Some waste management axioms:
- If you have a landfill, transfer station, compost site, or material recovery facility (MRF), it stinks.
- If your collection truck is dirty, it stinks.
- If the collection crew’s outfits are dirty, your truck stinks.
- If there’s litter near your facility you caused it.
- If there’s litter in the neighborhood on collection day, it’s your fault.
It doesn’t matter which way the wind is blowing, that a bunch of party people donated their leftovers to the countryside, or that a local processing plant just experienced a methanogenic moment. Whichever of the public’s senses is offended, odds are that you’re going to hear about it … and not in friendly tones. So with that bit of understanding in mind, let’s see what’s going on, and what you can do to protect your organization’s good name and reputation.
What’s Going On
The unstable nature of MSW poses inherent odor problems. As trash breaks down, chemical reactions between its components occur. During decomposition, organic molecules create their own parasitic, odor-causing molecules made up of oxygen, water, and bacteria, the latter feeding on decomposing matter and emitting odorous gases.
Organic odiferous substances in the MSW environment include: aldehydes (CHO group, any of various highly reactive compounds); alkaline, nitrogen derivatives like amines (from ammonia through replacement of hydrogen by hydrocarbon radicals); indoles (C8H7N, a decomposition product of proteins containing tryptophan) and skatoles (C9H9N, found in intestines, feces, and plants); sulfur-based acidic compounds like mercaptans and disulfides; fatty acids (any of numerous saturated alphantic monocarboxylic acids, occurring as esters in fats, waxes and oils, such as butyric, stearic and oleic organic acids); and hydrocarbons (CH, an organic compound occurring in petroleum, natural gas, coal).
Smell-producing inorganics include: ammonia (NH3, a pungent, colorless, gaseous alkaline compound) and hydrogen sulfide (H2S, a flammable, poisonous gas with the odor of rotting eggs).
The Search for Relief
Prevention of odors is preferable to allowing them to develop, and then working to alleviate them. Since the majority of odor-producing bacteria thrive in an oxygen-scarce environment, odor management in some situations can be a matter of maintaining an aerobic environment-turning a compost pile or windrow, for example. Since transfer stations, MRFs, or landfill operators must deal with the wide variety of materials that arrive on the doorstep-regardless of their condition-odor management more often than not necessitates the use of sophisticated technologies and/or commercial products to mask, deodorize, or neutralize the unpleasant gases.
The various odor control formulations on the market can be divided into five categories:
- Masking agents are chemicals which overpower malodors with other more pleasant odors without chemical reaction.
- Reactants are chemical combinations, which permanently alter odorous characteristics of the odor molecule.
- Counteractants are surfactants and plant essential oils of neutral pH that interfere with malodor by eliminating the objectionable characteristics of the molecules.
- Combining involves adding alcohol-based chemicals, which react with acidic odors and result in sweet-smelling esters.
- Construction refers to chemical compounds that build up on odor molecules by polymerization and result in a loss of odorous characteristics.
Reducing anaerobic, odor-producing situations may involve the introduction of Oxygen (O2)-a process known as oxidation-to take the breath away from the smelly strains. Affecting the water and oxygen supplies, or disrupting other metabolic functions of odor-causing bacteria are alternate methods. Neutralization of odor through “catalysis”-chemical reactions induced by a product that remains unchanged chemically at the end of the reaction-provides another possibility.
Odor Management Technologies Summary
Absorption: This is the process of removing odorous constituents of an airstream by absorbing them into a scrubbing liquid and reacting them by chemical combinations or oxidation.
Adsorption: Contained odorous air is introduced into a chamber and blown or pulled through beds of granulated carbon or permanganate pellet beds. Contaminants are trapped and oxidized; no water or solutions are used.
Biofiltration: The utilization of peat moss, soil, compost or other material as a permeable media to treat odorous air. The media serves as an adsorbent and surface for a biological mass that converts odors into non-odorous forms. Low-profile, underground units with gravel drain beds are overlaid by porous piping and covered by the media.
Dilution/Dispersion: The least-costly way to treat foul odors, it involves diluting odorous with non-odorous air until it is below threshold detection levels. Dispersion methods include: exhausting air through tall stacks, using a venturi arrangement to suck odiferous air into a chamber to be diluted by clean air, and combining an odorous air stream with a non-odorous one.
Incineration: For situations with waste-to-energy facilities nearby, odorous air can be drawn through ducts into the incinerator area and burned.
Lime: A corrosive chemical that increases alkalinity or pH of odorous material, to dissolve the sulfides through ionization and react fatty acid odors into salts.
Metal Salts: This is the introducing of ferric or ferrous chloride, or ferric or ferrous sulfate into wastewater treatment to bind and precipitate odiferous sulfides.
Metabolic Modification: The chemical approach to prevent the generation of odiferous hydrogen sulfide by disrupting the hydrogen sulfide generating ability of Sulfate Reducing Bacteria (found in wastewater). This circumvents treating odors after they have formed.
Oxidation: Oxidization-inducing chemicals, such as chlorine, hypochlorite, hydrogen peroxide, potassium permanganate, and chlorine dioxide are introduced to break odor molecules down into odorless elemental molecular forms. These are used in wastewater treatment. The incineration of odors by direct flame or catalytic system is a thermal oxidation process.
Ozone: Ozone is another oxidizing process, occurring in the vapor phase. O3, an unstable gas which reacts with atmospheric hydrogen sulfide and organics, is introduced to odiferous areas to degrade odor-causing molecules. Because ozone is toxic to humans, its use is limited to confined areas.
pH Adjustment: The raising of the pH of a wastestream to ionize hydrogen sulfide to the hydrosulfide ion, which is soluble and not volatile.
Raising the ORP: The introduction of oxidizing agents, liquid oxygen, compressed air, aeration systems, nitrates, or sulfide inhibitors to retard the activity of sulfate-reducing bacteria to form odiferous hydrogen sulfide. Oxygen Reduction Potential (ORP) refers to the ability of a substance to reduce or oxidize another material, and keeping it low or negative will prevent unwanted anaerobic bacteria from prospering and causing odor.
Scrubbers: The process of forcing odiferous air through a chamber to trap odor-molecules and reduce or render them odorless. Mist scrubbing directs foul air through a blower and a mist nozzle applies a chemical reagent diluted in water. Wet scrubbing refers to the use of water, in systems like counter-flow packed bed scrubbers and open-crossflow scrubbers, which force odorous air into chambers and introduce reagents diluted in water.
Vapor Phase Neutralization: Bypassing absorption, odiferous air is treated in the gas phase with the application of reactants, counteractants construction, or combining.
Combining: The treatment chemicals with alcohol components that react with acidic odors in the presence of a catalyst and result in mild, pleasant-smelling esters, which dissipate quickly.
Construction: Utilizing chemical compounds to build up odor molecules (polymerization), resulting in a loss of odorous characteristics. It is the opposite of oxidation, which breaks molecules down; construction builds them up into larger molecules, which are less volatile and prone to releasing odorous gas.
Counteractants: Through high-pressure fogging or air atomization, non-toxic chemical products composed of surfactants and plant essential oils of neutral pH are introduced to odiferous air. They interfere with the malodor, not by chemically reacting with it, but by eliminating the objectionable characteristics of the odiferous molecules.
Masking Agents: Chemical formulas, which overpower malodors with other, more pleasant odors, without chemical reactivity or reduction of the total odor load.
Reactants: Chemical combinations, which permanently alter odorous characteristics of the odor molecule in the vapor stage by changing their molecular structures to more complex, but less offensive forms. They can be applied through pressure or air-atomized spray, and added to scrubber solutions.
Stopping Smells Where They Start
Curbside collection systems are the first, and most likely, point at which residents encounter objectionable MSW odors. Collection frequency and use of collection carts with substantial, snug-fitting lids-difficult for animals to get into or tip over-are the primary lines of defense, but small powder deodorizer dispensers attached to curbside collection carts have been tested.
Collection vehicle cleanliness is another important component of the residential interface. Aside from any actual odors involved, a dirty truck looks “smelly” and unsanitary, so when it comes to public concern it makes little difference whether the smell is real or assumed. While keeping trucks clean is the first step in odor reduction, some haulers found that odors lingered even after thorough washing. Some states have strict regulations concerning hauling odors, often requiring onboard deodorizing devices that neutralize, contain, or mask objectionable smells during operations. No matter how effective deodorizing procedures are, the essence of a sound residential odor abatement program lies in clean, well-maintained equipment and on-time, frequent service.
Because transfer stations and MRFs are more likely to be located near residential areas, operators have to be especially innovative in this area of odor control. Fortunately, there are numerous odor-control products specifically designed for use at transfers stations and materials-recovery facilities.
While most landfills were sited in remote areas, as any owner will tell you, it wasn’t long before developers took advantage of attractive land prices and set up shop. As residences proliferated, so did people with telephones, along with such vagaries as wind direction, temperature, and general matters determining ambient levels of dissatisfaction with the surrounds.
Ditto composting facilities, where no one in the business dare forget the odor lessons learned from past failures. However, in many areas, centralized processing technologies have hit their stride and success stories are now commonplace.
The prescription for a successful MRF, transfer station, landfill, or composting operations is best summed up in the 7 P formula: Proper Prior Planning Prevents P-Poor Performance, another way of saying, before you go crazy trying to find the right deodorant, you should work first to prevent odor by getting the system in balance.Evaluating the Options Each facility and its site requirements are different. Considerations include: the strength and intensity of the odor problems, the size of the site, the size of the buffer zone, the size of the area requiring treatment, internal facility characteristics (existing ventilation systems), government and local regulations, available utilities, energy consumption parameters, and any number of other unique challenges. This information may be helpful in guiding your decision.