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Highlights • Ammonia toxicity was related to ammonium concentration, carbon/nitrogen ratio and pH. • Ammonium concentration greatly affected cell viability. • NH 4 +-N removal efficiency was increased by 96% in response to glycerol addition. • Strategies for alleviating ammonia toxicity were developed. Abstract Ammonia toxicity is a major disadvantage of microalgal growth when high-strength ammonium wastewaters like manure-free piggery wastewater (MFPW) were used as microalgal growth medium. In the present study, the effect of ammonium concentration, carbon/nitrogen ratio, and pH on ammonia toxicity of Chlorella vulgaris cultivated in the MFPW and nutrients removal was investigated. The three important parameters affected ammonia toxicity of C. vulgaris and nutrients removal of the MFPW significantly. The ammonium concentration of the MFPW could be decreased by air stripping. Microalga grew best at a carbon/nitrogen ratio of 25:1 with the maximum biomass concentration of 3.83 g L−1, the highest cell viability of 97%, and the removal of 100% ammonia, 95% of total phosphorus, and 99% of chemical oxygen demand. Ammonia toxicity was alleviated by pH control. The application of the established strategies can enhance nutrients removal of the MFPW while mitigating ammonia toxicity of C. vulgaris. [ABSTRACT FROM AUTHOR]

• A novel algal biofilm photobioreactor was developed. • The yield of microalgae on the membrane could reach as high as 7.37 g/m2. • The biofilm algae could be easily harvested by mechanical scraping. • The biofilm algae had high content of linoleic acid and linolenic acid. • The hog manure wastewater was efficiently treated. This study developed a high-efficiency algal biofilm photobioreactor for microalgae by designing a special array of curtain membrane components. This paper also discusses the growth and nutrient composition of Chlorella vulgaris , and hog manure wastewater utilization and purification. It was found that after about 5 days of culture, the biomass of C. vulgaris on the membrane could reach as high as 7.37 g/m2 and the algae were easily harvested by mechanical scraping. The lipid content of C. vulgaris on the membrane structure was 10.17% while the lipid content of the algae in suspension was 14.29%. The light intensity showed a significant effect on the fatty acid composition. The C. vulgaris grew very well, and achieved deep purification of the hog manure wastewater; the COD, TP, TN, and NH 4 +-N removal rates reached 95.67%, 64.40%, 69.55%, and 91.24%, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Over 90% harvesting efficiency achieved using non-sacrificial anode. • Extracellular polymeric substance is the main reason keeping bubbles from bursting. • Hydrogen bubbles' size increased when the diameter of the cathode wire increased. As a promising method for efficiently harvesting microalgae, electro-flotation's performance is related to various factors including electrode design and process operating parameters. In this paper, bubble generation behavior on stainless-steel cathodes, with wire diameters of 0.8 mm, 0.2 mm and 0.05 mm, was studied. The results show that the bubble size increased with the increasing diameter of the electrode wire. Over 90 % harvesting efficiency was achieved using non-sacrificial anode. Extracellular polymeric substance is the main reason keeping bubbles from bursting. [ABSTRACT FROM AUTHOR]

• Broken rice hydrolysate was used as carbon source. • The pH decreased sharply leading to failure of microalgal growth. • Ammonium led to a decrease in the pH of the medium. • Batch pH adjustment could increase biomass production of Chlorella vulgaris. • The cost of the culture medium decreased by 89.58%. The high cost of carbon source limits the heterotrophic culture of Chlorella. In this study, broken rice was hydrolyzed into glucose. Then, the broken rice hydrolysate (BRH) was utilized for heterotrophic cultivation of C. vulgaris instead of glucose. Results showed that algal cells released H+ when they consumed NH 4 +, leading to a sharp decrease in pH. Growth inhibition by acid could be avoided by using a pH buffer. Adding alkaline reagents intermittently during culture could not only reduce the amount of pH stabilizer but also obtain increased biomass production. When using Tris as pH stabilizer, the biomass productivity of C. vulgaris in BRH was the largest (1.01 g/L/d), followed by NaOH (1.00 g/L/d), and Na 2 CO 3 (0.95 g/L/d). Using BRH instead of glucose for heterotrophic cultivation of C. vulgaris could save 89.58% of the cost of culture medium. This study developed a novel strategy for cultivating C. vulgaris heterotrophically using BRH. [ABSTRACT FROM AUTHOR]