Contamination of Glass in Single Stream Recycling System
Typically, the glass contaminants are pottery, ceramics, Ovenware or Pyrex type of materials. The glass mixed colors, particularly the clear/green/amber or green/amber may be problematic at times although they work closely with their supplies in minimizing this. As noted before, the small amounts of amber/clear mixed glass or green/clear mixed glass can be accepted in making amber or green bottles (Fitzgerald et al., 2012). The recycled glass cullets quality receivable from the local MRFs have been good largely with a local single-stream MRF (Tennis Sanitation) with the provision of very good materials to them.
With respect to the considerable reduction in the color-separated glass cullets amount received, the single-stream recycling can be cited as most important factor for this decline. The color-separated glass has been seen as a significant drop that have been from the companies utilizing the single-stream recycling methods and it must be noted that major quantity of the glass is mixed and broken during the processing and/or collection of materials (Kinsella and Gertman, 2008).
When contaminants like pottery, ceramics, and other materials enter the screening process at the manufacturing facility of the glass container, two problems can arise. Firstly, as there have been different chemical and physical characteristics of these materials in comparison to the bottle glass, their meting takes place at an uneven rate or sometimes they dont melt at all. The problems are caused because of this in the melt furnace (formed of slag and clinkers) which can be carried over to the Refiner (Morawski, 2010). When the molten glass that contains ceramics or other materials un-melted chunks goes through the sheer, there can be jamming up of the sheer blades that stop that part of the operation. The whole manufacturing line stops for repairing or un-jamming the sheer that causes a production shutdown. There is need for equipments to be cooling down in correcting the problem and then again be started up (Beck, 2005). Although this downtime may be subject to minimization to less than 30 minutes, typically these events occur3 to 5 times a week that causes a considerable accumulated downtime amount.
Secondly, the contaminants gets into the operation with the off-spec run of containers production. Off spec can be because of the containers physical flaw (foreign materials apart from the container glass) or the containers color (mixed color or the foreign materials container glass) (Tim Goodman amp Associates, 2006). When a off spec glass containers batch is made, frequently this will be requiring disposition of the batch and the requirement of a new run in replacing the off spec containers. This shall be adding up to lost production time and higher costs.
Following containers including the glass separable by Disc Screens from the fiber materials, there is continuation of all containers to the Glass Breaker Screen. The designing of the Glass Breaker Screen separates glass from other materials such as metal cans, milk cartons, and plastic bottles. It provides allowance for the crushed glass in falling between discs, while the remaining containers (i.e. metal, aluminum, and plastic) and fiber do passing over the top. It also has the provision of glass cullets to be more the uniform sizing for remanufacturing stemming from optical separation (Berenyi, 2007). Then the light contaminants (i.e. light debris, fiber etc) are eliminated by the Air Knife in maximizing the quality of the end product. Lastly, identification of Optical Sorter has been with the pre-determined material(s) with the use of optical technology (for example, sensors, lasers, and cameras) and glass cullet is sorted by color.
Contamination of Plastic in Single Stream Recycling System
The attributes increasing the contamination to plastic are the single-stream recycling systems. Another factor that contributes to feedstock contamination is the storage and poor operating practices at some MRFs. There have also been problems observed by the recyclers in a range of MRFs that includes processing facilities that is source-separated (Sidique et al., 2010). If enough attention is not paid to the sorting process such as manual and lackadaisical sorting, without right separation equipment (aluminum and ferrous recovery systems), and the storage of the materials outside where the contaminants can be picked up or the weather conditions such as sunlight, snow, or rain can degrade the plastic (Oskamp et al., 1991).
It can be expected that the most problematic contaminants are inclusive of the metal and glass (Sidique et al., 2009). The plastic grades that are unacceptable can be easily sorted out although removing metal pieces and glass shards are much more difficult as they are mixed or embedded in with the plastic containers (Vicente and Reis, 2008). Amongst the operational problem types, these contaminants are responsible for
Breakage and wearing of blades of shredders and grinders because of glass and metal
Greater degree of sparking when the lumber cutting takes place because of pieces of metal in the extruded lumber
Wearing on motors, extruders, grinders, and screens that results in higher maintenance costs
Glass gets into bearings under belts or convey
Pieces of metal and glass in the end product that leads to the issues of product quality
Maintenance costs are higher overall and downtimes greater facility because of the cleaning and repairs (Lakhan, 2014)
As per the reports of the plastic processors, single-stream MRFs materials have the rate of yield to the extent of 68-70 percent. The polyethylene terephthalates Bales emanating from the systems of deposit return usually have a rate of yield of around 85 percent. While, seemingly yield differential of 5-10 percent may not be a very high percentage, considering the annual capacity of a facility is of 60 million pounds per year, the lost yield of every one percent represents a production of new waste to the tune of 50,000 pounds that will lead to value to the processor loss of 7,500 per month which can also be considered as additional cost per month. The mean loss of yield of the MRFs is only 5 percent because of poor quality and the loss of 37,500 per month, without the inclusion of cost to send these residuals to disposal (Reid and Khuong, 2001).
Contamination of Aluminum in Single Stream Recycling System
From the glass breaker screen, there is conveying of the overs to an optical sorter recovering PET. There is conveying of the remaining stream to a second optical sorter removing all HDPE colors. There is proceeding of the remaining stream for ferrous recovery to a magnet (Callan and Thomas, 2006). The remaining material after the magnet for aluminum recovery makes its proceeding to an eddy current separator. The residual stream remaining goes to a manual sort, where the separation equipment is missed by the recyclable materials and there is recovery of the separation equipment by pickers and sending it to the 2-way baler. Transportation takes place of all non-recovered material offsite for closing disposal.
The aluminum, PET, HDPE, ferrous streams are separable and storable in cages before the baling. There is inspection of each stream before baling for contaminants. Combination of the contaminants takes place into residual stream that for final disposal are sent offsite. Throughout the facility, the rolling stock is usable for moving the material. No modeling has been done to the rolling stock equipments individual pieces. Instead, there is usage of all rolling stock fuel with use of a single coefficient in L fuel units per incoming Mg.
The reports of aluminum have issues that are similar to that of plastic having association with single-stream MRFs (Lehrburger et al., 1991). One of the biggest aluminum can recyclers and aluminum rolling producers, Novelis has provided explanation that voluntary supplier action has failed to yield measurably improved quality. This has been consistent in the time of 20072008 commodities boom, when supplier profit and material revenue much exceeded historical standards. This has resulted in Novelis implementing for poor suppliers a financial penalty and discounted the prices paid by 10 cents per pound. Seemingly this was a rigorous measure as Novelis was not fully compensated by the surcharge for the profit losses because of the low productivity from the materials that were substandard. During the recent times, several suppliers left and a number of them were being redirected to a special facility of offsite cleaning, where there will be application of markedly lower prices in offsetting the investment return and operating costs of the site. This highlights the seriousness of the company about non-acceptance of the low quality material.
Contamination of Paper in Single Stream Recycling System
All recyclables, in SSR, in one collection bin have been commingled and the papers contamination by the streams (plastic, glass, and metal) other recyclables that has been a challenging problem. The heavyweight contaminants are being separated regularly by the MRFs, such as steel cans, plastic container, glass etc., with the use of screening and cleaning process. The MRFs have several stages that have been designed in removing any trapped metals (Lantz, 2008a). The recycling papers most challenging task is the removal of specific materials such as polymer materials including plastics called the stickies. Thousands of tiny particles can be created by a single plastic bag whose removal is quite challenging by cleaning or screening. If these plastics small particles end up in the sheet of paper, the deficiencies are caused and downgrading the product quality. If the material levels exceeds the maximum amount specified for each paper grade, the fiber material recovered cease to be tolerable. This can lead to the downgrading of the lower paper grade that results in a lower selling price (Lasmarias et al., 2003), or it s classification becomes valueless and its appropriateness is only for disposal. When to the landfills, the paper of poor quality has to be sent, the costs of papermaking for paper mills augments as they have been handling materials not usable in the process (Lantz, 2008b).
One more important concern is the single stream recovered paper in relation to the mixing of the paper grades, bleachable material combined with un-bleachable material. The bleaching enhances the pulps brightness in the paper mills in yielding the printing papers of high quality (SCA, 2010). In case of working with recycled paper, the produced papers quality is less compared to the ingredient paper as there is gradual shortening of the fibers following recycling repeatedly and becoming weaker. The land costs are also added to the high contamination of the paper processors/mills (Miranda and Blanco, 2010).
References
Beck, R.W. (2005) Pennsylvania Recovered Material Study Pennsylvania Department of Environmental Protection Philadelphia, PA, USA.
Berenyi, E. (2007) Materials Recycling and Processing in the United States 20072008 Yearbook and Directory Governmental Advisory Associates, Inc. Westport, CT, USA.
Callan, S.J. and Thomas, J.M. (2006) Analyzing demand for disposal and recycling services A systems approach, East Econ. J., 32, 221240.
Fitzgerald, G., Krones, J. and Themelis, N. (2012) Greenhouse gas impact of dual stream and single stream collection and separation of recyclables, Resour. Conserv. Recycl., 69, 5056.
Kinsella, S. and Gertman, R. (2008) Single Stream Recycling Best Practices Implementation Guide Conservatree San Francisco, CA, USA Environmental Planning San Jose, CA, USA.
Lakhan, C. (2014) Exploring the relationship between municipal promotion and education investments and recycling rate performance An Ontario case study, Resour. Conserv. Recycl., 92, 222229.
Lantz, D. (2008a) Metro Waste Paper Recovery Study, Resour. Recycl., 12, 2430.
Lantz, D. (2008b) Mixed results. Do the advantages of single-stream recycling hold up in a head-to-head comparison An examination of several single-stream and dual-stream programs tell the tale, Resource Recycling, 15.
Lasmarias, V., Sharma, S., Kortmeyer, J., Biza, P. and Gaksch, E. (2003) Removal of contaminants from recycled paper fibers, U.S. Patent Application No. 10/409,597.
Miranda, R. and Blanco, A. (2010) Environmental awareness and paper recycling, Cellulose Chemistry and Technology, 44(10)43149.
Morawski, C. (2010) Single Stream Uncovered, Resour. Recycl, 3, 1739.
Oskamp, S., Harrington, M.J., Edwards, T.C., Sherwood, D.L., Okuda, S.M. and Swanson, D.C. (1991) Factors influencing household recycling behavior, Environ. Behav., 23, 494519.
SCA (2010) Papermaking online Available from http//www.sca.com/Global/Publicationpapers/pdf/Brochures/Papermaking.pdfSidique, S.F., Lupi, F. and Joshi, S.V. (2009) Factors influencing the rate of recycling An analysis of Minnesota counties, Resour. Conserv. Recycl., 54, 242249.
Sidique, S.F., Lupi, F. and Joshi, S.V. (2010) The effects of behavior and attitudes on drop-off recycling activities, Resour. Conserv. Recycl., 54, 163170.
Tim Goodman amp Associates. (2006) Single-stream and Dual-stream Recycling, Comparative Impacts of Comingled Recyclables Processing, Minnesota Pollution Control Agency Minneapolis, MN, USA.
Vicente, P. and Reis, E. (2008) Factors Influencing Households Participation in Recycling, Waste Manag. Res., 26, 140146.
Lehrburger, C., Mullen, J. and Jones, C. V. (1991) Diapers Environmental Impacts and Lifecycle Analysis, Report to The National Association of Diaper Services in Philadelphia, Pennsylvania.
Reid, G. W. and Khuong, C. H. (2001) Energy Conservation Through Source Reduction, Municipal Environmental Research Laboratory, Cincinnati, U.S.
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