Municipal solid waste is the designation waste management professionals give to general, non-hazardous waste generated in households, office buildings, and even industrial facilities. Informal words for this waste are trash and garbage, but terminology is important in the field, so we do not use those words. Yard waste (e.g. grass clippings), kitchen waste (e.g. leftover food, bones), and old newspapers are all in the category of MSW - municipal solid waste. Now it is true that yard clippings and leftover food can be composted and that newspapers can be recycled, but that is a separate issue.
The Environmental Protection Agency estimates that 292.4 million tons of MSW were generated in the United States in 2019. They estimate the composition as follows: paper 23 percent. yard waste 12.1 percent. food 21.6 percent. That amounts to 4.8 lb/person/day.
Composting solves many problems, and although a collection scheme can be difficult to set up, the operating costs of large composting operations are relatively low. To compost, biodegradable waste is set in a pile and natural decay mechanisms reduce the volume. Composting works best when the waste material is not too far removed from nature. Yard waste is ideal, as composting is just a managed way of facilitating what would happen in nature. Most yard waste is cellulose and hemicellulose. Paper, which is also cellulose and derived from wood, can decompose through natural processes, but it is slower. For that reason paper is usually excluded from compost bins, although incidental paper is not a worry.
Another benefit of composting is that it can be done near where the waste is generated, and can be done on a small scale. However, there are advantages to very large composting operations as the heat the pile generates and environment it provides for bacteria and worms make the waste degrade more rapidly.
The material left after the compost has been undergoing natural decay for a few months is typically acceptable for fertilizer or soil for growing plants. It is also acceptable for landfill, but that costs money. The amount of waste going to composters increased considerably from 1990 to 2005, and now the EPA says 27 million tons of MSW is now composted. Most of this is yard waste.
There are many technologies for recycling because there are many types of waste. Metal is recycled in a manner different from
Paper is recycled through a process called pulping. The paper is shredded and harsh chemicals (hydrogen peroxide, sodium hydroxide) are added to break down the structural integrity of the paper, resulting in a slurry of cellulose. This pulp is then processed to remove impurities and adjust the pH, before it is used to remake paper. The recycled paper is usually considered inferior in quality to paper made from virgin wood, but it is good enough for many applications. In terms of sheet tonnage, paper and related products (e.g. cardboard) are by far the most recycled material, accounting for about two-thirds of material recycled, or 46 million tons.
Plastic recycling is imperfect because the feed is heterogeneous. At waste sorting facilities, plastics are separated from paper, wood, metal, etc. But there are different types of plastics. An attempt is made to separate them based on density, but it is always of limited efficacy.
The separated and washed plastic is shredded to tiny pieces. After further washing and separation of gross impurities, the pieces of plastic may be put into an organic solvent and heated to melting. The resulting liquid mass is viscous and can be made into plastic products. The EPA estimates 3 million tons of plastic waste are recycled in the US every year. That is less than 10 percent of plastic waste. We do much better at recycling paper than plastic. Over 60 percent of paper waste is recycled
Metal recycling is similar to plastics recycling. An attempt is made to separate the different kinds of metal. The metal is shredded to small pieces and then melted. Further purification may take place in the molten stage, but recycled metal is almost always a combination of more than one metal. When the molten metal is allowed to solidify, it is recycled metal. The quality of this metal is often good enough so that only a few applications can not use it. Much of the steel on the market is recycled and hence of various compositions. Over 8 million tons of metal are recycled in the US every year. That is between 20 and 30 percent of the metal waste produced.
Japan uses MSW to produce electric power; the practice is less common in the US, but waste-to-energy plants are an important part of our energy infrastructure.
Burning waste to make electric power is just like burning coal. It requires equipment to move around solids into the incinerator, and it produces bottom ash and flyash. The heating value of MSW averages about 5000 BTU/lb. Pollution abatement systems are required to remove the flyash and acid gases before the exhaust enters the atmosphere.
The ash and secondary waste from these facilities goes to landfills, but the volume has been reduced by 87 percent.
Despite the growth of composting and recycling, our society still dumps a lot of waste. The places where we put the waste used to be called “dumps” and are now called “landfills”. There are between 1200 and 1300 (https://www.statista.com/statistics/193813/number-of-municipal-solid-waste-landfills-in-the-us-since-1990/) actjve sanitary landfills in the US, and they accept 146 million tons of waste per year. Modern landfills are much safer than their counterparts from decades ago as all current US facilities are operated as sanitary landfills. The trend in recent decades has been for fewer but larger landfills.
Densely populated areas have trouble finding locations for landfills, and that results in waste being transported large distances sometimes. This transportation is often a big part of the reason it costs money to dispose of waste this way. Even after you get the waste to the landfill, the operators will charge you a “tipping fee” to deposit your waste. The costs vary from place to place, but the average nationwide tipping fee is $55.36/ton.
Old, closed landfills produce gas from decomposition of the waste. They are similar to swaps in this respect and while swamps can emit methane-rich “swamp gas”, landfill gas also has a combustible value. Indeed, landfills are the third largest source of methane emissions to the atmosphere - https://medium.com/living-in-a-climate-changing-world/yes-to-landfill-gas-to-energy-3f8341b16953 Sometimes it is flared or run through a catalytic oxidation unit. The gas can also be burned to produce electric power. Landfill-gas-to-energy projects are a pet project of many environmental activists. They have little downside other than capital cost, and payback time is estimated to be 5 years. An analysis published by the American Chemical Society in 2009 found landfill-gas-to-energy produced more greenhouse gases per kilowatt-hour of energy than direct burning in waste-to-energy systems. But in the absence of these energy harnessing systems, the gas would still end up in the atmosphere, so using landfill gas in this manner is better than flaring it.
Most office and industrial complexes keep MSW in an outside dumpster, from which waste management companies haul it away. The cost to have the waste management company remove your waste is often proportional to volume, not to mass. Compactors are available to compress the waste, increasing its density and thus reducing disposal costs.
As undesirable as it is, MSW is still considerably less expensive to dispose of than much of the waste we discuss on this site. Unlike radioactive, hazardous, or infectious biomedical waste, it does not need treatment or special packaging or immobilization. You should prefer to put objects into your MSW stream rather than the stream for regulated waste. Of course, in keeping with the waste management hierarchy, you should try to avoid creating the waste in the first place. And environmentally preferable purchasing can help reduce the quantity of waste. Estimates vary, but most say that 75-90 percent of waste generated at healthcare facilities is MSW.