Green Technology – Food Waste Purification with Oil-producing Microalgae Supplementary information

Green Technology – Food Waste Purification with Oil-producing Microalgae
Supplementary information
About the OUHK Research Team,
The research team comprises 5 staff and students from the OUHK. Under the leadership of
Prof. Ho Kin-chung, Assistant Professor Dr Yau Yiu-hung, Assistant Professor Fred Lee Wang-fat,
Assistant Professor Steven Xu Jing-liang and Assistant Lecturer Mr Wong Yee-keung from
School of Science and Technology joined the research, along with a group of students studying
Bachelor and MPhil degrees in Environmental Studies in the OUHK.
Research Methodology and Process
From April 2014 to April 2015, the research team will be conducting filtrate sampling and
analysis of food waste filtrate samples collected from Olympian City 2 regularly through the
‘Algal Culture Reactor’ set up at the site. The data collected will form the basis for the design of
future model for large-scale sewage treatment.
Two important principles of environmental protection could be fulfilled through the project,
including the cleaning up of sewage and reducing water pollution while promoting the research
on renewal energy. This project first stemmed from the huge amount of food waste from
restaurants in the shopping centre. In view of this, a food waste decomposer was installed at the
Olympian City 2 shopping centre to deal with the issue. The decomposer is able to turn solid
waste into organic fertilizer, but the fluid and filtrate become by-products. If not treated properly
before discharge, the filtrate could lead to serious water pollution problem affecting the Victoria
Habour.
In view of this, the School of Science and Technology of the OUHK therefore advised Sino
to tackle the issue through algal treatment. As the microalgae can digest Nitrogen and Phosphorus
in the sewage, the filtrate in a way becomes the “nutrient” for growing algae which in turn can
bring enormous economic value.
The team also identified the most suitable species of microalgae for the reactor. The culture
and adaption process of microalgae took place at the microalgae laboratory of the Open
University to serve as the backup for the onsite treatment of filtrate. After one to five days, the
filtrate could be cleaned up by microalgae with acceptable purity standards.
Research result
Because currently the major sewage treatment works in Hong Kong cannot substantially
remove nitrogen and phosphorus from the effluent, there is a potential to cause harmful algal
blooms (HABs). Therefore, to treat the food waste filtrate with microalgae can actually enhance
the process to secondary or even tertiary treatment. It provides high environmental benefits and
enables further improvement of coastal water quality. The research members hope to work out the
reactor with economically optimal performance in order to raise the sewage treatment from level
2 to level 3, comparable to the highest standard of water quality resulted from the bacteria
treatment by the sewage plant and thus effectively improves the water quality. It also produced the
species of microalgae with high diesel quantity.
According to the design of food waste decomposer in the Olympian City 2, the carbon
dioxide emissions from the food waste treatment process can be fed into the microalgal treatment
system, and be utilized by the microalgae for photosynthesis. It kills two birds with one stone.
Such a 'zero carbon emissions' process can further reduce 'carbon footprint' and greenhouse gas
emissions, and helps mitigate the threat of climate change.
Throughout the data collection in six months, the preliminary result showed that 1.215 gram
of microalgae could be produced by one litre of food waste filtrate. It led to the production of 316
milligram of biodiesel. In addition, the removal rates of ammonial-nitrogen, nitrate,
orthro-phosphate, total phosphorus and total suspended solid in the sewage could be decreased by
88.5%, 49.3%, 54.4%, 36.6%, 34.1%, which reflected the high effectiveness in reducing the
sewage pollutants.
A great quantity of solid and fluid food waste are produced at shopping malls in Hong Kong
every day. Provided that all filtrate of food waste at Olympic City 2 to undergo the microalgae
treatment, the emission of carbon dioxide will then be deducted by 12,800 kilogram (equal to the
daily absorption of carbon dioxide by 214,115 mature trees). It will bring benefit to combat the
climate change problem.
Research team’s insight
Dr Yau Yiu-hung, one of the research team members and course co-ordinator of
OUHK’s environment and safety programmes said that their team took six months to complete
stage one of the study and identified the most ideal species of microalgae for treating sewage and
producing biodiesel effectively. The experiment took place respectively at the laboratory and the
shopping centre with significant result. Since the Algal Culture Reactor was set beside the
decomposer at the mall, the researchers could directly conduct the treatment on filtrate and utilize
the carbon dioxide emitted from the decomposer. As for the next stage, the team will further study
the components of the filtrate, come up with the most optimal conditions, taking into account of
efficiency, time for treatment, energy produced, space and economic benefit, to let the microalgae
grow properly.
Another team member, Dr Fred Lee Wang Fat, Assistant Professor of OUHK’s testing and
Certification programmes said, besides refining for algae biofuels, some microalgal species
contain some polyunsaturated fatty acids, e.g. docosahexaenoic acid (DHA), which is favorable to
the brain development of infants. Possessing the characteristic of polyunsaturated fatty acids, it
can also be made into very cost-effective algae nutrition products, and even can be used to
produce pharmaceuticals, cosmetics, and food etc. Therefore it has very high development
potential. 'The OUHK research team is also actively exploring the possibility from microalgae on
producing DHA which helps the brain development of the infants and Omega-6 of fish oil.
Dr Steven Xu Jingliang Steven explained, ‘microalgae exist in freshwater and seawater
ecosystems. In fact, they are the culprits who caused harmful blue-green algal blooms in
Mainland China, and contaminated water supply systems in North America and Australia. In
Hong Kong and South China Sea, they are the causative agent of red tides. There are over a
hundred species of algae exist in the OUHK algal library. The Open University of Hong Kong,
after years of study, has become one of the authoritative research institutes in research area of
microalgae organisms. The use of non-toxic microalgae species in sewage treatment associated
with biofuel production is a process to convert harm into benefit.'
In addition, one of the research team members, Mr. Wong Yee Keung, assistant lecturer, is
one of the council members of "Association on Harmful Algal Blooms in the South China Sea". A
team led by Mr. Wong recently developed a new "Algal Culture Reactor" and won the
championship in the Hong Kong Institute of Engineers (HKIE) Environmental Project
Competition 2013–2014. It denotes the remarkable achievement of the OUHK research team in
this area over the years.