Effect of organic carbon enrichment on the treatment efficiency of primary settled wastewater by Chlorella vulgaris

Effect of macronutrients (carbon, nitrogen, and phosphorus) on the growth of Chlamydomonas reinhardtii and nutrient recovery under different trophic conditions

More stringent discharge standards have led to the development of an alternative nutrient recovery system from wastewater. Microalgae cultivation in wastewater treatment works has presented considerable promise from the perspective of sustainable resource management. Growth kinetics models are useful tools to optimize nutrient recovery from wastewater by algal uptake. Therefore, this research aims to identify the growth kinetics of Chlamydomonas reinhardtii under both heterotrophic and phototrophic conditions with different nutrient concentrations that typify those found in wastewater treatment works. In addition, the effects of macronutrients (C, N, and P) on heterotrophic and phototrophic microalgae growth and nutrient recovery were studied. Greater specific growth rates were achieved under heterotrophic conditions than in phototrophic cultivation. The maximum specific growth rates and nutrient recovery efficiencies were achieved at 5 mg P L-1 under both heterotrophic and phototrophic growth conditions. Nitrate was the preferred form of nitrogen source under heterotrophic conditions, while nitrogen sources did not present any significant influences in the phototrophic cultivation. Specific growth rates reported for both heterotrophic and phototrophic microalgae at lower carbon concentrations (3.10 d-1 and 0.46 d-1, sequentially) were higher than those at higher carbon concentrations (1.95 d-1 and 0.22 d-1, respectively). C. reinhardtii presented an extreme capacity to adapt and grow at all experimental conditions tested in heterotrophic and phototrophic cultivations.

The microalgae-based wastewater treatment system coupled with Cerium: A potential way for energy saving and microalgae boost

The microalgae-based system attracts more attention in wastewater treatment for high quality effluent, low carbon emission, and resource utilization. Light is the key factor for algae growth, but the light masking in sewage will cause low efficiency of the system. This study designed laboratory scale experiments with Chlorella to investigate the influence of cerium on the nutrient removal by algae wastewater treatment system under different light intensities. The best removal rates of NH₄-N, TP, and COD were 72.43%, 88.87%, and 68.08% under 50 µmol/(m ²·s) light intensity and 1 mg/L Ce. Low concentration of Ce could activate protein synthesis, electron transfer, and antioxidase, while excessive Ce might cause toxicity which could be relieved by strong light for energy supply and further activating superoxide dismutase (SOD) and catalase (CAT). Comparing to other similar experiences, this system reached an equal or greater performance on nutrients removal with better efficiency in light utilization. It might provide a new idea for microalgae-based system development.

A waste-based circular economy approach for phycoremediation of X-ray developer solution

A waste-based circular economy approach is proposed for the phycoremediation of an X-ray developer (XD) solution. The present study emphasizes the utilization of food waste (FW) and agri-compost media (ACM) as growth media for D. armatus for the subsequent bioremediation potential of XD solution-coupled lipid production. A 3:1 dilution (FW/ACM: XD.) was found to be suitable for the phycoremediation study of XD solution towards the % removal of biological oxygen demand (BOD), chemical oxygen demand (COD) and silver. The phycoremediation studies of diluted XD solution in FW demonstrated a 74.50% BOD removal, 81.69% COD removal, and 54.70% removal of silver. The growth of D. armatus in diluted XD solution in food waste was 1.37% lipid content. The phycoremediation of diluted XD solution with ACM resulted in 83.05% BOD removal, 88.88% COD removal and 56.30% silver removal with the concomitant lipid production of 1.42%. The optimal bioremediation coupled lipid production of D. armatus was observed on the 19th day of D. armatus cultivation in the developer effluent, along with food waste and agri-compost media, for 31 days. The study suggests a sustainable utilization of waste (FW and ACM) as a nutritive medium to scrutinize the phycoremediation of XD solution with a concomitant lipid production that can open up new avenues in phycoremediation coupled energy commodities production.

Effects of feast-famine nutrient regimes on wastewater algal biofuel communities

Microalgae accumulate lipids in response to nutrient deprivation, and these lipids are a biodiesel fuel stock. Algal cultivation with secondary wastewater effluent is one proposed platform for biofuel production, which provides nutrients to algae while further polishing wastewater effluent. Algal bioreactors were tested using a feast-famine feeding regiment in simulated secondary wastewater effluent to evaluate the effects on lipid content and algal community structure. Algal polycultures were inoculated into reactors fed with synthetic secondary wastewater effluent at pH 7.5 and 9 and operated under a feast-famine nutrient (N, P, and BOD) supply regime in sequencing batch reactors. Fatty acid methyl ester contents of the reactors were assessed, which showed a decrease in lipid content after the feast-famine cycling (from 12.2% initially to 5.2% after four cycles at pH 9). This decrease in lipid content was not correlated with an increase in carbohydrate storage within biomass, nor an increase in bacterial biomass abundance relative to algal biomass in the reactors. The eukaryotic microbial communities from reactors operated at pH 9 diverged from reactors operated at pH 7.5 during cycling, with the pH 9 reactors becoming dominated by a single Operational Taxonomic Unit aligning to the Scenedesmus genus. These results suggest that high pH and feast-famine nutrient cycling may select for a less diverse algal community with a lower lipid content within a secondary wastewater polishing scheme.

Cometabolic bacterial and fungal remediation as a promising strategy for recycled paper and cardboard mill wastewater treatment

Purpose

This paper aims to study the application of high-tolerance and flexible indigenous bacteria and fungi, along with the co-metabolism in recycled paper and cardboard mill (RPCM) wastewater treatment (WWT).

Design/methodology/approach

The molecular characterization of isolated indigenous bacteria and fungi was performed by 16S rRNA and 18S rRNA gene sequencing, respectively. Glucose was used as a cometabolic substrate to enhance the bioremediation process.

Findings

The highest removal efficiency was achieved for both chemical oxygen demand (COD) and color [78% COD and 45% color removal by Pseudomonas aeruginosa RW-2 (MZ603673), as well as approximately 70% COD and 48% color removal by Geotrichum candidum RW-4 (ON024394)]. The corresponding percentages were higher in comparison with the efficiency obtained from the oxidation ditch unit in the full-scale RPCM WWT plant.

Originality/value

Indigenous P. aeruginosa RW-2 and G. candidum RW-4 demonstrated effective capability in RPCM WWT despite the highly toxic and low biodegradable nature, especially with the assistance of glucose.

Progress and challenges of contaminate removal from wastewater using microalgae biomass

The utilization of microalgae in treating wastewater has been an emerging topic focussed on finding an economically sustainable and environmentally friendly approach to treating wastewater. Over the last several years, different types of con microalgae and bacteria consortia have been experimented with to explore their potential in effectively treating wastewater from different sources. The basic features considered while determining efficiency is their capacity to remove nutrients including nitrogen (N) and phosphorus (P) and heavy metals like arsenic (As), lead (Pb), and copper (Cu). This paper reviews the efficiency of microalgae as an approach to treating wastewater from different sources and compares conventional and microalgae-based treatment systems. The paper also discusses the characteristics of wastewater, conventional methods of wastewater treatment that have been used so far, and the technological mechanisms for removing nutrients and heavy metals from contaminated water. Microalgae can successfully eliminate the suspended nutrients and have been reported to successfully remove N, P, and heavy metals by up to 99.6 %, 100 %, and 13%-100 % from different types of wastewater. However, although a microalgae-based wastewater treatment system offers some benefits, it also presents some challenges as outlined in the last section of this paper. Performance in eliminating nutrients from wastewater is affected by different parameters such as temperature, biomass productivity, osmotic ability, pH, O₂ concentration. Therefore, the conducting of pilot-scale studies and exploration of the complexities of contaminants under complex environmental conditions is recommended.

A Review about Microalgae Wastewater Treatment for Bioremediation and Biomass Production—A New Challenge for Europe

Microalgae have received much attention in the last few years. Their use is being extended to different fields of application and technologies, such as food, animal feed, and production of valuable polymers. Additionally, there is interest in using microalgae for removal of nutrients from wastewater. Wastewater treatment with microalgae allows for a reduction in the main chemicals responsible for eutrophication (nitrogen and phosphate), the reduction of organic substrates (by decreasing parameters such as BOD and COD) and the removal of other substances such as heavy metals and pharmaceuticals. By selecting and reviewing 202 articles published in Scopus between 1992 and 2020, some aspects such as the feasibility of microalgae cultivation on wastewater and potential bioremediation have been investigated and evaluated. In this review, particular emphasis was placed on the different types of wastewaters on which the growth of microalgae is possible, the achievable bioremediation and the factors that make large-scale microalgae treatment feasible. The results indicated that the microalgae are able to grow on wastewater and carry out effective bioremediation. Furthermore, single-step treatment with mixotrophic microalgae could represent a valid alternative to conventional processes. The main bottlenecks are the large-scale feasibility and costs associated with biomass harvesting.

Revisiting carbon, nitrogen, and phosphorus metabolisms in microalgae for wastewater treatment

Threats posed to humans - including environmental pollution, water scarcity, food shortages, and resource crises drive a new concept to think about wastewater and its treatment. Wastewater is not only a waste but also a source of energy, renewable and/or non-renewable resources, including water itself. The nutrient in wastewater should not only be removed but also need to be upcycled. Microalgae based wastewater treatment has attracted considerable interests because algae have the potential to efficiently redirect nutrients from wastewater to the accumulated algal biomass. Additionally, microalgae are commercialized in human consumption and animal feed owing to their high content of essential amino and fatty acids, vitamins, and pigments. The whole process establishes a circular economy, totally relying on the ability of microalgae to uptake and store nutrients in wastewater, such as carbon (C), nitrogen (N), and phosphorus (P). It makes the study of the mechanisms underlying the uptake and storage of nutrients in microalgae of great interest. This review specifically aims to summarize C, N, and P metabolisms in microalgae for a better understanding of the microalgae-based wastewater treatment from the nutrient uptake pathway, and examine the key physiological factors or the operating conditions related to nutrient metabolisms that may affect the treatment efficiency. At last, I discuss the potential approaches to enhance the overall treatment performance by adjusting the critical parameters for C, N, and P metabolisms.

Integrating micro-algae into wastewater treatment: A review

Improving the ecological status of water sources is a growing focus for many developed and developing nations, in particular with reducing nitrogen and phosphorus in wastewater effluent. In recent years, mixotrophic micro-algae have received increased interest in implementing them as part of wastewater treatment. This is based on their ability to utilise organic and inorganic carbon, as well as inorganic nitrogen (N) and phosphorous (P) in wastewater for their growth, with the desired results of a reduction in the concentration of these substances in the water. The aim of this review is to provide a critical account of micro-algae as an important step in wastewater treatment for enhancing the reduction of N, P and the chemical oxygen demand (COD) in wastewater, whilst utilising a fraction of the energy demand of conventional biological treatment systems. Here, we begin with an overview of the various steps in the treatment process, followed by a review of the cellular and metabolic mechanisms that micro-algae use to reduce N, P and COD of wastewater with identification of when the process may potentially be most effective. We also describe the various abiotic and biotic factors influencing micro-algae wastewater treatment, together with a review of bioreactor configuration and design. Furthermore, a detailed overview is provided of the current state-of-the-art in the use of micro-algae in wastewater treatment.

Effect of culture conditions on biomass yield of acclimatized microalgae in ozone pre-treated tannery effluent: A simultaneous exploration of bioremediation and lipid accumulation potential

Microalgae has huge potential towards biological nutrient removal, but the challenges are remains in maximizing the biomass yield and so nutrient/pollutant removal efficiency. In this study, a response surface methodology-central composite design was applied to investigate the significant process variables (temperature, light intensity, inoculum density and light period) and its interaction effect on biomass yield of effluent acclimatized microalgae Nannochloropsis oculata, Chlorella vulgaris and Chlorella sorokiniana in ozone pre-treated tannery effluent (OPTE). At optimum culture condition N. oculata, C. vulgaris, and C. sorokiniana have yielded 0.67 g/L, 0.85 g/L, and 1.06 g/L biomass. Besides, correlation and regression analysis revealed the strong correlation between microalgal growth and nutrient removal rate. Among the species, C. sorokiniana has shown better remediation potential, at 27.5 °C, 150 μmol m^-2 s^-1 light intensity, 30% (v/v) inoculum, 16 h light period with the specific growth rate of 0.559 day^-1 and nutrient/pollutant removal efficiency of 90% C, 90% N, 100% P, 82% COD, and 100% chromium. But, N. oculata has revealed the better lipid accumulation potential (40%) in OPTE. Thus, the present study established the appropriate strains and conditions required for OPTE treatment along with the value-added biomass production in large scale.

Mixotrophic cultivation of Chlorella for biomass production by using pH-stat culture medium: Glucose-Acetate-Phosphorus (GAP)

Here the study designed a pH-stat culture medium that named as Glucose-Acetate-Phosphorus (GAP) for the mixotrophic cultivation of Chlorella for biomass production. With no addition of pH buffer, the culture pH during mixotrophic growth was effectively maintained steady between 7.5 and 8.5 by balancing the ammonium, acetate and glucose uptakes. Based on the GAP medium supplying with 2 g·L^-1 of total organic carbon, the biomass productions of four Chlorella species were determined as 4.08-4.56 g·L^-1. In contrast to the cultivation using medium Tris-Acetate-Phosphorus (TAP), a algal culture medium that usually regarded as specific for mixotrophy, the cultivation in GAP were about 1.79-1.86 times higher in biomass production and 83.9-88.9% lower in production cost. The developed GAP medium is a promising alternative for the mixotrophic cultivation of microalgae to produce biomass and cellular contents.

Optimization of algae mixotrophic culture for nutrients recycling and biomass/lipids production in anaerobically digested waste sludge by various organic acids addition

Anaerobically digested waste sludge contains very high concentrations of ammonium and phosphate that are difficult to be purified using traditional processes. Mixotrophic culture of microalgae is a potential way to achieve ammonium and phosphate removal, while harvesting considerable biomass for biodiesel production. In this study, four typical volatile organic acids that could be potentially produced from sludge fermentation were tested for algal mixotrophic culture in anaerobically digested waste sludge. The results showed that the addition of propionate and isovaleric acid had no significant improvement on biomass production, and even inhibited algal growth at low concentration. Fortunately, the addition of acetic and n-butyric acid (initial C/N = 10) increased biomass production by1.9-2.4 times compared to the blank culture. Higher biomass production increased ammonium and orthophosphate removal to 88.3-97.1% and 80.4-93.0%, respectively. Moreover, the optimal addition of volatile organic acids enhanced lipids production by 3.9-6.3 times, while achieving higher saturation degree in biodiesels. The results suggest that adding these optimal volatile organic acids is suitable to enhance nutrients recycling and algal biodiesel production from anaerobically digested waste sludge.

Utilization of tannery wastewater for biofuel production: New insights on microalgae growth and biomass production

Microalgae cultivation on tannery wastewater (TWW) has been examined in some studies as a possible biological application to reduce contamination load and discharge effluents safely. However, Growth aspects, different tolerate strains and enriching the medium were not well investigated. In our study we applied Scenedesmus sp., Chlorella variabilis and Chlorella sorokiniana with different TWW concentrations. C. sorokiniana and C. variabilis cell density, chlorophyll, and sugar content grew substantially as compared to control. C. sorokiniana biomass and total lipids folded three and two times in 25% and 40% TWW, respectively as compared to control. Scenedesmus sp. showed longer lag phase and lower performance compared to the other two strains. Kelp waste extract (KWE) was added to balance the nutrients supply for C. sorokiniana, of which growth and effluents indicators were then greatly promoted in all concentrations. As the lag phase was shortened from 8 to 4 days in 60% concentration, subsequently, chlorophyll, carbohydrates, biomass and total lipids appreciated by 184%, 400%, 162% and 135%, respectively. Furthermore, the COD and ammonium removals improved by 51% and 45%, respectively. These outcomes emphasize the suitability of using TWW for microalgae cultivation with the suitable concentration while adding kelp waste extract for further enhancement.

Characteristics of wastewater treatment by Chlorella sorokiniana and comparison with activated sludge

Characteristics of Chlorella sorokiniana treating wastewater with consideration of HRT (6 d, 16 h, 8 h), hydraulic conditions, light or dark culture were evaluated and compared with activated sludge. Results showed that optimal HRT was 8 h; if longer, effluent chemical oxygen demand (COD) and NH₄ ⁺-N in the dark began to rebound. Mixing was beneficial to COD removal of algae, while aeration was suitable for nutrient removal. Growth of C. sorokiniana in the light was mixotrophic growth and 1.3-1.7 times more than that of dark heterotrophic growth. The maximum specific growth rate (µ_max), productivity, and biomass yields on COD (Y_COD), N (Y_NH4), P (Y_P) of algae were higher in the light than that in the dark. COD assimilation capacity of algae was similar to activated sludge but with different dynamics. N and P assimilation capacity of algae was 1.4, 1.2-2.5 times more than activated sludge; N and P removal efficiency of algae was 5%-10%, 10%-55% respectively higher than activated sludge. This study confirmed the advantage of algae over activated sludge and reveal why algae could assist the activated sludge process.

Green microalgae for combined sewage and tannery effluent treatment: Performance and lipid accumulation potential

Microalgae have considerable interest owing to its phycoremediation potential and raw material for sustainable biofuel production. In this study, the performance of green algae Chlorella vulgaris (NRMCF0128) and Pseudochlorella pringsheimii (VIT_SDSS) was evaluated for the remediation of combined sewage and tannery effluent under different dilutions. Significant reduction in pollutant concentration was observed in the effluent: >65% for NH₃-N, 100% for PO₄-P, >63% for COD & >80% for total chromium, at higher dilutions (up to 30%) of tannery effluent (T) for both species. EDAX analysis confirms the intracellular accumulation of heavy metal chromium and other elements such as aluminum, zinc, and iron by both microalgae. In addition, the maximum yield of biomass achieved was 3.51 g/L (for 30% Tannery effluent) and 2.84 g/L (for 20% Tannery effluent) for Chlorella vulgaris &Pseudochlorella pringsheimii, respectively. Between the two species, Pseudochlorella pringsheimii has shown high lipid accumulation potential of 25.4% compared to Chlorella vulgaris (9.3%) at 20% Tannery effluent. Hence, it is evident that the green microalgae Pseudochlorella pringsheimii is promising for the sustainable treatment of combined sewage and tannery effluent along with biofuel production.

Biomass production and biochemical profiles of a freshwater microalga Chlorella kessleri in mixotrophic culture: Effects of light intensity and photoperiodicity

In this work, different light conditions (light intensity and photoperiodicity) were set up to investigate the impact of light on growth, chemical compositions and fatty acid profiles of Chlorella kessleri in mixotrophic cultures. Results indicated that C. kessleri could absorb and utilize glucose rapidly when light intensity was ≤ 90 µE m^-2 s^-1, and a maximum algal biomass of 1.17 g L^-1 was obtained in the cultures with 2 g L^-1 glucose at a light intensity and light/dark (L/D) cycle of 90 µE m^-2 s^-1 and 20L:4D, respectively. Additionally, this alga would accumulate a large amount of chlorophyll a (about 30 mg g^-1) in the mixotrophic cultures under a low light intensity (≤90 µE m^-2 s^-1), and the algal chemical compositions changed with light intensity and photoperiodicity. Results of fatty acid profiles suggested that the algal biomass could be used as animal feeds or a good-quality biodiesel feedstock.