Rotating algal biofilm reactor and spool harvester for wastewater treatment with biofuels by‐products

Abstract

Maximizing algae production in a wastewater treatment process can aid in the reduction of soluble nitrogen and phosphorus concentrations in the wastewater. If harvested, the algae-based biomass offers the added benefit as feedstock for the production of biofuels and bioproducts. However, difficulties in harvesting, concentrating, and dewatering the algae-based biomass have limited the development of an economically feasible treatment and production process. When algae-based biomass is grown as a surface attached biofilm as opposed to a suspended culture, the biomass is naturally concentrated and more easily harvested. This can lead to less expensive removal of the biomass from wastewater, and less expensive downstream processing in the production of biofuels and bioproducts. In this study, a novel rotating algal biofilm reactor (RABR) was designed, built, and tested at bench (8 L), medium (535 L), and pilot (8,000 L) scales. The RABR was designed to operate in the photoautotrophic conditions of open tertiary wastewater treatment, producing mixed culture biofilms made up of algae and bacteria. Growth substrata were evaluated for attachment and biofilm formation, and an effective substratum was discovered. The RABR achieved effective nutrient reduction, with average removal rates of 2.1 and 14.1 g m(-2) day(-1) for total dissolved phosphorus and total dissolved nitrogen, respectively. Biomass production ranged from 5.5 g m(-2) day(-1) at bench scale to as high as 31 g m(-2) day(-1) at pilot scale. An efficient spool harvesting technique was also developed at bench and medium scales to obtain a concentrated product (12-16% solids) suitable for further processing in the production of biofuels and bioproducts.

Advanced nutrient removal from surface water by a consortium of attached microalgae and bacteria: A review

“…There are many other types of photobioreactors treating contaminated waters using attached microalgae-bacteria biomass such as the rotating algal biofilm reactor (RABR) (Christenson and Sims, 2012). Wu et al (2011) planted a substrate ''Artificial Aquatic Mats" as a phototrophic bioreactor in a contaminated watershed with different lengths used depending on the water depth.…”

“…Thereby, a scheduled harvest of the attached biomass is essential to remove the biomass generated (reducing the adverse effects of biomass detachment on the effluent), reclaim the nutrients and regenerate the consortium for sustainable nutrient removal (Adey et al, 2011). However, significant labor or energy input is required in biomass harvesting due to the multiple bioreactor configurations and the surface conditions (Mulbry et al, 2010;Christenson and Sims, 2012;Sindelar et al, 2015).…”

Agriculture-independent, sustainable, fail-safe and efficient food production by autotrophic single-cell protein

“…These rotating cylinders achieve good hydration as well as good gas mass transfer and at the same time present a low-tech, low-cost option with stable long-term operation [93,94]. HAB have been successfully immobilized on biofilm carriers (AnoxKaldnes TM K1).…”

“…single-step and 2 nd -stage in two-stage bioprocesses, has to be cultivated differently in order to allow cell harvest. Microalgae were shown to grow as biofilm attached on cords that are wound around the cylinder [93]. For harvest, the cord is continuously unwound from and rewound to the cylinder and the biomass grown on the cord is dry-harvested by a "spool harvester" with a scraping mechanism [93].…”

“…Microalgae were shown to grow as biofilm attached on cords that are wound around the cylinder [93]. For harvest, the cord is continuously unwound from and rewound to the cylinder and the biomass grown on the cord is dry-harvested by a "spool harvester" with a scraping mechanism [93]. Taken together, it is hypothesized here that two-stage designs can be cultivated using a single cylinder: in the inside of the cylinders, 1 st -stage, HAB, are immoblized on biofilm carriers or entrapped into hydrogels.…”