VIABLE SOLUTION TO REDUCE FOOD WASTE AND CONVERT IT INTO ECO-FERTILIZER

Transcription

1 VIABLE SOLUTION TO REDUCE FOOD WASTE AND CONVERT IT INTO ECO-FERTILIZER Kenny Wong 1, Michael Lui 2 Abstract: Human generate numerous kinds of waste everyday, in which the treatment of wastes causes serious problems in many countries. In Hong Kong, we generate around 15,000 tonnes of waste everyday. Though some of the wastes are recycled and reused, the remaining amount is going into our 3 landfill sites. With the continuing increase in economic activities, it is expected that the remaining landfill spaces can last for no more than 8 years if the current discharge pattern continues. Hence there is a genuine need to identify viable solutions to recycle more waste or to convert waste into useable products. Among the waste types, we generate about 3,000 tonnes of food waste from domestic and commercial users everyday in Hong Kong. Food waste creates lots of problem; among them are leathate and odour issues in landfill sites. Hence there is an increasing need to control the disposal of organic wastes (e.g. food waste) to landfills, and it creates a demand for the development of effective food waste conversion process for waste reduction. In fact, an effective food waste conversion system will not just reduce the volume of waste in order to minimize the disposal cost, but also to regain the values of wastes by transforming them into eco-fertilizers. This paper presents the development and utilization of an effective in-situ food waste conversion system that can substantially and rapidly reduce food waste by over 70% in around 25 days instead of days by the conventional composting method. It employs a rotating drum to provide thorough mixing and aeration which facilitates complete digestion. High quality organic fertilizer can be produced from this effective system. 1 Principal Consultant, Environmental Management Division, Hong Kong Productivity Council, 78 Tat Chee Avenue, Kowloon, Hong Kong. kenny@hkpc.org 2 Consultant, Environmental Management Division, Hong Kong Productivity Council, 78 Tat Chee Avenue, Kowloon, Hong Kong. michael@hkpc.org 1

2 Background Hong Kong takes the advantage on maintaining a steady growth on econmoic activities alongside the roaring pace of economic development in China. The economic growth brings also the risk on environment with the increasing demand for natural resources, such as food, fossil fuels, lands, etc. Resources from the Eco-system are used to support the huge driving force requiring for human consumption and eventually abandoned as wastes. In such, the requirements on suppression of waste generation are now considered as one of the society s responsibilities. Among the 15,000 tonnes of waste generated in Hong Kong everyday, about 3,000 tonnes are food waste from domestic and commercial users. According to the Policy Framework for the Management of Municipal Solid Waste ( ), the Government of Hong Kong Special Administrative Region has suggested to adopt the integrated waste management facilities for treatment of the generated wastes, including food waste. However, even if a centralized plant is developed to treat the food waste to be generated in Hong Kong, the transportation of huge amount of food waste across the territory to the centralized plant for treatment may not be totally viable because of the high transportation cost as well as the possible odour and leathate contamination issues during transportation. Hence there is an increasing need to control the disposal of organic wastes (e.g. food waste) to landfills, and it also create a demand for the development of effective food waste conversion process aiming at waste reduction at source. The Hong Kong Productivity Council (HKPC) has developed an in-situ High Performance Food Waste Conversion Technology with the South China Agricultural University (SCAU) in Mainland China. The merit of the technology is that it can substantially and rapidly reduce food waste by over 70% in around 25 days instead of days by conventional composting method. The process can be operated continuously to reduce waste volume and to transform waste into organic fertilizer as a valuable product. Since most of the food waste can be completely converted into Eco-fertilizer, HKPC anticipates this effective technology can help major food waste generators that are now putting extensive efforts in handling the bulk volume of food waste in their daily operation to turn their trash (food waste) into treasure (organic fertilizer). In addition to the current financial burden from the commercial and industrial sectors for the haulage of waste from their site to landfill, they will need to face the possible introduction of Municipal Solid Waste (MSW) disposal charge by the Government of Hong Kong Special Administrative Region in the near future. The adoption of this technology for 2

3 on-site treatment will immediately help them not just to reduce their cost for haulage of waste, but also help them to generate revenue by producing valuable organic fertilizer. Waste Generation in Hong Kong To provide a glance on the quantities and generation trend of solid waste and food waste in Hong Kong, the data extracted from the Environmental Protection Department (EPD) on the disposal of solid waste from Year 2002 to 2006 are shown in Table 1 & 2 3. The trend on MSW dumping is further described in Table 3. From the data, there is a slight decline in MSW but the food waste produced from commercial and industrial activities in these five years has increased tremendously from 373 tonnes per day in 2002 to 727 tonne per day in From this up trend generation of food waste, this may speed up the control measure to be considered by the Government such as the imposing of charge for food waste disposal in the commercial and industrial sectors. Table 1:- Solid Waste of Hong Kong from Year 2002 to 2006 Solid Waste of Hong Kong Year 2002 Year 2003 Year 2004 Year 2005 Year 2006 Total Quantity (tpd) Municipal Waste (tpd) (45%) Landfilled Construction Waste (tpd) (48%) Special Waste (tpd) 1534 (7%) (tpd = tonne per day) (53%) 6728 (38%) 1588 (9%) (53%) 6595 (38%) 1620 (9%) (53%) 6556 (37%) 1746 (10%) (62%) 4125 (27%) 1635 (11%) Table 2:- Distribution of Municipal Solid Waste from Year 2002 to 2006 Municipal Solid Waste (MSW) of Year 2002 Year 2003 Year 2004 Year 2005 Year 2006 Hong Kong Total Quantity of MSW (tpd) Food Waste from domestic (tpd) Food Waste from commercial & Industrial (tpd) Table 3:- Trends of dumping of various types of waste in Hong Kong Waste Type Trends Total Solid Waste Decreasing Municipal Solid Waste Average Food Waste From Domestic Average Food Waste From Commercial & Industrial Increasing 3 Data derived from Monitoring of Solid Waste in Hong Kong, Waste Statistics in 2006,

4 Treatment Options Source separation is a global trend for solid waste control. If source separation can be performed successfully, the level of contamination can be controlled to a minimum. In some countries, household types of composting machines are used for food waste reduction. Food waste is decomposed with the assistance of electric heaters under aerobic condition. Normally the composting process takes days to complete. However it may not be viable in Hong Kong since most of the households are in congested apartments of several hundred square feet and they do not have sufficient space to house this type of composting machines. In other locations of the world, there are several options to deal with the municipal organic waste as follows: incineration landfilling composting However, all these options have their drawbacks. For incineration, the biodegradable organic matters are high in moisture content which induces a quite low calorific value and it also creates emission problem. Similar to incineration, high moisture content in organic waste may induce leachate problem which imposes a higher operation cost for landfilling. Offensive odour is also an issue. Regarding composting, a poor quality of organic waste that mixes with unwanted objects like sand, batteries, chemicals, glass, etc., will affect the compost quality. The collection of food waste from domestic households requires a very sophisticated system and yet it is very difficult to ensure the collected food waste is not contaminated from other wastes, such as batteries, chemicals, glass, etc. If the food waste is contaminated, the quality of the fertilizer / soil conditioner will be seriously affected. As a start, it is worthwhile to collect and handle the food waste that is generated from the commercial and industrial sectors as it is simpler to collect the food waste from these sectors and the chance of food waste contamination is much lower. The idea for the development of a single centralized plant to treat the food waste to be generated in Hong Kong may not be totally viable, because of the very high cost for the transportation of huge amount of food waste across the territory to the centralized plant as well as the possible odour and leathate contamination issues during transportation. Hence 4

5 there is an increasing need to control the disposal of organic wastes (e.g. food waste) to landfills, and it also create a demand for the development of effective food waste conversion process aiming at waste reduction at source. In 2006, Hong Kong has generated about 265,000 tonnes of food waste from commercial and industrial sectors. Assuming all the pure food waste can be collected effectively for on-site treatment and 70% reduction in total waste amount can be achieved, hence an amount of 185,500 tonnes of solid waste can be avoided from dumping at landfills. The remaining 30% will be converted into 79,500 tonnes of the organic fertilizer. This organic fertilizer will value at about HK$100 million each year based on an average price for domestic organic fertilizer at HK$1,250 per tonne. At present, there is no large-scale food waste conversion system for commercial usage in Hong Kong. It should be the right time to draw the attention of the society to support recycling by setting up this type of waste handling facilities. The development of the High Performance Food Waste Conversion System (FWCS) by the Hong Kong Productivity Council is to target for the decentralized on-site treatment of food waste from the commercial and industrial sectors. The targeted clientele of FWCS shall include those premises where pure food waste can be collected easily, such as food factories, hotels, restaurants, wet markets, theme parks, universities, shopping malls with restaurants, hospital canteens, freight caterers, etc. Currently the only financial burden for commercial and industrial waste generators to bear is to hire garbage-dumping contractors to haul the waste from their premises to the landfills. In order to suppress the amount of municipal solid waste to be dumped at landfills, the government is planning for a series of scheme to reduce, reuse and recycle wastes, and one of which would be the charge for the disposal of municipal solid waste. For instance, the construction waste disposal charge has been implemented since the beginning of 2006 to suppress the generation of construction waste and its disposal to landfills. It is anticipated that all the solid wastes including food waste from commercial and industrial activities will be charged for disposal to landfills in the future. Based on our developed technology, standalone systems can be fabricated to deal with various waste capacities and served as on-site treatment units. Since the food waste quantity can be greatly reduced by over 70% and the remaining amount will be converted to Eco-fertilizer, the cost previously paid for the haulage of waste for dumping will be greatly reduced. In addition to the savings in haulage, the produced organic fertilizer can also be sold to domestic organic farms or even the booming China market as an income. By applying the treatment technology to the society, it would reduce the quantity of food waste to be dumped. In such, the cost required to pay for the 5

6 landfill operators to process the waste can be reduced immediately. In the longer run, the life of our landfill sites can be prolonged. Market Needs According to the Food and Agriculture Organization of the United Nations, food production will need to increase by 60% in the next few decades to support the growing of world population to some 8000 million around The demand for food production will rely on increasing of yields through intensification of agriculture. Fertilizer application currently accounts for 43% of the nutrients that global crop production extracts each year and the contribution may be as high as 84% in the years to come. The recent records also show that the international trade fertilizers totaled around 60 million tonnes for an annual value of approximately US$9,600 million (or the equivalent to US$160 per tonne). Among the major fertilizer consumption countries, China consumed 46 million tones of fertilizers in 2005/06 5, which represented an average annual increase of 6.7% of the pass 4 years. Though China is the largest fertilizer producer in the world, it still requires the import of fertilizers. Hence it is estimated that China is willing to import good quality of organic fertilizer produced from organic waste. In Practice From Hong Kong s prospective, we generate about 3,000 tonnes of food waste from domestic and commercial users everyday. Food waste creates lots of problem; among them are leathate and odour issues in landfill sites. Even if a centralized plant is developed to treat the food waste to be generated in Hong Kong, the transportation of huge amount of food waste across the territory to the centralized plant for treatment may not be totally viable because of the high transportation cost as well as the possible odour and leathate contamination issues during transportation. Hence there is an increasing need to control the disposal of organic wastes (e.g. food waste) to landfills, and it also create a demand for the development of effective food waste conversion process aiming at waste reduction at source. The Hong Kong Productivity Council (HKPC) has developed an in-situ High Performance Food Waste Conversion Technology with the South China Agricultural University (SCAU) in Mainland China. The merit of the technology is that it can substantially and rapidly reduce food waste by over 70% in around 25 days instead of days by conventional composting method. The process can be operated continuously to 4 Data derived from Food and Agriculture Organization of the United Nations ( 6

7 reduce waste volume and to transform waste into organic fertilizer as a valuable product. Since most of the food waste can be completely converted in a sophisticated biological reaction chamber, HKPC anticipates this effective technology can help the commercial and industrial sectors that are now putting extensive efforts in handling the bulk volume of food waste in their daily operation to turn their trash (food waste) into treasure (organic fertilizer). In addition to the consideration of waste volume reduction and generation of organic fertilizer, the development of the technology aimed at overcoming the following disadvantages of conventional composting of food waste: High demand on pre-sorting and grinding High demand on using dedicated microorganism Insufficient odour treatment Insufficient treatment capacity High operation cost (electricity, manpower, etc.) Based on the above, we have developed the Food Waste Conversion System (FWCS) with the operation flowchart as shown in Figure 1: Figure 1: Operation Flowchart of the Food Waste Conversion System 5 Data derived from Fertilizer Consumption Statistics of International Fertilizer Association ( 7

8 The Food Waste Conversion System (FWCS) comprises a cylindrical Digestive Bioreactor, a Condenser and a Bio-filter as the core equipment. In conventional composting system, it normally possesses high power electric mixers and heating elements within the reactor. However, extensive pre-sorting requirement of food waste is required to minimize the chance of blocking and damaging of the mixer. There is no internal moving part within the Digestive Bioreactor of the FWCS. Instead, the Digestive Reactor revolves itself to achieve thorough mixing and contact with the developed microorganism inside the reactor. Two openings designated for materials input and withdrawal are separately installed at both ends of the Digestive Bioreactor. When the food waste is completed converted into Eco-fertilizer in about 5 days in the reactor, it can be taken out from the output opening of the bioreactor. Some of the Eco-fertilizer will be placed in the curing area for around 20 days to further improve maturity, while the remaining output will be returned to the bioreactor inlet and mixed with fresh food waste such that the fresh food waste will be in contact with the developed microorganism effectively. During operation, fresh air is supplied to the Digestive Bioreactor to facilitate aerobic digestion. Exhaust gases generated from the digestion process will be directed through the condenser and bio-filter for lowering of exhaust temperature and removal of odour respectively before discharge. All the process equipment are operated in an automatic mode by a dedicated control unit. A scenery park in Hong Kong has been finding its way to raise greening standard by minimizing organic waste disposal and converting them into Eco-fertilizer in addition to the existing waste management practice by utilizing recycling bin system for the collection of papers, plastics and metals. As the park is generating two major types of organic wastes, food waste and green waste from the restaurant activities and plant trimmings respectively, they have installed a Food Waste Conversion System (FWCS) in their parking aiming at not just reducing the total amount of organic waste to be disposed, but also re-gaining Eco-fertilizer from their generated waste that can be used within their own park. This is another big step of the park to further improve their waste management strategy. Every working day, food waste generated from the restaurant and the green waste generated from the park are delivered to the Refuse Chamber by staff of the kitchen and the garden respectively. The food waste generated from the restaurant includes the pre- and post-cooked wastes, whereas the green waste includes different species within the park area. Once the wastes are delivered to site, the food waste is put into the assigned plastic containers for temporary storage in order to prevent leakage of the wastewater to the ground, while green waste is put aside waiting for shredding. The FWCS on-site is shown in Figure 2 & 3 below. 8

9 Figure 2: Food Waste Conversion System (Side view) Figure 3: Food Waste Conversion System (Front view) Upon receipt of the food and green wastes, the operator prepares the feedstock by mixing food waste and shreds green waste in a predetermined ratio for regulating of the moisture content of the input material. Then the operator loads the mixture to the Digestive Bioreactor of the FWCS. Feedstock inside the Bioreactor undergoes decomposition reaction in aerobic condition with the microorganism that has been already built-up inside the reactor. After several days of reaction, feedstock is converted into Eco-fertilizer in the controlled 9

10 environment rapidly. According to our experience, a noticeable minimization in waste quantity for about 80% can be achieved after the feedstock has undergone the rapid decomposition reaction in the bioreactor. The pre-cured Eco-fertilizer is then put in bamboo baskets and kept in the on-site curing area for further curing in ambient condition for around 20 days. At the end of the curing period, Eco-fertilizer will be sieved by using a 5-mm mesh screen to retain the finer portion. These fine materials are collected as product to be used by the park as Eco-fertilizer for landscaping application. All the larger residues will be returned to the bioreactor as part of the mixing agent together with the mixtures of food and green wastes. In effect, the FWCS can be seen as a zero-waste discharge treatment unit. The recent records on showing the amount of wastes that have been treated and the laboratory analyses about the quality of the Eco-fertilizer are respectively shown in Table 4 and 5 for reference. From Table 4, we can see that about 80% of the wastes have been reduced by the system and the rest of materials are being converted into Eco-fertilizers. In order to keep track of the product quality, a monthly grab sample of product was collected and delivered to the environment and product innovation laboratory of HKPC, an accredited laboratory under the Hong Kong Laboratories Accreditation Scheme, for analysis on the levels of nutrient and other parameters (as shown in Table 5 below). Since there is no established waste-to-fertilizer standard in Hong Kong, GB (Control Standards for Urban Wastes for Agricultural Use) of the People of Republic China are taken as a reference to assess the product quality and consistency. Table 5 shows the results of analysis of the product samples that were taken from three consecutive months and compared against the GB standards. Table 4: Quarterly Record on the amount of input and output materials to FWCS Total Materials Vol. (L) Wt. (kg) (A) Material for Startup as Seeding (B) Food Waste Added (C) Green Waste Added (D) Coarse Eco-fertilizer set aside for curing (E) Sieved Eco-fertilizer (F) Inputs (A+B+C) (G) Materials remained in Bioreactor (H) Outputs (D+E) (J) % of Reduction ([1-H/(F-G)] *100) Remarks: Average Bulk Density of Materials Food waste = 0.9 Green waste = 0.25 Eco-fertilizer (before curing) = 0.5 Final product =

11 Table 5: Laboratory Results about the quality of Eco-fertilizer (final product) Samples Batch 1 Batch 2 Batch 3 GB Parameters Based on dry weight (mg/kg unless specified) Total Solids 79% 72% 78% 65 ~ 75% ph ~ 8.5 Total Nitrogen 2.7% 2.2% 2.8% > = 0.5% Total Phosphorus (as P 2 O 5 ) 0.61% 0.14% 1.2% > = 0.3% Total Potassium (as K 2 O) 1.2% 1.3% 1.8% > = 1 % Total Organic Carbon 30% 24% 29% > = 10% Total Arsenic = < 30 Total Cadmium = < 3 Total Chromium = < 300 Total Copper NA Total Lead = < 100 Total Mercury < 0.05 = < 5 Total Nickel N/A Total Selenium N/A Total Zinc N/A In addition, the produced Eco-fertilizer has also been examined for plant growing test at the park s nursery. Three common types of the flowers that usually applied in parks of Hong Kong were tested, namely hibiscus, periwinkle and apple mint. As an example shown in Figure 4, there are significant differences on the growth of apple mint among different amount of Eco-fertilizer added. It was found that the plants have higher yields with the addition of our Eco-fertilizer. On the right hand side of the photo no Eco-fertilizer was added to the plants, while a small amount of Eco-fertilizer was added to the plants in the middle of the photo. On the left-hand side of the photo, pot mix with about 30% of the Eco-fertilizer (maximum amount among the 3 sets of plants) gave the best result in the plant growing test. Figure 4: Plant growing test 11

12 Conclusion This paper reveals that the application of FWCS stands out a viable solution on recycling both food and green wastes into organic fertilizer. Moreover, the system is in manageable size and highly mobile for transportation to suit various applications. No matter the system is installed in residential areas or commercial premises, it can achieve a higher reduction rate in total volume of food waste as well as introduce a new resource from recycled materials. The system offers a viable solution not only on reducing waste at source, but also recovers useful matters from wastes. Reference Environmental Protection Department of Hong Kong, Monitoring of Solid Waste in Hong Kong, Waste Statistics in Hong Kong 2006, 3-9. Web information of the Food and Agriculture Organization of the United Nations ( Web information of the International Fertilizer Industrial Association ( 12