigma, USA) analysis.

All the batch sorption experiments were carried out in conical flasks (250 mL). To evaluate equilibrium contact time of biosorption process an equal amount (1.0 g L⁻¹) of dry native biosorbent was mixed with 200 mL of the solution having different initial Pb ion concentrations (20, 50, 70, 100, 150 and 200 mg L⁻¹). The measured natural pH value of the solution was found to be 2.6. This solution was shaken at 200 rpm rotational speed using an incubator shaker (Daihan LabTech, LSI-3016R, India) at room temperatures (303 ± 2 K). At different time intervals, viz. 10, 20, 40, 60, 90, 120, 150 and 180 min, a 5 mL volume of solution were taken out using a dispensary syringe (Hindustan Syringes, India) from the respective solutions. Then, it was filtered through Whatman No. 1 filter paper (O Sicerin & Biva, India). First, 1 mL of filtrate was discarded to avoid the possibility of adsorption by filter paper. The rest volume of filtrates was diluted 10-fold and then analyzed by using atomic absorption spectrometer (Varian, AA240AS, The Netherlands) for determining the residual Pb ion concentration in the solution. The standard method for Pb ion analysis prescribed in ASTM-D3559 was followed. Next, in order to investigate the effect of biosorbent dose on Pb ion uptake, a dose of 0.2, 0.4, 0.6, 0.8 and 1.0 g L⁻¹ of native biosorbent was used for Pb ion solution having the concentration of 50 and 100 mg L⁻¹. The effects of other parameters, such as solution pH (at the pH value of 2, 2.6, 4, 5 and 6), temperature (at 293, 303, 313 and 323 K) and rotational speed (50, 100, 150, 200 and 250 rpm) were investigated. For these experiments, three different initial Pb ion concentrations 50, 100 and 150 mg L⁻¹ and an optimum biosorbent dose 1.0 g L⁻¹ was used. The average value of three replicate were taken and the % error was less than ±3.5% of the average value.

The Langmuir isotherm model for Pb ion sorption onto parthenium (P. hysterophorus L.) fitted better to the experimental equilibrium sorption data. The calculated value of monolayer biosorption capacity of the biosorbent (q_m) by Langmuir isotherm model was 11.23 mg g⁻¹ (R² = 0.99) which is almost similar to experimentally obtained maximum uptake value.

The value of mean free energy of biosorption gives an idea about biosorption mechanism, whether the biosorption that occurred is physical or chemical (Srividya & Mohanty 2009). The value of E between 8 to 16 kJ mol⁻¹ signifies that the biosorption process takes place chemically, and the value of E less than 8 kJ mol⁻¹ signifies that the biosorption process takes place physically. In the present study, the value of E calculated is 12.03 kJ mol⁻¹, which suggests that chemical ion exchange mechanism could have taken a significant role in biosorption process. However, the correlation coefficients for the D-R isotherm model were found to be lower than that of Freundlich model.

The values of distribution coefficient (K_d) were calculated for 50 mg L⁻¹ of initial Pb ion concentration in solution at different temperatures, and corresponding values of ΔG were computed using Equation (12). The negative value of the change in Gibbs free energy (ΔG) signifies that the Pb ion sorption onto parthenium (P. hysterophorus L.) was a feasible and spontaneous process at studied conditions (Table 3). However, the decreasing trend of ΔG value with increasing temperature was observed which indicates that feasibility of the process decreases with increasing temperature. The values of change in enthalpy (ΔH) and entropy (ΔS) were calculated from the slope and intercept of ln K_d vs 1/T (Equation (13)) plot respectively. The estimated values of ΔH and ΔS were −7.06 kJ mol⁻¹ and −10.64 J mol⁻¹ respectively (Table 3). The negative value of ΔH suggests that biosorption of Pb ion onto parthenium (P. hysterophorus L.) was an exothermic process. Also, the ΔH value between 2.1 and 20.9 kJ mol⁻¹ suggested the biosorption of Pb ion on parthenium (P. hysterophorus L.) as a physical process. The negative value of the change in entropy (ΔS) is an indication of the decrease in the randomness at the solid/solution interface during the biosorption process.

The Pb ion uptake capacity of various biosorbents reported in the literature along with the absorbent parthenium (P. hysterophorus L.) used in this study is summarized in Table 4. From the present study, the maximum Pb ion uptake value q_m for parthenium (P. hysterophorus L.) was found to be 11.47 mg g⁻¹ for initial Pb ion concentration of 150 mg L⁻¹ at studied operating conditions. The maximum Pb ion uptake value by parthenium (P. hysterophorus L.) obtained in the present study is comparable with other biosorbent. The cost and practicability of the biosorption process mainly lie on the cost, availability, and sustainability of biosorbent. The biosorbent used in the present study is abundantly available free of cost, widely spread, and itself is an environmental threat having no commercial applications. Also, by adding the labor charge for raw adsorbent collection, drying and grinding, storage and transportation, the overall cost for biosorbent preparation is very low as compared to expensive adsorbent and resins. The biosorption results and this comparison indicate that parthenium (P. hysterophorus L.) appears to be an economical, sustainable and efficient biosorbent for Pb ion sorption from wastewater. Hence, parthenium (P. hysterophorus L.) as biosorbent for Pb ion biosorption could be a fruitful utilization of this hazardous weed.

In this study, a low-cost, sustainable biosorbent was prepared from waste biomass of hazardous parthenium (P. hysterophorus L.) weed and used it in biosorption process for the treatment of Pb ion contaminated wastewater. The functional groups present in biomass were identified by FTIR transmittance spectra analysis and found that C-X, C-N, C = O, and C-O-C group were the main responsible functional groups for Pb ion sorption. The percentage removal of Pb ion was 98.3% achieved for initial Pb ion concentration of 50 mg L⁻¹ at the operating condition of biosorbent dose as 1.0 g L⁻¹, pH 4, room temperature (303 ± 2 K), agitation speed as 200 rpm, and equilibrium contact time of 150 min. Also, it was observed that biosorption process was efficient when metal to the biosorbent ratio in solution was small (<0.05). The biosorption rate kinetics closely followed the pseudo-second-order kinetic model (R² = 0.99). The adsorption isotherm of Pb ion adsorption on parthenium (P. hysterophorus L.) weed was best described by Langmuir isotherm model (R² = 0.99) which suggest monolayer adsorption of Pb ion on the adsorbent. The calculated thermodynamic parameters indicate that biosorption process was a feasible, spontaneous process and exothermic in nature. The biosorption results suggested that parthenium (P. hysterophorus L.) weed is an efficient, low-cost and sustainable biosorbent for the removal of Pb ion from aqueous solutions.

The authors acknowledge the analytical facilities, i.e. FESEM, EDX analysis provided by Central Instruments Facility (CIF), IIT Guwahati.