UNIT V PLEASE READ CAREFULLY

MEE 5901, Advanced Solid Waste Management 1

Course Learning Outcomes for Unit V Upon completion of this unit, students should be able to:

1. Assess the fundamental science and engineering principles of solid waste management.

7. Examine the impact of solid waste on human populations.

Reading Assignment Chapter 6: Biological Processes

Unit Lesson The two key biological operations that are used in the treatment of municipal solid waste are composting and landfilling. Composting is an aerobic process. This is why compost piles need to be periodically turned to allow oxygen to diffuse into the microbes in the compost pile. Compost piles are ideal for treating highly organic wastes that include food wastes, garden wastes, yard and park wastes, and dewatered sludges from municipal wastewater treatment plants. The biggest advantage of compost piles is their ability to stabilize wastes, which results in the volume reduction of waste materials. Depending on the rate that organic materials are applied to the compost pile and on the health of the microbial population in the pile, periodic additions of new waste can be made to the pile. Treating readily biodegradable organic wastes in compost piles results in carbon dioxide being emitted. Besides reducing waste volumes, compost piles are capable of destroying pathogens that are contained in the waste. Stabilized waste that is free of metals and hazardous wastes can be packaged and sold as a fertilizer. Municipalities that use compost as a revenue source must control the chemical content of the waste going into the pile and perform toxicity and metal testing on the stabilized contents to confirm the safety of the product. In the case where stabilized compost piles are not to be placed into commerce, the compost can be used as a soil additive to agricultural lands (which also requires testing to confirm the absence of toxic compounds and metals) and as a soil fill to reclaimed land. The microbial population of municipal landfills operates by a different biological mechanism. Landfills operate by means of anaerobic processes that treat and stabilize waste refuse. Anaerobic degradation processes function in the absence of oxygen. This category of microbial treatment is associated with the production of methane that can be captured, compressed, and used as a fuel source to support combustion processes capable of producing energy and electricity. The methane generated by landfills can have an adverse impact on atmospheric conditions. Methane is 25 times more powerful than carbon dioxide when their global warming impact is considered (United States Environmental Protection Agency, n.d.). This is one of the reasons that methane is collected for energy conversion. Even landfills that have a well designed methane gas collection system will experience at least a 10% leakage rate to the atmosphere. In Europe, mechanical-biological treatment of municipal solid waste is becoming popular. Mechanical treatment utilizes separation processes like shredding and crushing operations to prepare the waste for composting or for landfilling. These combination operations break down the refuse into particle fractions. With a standardized particle size, municipalities in Europe have experienced a 40 to 60% reduction in the amount of waste going to landfills. The European Union (EU) also has experienced that by using separation processes as a pre-treatment, it changes the waste profile and particle size of what goes into landfills. This has resulted in pulling out readily degradable organic content from the landfill that leads to a reduction of the generation of methane by 95%.

UNIT V STUDY GUIDE

Role of Biological Processes in Stabilizing Municipal Solid Waste

MEE 5901, Advanced Solid Waste Management 2

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Europe is also developing advanced technologies for treating municipal solid waste. These include in-vessel treatment processes that can be located inside a building structure. These include tunnels, vertical towers or silos, rotating drums, and housed bays with forced mechanical aeration and agitation. Tunnel composting utilizes rectangular vessels that use push walls for moving the refuse through the system. Tunnels operate in a batch mode, but new continuous flow systems are starting to be piloted. These units are loaded from the top and aeration is through pipes and slats in the floor. Cool air is used both as an oxygen source and for keeping the temperature in the correct range. Moisture is added to the compost by an overhead spray system. Vertical compositing operates as a plug flow reactor that continuously moves the refuse through the system. Waste enters the top of the tower and is removed from the bottom. These tower systems mostly utilize a passive aeration system, but where there are multiple chambers that may be utilized, forced aeration systems become necessary. Rotating drums also operate in a continuous flow through system. The refuse is mixed by the baffles during the rotation of the drum. Aeration can be either passive or forced depending on the amount of refuse being treated. The drum is unique in that it can break open plastic bags and release the contents. The energy of rotation breaks the size of the larger materials, and, with a long enough retention time, the unit can eliminate the need for a shredding operation. Long bays inside of buildings store waste in piles. Augers are primarily used to turn over the waste piles to allow oxygen to penetrate to the microbial populations. During the turning process, the refuse is moved towards the end of the pile. The floor is often fitted with a forced air system to keep the piles aerobic and to keep a high rate of refuse stabilization. Odors are captured and prevented from escaping to the inside of the building and to the outside by a negative pressure system and high room air exchange rate. The air containing the odor is scrubbed in a chemical bath that destroys the odors. Another interesting technology is to dry the refuse as a pretreatment step referred to as bio-drying. The waste is heated, and air is passed through the heated refuse, which dries the waste and lowers the water content of the mixture. The efficiencies of mechanical and separation technologies are greatly improved when the waste enters these unit operations in a dry condition. Advanced treatment processes produce a superior compost product for sale in commerce. The EU is adopting manufacturing technologies and principles to treat municipal solid wastes. The revenue that is generated from the recycled materials pulled out of the waste helps to offset the high capital and operational costs of the equipment and staff needed to operate and maintain these systems. Keeping readily degradable organics out of the landfill greatly reduces the amount of methane that is generated and that needs to be captured and managed. The use of compost piles also treats refuse that could go into the landfill, which reduces the operating life of the facility for the community. By keeping organics out of the landfill, obnoxious odors are not generated and emitted into the atmosphere and downwind communities. In Europe, land is at a premium, and wastes are generally handled on a regional basis rather than by each individual community. The EU driver is a lack of available space while the driver for municipalities in the U.S. will be economics. For now, due to the high costs of using advanced treatment technologies, technology adoption in the U.S. will be low and limited to regions with a high density population. However, this may change as landfills built in the 1980s begin to fill up and new facilities become very costly to design, build, and permit. Municipalities will begin to look to privatize these services, and it will be these service providers who will begin to implement many of these technologies as they look to regionalize solid waste treatment for the communities in which they operate.

Reference United States Environmental Protection Agency. (n.d.). Overview of greenhouse gases. Retrieved from https://www3.epa.gov/climatechange/ghgemissions/gases.html

MEE 5901, Advanced Solid Waste Management 3

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Suggested Reading The topic of treatment of organic wastes, which is covered in this unit, is explored more in the article below. Take a few minutes to read this article to gain a deeper understanding of this topic. Zupancic, G. D., & Grilc, V. (2012). Anaerobic treatment and biogas production from organic waste. In S.

Kumar (Ed.), Management of organic waste (pp. 3-28). Retrieved from http://www.ewp.rpi.edu/hartford/~ernesto/S2014/SHWPCE/Papers/SW- BiochemicalTreat/Zupancic-OrganicWaste-AnaerobicTreat.pdf