Optimizing SRT for improved biomass production and nutrient removal from wastewater secondary effluent in a continuous mode MPBR system with Monoraphidium sp.: An experimental and growth kinetics model approach

Khan, Waris; Zhou, Canwei; Hu, Zhiyi; Zhang, Qiulong; Ye, Ye; Teng, Fei; Cai, Zhonghua; Tao, Yi

doi:10.1016/j.algal.2023.103321

Cited by 3 publications

(1 citation statement)

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“…N:P ratio for Scenedesmus has been reported to range from 5-13:1, with ratios below this range demonstrating a reduction in both biomass productivity and nutrient removal efficiencies (Arbib et al, 2013; Xin et al, 2010). In contrast, Monoraphidium exhibits higher biomass productivity at lower N:P ratio in the range of 0.5-3:1 (Dhup and Dhawan, 2014) and has demonstrated maximum removal capacity even at low nitrogen concentrations [e.g., 0.1 mg N·L -1 (Khan et al, 2023)] such as those seen during the second upset period. Moreover, Scenedesmus may be more susceptible to N-limited stress than Monoraphidium , as the latter can produce unique biomolecules (e.g., tocopherols) to help maintain cell structure during periods of N-limitation (Singh et al, 2020).…”

Section: Resultsmentioning

confidence: 99%

Community Structure and Function During Periods of High Performance and System Upset in a Full-Scale Mixed Microalgal Wastewater Resource Recovery Facility

Alam,

Hodaei,

Hartnett

et al. 2024

Preprint

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Microalgae have the potential to exceed current nutrient recovery limits from wastewater, enabling water resource recovery facilities (WRRFs) to achieve increasingly stringent effluent permits. The use of photobioreactors (PBRs) and the separation of hydraulic retention and solids residence time (HRT/SRT) further enables increased biomass in a reduced physical footprint while allowing operational parameters (e.g., SRT) to select for desired functional communities. However, as algal technology transitions to full-scale, there is a need to understand the effect of operational and environmental parameters on complex microbial dynamics among mixotrophic microalgae, bacterial groups, and pests (i.e., grazers and pathogens) and to implement robust process controls for stable long-term performance. Here, we examine the first full-scale, intensive WRRF utilizing mixed microalgal for tertiary treatment in the US (EcoRecover, Clearas Water Recovery Inc.) during a nine-month monitoring campaign. We investigated the temporal variations in microbial community structure (18S and 16S rRNA genes), which revealed that stable system performance of the EcoRecover system was marked by a low-diversity microalgal community (DINVSIMPSON = 2.01) dominated by Scenedesmus sp. (MRA = 55%-80%) that achieved strict nutrient removal (effluent TP < 0.04 mg.L-1) and steady biomass production (TSSmonthly avg. = 400-700 mg.L-1). Operational variables including pH, alkalinity, and influent ammonium (NH4+), correlated positively (p < 0.05, method = Spearman) with algal community during stable performance. Further, the use of these parameters as operational controls along with N/P loading and SRT allowed for system recovery following upset events. Importantly, the presence or absence of bacterial nitrification did not directly impact algal system performance and overall nutrient recovery, but partial nitrification (potentially resulting from NO2- accumulation) inhibited algal growth and should be considered during long-term operation. The microalgal communities were also adversely affected by zooplankton grazers (ciliates, rotifers) and fungal parasites (Aphelidium), particularly during periods of upset when algal cultures were experiencing culture turnover or stress conditions (e.g., nitrogen limitation, elevated temperature). Overall, the active management of system operation in order to maintain healthy algal cultures and high biomass productivity can result in significant periods (>4 months) of stable system performance that achieve robust nutrient recovery, even in winter months in northern latitudes (WI, USA).

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