Dual purpose microalgae-bacteria-based systems that treat wastewater and produce biodiesel and chemical products within a biorefinery.

Widespread application of algal biofilm-based systems in wastewater treatment has been limited despite the potential benefits of a low cost nutrient removal option and a source of biomass for bioproduct production. The performance and processes involved with algal biofilm-based systems in wastewater treatment are not adequately addressed in the available literature, which hinders design and scale up of effective systems for applications to municipal, industrial, and agricultural waste streams. A critical review is presented, which examines nutrient removal trends, biomass productivity, growth requirements, and challenges for algal biofilm-based biotechnology as applied to wastewater treatment both at bench scale and at pilot scale operations. Information on algal biofilms in natural environments derived from ecology and limnology disciplines was utilized in areas of limited research with regard to wastewater treatment. This critical review identified key areas that need to be addressed for designing, building, and testing algal biofilm-based technologies that integrate both nutrient removal from wastewater and enhanced biomass production to improve the performance of engineered systems. The review identifies the need for research on factors that affect algal growth, mass transport, species selection, algal–bacterial interactions, and validation of laboratory research in field scale tests for the development of an algal biofilm based technology platform for integrating wastewater treatment and biomass production.

Algal biofilm based technology for wastewater treatment

This paper explores diatom attachment to a range of laser etched polyimide surfaces to directly test 'attachment point theory'. Static bioassays were conducted on microtextured polyimide surfaces using four diatom species, Fallacia carpentariae, Nitzschia cf. paleacea, Amphora sp. and Navicula jeffreyi with cell sizes ranging from 1-14 microm. The microtextured polyimides were modelled from natural fouling resistant bivalve surfaces and had wavelengths above, below and at the same scale as the diatom cell sizes. Diatoms attached in significantly higher numbers to treatments where the numbers of attachment points was highest. The lowest diatom attachment occurred where cells were slightly larger than the microtexture wavelength, resulting in only two theoretical points of attachment. The results support attachment point theory and highlight the need to address larval/cell size in relation to the number of attachment points on a surface. Further studies examining a range of microtexture scales are needed to apply attachment point theory to a suite of fouling organisms and to develop structured surfaces to control the attachment and development of fouling communities.

Testing attachment point theory: diatom attachment on microtextured polyimide biomimics

Current global environmental issues raise unavoidable challenges for our use of natural resources. Supplying the human population with clean water is becoming a global problem. Numerous organic and inorganic impurities in municipal, industrial, and agricultural waters, ranging from microplastics to high nutrient loads and heavy metals, endanger our nutrition and health. The development of efficient wastewater treatment technologies and circular economic approaches is thus becoming increasingly important. The biomass production of microalgae using industrial wastewater offers the possibility of recycling industrial residues to create new sources of raw materials for energy and material use. This review discusses algae-based wastewater treatment technologies with a special focus on industrial wastewater sources, the potential of non-conventional extremophilic (thermophilic, acidophilic, and psychrophilic) microalgae, and industrial algae-wastewater treatment concepts that have already been put into practice.

https://onlinelibrary.wiley.com/doi/epdf/10.1002/elsc.201900071

Microalgae wastewater treatment: Biological and technological approaches.

Biofilm-based algal cultivation has received increased attention as a potential platform for algal production and other applications such as wastewater treatment. Algal biofilm cultivation systems represent an alternative to the suspension-based systems that have yet to become economically viable. One major advantage of algal biofilm systems is that algae can be simply harvested through scraping and thus avoid the expensive harvesting procedures used in suspension-based harvesting such as flocculation and centrifugation. In recent years, an assortment of algal biofilm systems have been developed with various design configurations and biomass production capacities. This review summarizes the state of the art of different algal biofilm systems in terms of their design and operation. Perspectives for future research needs are also discussed to provide guidance for further development of these unique cultivation systems.

Biofilm-based algal cultivation systems.

Adhesion of Chlorella vulgaris (chlorophyceae), Nitzschia amphibia (bacillariophceae) and Chroococcus minutus (cyanobacteria) to hydrophobic (perspex, titanium and stainless steel 316-L), hydrophilic (glass) and toxic (copper, aluminium brass and admiralty brass) substrata were studied in the laboratory. The influence of surface wettability, surface roughness, pH of the medium, culture age, culture density, cell viability and presence of organic and bacterial films on the adhesion of Nitzschia amphibia was also studied using titanium, stainless steel and glass surfaces. All three organisms attached more on titanium and stainless steel and less on copper and its alloys. The attachment varied significantly with respect to exposure time and different materials. The attachment was higher on rough surfaces when compared to smooth surfaces. Attachment was higher on pH 7 and above. The presence of organic film increased the attachment significantly when compared to control. The number of attached cells was found to be directly proportional to the culture density. Attachment by log phase cells was significantly higher when compared to stationary phase cells. Live cells attached more when compared to heat killed and formalin killed cells. Bacterial films of Pseudomonas putida increased the algal attachment significantly.

K. V. K. Nair

Papers

Laboratory studies on adhesion of microalgae to hard substrates