A Microalgae-Methanotroph Coculture is a Promising Platform for Fuels and Chemical Production From Wastewater

Abstract

Wastewater resource recovery facilities are major energy consumers in a community, as well as major contributors for greenhouse gas emission. Although anaerobic digestion is widely employed in wastewater treatment to reduce the amount of solid organic waste and the sludge produced, the use of the produced biogas is mostly limited to heating and electricity generation, while the nutrient rich digestate still requires further treatment. In this work, we propose a waste-to-value platform based on a microalgae-methanotroph coculture, which can convert anaerobic digestion-generated biogas into value-added products, while simultaneously removing nutrients from digestate. The platform takes advantage of the synergistic interactions within a microalgae-methanotroph coculture to achieve significantly improved productivity of microbial biomass and enhanced nutrient recovery performance. Using Chlorella sorokiniana-Methylococcus capsulatus (Bath) as the model coculture, we demonstrate that the coculture offers a highly promising platform for waste-to-value technologies, which can efficiently recover energy (from CH 4 ) and carbon (from both CH 4 and CO 2 ) to produce microbial biomass, while removing nutrients from wastewater to produce treated clean water. Compared to microalgae monoculture, the coculture achieved 120% improvement in biomass production, 71 and 164% improvement in total nitrogen and total phosphorous removal, respectively, when the same amount of biogas was provided.

Conversion of biogas from anaerobic digestion to single cell protein and bio-methanol: mechanism, microorganisms and key factors - A review

“…Hence, in the recent years, application of waste streams as nitrogen source for microorganisms' growth has shown a good promise with zero or negative cost when adopted to replace high-energy intensive process such as activated sludge. These waste streams include supernatant of the anaerobically digested sludge/bio-waste (ADs) [68,70,71], and food industry wastewater (FIWW), for instance, the effluent of a potato processing plant [53]. The ADs/FIWW can be considered as a promising alternative to the synthetic mediums for SCP production making the process economically more viable.…”

“…A challenging issue associated with the use of ADs as a culture medium for SCP production is that they contain high ammonium concentration [86, 87], e.g., 1000-3000 mg NH 4 + -N/L [85], which should be diluted to meet the desired ammonium concentration (below 150 mg [66,71]. This implies that a large volume of freshwater for the dilution process is required while going to produce SCP at a large scale.…”

“…This is not realistic because freshwater is becoming a scarce resource worldwide. In order to address this limitation, the secondary clarifier water (SCW) from the WRRFs could be used instead without affecting the microbial growth [71].…”

“…The gravitationally settled ADs, diluted with SCW, can be directly used as a culture medium without requiring pre-treatment, e.g., filtration or autoclaving, which present an inhibitive cost to this application. An example is the study of Roberts et al [71], who investigated biogas conversion into microbial biomass using a co-culture of Chlorella sorokiniana and Methylococcus capsulatus grown separately on the gravitationally settled ADs, pre-treated ADs and the sterilized AMS medium (as the control). According to their findings, the growth profile of the co-culture grown in the gravitationally settled ADs was comparable to those obtained using either the pre-treated ADs or the sterilized AMS medium.…”

“…In this process, the methanotrophs use the in situ generated O 2 by algae to convert CH 4 into biomass while generating CO 2 that is subsequently fixed by the algae. Such a process offers several advantages over the methanotrophs and methanotrophs-HOB processes: i) it does not require an external O 2 supply, ii) CH 4 [71] Notes:…”