Bioremediation of textile wastewater and successive biodiesel production using microalgae
Introduction
The growing human population has posed several challenges to the global economy particularly in terms of environmental conservation and energy security. Global economy is mainly relying on non-renewable and finite fossil fuels [1], [2], [3], [4]. This overuse of fossil fuels has resulted in two highly correlated challenges of environmental pollution and energy insecurity. These fossil fuels have considerably contributed to greenhouse gas (GHG) emissions where CO2 level has approached up to 400 ppm [5], [6], [7], [8]. Besides the use of fossil fuels in vehicular emissions, they are also use in diesel generators to produce electricity for small and medium enterprises (SMEs) in developing countries like Pakistan. This excessive use of fossil fuel (i.e. diesel) does not only cause financial liability to the local industry. Thus, local industry needs to look for alternative strategies to make their production cost competitive and environment friendly.
Textile industry is one of the most important industrial sectors of Pakistan that contributes a huge financial share. Recently, this industrial sector has confronted energy shortage that caused financial loss. This industry switched their energy sources from national grid to in-house diesel run generators to meet energy requirements. Although this strategy has partly worked and provided continuous energy to the industry but it also added financial liability. In order to save local textile industry, there is an immediate need to search for sustainable energy sources. Besides energy supply, textile industry is also facing the challenge of wastewater management. Textile industry consumes several hundred thousand gallons of water each day, and proportionally produces huge volume of wastewater [9]. Textile wastewater contains variety of dyes and auxiliary chemicals which may pose serious risks to the environmental recipients [10], [11], [12], [13], [14]. The global concerns of energy demand and non-tariff bindings regarding environmental conservation may risk the fate of textile exports of Pakistan. Local textile industry contributes 9% to the global textile needs [15] and more than 60% to the total exports of the country [16]. Textile sector earned $13.7 billion in 2013–2014 which dropped to $12.5 billion during 2015–2016 [17] mainly due to energy liabilities.
Textile wastewater treatment is a big challenge because it contains organic dyes, phosphates, nitrates etc. which cause multiple and multi-scale damage to the receiving environment [18], [19]. Pakistan require textile wastewater treatment and reclamation to meet its domestic and industrial water requirements [20]. Thus, sustainable energy supply and textile wastewater treatment appear the biggest challenges to Pakistan textile sectors [21], [22]. In order to meet energy supply, textile industry has already installed diesel run electricity generators. These generators require financial liabilities in terms of both diesel consumption and CO2 emissions. However, textile wastewater treatment still remains unaddressed challenge. CO2 emissions can be manage employing direct carbon capture, indirect carbon sequestration and biological carbon mitigation techniques. Textile wastewater effluents can be treated using several physico-chemical methods [23], [24], [25], [26], [27], [28], [29]. These physico-chemical processes inherit several drawbacks such as expensive, less efficient, limited application and sludge handling [8], [30], [31]. On the other hand, biological methods are cost effective and environmentally friendly [14]. Though biological processes are attractive, but microorganisms (bacteria and fungi) require additional carbon source for their growth to treat colored wastewater [32], [33].
Recently, microalgae have received great attention due to their potential to fix CO2 and bioremediation of textile wastewater [4]. Microalgae can simultaneously be used first for the remediation of textile wastewater and later can be used as a feedstock for the biodiesel production [34]. Thus, biodiesel can be used as an eco-friendly fuel in the generation of electricity and can fulfill the energy requirements of textile industry. Microalgae can use atmospheric CO2 (from diesel generator) as carbon source along with organic dyes, and convert them into carbohydrates through photosynthesis [35]. These carbohydrates are converted chemically and biochemically into lipids which can be used to produce biodiesel [36]. Microalgae biomass can contain up to 85% of total lipid content in dry biomass [37]. Therefore, microalgae biofuels have potential to replace fossils fuels [4], [38]. Microalgae are a potential feedstock for biofuel production due to the requirements of less amount of water for the growth as compared to terrestrial crops [39]. Microalgae have also been reported to remove CO2, nitrogen, phosphorus, and toxic metals from a different type of wastewaters [40], [41]. There are extensive studies available about the microalgae cultivation in industrial wastewaters [42], [43]. These organisms are photosynthetic and categorized under third generation biofuels. Different species of microalgae: Chlorella vulgaris, Chlorella pyrenoidosa, Spirogyra sp., Oscillatoria tenuisin and Scenedesmus sp. have shown their capability to remove reactive dyes from textile wastewater [44], [45]. Microalgae can be used to produce biodiesel [46], [47], [48], residual microalgae as fertilizer [49], and as cultivated biosorbent to treat wastewater [50], [51]. Microalgae may simultaneously solve all of the problems of local textile industry as proposed in Fig. 1.
This review targets to overview simultaneous bioremediation of TWW and the production of algal biomass, which can be useful in biofuels production. This review elaborates the role of microalgae in the bioremediation of TWW via biological and adsorption pathways, classification and short description of the cultivation methods, critical evaluation of microalgae cultivation, harvesting and oil extraction processes. It further discusses about future R&D perspectives about bioremediation-biodiesel process integration using microalgae and TWW.
Section snippets
Textile wastewater characterization
Textile industries consume huge volume of water for their operations and thus, proportionally generate wastewater. Textile wastewater accounts for 30% (288,326 million gallons) of total wastewater (962,335 million gallons) in the Pakistan [20] according to literature, different sectors produce wastewater annually [52]. Unfortunately, only < 8% of this wastewater gets treated prior to its disposal [20], [53]. Textile wastewater (TWW) mainly contains high concentration of different dyes [45].
Future prospects and conclusion
Several studies have already established that microalgae cultivation with a single objective i.e. for biodiesel production will not be sustainable option because; the cost of nutrients and other supplies cannot make this biodiesel economical and feasible against commercial biodiesel. Thus, it is important to reorient future research and development focus on microalgae biodiesel production [78]. Recent studies have feasibly redefined microalgae double role where it can be simultaneously employed
Acknowledgement
This work has been carried out under CIIT, Pakistan and IPE, China research collaboration. MSU Rehman, F Rehman and T Fazal are greatly thankful to the Higher Education Commission (HEC), Pakistan for providing generous financial assistance under NRPU Project No. 4547. MSU Rehman (2016PT012) and AU Khan (2017VEA0029) acknowledge fellowship under President's International Fellowship Initiative (PIFI), Chinese Academy of Sciences, Beijing, China. Authors also acknowledge National Natural Science
References (257)
- et al.
Cultivation, photobioreactor design and harvesting of microalgae for biodiesel production: a critical review
Bioresour Technol
(2011) - et al.
Phyco-remediation of industrial waste-water and flue gases with algal-diesel engenderment from micro-algae: a review
Fuel
(2016) - et al.
Carbon sequestration and the role of biological carbon mitigation: a review
Renew Sustain Energy Rev
(2013) - et al.
A review on developments in dyeing cotton fabrics with reactive dyes for reducing effluent pollution
J Clean Prod
(2015) - et al.
Colour removal of dyes from synthetic and real textile wastewaters in one- and two-stage anaerobic systems
Bioresour Technol
(2010) - et al.
Microbial decolorization of textile-dye-containing effluents: a review
Bioresour Technol
(1996) - et al.
Biosorption of Acid Red 274 (AR 274) on Enteromorpha prolifera in a batch system
J Hazard Mater
(2005) - et al.
Use of Chlorella vulgaris for bioremediation of textile wastewater
Bioresour Technol
(2010) - et al.
Adsorption of methylene blue on low-cost adsorbents: a review
J Hazard Mater
(2010) - et al.
Electrocoagulation for the treatment of textile industry effluent - A review
J Environ Manag
(2013)