Keywords

8.1 Introduction

Over the past few decades, the industrial revolution plays an instrumental role in the economic growth and prosperity of the country. But, with the rapid expansion of industries, an enormous pressure is exerted on the environment. It turned out that the residence of environmental contaminants in environmental media, viz. round water, surface water soil and sediments, poses a serious threat to the environment and human health (Ghasemi et al. 2014; Naushad et al. 2016a). Subsequently, the impacts on water resources seem to be more severe which cannot be overlooked. The problem of massive water pollution is demarcated as the consequence of the discharge of industrial wastewater into the water bodies. As a matter of fact, billions of tons of wastewater are generated by industries every year (Sagasta et al. 2015).

The wastewater discharged as such into the rivers, lakes and streams results in health hazards such as eye irritation, skin and neurological problems, degenerative heart disease, gastroenteritis, blue baby syndrome, typhoid fever, shigellosis, salmonellosis, campylobacteriosis, cholera, giardiasis, cryptosporidiosis and hepatitis A and liver cancer in animals (Eynard et al. 2000; Mahmood and Maqbool 2006; Akpor and Muchie 2011). In addition, wastewater effluents are accountable for ruining the quality of receiving water bodies resulting in problems of eutrophication of water bodies, biomagnification in the aquatic life and decreased dissolved oxygen (Welch 1992; Akpor and Muchie 2011). These problems are getting grimmer day by day. So, in order to protect the receiving waters from these obnoxious effects, specialized treatments are needed.

The researcher’s works around the clock to develop methods for tackling these profound effects of industrial pollutants are continuously going on. An array of technologies are available for the pollutants remediation, such as advanced oxidation, ozonation, chemical precipitation, ion exchange, coagulation, flocculation, electrodialysis, ultrasonic treatment, reverse osmosis, membrane filtration, solvent extraction and adsorption (Abdulkarim et al. 2002; Al-Ghouti et al. 2010; Bhattacharyya and Gupta 2008; Bratskaya et al. 2009; Chang et al. 2009; El Samrani et al. 2008; Hall et al. 1990; Ku and Jung 2001; Landaburu-Aguirre et al. 2010; Mohsen-Nia et al. 2007; Murthy and Chaudhari 2008; Nataraj et al. 2007; Ostroski et al. 2009; Suzuki et al. 2000; Terry 2010; Al-Othman et al. 2012; Mittal et al. 2016; Naushad and ALOthman 2015; Alqadami et al. 2017; Albadarin et al. 2017). But, many of these technologies are ineffective because of the shortcomings of generation of toxic fumes during chemical precipitation, high power consumption in reverse osmosis method, secondary pollution problem during ion-exchange method, increase sludge volume generation in coagulation/flocculation and membrane fouling during membrane filtration (Dialynas and Diamadopoulos 2009; Fu and Wang 2011; Shafiq et al. 2018). The adsorption process is considered a vivid remediation technology owing to its simplicity, reliability and low maintenance cost. Activated carbon holds a significant promise as an efficient adsorbent for pollutant removal (Ahmad et al. 2012; Naushad et al. 2016b). However, in spite of its high adsorption nature and maximum porous surface area, the problem of high cost of production has inclined the researchers towards the development of low-cost adsorbents. Date palm is one such low-cost adsorbent which have been extensively used throughout the world for removal of various types of pollutants. In this review, the research advances in the use of date palm for removal of various wastewater pollutants as well as its role in phytoextraction have been documented.

8.2 Chemical Composition and Properties of Date Palm

Date palm known as Phoenix dactylifera L. scientifically is one of the major commercially growing crops in Middle East Asia and North Africa (Ahmad et al. 2012). Its global production has observed to be around 7.68 million tons in 2010 (Tang et al. 2013). As far as regional distribution is concerned, it has been seen that around 60 million date palm trees are cultivated in Asia (for instance, Iran, Saudi Arabia, Kuwait, Bahrain, Turkmenistan, UAE, Iraq, Pakistan, Oman and Yemen) and approximately 32.5 million date palm are grown in Libya, Algeria, Mali, Egypt, Mauritania, Morocco and Niger countries of Africa region (Jamil et al. 2016; Shafiq et al. 2018). Besides being used as a fruit, date palm and its products are used for the purpose of pollutant removal over the centuries which are attributable to its chemical composition.

Indeed the chemical study of date palm revealed that it consists of cellulose (40–50%), hemicellulose (20–35%) and lignin (15–35%) as major components along with some minor components such as oil and proteins (Macedo et al. 2008). Cellulose is a crystalline polysaccharide consisting of a linear chain of up to 3000 β(1→4) linked d-glucose units. Hemicellulose though related to cellulose is unbranched and contains a lesser number of saccharide units compared to that of cellulose. The third major component, i.e. lignin, can contribute significantly to the adsorption property of date palm. Structurally, it contains complex and variable constituents. The three polypropylene units are present in its structure which are linked together by ether linkages (C–O–C) and carbon–carbon bonding (C–C). Therefore, its elemental composition has higher carbon percentage of around 62 wt% and lower oxygen percentage of 32 wt%. The presence of a large number of carbon atoms is commonly linked with a lower polarity and thus a better prospect for adsorption. As a consequence, the date palm is an ideal adsorbent for adsorption practices (Jibril et al. 2008).

8.3 Role of Date Palm in Environmental Remediation

Environmental remediation aims to reduce harmful substance exposure from groundwater, surface water and contaminated soil. To help with the remediation of affected sites, date palm has been widely explored as an adsorbent by researchers all around the world. Figure 8.1 depicts the role of date palm as an adsorbent in the removal of various industrial pollutants such as heavy metals , phenols, dyes as well as in phytoextraction.

Fig. 8.1
figure 1

Contribution of date palm in environmental remediation

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8.3.1 Removal of Heavy Metals

Contamination of water bodies by heavy metals is of serious environmental concern. Industries such as pulp and paper, tannery, mining, electroplating, smelting and textiles generate substantial amounts of heavy metals from wastewater which is discharged into the rivers and streams. Above their threshold limits, they tend to accumulate in the food chain, causing neurological disorders, cancer and accumulative poisoning (Abdulkarim and Al-Rub 2004; Al-Jlil 2010). Since the toxicity of heavy metals is one of the severe health issues for decades, therefore, efficacious recovery of heavy metals from the water bodies is the need of the time (Naushad et al. 2017). Date palm and its by-products have been investigated as a preferred solution towards removal of these toxic heavy metals by various researchers (Haleem and Abdulgafoor 2010; Al-Haidary et al. 2011).

Al-Jlil (2010) investigated the removal of various heavy metals such as Cr, Co, Cu, Zn, As, Pb and Cd from industrial wastewater by roasted date pits. The results revealed that the heavy metal concentration from industrial wastewater treated with roasted date pits was less than the permissible limits for crop production compared to untreated wastewater except for the Co ion whose concentration was observed to be two times higher than the permissible limits. However, the absence of Co ion was seen when roasted date pits are used in series with other adsorbents, i.e. bentonite clay.

The extent of adsorption of heavy metals is controlled by a number of factors such as contact time, pH, a dosage of the adsorbent, particle sizes, initial metal concentration and temperature. In a study by Al-Haidary et al. (2011), the adsorption of Pb from aqueous solution by date palm fibres and leaf base of palm (petiole) was examined by considering the effect of numerous parameters, for instance, contact time, solution pH, adsorbent dosage, particle sizes of date palm materials, ionic strength and temperature. An increase in adsorption of Pb ions was observed with increase in adsorbent dosage as well as with the increase in contact time. An increase in adsorbent dosage could result in an increase in the surface area, thereby providing more binding sites for adsorption. The linear Langmuir and Freundlich models were used to comprehend the adsorbate-adsorbent interaction. Based on Langmuir isotherm, the adsorption capacity of Pb ion onto date palm fibres and petiole was calculated as 18.622 and 20.040 mg/g, respectively. The pseudo-second-order kinetics model correlated well with the adsorption kinetics of Pb ion from aqueous solution onto palm fibres and petiole. In another study of heavy metal, i.e. Cu removal by date palm from aqueous solutions conducted by Belala et al. (2011a), the effect of adsorbent particle size on removal efficiency was examined. The authors concluded that the removal efficiency was highest with adsorbent particles of small size. Maximum efficiency was in the range between 60% and 80% with the adsorbent particle size below 1 mm. Further, the study performed by Al-Ghamdi et al. (2013) indicated that the adsorption of heavy metal Cd2+ increased to 51.1 mg/g from 29.06 mg/g with the decrease in particle size from 875 to 100 μm. However, increasing the solution pH from 1.69 to 3.71 resulted in an increase in adsorption capacity.

Besides being used as an adsorbent, the carbon-rich raw date palm can also be used for the preparation of activated carbon which has been extensively used as adsorbent material for removal of a variety of contaminants. The ability of date palm derived activated carbon to adsorb heavy metals from aqueous metal solutions and wastewater has been reported in several studies (Banat et al. 2003a; Hilal et al. 2012; Chaouch et al. 2013, 2014; Nwakonobi et al. 2018).

El Nemr et al. (2008) prepared activated carbon from date palm seed by dehydrating approaches using concentrated sulfuric acid for removal of Cr(VI) from aqueous solution. The results showed that adsorption capacity increases with a decrease in pH value. The maximum adsorption capacity reported was 120.48 mg/g. Nwakonobi et al. (2018) used activated carbon prepared from the date palm seeds for removal of heavy metals, viz. Pb, Cr and Cd, from brewery wastewater. The adsorption experiments were carried out in batch studies under conditions such as contact time and adsorbent dosage. It has been concluded that at 60 min of contact time, different adsorbent doses of 10 × 103, 20 × 103, 30 × 103 and 40 × 103 mg/L reduced the Cr and Pb concentration below the World Health Organization (WHO) maximum limits of 0.05 and 0.01 mg/L, respectively. Cd concentration was brought within WHO maximum limit (0.003 mg/L) using 30 × 103 mg/L of the adsorbent at 80 min of contact time. A summary of adsorption of different metal ions by date palm-based adsorbents is presented in Table 8.1.

Table 8.1 Removal of heavy metals from water and wastewater by date palm
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8.3.2 Hazardous Materials Removal

Phenol is regarded as one of the noxious pollutants found in the wastewater of ceramic, steel, petrochemical, oil, pharmaceutical , chemical and fertilizer industries (Aksu and Yener 2001). The presence of phenol in water bodies even at low concentration can cause chronic toxic effects. So, to remove phenol from the aqueous solution, adsorption onto the low-cost adsorbent such as date palm is widely employed. Banat et al. (2004) while investigating the adsorption of phenol onto raw and activated date pits concluded that activated date pits had 16 times higher adsorptive capacity compared to raw date pits. Thermodynamic parameters studied showed that the dye removal through adsorption was endothermic. Furthermore, an increase in phenol uptake by activated carbon was observed with an increase in initial phenol concentration from 10 to 200 ppm and temperature from 25 °C to 55 °C. While with an increase in solution pH (from 4 to 12), a decrease in phenol adsorption was noted. However, in a study by Mane et al. (2005), a decrease in the amount of phenol adsorption from 33.12 mg/g to 24.10 mg/g was observed with an increase in temperature from 30 to 60 °C. This indicated the exothermic nature of the reaction.

The research conducted by Abdulkarim et al. (2002) evaluated the phenol adsorption onto the date fruit pit prepared activated carbon . The results showed the high adsorption capacity of activated carbon for phenol, 2-nitrophenol and 2,4- and 2,4,6-trinitrophenol. Moreover, the experimental data for adsorption of phenols were found to fit both the Freundlich and Langmuir isotherms. Alhamed (2009) investigated the adsorption kinetics and performance of packed bed adsorbent for phenol removal using dates stones prepared activated carbon. Four different particle sizes (1.47, 0.8, 0.45 and 0.225 mm) of adsorbent were used for this study. The data of the adsorption kinetics of phenol exhibited a good fit with the pseudo-second-order kinetic equation.

8.3.3 Dye Removal

Dyes are coloured compounds used extensively by textile , tannery, paper, plastic, cosmetics, leather, food and pharmaceutical industries. It is estimated that worldwide over the year, around 7 × 105 tons of synthetic dyes are produced, 10% of which are discharged in the effluent during dyeing operations while 1–2% are known to lose in the effluent during manufacturing operations (Garg et al. 2004). As dyes are toxic and carcinogenic, so such dye-contaminated effluent when discharged into the natural receptor water could make water toxic to aquatic life. In addition, it has been reported that exposure to dye effluent may cause problems such as skin irritation, sore eyes, increased heart rate, jaundice carcinogenicity, chromosomal fractures and respiratory toxicity in humans (Papic et al. 2000; Ahmad and Alrozi 2011). Therefore, it is environmentally imperative to decrease the concentration of dyes in the wastewater before discharging it into the water bodies. Adsorption of dyes onto the date palm has been reported in the literature as a predominately accepted method for removal of different types of dyes including methylene blue, malachite green, crystal violet, eosin, acid black, etc. (Banat et al. 2003b, Belhachemi et al. 2009; Mahmoodi et al. 2010; Alshabanat et al. 2013; Alshabanat et al. 2016; Alzahrani and El-Mouhty 2016).

Table 8.2 summarizes a non-exhaustive list of studies related to the use of date palm and its by-products as well as activated carbon derived date palm for different dye removal. In particular, a study by Belala et al. (2011b) explored the biosorption of methylene blue from aqueous solution by date stones and palm trees waste. The maximum biosorption capacities obtained with date stones and palm trees waste for methylene blue were 43.5 and 39.5 mg/g, respectively. The authors also evaluate the experimental data through kinetic models. Results revealed the involvement of pseudo-second-order kinetics behind the adsorption of methylene blue on to palm trees waste and date stones.

Table 8.2 Summary of the removal of various dyes by the date palm
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Banat et al. (2003c) impregnated the raw date pits with 30% (wt.) KOH solution prior to carbonization (for 2 h at 600 ° C) and CO2 activation (for 1 h at 800 ° C) in order to study the effect of chemically activated date pits towards removal of methylene blue. An increase in adsorption capacity from 80.3 mg/g to 123.1 mg/g was observed upon chemical activation. The results were found to be opposite to that obtained during physical activation by Banat et al. (2003b). They reported a decrease in adsorption capacity from 80.3 mg/g to 12.9 mg/g and to 17.3 mg/g during activation of date pits at 500 °C and 900 °C, respectively. This points out that the uptake of dye by the activated carbon is not merely controlled by the surface area but also by the pore-size distribution and the adsorbent’s surface chemistry.

A comparative study of the removal of methylene blue by adsorption and photocatalytic degradation was reported by El-Sharkawy et al. (2007). Two types of activated carbon – steam-activated carbons and ZnCl2-activated carbons – were prepared from date pits. Among these two, the steam activated carbon was considered more efficient in the methylene blue dye decolourization. The higher surface area, the total pore volume and the basic nature of the surface are responsible for the better decolourization ability of steam activated carbon. Further, when the removal of methylene blue via adsorption and photocatalytic degradation was compared, it can be seen that with photocatalytic degradation, the complete removal of the dye occurs within 10–22 h. On the other hand, the methylene blue adsorbed on the activated carbon might not easily be recovered which therefore contribute to environmental pollution.

As apparent from the literature review, the date palm and its derived activated carbon is highly efficient in removal of methylene blue dye, but its adsorption capacity is not only limited to methylene blue (Table 8.2). The aqueous solutions contaminated with other dyes, for instance, crystal violet, malachite green, eosin and many more, could also be treated through the application of date palm. For example, in a study by Sulyman et al. (2016), adsorptive removal of crystal violet by date palm dead leaflets derived activated carbon was investigated. The equilibrium adsorption of crystal violet was determined under different initial dye concentration, pH contact time and adsorbent dose. The maximum adsorption capacity of date palm dead leaflets derived activated carbon was about 36.63 mg/g. In addition, it was found that dye removal increased with the increase in pH, adsorbent dose and contact time. Also, the isotherm equilibrium was well fitted by the Langmuir and Freundlich models.

8.3.4 Role in Phytoextraction

The content of heavy metals including chromium, copper, cadmium, arsenic, lead, zinc and nickel has increased continuously in the soil as a result of industrial activities. The presence of heavy metals in high concentrations not only inhibits the plant metabolic functions including physiological and biochemical processes, water absorption, photosynthesis, respiration, mitosis and plant’s cell organelles degeneration but also affects the size, composition and activity of soil microbes (Yao et al. 2003; Bhattacharyya et al. 2008).

The remediation of heavy metals from the contaminated soil through the phytoextraction method is now receiving research attention. Phytoextraction is one of the subprocesses of phytoremediation which encompasses the use of plants for the extraction of heavy metals from the contaminated soil. Date palms, however, are known to play an indispensable role in phytoextraction process. A huge number of studies have focused on the intercropping of various plant species with date palm for the removal of heavy metals (Hamid 2011; Mohebbi et al. 2012).

Hamid (2011) conducted an experiment to study the possibilities of remediation of heavy metals from the contaminated soil by alfalfa, maize and sunflower grown with and without date palm. He found that monoculture of sunflower had a significantly higher ability of cadmium uptake than alfalfa and corn. The copper and manganese uptake index was found to be higher in the monoculture of corn. Thus it can be seen that intercropping with date palm did not show a significant effect on the accumulation and removal of heavy metals. However, in another study by Mohebbi et al. (2012) on phytoextraction of heavy metals by corn, alfalfa and sunflower grown in monoculture and intercropping with date palm, it can be seen that date palm-intercropped sunflower has high biological concentration factor (BCF) values for Mn and Cu among other crops. The high value of BCF indicated retention of metals in roots thereby results in limiting the mobility of metals from roots to shoots.

Mohebbi (2012) in his study showed that Cu concentration in roots and shoots of corn, alfalfa and sunflower grown with and without date palm was more than 21 and 14 mg/kg, respectively. He concluded that among these three crops, the crop alfalfa exhibited the highest translocation factor when co-planted with date palm. On the contrary, higher translocation factor was recorded in monocropped sunflower compared to date palm co-planted sunflower.

8.4 Conclusion and Future Perspectives

Date palm which is known for its nutritional value has been proven to have considerable potential to remove the harmful substances from the wastewaters. As reported in the literature, the low-cost date palm has considered being a successful replacement for expensive activated carbon . This review is an attempt to cover the different areas where the date palm has been successfully used. Time and again, raw date palm and its by-products were tested as an adsorbent for effectual removal of various pollutants. However, different experimental conditions, such as solution pH, initial dye concentration, adsorbent dosage, contact time and temperature of the system, need to be taken into account during evaluation of the adsorptive capacity of date palm. Since, most of the studies revealed the pollutant removal from aqueous solution, hence, further study is needed to evaluate the pollutant removal from real wastewater. In addition, the actual mechanism behind the interaction between the adsorbent and the pollutant still requires detailed research.