Concentration and dewatering of micro-algal cultures with high throughput ceramic/metal membranes
The project objective is to develop a high throughput, efficient filter unit using MoleculeWorks thin ceramic/metal membrane sheets as a versatile tool for economical harvesting of microalgae. Microalgae have the highest growth rate among the crops known so far and are an attractive approach toward rapid conversion of CO2 into usable products by use of sunlight. With its high content of proteins and lipids, the microalgae can be used as biofuel feedstock, foods, animal feeds, and other high value products. Microalgal harvesting is one of major hurdles for the economical production of algae, because of i) small size (a few micrometers), ii) low solid content (0.02-0.06 wt. %), iii) similar density to water, and iv) complex composition of the culture. Membrane filtration is one of the most promising harvesting methods and offers several advantages. However, productivity and power consumption of the membrane filter needs to be substantially improved to become viable for widespread usage. Through this project work, two major innovations in the membrane product development are demonstrated. The first innovation is a thin ceramic/metal sheet membrane that provides high flux and biofouling resistance, compared to current membrane materials or products. The thin ceramic membrane is prepared by deposition and sintering of a ceramic membrane layer at thickness <5µm on a thin, porous nickel alloy support sheet of 40-60µm thickness. The ceramic membrane coating of pore sizes from 20 to 100nm smoothens the membrane surface and improves stability of the metal sheet. The pilot manufacturing process has been successfully developed to produce the ceramic/metal membrane sheets at 21 cm x 21 cm sizes. The manufacturing process is ready for scale up to production when large orders are received in the future. Hydrothermal stability of the ceramic/metal hybrid membrane is confirmed by accelerated aging tests in 120 oC hot water. High flux and fouling resistance of the ceramic/metal sheet membrane are consistently shown with nearly 20 different algal cultures supplied by the project collaborators (MBE, Duke Univ., PNNL). High flux and fouling resistance are also demonstrated for direct filtration of algal species and micro-organisms from seawater. The high flux is obtained at cross flow velocity of about 0.5 to 5 cm/s, which is about 10 to 100 times less than what is typically used for other membrane filters. The liquid pump size and power consumption can be reduced by decreasing the crossflow velocity. The mini-channel planar membrane module is another innovation demonstrated through Phase II project work. This new module design enables assembly of the thin membrane sheets into a working device with straight channels for both feed and permeate flows at channel size in the order of 1mm. This new membrane module provides high membrane area packing density and low pressure drops for the feed and permeate. The module design has been successfully developed by building module prototypes with 60 of 21 cm x 21 cm membrane sheets. The mechanical integrity and essential functions are demonstrated. The essential functions include i) flexibility to stack different numbers of membrane sheets, ii) ability to check individual membrane sheets and re-utilize the good ones, iii) quick back flushing through straight and mini-sized permeate channels, and iv) quick forward flushing through straight and mini-sized membrane channels. A mobile pilot filter unit has been built with dimensions of 60cm (depth) x 120cm (width) x 150 cm (height). The unit is designed to accommodate the modules of 20 m2 membrane area with the filtration rate up to 3 m3/h. The compact unit can be easily shipped to field sites. The pilot filter has been tested for about six months and produced valuable results for commercial demonstration unit development through improvements of the module designs/assembly and membrane cleaning method. However, scope of the project work in optimization of the pilot filter and field testing was compromised due to COVID-19 pandemic. Some intricate details of the module design and material selection, which could not be anticipated at beginning of this project, were revealed through the field filtration tests but could not be fully addressed within phase II project period. These problems, such as feed channel spacing, thin membrane sheet backing, and feed flow direction, are fully resolvable by improving the design and verifiable through systematic filtration tests. These improvements will be made to specific application in the future developmental and commercial demonstration pursuit. In commercialization aspect, three market segments are identified and have been investigated for filtration of microalgae and microorganisms: i) Microalgae Cultivators, ii) Ballast Water Treatment, and iii) cooling tower water treatment and pre-treatment of RO water in desalination plants.
- Research Organization:
- Molecule Works Inc.
- Sponsoring Organization:
- USDOE Office of Science and Technology (ST)
- DOE Contract Number:
- SC0018761
- OSTI ID:
- 1854540
- Type / Phase:
- SBIR (Phase II)
- Report Number(s):
- DOE-MWI-SC0018761
- Country of Publication:
- United States
- Language:
- English
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