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Frontiers in Chemical Engineering ·

Volume 8 - 2026 | https://doi.org/10.3389/fceng.2026.1894864

Light-induced lipid enhancement in domestic wastewater-grown Desmodesmus sp. for biodiesel production and bioremediation

  • S. A. S. B. Samaraweera1
  • S. Vaishnevan1
  • M. E. S. Dinithi1
  • Tharshaa Rajenthiram1
  • Noorunnisa M. Hanifa1
  • P. H. V. Nimarshana2
  • Myrsini Sakarika3
  • Thilini U. Ariyadasa1*corresponding author
  1. 1Department of Chemical and Process Engineering, Faculty of Engineering, University of Moratuwa, Moratuwa, Sri Lanka
  2. 2Department of Mechanical Engineering, Faculty of Engineering, University of Moratuwa, Moratuwa, Sri Lanka
  3. 3Center for Microbial Ecology and Technology (CMET), Ghent University, Gent, Belgium
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Abstract

Domestic wastewater treatment using microalgae has emerged as a promising alternative to conventional wastewater treatment technologies, as it simultaneously generates valuable biomass that could be utilized for the production of value-added bioproducts, including biodiesel. In the present study, the locally isolated microalga Desmodesmus sp. UOM-DS01 was cultivated in wastewater collected from a cafeteria of the University of Moratuwa, Sri Lanka, to identify its bioremediation potential, while assessing the feasibility of lipid accumulation under light stress for biodiesel production. Accordingly, 75% of cafeteria wastewater (CWW) and Bold’s Basal Medium supplemented with three times the standard nitrate concentration (3N-BBM) were employed as culture media. Desmodesmus sp. UOM-DS01 cultivated in CWW achieved biomass concentration of 0.65 ± 0.03 g/L, comparable to that obtained in 3N-BBM (0.54 ± 0.02 g/L), while simultaneously reducing freshwater consumption by 79.19%. In addition, the system achieved chemical oxygen demand, total nitrogen and total phosphorus removal efficiencies of 75.83 ± 2.10%, 47.69 ± 3.89% and 38.00 ± 3.93% respectively, demonstrating the capability of Desmodesmus sp. UOM-DS01 for simultaneous bioremediation and biomass production. Light-stressed cultivation (450 μmol photons/m 2 /s) enhanced lipid accumulation from 0.31 ± 0.02 g/L to 0.53 ± 0.01 g/L, while the estimated biodiesel properties of the extracted lipids complied with ASTM D6751-12 and EN standard. Nonetheless, further optimization of cultivation parameters and pilot-scale studies using CWW are required prior to large-scale implementation of simultaneous bioremediation and biodiesel production, for the advancement of sustainable resource recovery and renewable energy production.

Keywords

1 Introduction

The growing global population, along with ongoing resource-intensive economic development, is driving the demand for essential natural resources, with water scarcity emerging as a critical challenge. Projections from the United Nations indicate that by 2050, ∼57% of the global population will be living in areas facing severe water scarcity, highlighting the necessity of wastewater recycling and reuse (Boretti and Rosa, 2019). A critical yet often overlooked aspect of wastewater systems is domestic wastewater, which comprises a complex mixture of organic and inorganic pollutants, encompassing nutrients, pathogens, and hazardous chemicals (Islam, 2023). The direct disposal of untreated water into the ecosystem could cause eutrophication, air pollution, solid waste accumulation, and public health risks from waterborne diseases such as cholera and schistosomiasis (Ejiohuo et al., 2025; Hanifa et al., 2025a). Conventional treatment methods, including physical, chemical, and biological processes, are energy-intensive, costly, and often inefficient. In 2022, ∼42% of domestic wastewater worldwide was not safely treated before discharge, highlighting the importance of sustainable, low-cost alternatives (World Health Organization, 2024). In this context, microalgae-based wastewater treatment has gained attention as an innovative and sustainable approach for both wastewater bioremediation and resource recovery (Nishshanka et al., 2023).

Microalgae are photosynthetic microorganisms with high photosynthetic efficiency, faster growth rates, and higher carbon dioxide (CO2) fixation capacity, 10–50 times higher than terrestrial plants, and could be cultivated on non-arable lands (Semwal and Joshi, 2026; Thevarajah et al., 2026). Furthermore, microalgae could recover nutrients from wastewater, with total nitrogen (TN) and total phosphorus (TP) removal rates ranging from 22% to 100% and 20%–98%, respectively (Nishshanka et al., 2022). In addition, microalgae synthesize biomass containing 20%–60% lipids, 50%–70% proteins, and 12%–30% carbohydrates depending on the species, and the generated biomass could be converted into value-added bioproducts such as biodiesel, bioethanol, biogas, food supplements, nutraceuticals, bioplastics, biofertilizers, dyes and pigments (Mosibo et al., 2024; Thevarajah et al., 2024; Hanifa et al., 2025b). In particular, lipids synthesized by microalgae have gained significant attention as a biodiesel feedstock due to the high lipid productivity of microalgae, which could reach up to 15–300 times greater than that of traditional oil crops, while lipid accumulation could be further enhanced by manipulating the cultivation parameters (Rehman et al., 2022). Nevertheless, the large-scale production of microalgal biodiesel remains constrained by the high cost of synthetic nutrient media, which account for a substantial proportion of the overall cultivation cost. Domestic wastewater has emerged as a promising alternative cultivation medium that provides essential nutrients required for microalgae growth, while reducing freshwater consumption and nutrient input requirements. For instance, Mamani Condori et al. reported that the Chlorella sp. (MC18) and Scenedesmus sp. (MJ23-R) grew efficiently in 100% domestic wastewater while supplementation with vinasse, whey, or agro-food waste further enhanced biomass production and lipid accumulation. This study highlighted the potential of wastewater-based cultivation to improve the economic feasibility of large-scale microalgal bioprocesses for simultaneous wastewater treatment and biodiesel production (Condori et al., 2025). Therefore, microalgae present a more sustainable and renewable alternative to conventional biodiesel production that relies on food-based feedstocks, which raises concerns related to land use and food security.

Among a diverse array of microalgal species, Desmodesmus sp. has a high growth rate of 1.53 cell doublings per day and a favorable lipid profile with a high content of C16-C18 saturated fatty acids suitable for biodiesel production (Bomer and Leverett, 2024). For instance, Okpozu et al. reported that Desmodesmus armatus has the potential of phycoremediation of hydrolyzed cassava wastewater, where the chemical oxygen demand (COD), electrical conductivity, and total dissolved solids were reduced by 92%, 73% and 83%, respectively. In addition, fatty acid methyl esters (FAME) analysis indicated that the synthesized lipid profile consisted of C17-C19 fatty acids, which are highly suitable for biodiesel production (Okpozu et al., 2019). Moreover, Nzayisenga et al. studied the effects of light intensity (50, 150 and 300 μE m-2 s-1) on the fatty acid synthesis of four microalgal species cultivated in wastewater, among which Desmodesmus sp. exhibited a lipid profile with a high content of saturated fatty acids, suitable for use as a feedstock for biodiesel production (Nzayisenga et al., 2020).

Thus, there are previous studies that have investigated the bioremediation potential of Desmodesmus sp. in industrial effluents, along with simultaneous feedstock generation for biodiesel production. However, there are a limited number of studies that focus on the bioremediation and biodiesel feedstock production of Desmodesmus sp. cultivated in domestic wastewater. According to the authors’ best knowledge, no study has been conducted so far on the utilization of locally isolated Desmodesmus sp. for the bioremediation of domestic wastewater and its potential as a biodiesel feedstock under light stress.

In this regard, the current study has employed locally isolated microalga Desmodesmus sp. UOM-DS01 to assess the bioremediation potential of cafeteria wastewater (CWW) generated from the University of Moratuwa, Sri Lanka, which was comprehensively evaluated by monitoring reductions in COD, TN, and TP in CWW. Concurrently, the biofuel production potential of the resulting biomass was assessed through the quantification of lipid content before and after exposure to light stress, along with detailed fatty acid profile analysis and biodiesel property estimation. This integrated approach could advance the principles of the circular bioeconomy by valorizing wastewater into renewable energy, thereby enhancing resource sustainability.

2 Materials and methods

2.1 Microalgal species and pre-culture conditions

Desmodesmus sp. was isolated from Beira Lake, Colombo, Sri Lanka. The isolated microalgae were sent to Genetech, Colombo, Sri Lanka, for DNA extraction and PCR amplification. The chloroplast 23S rRNA gene was amplified using the primer pair p23SrV_f1 (5′-GGA CAG AAA GAC CCT ATG AA-3′) and p23SrV_r1 (5′-TCA GCC TGT TAT CCC TAG AG-3′). The PCR amplicons were subsequently subjected to Sanger sequencing by Macrogen Inc., Seoul, South Korea. The obtained nucleotide sequence was compared with reference sequences available in the National Center for Biotechnology Information (NCBI) GenBank database using the Basic Local Alignment Search Tool (BLAST). Based on the molecular analysis and morphological characteristics, the isolate was identified as Desmodesmus sp. UOM-DS01.

The seed culture was maintained in a photobioreactor described in Section 2.2 containing 1.5 L of modified Bold’s Basal medium (DuBois et al., 1956) supplemented with three times the standard nitrate (NO3 −) concentration (3N-BBM). Cultures were provided with cool white light (150 μmol photons/m2/s) from light-emitting diodes and maintained at room temperature (25 °C ± 2 °C) under a 12:12 h light:dark photoperiod.

2.2 Photobioreactor design

The growth experiments were conducted using laboratory-scale photobioreactors consisting of 2 L glass bottles with a three-port GL45 screw cap (Duran 1,129,751, Germany) consisting of an aeration inlet, a pressure compensation outlet, and a sampling port. Aeration and pressure compensation ports were equipped with 0.22 μm polytetrafluoroethylene (PTFE) membrane filters to ensure sterile aeration and minimize evaporative losses. The working volume of each photobioreactor was maintained at 1.5 L. Prior to the cultivation of Desmodesmus sp. UOM-DS01, the photobioreactors, accompanying accessories, and growth media underwent sterilization using autoclaving at 121 °C for 20 min. Illumination was provided by cool white light-emitting diodes, and the incident light intensity was measured using a photometer (LI-250A, LI-COR Biosciences, USA).

2.3 Microalgae cultivation

The CWW was collected from a cafeteria at the University of Moratuwa, Sri Lanka, during 3-time intervals per day. The collected wastewater was thoroughly mixed and filtered under vacuum using membrane filters (NY, 47 mm diameter, 0.45 μm, Germany) prior to being used as a culture medium. Based on preliminary cultivation experiments evaluating different CWW concentrations, 75% CWW was identified as the suitable dilution that supported the highest biomass production. The initial COD, TN, and TP of CWW were quantified at 576.00 mg O2/L, 13.00 mg/L, and 4.50 mg/L, respectively, with a pH of 6.55. The pH of the culture media was not adjusted throughout the cultivation period. After 10 days of pre-cultivation, seed cultures of Desmodesmus sp. UOM-DS01 were inoculated into photobioreactors containing 3N-BBM (control) and CWW at an initial biomass concentration of 0.3 g/L.

Initially, cultures were provided with a light intensity of 150 μmol photons/m2/s under a 12:12 h photoperiod to allow cell proliferation. Upon reaching the stationary growth phase, stress conditions were applied for 3 days by increasing the light intensity to 450 μmol photons/m2/s to induce lipid accumulation. The other cultivation conditions, including aeration rate, temperature, and light source, were maintained as described in Section 2.2. Cultures were harvested by centrifugation (Eppendorf 5804 R, Hamburg, Germany) at 4,500×g for 10 min, and the residual biomass was dried at 60 °C in a laboratory oven (Memmert UN110, Schwabach, Germany) for 24 h. Media preparation, photobioreactor setup, microalgae inoculation, and sampling were conducted under aseptic conditions.

2.4 Determination of microalgae growth

Biomass concentration was quantified by filtering 5 mL culture aliquots through a pre-weighed and pre-dried glass microfiber filter (Whatman GF/C, 47 mm diameter, 1.2 μm pore size; GE Healthcare, Chicago, IL, USA), followed by triple rinsing with distilled water. Prior to filtration, the biomass was centrifuged and washed twice with distilled water. The filters containing the retained biomass were subsequently dried in a laboratory oven (Memmert UN110, Schwabach, Germany) at 60 °C until a constant dry weight was achieved (Condori et al., 2025b). The biomass concentration was determined by using Equation 1.Where DWn is the biomass concentration (g/L) of microalga on the nth day, Wf is the final weight of the dried filters with microalgal biomass, Wi is the initial weight of the filters, and V is the volume of the culture aliquot.

D W n = W f − W i V (1)

2.5 Determination of nutrient removal efficiency

COD, TN, and TP levels in CWW were quantified before and after microalgal cultivation to evaluate nutrient removal efficiency. Following microalgae cultivation, the biomass was removed from CWW via centrifugation (6,300×g for 15 min) and filtration prior to COD, TN, and TP analyses. The aforementioned parameters were measured using the American Public Health Association (APHA) standard methods for the examination of water and wastewater. COD was determined using the closed reflux titrimetric method (Method 5220C). TN and TP were quantified using the macro- Kjeldahl method (Method 4,500 Norg B) and the vanadomolybdophosphoric acid colorimetric method (Method 4500-P C), respectively.

Nutrient removal efficiency (%) was calculated using Equation 2 . Where Ni is the initial nutrient concentration and Nf is the final nutrient concentration in the culture medium.

N u r i e n t r e m o v a l e f f i c i e n c y % = N i − N f N i × 100 (2)

2.6 Analysis of total lipid and total carbohydrate contents

Microalgal biomass was harvested as mentioned in Section 2.3, and lipids were extracted from 10 mg of oven-dried biomass according to a modified Bligh and Dyer method (Lee et al., 2013). Briefly, chloroform and methanol were added to the biomass in the ratio of 1:1 (v/v), followed by the addition of 0.8% NaCl to induce phase separation, resulting in a final solvent ratio of chloroform: methanol: 0.8% NaCl at 10:10:9 (v/v/v). The chloroform phase, containing the extracted lipids, was carefully transferred to a pre-dried and pre-weighed centrifuge tube, and evaporated under a nitrogen (N2) stream. Thereafter, the residual solvent was removed by drying at 60 °C in an oven until a constant mass was obtained. Lipid content of biomass was determined gravimetrically and expressed as a percentage of the dry biomass using Equation 3.where m1 is the weight of the biomass sample used in the lipid extraction process, m2 is the initial weight of the centrifuge tube, and m3 is the final weight of the centrifuge tube.

T o t a l l i p i d c o n t e n t = m 3 − m 2 m 1 × 100 % (3)

Carbohydrate content in biomass was analyzed using the phenol-sulfuric acid method (DuBois et al., 1956). Initially, 0.5 mL of acetic acid was added to 10 mg of dry microalgal biomass and heated in a water bath (Memmert WNB7, Germany) at 80 °C for 20 min, followed by the addition of 10 mL of acetone to extract pigments. Thereafter, the sample was centrifuged at 10,000 ×g for 5 min and the supernatant was discarded (Jia et al., 2015). 5 mL of 4 M trifluoroacetic acid was added, followed by heating in a boiling water bath for 4 h to hydrolyze carbohydrates. Subsequently, distilled water was added to bring the total volume up to 10 mL. Then 0.1 mL of the sample was taken into a glass tube, and 1 mL of 5% phenol solution and 5 mL of concentrated sulfuric acid were added. Tubes were allowed to stand for 10 min followed by heating at 30 °C in a water bath for 20 min. Finally, the absorbance of the sample was measured at 490 nm and total carbohydrate content was determined with reference to a standard calibration curve prepared using glucose.

2.7 Determination of fatty acid profiles of microalgal lipids

Microalgal lipids were extracted into chloroform as per the procedure mentioned in Section 2.6 and 0.5 mg of heptadecanoic fatty acid (C17:0; Sigma Aldrich H3500) was added to each sample as an internal standard, prior to evaporation under N2 (Ma et al., 2016). Thereafter, transesterification was performed by the addition of 5 mL of 1% (v/v) sulfuric acid in methanol and heating the samples in a 50 °C water bath overnight. The FAMEs thus synthesized were extracted into n-hexane (Islam et al., 2013). The fatty acid profile of microalgal lipids was determined using a gas chromatograph (Agilent 7980A, USA) with flame ionization detection (GC-FID) equipped with a DB-23 capillary column (60m × ϕ0.25 mm × 0.15 µm). An inlet temperature of 250 °C and an injection volume of 1 µL were used. Helium (He) was used as the carrier gas, at a constant pressure of 230 kPa and a 1:50 split ratio. Initial oven temperature was set to 50 °C for 1 min and then raised by 25 °C/min until a temperature of 175 °C was reached. Thereafter, the temperature increased by 4 °C/min until 230 °C and was held for 5 min. An FID detector temperature of 280 °C with hydrogen, air and He flow rates of 40 mL/min, 450 mL/min and 30 mL/min, respectively, were used. A 37-component FAME standard (Supelco 37 Component FAME Mix; CRM47885) was utilized to calibrate the column.

2.8 Biodiesel property analysis

The following Equations 4–9 were used to estimate the biodiesel properties based on the fatty acid profile of microalgal lipids (Mondal et al., 2021). where η i = − 12.503 + 2.496 ⁡ ln M i − 0.178 N where ρ i = 0.8463 − 0.49 / M i + 0.0118 N

I o d i n e v a l u e I V = ∑ i = 1 n 254 N D i M i (4)

K i n e m a t i c v i s c o s i t y V = exp ∑ i = 1 n w i ⁡ ln η i (5)

D e n s i t y ρ = ∑ i = 1 n w i ρ i (6)

S a p o n i f i c a t i o n v a l u e S V = ∑ i = 1 n 560 N M i (7)

C e t a n e n u m b e r C N = 46.3 + 5458 / S V − 0.225 I V (8)

O x i d a t i o n s t a b i l i t y = 117.9295 / X + 2.5905 (9)

Where Di is the weight percentage of the ith fatty acid, N is the number of double bonds in the fatty acid, Mi is the molecular weight of the ith fatty acid, and wi is the weight fraction of the ith fatty acid. X is the total content (weight percentage) of linoleic and linolenic acids.

2.9 Statistical analysis

All experiments were conducted in duplicate (n = 2), and the results are presented as mean ± SEM, where SEM is standard error of the mean. Statistical analysis was performed using Student’s t-test, including independent and paired tests as appropriate, with p < 0.05 deemed to be significant.

3 Results and discussion

3.1 Growth of Desmodesmus sp. UOM-DS01 in CWW

Figure 1 shows the growth curves of Desmodesmus sp. UOM-DS01cultivated in CWW and 3N-BBM over 13 and 15 days of cultivation periods, respectively, where the species demonstrated a similar growth in biomass concentration in both media (p > 0.05). Accordingly, biomass concentrations in CWW and 3N-BBM were 0.65 ± 0.03 g/L and 0.54 ± 0.02 g/L, respectively, upon reaching the stationary phase, indicating the essential nutrients in CWW were not limiting the biomass growth. The slightly higher biomass concentration observed in CWW may also be attributed to the presence of biodegradable organic carbon in the wastewater, which could have been assimilated by Desmodesmus sp. UOM-DS01 through mixotrophic metabolism. A similar observation has been reported for Scenedesmus sp. cultivated in municipal wastewater, resulting 0.069 g/L/d of biomass productivity in the mixotrophic mode (Devi et al., 2022).

Growth curves of *Desmodesmus* sp. UOM-DS01 cultivated in cafeteria wastewater and Bolds’ Basal Medium with three-fold nitrogen (3N-BBM).
Figure 1. Growth curves of Desmodesmus sp. UOM-DS01 cultivated in cafeteria wastewater and Bolds’ Basal Medium with three-fold nitrogen (3N-BBM).

Furthermore, cultivation in CWW demonstrated considerable potential for reducing freshwater consumption during microalgal biomass production. In the present study, the highest biomass concentration was achieved using 75% CWW as the cultivation medium, with a freshwater consumption of only 0.39 ± 0.02 L/g biomass produced. In contrast, biomass production using 3N-BBM required 1.85 ± 0.02 L/g biomass produced of freshwater. Therefore, the utilization of CWW as a nutrient source enabled a freshwater conservation of 1.47 ± 0.05 L/g of biomass produced, corresponding to a 79.19% reduction in freshwater consumption compared with 3N-BBM cultivation. Overall, these results demonstrate the potential of CWW as a cost-effective and resource-efficient alternative cultivation medium for large-scale microalgal biomass production.

3.2 Analysis of nutrient removal efficiency

As shown in Table 1, Desmodesmus sp. UOM-DS01 achieved 75.83 ± 2.10% COD removal from CWW and demonstrated TN and TP removal efficiencies of 47.69 ± 3.89% and 38.00 ± 3.93%, respectively, indicating substantial nutrient recovery during cultivation. CWW contains various organic compounds, including carbohydrates, proteins, fats, oils, and grease, which substantially contribute to an increased content of biodegradable soluble COD (Xin et al., 2010). Thus, the present study suggests that Desmodesmus sp. UOM-DS01 could reduce COD levels by absorption/uptake of soluble organic compounds, which are then either assimilated into biomass or utilized as carbon and energy sources.

TABLE 1. Nutrient removal efficiencies of Desmodesmus sp. UOM-DS01 cultivated in cafeteria wastewater.

Wastewater quality parametersInitial concentration (mg/L)Final concentration (mg/L)Nutrient removal efficiency (%)
COD576.00 ± 11.76139.20 ± 11.7675.83 ± 2.10
TN13.00 ± 0.726.80 ± 0.3447.69 ± 3.89
TP4.50 ± 0.092.79 ± 0.1738.00 ± 3.93

COD: chemical oxygen demand; TN: total nitrogen; TP: total phosphorus

Furthermore, in conventional wastewater treatment, COD reduction is typically achieved through biological processes involving aerobic or anaerobic microbial degradation of complex organic compounds (Fernando et al., 2021). However, these processes generate large volumes of low-value sludge composed of active and dead microbial biomass. Sludge disposal remains a significant environmental and operational challenge due to solid waste accumulation and the need for further treatment to meet regulatory discharge standards (Liwarska-Bizukojc et al., 2002). In contrast, microalgae-based wastewater treatment has the potential to offer a more sustainable alternative by reducing sludge generation while producing valuable biomass that could be further utilized for various applications aligned with circular bioeconomy practices. Therefore, the COD removal efficiency of Desmodesmus sp. UOM-DS01 observed in this study supports its potential for reducing organic loads in CWW while producing biomass rich in lipids and carbohydrates.

Moreover, nitrogen (N) is present in CWW in various forms, including amino groups, urea, NO3 −, nitrite, ammonia (NH4 +), and uric acid, whereas phosphorus (P) is primarily found as inorganic orthophosphate, diphosphate, and organic forms (Astuti et al., 2017). The bioavailable forms of N and P are essential for microalgal metabolism, as these nutrients are required for the synthesis of biomolecules such as proteins and nucleic acids in microalgal cells (Astuti et al., 2017). Previous studies have demonstrated that the N/P ratio in the growth medium substantially influences the nutrient removal efficiency of microalgae. For instance, Xin et al. observed higher P removal at lower N/P ratios (2:1 and 4:1), while N removal was more efficient at higher N/P ratios (5:1–8:1) (Xin et al., 2010). In contrast, the present study found that the N removal efficiency exceeded the P removal efficiency at the N/P ratio of 1.26:1, indicating that the microalgal species also influences the removal efficiencies in a given substrate.

COD removal efficiency reported in the current study was substantially higher than values reported in the literature (Table 2), although there are a few exceptions, such as those reported by Silambarasan et al. (Silambarasan et al., 2021). Furthermore, as detailed in Table 1, TN and TP removal efficiencies achieved by Desmodesmus sp. UOM-DS01 in the present study were lower compared to the removal rates of NO3 −, NH4 +, and phosphate (PO4 3-) reported for domestic wastewater in the literature, possibly due to the complex nature of N and P compounds in CWW. TN includes a broad spectrum of N-containing compounds, ranging from inorganic forms such as NH4 +and NO3 − to organic molecules, while TP similarly consists of both inorganic PO4 3- and organically bound P (Nishshanka et al., 2022). Although these compounds may undergo biotransformation into bioavailable ionic forms such as NO3 − and orthophosphate, which could be assimilated by microalgae, the conversion process may be hindered by the high concentration of colloidal and complex organic matter in CWW, which degrades at a substantially slower rate and may persist in the treated effluent. Additionally, a fraction of the N and P in CWW is bound within organic molecules, including protein, Maillard reaction products, and phospholipids, which are resistant to biodegradation, thereby limiting bioavailability for microalgal uptake and reducing the overall nutrient removal efficiency during biological treatment (Sandani et al., 2020). Consequently, the overall efficiency of TN and TP removal from such effluents tends to be lower than the removal rates observed by their more readily available ionic counterparts.

TABLE 2. Comparison of nutrient removal efficiencies of microalgae cultivated in domestic wastewater.

Microalgal speciesCOD removal (%)N removal (%)P removal (%)References
Desmodesmus sp.75.83 ± 2.1047.69 ± 3.8938.00 ± 3.93Present study
Scenedesmus abundans80.290.7386.31SundarRajan et al. (2020)
Chlorella variabilis74.8–89.893.8–96.197.1–99.9Tripathi et al. (2019)
Chlorella sp. and Scenedesmus sp.8394PO4 3--P: 95Silambarasan et al. (2021)
Chlorella sp.100nrnrAsli et al. (2019)
Desmodesmus sp. and Scenedesmus obliquusnr>75>75Nzayisenga et al. (2020)

COD: chemical oxygen demand; N: nitrogen; P: phosphorus; PO4 3- -P: phosphate phosphorus; nr: not reported

It is noteworthy that nutrient removal efficiency is affected by the microalgal species employed, as represented in Table 2, since nutrient requirement varies among species. Therefore, further investigations are required to substantially enhance the removal of N and P from CWW in future applications.

3.3 Analysis of biochemical composition

As shown in Figure 2A, the lipid content of Desmodesmus sp. UOM-DS01 cultivated in CWW under light stress was 0.53 ± 0.01 g/L, which was higher than the control (0.31 ± 0.06 g/L) (p < 0.05). This increase could be attributed to the upregulation of lipid biosynthesis pathways induced by stress conditions (Mehariya et al., 2022). Figure 2B shows the carbohydrate content in CWW, which substantially decreased from 0.45 ± 0.01 g/L on day 1 to 0.32 ± 0.01 g/L on day 2 (p < 0.05), indicating the mobilization of stored carbohydrates to support cellular adaptation. In contrast, 3N-BBM-grown cultures exhibited a notable increase in carbohydrate content, from 0.10 ± 0.01 g/L to 0.28 ± 0.01 g/L during the same period (p < 0.05), indicating the possible accumulation of surplus photosynthetic products. Nzayisenga et al. previously reported that light intensity of ∼24,000 lux increased the biomass and lipid content in Desmodesmus sp., which aligns with the present findings (Nzayisenga et al., 2020). However, the contrasting lipid dynamics between CWW and 3N-BBM observed in the present study support previous studies reported in the literature, which highlight the substantial impact of medium composition. Therefore, further studies are necessary to investigate the effect of light stress in different culture media to optimize lipid production in Desmodesmus sp.

**(A)** Lipid and **(B)** carbohydrate concentration of *Desmodesmus* sp. UOM-DS01 cultivated in cafeteria wastewater and Bold’s Basal Medium with three-fold nitrogen (3N-BBM) before stress induction (Day 1) and after stress induction (Day 2).
Figure 2. (A) Lipid and (B) carbohydrate concentration of Desmodesmus sp. UOM-DS01 cultivated in cafeteria wastewater and Bold’s Basal Medium with three-fold nitrogen (3N-BBM) before stress induction (Day 1) and after stress induction (Day 2).

3.4 Fatty acid methyl ester (FAME) analysis

Palmitic acid (C16:0) was the most abundant fatty acid in the lipids extracted from Desmodesmus sp. UOM-DS01 cultivated in CWW under light stress, comprising 25.49 ± 2.58% of the total fatty acid content (Table 3). This was followed by margaric acid (C17:0) (24.09 ± 1.97%), oleic acid (C18:1) (10.39 ± 1.00%), and stearic acid (C18:0) (9.75 ± 0.16%), indicating a predominance of saturated fatty acids. A similar trend was observed in Desmodesmus sp. UOM-DS01 cultivated in 3N-BBM medium, where palmitic acid accounted for 28.84 ± 2.37% of total lipids, followed by margaric acid (19.41 ± 0.38%), oleic acid (12.50 ± 1.57%), and stearic acid (11.29 ± 0.34%). However, the relative abundance of these major fatty acids was comparable between Desmodesmus sp. UOM-DS01 cultivated in CWW and 3N-BBM, with no statistically significant difference observed (p > 0.05).

TABLE 3. Fatty acid profiles (% of total fatty acids) of Desmodesmus sp. UOM-DS01 cultivated in cafeteria wastewater and Bolds’ Basal Medium with three-fold nitrogen (3N-BBM).

Fatty acid3N-BBM aCWW b
C4:06.33 ± 0.038.87 ± 1.05
C10:01.33 ± 0.052.00 ± 0.16
C11:01.70 ± 0.123.01 ± 0.01
C12:01.51 ± 0.091.73 ± 0.10
C13:00.92 ± 0.011.89 ± 0.30
C14:01.01 ± 0.141.10 ± 0.12
C15:00.55 ± 0.060.49 ± 0.09
C16:028.84 ± 2.3725.49 ± 2.58
C17:019.41 ± 0.3824.09 ± 1.97
C18:011.29 ± 0.349.75 ± 0.16
C18:112.50 ± 1.5710.39 ± 1.00
C18:24.24 ± 0.303.43 ± 0.54
C18:3n37.95 ± 1.113.87 ± 0.10

3N-BBM: Bold’s Basal Medium with three-fold nitrogen.

CWW:75% cafeteria wastewater.

The results of the current study are consistent with previous studies reported in the literature, demonstrating that microalgal strains suitable for biodiesel production generally exhibit high levels of C16 and C18 fatty acids (Deshmukh et al., 2019; Nzayisenga et al., 2020; Premaratne et al., 2021). Saturated fatty acids such as palmitic and stearic acids enhance the cetane number, resulting in shorter ignition delay and better combustion performance (Lin and Wu, 2022). In the present study, the total saturated fatty acid content exceeded that of unsaturated fatty acids in both cultivation media, further supporting the suitability of Desmodesmus sp. UOM-DS01 as a feedstock for biodiesel production, since high levels of unsaturation are typically less favorable due to reduced thermal and oxidative stability (Puhan et al., 2010). Furthermore, the nutrient composition of the growth medium substantially influences fatty acid profile. For instance, in the present study, Desmodesmus sp. UOM-DS01 cultivated in 3N-BBM exhibited a 3.35% higher C16:0 content compared to CWW, indicating that nutrient-replete conditions could influence lipid composition. Similar findings have been reported in previous studies, where various strains of Desmodesmus sp. exhibited high levels of palmitic acid and oleic acids (Massimi and Kirkwood, 2016; Nzayisenga et al., 2020).

Moreover, several studies have emphasized that biofuels rich in oleic acid exhibit superior combustion efficiency, ignition quality, and oxidative stability, while fatty acids with chain lengths of C16-C18 are widely recognized as ideal precursors for biodiesel production due to their optimal fuel properties (Arguelles et al., 2018; Nzayisenga et al., 2020; Lin and Wu, 2022; Nishshanka et al., 2022; Li et al., 2023; Akram et al., 2025). Hence, the results of this study indicate that the locally isolated Desmodesmus sp. UOM-DS01 could be a suitable feedstock for biodiesel production.

3.5 Analysis of biodiesel properties

The estimated biodiesel properties of Desmodesmus sp. UOM-DS01 cultivated in both CWW and 3N-BBM, calculated using the fatty acid composition (Section 2.8), are presented in Table 4 together with the ASTM D6751-12 and EN 14214:2012 standards for biodiesel. The estimated biodiesel properties were comparable between FAMEs derived from Desmodesmus sp. UOM-DS01 cultivated in CWW and 3N-BBM, indicating that the culture medium did not significantly influence the predicted fuel properties (p > 0.05). The iodine value (IV) quantifies the total degree of unsaturation in diesel, expressed as grams of iodine consumed per 100 g of oil. Elevated IVs increase the tendency for thermal polymerization and deposit formation on engine components such as nozzles and pistons (Schober and Mittelbach, 2007). Hence, the EN standard specifies a maximum allowable IV of 120 for biodiesel, and the IVs of FAMEs synthesized by Desmodesmus sp. UOM-DS01 in both CWW and 3N-BBM indicated compliance with regulatory requirements (Schober and Mittelbach, 2007).

TABLE 4. Properties of biodiesel synthesized from Desmodesmus sp. UOM-DS01 cultivated in Bold’s Basal Medium with three-fold nitrogen (3N-BBM) and cafeteria wastewater.

Biodiesel property3N-BBM aCWW bCommercial biodiesel standards
ASTM D6751-12EN 14214:2012
Iodine value (g I2/100 g oil)27.84 ± 2.9721.66 ± 1.96-<120
Kinematic viscosity (mm2/s)1.35 ± 0.001.31 ± 0.001.9–6.03.5–5.0
Density (g/cm3)0.87 ± 0.000.87 ± 0.00-0.86–0.90
Saponification value (mg KOH/100 g oil)239.08 ± 14.11256.44 ± 22.10<500-
Cetane number62.87 ± 2.0762.71 ± 2.46>47>51
Oxidative stability12.26 ± 1.1418.75 ± 1.43>3>8

3N-BBM: Bold’s Basal Medium with three-fold nitrogen.

CWW:75% cafeteria wastewater.

Kinematic viscosity is a critical fuel property that influences the atomization process within the engine and, consequently, affects overall engine performance, particularly in colder climates, where fuel viscosity increases as temperature drops (Woo and Kim, 2019). Additionally, biodiesel with elevated viscosity levels may result in engine deposits after combustion, however, lower viscosity levels may also cause problems such as reduced engine performance, poor fuel atomization and increased wear on engine. The results obtained here (Table 4) are lower than both standards, thus, further investigation to optimize processing parameters or modification strategies is required to enhance kinematic viscosity. Similarly, biodiesel density substantially affects atomization efficiency and engine output power, as diesel injection systems deliver fuel based on volume (Alptekin and Canakci, 2008). In the present study, the estimated density of biodiesel derived from Desmodesmus sp. UOM-DS01 was 0.87 ± 0.00 g/cm3, which is complying with EN specified range of 0.86–0.90 g/cm3.

The saponification value, indicative of fatty acid chain length and molecular weight, is a critical quality parameter for biodiesel feedstocks. Here, FAMEs derived from Desmodesmus sp. UOM-DS01 exhibited saponification values within the ASTM, recommended limit (<500), which further proves its suitability for biodiesel production. The cetane number is a critical parameter in determining biodiesel quality, as it directly impacts combustion performance, engine performance, and ignition quality. Consequently, international standards such as ASTM and EN require minimum values of 47 and 51, respectively (Giakoumis and Sarakatsanis, 2019). In this study, the cetane number of biodiesel derived from Desmodesmus sp. UOM-DS01 cultivated in 3N-BBM and CWW were 63.67 ± 2.07 and 64.24 ± 2.46, respectively, indicating that the FAMEs synthesized under both culture conditions meet the requirements of established commercial standards.

Oxidative stability is another important factor affecting biodiesel stability during extended storage, as oxidation products can severely affect the fuel quality, combustion efficiency, and engine performance (Knothe, 2005). Hence, the ASTM and EN standards specify that the oxidative stability of biodiesel should be higher than 3 h and 8 h, respectively. In the present study, it was observed that both microalgal cultures could be employed to produce biodiesel with oxidative stability complying with the ASTM standard (Nishshanka et al., 2023).

Additionally, the biodiesel quality parameters obtained in this study, including cetane numbers, iodine values and saponification values were comparable with the reported ranges of 48–65, 27–105, and 213–224, respectively, for Desmodesmus sp. UOM-DS01.Therefore, the overall analysis of biodiesel quality parameters in the current study demonstrates that locally isolated Desmodesmus sp. UOM-DS01 has the potential to serve as a viable feedstock for biodiesel production (Premaratne et al., 2021).

3.6 Future perspectives

The present study highlights the feasibility of utilizing CWW as an alternative cultivation medium for Desmodesmus sp. UOM-DS01, enabling simultaneous nutrient recovery and biodiesel feedstock production while significantly reducing freshwater consumption. Nevertheless, the large-scale implementation requires a comprehensive techno-economic assessment (TEA) and life cycle assessment (LCA) to evaluate the commercial and environmental viability. A comprehensive TEA should quantify whether the economic benefits of replacing synthetic culture media with CWW offset the costs associated with pretreatment of wastewater, aeration, high-light stress, biomass harvesting, lipid extraction, and downstream biodiesel production. Furthermore, LCA should evaluate the environmental benefits associated with freshwater conservation, nutrient recovery, greenhouse gas emissions, and energy consumption to identify the most sustainable configurations. Additionally, the economic feasibility of the light-induced lipid enhancement strategy should be evaluated by quantifying the trade-off between the increased energy consumption associated with artificial illumination and the enhancement in lipid productivity and biodiesel yield to determine its commercial viability at large scale. Moreover, to improve the economic viability of the proposed CWW-based cultivation strategy, the residual biomass generated after lipid extraction should be further valorized through an integrated microalgal biorefinery. The carbohydrate- and protein-rich biomass could be converted into biofertilizers, biostimulants, bioenergy, and other value-added bioproducts, thereby maximizing resource recovery, reducing process waste, and generating additional revenue streams to improve the overall profitability of the wastewater integrated microalgae cultivation systems (Condori et al., 2025a; Thevarajah et al., 2025). Therefore, future studies should focus on the pilot-scale validation and optimization of light-induced lipid enhancement strategy together with comprehensive TEA and LCA to determine the commercial feasibility and environmental sustainability of integrating CWW treatment with biodiesel production and residual biomass valorization.

4 Conclusion

The present study demonstrates that Desmodesmus sp. UOM-DS01 has the potential to recover nutrients from CWW, exhibiting removal efficiencies of 75.83 ± 2.10% for COD, 47.69 ± 3.89% for TN, and 38.00 ± 3.93% for TP. Furthermore, cultivation in CWW reduced freshwater consumption by 79.19% compared with conventional 3N-BBM cultivation, highlighting its potential as a resource-efficient alternative medium for sustainable microalgal biomass production. Additionally, under light stress conditions, lipid accumulation increased from 0.31 ± 0.02 g/L to 0.53 ± 0.01 g/L, highlighting Desmodesmus sp. UOM-DS01 as a promising feedstock for biodiesel production. The estimated biodiesel properties further demonstrated the potential of Desmodesmus sp. UOM-DS01 as a promising biodiesel feedstock, complied with ASTM D6751-12 and EN standards. However, prior to large-scale implementation, further research is required to optimize cultivation parameters for enhanced nutrient recovery and desirable fatty acid profiles, together with TEA and LCA to comprehensively evaluate the feasibility and sustainability of bioremediation-integrated biodiesel production systems.

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Footnotes

Edited by: Lakhan Kumar, Maulana Azad National Institute of Technology, India

Reviewed by: Anushree Malik, Indian Institute of Technology Delhi, India

Raj Boopathy, Nicholls State University, United States

Marco Alberto Mamani Condori, National University of Saint Augustine, Peru

Statements

Conflict of interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Funding

The author(s) declared that financial support was not received for this work and/or its publication.

Data availability

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

Author contributions

SS: Investigation, Writing – original draft. SV: Writing – original draft, Investigation. MD: Writing – original draft, Investigation. TR: Writing – original draft. NH: Writing – original draft. PN: Writing – review and editing. MS: Writing – review and editing. TA: Conceptualization, Methodology, Writing – review and editing, Project administration, Supervision.

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Citation

Samaraweera, S. A. S. B., et al. (2026). Light-induced lipid enhancement in domestic wastewater-grown Desmodesmus sp. for biodiesel production and bioremediation. Frontiers in Chemical Engineering, Volume 8. https://doi.org/
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Copyright © 2026 Samaraweera, Vaishnevan, Dinithi, Rajenthiram, Hanifa, Nimarshana, Sakarika and Ariyadasa.

License: https://creativecommons.org/licenses/by/4.0/

*Correspondence: Thilini U. Ariyadasa

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