Free ammonia offers algal crop protection from predators in dairy wastewater and ammonium-rich media

Continuous measurements of volatile gases as detection of algae crop health

Wide adoption of algae cultivation to produce environmentally sustainable biofuels and fine chemicals is currently hampered by large losses (10 to 30%) incurred by grazer infections. We show the usage of real-time chemical ionization mass spectrometry to rapidly identify gaseous indicators of grazer infections in cyanobacteria cultures. Grazing was detected significantly faster (up to 3 d) using real-time mass spectrometry than the current methods of microscopy and qPCR. By employing this technology, cultivators may be empowered to treat grazer infestations sooner, thereby protecting the crop and enhancing profitability.

Algae cultivation in open raceway ponds is considered the most economical method for photosynthetically producing biomass for biofuels, chemical feedstocks, and other high-value products. One of the primary challenges for open ponds is diminished biomass yields due to attack by grazers, competitors, and infectious organisms. Higher-frequency observations are needed for detection of grazer infections, which can rapidly reduce biomass levels. In this study, real-time measurements were performed using chemical ionization mass spectrometry (CIMS) to monitor the impact of grazer infections on cyanobacterial cultures. Numerous volatile gases were produced during healthy growth periods from freshwater Synechococcus elongatus Pasteur Culture Collection (PCC) 7942, with 6-methyl-5-hepten-2-one serving as a unique metabolic indicator of exponential growth. Following the introduction of a Tetrahymena ciliate grazer, the concentrations of multiple volatile species were observed to change after a latent period as short as 18 h. Nitrogenous gases, including ammonia and pyrroline, were found to be reliable indicators of grazing. Detection of grazing by CIMS showed indicators of infections much sooner than traditional methods, microscopy, and continuous fluorescence, which did not detect changes until 37 to 76 h after CIMS detection. CIMS analysis of gases produced by PCC 7942 further shows a complex temporal array of biomass-dependent volatile gas production, which demonstrates the potential for using volatile gas analysis as a diagnostic for grazer infections. Overall, these results show promise for the use of continuous volatile metabolite monitoring for the detection of grazing in algal monocultures, potentially reducing current grazing-induced biomass losses, which could save hundreds of millions of dollars.

Nutrients recycling and biomass production from Chlorella pyrenoidosa culture using anaerobic food processing wastewater in a pilot-scale tubular photobioreactor

Microalgae cultivation in anaerobic food wastewater was a feasible way for high biomass production and nutrients recycling. In this study, Chlorella pyrenoidosa culture on anaerobic food wastewater was processed outdoors using a pilot-scale tubular photobioreactor. The microalgae showed rapid growth in different seasons, achieving high biomass production of 1.83-2.10 g L^-1 and specific growth rate of 0.73-1.59 d^-1. The biological contamination and dissolved oxygen were controlled at suitable levels for algal growth in the tubular photobioreactor. Lipids content in harvested biomass was 8.1-15.3% of dried weight, and the analysis in fatty acids revealed high quality with long carbon chain length and high saturation. Additionally, algal growth achieved effective pollutants purification from wastewater, removing 42.3-53.8% of COD_Cr, 82.6-88.7% of TN and 59.7-67.6% of TP. This study gave a successful application for scaled-up microalgae culture in anaerobic food processing wastewater for biodiesel production and wastewater purification.

The joint effect of ammonium and pH on the growth of Chlorella vulgaris and ammonium removal in artificial liquid digestate

Although ammonium containing digestate is an ideal alternative medium for microalgae cultivation, high ammonium or unfavorable pH may inhibit microalgal growth. In this study, the joint effect of ammonium and pH on the growth of C. vulgaris and nutrient removal in artificial digestate was investigated. Our results show that ammonium and pH both affected algal growth, but free ammonia (FA) was the main actual inhibitory factor. Algal specific growth rate presented a negative correlation with FA and their relationship was well fitted by a linear regression model. Microalgal growth was little affected below 36.8 mg L^-1 FA, while the obvious inhibition occurred at 184 mg L^-1 FA (EC₅₀), indicating a high tolerance to FA. Ammonium removal was well described by a first-order kinetics model. FA stress stimulated the production of extracellular organic matters (EOMs), which was good for microalgae adaptation but adverse to pollutant removal.

Current practices and challenges in using microalgae for treatment of nutrient rich wastewater from agro-based industries

Considerable research activities are underway involving microalgae species in order to treat industrial wastewater to address the waste-to-bioenergy economy. Several studies of wastewater treatment using microalgae have been primarily focused on removal of key nutrients such as nitrogen and phosphorus. Although the use of wastewater would provide nutrients and water for microalgae growth, the whole process is even more complex than the conventional microalgae cultivation on freshwater media. The former one adds several gridlocks to the system. These gridlocks are surplus organic and inorganic nutrients concentration, pH of wastewater, wastewater color, total dissolved solids (TDS), microbial contaminants, the scale of photobioreactor, batch versus continuous system, harvesting of microalgae biomass etc. The present review discusses, analyses, and summarizes key aspects involved in the treatment of wastewaters from distillery, food/snacks product processing, and dairy processing industry using microalgae along with sustainable production of its biomass. This review further evaluates the bottlenecks for individual steps involved in the process such as pretreatment of wastewater for contaminants removal, concentration tolerance/dilutions, harvesting of microalgae biomass, and outdoor scale-up. The review also describes various strategies to optimize algal biomass and lipid productivities for various wastewater and photobioreactor type. Moreover, the review emphasizes the potential of co-cultivation of microorganism such as yeast and bacteria along with microalgae in the treatment of industrial wastewater.

Application of biosurfactant from Bacillus subtilis C9 for controlling cladoceran grazers in algal cultivation systems

Open algal cultivation platforms often suffer crop losses to herbivorous grazers that have potential to devastate biomass production within a few days. While a number of studies suggest synthetic chemicals as control agents for voracious algal grazers, environmental and safety concerns associated with the use of these chemicals encourage the exploration of alternative biological control agents. We hereby propose the application of a biosurfactant produced by Bacillus subtilis C9 (referred to as C9-biosurfactant) for controlling cladoceran grazers commonly found in algal cultivation systems. The results indicated that C9-biosurfactant completely eradicated Daphnia pulex and Moina macrocopa within 24 hours when concentrations were equal to or exceeded 6 mg/L. Moreover, supplying C9-biosurfactant into the cultures of selected algal species with and without cladoceran grazers indicated no adverse effect of C9-biosurfactant on the growth and lipid productivity of algal crops, while cladocerans were selectively controlled by C9-biosurfactant even under the presence of their prey. These results thus indicate that C9-biosurfactant could be an effective biocontrol agent for cladoceran grazers at industrial algal cultivation.

Enhanced lipid and biomass production using alcohol wastewater as carbon source for Chlorella pyrenoidosa cultivation in anaerobically digested starch wastewater in outdoors

Alcohol wastewater (AW) as carbon source for enhancing Chlorella pyrenoidosa growth and lipid accumulation in anaerobically digested starch wastewater (ADSW) was performed in outdoor cultivation. The biomass and lipid production significantly increased while adding optimal amount of AW (AW/ADSW=1:15) during exponential phase. In comparison with blank ADSW culture, the optimal AW addition increased the biomass production, lipid content and productivity by 35.29%, 102.68% and 227.91%, respectively. However, AW addition caused severe bacterial contamination and the total bacterial increased by 4.62-fold. Simultaneously, the optimal consortia of microalgae/bacteria effectively removed nutrients from the wastewater, including 405.18±36.47mgCOD_Cr/L/day, 49.15±5.54mgN/L/day and 6.72±1.24mgP/L/day.