Biological Approaches Integrating Algae and Bacteria for the Degradation of Wastewater Contaminants-A Review.

Merwin Mammen Mathew,Ram Kumar,Vaidehi Vats,Hans-Uwe Dahms,Raunak Dhanker,Jiang-Shiou Hwang,Kanchan Khatana

doi:10.3389/fmicb.2021.801051

Abstract

The traditional approach for biodegradation of organic matter in sewage treatment used a consortium of bacterial spp. that produce untreated or partially treated inorganic contaminants resulting in large amounts of poor-quality sludge. The aeration process of activated sludge treatment requires high energy. So, a sustainable technique for sewage treatment that could produce less amount of sludge and less energy demanding is required for various developed and developing countries. This led to research into using microalgae for wastewater treatment as they reduce concentrations of nutrients like inorganic nitrates and phosphates from the sewage water, hence reducing the associated chemical oxygen demand (COD). The presence of microalgae removes nutrient concentration in water resulting in reduction of chemical oxygen demand (COD) and toxic heavy metals like Al, Ni, and Cu. Their growth also offers opportunity to produce biofuels and bioproducts from algal biomass. To optimize use of microalgae, technologies like high-rate algal ponds (HRAPs) have been developed, that typically use 22% of the electricity used in Sequencing Batch Reactors for activated sludge treatment with added economic and environmental benefits like reduced comparative operation cost per cubic meter, mitigate global warming, and eutrophication potentials. The addition of suitable bacterial species may further enhance the treatment potential in the wastewater medium as the inorganic nutrients are assimilated into the algal biomass, while the organic nutrients are utilized by bacteria. Further, the mutual exchange of CO2 and O2 between the algae and the bacteria helps in enhancing the photosynthetic activity of algae and oxidation by bacteria leading to a higher overall nutrient removal efficiency. Even negative interactions between algae and bacteria mediated by various secondary metabolites (phycotoxins) have proven beneficial as it controls the algal bloom in the eutrophic water bodies. Herein, we attempt to review various opportunities and limitations of using a combination of microalgae and bacteria in wastewater treatment method toward cost effective, eco-friendly, and sustainable method of sewage treatment.

Highlights

Bacteria and algae are extensively used in the treatment of wastewater (Almomani et al, 2019)
The microalgae in turn utilize this CO2 to produce carbohydrates and O2 through photosynthesis, of which the former is needed for biomass production, while the latter serves as the terminal electron acceptor for aerobic respiration in bacteria
The integrated approach has some merits to its usability (Katam and Bhattacharyya, 2021). These include the (a) ability for single step removal of nutrients and organic carbon, (b) such systems have lower requirement for mechanical aeration, due to which their carbon footprint is less, (c) resourceful biomass generated in the form of biomass that can be used for the synthesis of biodiesel or biogas, (d) lower quantities of sludge generated in comparison to typical treatment technologies that use bacteria, and (e) the wastewater effluent produced is disinfected from pathogens within the system due to which additional chemicals are not required later. They have found certain demerits of this approach too, which are (a) light dependency of microalgal growth which is not true for pure activated sludge process, (b) high pH of medium generated due to photosynthesis by microalgae that negatively impacts the bacterial consortium associated with the activated sludge process, (c) the slow growth rate of microalgae which leads to higher Solid Retention Time (SRT) than what is required by heterotrophic organisms, and (d) difficulty associated with the separation of microalgal biomass from the mixed liquor so that lipids and pigment can be extracted

Summary

Introduction

Bacteria and algae are extensively used in the treatment of wastewater (Almomani et al, 2019). In the case of the wastewater treatment by an algal-bacterial co-culture approach, we need not to switch between the different operating environments to facilitate inorganic N and P removal, it just requires the single stage treatment, which in result reduces the complexity of the treatment process (Figure 4).

Results

Conclusion