Effect of environmental factors on the biomass and lipid production of microalgae grown in wastewaters

Bioremediation potential of the Chlorella and Scenedesmus microalgae in explosives production effluents

This study explores microalgae-based bioremediation for treating black gunpowder production effluents, an understudied yet environmentally significant stream. Two native microalgae, Chlorella sp. MC18 (CH) and Scenedesmus sp. MJ23-R (SC), were assessed for growth kinetics and nutrient removal capabilities in culture media containing different proportions of untreated raw wastewater. Results show both species thrived in 100 % raw wastewater, displaying robust growth and substantial biomass production in parallelepiped-shaped photobioreactors. SC showed superior performance, with higher maximum specific growth rate (0.549 d-1), biomass yield (454.57 mg L-1) and biomass productivity (64.94 mg L-1 d-1) compared to CH (0.524 d-1, 380.60 mg L-1, 54.37 mg L-1 d-1, respectively). The use of 100 % raw wastewater as a culture medium eliminated the need for additional freshwater input, thus reducing the water footprint. The bioremediation process also resulted in a high removal efficiency in turbidity (>95 % CH, >76 % SC), total suspended solids (>93 % CH, >74 % SC), biochemical oxygen demand (BOD5) (>62 % CH, >93 % SC) and chemical oxygen demand (COD) (>63 % CH, >87 % SC), bringing the effluent into compliance with environmental regulations. Although nitrogen (>45 % CH, >57 % SC) and sulphate (>43 % CH, >35 % SC) removal efficiencies was high, potassium bioremediation was limited (<6 %). The proximate chemical composition of the microalgal biomass revealed different allocations to carbohydrates, lipids and proteins. The results suggest promising applications for biofuel production and aquaculture. This research highlights the potential of microalgae-based bioremediation for sustainable wastewater management in the explosives industry, contributing to the UN Sustainable Development Goals and promoting green industrial practices.

A review on biodiesel production from microalgae: Influencing parameters and recent advanced technologies

Microalgae are the important part of carbon cycle in the nature, and they could utilize the carbon resource in water and soil efficiently. The abilities of microalgae to mitigate CO₂ emission and produce oil with a high productivity have been proven. Hence, this third-generation biodiesel should be popularized. This review firstly introduce the basic characteristics and application fields of microalgae. Then, the influencing parameters and recent advanced technologies for the microalgae biodiesel production have been discussed. In influencing parameters for biodiesel production section, the factors of microalgae cultivation, lipid accumulation, microalgae harvesting, and lipid extraction have been summarized. In recent advanced technologies for biodiesel production section, the microalgae cultivation systems, lipid induction technologies, microalgae harvesting technologies, and lipid extraction technologies have been reviewed. This review aims to provide useful information to help future development of efficient and commercially viable technology for microalgae-based biodiesel production.

Impact of pyrene (polycyclic aromatic hydrocarbons) pollutant on metabolites and lipid induction in microalgae Chlorella sorokiniana (UUIND6) to produce renewable biodiesel

Pyrene (polycyclic aromatic hydrocarbon), an anthropogenic organic pollutant prevalent in various ecological units, receives more attention for bioremediation and energy transformation using microalgae. In this study, we have used pyrene pollutant (50-500 ppm) to evaluate the half-maximal inhibitory concentrations (IC₅₀) of Chlorella sorokiniana and the impact on metabolites as well as the induction of lipid biosynthesis to produce renewable biodiesel. Pyrene concentration at 230 ppm (IC₅₀) caused half-maximum inhibition for the 96 h incubation. The harvest in the stationary stage (day 16) for C. sorokiniana revealed a biomass generation of 449 ± 7 mg L^-1 and 444 ± 8 mg L^-1 dcw in the control medium and pyrene IC₅₀ medium, respectively. An insignificant decline in biomass generation (1.2%) was observed due to the stress effect of the pyrene IC₅₀ medium on metabolic biosynthesis. Although contrary to biomass generation, IC₅₀ of pyrene assisted to induce lipid biosynthesis in C. sorokiniana. The improvement in lipid biosynthesis was observed as ~24% higher in pyrene IC₅₀ compared to the control medium. The chemical composition of the microalgae biomass, metabolites, and lipids was examined using FTIR spectra. The extracted lipid was transesterified to produce biodiesel via methanolic-H₂SO₄ catalysis. The renewable biodiesel obtained was evaluated using FTIR and ¹H NMR spectra. The transformation efficiency of the lipid of C. sorokiniana in biodiesel was calculated as ~81%. This research offers the incentive in lipid biosynthesis in microalgae cells using pyrene for the production of renewable and sustainable ecological biofuels along with bioremediation of pyrene.

A Review on Synchronous Microalgal Lipid Enhancement and Wastewater Treatment

Microalgae are unicellular photosynthetic eukaryotes that can treat wastewater and provide us with biofuel. Microalgae cultivation utilizing wastewater is a promising approach for synchronous wastewater treatment and biofuel production. However, previous studies suggest that high microalgae biomass production reduces lipid production and vice versa. For cost-effective biofuel production from microalgae, synchronous lipid and biomass enhancement utilizing wastewater is necessary. Therefore, this study brings forth a comprehensive review of synchronous microalgal lipid and biomass enhancement strategies for biofuel production and wastewater treatment. The review emphasizes the appropriate synergy of the microalgae species, culture media, and synchronous lipid and biomass enhancement conditions as a sustainable, efficient solution.

Multivariate criteria applied in the performance of Tifton 85 grass in a constructed wetland: effects of organic, nutritional, and sodium loads from swine wastewater

The purpose of this study was to analyze the effects of the application of multivariate criteria of principal components and hierarchical clustering as a mechanism for monitoring the performance of Tifton 85 grass (Cynodon spp.) planted in horizontal subsurface flow constructed wetland reactor (HSSF-CW) under different organic (OLR), nutritional and sodium loads of swine wastewater (SW). The HSSF-CW planted with Tifton 85 grass was used as a swine wastewater after treatment applying organic loading rates between 26.1 (1st cut) and 360.6 kg ha^-1 day^-1 COD (8th cut). The maximum performances of HSSF-CW consisted of 52.0 t ha^-1 of productivity and 24.0% of crude protein, with the application of 59.7, 64.2, and 31.2 kg ha^-1 day^-1 of TKN, P_T, and K⁺, respectively. The eleven original variables generated four new components, with PC₄ accounting for 94.0% of total variance, a condition strengthened with four data groupings greater than 48% similarity and three data groupings greater than 95% similarity between the variables. There was a strong association between of nitrogen, phosphorus, and potassium concentration by the hierarchical grouping and the intermediate cuts and lower temperatures.

Chlorella vulgaris cultivation in simulated wastewater for the biomass production, nutrients removal and CO2 fixation simultaneously

Chlorella vulgaris (C. vulgaris) was promising microalgae to simultaneously achieve biomass production, carbon dioxide (CO₂) fixation, nutrients removal and proteins production especially under different conditions of CO₂ gas and wastewaters. Results presented that maximal specific growth rate of C. vulgaris was 0.21-0.35 d^-1 and 0.33-0.43 d^-1 at 0.038% and 10% CO₂ respectively, and corresponding maximal CO₂ fixation rate was attended with 4.51-14.26 and 56.26-85.72 mg CO₂·L^-1·d^-1. C. vulgaris showed good wastewater removal efficiency of nitrogen and phosphorus at 10% CO₂ with 96.12%-99.61% removal rates. Nitrogen fixation amount achieved 41.86 mg L^-1 when the initial NH₄Cl concentration was set at 60 mg L^-1 at 10% CO₂. Improved total protein (25.01-365.49 mg) and amino acids (24.56-196.44 mg) contents of C. vulgaris biomass was observed with the increasing of added CO₂ and ammonium concentrations. Moreover, the developed kinetic function of C. vulgaris growth depends on both phosphorus quota and nitrogen quota with correlation coefficient (R²) ranged from 0.68 to 0.97. Computed maximal consumed nutrients concentrations (ΔC_max) based on Logistic function are positively related to initial NH₄⁺-N concentrations, which indicated that adding ammonium could stimulate the utilization of both phosphorus and nitrogen.

Biofilms attached to Myriophyllum spicatum play a dominant role in nitrogen removal in constructed wetland mesocosms with submersed macrophytes: Evidence from 15N tracking, nitrogen budgets and metagenomics analyses

The mechanisms behind nitrogen removal by the submersed macrophyte-biofilm complex in wetlands remain to be fully elucidated. This study investigated the role of Myriophyllum spicatum and the biofilm on their leaves in nitrogen removal in mesocosm experiments. ¹⁵N tracking showed that 61.9% and 30% of the ¹⁵N, respectively, was removed from the system and assimilated by the macrophyte-biofilm complex after loading with 5.4 mg L^-115N labelled NH₄⁺ for 17 days. Nitrogen budget results showed that about 0.2%, 0.2% and 3.6% of the nitrogen were emitted as water-, HCl- and NaOH-soluble nitrogen-gas species, respectively. Bacteria (76.7-91.8%) were the predominant domain in all samples, followed by eukaryotes (8.0-23.0%), archaea and viruses. Network analyses showed that there were positive- and negative-correlative relationships among nitrogen-cycling genes and nitrifiers and denitrifiers. Our data highlight the important role of biofilm on submersed macrophytes for nitrogen removal.

Continuous 3-year outdoor operation of a flat-panel membrane photobioreactor to treat effluent from an anaerobic membrane bioreactor

A membrane photobioreactor (MPBR) plant was operated continuously for 3 years to evaluate the separate effects of different factors, including: biomass and hydraulic retention times (BRT, HRT), light path (Lp), nitrification rate (NOxR), nutrient loading rates (NLR, PLR) and others. The overall effect of all these parameters which influence MPBR performance had not previously been assessed. The multivariate projection approach chosen for this study provided a good description of the collected data and facilitated their visualisation and interpretation. Forty variables used to control and assess MPBR performance were evaluated during three years of continuous outdoor operation by means of principal component analysis (PCA) and partial least squares (PLS) analysis. The PCA identified the photobioreactor (PBR) light path as the factor with the largest influence on data variability. Other important factors were: nitrogen and phosphorus recovery rates (NRR, PRR), biomass productivity (BP), optical density of 680 nm (OD680), ammonium and phosphorus effluent concentration (NH₄, P), HRT, BRT, air flow rate (F_air) and nitrogen and phosphorus loading rates (NLR and PLR). The MPBR performance could be adequately estimated by a PLS model based on all the recorded variables, but this estimation worsened appreciably when only the controlled variables (Lp, F_air, HRT and BRT) were used as predictors, which underlines the importance of the non-controlled variables on MPBR performance. The microalgae cultivation process could thus only be partially controlled by the design and operating variables. A high nitrification rate was found to be inadvisable, since it showed an inverse correlation with NRR. In this respect, temperature and microalgae biomass concentration appeared to be the main factors to mitigate nitrifying bacteria activity.