Culture of Microalgae <Emphasis Type="Italic">Chlamydomonas reinhardtii</Emphasis> in Wastewater for Biomass Feedstock Production

The objective of this research was to develop large-scale technologies to produce oil-rich algal biomass from wastewater. The experiments were conducted using Erlenmeyer flasks and biocoil photobioreactor. Chlamydomonas reinhardtii was grown in artificial media and wastewaters taken from three different stages of the treatment process, namely, influent, effluent, and centrate. Each of wastewaters contained different levels of nutrients. The specific growth rate of C. reinhardtii in different cultures was monitored over a period of 10 days. The biomass yield of microalgae and associated nitrogen and phosphorous removal were evaluated. Effects of CO₂ and pH on the growth were also studied. The level of nutrients greatly influenced algae growth. High levels of nutrients seem to inhibit algae growth in the beginning, but provided sustained growth to a high degree. The studies have shown that the optimal pH for C. reinhardtii is in the range of 7.5. An injection of air and a moderate amount of CO₂ promoted algae growth. However, too much CO₂ inhibited algae growth due to a significant decrease in pH. The experimental results showed that algal dry biomass yield reached a maximum of 2.0 g L⁻¹ day⁻¹ in the biocoil. The oil content of microalgae of C. reinhardtii was 25.25% (w/w) in dry biomass weight. In the biocoil, 55.8 mg nitrogen and 17.4 mg phosphorus per liter per day were effectively removed from the centrate wastewater. Ferric chloride was found to be an effective flocculent that helps the algae settle for easy harvest and separation from the culture media.     

Cultivating <Emphasis Type="BoldItalic">Chlorella</Emphasis> sp. in a Pilot-Scale Photobioreactor Using Centrate Wastewater for Microalgae Biomass Production and Wastewater Nutrient Removal

This study is concerned with a novel mass microalgae production system which, for the first time, uses “centrate”, a concentrated wastewater stream, to produce microalgal biomass for energy production. Centrate contains a high level of nutrients that support algal growth. The objective of this study was to investigate the growth characteristics of a locally isolated microalgae strain Chlorella sp. in centrate and its ability to remove nutrients from centrate. A pilot-scale photobioreactor (PBR) was constructed at a local wastewater treatment plant. The system was tested under different harvesting rates and exogenous CO₂ levels with the local strain of Chlorella sp. Under low light conditions (25 μmol·m^-2s^-1) the system can produce 34.6 and 17.7 g·m^-2day^-1 biomass in terms of total suspended solids and volatile suspended solids, respectively. At a one fourth harvesting rate, reduction of chemical oxygen demand, total Kjeldahl nitrogen, and soluble total phosphorus were 70%, 61%, and 61%, respectively. The addition of CO₂ to the system did not exhibit a positive effect on biomass productivity or nutrient removal in centrate which is an organic carbon rich medium. The unique PBR system is highly scalable and provides a great opportunity for biomass production coupled with wastewater treatment.     

The Utilization of Post-chlorinated Municipal Domestic Wastewater for Biomass and Lipid Production by <Emphasis Type="Italic">Chlorella</Emphasis> spp. Under Batch Conditions

South Africa has a rich microalgal biodiversity which has the potential to be used for renewable bio-fuel production in the region. Bioprospecting for oleaginous microalgae in KwaZulu Natal Province, South Africa, resulted in the establishment of a microalgal culture collection system for alternative energy research in the country. A potential hyper-lipid-producing Chlorella spp. strain was isolated, purified, and cultured in supplemented post-chlorinated wastewater for biomass and lipid production at the laboratory scale under batch mode. The microalgal strain was cultivated in different strengths of BG-11 media supplemented with wastewater from a local municipal domestic wastewater treatment plant. The Chlorella spp. was grown using ambient dissolved carbon dioxide in shake flasks under photosynthetically active radiation (±120 μmolm⁻²s⁻¹). Microalgal biomass and lipid productivity were monitored at 24-h intervals in the batch mode. The microalgal biomass was analyzed by direct light microscopy and indirectly by spectrophotometry at 600 nm, and the lipids were extracted and quantified. The growth rate of the Chlorella spp. was enhanced in post-chlorinated wastewater supplemented with 5 mM NaNO₃ with maximal biomass productivity. A dramatic increase in lipid yield was achieved with the post-chlorinated wastewater supplemented with 25 mM NaNO₃. Low dosages of free chlorine were found to enhance microalgal growth. These findings serve as a basis for further scale-up trials using municipal wastewater as a medium for microalgal biomass and lipid production.     

Bioremediation strategies of palm oil mill effluent and landfill leachate using microalgae cultivation: An approach contributing towards environmental sustainability

Palm oil mill effluent (POME) is defined as the wastewater that contains high concentrations of organics, nutrients and oil and grease generated from the production process of palm oil. Therefore, proper discharge and management of POME is important to avoid deleterious impact on the environment. In fact, solid waste generation is a precursor for its disposal issues as most of the solid waste generated in developing nations is dumped into landfills. This has led to the threat posed by the generation of landfill leachate (LL). LL is a complex dark coloured liquid consisting of organic matter, inorganic substances, trace elements and xenobiotics. Hence, it is essential to effectively treat the landfill leachate before discharging it to avoid contamination of soil, surface & groundwater bodies. Conventional treatment methods comprises of physical, biological and chemical treatment, however, microalgal-based treatment could also be incorporated. Furthermore, with the benefits offered by microalgae in valorisation, the application of microalgae in POME and leachate treatment as well as biofuel production, is considerably viable. This paper provides an acumen of the microalgae-based treatment of POME and LL, integrated with biofuel production in a systematic and critical manner. The pollutants assimilation from wastewater and CO₂ biosequestration are discussed for environmental protection. Cultivation systems for wastewater treatment with simultaneous biomass production and its valorisation, are summarised. The study aims to provide insight to industrial stakeholders on economically viable and environmentally sustainable treatment of wastewaters using microalgae, and eventually contributing to the circular bioeconomy and environmental sustainability.     

Isolation of Industrial Important Bioactive Compounds from Microalgae

Microalgae are known as a rich source of bioactive compounds which exhibit different biological activities. Increased demand for sustainable biomass for production of important bioactive components with various potential especially therapeutic applications has resulted in noticeable interest in algae. Utilisation of microalgae in multiple scopes has been growing in various industries ranging from harnessing renewable energy to exploitation of high-value products. The focuses of this review are on production and the use of value-added components obtained from microalgae with current and potential application in the pharmaceutical, nutraceutical, cosmeceutical, energy and agri-food industries, as well as for bioremediation. Moreover, this work discusses the advantage, potential new beneficial strains, applications, limitations, research gaps and future prospect of microalgae in industry.     

Mixotrophic Cultivation of Microalgae for Biodiesel Production: Status and Prospects

Biodiesel from microalgae provides a promising alternative for biofuel production. Microalgae can be produced under three major cultivation modes, namely photoautotrophic cultivation, heterotrophic cultivation, and mixotrophic cultivation. Potentials and practices of biodiesel production from microalgae have been demonstrated mostly focusing on photoautotrophic cultivation; mixotrophic cultivation of microalgae for biodiesel production has rarely been reviewed. This paper summarizes the mechanisms and virtues of mixotrophic microalgae cultivation through comparison with other major cultivation modes. Influencing factors of microalgal biodiesel production under mixotrophic cultivation are presented, development of combining microalgal biodiesel production with wastewater treatment is especially reviewed, and bottlenecks and strategies for future commercial production are also identified.     

Cultivation of Chlorella protothecoides with Urban Wastewater in Continuous Photobioreactor: Biomass Productivity and Nutrient Removal

The capability to grow microalgae in nonsterilized wastewater is essential for an application of this technology in an actual industrial process. Batch experiments were carried out with the species in nonsterilized urban wastewater from local treatment plants to measure both the algal growth and the nutrient consumption. Chlorella protothecoides showed a high specific growth rate (about 1 day^?1), and no effects of bacterial contamination were observed. Then, this microalgae was grown in a continuous photobioreactor with CO₂–air aeration in order to verify the feasibility of an integrated process of the removal of nutrient from real wastewaters. Different residence times were tested, and biomass productivity and nutrients removal were measured. A maximum of microalgae productivity was found at around 0.8 day of residence time in agreement with theoretical expectation in the case of light-limited cultures. In addition, N-NH₄ and P-PO₄ removal rates were determined in order to model the kinetic of nutrients uptake. Results from batch and continuous experiments were used to propose an integrated process scheme of wastewater treatment at industrial scale including a section with C. protothecoides.     

Growth of Chlorella vulgaris on Sugarcane Vinasse: The Effect of Anaerobic Digestion Pretreatment

Microalgae farming has been identified as the most eco-sustainable solution for producing biodiesel. However, the operation of full-scale plants is still limited by costs and the utilization of industrial and/or domestic wastes can significantly improve economic profits. Several waste effluents are valuable sources of nutrients for the cultivation of microalgae. Ethanol production from sugarcane, for instance, generates significant amounts of organically rich effluent, the vinasse. After anaerobic digestion treatment, nutrient remaining in such an effluent can be used to grow microalgae. This research aimed to testing the potential of the anaerobic treated vinasse as an alternative source of nutrients for culturing microalgae with the goal of supplying the biodiesel industrial chain with algal biomass and oil. The anaerobic process treating vinasse reached a steady state at about 17 batch cycles of 24 h producing about 0.116 m³CH₄ kgCOD_vinasse ^?1. The highest productivity of Chlorella vulgaris biomass (70 mg l^?1 day^?1) was observed when using medium prepared with the anaerobic digester effluent. Lipid productivity varied from 0.5 to 17 mg l^?1 day^?1. Thus, the results show that it is possible to integrate the culturing of microalgae with the sugarcane industry by means of anaerobic digestion of the vinasse. There is also the advantageous possibility of using by-products of the anaerobic digestion such as methane and CO₂ for sustaining the system with energy and carbon source, respectively.     

Cultivation of Chlorella vulgaris in Dairy Wastewater Pretreated by UV Irradiation and Sodium Hypochlorite

There is potential in the utilization of microalgae for the purification of wastewater as well as recycling the resource in the wastewater to produce biodiesel. The large-scale cultivation of microalgae requires pretreatment of the wastewater to eliminate bacteria and protozoa. This procedure is costly and complex. In this study, two methods of pretreatment, UV irradiation, and sodium hypochlorite (NaClO), in various doses and concentrations, were tested in the dairy wastewater. Combining the efficiency of biodiesel production, we proposed to treat the dairy wastewater with NaClO in the concentration of 30 ppm. In this condition, The highest biomass productivity and lipid productivity of Chlorella vulgaris reached 0.450 g L^?1 day^?1 and 51 mg L^?1 day^?1 after a 4-day cultivation in the dairy wastewater, respectively.     

Photoautotrophic and Mixotrophic Cultivation of Polyhydroxyalkanoate-Accumulating Microalgae Consortia Selected under Nitrogen and Phosphate Limitation

Microalgae consortia were photoautotrophically cultivated in sequencing batch photobioreactors (SBPRs) with an alteration of the normal growth and starvation (nutrient limitation) phases to select consortia capable of polyhydroxyalkanoate (PHA) accumulation. At the steady state of SBPR operation, the obtained microalgae consortia, selected under nitrogen and phosphate limitation, accumulated up to 11.38% and 10.24% of PHA in their biomass, which was identified as poly(3-hydroxybutyrate) (P3HB). Photoautotrophic and mixotrophic batch cultivation of the selected microalgae consortia was conducted to investigate the potential of biomass and PHA production. Sugar source supplementation enhanced the biomass and PHA production, with the highest PHA contents of 10.94 and 6.2%, and cumulative PHA productions of 100 and 130 mg/L, with this being achieved with sugarcane juice under nitrogen and phosphate limitation, respectively. The analysis of other macromolecules during batch cultivation indicated a high content of carbohydrates and lipids under nitrogen limitation, while higher protein contents were detected under phosphate limitation. These results recommended the selected microalgae consortia as potential tools for PHA and bioresource production. The mixed-culture non-sterile cultivation system developed in this study provides valuable information for large-scale microalgal PHA production process development following the biorefinery concept.     

Lipid Production by Culturing Oleaginous Yeast and Algae with Food Waste and Municipal Wastewater in an Integrated Process

Food waste and municipal wastewater are promising feedstocks for microbial lipid biofuel production, and corresponding production process is to be developed. In this study, different oleaginous yeast strains were tested to grow in hydrolyzed food waste, and growths of Cryptococcus curvatus, Yarrowia lipolytica, and Rhodotorula glutinis in this condition were at same level as in glucose culture as control. These strains were further tested to grow in municipal primary wastewater. C. curvatus and R. glutinis had higher production than Y. lipolytica in media made from primary wastewater, both with and without glucose supplemented. Finally, a process was tested to grow C. curvatus and R. glutinis in media made from food waste and municipal wastewater, and the effluents from these processes were further treated with yeast culture and phototrophic algae culture; 1.1 g/L C. curvatus and 1.5 g/L R. glutinis biomass were further produced in second-step yeast cultures, as well as 1.53 and 0.58 g/L Chlorella sorokiniana biomass in phototrophic cultures. The residual nitrogen concentrations in final effluents were 33 mg/L and 34 mg/L, respectively, and the residual phosphorus concentrations were 1.5 and 0.6 mg/L, respectively. The lipid contents in the produced biomass were from 18.7% to 28.6%.     

A new strategy for lipid production by mix cultivation of Spirulina platensis and Rhodotorula glutinis

Mix cultivation of microalgae (Spirulina platensis) and yeast (Rhodotorula glutinis) for lipid production was studied. Mixing cultivation of the two microorganisms significantly increased the accumulation of total biomass and total lipid yield. Dissolved oxygen and medium components in the mixed fermentation medium were analyzed. Mix cultivation in monosodium glutamate wastewater was further studied. Result indicated 1,600 mg/L of biomass was obtained and 73% of COD were removed.     

The Utilization of Algae and Seaweed Biomass for Bioremediation of Heavy Metal-Contaminated Wastewater

The presence of heavy metals in water bodies is linked to the increasing number of industries and populations. This has serious consequences for the quality of human health and the environment. In accordance with this issue, water and wastewater treatment technologies including ion exchange, chemical extraction, and hydrolysis should be conducted as a first water purification stage. However, the sequestration of these toxic substances tends to be expensive, especially for large scale treatment methods that require tedious control and have limited efficiency. Therefore, adsorption methods using adsorbents derived from biomass represent a promising alternative due to their great efficiency and abundance. Algal and seaweed biomass has appeared as a sustainable solution for environmentally friendly adsorbent production. This review further discusses recent developments in the use of algal and seaweed biomass as potential sorbent for heavy metal bioremediation. In addition, relevant aspects like metal toxicity, adsorption mechanism, and parameters affecting the completion of adsorption process are also highlighted. Overall, the critical conclusion drawn is that algae and seaweed biomass can be used to sustainably eliminate heavy metals from wastewater.     

Multistage defense response of microalgae exposed to pharmaceuticals in wastewater

Recently, the use of microalgae for bioremediation of pharmaceuticals (PhAs) has attracted increasing interest. However, most studies focused more on microalgae removal performance, its defensive response to the PhAs during wastewater treatment remains unexplored. Herein, microalgal three defensive systems have been investigated in synthetic wastewater, with six PhAs as the typical drug. Results show that PhAs could bind to EPS, and this action in turn could help to alleviate the direct toxicity of PhAs to microalgae. Subsequently, the physiological analyses revealed the increase of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities, potentially reducing the oxidative stress induced by PhAs. Furthermore, the enzyme activities of cytochrome P450 (CYP450) and glutathione-S-transferase (GST) were significantly upregulated after exposure to SMX, CIP and BPA, followed by a significant decrease in biodegradation rates after the addition of CYP450 inhibitors, suggesting that the biotransformation and detoxification of PhAs occurred. Meanwhile, molecular docking further revealed that CYP450 could bind with PhAs via hydrogen bond and hydrophobic interaction, which proved their abilities to be metabolized and form transformation products in microalgae. These findings provide an advancing understanding of microalgae technologies to improve the treatment of wastewater contaminated with PhAs.     

Low-Cost Production of Green Microalga Botryococcus braunii Biomass with High Lipid Content Through Mixotrophic and Photoautotrophic Cultivation

Botryococcus braunii is a microalga that is regarded as a potential source of renewable fuel because of its ability to produce large amounts of lipid that can be converted into biodiesel. Agro-industrial by-products and wastes are of great interest as cultivation medium for microorganisms because of their low cost, renewable nature, and abundance. In this study, two strategies for low-cost production of B. braunii biomass with high lipid content were performed: (i) the mixotrophic cultivation using molasses, a cheap by-product from the sugar cane plant as a carbon source, and (ii) the photoautotrophic cultivation using nitrate-rich wastewater supplemented with CO₂ as a carbon source. The mixotrophic cultivation added with 15 g L^?1 molasses produced a high amount of biomass of 3.05 g L^?1 with a high lipid content of 36.9 %. The photoautotrophic cultivation in nitrate-rich wastewater supplemented with 2.0 % CO₂ produced a biomass of 2.26 g L^?1 and a lipid content of 30.3 %. The benefits of this photoautotrophic cultivation are that this cultivation would help to reduce accumulation of atmospheric carbon dioxide and more than 90 % of the nitrate could be removed from the wastewater. When this cultivation was scaled up in a stirred tank photobioreactor and run with semi-continuous cultivation regime, the highest microalgal biomass of 5.16 g L^?1 with a comparable lipid content of 32.2 % was achieved. These two strategies could be promising ways for producing cheap lipid-rich microalgal biomass that can be used as biofuel feedstocks and animal feeds.     

废水生物脱氮工艺中N2O排放数学模型研究进展

N_2O是一种重要的温室气体,而污水生物脱氮处理过程是N_2O的潜在产生源之一。随着污水处理量和处理程度的不断提高,N_2O的排放量也将不断增大。建立N_2O排放数学模型对污水生物脱氮系统中N_2O生成机制的深入研究和污水处理行业N_2O削减工艺技术的开发具有重大的理论及实践意义。本文归纳了生物脱氮工艺的原理,系统阐述了生物脱氮工艺中N_2O的生成机理和排放数学模型的类型、建立方法及应用情况。在此基础上,对生物脱氮工艺中N_2O排放数学模型的研究现状和研究方向进行了总结和展望,以期为N_2O排放数学模型的完善、N_2O排放量的削减、污水生物脱氮工艺的优化及污水处理行业的可持续发展提供理论基础和科学依据。     

Co-Culture of Microalgae, Cyanobacteria, and Macromycetes for Exopolysaccharides Production: Process Preliminary Optimization and Partial Characterization

In this study, the biomass and exopolysaccharides (EPS) production in co-cultures of microalgae/cyanobacteria and macromycetes was evaluated as a technology for producing new polysaccharides for medical and/or industrial application. Based on biomass and EPS productivity of monocultures, two algae and two fungi were selected and cultured in different co-culture arrangements. The hydrosoluble EPS fractions from mono- and co-cultures were characterized by 13C NMR spectroscopy and gas chromatography coupled to mass spectrometry and compared. It was found that co-cultures resulted in the production of an EPS different from those produced by monocultures, showing fungal predominance with microalgal/cyanobacterial traces. Co-cultures conditions were screened (temperature, agitation speed, fungal and microalgae inoculation rate, initial pH, illumination rate, and glucose concentration) in order to achieve maximum biomass and EPS production, resulting in an increase of 33 and 61% in exopolysaccharides and biomass productions, respectively (patent pending).     

Is Genetic Engineering a Route to Enhance Microalgae-Mediated Bioremediation of Heavy Metal-Containing Effluents?

Contamination of the biosphere by heavy metals has been rising, due to accelerated anthropogenic activities, and is nowadays, a matter of serious global concern. Removal of such inorganic pollutants from aquatic environments via biological processes has earned great popularity, for its cost-effectiveness and high efficiency, compared to conventional physicochemical methods. Among candidate organisms, microalgae offer several competitive advantages; phycoremediation has even been claimed as the next generation of wastewater treatment technologies. Furthermore, integration of microalgae-mediated wastewater treatment and bioenergy production adds favorably to the economic feasibility of the former process—with energy security coming along with environmental sustainability. However, poor biomass productivity under abiotic stress conditions has hindered the large-scale deployment of microalgae. Recent advances encompassing molecular tools for genome editing, together with the advent of multiomics technologies and computational approaches, have permitted the design of tailor-made microalgal cell factories, which encompass multiple beneficial traits, while circumventing those associated with the bioaccumulation of unfavorable chemicals. Previous studies unfolded several routes through which genetic engineering-mediated improvements appear feasible (encompassing sequestration/uptake capacity and specificity for heavy metals); they can be categorized as metal transportation, chelation, or biotransformation, with regulation of metal- and oxidative stress response, as well as cell surface engineering playing a crucial role therein. This review covers the state-of-the-art metal stress mitigation mechanisms prevalent in microalgae, and discusses putative and tested metabolic engineering approaches, aimed at further improvement of those biological processes. Finally, current research gaps and future prospects arising from use of transgenic microalgae for heavy metal phycoremediation are reviewed.     

Enhanced Lipid Production by Co-cultivation and Co-encapsulation of Oleaginous Yeast Trichosporonoides spathulata with Microalgae in Alginate Gel Beads

This study attempted to enhance biomass and lipid productivity of an oleaginous yeast Trichosporonoides spathulata by co-culturing with microalgae Chlorella spp., optimizing culture conditions, and encapsulating them in alginate gel beads. The co-culture of the yeast with microalgae Chlorella vulgaris var. vulgaris TISTR 8261 most enhanced overall biomass and lipid productivity by 1.6-fold of the yeast pure culture at 48 h and by 1.1-fold at 72 h. After optimization and scale-up in a bioreactor, this co-culture produced the highest biomass of 12.2 g/L with a high lipid content of 47 %. The dissolved oxygen monitoring system in the bioreactor showed that the microalgae worked well as an oxygen supplier to the yeast. This study also showed that the co-encapsulated yeast and microalgae could grow and produce lipid as same as their free cells did. Therefore, it is possible to apply this encapsulation technique for lipid production and simplification of downstream harvesting process. This co-culture system also produced the lipid with high content of saturated fatty acids, indicating its potential use as biodiesel feedstock with high oxidative stability.     

Pretreatment of swine wastewater using anaerobic filter

Efforts were made to assess the efficiency of an anaerobic filter packed with porous floating ceramic media and to identify the optimum operational condition of anaerobic filter as a pretreatment of swine wastewater for the subsequent biological removal of nitrogen and phosphorus. A stepwise decrease in hydraulic retention time (HRT) and an increase in organic loading rate (OLR) were utilized in an anaerobic filter reactor at mesophilic temperature (35°C). The optimum operating condition of the anaerobic filter was found to be at an HRT of 1 d. A soluble chemical oxygen demand (COD) removal efficiency of 62% and a total suspended solids removal efficiency of 39% at an HRT of 1 d were achieved with an OLR of 16.0 kg total COD/(m³·d), respectively. The maximum methane production rate approached 1.70 vol of biogas produced per volume of reactor per day at an HRT of 1 d. It was likely that the effluent COD/total Kjeldahl nitrogen ratio, of 22, the COD/total phosphorous ratio of 47, and the high effluent alkalinity >2500 mg/L as CaCO₃ of the anaerobic filter operated at an HRT of 1 d was adequate for the subsequent biological removal of nitrogen and phosphorus.