Community Meeting Q&A
Q: What substances will be coming out of the stacks?
A: PPNE’s operations will release some substances into the air, as follows:
- The municipal solid waste (MSW) building will have dust from handling the MSW, organic compounds from decomposing material in the MSW, and exhaust from the handling equipment (front-end loaders).
- The biosolids building will have dust from handling the biosolids, organic compounds released from the heated biosolids, and dryer exhaust from fuel combustion.
- The glass handling building will have dust from handling the glass, and some wintertime fuel combustion exhaust for building heat.
Organic compounds can be a source of odor. PPNE will control air emissions, including odor, using best available technology and procedures, as follows:
- Dust will be minimized through handling practices and water misting, and controlled with fabric filters.
- Exhaust from heaters and handling equipment will be minimized by using clean fuels (natural gas for heaters and ultra-low sulfur diesel for handling equipment).
- MSW odor will be minimized through best management practices to minimize decomposition onsite, including indoor handling, daily cleanup and sweeping, and minimizing the time MSW spends onsite.
- The biosolids handling area will use ozonation to destroy odorous compounds. Ozonation applies an electric charge to oxygen in the air, which then reacts with organic compounds in the air to destroy them.
- The biosolids drying process will have specialized air pollution control equipment. The equipment will either be:
o A bio filter, which uses microbes contained within a filter to biologically degrade organic compounds, followed by a carbon absorber, which uses activated charcoal to trap organic compounds for offsite disposal; or
o A thermal oxidizer, which burns organic compounds to destroy them.
PPNE’s buildings will have ventilation fans for worker safety and comfort, and process stacks to ensure that air emissions disperse properly. PPNE’s Environmental Impact Report includes an analysis of the potential effects of the air emissions. Emissions from all of the stacks and vents, plus exhaust and dust from project truck traffic, were analyzed using an EPA-approved computer model to show what the air concentrations would be anywhere within 5.5 miles of the facility under any weather condition. Model results are compared to EPA and Massachusetts Department of Environmental Protection (MassDEP) health-protective standards. For odor, model results are compared to a dilution threshold that is unlikely to cause a nuisance condition. The predicted air pollutant and odor concentrations are shown to comply with the national and Massachusetts standards, and to comply with the protective odor dilution threshold at residences. As a comparison for perspective, the incremental additional particulate matter from a year-long exposure to the worst-case impact would be the same as the spending an additional 90 minutes in highway traffic, or 30 minutes in a kitchen cooking with a gas stove. Impacts at the nearest household will be much lower and would be the same as spending 20 minutes in highway traffic or 7 minutes in a kitchen cooking with a gas stove.
PPNE’s air emissions will not contribute significantly to total regional air emissions. Emissions of particulate matter will be less than 0.1 percent] of county-wide emissions, and emissions of organic compounds will be less than 0.01 percent of county-wide emissions.
Q: What chemicals will be used to minimize odor?
A: Please review the links below for a specification sheet and a safety date sheet for an odor counteractant. When diluted as it should be, it is non-toxic and can be applied in an airborne environment. Please note that the non-diluted agent is stored inside of the building and can be stored on a “spill pallet”. This agent is then fed into the misting system using a venturi metering pump. This type of agent is used throughout the country and is common practice.
Q: What type of dryer is being used with the biosolids?
A: Belt dryers are assumed for preliminary design and will be utilized to produce dried biosolids. The dryer and facilities to house drying process equipment will be designed with built-in safety features to address potential fire risks associated with the following:
- Potential for fire within the dryer during drying operation
- Potential for fire resulting from dust generated from the dried material
- Potential for fire associated with storage of dried biosolids in silos
The National Fire Protection Association (NFPA) 820, Standard for Fire Protection in Wastewater Treatment and Collection Facilities, provides guidance for fire protection and electrical classification for wastewater facilities. In accordance with NFPA 820, Table 6.2.2(b), the drying facilities will be equipped with the following:
- Fire protection measures including hydrant protection, fire alarm system, and a fire suppression system (automatic sprinkler, water spray, foam, gaseous, or dry chemical).
- Fire protection measures including hydrant protection and fire alarm system for dried biosolids storage areas.
In addition to the NFPA 820 guidelines for drying facilities summarized above, the drying equipment will be equipped with inherent safety protection measures including heater controls and feedback loops, drying chamber temperature controls and feedback loops, process air temperature controls and feedback loops, and a fire suppression system. These systems and controls provide protection against fire hazard risks due to high temperature and dust:
- The dryer belt conveyor will be designed to minimize pass-through of dust in the process air stream. Finer dust particles that pass through the belt are either carried to the condenser’s filter media and removed, or remain in the chamber where wash-out system will routinely clean the system with spray nozzles.
- Various sections of the drying equipment that convey dried biosolids and recirculating dryer gas for drying will be equipped with thermocouples. Chamber temperature will be monitored continuously, and a PLC control system will utilize this data to regulate the amount of heat added to the system. For example, a high temperature may indicate that insufficient product is being diverted through the dryer, and the heat supplied may be reduced.
- The dryer will be equipped with a quench spray system. If triggered (at a high temperature set point), the quench system will activate and saturate the dryer as an immediate safety measure.
- The dryer exhaust gas will be recirculated and reused to ensure an oxygen-deficient atmosphere in the dryer.
The dried biosolids product will be cooled prior to storage to reduce the risk of auto-oxidation. Fire hazards during dried biosolids storage in silos will be addressed using inert gas (nitrogen) blanketing systems to maintain an oxygen deficient environment in the silo. In addition, the silo will be equipped with thermal sensors or carbon monoxide sensors to detect any potential rise in temperature.
For additional information, please review the following documents:
Q: Is there a list of similar facilities and their capacities in MA?
Please review the document linked below for a list of similar facilities in the Commonwealth of Massachusetts.