Flocculation and mechanism of self-flocculating lipid producer microalga Scenedesmus quadricauda for biomass harvesting

In this study, the extracellular polymeric substance of Scenedesmus quadricauda called EPS-S.q and its bioflocculatoin mechanism were investigated. Results showed EPS-S.q was successfully used as bioflocculating agent for S. quadricauda biomass harvesting and flocculation efficiency of up to 86.7% to S. quadricauda cells could be achieved in presence of Zn²⁺. EPS-S.q was the flocculating agent for self-flocculating microalga S. quadricauda and bioflocculation mechanism was polymer bridging. The sugar and protein mass fraction of dry EPS-S.q was sugar 56.7% and protein 41%. The infrared spectrum further indicated the presence of hydroxyl, carboxyl and amino groups. Moreover, pH decrease induced the flocculation of S. quadricauda and 78.4% of flocculation efficiency was the highest at pH 3. In addition, chemical flocculant FeCl₃ was efficiently used for S. quadricauda harvesting and up to 96.8% of flocculation efficiency could be achieved for S. quadricauda culture with biomass concentration 0.21–0.39 g L⁻¹ at pH 7.     

Waste-free technology of wastewater treatment to obtain microalgal biomass for biodiesel production

Five axenic cultures of microalgae were isolated from the wastewater of Almaty city and identified as Chlorella vulgaris strain № 1, Chlorella sp. strain № 3, Scenedesmus obliquus, Phormidium foveolarum and Lyngbya limnetica. Among these strains, C. vulgaris strain № 1 was characterized by the maximum growth rate and the highest productivity. Mass cultivation of this strain in wastewater resulted in accumulation of 5 × 10⁷ cells per ml in 16 days, and in the removal of ～95% of pollutants from water. Cells of C. vulgaris consisted of ～35% proteins, 29% carbohydrates, 30% lipids, and 6% ash, as calculated on a dry weight basis. The major fatty-acids of C. vulgaris were represented by palmitic, cis-7,10-hexadecenoic acid, linoleic, and α-linolenic acids. Culturing in wastewater decreased the unsaturation index of FAs. Thus, C. vulgaris cells are suitable for both waste water purification and accumulation of biomass for further biodiesel production.     

Dual role of microalgae: Phycoremediation of domestic wastewater and biomass production for sustainable biofuels production

Global threats of fuel shortages in the near future and climate change due to green-house gas emissions are posing serious challenges and hence and it is imperative to explore means for sustainable ways of averting the consequences. The dual application of microalgae for phycoremediation and biomass production for sustainable biofuels production is a feasible option. The use of high rate algal ponds (HRAPs) for nutrient removal has been in existence for some decades though the technology has not been fully harnessed for wastewater treatment. Therefore this paper discusses current knowledge regarding wastewater treatment using HRAPs and microalgal biomass production techniques using wastewater streams. The biomass harvesting methods and lipid extraction protocols are discussed in detail. Finally the paper discusses biodiesel production via transesterification of the lipids and other biofuels such as biomethane and bioethanol which are described using the biorefinery approach.     

Comparison of dairy wastewater and synthetic medium for biofuels production by microalgae cultivation

This study is concerned with comparing raw dairy wastewater (DWW) with blue-green medium (BG11 medium) for biofuel production. Three microalgae strains (Chlorella sp., Scenedesmus sp., and Chlorella zofingiensis) were cultured in tubular bubble column photobioreactors with two media separately. After 8 days of cultivation, DWW was demonstrated to be more suitable medium for microalgae biomass and lipid production than BG11 medium. The biomass and lipid produced within wastewater provided suitable feedstocks for anaerobic digestion and biodiesel conversion. Nutrients in wastewater were efficiently removed (>90% total nitrogen removal, approximately 100% ammonia removal, and >85% total phosphorus removal) during this process.     

Enhancing biomethane production from flush dairy manure with turkey processing wastewater

The objective of this study was to assess the quantity and quality of biogas produced by co-digesting flushed dairy manure (FDM) and turkey processing wastewater (TPW). An attached growth digester with working volume of 15 L and a 3 L head space was operated at a 5 d hydraulic retention time using five feed mixes containing 100, 67, 50, 33, and 0% FDM by volume. The biogas yield ranged from 0.072 to 0.8 m³ [g VS^?1] and the methane content (quality) of the gas ranging from 56% to 70%. Both the quantity and quality of the biogas increased as the proportion of TPW in the feed increased. An energy balance for the digester based on a dairy farm with 150 animals, showed that augmenting FDM with TPW at 1:1 and 1:2 ratios, feeds C and D, respectively, produced biogas with net positive energy to all year round. The gas produced was enough to run a 50 kW generator to produce electricity for about 5.5 and 9 h for the 1:1 and 1:2 feed mixes. However, the economics were not favorable if the benefits of the digester are based only on the value electricity to be produced. Either, other possible revenues such as carbon credit, renewable energy credits, green tags for electricity, putting a value to the environmental benefits of AD should be considered or subsidies from grants or other incentives programs to make the system economically viable.     

Kinetic analysis of biohydrogen production from complex dairy wastewater under optimized condition

Present work describes a kinetic analysis of various aspects of biohydrogen production in batch test using optimized conditions obtained previously. Monod model and Logistic equation have been used to find growth kinetic parameters in batch test under uncontrolled pH. The values of μ_m, K_s, and X_m were 0.64 h⁻¹, 15.89 g-COD L⁻¹, and 7.26 g-VSS L⁻¹, respectively. Modified Leudeking-Piret and Michaelis–Menten equation corroborates a flux of energy to hydrogen production pathway and energy sufficiency in the system. Modified Gompertz equation illustrates that the overall rate and hydrogen yield at 15 g-COD L⁻¹ was higher compared to a dark fermentation of other wastewaters. Besides, Andrew's equation also suggests that since the higher value of K_I (19.95 g-COD L⁻¹), k (255 mL h⁻¹ L⁻¹) was not inhibited at high S. The experimental results implied that the entire products during the fermentation process were growth and substrate degradation associated. The result also confirms that the acetate and butyrate were substantially used for hydrogen production in acidogenic metabolism under uncontrolled pH.     

An energy evaluation of coupling nutrient removal from wastewater with algal biomass production

Recently, several life cycle analyses of algal biodiesel from virtual production facilities have outlined the potential environmental benefits and energetic balance of the process. There are a wide range of assumptions that have been utilized for these calculations, including the addition of fertilizers and carbon dioxide to achieve high algal yields in open ponds. This paper presents an energy balance of microalgal production in open ponds coupled with nutrient removal from wastewater. Actual microalgal yields and nutrient removal rates were obtained from four pilot-scale reactors (2500 gallons each) fed with wastewater effluent from a conventional activated sludge process for 6 months, and the data was used to estimate an energy balance for treating the total average 12 million gallons per day processed by the wastewater treatment plant. Since one of the most energy-intensive steps is the dewatering of algal cultures, several thickening and dewatering processes were compared. This analysis also includes the energy offset from removing nutrients with algal reactors rather than the biological nutrient removal processes typically utilized in municipal wastewater treatment. The results show that biofuel production is energetically favorable for open pond reactors utilizing wastewater as a nutrient source, even without an energy credit for nutrient removal. The energy content of algal biomass was also considered as an alternate to lipid extraction and biodiesel production. Direct combustion of algal biomass may be a more viable energy source than biofuel production, especially when the lipid content of dry biomass (10% in this field experiment) is lower than the high values reported in lab-scale reactors (50–60%).     

Comparison of the effectivities of two-phase and single-phase anaerobic sequencing batch reactors during dairy wastewater treatment

The performances of anaerobic sequencing batch reactors fed with two different substrates were studied. The substrates were raw acid whey and acid whey fermented with Kluyveromyces lactis in order to investigate the suitability of ethanol for biogas production. The organic loading rates (OLRs) during the experiment ranged from 1.6 to 12.8 g COD dm⁻³ d⁻¹ and the corresponding decreasing hydraulic retention times from 40 to 5 days for both reactor systems. The efficiency of each system depended on the OLR: the highest COD removal rate was observed at the lowest OLR applied (about 100% in both systems), and at maximum OLR the COD removal efficiency was 68% for the reactors fed with the raw whey and 80% for those fed with the pre-fermented whey. Under the same high OLR conditions the methane yield was 0.122 dm⁻³ CH₄ g⁻¹ COD_degraded for the anaerobic digesters fed with the untreated whey, and 0.197 dm⁻³ CH₄ g⁻¹ COD_degraded for those fed with the pre-fermented whey. The digesters functioned without pH control. At the maximum OLR the pH in the reactors fed with the raw acid whey was 5.1, while in those fed with the pre-fermented whey it was 7.15.The results demonstrate that the use of the pre-fermented acid whey as substrate for anaerobic digestion without pH control is feasible, especially at high OLR levels. This substrate is preferable to the raw acid whey, because of the ethanol formed as a non-acidic fermentation product of the yeast.     

Hydrogen production from dairy wastewater using catalytic supercritical water gasification: Mechanism and reaction pathway

The supercritical water gasification (SCWG) of real dairy wastewater (cheese-based or whey) was performed in a batch reactor in presence of two catalysts (MnO₂, MgO) and one additive (formic acid). The operational conditions of this work were at a temperature range of 350–400 C and the residence time of 30–60 min. The catalysts and formic acid were applied in 1 wt%, 3 wt%, and 5 wt% to determine their effect on hydrogen production. The concentrations of catalysts and formic acid were calculated based on the weight of feedstock without ash. The results showed that increased temperature and prolonged residence time contributed to the hydrogen production (HP) and gasification efficiency (GE). The gas yield of hydrogen in the optimum condition (400 C and 60 min) was achieved as 1.36 mmol/gr DAF (dry ash free). Formic acid addition was favored towards enhancing hydrogen content while the addition of metal oxides (MnO₂ and MgO) had an apex in their hydrogen production and they reached the highest hydrogen in 1 wt% concentration then ebbed. Moreover, GE was increased by the addition of the catalysts and formic acid concentrations. The highest hydrogen content (35.4%) was obtained in 1 wt% MnO₂ and the highest GE (32.22%) was attained in the 5 wt% formic acid concentration. A reaction pathway was proposed based on the GC-MS data of feedstock and produced liquid phase at different condition as well as similar studies.     

Integrated bio-electrogenic process for bioelectricity production and cathodic nutrient recovery from azo dye wastewater

Microbial electrochemical treatment (MET) process was designed to evaluate complete mineralization of partially treated dye effluent obtained from anoxically operated Periodic discontinuous batch reactor (PDBR) for simultaneous bioelectricity generation and recovery of nutrients. In MET bioreactor, anode and cathode chambers were fed with designed synthetic wastewater (DSW) and PDBR dye effluents. The dye metabolite (NH₄⁺) will be converted to nitrates by the activity of aerobic biocatalyst present in cathode chamber to be used as biofertilizer. Dye removal of 90.2% was observed with good electrogenic activity (voltage (OCV)/current; 395 mV/1.77 mA). The mineralization of dye and its intermediates were assessed by reduction in overall toxicity from 23% to 4%. Chemical oxygen demand (COD) removal efficiency of 75% (anode) and 88% (cathode) were observed in correspondence to higher azoreductase (18.7 U; 48 h) and dehydrogenase (1.66 μg/ml of toluene; 24 h) enzyme activities which correlated well with metabolic activities of biocatalyst. Bioelectrocatalytic behavior of mixed biocatalyst on the basis of redox catalytic currents and prevalence of redox mediators signified the specific function of electron transfer toward dye mineralization. The results obtained suggest that the use of MET can considerably degrade toxic pollutants and provides nitrate rich solution (biofertilizer). Utilization of recovered nutrients directly to farms without any energy intensive methods is reported in this communication.