August 24, 2012
By Professor George K. Criner and Travis L. Blackmer of the School of Economics at the University of Maine
The handling of waste has changed through the generations as our knowledge, technology, and economic well-being has improved. As a necessary consequence of the production and consumption of food, consumer goods and other products, our society generates a substantial volume of material. Most of this material is ultimately discarded and requires collection, reuse, recycling or disposal.
This report summarizes and discusses the results of two 2011 waste sorts conducted on Maine residential waste and makes comparisons with previous research. It includes comments on the relative ease of recycling or composting various materials.
Seventeen municipal waste programs, representing a wide range of community size, geographic location and solid waste program type, were selected to participate in this study. This sample represents 12 of Maine’s 16 counties and approximately 11 percent of the state’s total population. Most of the waste programs selected service an individual town or city, though some represent more than one municipality.
Eight of the municipalities had full or partial curbside garbage collection, and eight also had curbside collection of recyclables. Some of the municipalities had pay-as-you-throw (PAYT) programs in which residents pay for each bag of trash they discard. Three participating municipalities used single-stream recyclable collection.
Waste Sample Selection
The waste sample selection process was designed to ensure as much random selection as possible, while matching the collection system used by each municipality. At facilities where residents dropped off their garbage, the project team requested that every nth individual include their trash in the sample. The number between individuals sampled (n) was determined by the expected amount of total trash that would be dropped off that day, as predicted by the site’s facility manager. In municipalities where trash was collected curbside, an attempt was made to select from multiple neighborhoods, and again, trash from every nth household was collected. Usually this was from residences at least five houses apart. In total, ten tons of trash were collected and sorted.
The waste examined in this study is typical of what would be found in a regular 30-gallon plastic trash bag and does not include larger “bulky” items such as furniture, appliances, car tires and corrugated cardboard boxes. This non-bulky waste stream is often referred to as “baggable trash.”
The project team sorted the baggable trash into nine major categories and more than 60 subcategories. These classifications correspond to those used by other states in recent waste characterization studies, allowing for possible comparisons. As is the convention with waste management studies, all measurements were made by weight.
Waste Composition for the Nine Major Categories
Construction and Demolition Debris (C&D)
Household Hazardous Waste (HHZ)
Food waste made up 27.86 percent of the total waste sampled. Food waste, which is nitrogen-rich and highly compostable, is sometimes referred to as a “green waste.”
The other four organics subcategories accounted for 15.42 percent of the total waste stream. The two largest of these subcategories were Other Organics, composed mainly of cat litter and animal feces, and Diapers. For health and sanitation reasons these materials are not included in composting programs.
The Leaves & Grass and Prunings & Trimmings subcategories accounted for 1.5 percent of the trash sampled. This waste has a relatively high concentration of carbon, and when combined with food waste yields a carbon-nitrogen ratio well-suited for composting.
% of Total Waste
% of Organic Waste
Leaves & Grass
Prunings & Trimmings
Paper accounted for more than a quarter of the total waste collected. The two largest paper subcategories were Compostable Paper and Other Recyclable Paper. Together, these subcategories accounted for just over half of the paper waste. Trash sorters observed that paper towels and plates made up the greatest volume of compostable paper, reporting that it was not unusual to receive a garbage bag with over half of its volume consisting solely of these two items.
Remainder/Composite Paper, the third largest subcategory, includes items that cannot be easily diverted from the normal waste stream due to their heterogeneity and complexity (i.e., two materials fused together). Examples include foil-covered paperboard and wax-coated paper.
% of Total Waste
% of Paper Waste
Other Recyclable Paper
High Grade Office
Uncoated Corrugated Cardboard/Kraft Paper
Phone Books & Directories
Items made of plastic accounted for 13.44 percent of the total waste stream.
The most common plastic subcategory was Plastic Film, which constituted over one-third of the plastic waste and nearly 5 percent of the total waste. While it is possible to recycle non-food plastic film, less than 5 percent of Maine municipalities currently offer this type of recycling.
The second and third largest plastic subcategories were Remainder/Composite Plastic and Durable Plastic. Many durable plastics have the potential to be recycled, although recycling programs for these plastics are not generally available.
The remaining plastic subcategories accounted for roughly 5 percent of the total waste sampled. Many of these materials are recyclable. The combined amount of recyclable #1-#7 plastics and Styrofoam accounted for 4.74 percent of the waste stream.
Only 0.36 percent of the waste stream was made up of plastic beverage containers redeemable under Maine’s bottle bill legislation. A 2011 Container Recycling Institute publication reports that on average only 24 percent of bottles eligible for deposit are recycled in states without a bottle bill, while over two-thirds are recycled in states like Maine, where bottle bill legislation is long-established.
% of Total Waste
% of Plastic Waste
All Plastic Film
Durable Plastic Items
#3 - #7 Plastics
PET Containers (non-bottles)
Redeemable Plastic Beverage Containers
HDPE Containers (non-bottles)
Materials that could not be sorted into any other category were classified as “Other Waste.” Other waste accounted for 5.77 percent of the trash sampled.
Bottom fines and dirt accounted for less than one-half of a percent of the total waste stream. Only one bulky item was found; this was a suitcase weighing 7.8 pounds. The largest component of the other waste category was Textiles, which made up 4.26 percent of the total waste sampled. Many of the clothing items found were in wearable condition, and some in new condition. While some textile recycling programs exist, Maine municipalities may wish to increase their textile recycling options.
% of Total Waste
% of Other Waste
Bottom Fines & Dirt
Construction and Demolition
Construction and demolition (C&D) waste comprised 3.35 percent of all waste sampled. In accordance with other studies, seven initial C&D categories were utilized. Perhaps as a result of only collecting and sorting baggable waste, a large volume and variety of C&D was not found. In fact, aside from wood waste, very few items were found that did not belong in the Wood or Remainder/Composite subcategories. To simplify and make weighing manageable, an “All Other C&D” subcategory was created to encompass all of the non-wood C&D waste.
% of Total Waste
% of C&D Waste
All other C & D
Total C&D Waste
Metal accounted for 3.26 percent of the total waste stream. Tin/Steel Containers made up almost half of the metal waste sorted. Food-soiled aluminum foil, not deemed recyclable, was the largest component of the Remainder/Composite Metal subcategory. Redeemable Aluminum Beverage Containers, suitable for redemption under Maine’s bottle bill, accounted for less than one-tenth of a percent of the total waste sample.
% of Total Waste
% of Metal Waste
Redeemable Aluminum Beverage Containers
Compressed Fuel Containers
Non-redeemable Aluminum Beverage Containers
Glass accounted for 2.71 percent of the waste stream. The top subcategories, Clear Class Containers and Redeemable Glass Beverage Containers, are easily recyclable and accounted for 2.38 percent of the baggable trash sampled. Redeemable Glass Beverage Containers made up only 0.41 percent of the waste sampled.
% of Total Waste
% of Glass Waste
Clear Glass Containers
Redeemable Glass Beverage Containers
Green & Other Glass Containers
Flat Glass (uncoated)
Amber Glass Containers
Household Hazardous Waste
The household hazardous waste (HHZ) category includes unwanted residential products that exhibit one or more of the following qualities under Maine’s HHZ rules: flammable, corrosive, reactive or toxic. HHZ accounted for 1.72 percent of the total trash sampled.
Other Hazardous Waste, the largest subcategory, consisted mainly of items contaminated with bodily fluids. Paint and Batteries were also found in large amounts. Items in the Other Hazardous Waste, Paint, and Batteries subcategories accounted for over 81 percent of the hazardous waste found.
% of Total Waste
% of HHZ Waste
Other Hazardous Waste
Vehicle & Equipment Fluids
Empty Metal, Glass, Plastic Containers
Pesticides & Fertilizers
Ballasts, CFLs, & Other Fluorescents
Total Household Hazardous
The smallest of the nine major categories was electronics, accounting for just 0.92 percent of waste stream. Small consumer electronics made up 73.66 percent of the Electronics category. No TVs or computer monitors were found, which was expected as these are bulkier items not typical of baggable trash.
% of Total Waste
% of Electronic Waste
Small Consumer Electronics
Other Large Electronics
TVs & Computer Monitors
Comparison to 1991/1992 Data
Prior to this analysis, no large-scale survey of Maine’s residential waste had been conducted since 1991/1992. The previous study by Criner, Kaplan, Juric, and Houtman analyzed baggable trash collected at 14 Maine municipalities in four seasonal waste sorts. The following section compares data from these sorts with data from our current study in an attempt to identify the changes that have occurred to our waste stream over time.
Some waste components cannot be directly compared between 1991/1992 and 2011, as the studies used slightly different trash classification systems. A note of caution is also needed in regard to comparing changes in composition percentages. Percentages of all subcategories must always sum to 100, so an increase or decrease in the weight of one subcategory will alter the percentages of all other subcategories.
Paper in Maine’s residential waste stream decreased considerably, from 33.04 percent in 1991/1992 to 25.57 percent in 2011. Percentages of all comparable paper types also decreased.
The greatest decrease was in the Newsprint subcategory, which made up 9.88 percent of waste sampled in 1991/1992 but just 2.48 percent of the 2011 waste. There were also decreases (by roughly one-half each) in amounts of high-grade office paper, corrugated cardboard and telephone books. Improved recycling programs have no doubt contributed to these decreases, but another factor is the overall movement away from printed media (e.g. more people are reading the newspaper online).
In the last two decades, the percentage of plastic in Maine’s residential waste stream has more than doubled. Many plastic types cannot be directly compared between the studies, as four subcategories were used to classify plastic in 1991/1992 and 11 were used in 2011.
Between 1991/1992 and 2011 there was an increase by almost two percentage points in the amount of rigid plastics (which here includes the 2011 subcategories #3-#7 Plastics, PET Bottles, PET Containers, and Redeemable Plastic Beverage Containers) in the total waste sampled. There were decreases, however, in percentages of HDPE plastics and plastic bags.
The overall increase in plastics in baggable trash supports the perception that more and more items are being made from, or wrapped in, plastics. Plastic film, which was included in the 1991/1992 Other Plastic subcategory, has since become the principal plastic component of the waste stream. In 2011, plastic film accounted for 35.61 percent of all plastic waste and nearly 5 percent of the total trash sorted.
The percentage of metal was similar in both studies at 3.29 percent of the waste stream in 1991/1992 and 3.26 percent of the waste stream in 2011. However, percentages of various metal subcategories changed. There was a decrease in the percentage of tin/steel containers, but an increase in the percentage of other ferrous and non-ferrous metals. The percentage of aluminum also decreased substantially, although at 0.39 percent in 1991/1992 and 0.10 percent in 2011, it was not a significant portion of the waste stream in either sort.
Food waste accounted for 27.81 percent of the sampled baggable trash in 1991/1992 and 27.86 percent in 2011, remaining essentially unchanged between the two studies. However, food has surpassed paper as the largest major component of the residential waste stream. This change may be the result of the considerable increases in paper recycling since the mid-1990s.
The percentage of glass in the residential waste stream decreased from 4.06 percent in 1991/1992 to 2.71 percent in 2011. A significant reduction can be seen in Clear Glass Containers, which accounted for 3.39 percent of the trash sampled in 1991/1992 and only 1.96 percent in 2011. This may be due not only to the increased availability of glass recycling but also the general shift away from using glass containers toward using plastic.
Some materials, such as textiles, made up similar percentages of the residential waste stream in 1991/1992 and 2011. Textiles accounted for 4.24 percent of the trash sorted in 1991/1992 and 4.26 percent of the trash sorted in 2011. The percentages of hazardous materials in the residential waste stream also did not change significantly. At 1.32 percent in 1991/1992 and 1.72 percent in 2011, they stayed within the 1-2 percent expected range for baggable waste.
Cat litter, the primary component of the Cat Litter/ Pet Bedding subcategory in 1991/1992, and the Other Organics subcategory in 2011, was a noticeable component of the waste stream in both trash sorts. While a perfect comparison between the two studies is not possible, the amount of cat litter in our baggable trash seems to have increased as Cat Litter/Pet Bedding accounted for 3.86 percent of the waste stream in 1991/1992, and Other Organics accounted for 10.97 percent in 2011. Although cat litter has the potential to be composted, care must be taken as it can contain bacteria and parasites harmful to humans, particularly pregnant women.
Analysis and Discussion
The first way we analyze the baggable trash sampled in this study is by classifying it into three streams: Waste, Recyclable, and Compostable. These three streams are not exclusive, but are helpful in determining how much of what Maine residents are throwing away could be diverted to better uses. For discussion purposes only, we define “Waste” as materials not easily diverted from the waste stream through current Maine composting or recycling programs. The waste sampled in this study had a roughly 40-40-20 breakdown between Waste materials, Compostable materials, and Recyclable materials.
Waste comprised 39.87 percent of the trash sampled. Efforts could be made to reduce much of this waste at its source by encouraging the use of recyclable materials and/or the use of more reusable items (e.g. refillable razors). The potential also exists for several materials in this category, such as textiles and grocery bags, to be recycled at much higher rates in the future if better recycling programs can be developed.
Compostable materials, at 38.41 percent, comprised nearly as much of the trash as waste. Food waste and compostable paper comprised 93.2 percent of the compostable stream. Creating municipal or regional composting programs and increasing awareness about backyard composting could greatly reduce the cost of disposing of solid waste in the state.
Recyclable materials comprised just over 20 percent of the waste sampled. This category contains desirable materials that should be diverted from the normal waste stream to more economical uses. Some municipalities could greatly improve their capture of these materials. While Maine communities have been providing recycling programs to residents since the early 1990s, and recycling initiatives have been increasing with time, municipalities and businesses are still recycling much less of their waste than the state’s 50 percent recycling goal that was established by the Maine Congress in 1989. This deadline for this law has been extended each time it is not met.
The three largest components of the waste stream were food waste, other organics and compostable paper. Food waste and compostable paper have a high potential to be diverted from the normal waste stream, while items in the other organics subcategory do not, as much of these contained fecal matter. Items in several of the other subcategories, such as other recyclable paper, magazines/catalogs and newsprint, are easily recyclable. Textiles are potentially recyclable, but better textile recycling programs are in need of development. Remainder/composite paper is not currently recyclable, but technical methods may be developed to facilitate this. The majority of plastic film, however is contaminated with food, making it unfit for recycling.
The observed decrease in paper and glass waste from the early 1990s to the present can be explained by the increased use of plastic in packaging and product manufacturing. The composition of plastics and their respective recycling requirements have accordingly become more complex with the development of new types of plastic.
Importantly, this analysis shows that 38 percent of current trash has the potential to be composted. Significant revenue loss also appears to occur in the improper disposal of recyclable materials, which make up 21 percent of the current residential waste stream. Though recycling rates have increased from 32.5 percent in 1993 to nearly 39 percent in 2010, vast improvements can still be made, as recycling rates have been stagnant in more recent years. Efforts to increase awareness about composting and recycling, as well as efforts to improve municipal recycling programs, should continue.
Maine has the potential to accomplish its goal of reducing waste through increased recycling, which would lower costs to municipalities and prolong the life of landfills.
Travis Blackmer is a graduate student at the University of Maine and led the School of Economics Waste Composition Research Project. Professor George K. Criner teaches in the School of Economics at the university.