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Remediation Technologies Screening Matrix, Version 4.0  
Chapter 14 Bioreactors
Table of Contents


14-2 Hazard Analysis

Principal unique hazards associated with bioreactors include:

Physical Hazards Chemical Hazards Radiological Hazards Biological Hazards

a. Physical Hazards

(1) Description: Storage of methanol or other additives or supplements may cause fire or explosion if these materials are spilled and allowed to mingle with incompatible chemicals, or are ignited by a potential source of ignition.

Control: Flammable and combustible materials must be stored in accordance the requirements of 29 CFR 1910.106, Flammable and Combustible Liquids. Appropriate fire and electrical codes must be followed. Verify that the hazardous area classifications, as defined in NFPA 70-500-1 through 500-10, are indicated on the drawings. All controls, wiring, and equipment near the tanks should be in conformance with the requirements of EM 385-1-1, Section 11.G and NFPA 70 for the identified hazard areas. Equipment should be grounded and/or provided with ground fault interrupter circuit (GFIC) protection if required by EM 385-1-1, Section 11 or NFPA 70 requirements. Only trained, experienced workers should be permitted to work around the storage areas. The tank vents should be directed so as to prevent contact with sources of ignition. Fire extinguishers rated for energized electrical systems should be readily available where electrical equipment is installed and operated. CONTROL POINT: Design, Construction, Operations, Maintenance

(2) Description: Because bioreactors typically generate carbon dioxide gas as a byproduct, workers entering tanks or clarifiers may be exposed to confined spaces with oxygen-deficient atmospheres.

Control: Prior to entry into tanks, vessels, or other confined space, testing of atmospheres within the confined space may be required following applicable Occupational Safety and Health Administration (OSHA) standard 29 CFR 1910.146. Air-handling systems should be designed to minimize or eliminate oxygen-deficient locations. CONTROL POINT: Design, Operations, Maintenance

(3) Description: Permanent and temporary electrical equipment which is not ground-fault protected, and comes in contact with water or other liquids, may cause an electrocution hazard.

Control: Verify that the hazard area classifications, as defined in NFPA 70-500-1 through 500-10, are indicated on the drawings. All controls, wiring, and equipment should be in conformance with the requirements of EM 385-1-1, Section 11.G and NFPA 70 for the identified hazard areas. Ground-fault protection should be provided where required by EM 385-1-1, Section 11 and NFPA 70 requirements. Only trained and experienced workers should be permitted in the areas. CONTROL POINT: Design, Construction, Maintenance

(4) Description: Blowers may be equipped with unguarded pulleys which may cause cuts or entanglement of loose clothing. Floating aerators may be equipped with unguarded propeller blades.

Control: Pulleys and other moving or rotating mechanical devices on blowers should be guarded, and workers should only operate the equipment with guarding in place. Emergency shut-off systems should be designed and installed if there is a threat of workers falling into actively aerated tanks or ponds with bladed aerators. Lock-out procedures should be in place for shutting down aerators prior to operations on a pond or tank water surface. Tanks should be equipped with guard rails, grab rails, and ladders where practical. CONTROL POINT: Design, Operations, Maintenance

(5) Description: Permanent or semi-permanent treatment buildings may present life safety hazards such as inadequate egress, fire suppression systems, and/or emergency lighting systems.

Control: Permanent and semi-permanent treatment system buildings should be constructed in accordance with ANSI 58.1: Minimum Design Loads for Buildings and Other Structures; the National Fire Code; the National Standard Plumbing Code; Life Safety Code; and the Uniform Building Code. Depending on where the project is located, the structures must also comply with either the Air Force Manuals on Air Force bases, the USACE Technical Manuals on Army installations, or Local Building Codes on Superfund, BRAC, or FUDS project sites. CONTROL POINT: Design, Operations

(6) Description: If pure oxygen is being used for aeration, workers may be at an increased risk of spreading a fire due to an oxygen-enriched atmosphere. Usually air, rather than pure oxygen, is used for aeration.

Control: Oxygen systems should be designed and constructed in accordance with the applicable provisions of NFPA 50 Bulk Oxygen Systems at Consumer Sites and provided with safety relief devices in accordance with CGA S-1.3 Safety Relief Devices for Compressed Gas Storage Containers. Oxygen delivery systems should be regularly inspected for leaks, and all sources of ignition should be controlled during application of oxygen. CONTROL POINT: Operations, Maintenance

(7) Description: Emergency shower/eye wash equipment required per 29 CFR 1910.151 are not always provided with adequate floor drains, thereby creating potential electrical hazards and walking surface hazards during required testing/use.

Control: Showers/eye wash equipment should be equipped with accompanying functional drains to isolate and collect the shower/eye wash water from unprotected electrical equipment and walking surfaces that, when wet, create slipping hazards. CONTROL POINT: Design

b. Chemical Hazards

(1) Description: Workers may be exposed to waste contaminants by inhalation, ingestion or absorption. Biological activity of the bioreactors may be enhanced with the addition of nutrients or other chemical agents. These agents may include nutrients, methanol, or other chemicals for pH adjustment (e.g. acids and bases). Workers may be exposed to these chemicals during their application either as a powder or in a liquid state. Acute overexposure symptoms may include irritation of the eyes, skin, and respiratory tracts.

Control: Precautions to help prevent worker overexposure to waste contaminants or additives include the use of personal protective equipment (PPE) during the application process, and design of mechanical addition systems which minimize exposure. PPE requirements may include air-purifying respirators with approved filter/cartridges (e.g. HEPA(N100, R100, P100) filters for particulates, OV cartridges for vapors, or combination filter/cartridges for dual protection), chemically-resistant rubber gloves (e.g. nitrile for gasoline), splash goggles, and aprons. CONTROL POINT: Design, Operations, Maintenance

(2) Description: Biological degradation of certain organic compounds may produce toxic intermediate products (e.g. degradation of TCE can produce DCE and VC). Vinyl chloride exists as a gas and may accumulate to higher levels in boreholes or in the system. Workers may be exposed to intermediate products during operation or maintenance of the system. Anaerobic processes can produce toxic and/or explosive products such as methane or hydrogen sulfide, particularly in confined space areas. Workers may also be exposed to VOCs released from aeration tanks.

Control: Controls to minimize exposure include ventilation of the affected area. Air-supplied respiratory protection may be required, (e.g. air-purifying respirators are not recommended for vinyl chloride). Remediation designers should understand and anticipate the generation and management of general and specific process products (e.g. CO2, H2S, VC), and design for their management. Also, operational considerations include covering aeration tanks to prevent the release of VOCs into the work environment. Usually the dissolved oxygen level within aerobic bioreactors is monitored to determine if aerobic conditions are being maintained. It may be necessary to periodically check for the presence of hydrogen sulfide, or to install automated alarms. CONTROL POINT: Design, Operations, Maintenance

c. Radiological Hazards

Description: Radiological materials may have been buried, or naturally occurring radioactive material (NORM) may be present in soils, sludge, or groundwater. Some radioactive materials may present an external hazard. All radioactive materials may present an internal exposure hazard through inhalation or ingestion, although this may be a rare hazard.

Control: The presence of radioactive materials may be known or the soil, sludge or groundwater may be tested to determine if radioactive materials are present. If any radioactive material above background levels is found, a qualified health physicist should be consulted to determine the exposure potential, and any necessary engineered controls or PPE. CONTROL POINT: Design, Operations

d. Biological Hazards

(1) Description: Bioreactors may expose workers to pathogenic microbes during operation and maintenance. However, exposure to pathogens is usually not a significant concern unless the wastes being fed into the reactors contain pathogenic agents. If the bioreactors are equipped with open aerators, microbe-entrained mists may become airborne. Inhalation of pathogenic microbes may cause allergic reactions or illness. During sludge handling activities, workers' hands may be exposed to microbes and result in accidental ingestion of pathogenic material.

Control: The amount of aerosol/mist, and consequently the amount of exposure, may be controlled by installing aerators that minimize generation of mists, and/or by the installation of partitions or barriers to contain the mist. Skin exposure may be minimized through the use of PPE, such as chemically-resistant gloves (e.g. nitrile), splash aprons, and face shields. CONTROL POINT: Design, Operations, Maintenance

(2) Description: Biological sludge after drying may become airborne, and thus accidentally inhaled or ingested.

Control: Sludge drying beds are the most widely used method of dewatering sludges from municipal wastewater in the United States. Pathogens are usually a much greater concern for municipal wastewater applications than for hazardous waste applications. When necessary, disinfection of sludge is usually accomplished through pasteurization or long-term storage. Maintaining sludge in a damp condition will minimize free dust; however, sludge is often dewatered prior to disposal. Appropriate PPE (e.g. an air-purifying respirator with HEPA(N100, R100, P100) filters/cartridges) may be used when handling sludge. CONTROL POINT: Operations, Maintenance


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