semi-arid regions

Bioresource Technology xxx (2016) xxx–xxx

Contents lists available at ScienceDirect

Bioresource Technology journal homepage: www.elsevier.com/locate/biortech

Review

Waste biorefinery in arid/semi-arid regions Juan-Rodrigo Bastidas-Oyanedel, Chuanji Fang, Saleha Almardeai, Usama Javid, Ahasa Yousuf, Jens Ejbye Schmidt ⇑ Institute Center for Energy – iEnergy, Masdar Institute of Science and Technology, PO Box 54224, Abu Dhabi, United Arab Emirates

h i g h l i g h t s  The review discuss the water scarcity as main restriction of biorefinery in arid regions.  The review focus on MENA region available biomass to be used in biorefinery processes.  The review presents prices and market size of potential products from waste biorefinery in the MENA region.

a r t i c l e

i n f o

Article history: Received 3 February 2016 Received in revised form 1 April 2016 Accepted 2 April 2016 Available online xxxx Keywords: Waste biorefinery Seawater biorefinery Arid biorefinery Water scarcity

a b s t r a c t The utilization of waste biorefineries in arid/semi-arid regions is advisable due to the reduced sustainable resources in arid/semi-arid regions, e.g. fresh water and biomass. This review focuses on biomass residues available in arid/semi-arid regions, palm trees residues, seawater biomass based residues (coastal arid/semi-arid regions), and the organic fraction of municipal solid waste. The present review aims to describe and discuss the availability of these waste biomasses, their conversion to value chemicals by waste biorefinery processes. For the case of seawater biomass based residues it was reviewed and advise the use of seawater in the biorefinery processes, in order to decrease the use of fresh water. Ó 2016 Elsevier Ltd. All rights reserved.

Contents 1. 2.

3.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Valorization of palm residues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Biomass resource from dates waste and palm residues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Current status of palm waste management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Valorization of palm residues through biorefining technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1. Biofuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2. Activated carbon. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3. Biochar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.4. Organic fertilizer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.5. Natural fiber composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.6. Nanocomposite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Saltwater-based biorefinery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Seawater-based biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. Seawater-based biorefinery products. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1. Proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2. Collagen and gelatin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3. Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.4. Enzymes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.5. Chitin and chitosan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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⇑ Corresponding author. E-mail address: [email protected] (J.E. Schmidt). http://dx.doi.org/10.1016/j.biortech.2016.04.010 0960-8524/Ó 2016 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Bastidas-Oyanedel, J.-R., et al. Waste biorefinery in arid/semi-arid regions. Bioresour. Technol. (2016), http://dx.doi.org/ 10.1016/j.biortech.2016.04.010

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J.-R. Bastidas-Oyanedel et al. / Bioresource Technology xxx (2016) xxx–xxx

4.

5. 6.

3.2.6. Biofuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.7. Other products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Biorefinery of the organic fraction of municipal solid waste. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Creating value from waste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.1. Biogas and electricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.2. Organic acids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.3. Bioplastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. Cost and externalities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction Arid and semi-arid regions are defined by their water scarcity. A water scarcity indicator is the annual renewable freshwater (m3/inhabitant/year) (FAO, 2012), where values below 500 are considered of Absolute water scarcity, values between 500 and 1000 are chronic water shortage, between 1000 and 1700 are regular water stress, and above 1700 are occasional or local water stress. As an example of arid region, the Middle East and north Africa (MENA) region is comprised of 20 countries (WB, 2015) with water scarcity concerns. From the 20 MENA countries, 14 are in absolute water scarcity, 4 in chronic water scarcity, and two in occasional of local water stress. Biomass availability in arid regions can be obviously considered limited for the fresh water scarcity which constrains forestry, and limited amount of agricultural activities compared with not arid regions. Biomass residues available in arid/semi-arid regions may be derived from Palm trees related activities (El-Juhany, 2010), as the in the MENA region, fisheries and marine capture-farmingprocessing in coastal arid/semi-arid areas (FAO, 2013), and the organic fraction of municipal solid waste (Hoornweg and BhadaTata, 2012). The biorefinery of such of biomass residues can produce valuable products, e.g. activated carbon, organic acids, biogas, that can contribute to the economy of the arid regions. Table 1 shows prices and market size of products that can be produce by waste biorefinery, and conventional products that can be alternatively produced by the biorefinery of residues (Alibaba, 2015; Bastidas-Oyanedel

Table 1 Bulk prices and market size of potential products from the valorization of solid organic waste in MENA region.

a b c d e f

Compound

Price (USD/tonne)

Market size (tonne/year)

Activated Carbon Biochar Glass Fiber Acetic acid Butyric acid Propionic acid Caproic acid Lactic acid Ethanol Butanol Diesel Jet Fuel Natural Gas

800–2000a 250-800a 800–1500a 400-800d 2000–2500d 1500–1700d 2000–2500d 1000–2100d 800–2000d 1000–1800d 456e 459e 0.05–0.12e

1.37
106 (2013)b 105 (2013)c 4
106 (2011)c 3.5
106 (2013)d 3
104 (2013)d 1.8
105 (2013)d 2.5
104 (2013)d 1.2
104 (2013)d 5.1
107 (2013)d 3
106 (2011)d 1.2
109 (2009)d 2.5
108 (2008)d 2.9
109 (2013)f

Alibaba (2015). GlobeNewswire (2015). BusinessWire (2014). Bastidas-Oyanedel et al. (2015). Indexmundi (2015) IEA (2014).

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et al., 2015; BusinessWire, 2014; GlobeNewswire, 2015; IEA, 2014; Indexmundi, 2015). Therefore waste biorefineries in arid/semi-arid regions have a main challenge, to minimize the use of freshwater for their processes, and adapt to the available biomass residues. The present review aims to describe and discuss the availability of these waste biomasses, their conversion to value chemicals, minimizing the use of fresh water in some cases. The review is divided into: valorization of date palm residues, Saltwater-based biorefinery, and biorefinery of the organic fraction of municipal solid waste. 2. Valorization of palm residues 2.1. Biomass resource from dates waste and palm residues The date palm (Phoenix dactylifera L.) is a major fruit crop in most MENA countries. It has historically been connected to sustaining human life and traditional heritage of the people in the old world as a major agricultural crop. MENA countries possess 70% of the 120 million world’s date palms (El-Juhany, 2010). Dates fruits are the most important agricultural product of many countries in the MENA. The culture of date palms involves the generation of leaf residues. Generally, each date palm tree produces 10–30 dried leaves annually. An average naturally dried leaf (includes leaflets and rachis) has a mass of 2–3 kg (Mallaki and Fatehi, 2014). Hence, each date palm is estimated to yield approximately 50 kg leaf residues per year. The annual global production of lignocellulosic feedstock from date palm leaf residues is estimated to be over 6 million tonnes. Another biomass resource from date palm includes discarded dates fruits. Total global production of dates in 2013 was 7.6 million tonnes (FAO, 2015). However, 25% of the dates could be considered as a waste product due to the very low quality (Bassam, 2010), which means a production of 1.9 million tonnes waste biomass including around 1.7 million tons of flesh with high carbohydrate content (70–80%) (Al-Farsi et al., 2005), and 0.2 million tons of date seed, also named as date pits, and date stone, and constitute about 10% of the date weight (Ahmad et al., 2012). 2.2. Current status of palm waste management Date palm lignocellulosic residues, e.g. leafs, have not drawn sufficient attention for its valorization. This dry organic biomass is not consumed by animals and has traditionally been used in shading, house construction, crates, ropes, baskets, and other handicrafts (Chao and Krueger, 2007). Apart from that, the lignocellulosic biomass is burned without appropriate application. Regarding the discarded dates, these are used for limited applications such as animal feed and a component for compost preparation. Thus most of the wastes are problematic to environment

Please cite this article in press as: Bastidas-Oyanedel, J.-R., et al. Waste biorefinery in arid/semi-arid regions. Bioresour. Technol. (2016), http://dx.doi.org/ 10.1016/j.biortech.2016.04.010

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regardless of contributing to a great loss of raw materials (Chandrasekaran and Bahkali, 2013). 2.3. Valorization of palm residues through biorefining technology Biorefinery research and development has become a global effort in response to a variety of drivers, including energy security, rural development, and environmental concerns (Ragauskas et al., 2014). The advances of valorization of date fruit processing byproducts and wastes using bioprocessing technology has been well reviewed by Chandrasekaran and Bahkali (2013). The prospects of valorization of these by-products and wastes through fermentation and enzyme processing technologies towards the production of biofuels, biopolymers, biosurfactants, organic acids, antibiotics, industrial enzymes and other possible industrial chemicals were discussed. However, valorization of date palm residues by employing bioprocessing technology, to our knowledge, has not been reviewed. In this context, prospects of utilizing date palm residues for biofuels, bio-based chemicals and materials production through bioprocessing way are discussed here below. 2.3.1. Biofuels Ethanol derived from biomass has the potential as a substitute for fossil fuel which is renewable, non-toxic, biodegradable and ecofriendly. Recent results have demonstrated that biomass conversion into biofuels can deliver a sustainable and renewable energy source for liquid transportation fuels (Faaij, 2006). Bioethanol production from date palm residues was firstly reported by (Fang et al., 2015a, 2015b). Hydrothermal pretreatment was employed on leaflets and rachis with achievement of high glucan (>90% for both leaflets and rachis) and xylan (>75% for leaflets and 79% for rachis) recovery. Under the optimal condition of hydrothermal pretreatment (210 °C/10 min) highly digestible (glucan convertibility, 100% to leaflets, 78% to rachis) and fermentable (ethanol yield, 96% to leaflets, 80% to rachis) solid fractions were obtained. Fermentability test of the liquid fractions proved that no considerable inhibitors to Saccharomyces cerevisiae were produced in hydrothermal pretreatment. The results indicate that production of bioethanol by hydrothermal pretreatment could be a promising way of valorization of date palm residues in arid regions (Fang et al., 2015a). Interestingly, Fang et al. (2015b) proposed a novel method in which seawater was used as the reaction media in hydrothermal pretreatment of leaflets, taking consideration of the high water consumption in lignocellulosic biorefinery, and scarcity of freshwater in arid regions. The study showed that pretreatment at 200 °C/10 min using artificial seawater (35 ppt) produced comparably digestible (91.4% ± 1.7% glucose conversion) and fermentable solids (85.8% ± 0.7% ethanol yield) as when using fresh water (95.6% ± 2.9% glucose conversion, and 89.4% ± 0.7% ethanol yield). Moreover, no significant difference of inhibition to S. cerevisiae was observed between liquids from pretreatment with seawater and freshwater. Seawater, as indicated by the study, is thought to be a promising alternative to freshwater for lignocellulosic biorefineries in coastal and/or arid/semiarid regions, with special attention for the MENA region (Fang et al., 2015b). 2.3.2. Activated carbon Activated carbon (AC) is one of the most widely used adsorbents. AC is conventionally synthesized using char from the pyrolysis of organic material, which then undergoes a physical or chemical activation process at a high temperature (Islam et al., 2015). Date palm waste like date seeds, is one of the agricultural by-products used as the source of activated carbon. Active carbon can be produced by two ways, physical activation, which involves carbonization or calcination of the raw materials at elevated temperatures (500–900 °C) in an inert atmosphere followed by mild

3

oxidation (gasification) of the substance with steam, air and/or carbon dioxide at high temperatures (800–1,000 °C), and chemical activation, which involves impregnation of the precursor with chemical activating agents, mostly dehydrating agents such as KOH, ZnCl2, phosphoric acid (H3PO4), among other, followed by pyrolysis at relatively low temperature than physical activation temperature (Ahmad et al., 2012). Alaya et al. (2000) applied one-step pyrolysis scheme in preparation of AC in the range of 600–700 °C from date palm wastes (branches, leaves and date pits). Carbon precursors derived from the above wastes proved to be feasible raw materials that produced good absorbing AC. Girgis and El-Hendawy (2002) used date pits as a precursor for the production of AC using H3PO4 followed by pyrolysis at 300 °C, 500 °C, and 700 °C, finding that AC obtained at 500 °C, and 700 °C are good to excellent adsorbents, attaining fairly developed porosity at 700 °C, contrary to the earlier well established temperature of 500 °C recommended for treatment of agricultural precursors. Another study performed by Haimour and Emeish (2006) also reported the utilization of date pits wastes for production of AC with H3PO4, compared with ZnCl2, using a fluidized-bed reactor. The iodine number of the produced AC was higher when using phosphoric acid than when using zinc chloride. But the yield obtained when using H3PO4 was lower than the yield when using ZnCl2. An innovative method of producing AC from date pits via sequential hydrothermal carbonization (HTC) and sodium hydroxide activation of resulting hydrochar was employed by Islam et al. (2015). It was found that NaOH activation enhanced the porosity and surface functionality of the hydrochar, and temperature was found to negatively affect the adsorption capacity of the prepared AC, which exhibited 612.1, 464.3 and 410.0 mg/g maximum methylene blue adsorption capacities at 30, 40 and 50 °C, respectively. The results prove that HTC and NaOH activation is an effective method in preparing highly porous AC from date seed, showing good potential for cationic dye removal from liquid phase (Islam et al., 2015). 2.3.3. Biochar Biochar is a solid product produced from thermal conversion of unstable carbon-enriched materials into stable carbon-enriched charred materials that can be incorporated into soil as a mean for agronomic or environmental purposes (Lehmann et al., 2011). The investigation of biochar derived from date palm waste is still in the nascent stage (Sait et al., 2012). A few studies on production of biochar from date palm residues through pyrolysis have just been reported (Jouiad et al., 2015; Khalifa and Yousef, 2015; Usman et al., 2015). Usman et al. (2015) investigated the influence of pyrolysis temperature (300–800 °C) on composition and surface chemistry of biochar prepared from date palm wastes (leaves, branches, and stem barks). The results showed that fixed C, ash and basic cations of biochar increased while its moisture, volatiles and elemental composition (O, H, N and S) decreased with increasing pyrolysis temperature. Date palm-derived biochar treated at P500 °C with a volatile matter less than 10% and O/C of 0.02– 0.05, could be more appropriate for C sequestration, representing its potential as an alternative material for environmental management (Usman et al., 2015). Another investigation by Jouiad et al. (2015) compared biochars from date palm fronds and rhodes grass produced by pyrolysis condition (1 atm, 400 °C, duration of 11 h) in terms of chemical composition, thermal stability, and respective microstructures. Both biochars showed similar capacity of water retention because macropores in the size range of 2–7 lm are dominant in both Rhodes grass and date palm biochars. As for the application of biochar derived from date palm waste, few studies have been reported. Khalifa and Yousef (2015) treated the biochar produced from date palm fronds through pyrolysis at 400 °C with a sandy textured soil with respect to soil quality

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improvement. The results showed that treatment with biochar increased soil water retention up to 20%, increased Cation Exchange Capacity (CEC) slightly from 2.5 up to 6.7 meq 100 g 1 and lowered the sodium adsorption ratio (SAR) of soil to below sodic levels (<13). Biochar application at 50 g/kg soil appears to be the rate at which changes in soil quality become apparent. The study indicates that treatment of soil with biochar induces changes in soil that are favorable but long term studies are required to monitor the extent of these effects. 2.3.4. Organic fertilizer The growth of global food production, and increased price of energy has led to increased demand for fertilizers. Burning lignocellulosic residues for the production of organic fertilizer has incurred many issues like air pollution, loss of nutrients, and destruction of the physical and biological properties of the soil. Nakhshiniev et al. (2012) applied hydrothermal treatment of date palm trunk residues at mild reaction conditions (temperature range 160–220 °C, pressure range 0.6–2.4 MPa) for 30 min to accelerate the posterior aerobic digestion rate and promote recovery of nutrients on-site. The treatment temperature of 180 °C (with 30 min holding time) was the most effective pretreatment temperature for subsequent aerobic degradation by solubilizing the largest portion of hemi- cellulose polysaccharides within the CW structure. It was assumed by Nakhshiniev et al. (2012) that hydrothermal treatment can successfully be used as a pretreatment step to accelerate the aerobic digestion rate of date palm residues for the production of organic fertilizers. 2.3.5. Natural fiber composites Natural fiber composites from lignocellulosic fibers extracted from wood and annual plants have received growing attention as an alternative to glass fibers due to their renewable character combined with their low cost and abundance (Sbiai et al., 2011). Different chemical treatment methods have been applied for date palm fibers. Alawar et al. (2009) used sodium hydroxide (with concentration of 0.5%, 1%, 1.5%, 2.5% and 5%) and hydrochloric acid (with concentration of 0.3 N, 0.9 N, and 1.6 N) to treat fibers (100–1000 lm) from date palm stem, aiming to investigate effect of different treatment process on the date palm fibers. Surface morphology showed improved with soda treatment, which also enhanced the tensile strength. Hydrochloric acid, however, was rejected due to its negative impact on the tensile strength and surface morphology of date palm fibers. A detailed study of the effects of different size range of date palm fibers (800–600, 600–400, and 400–200 lm) from bast surroundings of date palm stem, on alkali treatment was done by Abdal-hay et al. (2012). Date palm fibers with fine fiber were found to be more amenable to chemical modification. It was found that ultimate tensile strength of date palm fibers were significantly increased after alkali treatment, which is consistent with the investigation by Alawar et al. (2009). Moreover, tensile strength, elastic modulus and the fiber–matrix interaction of the composite were improved. In a few instances, an enhanced polar modification of the fiber surfaces is desired to accommodate polymer matrices such as polyphenol or polyepoxy. Sbiai et al. (2011) used 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical to selectively oxidize hydroxyl functions located at the surface of date palm fibers. Surface carboxylation as well as the oxidation heterogeneity when going from surface to core of the fibers, were observed. The TEMPO-mediated oxidation of lignocellulosic fibers, open the way for their utilization as fillers within an epoxy matrix or other matrix capable of reacting with carboxylic functions. 2.3.6. Nanocomposite Nanocomposites has been extensively used as model fillers in synthetic and natural polymeric matrices since the first

announcement of using cellulose whiskers as a reinforcing phase (Bendahou et al., 2009). Rachis were more preferred to be used for extraction of cellulose fibers compared with leaflets (Bendahou et al., 2009) due to the higher cellulose content (44 wt% compared to 35 wt% for leaflets) and lower lignin content (14 wt% compared to 27 wt% for the leaflets), and the higher aspect ratio of cellulose nanocrystals (around 43 compared to around 30 for the leaflets) (Bendahou et al., 2009). Casting/evaporation usually was used for making the nanocomposite films (Bendahou et al., 2009; Boufi et al., 2014). Favorable interactions between the polymeric matrix (natural rubber) and the cellulosic nanoparticles were evidenced by Bendahou et al. (2010). Higher aspect ratio of cellulose nanocrystals were found to result in higher reinforcing capacity in the studies by Bendahou et al. (2009) and Boufi et al. (2014). 3. Saltwater-based biorefinery Conventional full-scale biorefinery plants require freshwater for the process itself. In the US, an average full-scale bioethanol plant uses freshwater at a rate of 640,000–1,120,000 m3/year (Schaidle et al., 2011). In locations where freshwater is scarce (FAO, 2012; WB, 2015), arid-biorefinery plants main challenge is to minimize their freshwater use. The use of natural occurring salt water seems a plausible alternative, mainly for coastal areas where seawater is available. 3.1. Seawater-based biomass The relevance of seawater biomass activities, e.g. marine animal catches/farming and algae, in coastal arid/semi-arid areas is relevant, since it decreases the dependency on fresh water resources for producing food, and also overcomes the issues of salty and poor-nutrient soil land for growing crops that is often related to arid regions. Fish/shellfish and algae captures and farming activities offer a source of biomass residues in arid regions. About 20–80% (depending upon the level of processing and type of fish/shellfish) of the seafood is waste during the fish/shellfish processing, i.e. stunning, grading, slime removal, deheading, washing, scaling, gutting, cutting of fins, meat bone separation and fillets (Ghaly et al., 2013). The residues include fish scraps (racks) skin, heads, tails, fins, viscera, shells (Chowdhury et al., 2010). Fish/shellfish waste is otherwise dump into the sea or landfill sites (Martin, 1999). Macro and micro algae are excellent resources of bioactive metabolites that could be exploited in coastal arid areas as food ingredients in both human and animal feed, and in agriculture as plant growth stimulants (Kim, 2014). Macroalgae conventional application is as a source of carotenoid pigments, polysaccharides, polyamines, and polyunsaturated fatty acids (Jung et al., 2013; Kim, 2014). Microalgae have been study for the production of biodiesel (Sialve et al., 2009). 3.2. Seawater-based biorefinery products The use of seawater as a biorefinery reaction media has been reviewed by Domínguez de María (2013). The author reviewed 3 main potential uses of seawater in chemoenzymatic processes, fermentative processes, and chemocatalytic processes. Fang et al. (2015b) reported the use of seawater as an alternative of freshwater for the thermal and/or enzymatic pretreatment of date palm residues, and the bioethanol production. Seawater-based pretreatment produced comparably digestible and fermentable solids to those obtained by freshwater experiments. Also, the authors reported not significant differences of S. cerevisiae growing on both types of pretreated liquids. Seawater-based biorefinery for the production of succinic acid have been reported by Lin et al.

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(2011). In that study, succinic acid was produced from the conversion of wheat hydrolysates by Actinobacillus succinogenes, at a concentration of 42 g/L, using seawater at a total salt concentration of 35 g/kg. Knowing that seawater can be used as a reaction media in biorefinery, the residues from both seawater fish and algae can be used for the production of value added products on seawater, such as proteins, collagen and gelatin, oil, enzymes, chitin and chitosan, biofuels, among others (Ghaly et al., 2013). 3.2.1. Proteins Fish waste, composed by head, tail, skin, gut, fins, and frames in average contains 58% (w/w) of protein (Ghaly et al., 2013). Proteins from fish and shrimp waste can be extracted by enzymatic hydrolysis using proteases as alcalase, neutrase, protex, protemax, and flavorzyme) or chemical methods (Ferrer and Goajira, 1996; Ghaly et al., 2013; Kim, 2014). Fish and shrimp protein hydrolysate is the main form of seafood by-products with human food (Kim, 2014) and animal feed (Oliveira Cavalheiro et al., 2007) applications. In this regard, Fanimo et al. (2000) have found that a fish meal protein diet showed better net protein utilization in rats than a shrimp meal diet. Fish/shrimp waste proteins can be also converted to aminoacids, by enzymatic hydrolysis, and to bioactive peptides with antihypertensive, antithrombotic, immune modulatory and antioxidative properties (Ghaly et al., 2013), antidiabetic, anticancer, calcium binding, and hypocholesterolemic properties have been also reported (Kim, 2014). 3.2.2. Collagen and gelatin The fish skin, fins bones and scale waste are a good source of collagen and gelatin as an alternative to the most widely used, i.e. porcine and bovine (Kim, 2014). Collagen and gelatin are used in food, cosmetic and biomedical/pharmaceutical industries. Fishbased collagen/gelatin is of high importance for MENA countries with Halal and Kosher religious beliefs (Kim, 2014). Other advantage over bovine-based gelatin is the zero risk of contracting spongiform encephalopathy (mad cow) disease from fish-based gelatin (Ghaly et al., 2013). 3.2.3. Oil Average oil content on fish waste is 20% (w/w) (Ghaly et al., 2013). The oil content in the fish waste would be of high potential as oil source for human consumption. The fish oil consists of two main fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are polyunsaturated fatty acids and are classified as omega-3 fatty acids (Ghaly et al., 2013). Fish oil is used in a variety of markets, including industrial uses, food, feed, aquaculture, nutraceutical applications, functional applications for the mitigation of diseases related to heart, brain, cancer, thrombosis, diabetes and depression, and its industrial use in leather, paint, fuel, lubricants, printing ink, soaps (Kim, 2014). 3.2.4. Enzymes The fish viscera are a rich source of enzymes, including pepsin, trypsin, chymotrypsin and collagenase, with applications in collagen/gelatin extraction, and protein conversion to amino acids (Ghaly et al., 2013). Other sources of fish enzymes are the head, skin, bones and blood (Kim, 2014). Specific enzymes as polyphenolases can be extracted from shrimps, urease from fish liver, and lipases from fish intestine and liver (Kim, 2014). Among the different potential applications of fish-derived enzymes, these could be used as a processing aid for many seafood products, human skin-peeling agents in cosmetic industry, and dairy industry (Kim, 2014).

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3.2.5. Chitin and chitosan Shrimps and crabs exoskeleton waste is a source of chitin, with is the world second most important natural polymer, after cellulose (Kim, 2014). Chitin and his derivative, chitosan, are nontoxic, antibacterial, biodegradable and biocompatible biopolymers, widely used for biomedical applications, such as tissue engineering scaffolds, drug delivery, wound dressings, separation membranes and antibacterial coatings (Kim, 2014). Chitin and chitosan are also used in food and beverages industries as dietary fiber, food stabilizer, and in fruit preservation by antibacterial and antifungal films, other uses include water and wastewater treatment as filtering agent, in agriculture for seed coating and foodstuff for animal, and in biotechnology for enzyme and cell immobilization and as nanoparticles (Kim, 2014). 3.2.6. Biofuels Chowdhury et al. (2010) have reviewed that conventionally anaerobic digestion has been used for the treatment of fishprocessing wastewater, with the production of biogas. In the review it is reported a maximum organic loading of 8 kg_COD/m3/d with an organic removal of 80–95%, with a methane production of 0.46 m3_CH4/kg_CODdegraded, achieved by an upflow anaerobic sludge blanket reactor treating mixed sardine and tuna canning wastewater. Kafle et al. (2013) have found that the methane potential of fish-waste silage was 441–482 mL_CH4/gVS. In a different study, Marquez et al. (2013) studied the conversion of sea wrack, dislodge seaweed and sea-grass, to biomethane at 27 °C and using seawater in batch mode. They obtained a maximum methane potential of 94.33 mL CH4/g_VSseawrack, at a seawater total salinity of 42 g/kg. Regarding the biorefinery of microalgae residues by anaerobic digestion, Sialve et al. (2009) review has concluded that the conversion of algal residues, after lipid extraction, into methane can recover more energy than the energy content in the extracted lipids. In the review the maximum and minimum reported energy content for methane and lipids are 20.1 kJ/gVS for methane and 6.6 kJ/gVS for lipids, and 27.6 kJ/gVS (methane) and 23.2 kJ/gVS (lipids). Ehimen et al. (2011) have obtained a maximum methane potential of 308 mLCH4/gVS from Chlorella lipd extraction residues at 40 °C. In both papers the authors have not specified the salinity concentration of the aqueous phases where the anaerobic digestion was performed. Nobre et al. (2013) have studied the conversion of Nannochloropsis sp. microalga residues, from lipid and pigment extraction, to biohydrogen through dark fermentation by Enterobacter aerogenes, obtaining biohydrogen yields of 60 mLH2/gdrybiomass. Jung et al. (2013) have reviewed the potentials of macroalgae biorefinery. The review shows that macroalgae is mainly used for human food and algal hydrocolloids as agar, alginate and carrageenan. The authors also discussed the use of macroalgae residues, from hydrocolloid and pigment extraction, to be used in the production of biogas, bioethanol and biobutanol. 3.2.7. Other products Fish bones, are a rich source of minerals including calcium, phosphorus, and hydroxyapatite which can be used as a bone graft material in medical and dental applications (Ghaly et al., 2013). Aerobic composting process of fish-waste have been studied by Martin (1999) and Liao et al. (1997). Martin (1999) cocomposted fish-waste and peat, resulting in a rich nutrient quality compost and a liquid leachate that could be used as an inexpensive nutrient source for pure culture fermentation process. The authors have successfully grown the fungus Scytalidium acidophilum in the compost liquid leachate. The resulting compost could be also employed in the growth of mushrooms as advise by the author. Liao et al. (1997) have reduced ammonia emission from fish waste

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composting piles by adding peat moss and vermiculite, or using alder as a bulking agent. 4. Biorefinery of the organic fraction of municipal solid waste Municipal solid waste produced in arid region is mainly landfilled (Hoornweg and Bhada-Tata, 2012). Landfilling is considered a simple mean of waste disposal, causing economical and environmental impacts (Bolan et al., 2013). The incineration of waste to produce energy is a solution to divert waste from landfills, however, the operating costs are said to be high, and there is a lost of resources, e.g. nutrients (Uçkun Kiran et al., 2014), that can be recovered by bioprocesses (Wang et al., 2016). The biorefinery of these organic wastes can potentially produce high value chemicals, energy, and nutrients, reducing the emissions of greenhouse gasses. 4.1. Creating value from waste The use of the organic fraction of municipal solid waste for the production of methane (biogas), organic acids, bioplastics and soil improvers have been reported (Amulya et al., 2015; Bolan et al., 2013; Bonk et al., 2015; Karthikeyan et al., 2015; Qian et al., 2016; Satchatippavarn et al., 2015; Wan et al., 2013). 4.1.1. Biogas and electricity Bolan et al. (2013) reviewed the production, and capture of biogas from landfills, and its conversion to electricity. The authors report that in Amman, Jordan, the Ruseifeh landfill produces 1856 tonnes_CH4/year, with a net electricity production of 9180 MWh/year. Sowunmi et al. (2015) have estimated the impact on the electricity generation from biogas produced by organic waste generated in the Emirate of Abu Dhabi, estimating that the organic waste converted to biogas could potentially provide 6% of the domestic electricity use in Abu Dhabi. 4.1.2. Organic acids Karthikeyan et al. (2015) study on solid–liquid-separating continuous stirred tank reactor converting food waste into organic acids, have produced a maximum of 28 g/L total organic acids, mainly composed by acetic, propionic and butyric acid. Bonk et al. (2015) report the economic assessment of the conversion of the Abu Dhabi’s organic fraction of municipal solid waste (OFMSW) to hydrogen, organic acids, and soil improvers by dark fermentation. The total capital investment is estimated to 76 million USD with a capacity of treating 350 ktonnes_OFMSW/year. The produced organic acids, i.e. acetic acid, butyric acid, can be purified at a maximum cost of 15 USD/m3effluent, and a minimum selling price of 549 USD/tonneorganic_acids. There are various techniques available for the recovery of organic acids from fermentation broths, including; adsorption (Zhou et al., 2013), solvent extraction (Alkaya et al., 2009), membrane based solvent extraction (Choudhari et al., 2014), electro dialysis (Lopez and Hestekin, 2013; Prochaska and Woz´niakBudych, 2014), membrane separation (Xiong et al., 2015). 4.1.3. Bioplastics Amulya et al. (2015) reported the production of bioplastics, polyhydroxyalkanoates (PHA), using food waste, in a multistage process including dark fermentation (stage 1), for organic acid production, culture enrichment (stage 2), and PHA production (stage 3). The authors obtained a copolymer composed by Poly3-hydroxybutyrate (P3HB) and Poly-3-hydroxyvalerate (P3HV). PHAs have gained interest due to their biodegradability and thermoplastic properties that are similar to petroleum derived plastics.

4.2. Cost and externalities It is essential for a community to understand the costs and externalities associated with landfilling and dumping of municipal solid waste. The cost of sanitary landfill and open dumping, practices in MENA region, range from 2 to 100 USD/tonne (Hoornweg and Bhada-Tata, 2012). For the particular case of Abu Dhabi, the cost of landfill and open Dumping of OFMSW is estimated to 7–14 million USD/year (Bonk et al., 2015; Hoornweg and BhadaTata, 2012). Compared with the estimated cost of dark fermentation plant for treatment of OFMSW, 76 million USD, landfill and dumping are ‘‘economically” feasible only for a time frame of 5–10 years, with lost of resources, greenhouse emissions, and use of land that otherwise could be used for better purposes.

5. General discussion Waste biorefinery in arid regions is advisable since the reduced sustainable resources linked to these regions, as fresh water and biomass, and creating value from waste. In arid/semi-arid regions, waste biorefinery could help decreasing the import of virtual water, recovering nutrients, and producing soil improvers for arid/semiarid agriculture and/or landscaping. In the previous sections it was reviewed 3 types of biomass residue resources available in arid/semi-arid regions, palm trees residues (in the MENA region), seawater biomass (in coastal arid/ semi-arid areas), and the organic fraction of municipal solid waste. Different waste biorefinery process and their respective value products were described for each type of available biomass. For most of the proposed resulting products there is a trade market, as presented in Table 1. Nevertheless, the main issue of waste biorefinery technologies is that the industry and the waste management industry consider them as non-mature technologies, unless few cases as anaerobic digestion, that have been widely used in the wastewater treatment sector. This creates opportunity to waste management industry and academia to collaborate and work together, e.g. capacitation of personnel, building, monitoring and operating demonstration plants based on biorefinery technologies, with the main objectives of save resources and create value from waste, instead of landfilling/ dumping these precious resources. Other bioprocess as the ethanol production from organic residues, or the extraction of proteins/oils, are advisable when the organic waste is of one kind, abundant, and rich on the targeted compound, i.e. sugars in the case of ethanol production, proteins and oil in the case of extraction. Anaerobic digestion of organic waste is a mature technology. It can operate with different mixtures of organic wastes. The main product is biogas, composed by methane and CO2, biogas can be then converted into power generation. Other product of anaerobic digestion is the solid fraction that can be further composted. The resulting compost can be used as soil improver. This is of crucial importance in arid/semi-arid regions since the salinity and poornutrient soil that is often found in these regions could be recovered for crop farming and/or landscaping. Anaerobic digestion can also be modified in order to produce organic acids, hydrogen, and solids (compost), i.e. in some cases, biorefinery processes are flexible, and this flexibility could be exploited by the industry sector. Another important issue is the organic waste collection logistics. Should industrial and municipal waste be all collected and processed in the same place? Or should the organic waste be processed closer to the source? The answers to these questions need further examination in a case-by-case strategy, using techno-economical and environmental assessment tools.

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Economic and social impacts of waste biorefinery processes in arid regions needs further research. Waste biorefinery is beneficial, not only, for environmental reasons, maximizing resources, recycling of nutrients. But also from the economic point of view, it would generate revenues, or at least decrease waste management costs, diverting and reducing landfill and dumping sites. The opening of markets for waste biorefinery products will also help diverting and reducing landfill and dumping sites. The use of a biorefinery applied to arid/semi-arid regions approach, i.e. focused on the reduction of water utilization, utilizing complex and various types of organic wastes for the production of diverse products seems appropriate. This arid-biorefinery approach needs more focus and research on techno-economical aspects, and social impacts. 6. Conclusions The waste biorefinery processes of three types of biomass residues available in arid/semi-arid regions, palm trees residues, seawater biomass residues, and the organic fraction of municipal solid waste, have been reviewed. Water scarcity in arid/semi-arid region was highlighted. The use of waste arid-biorefinery processes focused on the use of different types of organic residues and the reduction of water utilization for the production of diverse value (bio)chemicals seems appropriate. This arid-biorefinery approach needs more focus and research on techno-economical aspects, and social impacts. Acknowledgements The authors would like to acknowledge the financial support from Masdar Institute of Science and Technology, to help fulfill the vision of the late President Sheikh Zayed Bin Sultan Al Nahyan for sustainable development and empowerment of the United Arab Emirates and humankind, funding project 2GBIONRG (12KAMA4). References Abdal-hay, A., Suardana, N.P.G., Jung, D.Y., Choi, K.-S., Lim, J.K., 2012. Effect of diameters and alkali treatment on the tensile properties of date palm fiber reinforced epoxy composites. Int. J. Precis. Eng. Manuf. 13, 1199–1206. Ahmad, T., Danish, M., Rafatullah, M., Ghazali, A., Sulaiman, O., Hashim, R., Ibrahim, M.N.M., 2012. The use of date palm as a potential adsorbent for wastewater treatment: a review. Environ. Sci. Pollut. Res. 19, 1464–1484. Al-Farsi, M., Alasalvar, C., Morris, A., Baron, M., Shahidi, F., 2005. Comparison of antioxidant activity, anthocyanins, carotenoids, and phenolics of three native fresh and sun-dried date (Phoenix dactylifera L.) varieties grown in Oman. J. Agric. Food Chem. 53, 7592–7599. Alawar, A., Hamed, A.M., Al-Kaabi, K., 2009. Characterization of treated date palm tree fiber as composite reinforcement. Compos. Part B Eng. 40, 601–606. Alaya, M., Girgis, B., Mourad, W., 2000. Activated carbon from some agricultural wastes under action of one-step steam pyrolysis. J. Porous Mater. 517, 509–517. Alibaba, 2015. Chemical Bulk Prices [WWW Document]. Chinese e-commerce, URL (accessed 12.15.15). Alkaya, E., Kaptan, S., Ozkan, L., Uludag-Demirer, S., Demirer, G.N., 2009. Recovery of acids from anaerobic acidification broth by liquid-liquid extraction. Chemosphere 77, 1137–1142. Amulya, K., Jukuri, S., Venkata Mohan, S., 2015. Sustainable multistage process for enhanced productivity of bioplastics from waste remediation through aerobic dynamic feeding strategy: process integration for up-scaling. Bioresour. Technol. 188, 231–239. Bassam, N., 2010. Handbook of Bioenergy Crops, first ed. Eearthscan Ltd, London. Bastidas-Oyanedel, J.-R., Bonk, F., Thomsen, M.H., Schmidt, J.E., 2015. Dark fermentation biorefinery in the present and future (bio)chemical industry. Rev. Environ. Sci. Bio-Technol. 14, 473–498. Bendahou, A., Habibi, Y., Kaddami, H., Dufresne, A., 2009. Physico-chemical characterization of palm from Phoenix dactylifera L., preparation of cellulose whiskers and natural rubber-based nanocomposites. J. Biobased Mater. Bioenergy 3, 81–90. Bendahou, A., Kaddami, H., Dufresne, A., 2010. Investigation on the effect of cellulosic nanoparticles’ morphology on the properties of natural rubber based nanocomposites. Eur. Polym. J. 46, 609–620.

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Please cite this article in press as: Bastidas-Oyanedel, J.-R., et al. Waste biorefinery in arid/semi-arid regions. Bioresour. Technol. (2016), http://dx.doi.org/ 10.1016/j.biortech.2016.04.010