Microalgae-bacteria Consortium Research Articles

Evaluation of bio-crude oil through hydrothermal liquefaction of microalgae-bacteria consortium grown in open pond using wastewater

The present study demonstrates a promising approach for production of bio-crude oil via hydrothermal liquefaction of microbial biomass grown in large-scale open raceway pond. Three key attributes to achieve process feasibility are co-cultivation of microalgae and bacteria resulting in high biomass titre, utilization of paper industry wastewater as cheap source of nutrients and water, and one-step direct conversion of biomass into bio-crude oil. High biomass titre of 4 g L−1 with 90% of COD removal efficiency was achieved, depicting robust performance of the microalgae-bacteria consortium in industrial wastewater and under fluctuating environmental condition. Statistical optimization resulted in highest bio-crude oil yield of 21.7 (%, w/w) under optimal temperature, biomass loading and reaction time of 299.7 °C, 16.1 (%, w/v) and 65 min, respectively. Bio-crude oil with energy recovery of 43% and heating value of 33.1 MJ kg−1 reflects 81.7% and 73.4% heating value of biodiesel and diesel, respectively. While high percentage of hydrocarbon content in bio-crude oil indicates good oil quality, the presence of significant esters fraction might offer resemblance to biodiesel. Lower H/C ratio and higher O/C ratio in comparison to diesel indicate requirement of upgradation of bio-crude oil before it can be realized at commercial scale.

Continuous biomass and lipid production from local chlorella-bacteria consortium in raw wastewater using volatile fatty acids.

To evaluate mixotrophic cultivation of microalgae-bacteria consortium in raw wastewater by stepwise addition of fermented effluent containing volatile fatty acids (VFAs). Stepwise increase of VFAs enhanced algal biomass and lipid production, ammonia and phosphate removals. The highest biomass and lipid yield were 1.94g L-1 and 310mg L-1 when the addition of fermented effluent containing VFAs increased to 30% (v/v). With the same cultivation conditions, the maximum removals efficiency of ammonia and phosphate were 26.4 and 11.3mg L-1 d-1. Bacterial diversities increased with the increasing concentration of VFAs and their communities were identified as phyla Actinobacteria, Bacteroidetes, Cyanobacteria and Proteobacteria. Although bacterial quantities increased with algae growth concurrently, the objective of culturing microalgae-bacteria consortium in raw wastewater without sterilization to produce biomass and lipid yield still can be realized.

A novel photo-respirometry method to characterize consortia in microalgae-related wastewater treatment processes

In this paper, a new photo-respirometry method for determining the rates of the main metabolic processes of microalgae-bacteria consortia in microalgae-based wastewater treatment processes has been developed and tested. The proposed protocol consists on applying dark and light periods to a microalgae-bacteria consortium in the presence of different substrates and measuring the rate of oxygen production. This allows determining the activity of microalgae, heterotrophic bacteria and nitrifying bacteria separately.The method has been optimized in terms of the operation strategy, including the starvation period required, the biomass concentration and the irradiance during the measurements. Results show that a starvation period of one to three days is necessary depending on the nutrient concentration. The optimal experimental conditions determined were a biomass concentration of 0.5 g/L and an irradiance of 200 μmol photons/m2·s. Furthermore, microalgae-bacteria samples from seven photobioreactors (indoor and outdoor) with different nutrient sources have been evaluated applying the methodology proposed. Regardless of the wastewater type, the microalgae activity is the main metabolic process, with heterotrophic activity increasing along with the chemical oxygen demand (COD) in the wastewater. Nitrifying activity was only observed when high ammonium concentrations were present. The developed method is a powerful tool to adequately manage and operate wastewater treatment processes using microalgae/bacteria consortia, providing valuable information to model wastewater treatment systems with microalgae and determine kinetic parameters.

Microalgae-bacteria consortia in high-rate ponds for treating urban wastewater: Elucidating the key state indicators under dynamic conditions

On-line performance indicators of a microalgae-bacteria consortium were screened out from different variables based on pH and dissolved oxygen on-line measurements via multivariate projection analysis, aiming at finding on-line key state indicators to easily monitor the process. To fulfil this objective, a pilot-scale high-rate pond for urban wastewater treatment was evaluated under highly variable conditions, i.e. during the start-up period. The system was started-up without seed of either bacterial or microalgal biomass. It took around 19 days to fully develop a microalgal community assimilating nutrients significantly. Slight increases in the biomass productivities in days 26–30 suggest that the minimum time for establishing a performant bacteria-microalgae consortium could be of around one month for non-inoculated systems. At this point, the process was fully functional, meeting the European discharge limits for protected areas. The results of the statistical analyses show that both the pH and the dissolved oxygen concentration represent accurately the biochemical processes taking place under the start-up of the process. Both pH and dissolved oxygen represented accurately also the performance of the high-rate algal pond, being affordable, easily-implemented, options for monitoring, control and optimization of industrial-scale processes.

Selection of photosynthesis and respiration models to assess the effect of environmental conditions on mixed microalgae consortia grown on wastewater

This study aimed at evaluating the effects of different environmental conditions (irradiance, temperature, pH and dissolved oxygen) on a microalgae-bacteria consortium cultivated in a pilot-scale open pond and fed on the liquid fraction of anaerobic digestate. A standardized photo-respirometry protocol was followed to evaluate the activity of microalgae under different conditions. Two datasets (specific photosynthetic oxygen production rates and respiratory oxygen consumption rates) were obtained for each environmental parameter, throughout the entire range of conditions found in the outdoor cultivation system. Different kinetic models available in literature were fitted to experimental data and the resulting outputs were compared through model selection estimators, in order to select the most appropriate equations. The proposed set of equations constitute a modelling tool for the prediction of algal growth rates in algae-bacteria systems, as a function of environmental conditions.

Cultivation of an Algae-Bacteria Consortium in a Mixture of Industrial Wastewater to Obtain Valuable Products for Local Use

Profitability of biofuel production from microalgae is difficult to achieve but co-locating production with wastewater treatment plants is a possible avenue help to reduce costs. A microalgae culturing project was conducted using wastewater from an industrial park to obtain valuable metabolites from the biomass to eventually use them locally. Different growth conditions were tested with a mixture of wastewater as the culture medium and a native microalgae-bacteria consortium isolated locally. The results showed that this consortium grows well in wastewater and that different fatty acids profiles are produced under the different growth conditions. The optimal culture conditions to produce biomass and extracted lipids are in mixotrophic mode under an irradiance of 200 μmol m−2 s−1 with an injection of 1% of CO2. High amounts of other fatty acids were also produced and could potentially be used to make other co-products. In addition to reducing wastewater treatment costs, the manufacture of biosurfactants could bring additional income to the overall microalgae production process.

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

The cultivation of a microalgae-bacteria consortium in a ternary blend of wastewaters was carried out by varying three variables (organic carbon content in the form of glycerol, CO2 addition, and light intensity) using a 23 full factorial design. An analysis of variance was performed to assess the effects of each factor and their interactions on the responses of biomass productivity, lipid content, and nutrients uptake. Also, a principal component analysis (PCA) was conducted to study correlations among the variables. Light intensity and its interaction with organic carbon were the main factors affecting cells growth. The biomass productivity (maximum value of 105.2 mg⋅L−1⋅d−1) was negatively affected by organic carbon and CO2 addition and positively affected by light intensity. Higher lipid contents (maximum value of 17.2%) were found at conditions of low light intensity and high organic carbon in the cultures. Lipid production was related to ammonia-N uptake by the cells. The addition of organic carbon aided the uptake of nitrates-N, ammonia-N, and total organic carbon, and the light intensity reduced these values (maximum values of 100%, 90% and 86%, respectively). The PCA corroborated the relations found between the factors and responses in the factorial analysis and revealed correlations among the responses measured. The main source of nitrogen at conditions of high light intensities was nitrates, while ammonia was the preferred nitrogen source when the cultures were grown under high organic carbon contents as it was indicated by the values of nutrients uptake.

Biotreatment of landfill leachate by microalgae-bacteria consortium in sequencing batch mode and product utilization

Biotreatment of leachate by microalgae-bacteria in a sequencing batch mode using a photobioreactor was investigated. The microalgae-bacteria biomass initial concentration was maintained at 3:1 ratio. The increase in the initial concentration of the biomass in the 2nd batch favoured biomass growth, doubling biomass productivity, compared to the 1st batch. In both batches, N-NH4 was completely removed from the leachate. In the 2nd batch, the nitrate, COD and phenol removal efficiencies were above 90%. The relative toxicity reduced from 57.32 to 1.12% at the end of 2nd batch. The fatty acids content (C16-18) varied from 85.47 to 87.65% for the 1st batch and 86.72 to 87.69% for the 2nd batch. The crude glycerol content varied from 34.54 to 42.36% for the 1st batch and 33.64 to 39.55% for the 2nd batch. The coexistence of microalgae and bacteria played an important role in leachate treatment and biomass production for biorefinery purposes.

Food processing wastewater purification by microalgae cultivation associated with high value-added compounds production — A review

Abstract Microalgae have been considered as an efficient microorganism for wastewater treatment with simultaneously bioenergy and high value-added compounds production. However, the high energy cost associated with complicated biorefinery (e.g. microalgae cultivation, harvesting, drying, extraction, conversion, and purification) is a critical challenge that inhibits its large-scale application. Among different nutrition (e.g. carbon, nitrogen and phosphorous) sources, food processing wastewater is a relative safe and suitable one for microalgae cultivation due to its high organic content and low toxicity. In this review, the characteristic of different food wastewater is summarized and compared. The potential routes of value-added products (i.e. biofuel, pigment, polysaccharide, and amino acid) production along with wastewater purification are introduced. The existing challenges (e.g. biorefinery cost, efficiency and mechanism) of microalgal-based wastewater treatment are also discussed. The prospective of microalgae-based food processing wastewater treatment strategies (such as microalgae-bacteria consortium, poly-generation of bioenergy and value-added products) is forecasted. It can be observed that food wastewater treatment by microalgae could be a promising strategy to commercially realize waste source reduce, conversion and reutilization.

Wastewater-leachate treatment by microalgae: Biomass, carbohydrate and lipid production

Increases in wastewater discharges and the generation of municipal solid wastes have resulted in deleterious effects on the environment, causing eutrophication and pollution of water bodies. It is therefore necessary to investigate sustainable bioremediation alternatives. Wastewater treatment using consortia of microalgae-bacteria is an attractive alternative because it allows the removal and recycling of nutrients, with the additional advantage of biomass production and its subsequent conversion into valuable by-products. The present study aims to integrate wastewater and landfill leachate treatment with the production of microalgal biomass, considering not only its valorization in terms of lipid and carbohydrate content but also the effect of nutrient limitation on biomass formation. The effect of treating a mixture of raw wastewater with different leachate ratios (0%, 7%, 10% and 15%) was investigated using a microalgae-bacteria consortium. Two microalgae (Desmodesmus spp. and Scenedesmus obliquus) were used. Nutrient removal, biomass concentration, carbohydrate, lipid and Fatty Acid Methyl Ester (FAMEs) content and morphological changes were evaluated. Removals of 82% of NH4+ and 43% of orthophosphate from a wastewater-leachate mixture (containing 167 mg/L NH4+ and 23 mg/L PO43-) were achieved. The highest final yield was obtained using Desmodesmus spp. (1.95 ± 0.3 g/L). The microalgae were observed to accumulate high lipid (20%) and carbohydrate (41%) contents under nutrient limiting conditions. The concentration of Polyunsaturated Fatty Acids (PUFAs) also increased. Morphological changes including the disintegration of coenobia were observed. By using a mixture of wastewater-leachate it is possible to remove nutrients, since microalgae tolerate high ammonia concentrations, and simultaneously increase the algal biomass concentration containing precursors to allow biofuel production.

Microalgae–bacteria consortium treatment technology for municipal wastewater management

The discharge of inadequately treated municipal wastewater in the developing countries is the major cause of environmental pollution in urban areas. However, the effort was made to minimize this burden using conventional wastewater treatment methods that require high capital and operational costs and are not affordable. Researchers are still looking for the cost-effective, efficient and environmentally compatible wastewater treatment technologies. Hence, this study aimed to investigate the potential of native microalgae–bacteria consortia for the removal of nutrient and organic pollutants from primary-treated municipal wastewater. Microalgae–bacteria treatment system was established by combining pre-cultured native algae consortia dominated by Chlorella sp., Chlamydomonas sp. and Scenedesmus sp. of the class Chlorophyceae with naturally existing municipal wastewater bacteria. Microalgae–bacteria culture acclimatization was performed and the actual experiment was carried out at 18% culture to wastewater by volume in photobioreactor at a light intensity of 120 μE/m2s. The maximum removal of TKN 69%, TP 59%, PO43−_ P 73%, COD 84% and BOD5 85% was observed in the combined treatment system, whereas for bacteria stand-alone treatment system, the maximum removal of TKN 31%, TP 56%, PO43−_ P 50%, COD 44% and BOD5 52% was recorded. Statistically significant differences were observed for the removal of NH3–N, TKN and PO43−_ P at p < 0.05 but statistically insignificant differences were observed for TP, COD and BOD5 in the combined treatment system. The study results suggest that the native microalgae consortia identified in the local environment can effectively reduce organic and nutrient pollutants from the primary-treated municipal wastewater. Generally, the performance evaluation of combined microalgae–bacteria treatment technology was efficient in municipal wastewater management and promising to scale up at industrial level.

Production of microbial biomass feedstock via co-cultivation of microalgae-bacteria consortium coupled with effective wastewater treatment: A sustainable approach

A sustainable process was demonstrated towards production of biomass feedstock coupled with wastewater treatment. Sustainability was endeavored to be achieved via symbiotic growth of microalgae and bacteria coupled with utilization of wastewater as cheap source of nutrient and water. The best microalgae-bacteria consortium comprised of two microalgae Chlorella sorokiniana strain DBWC2 &Chlorella sp. strain DBWC7 and two bacteria Klebsiella pneumoniae strain ORWB1 &Acinetobacter calcoaceticus strain ORWB3. When the consortium was characterized on artificial wastewater and raw dairy wastewater, a significant improvement in the microalgal growth, total biomass titer, chemical oxygen demand (COD), and nitrate removal efficiency was observed as compared to microalgae alone. Total biomass titer, nitrate removal, COD removal efficiency was found to be 2.84 g L−1, 93.59%, 82.27% and 2.87 g L−1, 84.69%, 90.49% in artificial wastewater and raw dairy wastewater respectively. The selected microalgae-bacteria consortium may be a potential platform towards sustainable production of microbial biomass using wastewater.

FACTORS THAT AFFECT THE REMOVAL OF NITROGEN AND PHOSPHOROUS FROM PIGGERY WASTEWATER USING MICROALGAE –BACTERIA CONSORTIUM

Currently, most piggery farms in Viet Nam use biogas tank as a primary wastewater treatment system. However, even after the anaerobic treatment process, the concentration of nutrients was still high and exceeded the national effluent standard. If the wastewater was directly discharged into the water bodies, it was certainly hazardous to the environment and causes eutrophication. To remove the residual nutrients, several processes have been used, mostly chemical processes. The disadvantages of those chemical processes are high cost and the increase in amount of sludge. In this study, the biological method using microalgae-bacteria consortium was applied for the removal of nitrogen and phosphorous from wastewater from biogas treatment process. This study focused on factors which affect nitrogen and phosphorous removal efficiency in a batch reactor using microalgae-bacterial consortium. Studying on Chlorella sp A8. Activated sludge co-cultivation at different ratio (Chl/AS) gave good results in hydraulic retention time of 20 to 24 hours when C/N in wastewater was 4/1(m/m). In the fully mixing condition, DO range from 0.3 - 0.5 mg O2/L, the highest removal efficiencies of COD was 71 - 76 %; NH4+-N was 40 - 47 % and PO43--P was 64 - 77 % at Chl /As was 1.5:1, 2.5:1 and 1:1( g/g).

Activity assessment of microalgal-bacterial consortia based on respirometric tests.

Respirometric techniques are useful tools to evaluate bacterial activities in activated sludge processes due to their fast execution and the possibility to obtain several kinetic parameters from a single test. Using such techniques in microalgae-bacteria consortia treating wastewater could allow a better understanding of mutual interactions between the microbial populations as a function of environmental parameters. This work aims at developing and testing a novel experimental respirometric protocol to determine oxygen uptake rates and oxygen production rates by a microalgae-bacteria consortium. The defined protocol is characterized by alternating light/dark regimes and by dosing substrates/inhibitors to selectively activate/inactivate microalgal and bacterial metabolisms. The protocol was then applied on microalgal and bacterial consortia, which were grown on the liquid fraction of black water from biogas plants fed on agricultural and municipal waste sludge. Results elucidate the presence and activity of microalgae and nitrifying bacteria in the tested systems, suggesting that the respirometric tests could be included into monitoring procedures of photobioreactors/algal ponds.

Full-scale photobioreactor for biotreatment of olive washing water: Structure and diversity of the microalgae-bacteria consortium

The performance of a full-scale photobioreactor (PBR) for the treatment of olive washing water (OWW) was evaluated under different HRTs (5–2days). The system was able to treat up to 3926L OWWday−1, and consisted of an activated-carbon pretreatment column and a tubular PBR unit (80 tubes, 98.17L volume, 2-m height, 0.25m diameter). PBR was an effective and environmentally friendly method for the removal of phenols, COD, BOD5, turbidity and color from OWW (average efficiencies 94.84±0.55%, 85.86±1.24%, 99.12±0.17%, 95.86±0.98% and 87.24±0.91%, respectively). The diversity of total bacteria and microalgae in the PBR was analyzed using Illumina-sequencing, evaluating the efficiency of two DNA extraction methods. A stable microalgae-bacteria consortium was developed throughout the whole experimentation period, regardless of changes in HRT, temperature or solar radiation. MDS analyses revealed that the interplay between green algae (Sphaeropleales), cyanobacteria (Hapalosiphon) and Proteobacteria (Rhodopseudomonas, Azotobacter) played important roles in OWW bioremediation.

Nitrogen and phosphate removal from wastewater with a mixed microalgae and bacteria culture

Microalgae are able to convert nutrients (nitrogen and phosphorus) from wastewater into biomass and bio-products, thus improving the sustainability of wastewater treatment. In High Rate Algal Ponds (HRAP), biomass productivity and water treatment efficiency are highly dependent on environmental parameters such as temperature, light intensity and photoperiod. The influence of temperature and photoperiod on biomass productivity and the removal of dissolved nitrogen and phosphorus from municipal wastewater by a native microalgae-bacteria consortium was assessed in batch cultures in view of the development of an HRAP at a larger scale. Temperature affected the growth rate and microalgae biomass production as well as ammonium and phosphate removal rates. At the temperatures 15 and 25°C, the average total nitrogen and phosphorus removal extents ranged from 72 to 83% and 100% respectively. Additionally 33.0±0.1% of the total nitrogen was eliminated by stripping at 25°C, and 50±2% was assimilated by the microorganisms under all conditions tested.

Characterization of microalgae-bacteria consortium cultured in landfill leachate for carbon fixation and lipid production

The characteristics of cultivating high-density microalgae-bacteria consortium with landfill leachate was tested in this study. Landfill leachate was collected from Laogang landfill operated for over 10 years in Shanghai, China. The maximum biomass concentration of 1.58g L(-1) and chlorophyll a level of 22mg L(-1) were obtained in 10% leachate spike ratio. Meanwhile, up to 90% of the total nitrogen in landfill leachate was removed in culture with 10% leachate spike ratio with a total nitrogen concentration of 221.6mg L(-1). The fluorescence peak of humic-like organic matters red shifted to longer wavelengths by the end of culture, indicating that microalgae-bacteria consortium was effective for treating landfill leachate contaminants. Furthermore, with the leachate spike ratio of 10%, the maximum lipid productivity and carbon fixation were 24.1 and 65.8mg L(-1)d(-1), respectively. Results of this research provide valuable information for optimizing microalgae culture in landfill leachate.

Treatment of agro-industrial wastewater using microalgae–bacteria consortium combined with anaerobic digestion of the produced biomass

Two combined processes were studied in order to produce second generation biofuels: microalgae biomass production and its further use to produce biogas. Two 5L photobioreactors for treating wastewater from a potato processing industry (from now on RPP) and from a treated liquid fraction of pig manure (from now on RTE) were inoculated with Chlorella sorokiniana and aerobic bacteria at 24±2.7°C and 6000lux for 12h per day of light supply. The maximum biomass growth was obtained for RTE wastewater, with 26.30mg dry weightL−1d−1. Regarding macromolecular composition of collected biomass, lipid concentration reached 30.20% in RPP and 4.30% in RTE. Anaerobic digestion results showed that methane yield was highly influenced by substrate/inoculum ratio and by lipids concentration of the biomass, with a maximum methane yield of 518mL CH4 g COD−1added using biomass with a lipid content of 30% and a substrate/inoculum ratio of 0.5.

Nitrogen transformations under different conditions in open ponds by means of microalgae–bacteria consortium treating pig slurry

Four open ponds inoculated with microalgae-bacteria consortium treating different swine slurries (fresh and anaerobically digested) were evaluated in terms of nitrogen transformation under optimal and real conditions of temperature and illumination. Ammonium complete depletion was not achieved. Ponds operated under real conditions presented lower ammonium removal. Elimination capacities were around 26 mg N/Ld and were subsequently increased with increasing inlet ammonium loading rate. Different nitrogen transformation was observed depending on substrate source. When anaerobically digested slurry was fed to the ponds, nitrification followed by biomass uptake and denitrification were the main nitrogen transformation taking place depending on inlet ammonium loading rate and operational conditions. Ponds fed with fresh slurry exhibited denitrification as the main nitrogen removal mechanism for the pond operated under real conditions while under optimal conditions stripping, denitrification and biomass uptake contributed similarly. Therefore, this study confirmed that the so-claimed nitrogen recovery by microalgae biomass is frequently overestimated.