Elsevier

Bioresource Technology

Volume 266, October 2018, Pages 374-381
Bioresource Technology

High-efficiency nutrients reclamation from landfill leachate by microalgae Chlorella vulgaris in membrane photobioreactor for bio-lipid production

https://doi.org/10.1016/j.biortech.2018.06.077Get rights and content

Highlights

  • Microalgae biomass was improved from 0.66 to 0.95 g/L in the m-PBR.

  • Nutrients reclamation efficiencies of landfill leachate were analyzed.

  • N reclamation efficiency was lower than 50% while P was higher than 70%.

  • Lipid had good properties with high cetane number and low linolenic acid content.

Abstract

Using microalgae to treat landfill leachate is a promising approach due to the effective nutrients reclamation ability and additional profit of bio-lipid production. To offset the negative effect of landfill leachate on microalgae cells, a membrane photobioreactor (m-PBR) was adopted in the study, in which microalgae biomass concentration was improved from 0.66 in traditional photobioreactor (T-PBR) to 0.95 g/L. Nutrients reclamation efficiencies of leachate were analyzed according to elemental balance, and the results showed that nitrogen reclamation efficiency was generally lower than 50% while phosphorus reclamation efficiency was higher than 70% due to elemental availability. The nitrogen and phosphorus reclamation efficiencies in the m-PBR were much higher than that in the T-PBR. Besides, lipid produced from the m-PBR had a high cetane number of 60.96% and low linolenic acid content of 8.32%, which demonstrated good combustion properties of the microalgae-based lipid when using landfill leachate as nutrients source.

Introduction

Industrialization and urbanization of the society in recent years have led to a rising risen in generation of solid wastes (Li et al., 2018). Landfilling is the most commonly adopted method for solid wastes disposal, but this method generates huge amount of landfill leachate daily. The landfill leachate can cause severe pollution on water body when it is directly discharged into water system attributing to high pollutants content, like ammonia nitrogen and COD (Zainol et al., 2012). Besides the environmental pollution, energy crisis caused by ever-increasing depletion of traditional fossil fuels is another problem for human beings. It is urgent to explore effective approaches to relief the energy and environmental pressures. Microalgae cell, as sunlight-driven cell factory, can utilize the inorganic salts in landfill leachate as nutrient source and sequestrate CO2 in flue gas as carbon source for photosynthesis to produce bio-energy, like bio-lipid and carbohydrate (Liao et al., 2017), realizing carbon mitigation, landfill leachate management and energy production at the same time. Therefore, microalgae-based energy conversion technology with landfill leachate as nutrients source is regarded as a most promising approach to relief burdens of water pollution and energy crisis, which has attracted wide attentions.

Lin et al. (2007) examined the possibility of microalgae cultivation with landfill leachate and found that C. pyrenoidosa grew well in the leachate with ammonia nitrogen concentration of less than 100 ppm. Edmundson and Wilkie (2013) demonstrated that a maximum productivity of 0.55 g/L/d and cell yield of 91% can be obtained with Scenedesmus sp. by adjusting pH of leachate to 7.0 ± 0.1. Zhu et al. (2016) reviewed the feasibility of biofuel production via microalgae cultivation using waste biogas slurry as culturing medium. However, most microalgae can hardly grow in the unpretreated landfill leachate attributing to high toxicity (Cheah et al., 2016). Although composition of landfill leachate varies depending on the component of solid wastes and landfill operating conditions, the leachate generally contains high concentrations of pollutants which are highly inhibitive to microalgae cells, like ammonia nitrogen, recalcitrant organic matters and heavy color (Sonawane et al., 2017). For example, landfill leachate usually contains more than 500 mg/L of ammonia nitrogen (Khanzada and Övez, 2017, Moody and Townsend, 2017, Zhao et al., 2014). It is reported that the maximum biomass concentration of C. vulgaris was severely reduced when ammonia concentration in microalgae culture medium was higher than 50 mg/L (Liu et al., 2015). Thus, microalgae growth is usually poor when microalgae is directly cultivated in un-pretreated landfill leachate and it is necessary to explore some methods to avoid toxic effects of landfill leachate on microalgae cells (Richards and Mullins, 2013).

To enhance microalgae-based lipid productivity when cultivated with landfill leachate, previous studies mainly focused on finding the tolerant microalgae species, pretreatment of landfill leachate and optimization of cultivation conditions (Tsarpali et al., 2012, Zhao et al., 2014). For example, Zhao et al. (2014) enhanced the ammonia nitrogen removal efficiency from 50% to 90% with microalgae-bacteria consortium by reducing ratio of landfill leachate in freshwater from 20% to 10%. At the same time, the maximum lipid productivity was enhanced from 12.5 to 24.1 mg/L/d. Other methods, like selection of ammoniacal nitrogen tolerant microalgae and optimization of microalgae cultivation conditions, were tried to enhanced microalgae biomass and lipid (Lin et al., 2007, Paskuliakova et al., 2016, Yan et al., 2016). However, the selected microalgae species were usually not widely suitable for most types of landfill leachate and the pretreatment of leachate could not effectively improve microalgae bio-lipid productivity since the inhibition effect of leachate on microalgae cells was not avoided, particularly the light shading effect caused by heavy color of the leachate. In addition, such a dilution process required a huge amount of fresh water, which intensified the shortage of fresh water resources (Chang et al., 2016a). Until now, an effective approach that can avoid the toxic effect of leachate on microalgae cells and avoid pretreatment of leachate is lack.

Herein, to avoid the negative effect of un-pretreated landfill leachate on microalgae cell, a membrane photobioreactor (PBR) was adopted in this study to produce microalgae bio-lipid with landfill leachate as nutrients sources. In the PBR, ion exchange membranes were equipped to separate microalgae culture medium and leachate, thus to offset the negative effect of inhibitive matters in landfill leachate on microalgae growth and lipid synthesis. During experiments, valuable inorganic ions like ammonia nitrogen and phosphate in leachate continuously transported into microalgae culture from the wastewater chamber across the membrane, while other suspended solids in leachate could hardly transport across the membrane. Since most of the inorganic ions (ammonia nitrogen, phosphate, etc.) that transported from the landfill leachate were consumed by microalgae cells, the ammonia concentration in microalgae culture could hardly accumulate to very high level and thus the toxic effects of high ammonia concentration on microalgae cells was avoided. In another word, the adopted membrane PBR could avoid toxic effect of landfill leachate on microalgae cells without any pretreatment of the leachate, thus effectively enhance microalgae growth and lipid productivity when using landfill leachate as nutrients source.

Section snippets

Microalgae and culture medium

The freshwater microalgae (Chlorella vulgaris FACHB-31) was obtained from the Freshwater Algae Culture Collection of Hydrobiology, Chinese Academy of Science, China. Microalgae was pre-cultivated and kept in BG-11 medium (Chang et al., 2016b) that contains 1.500 g NaNO3, 0.040 g K2HPO4, 0.075 g MgSO4 7H2O, 0.036 g CaCl2 2H2O, 0.006 g Citric acid, 0.006 g ferric citrate green, 0.001 g EDTANa2, 0.020 g Na2CO3 and 1 mL A5 trace mental solution in 1 L deionized water. The A5 trace mental solution

Microalgae growth in the m-PBR and the T-PBR

The physicochemical parameters of landfill leachate were measured and presented in Table 1. It can be observed that the landfill leachate contains high content of valuable component which can be used by microalgae cells as nutrients, such as NH4+ (135.9 ± 4.3 mg/L), NO3- (632.4 ± 10.8 mg/L) and PO43- (15.3 ± 0.8 mg/L). But there are also some inhibitive properties for the leachate that can cause negative effects on microalgae growth and lipid synthesis, and in turn decrease the nutrients

Conclusions

In the study, nutrients reclamation efficiencies of landfill leachate by microalgae were analyzed and enhanced with a m-PBR. For the microalgae Chlorella vulgaris, N reclamation efficiency was generally lower than 50% and P reclamation efficiency was higher than 70% due to elemental availability when using biological effluent as nutrients source. Microalgal biomass concentration, nutrients reclamation efficiency, lipid productivity and quality were simultaneously improved by using a membrane to

Acknowledgments

The authors are grateful for the financial support provided by the Scientific and Technological Research Program of Chongqing Municipal Education Commission of China (KJ1600901), Foundation and Frontier Research Project of Chongqing of China (cstc2016jcyjA0311, cstc2017jcyjAX0268), Chongqing Municipal Solid Waste Resource Utilization & Treatment Collaborative Innovation Center (Shljzyh2017-003), Foundation and Frontier Research Project of Chongqing of China (cstc2015jcyjA20005), Scientific and

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