1st Installment Bioreactors Morgan

This is my first installment about bioreactors.

Bioreactors work by using a natural process that is as old as life itself. For life to survive, it must have an energy source and water. How we can use these needs to remove pollutants from contaminated air streams will be the focus of my 2 part report.

In regards to air pollution, bio reaction is simply the use of microorganisms to consume and remove pollutants from a contaminated air stream. Almost any substance, with the help of microbes, will decompose given the proper environment. This is especially true for organic compounds. But certain microbes can also consume inorganic compounds such as hydrogen sulfide and nitrogen oxides.  

The major benefit of bioreactors is cost. The capital cost of a bioreactor is usually just a fraction of the cost of a traditional control device. Operating costs are usually considerably less than the costs of traditional technology, too. Thermal and catalytic control units consume large volumes of expensive fuel. Bioreactors only use small amounts of electrical power to drive two or three small motors. Normally, bioreactors do not require full-time labor and the only operating supplies needed are small quantities of macro nutrients. Bio filters, the most common type of bioreactor, use beds (media where microbes live) made from naturally occurring organic materials such as: yard cuttings, peat, bark, wood chips, etc. These are slowly consumed by the microbes. These organic beds usually can supply most of the macro nutrients needed to sustain the biomass. The beds must be replaced every 2 to 5 years, depending on the choice of bed material. Bio reaction is a "green" process, whereas the traditional approaches are not. The combustion of any fuel will generate oxides of nitrogen, particulate matter, sulfur dioxide, and carbon monoxide. Bioreactors usually do not generate any hazardous pollutants. Products of a bio reaction are water and carbon dioxide. Bioreactors do work, but microbes are finicky in what they will eat. Microbes need the right pollutant concentration, temperature, humidity and pH. There are many opportunities to make mistakes in design and operations of a bio reaction system. Anyone thinking about building one should discuss their situation with a manufacturer or an expert in the field. If a particular air pollution control situation qualifies, the cost benefits can be substantial.

Microbes have inhabited the Earth since the time that the Earth cooled sufficiently to allow any form of life to exist. Microbes have a simple life cycle; they are born, eat, grow, reproduce and die. Their diet is based primarily on carbon-based compounds, water, oxygen and macro nutrients. Bioreactors use microbes to remove pollutants from emissions by consuming the pollutants. The concept is simple, but the execution can be quite complicated. Bioreactors have been used for hundreds of years to treat sewage and other odoriferous, water-borne waste. About sixty years ago, Europeans began using bioreactors to treat contaminated air, particularly emissions from sewage treatment plants and rendering plants. The initial process used a device called a "bio filter." A bio filter is usually a rectangular box that contains an enclosed plenum on the bottom, a support rack above the plenum, and several feet of bed on top of the support rack. A large number of materials are used for bed media such as peat, composted yard waste, bark, coarse soil, gravel or plastic shapes. Sometimes oyster shells used for neutralizing acid c Compounds not soluble in water are not good candidates for this technology.  Build-up and fertilizer for macro nutrients are mixed with bed media. The support rack is perforated to allow air from the plenum to move into the bed media to contact microbes that live in the bed. The perforations also permit excess, condensed moisture to drain out of the bed to the plenum.

A fan is used to collect contaminated air from a building or process. If the air is too hot, too cold, too dry, or too dirty, it may be necessary to pretreat the contaminated air stream to obtain optimum conditions before introducing it into a bioreactor. Contaminated air is duct to a plenum. As the emissions flow through the bed media, the pollutants are absorbed by moisture on the bed media and come into contact with microbes.  Microbes reduce pollutant concentrations by consuming and metabolizing pollutants. During the digestion process, enzymes in the microbes convert compounds into energy, CO2 and water. Material that is indigestible is left over and becomes residue. This is a very simple and brief explanation on how a bioreactor functions. In real-life, things get a bit complicated. Variables that affect the operation and efficiency of a bioreactor include: temperature, pH, moisture, pollutant mix, pollutant concentration, macro nutrient feeding, residence time, compacted bed media, and gas channeling. These are crucial variables for which optimum conditions must be determined, controlled and maintained. In the body of this report, a complete explanation of these processes is given. Is a bioreactor right for your situation? This is not an easy question to answer. The purpose of this report is to provide tools that you can use to determine if a specific contaminated air stream is a good candidate for bio reaction treatment. Bioreactors are far less expensive than traditional control technologies to install and operate and, in many cases, bioreactors approach efficiencies achieved by traditional control technologies.

Because bioreactors use living cultures, they are affected by many variables in their environment. Below are variables and limitations that affect the performance of all bioreactors, regardless of process type. All variables discussed here are important. However, probably the most important variable affecting bioreactor operations is temperature. A blast of hot air can totally kill a biomass faster than any other accident. Most microbes can survive and flourish in a temperature range of 60 to 105 /F (30 to 41/C). It is important to monitor bed temperature at least daily, but every eight hours would be safer. A high temperature alarm on the emissions inlet is also a good safety precaution.

When emissions from a process are too hot, operators often pass hot emissions through a humidifier that cools gases down by evaporative cooling. This is the most economical method available for cooling emissions from 200 to 300 /F (93 to 149 /C) to below 105 /F (41/C). Besides the cooling effect, this process also increases the moisture content (humidifies emission stream), a desirable side effect. Although a blast of really hot air is the most lethal variable for microbes, cold air also stops, but does not kill, microbes. Cold air can reduce microbe activity to the point that they stop consuming pollutants and go into a state of suspended animation. Even freezing does not kill microbes. After thawing, they can be re-acclimated in a relatively short period. For optimum efficiency during winter months, it may be necessary to heat emissions using direct or indirect methods. If heating is required, first look for a waste heat source such as excess steam, boiler blow down, or product cooling waste heat. As with cooling emissions, analyze your source carefully to assure nothing is being added to the emission stream that will harm microbes in the bioreactor, or will add to the overall pollution load. Additionally, some operators, especially in northern states, insulate the bioreactor's exterior to reduce heat loss.