Cultivation of microalgae Chlorella vulgaris, Monoraphidium sp and Scenedesmus obliquus in wastewater from the household appliance industry for bioremediation and biofuel production

Abstract

Microalgae Chlorella vulgaris, Scenedesmus obliquus, and Monoraphidium sp were cultivated in effluent from the household appliance industry as an alternative medium for bioremediation due to the high variability of chemical and biological substances in wastewater. The experiments were carried out using biological effluent (BE), chemical effluent (CE), and a combination of the two (MIX). The results showed a maximum biomass yield of 1056 mg/L (± 0.216) in the BE cultivation of the microalga Scenedesmus obliquus, 969 mg/L (± 0.20) in the BE of the microalga Monoraphidium sp. and 468 mg/L (± 0.46) in the CE of Chlorella vulgaris. In addition, they showed $N{O}_3^{-}$ removal (100%) in the CE and MIX for cultivation with Chlorella vulgaris and 100% BE and 75% MIX with Monoraphidium sp. For the $P{O}_3^{4-}$ (75.3%, 99% e 97.9%) in the cultures with C. vulgaris BE, CE, and MIX respectively, with Monoraphidium sp. 58% in BE and 42% in CE and MIX. With S. obliquus, 100% removal was observed in all 3 treatments. Metal removal was also observed. The C. vulgaris culture showed lipid contents of 16%, 12%, and 17% for BE, CE, and MIX, respectively. For Monoraphidium sp., 14.5% for BE, 16% for CE, and 14% for MIX. In the culture of S. obliquus, 17%, 15.5%, and 16.5% for BE, CE, and MIX, respectively.

Introduction

Due to the high demand for energy and population increase at the global level, Microalgae technology has been an alternative resource with the biotechnological potential to produce renewable fuels and high-value-added products due to the following advantages: higher carbon dioxide fixation, high biomass growth rate; capacity to store carbon in carbohydrate and lipid forms (50%) for biofuel recovery (Andrade and Filho 2014; Banu et al. 2020; Mathimani and Prabaharan 2017).

Microalgae can produce and accumulate biochemical compounds with applications in human and animal nutrition, health, cosmetics, pharmaceuticals, analytics, and biofuels. In addition, it could also capture CO₂ and participate in bioremediation during wastewater treatment (Hallmann and Rampelotto 2019).

Bioremediation of effluents has become essential, as it is a sustainable treatment that considers economic, social, and environmental aspects. Microalgae can potentially reduce energy use in waste management strategies and remove nutrients such as carbon, phosphorus, and nitrogen (Ali et al. 2021).

Microalgal biomass generated at the end of the bioremediation process has great potential as raw material for bioenergy production (Goswami et al. 2021; Lee 2022; Li et al. 2022; Pittman et al. 2011; Qari et al. 2017; Raheem et al. 2018), biopolymers (Samantaray and Mallick 2012; Martins et al. 2014), biofertilizers (Uysal et al. 2015) and bioplastics (Rahman and Miller 2017; Das et al. 2018).

Different types of effluents are reported in the literature as an alternative for microalgae cultivation as biodigested agroindustrial wastes (Franchino et al. 2013), swine wastewater (Chen et al. 2021; Deng et al. 2017; Sun et al. 2018), aquaculture effluents (Viegas et al. 2021), textile effluent (Fazal et al. 2021; Wu et al. 2017), dairy effluent (Ahmad et al. 2018; Costa et al. 2021; Kiani et al. 2023; Pandey et al. 2019) brewing effluent (Ferreira et al. 2017), poultry slaughterhouse effluent (Oliveira et al. 2018), artificial wastewater (Ruiz-Marin et al. 2020) and urban wastewater (Batista et al. 2015; Lavrinovičs et al. 2022; Zhang et al. 2014). The results were pesticide manufacturing effluent (Shrikant and Madaan 2021), industrial palm oil effluent (Ahmad et al. 2022), and phenolic wastewater (Zhao et al. 2022).

However, there is a lack of studies on effluents from household appliance companies. The main products that the segment traditionally known in the market as white line are refrigerators, vertical and horizontal freezers, air conditioners, dishwashers, washing machines, dryers, and microwave ovens.

Given the above, this work aimed to evaluate the use of industrial effluent from the household appliances sector as a medium for cultivating microalgae Chlorella vulgaris, Monoraphidium sp. e Scenedesmus obliquus. The removal of nutrients, biomass yield, and lipids were also evaluated, aiming at the production of biofuels.

Materials and methods

Microalgae and culture conditions

Chlorella vulgaris, Monoraphidium sp. e Scenedesmus obliquus were from the Planctology Laboratory (PL) of the Center for Applied Biotechnology to Aquaculture (CEBIAQUA) located at the Federal University of Ceará (UFC) in Fortaleza—CE. The culture medium used was modified Guillard f/2, widely used in both marine and freshwater microalgae (LOURENÇO, 2006). The culture medium used was f/2 medium; the lighting was provided by LED lamps with a power of 9W and 5000 lx with a photoperiod of 12/12 h: constant aeration, an average pH of 7.8 (± 0.40), and room temperature of 27 °C.

Wastewater

The effluents were collected at the treatment plant of an appliance industry located in the industrial district of the metropolitan region of Fortaleza/ Ceará-Brazil. Two types of effluents were collected: Biological Effluent (BE) from the cafeterias and bathrooms and Chemical Effluent (CE) from the entire industrial process, such as paintings; both underwent pre-treatment in a treatment plant within the company. 200 L were collected from each effluent to supply all reactors and initial analyses.

Experimental design

Chlorella vulgaris, Monoraphidium sp., and Scenedesmus obliquus were initially cultivated in standard medium Guillard f/2 and distributed in the reactors in triplicate (n = 3) with the volume of 10L in each reactor, the initial density of the strains was 219.7 × 10⁵ cells mL ⁻¹ for Chlorella vulgaris, 225.2 × 10⁵ cells mL ⁻¹ for Monoraphidium sp and 41.5 × 10⁵ cells mL ⁻¹ for Scenedesmus obliquus. The experimental design (Fig. 1) was made vertically composed of 21 reactors. The reactors were polycarbonate, transparent, and had a capacity of 20 L. LED lamps performed the lighting with the power of 9W in the intensity of 5000 Lux with a photoperiod of 12/12 h and constant aeration. The experiment was carried out in 3 batches, one for each microalgae and each batch lasting 10 days. The experimental design was made as follows:

• a) Biological Effluent Control (BE-CTRL) with pure effluent (100%).

• b) Control Chemical Effluent (CE-CTRL) with pure effluent (100%).

• c) Effluent Mix Control (MIX-CTRL) in proportion 1:1 of BE/CE effluents.

• d) Microalgae Control (MC-CTRL), only with the microalgae in its standard medium (F/2).

• e) Microalgae Biological Effluent (BE) at 8:2.

• f) Microalgae Chemical Effluent (CE) at 8:2.

• g) Effluent Mix with Microalgae (MIX) in a ratio of 4:4:2.

Fig. 1.

Experimental design: a microalgae inoculum; b experimental setup. BE biological effluent with microalgae, CE chemical effluent with microalgae, MIX mix effluent with microalgae, MC microalgae, BE-CTRL biological effluent control, CE-CTRL chemical effluent control, MIX-CTRL mix effluent control; c monitoring microalgal growth

Microalgae growth

Microalgae growth was measured by cell count in the Neubauer chamber, using optical microscope phase contrast (OLYMPUS BX-40), and the cell density (CD) was measured using a spectrophotometer (HACH DR/2000) at λ = 680 nm using 25 mL aliquots. In addition, daily growth rates (K) (divisions day ⁻¹) and maximum cell density (MCD) were determined using the (CD) according to Eq. (1) described by Lourenço (2006):

$$K=\frac{lo{g}_2\frac{N_F}{N_i}}{\mathrm{\Delta }t},$$ 1

where K is the growth rate (divisions day ⁻¹), Ni is the initial CD, Nf is the CD on the day the culture obtained the maximum cell concentration, respectively, and Δt the cultivation time in days.

Physico-chemical parameters

Physico-chemical parameters were analyzed: pH, conductivity, total solids, and temperature determined by a portable multiparameter HI 9811-5. Nutrients such as phosphate, ammonia, chlorine, nitrite, nitrate, chromium, aluminum, zinc, and manganese were analyzed using analytical methods mentioned in the American Public Health Association (APHA 1995). The efficiency of nutrient removal from the effluent was analyzed using nutrient balance at the beginning and end of the crop, according to Eq. (2)

$$E\left(\%\right)=\frac{C_i-C_F}{C_i}$$ 2

E (%) is the removal efficiency, Ci is the initial nutrient concentration, and Cf is the final concentration.

Biomass and lipid content

After removing aliquots to determine the parameters, the algal biomass was recovered by chemical flocculation using NaOH 0.5 M. After separation in two phases, with the biomass decanted, the supernatant was siphoned and then washed in running water. The wet biomass was dehydrated in an oven with air circulation at 60 °C for 24 h. The dry biomass was quantified from Eq. (3)

$$BS=\frac{B2-B1}{V}$$ 3

where BS is the dry biomass (g L⁻¹), B1 is the weight of the empty petri dish (g), B2 is the weight of the petri dish with algal biomass, and V is the volume used (L).

Lipid content was determined by the Bligh and Dyer (1959). The dry biomass was placed in a beaker, where 2 mL of distilled water was added for each 0.5 g of dry biomass. 7.5 mL of chloroform solution: 1:2 methanol was added to the wet biomass, followed by manual agitation for 3 min. Then, 10 mL of 1.5% anhydrous sodium sulfate solution and 2.5 mL of distilled water were added and manually stirred for 30 s. The biomass was then separated by centrifugation at 4500 rpm for 10 min. After centrifugation, the sample is taken to the separation funnel for 5 to 10 min until the phases are separated. The organic phase was transferred to a beaker and dried in an oven at 60 °C until constant mass, leaving only the total lipids in solid form, which were weighed in an analytical balance.

Statistical analysis

Analysis of variance (ANOVA) (P ≤ 0.05). When significant differences were found between treatments (P ≤ 0.05), the Tukey test was used. All statistical data were performed using Statistica.

Results and discussion

The development of microalgae initially went through a period of adaptation of cells to alternative culture media. Initially, all reactors were acclimatized to the new cultivation conditions (nutrients, pH, temperature, and luminosity). Treatments evaluated were microalgae in standard medium (MC), biological effluent (BE), chemical effluent (CE), and a combination of biological effluent with chemical effluent (MIX).

Microalgal growth

Cell growth was monitored by counting cells under an optical microscope until the end of the species exponential phase, according to Lourenço (2006). Microalgae cultivation in effluents presents advantages for biomass production of commercial value for industry (Leite et al. 2013; Khan et al. 2018).

Cell growth can be observed in Fig. 2, where the microalgae passed through a phase of adaptation to the effluent of an appliance industry. Figure 2a shows the cell growth of the microalgae Chlorella vulgaris cultivated in industrial effluent, with an initial cell density of 219.7 × 10⁵ cells mL⁻¹. BE, MIX, and MC showed an exponential phase on the 6th day with 737 × 10⁴ cells mL⁻¹, 725 × 10⁴ cells mL⁻¹, and 890 × 10⁴ cells mL⁻¹, respectively.

Fig. 2.

Microalgal growth curve a Chlorella vulgaris; b Monoraphidium sp.; c Scenedesmus obliquus in different treatments of effluent from the household appliance industry. BE biological effluent with microalgae, CE chemical effluent with microalgae, MIX mix effluent with microalgae, MC microalgae

CE treatment presented 568 × 10⁴ cells mL^−1, indicating a prolonged adaptation of the microalgae to the culture medium. Figure 2b shows the growth of the microalga Monoraphidium sp. with an initial inoculum cell density of 225.2 × 10⁵ cells mL⁻¹, which performed better in the biological effluent and adapted more quickly to the medium, showing an exponential phase on the 6th day with 925 × 10⁴ cells mL⁻¹. CE and MIX treatments showed a phase of adaptation until the 4th day. Growth of the microalgae S.obliquus was observed in Fig. 2c. Although it started with a low number of cells (41.5 10⁵ cells mL⁻¹), it adapted well, and the CE treatment, unlike the other two microalgae, was the one that showed the best cell growth.

In the treatments, although they do not present a high efficiency in cell growth, microalgae corroborate with Wang et al. (2009), which indicate that effluents are sources of nutrients for the cultivation of microalgae.

Growth rate was also evaluated; in Table 1, growth rate data of the species Chlorella vulgaris, Monoraphidium sp. Scenedesmus obliquus has treatments such as Control (MC), Biological Effluent (BE), Chemical Effluent (CE), and mixed effluent (MIX). It is possible to observe a higher growth rate in the control (MC) and a low rate in the other treatments, which can be attributed to the adaptation phase of microalgae to the effluent.

Table 1.

Growth rate of Chlorella v., Monoraphidium sp., Scenedesmus o. in culture with effluent from the household appliance industry

Microalgae	Treatment	Growth rate (day−1)	Maximal cell density (cells.mL−1)
Chlorella vulgaris	MC	0.1104	962 × 104
	CE	0.0418	568.3 × 104
	BE	0.0964	736.7 × 104
	MIX	0.0537	759.2 × 104
Monoraphidium sp.	MC	0.0354	455.8 × 104
	CE	0.0301	727.5 × 104
	BE	0.0323	925 × 104
	MIX	0.0301	537.5 × 104
Scenedesmus obliquus	MC	0.1204	253.3 × 104
	CE	0.0864	387.5 × 104
	BE	0.0520	289.2 × 104
	MIX	0.1115	271.7 × 104

Where Microalgae grown in standard medium (MC), biological effluent (BE), chemical effluent (CE) and a combination of biological effluent with chemical effluent (MIX)

Mercado et al. (2020) investigated the increase in biomass and lipid productivity of Scenedesmus sp. effluent in the dairy industry and showed a growth rate of 0.51 and 0.54 d⁻¹.

Franchino et al. (2013) evaluated the cultivation of three species of microalgae, Neochloris oleoabundans, Chlorella vulgaris, and Scenedesmus obliquus, in an agrozootechnical digester. C. vulgaris growth rates were 0.64, 0.52, 0.51, 0.49 d⁻¹, S. obliquus. growth rates were 0.49, 0.44, 0.23, 0.31 and 0.23 d⁻¹ and N. oleoabundans growth rates were 0.27, 0.37, 0.30 and 0.26 d⁻¹. For all three strains, the average productivity under four different digest dilution ratios showed only small differences.

Physico-chemical parameters

The pH is an essential parameter for cultivation that affects the growth and metabolism of microalgae. The ideal pH for microalgae cultivation usually ranges from 7.0 to 7.6 (neutral pH). Still, the pH tolerance is species-specific, and the maximum biomass yield for S. obliquus was observed in pH 7.0 and 8.5, respectively. It is possible to observe that in the pH of all treatments, there is a slight variation (Fig. 3), but they remain in the ideal range to grow microalgae in industrial effluent that can be maintained at pH 8–9 (Wu et al., 2017).

Fig. 3.

Effect of pH and temperature on the cultivation of microalgae in effluents from the household appliance industry. a and b effect of pH and temperature with microalgae Chlorella vulgaris; c and d effect of pH and temperature with microalgae Monoraphidium sp; e and f effect of pH and temperature with microalgae Scenedesmus obliquus. BE biological effluent with microalgae, CE chemical effluent with microalgae, MIX mix effluent with microalgae, MC microalgae

Furthermore, the results of the following experiment demonstrated that the highest variation was recorded in the CE treatment (7.8 and 8.7), and on the 6th day, the pH level in the CE decreased considerably in the C. vulgaris batch (Fig. 3a). Still, the microalgae Monoraphidium sp. showed constant CE treatment with pH between 8.1 (± 0.05) (Fig. 3c).

In the batch with the microalga S. obliquus (Fig. 3e), the MIX treatment reduced pH on day 7, and BE showed a lower pH than the other treatments. The growth of microalgae in culture involves the consumption of CO₂ dissolved in the medium, increasing the system's pH. Previous research has shown that the growth of microalgae causes an increase in the pH of the culture medium attributed to the photosynthetic activity of the microalgae, which consumes CO₂ and releases oxygen, consequently at the same time-consuming CO2 converting it into algal biomass (Liu et al. 2020; Lourenço, 2006).

pH plays a vital role in algae cultivation, as it is responsible for the availability and solubility of nutrients and CO₂. The ideal pH for growing microalgae generally ranges from 7.0 to 7.6 (neutral pH), but the pH tolerance is specific to each species, and the maximum biomass yield for S. obliquus was observed in pHs 7.0 and 8.5, respectively (Arutselvan et al. 2022; Shahid et al. 2020).

In addition, pH is an important parameter; in cultures with alkaline conditions, the contamination risks are reduced. This parameter also affects the composition of the medium; NH₃–N is a nitrogen source favored by microalgae due to the lower energy required for its assimilation (López-Sánchez et al. 2022).

Cultivating the microalgae C. vulgaris presents the highest temperatures among cultures with values of up to 31.4 °C (Fig. 3b, d, and f). It is possible to observe that the 3 treatments present higher temperatures in the first days than the control treatment (MC).

Figure 3d shows the temperature behavior in the cultivation with the microalgae Monoraphidium sp. There was a variation of 22 °C (± 0.10) to 30 °C (± 0.15); all treatments (MC, BE, CE, and MIX) showed the same behavior throughout the cultivation, increasing until the 7th day. As in Fig. 3f, the highest temperature (29.9 °C) can also be observed on the 7th day in the cultivation of the microalgae Scenedesmus obliquus.

The growth of Monoraphidium microalgae in domestic effluents recorded lower temperatures on the fourth day (21.8 °C) and a maximum of 27 °C, with a temperature variation of 5.2 °C during the experiment (Godoy et al. 2020). The temperature variation may be due to the variation in the ideal ambient temperature for these microorganisms. However, considering that there was no significant difference between treatments, it is possible that this variable did not interfere with the yield and efficiency of microalgae removal.

The parameters of total solids and conductivity are presented in Figs. 4 and 5. It is possible to observe that the conductivity in the cultures with the three microalgae showed an increase of this parameter in the controls (BE-CTRL, CE-CTRL, and MIX-CTRL) treatments with microalgae during the experiment.

Fig. 4.

Conductivity parameters evaluated during the cultivation of microalgae in effluents from the household appliance industry: a cultivation with Chlorella vulgaris; b cultivation with Monoraphidium sp; c cultivation with Scenedesmus obliquus. BE biological effluent with microalgae, CE chemical effluent with microalgae, MIX mix effluent with microalgae, MC microalgae, BE-CTRL biological effluent control, CE-CTRL chemical effluent control, MIX-CTRL mix effluent control

Fig. 5.

Total solids parameters evaluated during the cultivation of microalgae in effluents from the household appliance industry: a cultivation with Chlorella vulgaris; b cultivation with Monoraphidium sp; c cultivation with Scenedesmus obliquus. BE biological effluent with microalgae, CE chemical effluent with microalgae, MIX mix effluent with microalgae, MC microalgae, BE-CTRL biological effluent control, CE-CTRL chemical effluent control, MIX-CTRL mix effluent control

In the cultivation of the microalgae Chlorella vulgaris. The effluents control BE-CTRL, CE-CTRL, and MIX-CTRL presented the maximum conductivities of 1190 µS/cm, 1473 µS/cm, and 1340 µS/cm, respectively (Fig. 4a). The BE with the minimum conductivity of 868 on the 4th day. Therefore, removals of 27%, 31%, and 31% (BE, CE, and MIX) were observed, respectively.

Cultivation with the microalgae Monoraphidium sp also showed a reduction in conductivity; all treatments showed approximately 20% removal (Fig. 4b). Figure 4c also shows a reduction in this parameter in cultivation with Scenedesmus o., with reductions of 21%, 27% and 23% for the EB, CE, and MIX treatments respectively.

Along with the conductivity, Fig. 5a, b, and c show a reduction in total solids decreased in effluents cultivated with microalgae compared to untreated effluents. In this parameter, cultivation with the microalga Chlorella vulgaris resulted in a 38%, 36%, and 26% removal of solids. Treatment with S.obliquus showed a reduction of 20%, 26%, and 23%, and treatment with Monoraphidium sp reduced 17%, 19%, and 24% in the BE, CE, and MIX treatments, respectively. As microalgae absorb and/or consume ions and dissolved organic material during growth, a reduction in these values (conductivity and total solids) is expected before and after microalgae cultivation (Mirzaei et al. 2024).

Nutrient removal

Table 2 shows some effluents used as a medium for the cultivation of microalgae to be remediated with the removal of nutrients and produce high-value-added bioproducts. In addition, they show results corresponding to the nutrient intake of the 3 different species of microalgae Chlorella vulgaris, Scenedesmus obliquus, and Monoraphidium sp. in the present study.

Table 2.

Potential for bioremediation of microalgae

Wastewater	Microalgae	Nutrients	Removal (%)	References
Swine wastewater	Chlorella vulgaris	Total nitrogen Total phosphorus	89.95 93.68	Chen et al. 2021
Textile wastewater	Chlorella vulgaris	Total nitrogen Total phosphorus	80	Fazal et al. 2021
Domestic wastewater	Scenedesmus sp.	Total nitrogen Nitrate Phosphate	70–98	Nayak et al., 2016
Poultry wastewater	Scenedesmus obliquus	Total nitrogen Phosphate	> 97  > 97	Oliveira et al. 2018
Dairy wastewater	Chlorella zofingiensis	Total nitrogen Phosphorus	51.7 97.5	Huo et al., 2012
Municipal wastewater	Chlorella vulgaris	Total nitrogen Total phosphorus	94 98.6	Sisman-Aydin 2022
Industrial wastewater	Monoraphidium sp.	Orthophosphate	50	Godoy et al., 2020
synthetic wastewater	Chlorella vulgaris	Total nitrogen Total phosphorus	95.82 100	Liu et al. 2019
Dairy wastewater	Monoraphidium sp.	Nitrate Phosphate	85 60	Kuravi and Mohan 2022
Effluent from the household appliance industry	Chlorella vulgaris	Ammonia Nitrate Phosphate	99 10 99	This study
Effluent from the household appliance industry	Monoraphidium sp.	Ammonia Nitrate Phosphate	100 100 58.2	This study
Effluent from the household appliance industry	Scenedesmus o	Ammonia Phosphate	100 100	This study

Table 2 according to Schargel et al. (2022), microalgae can assimilate and incorporate the sources of nitrogen, ammonia, and nitrate that require less metabolic energy, and then the sources of free phosphorus into their cells to carry out the processes of photosynthesis and respiration, these compounds being the main nutritional requirements for the growth and development of microalgae, when inoculated in a solution rich in these elements. Thus, Arutselvan et al. (2022) studied the cultivation of Chlorella vulgaris in effluent from the textile industry and obtained efficient removal of phosphate, nitrate, total solids, and metals. In addition to being able to observe large amounts of lipids retained in its biomass due to the conditions that induce metabolic stress in the organism, that is, the microorganism can remediate the effluent and even generate a bioproduct in the form of a circular economy.

Table 3 shows the removal of nutrients with the cultivation of microalgae in industrial effluents from the white goods sector in the BE, CE, and MIX effluents. Corroborating with Benítez et al. (2018) who studied the cultivation of Chlorella vulgaris by removing nitrogen and phosphorus, as a potential secondary wastewater treatment process in Ecuador. The experimental results indicated that the microalgae cultures were able to successfully remove nitrogen and phosphorus with removal efficiencies of –N and –P of 52.6% and 55.6%, $N{H}_4^{3-}$ and $P{O}_4^{3-}$ of 67.0% and 20.4%.

Table 3.

Removal of nutrients from biological effluent (BE), chemical effluent (CE) and a combination of biological effluent with chemical effluent (MIX)

Microalgae	Treatment	Nutrients	Removal
Chlorella vulgaris	Biological effluent	Phosphate	75.3%
	Chemical effluent	Phosphate Ammonia Nitrate	99% 99% 100%
	Effluent mixture	Phosphate Ammonia Nitrate	97.7% 85% 100%
Monoraphidium sp	Biological effluent	Phosphate Nitrate	58.2% 100
	Chemical effluent	Phosphate Ammonia	42.1% 100%
	Effluent mixture	Phosphate Ammonia Nitrate	42% 100% 75.2%
Scenedesmus obliquus	Biological effluent	Phosphate	100%
	Chemical effluent	Ammonia Phosphate	100% 100%
	Effluent mixture	Phosphate Ammonia	100% 100%

Metal removal was also evaluated in this study. Table 4 presents the removal of manganese, zinc, aluminum, and chromium in the crops. According to Mercado et al. (2020), as regards heavy metals, it has been demonstrated that microalgae have developed mechanisms to tolerate the toxicity of these elements, which constitutes an advantage in the bioremediation processes of industrial and domestic effluents. Biosorption refers to the adhesion of ions to the cell surface, while bioaccumulation involves the absorption of ions and molecules within the cells. Among these two mechanisms, biosorption plays a more significant role in the bioremoval of these compounds (Mirzaei et al. 2024).

Table 4.

Removal of metals from biological effluent (BE), chemical effluent (CE) and a combination of biological effluent with chemical effluent (MIX)

Microalgae	Treatment	Metals	Removal
	Biological effluent	Manganese Zinc Aluminium	100% 100% 100%
Chlorella vulgaris	Chemical effluent	Manganese Zinc Chromium	100% 100% 100%
	Effluent mixture	Manganese Zinc Chromium Aluminium	100% 100% 100% 100%
	Biological effluent	Zinc	59%
Monoraphidium sp	Chemical effluent	Zinc	55%
	Effluent mixture	Zinc	41.3%
	Biological effluent	Manganese Zinc	40% 28%
Scenedesmus obliquus	Chemical effluent	Manganese Zinc	91% 38%
	Effluent mixture	Manganese Zinc	88% 32%

Biosorption studies of Scenedesmus sp. showed the potential to remove heavy metals, Cu (73–98%), Zn (65–98%), Cr (81–96%), and Pb (75–98%) from tannery effluents under laboratory conditions (Ajayan et al. 2015).

Biomass and lipid content

Biomass yield was evaluated at the end of the cultivation of the species in each treatment. Figure 6 shows the yield of microalgal biomass resulting from the cultivation of Chlorella vulgaris., Monoraphidium sp., and Scenedesmus obliquus. In the graph, it is possible to observe a higher yield in the cultivation of the microalgae S. obliquus, which presents 1056 mg/L (± 80.0) of biomass in the treatment BE, 1036 mg/L (± 126.5) in the MIX, 820 mg/L (± 164.8) in the CE, while the control MC yields 531 mg/L (± 26.1).

Fig. 6.

Biomass yield of microalgae Monoraphidium sp., Chlorella vulgaris, Scenedesmus obliquus in different treatments. BE Biological effluent with microalgae, CE chemical effluent with microalgae, MIX mix effluent with microalgae, MC microalgae

The biomass yield of Chlorella vulgaris was also evaluated (Fig. 6), showing a lower microalgal biomass yield in the three treatments, where they presented a yield of 468 mg/L (± 153), 463 mg/L (± 44.9), 445 mg/L (± 32) and 260 mg/L (± 2.3) for CE, BE, MIX and MC respectively.

Some studies have been conducted to increase microalgal biomass by optimizing cultivation strategies. Liu et al. (2019) cultivated Chlorella sp. in photobioreactors and obtained a maximum biomass yield of 409 mg/L. The results showed that HMTC (Two-stage heterotrophic + mixotrophic culture) was the best cultivation strategy for improving the microalgal biomass.

In the cultivation with the microalgae Monoraphidium sp., a good yield of microalgal biomass was observed in the treatment BE with 969.2 mg/L (± 100.6) and in the treatments CE (630 ± 36.1 mg/L) and MIX (672 ± 150.9 mg/L) the double of the control MC (303.7 ± 14.2 mg/L).

It is evident that with the three microalgae, the highest biomass yield was with the biological effluent (BE) due to the availability of sufficient sources of P and N. Microalgae use C, N, and P from wastewater to synthesize proteins, nucleic acids, phospholipids, and chlorophylls (Silambarasan et al. 2023).

RajivGandhi et al. (2022) focused on isolating Chlorella vulgaris from industrial wastewater and its use as an effective raw material to produce renewable biodiesel, obtaining 756 mg L⁻¹ of biomass. Holbrook et al. (2014) cultivated the microalgae Monoraphidium sp. raw material for biodiesel and present at the end of cultivation 1.52 g/L of algal biomass. Microalgae Scenedesmus obliquus was cultivated in bovine wastewater with good potential for bioremediation with high removal rates of CODs, NH₄ and $P{O}_4^{3-}$ and obtained a biomass yield of up to 358 mg L⁻¹d⁻¹ and 183 mg L⁻¹d⁻¹ in batch and continuous mode (De Mendonça et al. 2018).

Lipid content can be presented in Table 5, which shows studies that reported results of lipid content in microalgae cultures in different effluents as an alternative culture medium. The current work shows results for the cultivation of Chlorella vulgaris with lipid contents of 16%, 12%, and 17% for BE, CE, and MIX, respectively. For the cultivation of Monoraphidium sp., 14.5% for BE, 16% for CE, and 14% for MIX. In the cultivation of Scenedesmus obliquus, 17%, 15.5%, and 16.5% for BE, CE, and MIX, respectively.

Table 5.

Lipid content Chlorella vulgaris, Monoraphidium sp. and Scenedesmus obliquus compared to literature

Microalgae	Wastewater type	Lipid content %	References
Scenedesmus sp.	Industrial effluent	13	Mohammadi et al. 2018
Chlorella vulgaris	Industrial effluent	9.81	Zhao et al. 2014
Chlorella vulgaris	Textile effluent	31.20	Arutselvan et al. 2022
Chlorella vulgaris	Effluent from the household appliance industry	16	This study
Chlorella vulgaris		12	This study
Chlorella vulgaris		17	This study
Monoraphidium sp.		14.5	This study
Monoraphidium sp.		16	This study
Monoraphidium sp.		14	This study
Scenedesmus obliquus		17	This study
Scenedesmus obliquus		15.5	This study
Scenedesmus obliquus		16.4	This study
Chlorella sorokiniana	Aquiculture	31.85	Ansari et al. 2017
Scenedesmus obliquus	Municipal	26.6	Ansari et al. 2019

Corroborating with these results, Batista et al. (2015) cultivated C. vulgaris and S.obliquus and a consortium between them in urban effluent. They obtained similar results with lipid contents of 8.1% for C. vulgaris, 10% for S.obliquus, and 13.6% for the consortium. Koley et al. (2018) reported a study with S. obliquus with a lipid content of 11.5% under ambient conditions. In a municipal effluent treatment study (post-treated), Alva et al. (2013) reported the production of the lipid content (28.3%) of the microalgae S. acutus. Qin et al. (2016) investigated the lipid content of Chlorella sp. (21.09%), C. zofingiensis (20.62%), Chlorella sp. and Scenedesmus sp. (19.34%) cultivated in dairy effluents.

Conclusions

The cultivation of the microalgae Chlorella vulgaris, Monoraphidium sp., and Scenedesmus obliquus. Industrial effluent of the white line sector demonstrated high removal efficiency and can be used for bioremediation. In addition, it was possible to analyze the behavior of effluents for different parameters; the biological effluent showed better results in some parameters. However, the effluent mix demonstrated great potential and was an option for the company in effluent optimization. There is a need for biomass valorization through bioactive compounds recovered as lipids that can be transformed into biofuels. Therefore, the possibility of biofuel production alongside bioremediation of effluent nutrients improves the sustainability and profitability of the entire system and could be one of the best strategies for the future of bioenergy.

Author contributions

Kelly Lima de Oliveira, José Lucas da Silva Oliveira e Egídia Andrade Moraes realizaram os experimentos, contribuiram com a manutenção da bancada experimental, e realizaram métodos analíticos. Kelly Lima de Oliveira, analisou os dados e escreveu o manuscrito. Kelma Maria dos Santos Pires Cavalcante, Mona Lisa Moura de Oliveira e Carlúcio Roberto Alves forneceram feedback que ajudou moldar a pesquisa e análise, e revisou o manuscrito. Mona Lisa Moura de Oliveira, administração de projetos e aquisição de financiamento. Todos os autores leram e aprovaram o texto final manuscrito.

Data availability

Not applicable.

Declarations

Conflict of interest

The authors declare that there is no conflict of interest associated with this study.