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Management & Engineering 03 (2011) 1838-5745
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Management & Engineering
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Mode of Developing New Energy Sources: Garden Waste to
Produce Ethanol Technology
Zhi Li, Lijun Sun
School of Economics and Management, Beijing Forestry University 100083, China
KEYWORDS
ABSTRACT
Garden waste,
Garden waste for ethanol
production technology,
New energy development model
Nowadays the main processing methods about the garden waste recycling, such as
incineration, landfill, composting, and rough, still have some defects and problems. On the
basis of extensive experiments on the garden wastes, we are introducing a new technology to
produce ethanol by garden waste ,which can not only make full use of garden waste and
reduce maintenance costs of urban greening, but also provide a new energy development
model, and to a certain extent, ease the energy crisis our country. It has enormous economic,
social and ecological benefits.
© ST. PLUM-BLOSSOM PRESS PTY LTD
1 Introduction
Garden plants garden plant waste mainly refers to natural or artificial pruning litter produced by the plant debris, including wastes,
clippings, pruning trees and shrubs, with its main components of wood fiber [1]. With increasing urban green coverage, the number of
garden waste growing day by day , if we don’t treat it seriously, it will not only affects the appearance of the city, but also cause
environmental pollution. At present the basic approach is incineration, landfill, etc. Chen Xiang, Xian Xudong, Bao Bing (2009) held
the view that landfill or incineration will cause environmental pollution and resource waste, and proposed other approaches like
compost, green coverage and utilization of product development approach [2]. Lv ZiWen, Fang Hailan (2007), Liang Jing (2009),
Yang Hui (2010) introduced landscape waste treatment and disposal methods in U.S specifically, such as compost proportion,
composition and classification, collection methods, optimization of composting process parameters (e.g.particle size, humidity,
carbon and nitrogen ratio and pH value, etc.), standards of product quality and technical specifications and so on, they proposed some
recommendations such as classified collection of garden waste and garbage, set up a special court for smashing the branches,
compost to field and so on [3-5]. Beijing, as the country's capital, its green coverage had straight up in recent years, and in 2007
reached 43.0%. With the acceleration and expansion of green field, landscaping waste has become a huge source of pollution to
urban environment .In 2007, Beijing generated 2.36 million ton landscape waste, most of which was landfilled as a solid waste, and
the resource re-utilization rate is only 0.7%. In this regard, Yu Xin, Sun Xiangyang, Xu Jia (2009), through surveys, made an
empirical analysis of the landscape in Beijing and its re-use of waste, presented three approaches, that is ,the re-use composting,
production of new flowers matrix, covering the production of organic gardening. [6]
Developing new energy, carrying out industrial revolution, is an effective way to achieve sustainable development and a low carbon

Corresponding author .
Email: [email protected]
English edition copyright © ST. PLUM-BLOSSOM PRESS PTY LTD
DOI:10.5503/J.ME.2011.03.015
87
economy [7-9]. In a variety of new energy, biomass attracted the attention of many scholars, Dong Youfu, Hou Fang’an (2007) and Liu
Jianfu, Bai Yurui (2009) held that with the deterioration of the global environment and energy crisis, renewable energy represented
by enhanced solar and biomass had increasingly become the focus of attention, so we should be fully aware of the value of crop straw,
and promote the comprehensive utilization of straw [10, 11]. LiTao, Zhuo Haifeng (2008) describes the environmental pollution and
resources waste caused by incineration of straw, and proposed several measures such as straw Production of feedstaff, straw
processing, gas producing [12]. As for the way of straw utilization, scholars also discussed. Zhang Zhenhan (2006) proposed the straw
power generation and plate-making technology [13]. Xie Zuqi, Liu Jianhui (2007) proposed straw gasification technology [14].
Can we combine garden waste disposal and new energy development together and propose a new low-carbon economy model to
make full use of the biomass energy of garden waste? There are still no such studies. So, through the analysis of the experimental on
the garden waste such as weeds and sawdust , we are exploring the this new energy technology development ,which is to use garden
waste to produce ethanol.
2 The Status of Garden Waste Recycling
United States, Canada, Belgium and Australia and other countries have made a very good use garden waste so far. In the U.S., urban
greening has come out of the traditional methods and been replaced by producing renewable soil, compost instead of natural soil in
city greening. Many studies in United States have shown that the re-use of garden plant waste is more economical and more
environmentally friendly than landfill and incineration. According to statistics, the cost of puting garden waste into landfill is 350
dollars, the carbon dioxide produced by the burning of garden waste a ton is 230 kg, so many states in US have enacted laws relating
to the funding security measures to implement garden waste recycling. Because of the protection policy and funding, the garden
waste recycling ratio in the United States increased each year from 12.4% in 1990 to 62.0% in 2005.
In 2007, Chao Yang District in Beijing established the first domestic large-scale professional garden plant waste disposal site. After
reduction treatment and a series of manufacturing processes, waste disposal sites can produce the necessary bio-organic fertilize ,
organic substrates ground cover and other products in the urban greening. In addition, Guangzhou, Shenzhen and other economically
developed regions have started the garden waste recycling as well. Management Office in Shenzhen City has been operating for 11
years since 1998. The amount disposed by the Crush site is very large.
3 The Problems of Current Methods
Current treatment of plant wastes are incineration, landfill, composting, and rough and so on.
3.1 Incineration
Burning garden wastes can produce large amounts of harmful gases (such as nitrogen oxides), which pollute the atmosphere. Besides,
it can bring a large number of carcinogenic particles (such as dioxin, trip-benzopyrene and quadr-benzopyrene), which do harm to
human health, so this kind of approach has been gradually prohibited in recent years.
3.2 Landfill and composting
Landfill disposal and composting wastes is still the common means. Composting refers to the occurrence of biochemical degradation
and the formation of organic fertilizer by the use of microorganisms in a certain temperature, humidity, pH and other conditions.
Garden organic waste is rich in N, P, K and other nutrients. Through composting and other treatment ,it can be used as fertilizer in the
soil, which can effectively restore soil nutrients, increase soil organic matter content, stimulating microbial activity, improve soil
physical structure and chemical composition, increase soil porosity, and enhance soil capacity to retain water and fertilizer. At present,
major cities such as Shanghai, Beijing, Guangzhou and Shenzhen, have started composting of the garden waste
However, as garden wastes contain less water and are light in weight, the transport and removal costs may increase through the
landfill. In addition, landfill and composting sites need a large space and a long fermentation period and the degradation and
transformation is not complete, this method will not only bring about secondary pollution, but also lead to other security issues.
3.3 Plate
National attitudes to protect forest resources become increasingly clear, measures such as cutting of forests to limit and logging ban
have been taken more seriously. In next few years China's timber harvesting will be reduced to very low commodity level, plate
production industries face enormous challenges and the supply of raw materials will become a bottleneck. To find new materials to
replace natural wood may be a way out. Wastes after rough handling, can also be pressed into sheets, but these plates crushed by
garden wastes are of loose granular material and are poor in bearing pressure, so there still be some challenges in their use and
consumer acceptance.
3.4 Feed production
Lawn can be collected and dried into hay or made into feed. However, because plant wastes and weed contain tannin, which may
cause animals’ resist. Besides, the green wastes are of lower protein content and lack in vitamins, so the bioavailability is poor and
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thus should not be used as the feed directly.
4 Garden Waste to Produce Ethanol Technology
Because of the intensification of the global energy crisis, many countries are devoted to the development and utilization of renewable
energy. Biomass energy gets people's special attention for its cleanliness and extensive usage. Bran, straw, chaff, weeds and
industrial waste, sawdust and other celluloses has not been fully utilized except that a small amount of them are made for paper.
According to foreign statistics, the total output accounts for approximately 50% of biological resources and adds up to100 ~ 50
billion t a year. The fermentation process of weed to produce fuel is shown in Figure 1.
Garden wastes
e.g. weed
Sulfuric acid
Ammonia
Cooking and steaming
SQY-1
Ethanol
H2O
SQY-2
Filtration
Filtrated waste
Filtrate
Liquid-state
fermentation
Distillation
Cellulose enzyme
Waste liquid
SSF
rectification
Yeast
Solid state
Waste
distillation
residue
SCP
Ethanol
Figure 1 Fermentation process to produce fuel ethanol
4.1 Cooking and steaming
As shown in Figure 1, mix the weed and 1% of sulfuric acid by a certain rate(solid to liquid is 1:10) at 121 ℃ for 120min, then
filtrate and wash it by hot water, which weighs 4 times of that of garden waste .As the filtrate contains some sulfuric acid, the filtrate
was re-pumped back to the cooking pot, and the waste into the solid-state fermentation pot (control the residual acidity is about
pH4.8). In continuous operation, when the system starts, add 1% of sulfuric acid. Once the operating system running continuously,
we can control the acidity by adding a small amount of concentrated sulfuric acid through the cooking process.
4.2 Fermentation and distillation
When the concentration of reducing sugar in the filtrate reaches 5%, put some filtrate into the cooking pot, and others into the
fermenting tank , and then cool it with ammonia or the neutralization of ammonium bicarbonate and sulfuric acid in the pot. As the
reducing sugar in the hydrolysis fluid during the pretreatment of corn by dilute acid is mainly xylose, put activated SQY-1 which can
ferment pentose to produce alcohol in the fermentation tank and start the fermentation at a stirring speed of 80r/min for 48h. When
fermentation is completed, put the fermented liquid into the distillation of crude distillation tower, and we will get alcohol at the
concentration of about 50% (v / v).
4.3 Fermentation and distillation in solid state
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Solid-state fermentation (Solid-state fermentation, referred to as SSF) refers to the transformation process of the biological raw
materials without free water by micro-organisms. The traditional submerged fermentation (Submerged fermentation) is to use the
diluents or suspension of raw materials for fermentation. In the SSF process, there is usually a thin layer of water on the surface of
the solid matrix and the weight ratio of water and solid substrate is between 4:1and 6:1 on average. Compared with submerged
fermentation, the advantages of SSF are: less volume of the fermentation vessel; less energy costs of sterilization; more easily
ventilated in solid substrate; less capital spending or operating expenses in wastewater treatment; less costs in the products collection
and feed drying; less risk of bacterial contamination for it is less conducive to bacteria’s growth; in Add the solid residue(weighed as
25IFPU / g dry matter) into cellulase, and activated high-temperature yeast SQY-2 as well, then start the solid-state static
fermentation after an even mixing. Take CO 2 out during the process to control the temperature, the amount of oxygen dissolved and
the heat loss. After 60 hours’ fermentation and the process of solid-state distillation, we can obtain 50% (v / v) alcohol.
4.4 Rectification
Rectify the alcohol distilled from SSF and the distillated liquid to obtain 95% (v / v) alcohol, and the alcohol obtained can be used as
fuel to solve the current energy crisis.
4.5 SCP production
As the liquid waste contains large amounts of distilled NH4 +, you can use it to produce feedings SCP. Mix the liquid residue
distillery waste with the solid ones, access yeast to produce SCP, which can not only solve the environmental pollution problems, but
also realize the comprehensive utilization of agricultural waste.
5 Conclusion
Garden waste recycling is an effective approach to achieve scientific development in landscape greening and zero emissions in
garden waste, which is consistent with the sustainable development. Using such a new technology as Garden waste to produce
ethanol can achieve the unity of ecological, social and economic benefits .As a result we should spread it in the process of new
energy development , in order to better deal with the problems in the recycling of garden waste and promote the exploration of new
energy and development of low carbon economy.
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