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This study was aimed to investigate the potential adsorptive behavior of mixed algae for decolorization of methylene blue dye from aqueous solution in the form of free and immobilized. Effects of initial pH value (3-9), biosorbent dosage (0.02-0.5)g/L, and initial concentration (10-50) mg/L for different contact time (0-180) min at 200 rpm shaking speed were investigated. In addition, experimental data were analyzed using adsorption (Langmuir and Freundlich) isotherms as well as kinetic models. The results demonstrated that the maximum decolorization percentage was 93% and 91% by free and immobilized algae, respectively for pH 6, 10 initial concentration, 0.3g/100mL algae dosage, and 90 min contact time. The results revealed that the Langmuir isotherm model was adequate for describing the dye removal process (R2= 0.99) for both forms. Results of pseudo-second order kinetic model revealed best fitting with the sorption data indicating that chemisorption process is the dominant mechanism controlling the dye removal. Furthermore, the characterization study performed using FT-IR and scanning electron micrograph techniques, revealed that the used algal biomass has good biosorption capabilities associated to active groups and surface structure and confirming that the immobilization was successful.

This study investigated nutrient removal from anaerobic digestion effluent by cultivating mixed-culture microalgae enriched from anaerobic sludge under different pH conditions: RUC (uncontrolled), R7–8 (maintained at 7–8), and R<8 (maintained below 8). Significant amounts of NH4+-N were lost by volatilization in RUC cultures due to increased pH values (≤8.6) during the early period of cultivation. The pH control strategies significantly affected the biological NH4+-N removal (highest in R7–8), microalgal growth (highest in R7–8), biomass settleability (highest in R<8), and microalgal growth relative to bacteria (highest in R<8) in the cultures. Parachlorella completely dominated the microalgal communities in the inoculum and all of the cultures, and grew well at highly acidic pH (<3) induced by culture acidification with microalgal growth. Microalgae-associated bacterial community structure developed very differently among the cultures. The findings call for more attention to the influence and control of pH changes during cultivation in microalgal treatment of anaerobic digestion effluent.

In this study, the effects of a mixed algal blend (Chlorella vulgaris, Euglena viridis, and Spirulina platensis) at different levels were evaluated on growth, hematological immune responses, and expression of immune genes in Labeo rohita against post-challenges of Aeromonas hydrophila. Fish samples were fed a diet containing different levels of mixed blend algal (0, 0.01, 0.02, 0.04 and 0.08% of basal diet). At the end of the feeding period, the fish were challenged with A. hydrophila and fish mortality was recorded over a 14-days period. To evaluate the serum biochemical (albumin, globulin), hematological parameters (Hb, RBC and WBC) and immune parameters (neutrophil activity, lysozyme activity, myeloperoxidase activity, antiprotease activity, ceruloplasmin activity, and bactericidal activity), as well as the expression of immune genes (NKEF-B, Lysozyme C and G, TNF α, TLR22, β2M, and β-actin), fish were sampled on Day 7, 14, 21 and 28. Fish were challenged with virulent A. hydrophila 30 days post-feeding and mortalities were recorded over 30 days post-infection. Results demonstrate that fish fed with a mixed algal blend showed that total body weight gain, specific growth rate, total serum protein, globulin, total hemoglobin content, white blood cells, neutrophil, lysozyme, bactericidal, myeloperoxidase, and antiprotease activity in dietary algae blended application was higher than in the control (p < 0.05). According to the results, relative expression of target genes showed significant increases of 0.02 to 0.04% in the treatment group compared to the control group (p < 0.05). At the end of the 30-day exposure to A. hydrophila, the fish that received the mixed algal blend had a significantly higher rate of survival than the control group, with the highest survival rate recorded in the 0.02% mixed algal blend (p < 0.05). According to the effective results of the mixed algal blend on stimulating the immune system and increasing fish resistance to A. hydrophila, it is recommended to use 0.02 to 0.04% of this mixed algal blend in rohu, L. rohita diets.

Tetracycline antibiotics have been increasingly used in medical applications and have been found in wastewater treatment plants as a result of human and industrial activities. This study investigates the combined effects of tetracycline antibiotics on the performance of an algal photo-bioreactor operated under different antibiotic concentrations in the ranges of 0.25 to 30 mg/L and considers the inhibition of algal growth, carbon and nutrient removal rates, and eukaryotic and cyanobacterial algal community changes. The results indicated that increases in the concentration of tetracycline mixtures have adverse effects on the algal community and the performance of a photo-bioreactor, and the eukaryotic algae species were more sensitive to tetracycline antibiotics than were the cyanobacterial species. Cultivation tests showed that approximately 94 % growth inhibition of mixed algae occurred at 30 mg/L.

In this study, a mixed microalgal culture grown in secondarily treated domestic wastewater effluent was investigated for biodiesel production using in situ transesterification method with conventional heating. The total lipid content of the mixed culture was found as 26.2 % ± 0.6 by weight of dry biomass, and 74 % of the lipids were contributed by total glycerides. In situ transesterification with conventional heating process under acidic conditions produced higher biodiesel yield with chloroform as the co-solvent (82.1 % ± 3.9) compared to hexane (55.3 % ± 3.9) under the same reaction conditions. The gas chromatography analysis showed that FAME composition was mainly composed of palmitic, palmitoleic, stearic, oleic, linoleic and linolenic acid methyl esters., and thus the mixed microalgal culture fed by domestic wastewaters has had comparable biodiesel conversion yields and FAME composition to mono-culture and pure cultures fed by synthetic culture media. Hence, this study showed that secondarily treated domestic wastewater could potentially be a suitable and sustainable medium for microalgae grown to be used as biodiesel feedstock.

Microalgae-based treatment systems have been successfully used for the polishing of domestic wastewater. Research is underway in studying the suitability of using these systems as main treatment units. This study focuses on comparing the performances of a mixed microalgal culture and an aerobic bacterial culture, based on the kinetic evaluation, in removing organic carbon from a kitchen wastewater. The two systems were operated at six different solid retention times (SRTs)—2, 4, 6, 8, 10, and 12 days in continuous mode. The influent and effluent samples were analyzed for chemical oxygen demand (COD), total organic carbon (TOC), total nitrogen (TN), phosphates, and surfactants. Steady-state kinetics ( k , K s , Y , and k d ) for organic carbon removal were obtained by fitting experimental data in linearized Michaelis-Menten and Monod equations. The mixed microalgal system showed similar or better performance in COD and TN removal (88 and 85%, respectively) when compared with the COD and TN removal by the aerobic bacterial system (89 and 48%). A maximum lipid yield of 40% ( w / w of dry biomass) was observed in the microalgal system. Saturated fatty acids accounted for 50% of the total observed FAME species. The study indicates that the mixed microalgal culture is capable of treating kitchen wastewater and has the potential to replace aerobic bacteria in biological treatment systems in certain cases.

Nitrogen is one of the essential components for cellulase production by fungi and is available in algal proteins. The present study investigates different nitrogen sources such as microalgae extract, yeast extract, peptone, and ammonium nitrate for cellulase production by mono and mix cultures of Trichoderma reesei and Aspergillus niger for the first time. Microalgae are pretreated using different pretreatment strategies to be used as the nitrogen source. The microalgae pretreatment for protein extraction is relatively poorly investigated compared to other protein sources. The prosperous extraction of proteins from mixed microalgae can improved the economic feasibility of the process. Also, the research area on mixed microalgae attracts more attention than traditional pure cultures. The protein extraction results reveal that the highest protein extraction yield (98.1%) was achieved using the sequence of ultrasonic waves and dilute alkaline. Furthermore, results of cellulase production by mono and mix cultures of fungi show that the highest cellulase activity (3.25 U/mL) and the highest reducing sugar production (9.85 g/L) were obtained in the media containing the microalgae extract by mixed fungi culture. This study demonstrates that microalgae can be introduced as a cheap candidate for improvement in cellulase production, which is more economical for industrial usage. Also, the obtained results are of great significance for the further development of such strategies for the modification of fungal culture media for high-quality cellulase production. Graphical Abstract

In this study, the effect of sludge retention time (SRT) on biomass production and nutrient removal was determined by constant hydraulic retention time (HRT) with mixed microalgae culture. The SRTs of 2, 3, 6, 12, and 24 days with constant 24 h HRT were studied in microalgae membrane photobioreactor (msMpBR) by using hollow fiber (HF) membranes with a pore diameter of 0.45 μm. According to the results, the best removal was achieved within 3 days of SRT. Chlorophyll-a/mixed liquor suspended solid (MLSS) ratios were found to be 0.033. Total nitrogen (TN) and phosphate phosphorus (PO4–P) removal rates were found to be 5.55 mg N/L day−1, and 0.4 mg PO4–P/L day−1, respectively. The volumetric microalgae production was found to be 0.118 g/L day−1. Also, Chaetophora sp. and Navicula sp. cultures were found to be dominant in steady state. The percentage of lipid and protein in dry biomass was obtained to be 8.94% and 30.34%, respectively. It is advisable to use algal membrane photobioreactor, and mixed microalgae cultures instead of specific microalgae cultures, which could be readily affected by seasonal changes and outdoor conditions in wastewater treatment.

Hydrogen production from mixed microalgae biomass, predominantly containing Scendesmus and chlorella species, was investigated with a focus on enhancement strategies, in particular (i) pH control (at 5.5) and (ii) methanogenic inhibitor (BESA) addition along with pH control at 5.5. The results obtained showed that the later condition remarkably increased the performances. This was mainly ascribed to the occurrence of a suitable environment for the hydrogen producers to perform actively. Hydrogen production under these conditions (i.e., both pH 5.5 and pH5.5+BESA) was significantly higher than that of the control experiment. Using the pH control at 5.5 and BESA addition, peak hydrogen production rate (HPR) and hydrogen yield (HY) were attained as 210 mL/L/d and 29.5 mL/g VSadded, respectively. This improvement was nearly 3-folds higher compared with the control experiment with an HPR of 62 mL/L/d and an HY of 9.5 mL/g VSadded.

Biogas yield obtained from anaerobic digestion of swine wastewater (SWW) needs to be increased to produce electrical energy. To enhance biogas and prevent pollution, use of mixed culture microalgae grown in wastewater (MWW) with SWW has attracted a lot of interest. This research was focused on the possibility of utilizing MWW. Six experiments using raw SWW and MWW, and their co-digestion were conducted on a laboratory scale in one-litre reactors with the ratio of inoculum and substrate of 70:30 under without and with alkaline pretreatment (using 3% NaOH for pH adjustment every 15 min at pH 11 for 3 h). The results showed that co-digestion had the major effect on increasing biogas and methane yields (0.735 and 0.326 m3/kg of volatile solids (VS) removed), and the highest chemical oxygen demand and VS removal (60.29% and 63.17%). For pretreatment, the effect of ammonia inhibition at a high pH of 11 had more influence on biodegradation than the effect of destruction of MWW's cell walls, resulting in a low biogas production of pretreated MWW and pretreated co-digestion. These findings affirm the potential of co-digestion, and the possibility of using both single and co-substrate MWW. Pretreatment could be improved at a lower alkaline pH condition. A pilot scale of co-digestion should be performed.