Weizheng Zhou

Cultivation of Chlorella zofingiensis in bench-scale outdoor ponds by regulation of pH using dairy wastewater in winter, South China

Cultivation of Chlorella zofingiensis and nutrients removal in dairy wastewater were investigated in bench-scale outdoor ponds in winter, South China. The impacts of the two types of pH regulations, 5 ≈ 6% CO(2) and acetic acid (HAc) on this process were studied. After 6 days cultivation, the removal rates of total nitrogen (TN) and orthophosphate (PO(4)(3-)) using CO(2) regulation were better than those using HAc. The removal rates of PO(4)(3-) and TN were 97.5% and 51.7%, respectively using CO(2) regulation; 79.6% (TN) and 42.0% (PO(4)(3-)) were obtained using HAc regulation. Higher biomass, protein, sugar content, and stable pH control were found using CO(2) regulation. However, significantly higher lipid content (31.8%) was observed using HAc regulation. The dominant differences of fatty acids were the content of C18:1 and C18:3. The growth characteristics and environmental conditions especially during the typical logarithmic phase were also analyzed.

Microalgae pretreatment with liquid hot water to enhance enzymatic hydrolysis efficiency

Nowadays, microalgae are being considered as promising raw material for bioethanol production. In this work, three process variables during liquid hot water (LHW) pretreatment prior to enzymatic hydrolysis by response surface methodology on Scenedesmus sp. WZKMT were investigated to enhance glucose recovery. Results indicated that the order of significance for three parameters was temperature>solid-to-liquid ratio>time. The optimal condition was 1:13 (w/v), 147°C and 40min. The concentration and recovery of glucose under this condition were 14.223g·L(-1) and 89.32%, respectively, which were up to 5-fold higher than the samples without LHW pretreatment. In addition, the surface morphologies of microalgae cells before and after LHW pretreatment were also verified using scanning electron microscopy (SEM). LHW pretreatment can greatly enhance the enzymatic efficiency, and can be regarded as an ideal pretreatment method for glucose recovery from microalgae.

Biomass measurement of microalgae cultivated under photoautotrophic conditions for biofuels.

Linear regression equations for dry cell weight versus optical density (OD680) for 16 strains of microalgae were developed. Carbon contents of the green algae and diatoms were between 40.56–49.62% and 25.74–41.7%, respectively. The ventilation (especially the addition of CO2) and high light intensity significantly improved the microalgae growth rates and biomass amounts. Dry cell weight of eight strains up to 2.119–3.452 g·L−1 were achieved when ambient air containing 5% CO2 (v/v) and high light intensity were applied. The microalgal lipids contained fatty acid methyl esters mainly with C16:0, C18:1, C18:2, and C18:3, which were considered suitable for producing biodiesel.

Effects of simulated flue gas on components of Scenedesmus raciborskii WZKMT

Scenedesmus raciborskii WZKMT cultured with simulated flue gas was investigated. Cellular components, including total sugar, starch, chlorophyll, protein and lipid, were compared between simulated flue gas and 7% (v/v) CO2. Dissolution of SO2 and NO in simulated flue gas led to pH decrease and toxicity to microalgae cells. Furthermore, the death or aging of microalgae cells reduced the buffer capacity and caused decrease of simulated flue gas absorption. With 7% CO2, the highest total sugar and starch content could attain to 66.76% and 53.16%, respectively, which indicated S. raciborskii WZKMT is a desired feedstock candidate for bioethanol production. Microalgae growth and starch accumulation was inhibited, while cells produced more chlorophyll, protein and lipid when simulated flue gas was the carbon source. Fatty acids composition analysis indicated that there was no significant distinction on fatty acids relative content (fatty acid/TFA) between cells aerated using simulated flue gas and 7% CO2.

Outdoor Growth Characterization of an Unknown Microalga Screened from Contaminated Chlorella Culture

Outdoor microalgae cultivation process is threatened by many issues, such as pest pollution and complex, changeable weather. Therefore, it is difficult to have identical growth rate for the microalgae cells and to keep their continuous growth. Outdoor cultivation requires the algae strains not only to have a strong ability to accumulate oil, but also to adapt to the complicated external environment. Using 18S rRNA technology, one wild strain Scenedesmus sp. FS was isolated and identified from the culture of Chlorella zofingiensis. Upon contamination by Scenedesmus sp., the species could quickly replace Chlorella zofingiensis G1 and occupy ecological niche in the outdoor column photobioreactors. The results indicated that Scenedesmus sp. FS showed high alkali resistance. It also showed that even under the condition of a low inoculum rate (OD680, 0.08), Scenedesmus sp. FS could still grow in the outdoor raceway pond under a high alkaline environment. Even under unoptimized conditions, the oil content of Scenedesmus sp. FS could reach more than 22% and C16–C18 content could reach up to 79.68%, showing that this species has the potential for the biodiesel production in the near future.

Culture of four microalgal strains for bioenergy production and nutrient removal in the meliorative municipal wastewater.

ABSTRACT Microalgae have been considered as the most promising sources of alternative bioenergy. For the purpose of saving costs, the present work focused on the potential use of microalgae in the meliorative municipal wastewater, which contains 90% municipal wastewater and 10% dairy wash wastewater. Four microalgal species, Palmellococcus miniatus, Neochloris oleoabundans, Scenedesmus quadricanda #507, and Chlorella zofingiensis, were cultured in pure municipal wastewater and meliorative municipal wastewater, respectively, for 5 days. Their biomass accumulation and removal rates of nitrogen and phosphate were measured. Results showed that the growth rates of Neochloris oleoabundans, Palmellococcus miniatus, and Chlorella zofingiensis in meliorative municipal wastewater (>0.8 g·L–1·d–1) were significantly higher than that in municipal wastewater (2.6 g·L–1·d–1), while there was no significant difference between the growth rates of Scenedesmus quadricanda #507 in meliorative municipal wastewater and in municipal wastewater. Neochloris oleoabundans exhibited the highest growth rate (0.86 g·L–1·d–1) and relatively high nutrient removal capacity. Scenedesmus quadricanda #507 had the highest P removal rate of over 94%. The four species have a similar N removal rate at about 90%. The results showed that the highest average removal rate of N and P were about 23.1 mg·L–1·d–1 and 7.1 mg·L–1·d–1. Furthermore, the content of lipid or carbohydrates increased and a different profile of fatty acids were found compared to those in municipal wastewater. Cellular components changes of microalgae in meliorative municipal wastewater were favorable as raw materials for bioethanol and biodiesel production. Cultivation with meliorative municipal wastewater is a win-win culture mode that facilitates the biomass production, lipid and carbohydrate accumulation, and wastewater purification.

Biomass Accumulation of Chlorella Zofingiensis G1 Cultures Grown Outdoors in Photobioreactors

The complicated and changeable weather conditions and pest invasion increase difficulties in outdoor microalgae cultivation. In this paper, outdoor microalgae cultivation experiments were investigated in Foshan city, South China. During June and August when the temperature is high, the cooling system-water spray combined shade tarpaulin can effectively reduce the temperature to 4–7˚C in the 40 L vertical tubular outdoor photobioreactors. Under 300 mg/L urea and 200 mg/L ammonium bicarbonate conditions, Chlorella zofingiensis G1 had the largest biomass accumulation. Addition of acetic acid to adjust the pH of the medium can effectively improve the C. zofingiensis G1 biomass in the photobioreactor, which was four times more than that only through air ventilation conditions. The biomass accumulation of C. zofingiensis G1 was essentially unchanged during night time.

Metagenomic analysis for the microbial consortium of anaerobic CO oxidizers

Metagenomics analysis has been applied to identify the dominant anaerobic microbial consortium of the carbon monoxide (CO) oxidizers in anaerobic sludge. Reads from the hypervariable V6 region in the bacterial 16s rDNA were aligned and finally clustered into operational taxonomic units (OTUs). The OTUs from different stages in anaerobic CO condition were classified. Alphaproteobacteria, clostridia, betaproteobacteria and actinobacteria were the most abundant groups, while alphaproteobacteria, betaproteobacteria and actinobacteria were variable groups. CO consumption and production efficiency of the microbial consortium were studied. Semi‐continuous trials showed that these anaerobic CO oxidizers formed a stable microbial community, and the CO conversion rate was at over 84%, with the highest CO consumption activity of 28.9 mmol CO/g VSS●day and methane production activity at 7.6 mmol CH4/g VSS●day during six cycles.