A novel photo-respirometry method to characterize consortia in microalgae-related wastewater treatment processes

Abstract

In this paper, a new photo-respirometry method for determining the rates of the main metabolic processes of microalgae-bacteria consortia in microalgae-based wastewater treatment processes has been developed and tested. The proposed protocol consists on applying dark and light periods to a microalgae-bacteria consortium in the presence of different substrates and measuring the rate of oxygen production. This allows determining the activity of microalgae, heterotrophic bacteria and nitrifying bacteria separately. The method has been optimized in terms of the operation strategy, including the starvation period required, the biomass concentration and the irradiance during the measurements. Results show that a starvation period of one to three days is necessary depending on the nutrient concentration. The optimal experimental conditions determined were a biomass concentration of 0.5 g/L and an irradiance of 200 μmol photons/m 2 •s. Furthermore, microalgae-bacteria samples from seven photobioreactors (indoor and outdoor) with different nutrient sources have been evaluated applying the methodology proposed. Regardless of the wastewater type, the microalgae activity is the main metabolic process, with heterotrophic activity increasing along with the chemical oxygen demand (COD) in the wastewater. Nitrifying activity was only observed when high ammonium concentrations were present. The developed method is a powerful tool to adequately manage and operate wastewater treatment processes using microalgae/bacteria consortia, providing valuable information to model wastewater treatment systems with microalgae and determine kinetic parameters.

Modeling of photosynthesis and respiration rate for microalgae–bacteria consortia

“…The final value obtained was 1.08 h −1 . A further detailed description of the equipment, the experimental protocol and the metabolic rates calculations are described in (Sánchez‐Zurano et al, 2020).…”

“…In microalgae–bacteria cultures, the use of respirometry allows one to determine the phototrophic activity by measuring the oxygen production rate (OPR) under light conditions and the oxygen uptake rate in the dark. The methodology allows to assess heterotrophic and nitrifying activity in microalgal–bacterial consortia too (Petrini et al, 2020; Sánchez‐Zurano et al, 2020). These measurements, which are based on oxygen production/consumption, are rapid and easily obtainable (Tang et al, 2014).…”

Role of Microalgae in the Recovery of Nutrients from Pig Manure

“…The protocol and methodology applied allowed us to distinguish between the metabolisms of the three main populations that appear in microalgae-bacteria wastewater: microalgae, heterotrophic bacteria, and nitrifying bacteria [8]. In the first place, microalgae-bacteria cultures were subjected to nutrient starvation (continuous light of 200 µE•m −2 •s −1 and an aeration rate of 0.2 v•v −1 •min −1 ) during 24 h to remove the organic matter and the ammonium present in the media.…”

“…During the day, microalgae consume inorganic carbon, nitrogen, and phosphorus (as well as other compounds) to produce biomass while simultaneously releasing oxygen. Oxygen produced by microalgae is used by heterotrophic bacteria to oxidise organic matter into inorganic compounds [8], producing carbon dioxide that is consumed by microalgal cells [9]. However, the reality of these interactions is far more complex, with different microalgal and bacterial populations taking place at the same time, including the aerobic growth of heterotrophic biomass, denitrification by the anoxic growth of heterotrophic biomass, and nitrification by the aerobic growth of nitrifying bacteria (AOB and NOB) [10].…”

“…This strategy has also been applied to quantify photosynthesis and respiration rates of cultures of phototrophic organisms such as microalgae and cyanobacteria [17][18][19]. More recently, techniques based on respirometry for activated wastewater treatment and phototrophic axenic cultures have been adapted to the microalgae-bacteria consortia that appear in wastewater [8,20,21].…”