Influence of solids residence time and carbon storage on nitrogen and phosphorus recovery by microalgae across diel cycles

D. A. Gardner-Dale, I. M. Bradley, J. S. Guest

Research output: Contribution to journalArticle

Abstract

Microalgal treatment systems could advance nutrient recovery from wastewater by achieving effluent nitrogen (N) and phosphorus (P) levels below the current limit of technology, but their successful implementation requires an understanding of how design decisions influence nutrient uptake over daily (i.e., diel) cycles. This work demonstrates the ability to influence microalgal N:P recovery ratio via solids residence time (SRT) while maintaining complete nutrient removal across day/night cycles through carbon storage and mobilization. Experiments were conducted with two microalgal species, Scenedesmus obliquus and Chlamydomonas reinhardtii, in photobioreactors (PBRs) operated as cyclostats (chemostats subjected to simulated natural light cycles) with retention times of 6–22 days (S. obliquus) and 7–13 days (C. reinhardtii). Nutrient loading and all other factors were fixed across all experiments. Elevated SRTs (>8 days) achieved limiting nutrient concentrations (either N or P) below the detection limit throughout the diel cycle. N:P mass ratio in algal biomass was linearly correlated with SRT, varying from 9.9:1 to 5.0:1 (S. obliquus) and 4.7:1 to 4.3:1 (C. reinhardtii). Carbohydrate content of biomass increased in high irradiance and decreased in low irradiance and darkness across all experiments, whereas lipid dynamics were minimal over 24-h cycles. Across all nutrient-limited cultures, specific (i.e., protein-normalized) dynamic carbohydrate generally decreased with increasing SRT. Nighttime consumption of stored carbohydrate fueled uptake of nutrients, enabling complete nutrient limitation throughout the night. Dynamic carbohydrate consumption for nutrient assimilation was consistent with dark protein synthesis but less than that of heterotrophic growth, underscoring the need for algal process models to decouple growth from nutrient uptake in periods of low/no light. The ability to tailor microalgal N:P uptake ratio and target an optimal energy storage metabolism with traditional engineering process controls (such as SRT) may enable advanced nutrient recovery facilities to target continuous and reliable dual limitation of nitrogen and phosphorus.

Original languageEnglish (US)
Pages (from-to)231-239
Number of pages9
JournalWater Research
Volume121
DOIs
StatePublished - Sep 15 2017

Fingerprint

nutrient
Nutrients
residence time
carbohydrate
phosphorus
nitrogen
experiment
Carbohydrates
Recovery
Phosphorus
Nitrogen
Experiments
nutrient uptake
carbon sequestration
irradiance
protein
biomass
Biomass
Proteins
Carbon

Keywords

  • Diurnal
  • Lipids
  • Nutrients
  • Resource recovery
  • Sewage
  • Starch

ASJC Scopus subject areas

  • Ecological Modeling
  • Water Science and Technology
  • Waste Management and Disposal
  • Pollution

Cite this

Influence of solids residence time and carbon storage on nitrogen and phosphorus recovery by microalgae across diel cycles. / Gardner-Dale, D. A.; Bradley, I. M.; Guest, J. S.

In: Water Research, Vol. 121, 15.09.2017, p. 231-239.

Research output: Contribution to journalArticle

Gardner-Dale, D. A.; Bradley, I. M.; Guest, J. S. / Influence of solids residence time and carbon storage on nitrogen and phosphorus recovery by microalgae across diel cycles.

In: Water Research, Vol. 121, 15.09.2017, p. 231-239.

Research output: Contribution to journalArticle

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