Standard vs Custom Battery Packs - Decoding the Power Play
Waste to energy
1. Waste to Energy
TOPIC: WASTE CONVERSION CASE STUDY
Presented By:
Ms. T Fahima Firdouse (19PEF002),
II-M.E Food Technology,
Department Of Food Processing And Preservation Technology.
Mrs.R.Chitra (Ap/ss),
Department Of Electronics And Communication Engineering,
Avinashilingam Institute For Home Science And Higher Education for Women,
Coimbatore.
2. TABLE OF CONTENTS:
Introduction
Waste and resource action programme(WRAP)
UK Preferred technology
A Case for Success
SUEZ’s advanced anaerobic digestion process unit
Process of waste conversion
Conclusion
Reference
3. INTRODUCTION
United Kingdom households generate 7 million tons of food waste per year, a majority of
which (4.2 million tons) is considered avoidable, meaning it was edible prior to being
thrown away.
Curtailing food waste has been on the government’s radar for decades; in 1999, the
European Union announced the European Landfill Directive, which, aims to reduce
reliance on disposing of organics in landfills.
The target for member states is to divert 65 percent of organics by 2020.
4. In the UK, the directive has promoted many waste reduction initiatives that span the
food supply chain.
From manufacturing to consumption, entities are voluntarily taking steps to drive
change in how products are designed, produced, sold, consumed, and re-used or
recycled. This evolution is also driving change in the waste management industry.
5. Waste and Resources Action Programme (WRAP)
According to the Waste and Resources Action Programme (WRAP), avoidable food
waste in the UK was responsible for generating 20 million tons of carbon dioxide
(CO2) equivalent in 2016, representing 3 percent of the UK’s domestic
greenhouse gas emissions and equivalent to the amount of emissions produced
by 7 million cars per year.
Capturing and processing food waste holds valuable opportunity, to recover
renewable energy and mitigating the detrimental environmental impacts of disposing
food waste in the same manner as non-organics.
6. UK PREFERRED TECHNOLOGY
Alternative treatments to process food waste and mixed solid waste (MSW) are plentiful and include
technologies such as gasification, pyrolysis, plasma and biological drying.
Anaerobic digestion, however, is a preferred method that is currently used to treat 1.78 million tons
of UK food waste per year.
This treated waste produces just under 60 MWe of renewable electricity, which is predominantly
sent to the national grid.
One of the biggest benefits of anaerobic digestion is that it is considered a recycling method rather
than energy recovery, ranking higher on the UK’s waste management hierarchy.
7.
8. A Case for Success
The Bridgewater Advanced Digestion Facility in Walpole, UK is one example of a plant
that uses anaerobic digestion to process food waste.
Owned and operated by Viridor Waste Management, Bridgewater ADT treats around
20,000 tons of residentially source segregated food waste (SSFW) from the Somerset
Waste Partnership, which jointly manages waste collection from all 239,000 homes in
Somerset, UK. .
9. Overall the plant design capacity is up to 30,000 tons per year to handle any
future increase in collection.
The plant employs SUEZ’s advanced anaerobic digestion process, which
includes pretreatment to separate organic content from the contaminants in the
SSFW stream. The pre-treatment technology was used and converts incoming
solid SSFW into a digestible slurry, which is fed to downstream anaerobic
digestion
10. “The Bridgewater Advanced Digestion Facility is a
product of Somerset County’s partnership with Viridor
Waste Management to recycle household food waste into
methane gas to generate clean, green power for homes
and businesses, and fertilizer for the local agricultural
community”.
12. PROCESS OF WASTE CONVERSION
The first step in the process is the mentioned pre-treatment, whereby raw SSFW received
at the facility is sent through SUEZ’s RE:Sep process.
The SSFW is fed into a shredder where it is broken down into smaller pieces.
Depending on the nature of the SSFW, the dry solids content can be 20 to 30 percent.
Once shredded, the SSFW is conveyed to turbo dissolvers where liquid is added to bring
the dry solids content down to promote blending of the organic material into a
homogeneous slurry (solid particle are uniformly distributed in liquid medium).
13. The SSFW slurry leaves the turbo dissolvers and flows by gravity to the first step of contaminant
removal.
The slurry is passed across a rotary drum screen, removing all contaminants and packaging larger
than the screen opening. Heavy contaminants such as metal and stone settle in the turbo dissolvers,
which are periodically removed.
For maximum recovery, the reject fraction from the screen is conveyed to a second step organics
capture. At this step, a hammermill uses direct force on materials to press and pulverize material
fed to it, resulting in the separation of any attached organics to the contaminants, as well as
producing a slurry from large, hard organics.
14. The organic slurry passes through the screen inherent in the hammermills and is
combined with the slurry flow from the rotating drum screen previously mentioned.
Reject material from the hammermill is the only contaminant stream coming from the
RE:Sep system, and is typically quite dry at over 50 percent dry solids content.
The combined slurry then travels through a grit channel where the velocity is slowed
and at roughly 10 percent solids content, the grit settles out. To improve grit removal,
however, in an effort to prolong the life of downstream equipment, a hydrocyclone was
added to the pre-treatment process to assist with grit removal.
15. The clean slurry is pumped to a hydrolysis buffer tank where it is held for four to
five days to provide equalization volume and to ensure continuous feed to the
downstream digester.
Hydrolysis and acidification occur creating a low pH environment, pre-conditioning
the slurry for maximum digestion.
Prior to digestion, the slurry goes through a final pre-treatment step, of
pasteurization through the Monsal* 70 pasteurization process. In pasteurization, the
slurry is held at 70°C for one hour to comply with the UK Animal By-Products
Directive.
16. The pre-treated slurry is then sent to the site’s 4,000 m3 mesophilic anaerobic digester, which
is a continuously stirred tank reactor, maintained by the Monsal Sequential Gas Mixing
System. With a retention time of 18 to 22 days, the digester converts the organic food waste
slurry into 12,000 m3/day (300 scfm) of biogas.
The biogas is collected and used in two GE Jenbacher+ combined heat and power (CHP)
engines that produce renewable electricity and heat. The design plant capacity is 1.5 MWe per
30,000 tons of food waste.
Residual digestate is dewatered through an onsite centrifuge, creating a digestate cake that is
approximately 25 to 30 percent dry solids by weight..
17. The inherent nutrient content of the feedstock is carried throughout the entire process
and is concentrated in the cake, which can be used as a nutrient fertilizer on agricultural
land. Furthermore, as all of the material have undergone pasteurization, use is not
restricted.
As mentioned earlier, liquid is added to the turbo dissolvers in the RE:Sep process.
Considering the high strength of the centrate, it is treated in a sequential batch reactor
(SBR) to degrade ammonia and COD.
18. Anaerobic digestion for SSFW from residential collection, the described plant
design is applicable to a wide variety of food waste sources.
Anaerobic digestion in the UK has been very successful, however some of that
success must be attributed to the forethought of government and legislators to
incentivize its use. Similar trends can be seen throughout Europe thanks to the
influence of the European Union’s Landfill Directive
19. CONCLUSION:
Larger challenges for adoption exist in countries where legislation and incentives are not
widespread.
North America would seem to be a prime market for anaerobic digestion of food waste; however,
the economic model for a sustainable plant is not yet robust.
Still, the global trend towards adoption of anaerobic digestion of food waste is upward.
Anaerobic digestion offers a sustainable waste solution.
By capturing and degrading organic waste in a controlled environment, waste providers and
municipalities can ensure a cleaner environment while contributing to a much larger effort to
reduce and reuse.
