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  • Reduced Disposal Costs: ​The ability of the WWTP to take in additional organic waste from the Town, could potentially reduce disposal costs both for town residents, local businesses, commercial industries and the Department of Public Works (DPW). Due to the municipal nature of the project site, any savings or revenue of the project benefits all town taxpayers. Plymouth is currently paying in the range of $250,000 - $350,000 per year to dispose of its sludge and the addition of an anaerobic digester can significantly decrease disposal costs. Municipal wastewater digesters typically have sludge volume reductions between 45-50%, with advanced digester technologies, such as those investigated in this report, up to 80-90%.

  • Lower Tipping Fees:   Separating out digestible material from the waste stream for separate collection (Source Separated Organics - SSO's) will lessen the solid waste volume going to a landfill, in turn lowering tipping fee expenses allocated to the generators and haulers (both private and public sectors). Also, significantly reducing sludge volumes that require transportation and disposal will lower tipping fees charged to the town.

  • Potential Revenue Streams:  The Town of Plymouth has potential revenue streams through tipping fees from accepting organic waste from local generators and sludge from surrounding wastewater treatment plants; off-set electrical power and hot water heating use for the Plymouth WWTP; electrical capacity sent to the grid; upgrading the biogas to a pipeline quality gas standard and sold directly into the pipeline system; upgrading biogas to produce compressed natural gas (CNG) for vehicles; creating a marketable byproduct from the digestate that can be utilized as soil amendment and/or fertilizer. ​ 

  • ​Increased Employment: The construction necessary, as well as sub-contracting to local engineering and design groups, will generate new jobs and revenue.

  • MassDEP Organics Waste Ban: The MassDEP has proposed an organics waste ban, set to go into effect in July 2014 in Massachusetts, which will prohibit large institutions and businesses (e.g. hospitals, large restaurants, hotels, universities, etc.) from sending organic waste into landfills or incinerators. By creating a local, organic recycling facility, the costs and emissions associated with the disposal of food waste will be significantly lowered. The space in landfills is only becoming more limited, and this ban hopes to divert at least a third of the nearly 1.4 million tons of organic waste produced every year in Massachusetts.

  • Typical Incineration and Disposal Methods of Sludge:  Sludge incinerators and landfills are an unsustainable and dying technology. Incineration and disposal rates as well as transportation costs continue to rise, and as incinerators go offline and landfills fill-up, it is not a viable long-term solution for the Plymouth WWTP to continue finding alternative incinerators and out of state landfills.   

ECONOMIC and REGULATORY

Below are the potential economic impacts of the addition of an anaerobic digester to the Plymouth Wastewater Treatment Plant.  They are largely reduced disposal and operational costs.

  • Enhanced Air Quality:  Broadly, anaerobic digestion will enhance air quality through reduced greenhouse gas emission and local air pollution, reduced CO2 emissions, and will divert methane from being released into the atmosphere to be used instead for productive purposes.

  • Reduced Emission from Transportation: The solid waste from the Plymouth WWTF is currently transported out of state to Rhode Island. In comparison, a local waste management will reduce emissions associated with the transport of food waste and sludge to faraway disposal sites.

  • Methane Diversion:  When organic waste is landfilled it undergoes anaerobic digestion and releases considerable amounts of methane, a greenhouse gas with 23 times the global warming potential of CO2. With an anaerobic digester, the WWTF will capture this methane for use as energy and decrease methane emissions into the atmosphere.

  • Reduced Consumption of Fossil Fuels​:  Using local organic waste to generate methane and electricity will help displace fossil fuels.

  • Diversion of Organic Waste from Landfills:  The capacity of Massachusetts landfills is continually decreasing, with an expected drop from 2.1 million tons this year to approximately 600,000 tons/year by 2020. Massachusetts produces nearly 1.4 million tons of organic waste every year, so diversion of as much of this as possible is essential.

  • Diversion of Organic Waste from Incineration: There are concerns about sludge incineration because of emissions, high costs, and the need for additional fuel to operate. An anaerobic digester and CHP system will eliminate the need for incineration and disposal of the sludge from the Plymouth WWTP.

  • Good Location: The town of Plymouth owns 100 acres around the WWTP, and is well-suited for the upgrades and construction needed to handle additional waste processing. It is zoned Municipal Waste.

  • ​Reduced Odor:​  Anaerobic digestion reduces odor significantly because it is contained in an airtight structure, and as a process inherently breaks down volatile organic compounds (VOC's - the putrescible, odor causing matter) in a substrate, reducing odor by 90%.

  • Pathogen Removal: Many of the pathogens and toxins that exist in wastewater sludge and some organic material, are broken down and destroyed through the AD process.  To further stablize the digestate and remove remaining pathogens to protect the environment, additional treatment to the digestate can be done including aerobic composting, pasteurization, and pyrolysis removing toxins and pathogens.  Pathogen removal can be as high as 99%.

  • Back Up Power Supply: The CHP system can serve as backup in response to inconsistent power supply or anticipated power outages/shortages, especially for municipal buildings such as schools.

  • Useful Land Applicable End Product: Anaerobic digestion creates a nutrient rich end product called digestate that can be applied to crops, brownfields, marketed and sold, municipal lawn care, etc.  Digestate options include:

1. Spread 'as is' on fields.  This will  be dependent on distance, crop type, and regulations.

2. Separate solids and liquid.  The solid portion can be applied as a soil amendment, while the remaining effluent (~3% solids) can be sprayed on fields as a fertilizer.

3. Composted.  The digestate is separated to a 15 - 20% solids which is then sent to a composting facility.  The remaining liquid can be sent back to the digester to make a slurry with the remaining feedstock, or be sold as a liquid fertilizer

 

  • Decreased Use of Chemical Fertilizers: Inorganic chemical fertilizers are energy-intensive to produce and transport and have a variety of adverse effects such as leaching into and polluting local waterways. Digestion creates a natural fertilizer end product that can be used in place of inorganic chemical fertilizers.

  • Increased Community Pride: The Plymouth community can take pride in the fact that they are significantly reducing their organic waste stream and their dependence on imported fossil fuels through the use of anaerobic digestion technology, contributing to local economic and environmental resiliency. Residents and business owners can take pride in their greener local institutions (Supermarkets, Restaurants, etc).

  • Back up Power Supply:  The CHP system can serve as backup in response to inconsistent power supply or anticipated power outages/shortages, especially for municipal buildings such as schools.

ENVIRONMENTAL and SOCIETAL

Below are the potential environmental impacts of the addition of an anaerobic digester to the Plymouth Wastewater Treatment Plant.  The most significant impacts arise because of redirecting organic waste from landfills and repurposing it as a renewable energy, including a decrease in methane emissions and decreased consumption of fossil fuels.   Additionally, anaerobic digestion can assist the wastewater treatment plant processes in reducing total volume, solids, and destroy the odor causing material, in turn benefitting the WWTP's neighbors and the Plymouth community by reducing potential unpleasant odors.

Plymouth Project Impacts

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