Study on compact device for waste processing based on mechanical biological treatment in Dong Van town, Duy Tien district, Ha Nam province, Vietnam

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ĐẠI HỌC QUỐC GIA HÀ NỘI TRƯỜNG ĐẠI HỌC KHOA HỌC TỰ NHIÊN ------------o0o------------ NGUYỄN VĂN THÁI STUDY ON COMPACT DEVICE FOR WASTE PROCESSING BASED ON MECHANICAL BIOLOBICAL TREATMENT IN DONG VAN TOWN, DUY TIEN DISTRICT, HA NAM PROVINCE, VIETNAM CHUYÊN NGÀNH: QUẢN LÝ CHẤT THẢI VÀ XỬ LÝ VÙNG Ô NHIỄM (CHƯƠNG TRÌNH ĐÀO TẠO QUỐC TẾ) LUẬN VĂN THẠC SĨ CÔNG NGHỆ HÓA HỌC NGƯỜI HƯỚNG DẪN KHOA HỌC: PGS. TS NGUYỄN THỊ DIỄM TRANG HÀ NỘI- NĂM 2007 HANOI UNIVERSITY OF SCIENCE DRESDEN UNVERSITY OF TECHNOLOGY NGUYEN VAN THAI STUDY ON COMPACT DEVICE FOR WASTE PROCESSING BASED ON MECHANICAL BIOLOBICAL TREATMENT IN DONG VAN TOWN, DUY TIEN DISTRICT, HA NAM PROVINCE, VIETNAM MASTER THESIS Field: waste management and contaminated site treatment Supervisor: Assc. Prof. Dr. Nguyen Thi Diem Trang HANOI, DECEMBER 2007 INTRODUCTION The rapid economic development has resulted in the difficult task of identifying way to manage the increasing waste generation, especially solid waste problem. Solid waste is generated from production and life activities in all sectors such as households, industry, hospitals, commerce, and agriculture. Vietnam, a developing country, is certainly facing with a big problem of rapid waste generation. Therefore, finding out effective solutions of waste management and treatment has become an important issue in Vietnam. Actually, the Vietnamese government has tried to carry out preliminary steps in order to control waste generation in recent years. However, most of these steps just focus on available technologies in large-scale applications in industrial cities. Whereas waste treatment technologies in small-scale applications has not been paid much attention. The main reasons are due to high cost and skillful requirements of operation and management. Moreover, there has not any effective waste management model for small capacity in townships where the population is not so big and amount of waste is 20 – 40 tons/day [Dong Van URENCO, 2006]. If waste management does not implement well in these areas, risks from pollution will, as a result, be highly serious. Therefore, finding out the best solutions to protect environment is a very necessary and urgent matter in townships. Taking that serious problem into account, one of model companies named Hydraulic and Machine Company Ltd. has completely manufactured an effective system, which was named Compact Device, for municipal solid waste treatment (so-called CD-Waste System). This system was designed based on mechanical biological treatment system which has been applied since long time before. It has considered to be suitable in small-scale applications in townships. Besides, another company named Dong Van Urban Environment Company Ltd. has also been established in Dong Van town, Hanam province in order to respond to national 1 policies of socialization in environmental protection. The two companies have closely cooperated to implement a project named “Waste Collection and Treatment System Using CD-Waste Technology with Capacity 20-30 tons per day” in Dong Van town, Duy Tien district, Hanam Province. Based on this project, I had carried out this study named “Study on Compact Device for Waste Processing based on Mechanical Biological Treatment in Dong Van town, Duy Tien district, Hanam province, Vietnam” . This study aims at:  Completion of clearness about theoretical and practical issues from CD- Waste Technology applications.  Assessment of CD-Waste Technology applicability in Dong Van town, Duy Tien District, Hanam Province  Cost planning and pre-calculation of waste treatment Plant in Dong Van Town, Duytien District, Hanam Province. 2 Chapter 1: OVERVIEW 1.1 Waste 1.1.1 Definitions and concepts The term waste is defined in the Vietnamese law on environmental protection of November 29 th, 2005. According to this definition “Waste means materials that take solid, liquid, gaseous, or other forms, are discharged from production, service, daily life or other activities [Environment law, 2005]. Municipal solid waste (MSW) includes the solids discarded by the end of consumers, i.e. private households, small business and public areas and typically collected by public authorities for disposal. Normally, separated collected waste for recycling such as paper, metals, aluminum, glass etc. is included in the MSW quantities given. MSW refers specifically to that part of MSW which is sent to landfill, incineration, or other final treatment [Christian Ludwig et al., 1999]. Waste management refers to all activities engaged with waste segregation, collection, transport, reduction, reuse, recycling, treatment and disposal [Environment law, 2005]. 1.1.2 Waste generation in Vietnam Solid waste generation in Vietnam is approximately 15 million tons per year. Among them, municipal waste generation is about 12.8 million tons (making up 80%), and industrial and agricultural waste generation normally contribute the rest 2.2 million tons per year (making up 20%) as shown in figure 1 [VEM, 2004 ]. 1.60% 17% municipal waste 1.40% hazardous healthcare waste industrial waste others 80% Figure 1: Different waste generated (by percent) in Vietnam, 2003 3 In Vietnam, big and industrial cities are major waste generation sources. According to national statistical report in 2004, big cities and urban areas keep only 24 percent of the total nationwide population; however, they produce over 6 million tons of municipal waste (making up 50% of nationwide municipal waste amount). This is due to an affluent lifestyle, larger quantities of trade and commercial activities, and more intense industrialization and urbanization. Along with, these activities also increase high proportion of hazardous waste (such as batteries and chemical solvents) and non-degradable waste (such as plastic, metal, and glass) normally found in municipal solid waste. In contrast, people living in rural areas make up 76% of the total nationwide population but produce just less than half of waste generation rate of those in urban areas. As shown in waste generation rate is approximately 0.3 kg/cap/day in rural areas compared to 0.4 kg/cap/day in urban areas. Table 1: Municipal solid waste generation at the glance [VEM, 2004] Municipal solid waste generation (tons/y) • National • Urban areas • Rural areas 12,800,000 6,400,000 6,400,000 Municipal waste generation (kg/per/day) • National 0.7 • Urban areas 0.4 • Rural areas Collection of waste (% of waste generated) 0.3 • Urban areas • Rural areas 71% <20 % • Among urban poor 10-20% Number of solid waste disposal facilities • Dumps and poorly operated landfills • Sanitary landfills 74 17 Generally, comparing to the standard on domestic solid waste (DSW) in other countries, the amount of domestic in Vietnam is much lo wer [Luu Duc Hai, 2001]. Forecasting in 15-20 years, domestic solid waste amount in big cities in 4 Vietnam will reach the same level of 1.2 kg/cap/day as big cities in other Asian countries [Pham Ngoc Dang, 2000]. Waste composition varies spatially and temporally based on life and industrial activities. Each city has its own lifestyle, civilization level, and development rate. As a result, they have different waste composition. Besides, waste composition normally varies in different times of the year. For e xample, in holidays and festive occasions such as Lunar New Year, organic and yard waste ratios are commonly higher than those in the rest of the year [Nguyen Khac Kinh et al., 2001]. Generally, there are two main components in DSW in Vietnam: (i) bio -waste (making up 30-50%); and (ii) soil, sand, construction materials and other inorganic stuffs (making up 20-40%) [Nguyen Thanh Yen, 2004]. Compared to those of many other countries, increasing rates of glass, plastic, metal, paper are lower due to waste activities of potential scavengers (garbage pickers) in Vietnam [Nguyen Thuy Thu Thi, 2005]. Table 2 shows domestic solid waste compositions in some big cities in Vietnam. Table 2: Composition of MSW in some cities in Vietnam in 2002 [NEA, 2003] Unit:% Composition Organic Rubber, plastic Paper Metal Glass, ceramics Construction waste 1.1.3 Provinces, cities Viet Tri Ha Long 55.0 49 4.5 3 7.5 5 0.2 1 0.6 4 32.1 39 Hanoi 53 9 1 5 3 28 Tay Ninh 63 8-12 5-6 1-4 2-4 13-22 Municipal solid waste management in Vietnam 1.1.3.1 Waste collection Municipal solid waste collection in urban areas in Vietnam has been systematically organized. And, state-owned companies so-called Urban Environment Companies (URENCOs) in the whole country are responsible for waste collection. Each city and/or town has either one or more than one URENCOs. It depends on their size and population. Nowadays, some private companies begin 5 to take part in implementation of waste collection in some cities and towns. This trend is expanding in many urban areas in accordance to the Government‟s policy as an attraction of all economic sectors to take part in municipal waste collection and treatment. Waste collection rate has been improving, however it remains low in many cities. The national average collection rate of municipal waste in urban areas rose from 65% to 71% between 2000 and 2003. Collection rates are typically higher in larger cities, and range from 45% in Long An to 95% in Hue City in 2003 [NEA, 2003]. But in small and medium town the waste collection rate is only 20-30% of the total volume of solid waste discharged [Nguyen Loan Thi, 2003]. In addition, funding sources for the operation of waste collecting and transporting organization in urban and rural areas is somewhat dependent on the budget of local administration and contribution of households as user‟s fee (the contribution rate is decided by the local administration and often is VND 2,0003,000/person/month in major cities. Figure 2 shows the model of solid waste collection and treatment in urban areas in Vietnam in which mainly urban environment organizations collect and transport waste to landfills. Collection Waste sources Transport Collecting organization Handcart Household office school hospital market roads Transport Transfer station truck Handcart URENCOs and Environment sanitation cooperatives environment sanitation team Treat ment Transfer stations of wastes collected daily Landfills Figure 2: Model of collection and treatment of municipal solid waste in Vietnam [Nguyen Danh Son et al., 2005] 6 Besides, complete separation of solid waste at source has not yet been done widely in Vietnam at present. Waste separation at source is being experimented in some major cities (Hanoi, Da Nang, Ho Chi Minh…) and will be expand in the future to reduce the pressure for treatment of solid waste (disposal, reusing, recycling, composting etc.) 1.1.3.2 Municipal solid waste disposal Waste recovery, recycle and reuse are somewhat limited in state level. Most of the solid waste is treated by disposal at landfills. Landfills in all localities including major cities which have already been built do not reach sanitary standards and are not planned to match the rapid development of industrialization and urbanization. Of the 91 disposal sites in the whole country, only 17 are consi der as sanitary landfills [VEM, 2004]. By the middle of 2004 only half of the provinces and cities in the country (32/64) had the investment projects on the construction of sanitary landfills, of which 13 cities have already started construction [VEM, 2004]. The existence of landfills in different localities has caused urgent environmental problems to not only surrounding communities but also people in the areas where waste is collected. Incinerating waste is not a common practice in Vietnam. A few hospitals in the country have incinerators which they use but overall the healthcare industry‟s waste is primarily disposed in landfills. For the hospital waste that is incinerated, little data is available on the amount or type of waste being incinerated because they do not keep records [Nguyen, 2005]. Whatever the case, even though the incinerators are assessed by the government for technical standards and gas emissions, Vietnam lacks the technology to be able to analyze dioxin concentrations emitted by the incinerators [Nguyen, 2005]. 1.1.3.3 Reusing and recycling Reusing and recycling of solid waste are a trend of development in environmental management in general and waste management in particular. A network of recycling waste has been formed for many decades with collectors of 7 domestic waste from households (waste paper, plastic, metal and glass), dealing points of collected waste materials and recycling establishments. For municipal waste, the Vietnamese government can subsidize recycling and treatment facilities and it is important to build up municipal capacity to recycle waste. The private sector should be encouraged to manage and recycle industrial and hazardous waste, which are usually not managed by municipalities. The Vietnamese government is advocating the establishment of a new industry that is waste recycling industry. The channel of reusing and recycling of solid waste in urban areas in Vietnam can be imagined as shown in figure 3. Waste collecting groups Waste pickers on the streets Waste pickers at the landfills Sidewalk depots operators Household goods not used Itinerant buyers Recycling industry Figure 3: Channels of Municipal Waste Reuse [Nguyen Danh Son et al., 2005] 1.1.3.4 Composting and recovery Composting is a very useful form for recycling of organic wastes to produce a clean soil conditioner and could help to increase the recovery rate of recyclable materials. Composting also is a good way to reduce environmental pollution at landfill if organic waste was disposal. This could contribute to a more efficient municipal solid waste treatment, but it is not yet widespread for a number of reasons such as: inadequate attention to the biological process requirements; poor feed stock and poor quality of the fertilizers; poor marketing experiences. To support composting, the development of a strong market for intensive agriculture is necessary. The effectiveness of centralized composting facilities could increase considerably. Centralized composting facilities are large-scale waste treatment plants 8 that draw on an urban area for their organic waste supply. Several of these facilities are currently operating in Vietnam, but no data are available on their costeffectiveness (Table 3). Table 3: Status of selected Centralized Composting Facilities in Vietnam [VEM, 2004] Location of Facility Capacity (tons/day) Opened Nam Dinh City 250 2003 Hoc Mon, Ho Chi Minh City 240 1982; closed 1991 Source of Organic Waste Mixed municipal waste Mixed municipal waste 159 2004 Mixed municipal waste Cau Dien, Hanoi 140 1992; expanded in 2002 Market and street waste Phuc Khanh, Thai Binh1 75 2001 N/A Thuy Phuong, Hue Trang Cat, Hai Phong City 50 2004 Sewers, mixed municipal waste Viet Tri City, Phu Tho Province 35 1998 N/A Phuc Hoa – Vung Tau city 30 N/A N/A Status Operating. Compost provided to farmers free of charge. Closed due to difficulties in selling compost Operating. Sells compost for 1100 VND/kg to coffee and rubber farmers. Operating. Selling three products with different quality for 800, 1200, and 2000 VND/kg Operating Trial period Operating. Selling 3 products with different quality for 200, 250 and 900 VND/kg Operating The compost produced at these plants often contains broken bits of glass, metals and is therefore difficult to sell. Since centralized composting plants in other Asian countries have failed when relying on mixed municipal waste as their main feedstock, source separation initiatives are being tested in Vietnam. In Hanoi, for example, waste from markets or separated household waste from test areas are being used as clean sources of organic matter for composting plant. Thank to source separation the quality of composting product is improved. In addition, old landfills have been used as sources of income. Organic waste decomposes naturally in 9 landfills and, if it is not contaminated by glass, heavy metals, or other pollutants, it can be recovered for use as a soil conditioner. 1.1.4 Situation of Vietnamese technology for domestic waste treatment Some waste treatment technologies in large-scale applications in urban areas have been designed and installed in Vietnam. They were combined to treat solid waste, wastewater as well as polluted air. Technologies which meet Vietnamese environment standards are 1/2 - 2/3 cheaper than those of imported technologies. For example, some waste treatment plants in Vietnam have been designed and built by Vietnamese engineers such as: Dong Vinh Waste Treatment Plant in Vinh CityNghe An Province. This plant uses Seraphin technology with the capacity from 80 100 tons/day. In Hue City there is another plant named Thuy Phuong Waste Treatment Plant. It applies technology of An Sinh Company (ASC technology) with the capacity of 300 tons/day. By applying this technology, 85 – 90% waste can be recycled, and only 10-15% waste was disposed in landfills and no leachate releases [INEST, 2003]. However, the manufacture of equipments and technologies remain in private sector. Most of technologies have been designed and installed by institutes and environment centers and/or environmental consultant companies. There has no professional producing firm so far to produce environmental equipments and there has also no trademark related to environmental industry. Although, big demand on waste treatment is really necessary, capital for investment is insufficient and there has no professional investor for manufacturing, business of environment equipments. Moreover, most of waste treatment technologies have been applied in largescale in Vietnam. However, there have some difficulties during waste treatment in townships in small- and medium-scale due to the followings reasons:  Scales of applications as designed are only for treating big waste amounts (for 80-100 tons/day), whereas, amounts of waste generated in townships are around 30 tons/day. 10  High requirements of operation skills.  Lack of money for waste collection, transport and treatment [Dong Van URENCO, 2006]. Thus, it is really necessary to produce optimal technologies for waste treatment in townships. Taking this problem into concern, Hydraulic Machine Company Ltd., a company designs synchronous equipments as well as specific equipments for industries, has introduced an equipment system for waste treatment in small- and medium-scale named CD-Waste technology with small capacity of 20 - 30 tons/day. This technology has demonstrated to be effective and suitable with small-scale applications in townships [Dong Van URENCO, 2006]. 1.2 Current situation of waste management in Dong Van town, Duy Tien district, Ha Nam province 1.2.1 Introduction to Dong Van town Being a town located in the West of Duy Tien District, Ha Nam province, Dong Van covers a natural area of 383.15 ha, in which 222.82 ha is for agriculture, 47.5 ha is urban land. Total population of the town is 5,202 people including 1,344 households, in which 858 households that make up 64% are small scale industry, commerce and service, 388 households rely on agricultural based economy, making up 29%. Average income per capita is VND 4.56 million /year in 2005. And 21.61% of GDP mechanism is from agriculture and 78.39% is from industry, small scale industry and service [Dong Van URENCO, 2006]. Dong Van has advantage in traffic with train station and highway running over. It also has potentialities for industrial development and urbanization, in which a part of Dong Van is industrial zone. Industrial zone invested by 33 units and companies with more than 2000 workers. Previously, Dong Van was named as “waste town” because waste was not collected. Sanitary landfills are not planned. Landfilling was a traditional method that used to be carried out for waste collection and treatment activities of the town. Groups of environment sanitation were spontaneously established in the town. Daily 11 collection capacity was about 2.5 to 3 tons of waste. Actually, there is a landfill in town. This landfill of the town had an area of about 1,000 m 2 . It has deep of 2.5 – 3m. It is located 2km far from the town. Up to now, the covered area of this landfill is 400m2 [Dong Van URENCO, 2006]. However, because landfill does not strictly manage, serious pollution has been caused. Besides, bad odor was released, leachate that infiltrates into underground water system also cause pollution. More seriously, waste is discharged in to highway sides, it makes lots of nylon bags and the other dirty things flying to the roads. It caused dangerous for transportation vehicles on the town. Dong Van and other areas have to face up with many difficulties in waste management because there is no waste treatment system in the whole district. Moreover, the district is far from the center of province, thus it is difficult to transport waste into landfill. With this situation, a citizen in Dong Van town whose name Do Phat Trien established “Dong Van urban environment company Ltd.,” in October, 2006 trading in waste collection and treatment within the town area and other surrounding communes. This company has cooperated to Hydraulic Machine Company Ltd. in pilot operation of waste collection and treatment system with Compact Device technology (CD-Waste technology). This system has been operating for more than 10 months. 1.2.2 Dong Van Urban Environment Ltd. Company The establishment of urban environment company connecting waste collection, transportation and treatment (by using CD–Waste processing) at small and medium scale in towns is a new approach of waste management in local area. During 10 months period, Dong Van Urban Environment Company (Dong Van URENCO) is a new company, its collection scale is still small. The existing number of collection workers is 19 people and divided into three groups. 1. Waste collection group by handcrafts (consisting of seven people): collecting waste from wards, quarters and markets by handcrafts and after that waste was concentrated in certain areas 12 2. Transportation group (consisting of three people): collecting waste from collection system point on small trucks and transport to treatment area. 3. Waste separation and treatment group (consisting of nine people): carrying out visual inspection and pick up waste on conveyors, putting waste into composting tower and mature tower, moving inert waste into combustor, packaging and transporting compost materials, transporting classified nylon to sell to purchasers. Waste collection activities are taken place along streets. Waste is put in plastic buckets and placed at roads‟ sides. Collection time is from 15h –18h. With present capacity, the company can only collect waste at residential areas close to big roads and markets. The estimated collection efficiency is 50%60%. The collected waste amount is about 2.5-3 tons/day. In the first pilot period, the waste treatment using CD-Waste technology is achieved good result. It has reduced environmental pollution. Some materials are recycled and reused. This model has brought a deep change in waste management method in town. It has associated waste collection, transportation and treatment system in an enterprise. Although, CD-Waste system has just applied in small scale in Dong Van town, the effectiveness is quite good. This system was designed by Vietnamese engineering based on mechanical biological treatment method that was applied for long time in the world. However, this system has not been considered about the theoretical of mechanical biological treatment. Therefore, it is necessary to study on this system in order to reach a standard as mechanical biological treatment 1.3 Introduction of mechanical biological treatment 1.3.1 Definition of mechanical biological treatment Mechanical biological treatment (MBT) of municipal solid waste is defined as the processing or conversion of waste from human settlements (household…) which include biologically degradable component by a combination of mechanical 13 processes (eg. crushing, sorting, screening) and biological processes (aerobic “rotting”; anaerobic fermentation) [Christian Ludwig et al.,1999]. Mechanical biological treatment is primarily considered as a method for dealing with the residues of mixed waste once the dry-recyclable fraction (eg. paper, card, plastics cans, glass etc. and to an extent garden waste) has been reduced and in some cases largely removed, through separate collection systems from households. The MBT process is normally considered as a “pre-treatment” for landfill but as technologies improve and legislation becomes clearer, other applications geared more to recovery and recycling may be possible. However, MBT also plays a key role in strategies including separate collection of food waste. <4% Fe- metals Input material MSW (100%) <1% Non- ferrous metals Mechanical processing & material flow separation <4% 3540% Glass (optional) High calorific fraction (RDF) 55% organic rich material Biological treatment Anaerobic stage Optional 20% Process losses (optionally max. 10% as biogas) 35% Pre treated waste for deposition Figure 4: Flow chart of mechanical biological treatment [Christian Ludwig et al., 1999] At the beginning of the development MBT, it was applied as a pre treatment technology for residual waste before landfilling. It aimed primarily at the reduction 14 of the mass, volume, toxicity and biological reactivity of waste, in order to minimize environmental impacts from waste deposition such as landfill gas and leachate emissions as well as settlements of the landfill body. Concerning these points MBT completed with waste incineration. The recovery of reusable waste components such as metals and plastics then was only an incidental to the minimization of the waste amounts. In recent years, the recovery of waste components for industrial reuse has become an integral part in development of MBT, especially concerning the production of refused derived fuels (RDF). Thus MBT is now an integrated technology for the material flow management of MSW, where almost half of the input flow is recovered for industrial reuse and only one third remains for deposition. Figure 4 shows an example about an MBT plant to separate and to treat waste. 1.3.2 Technology of mechanical and biological treatment Mechanical biological treatment comprises several mechanical and biological process steps and combination thereof (figure 5). Mechanical separati on Waste input Size reduction Screening Metals Biological treatment Other recyclab les Mechanical separati on Inert to landfill Figure 5: Typical MBT Process [Heerman, 2002] 1.3.2.1 Mechanical pretreatment The first step of the treatment consists of a mechanical process. The main step of mechanical process is shown as following: Size reduction Size reduction is the unit operation used to reduce the size of the materials in municipal solid waste. Size reduction is used to process materials for direct use for 15 compost. It is an integral part of full-scale resources recovery facilities. It plays an important role in waste processing, since it typically is one of the first in the series of unit processes. Therefore, type and degree of size reduction has the major effect on the performance of all equipment used in subsequent handling and separation. Screening Screening segregates material of various sizes into specific particle size categories. Waste can be screened according to the size and at the same time separated based on material characteristics, assuming that the materials remain in the same particle size range. Thus screens can also be used for separation [B. Bilitewski et al., 2000]. The screen‟s efficiency rating is based on the effective separation of the screening process and is identified by the relationship between the fine fraction that passes through the screen and the fine fraction in the initial feed. Magnetic separation Magnetic separation is the most commonly used technology for separating ferrous from non ferrous metals. The removal of ferrous components is achieved by using a permanent magnetic field. It generally uses an overhead magnetic separation system that attracts ferrous material and conveys it away either perpendicular or parallel to the waste transportation direction. Density separation Density separation is a technique widely used to separate materials based on applied to the separation of shredded waste into major components: (1) the light fraction, composed primarily of paper, plastics and organics and (2) the heavy fraction which contain metals, wood, and other relatively dense inorganic materials. Therefore thank to mechanical treatment municipal solid waste is sorted, sieved, shredded, magnetically separated and homogenized. As result waste is classified in several fractions, namely reusable materials, a fraction of high calorific value, a heavy mineral fraction and a fraction rich inorganic which is readily biodegraded [Christian Ludwig et al., 1999]. 16 The main goals of the mechanical treatment are the recovery of valuable and reusable components and create the conditioning of the waste (volume reduction, particle size reduction, concentration of certain compounds) for an optimal subsequent biological or thermal treatment. 1.3.2.2 Biological treatment In the second step, a biological treatment under either oxy or anoxic conditions follows mechanical treatment. Under oxygen conditions, the fraction rich in organic matter is composted in drums or bins as well as in tunnels or windrows requiring periodical agitation (turning). Fermentation under anoxic conditions requires a closed system where resulting gases (mainly methane) can be collected. The gas can be utilized for heating or as energy source advantage of this technology. The finally residual fractions originating from the mechanical biological pretreatment can be incinerated for volume reduction and energy recovery or disposed in landfills. In this part aerobic composting will be considered. Composting is a microbial process in which organic materials are aerobically decomposed under controlled conditions to produce humus like product, compost. The composting feedstock can have a variety of sources: residences, restaurants, and other commercial establishment, and agricultural sources among others. The use of aerobic composting has become an effective landfill diversion tool for organic materials and a viable recovery and management option for municipalities. Composting system of various types has become an important part of many integrated management systems. When composting is implemented, there are some factors effecting on composting process. Nutrient Since the decomposition of organic substances is performed by microorganism, a balanced nutrient ratio is required. Therefore, in addition to the decomposable organic substances, the following mineral substances are also desirable: 17  Nutrients (e.g., nitrogen, phosphorus, potassium),  Trace elements for microorganisms and plants,  Alkaline buffers for the neutralization of CO2 and organic acids,  Adsorption surfaces for the intermediate and final products of the decomposition process,  Growth media for numerous type of microorganisms [B. Bilitewski et al., 2000]. Moisture The presence of waste is necessary to the composting process, however the balance of water to solids is a delicate parameter that can have a large impact on aerobic activity. For the purpose of composting and organic feedstock analysis, moisture content is expressed as the weight of water as a percentage of the total or wet weight of the material Moisture content = [(wet weight – dry weight)/wet weight] * 100 The literature reports a variety of ranges for optimum moisture content. This number greatly depends on the type of feedstock, its particle size and the rate and type of composting desired. Generally, ranges of 50-60% are desirable [Christian Ludwig et al., 1999]. Moisture contents above 65-70% interfere with desired oxygen levels. If the moisture content drops below 45- 50% it will interfere with microbial activity. C:N ratio There is a significant amount of data and information in the literature recognizing the importance of the carbon to nitrogen ratio (represented as C:N) to the composting process. Attainment of an adequate ratio will produce significant biological activity and minimize the potential for odors. A ratio between 25:1 and 35:1 is generally agreed upon as optimal for composting [Andi. F.et al., 1997]. In the case of a heterogenous feedstock, the combination of many materials of varying C:N ratios can be balanced to produce a mix with an overall ratio in the desirable range. If there is too much carbon, biological activity will decrease‟ if there is too 18
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