WEF Residuals and Biosolids Specialty Conference

The WEF Residuals and Biosolids Specialty Conference offered many forums to learn and discuss climate change, global warming, greenhouse gases and carbon footprints.

The Opening General Session was organized by Jeff LeBlanc , and Bill Toffey, and offered several papers on climate change. Usually, the keynote session is full of praise for the organizers and attendees, speakers start out with a humorous anecdote, and are full of success stories. However, this session was very somber. The lights were turned off and the screen held images of a future world with rising seas, changing shorelines and expanding deserts. Graphs showed the exponential increase in greenhouse gases and the disproportionate contribution of greenhouse gases by the United States.

Presentations included "An Inconvenient Truth" presented by Andrew Pitz of the Climate Project, and "Climate Change and Biosolids“ An International Perspective" presented by Steve Ntifo, from Water UK.

Along the lines of what can be done about climate change, a presentation by Scott Subler, of the Environmental Credit Corporation was titled "Opportunities for Carbon Credits for Biosolids Projects".

Information included in his presentation follows:

"What are carbon credits?  Carbon credits are a new financial commodity representing certified reductions in the emission or accumulation of greenhouse gases in the atmosphere. Greenhouse gases trap heat from the sun and help regulate the temperature of the earth's atmosphere. As concentrations of atmospheric greenhouse gases increase due to human activities, global average temperatures may rise - with potentially costly consequences. Man-made greenhouse gases, produced from industrial, agricultural, and municipal sources, include carbon dioxide, methane, nitrous oxide and several other chemical compounds.

How are carbon credits created?  Carbon credits can be created from agricultural, waste management and renewable energy projects that reduce greenhouse gas emissions. By implementing appropriate practices and technologies according to specific protocols, reductions in greenhouse gas emissions can be monitored, documented, independently verified, and registered to an account (e.g. within the Chicago Climate Exchange) as certified, tradable carbon credits."

Wastewater Treatment Plant and biosolids managers can create carbon credits from:

* Agricultural soil and forest carbon sequestration - when we land apply biosolids or biosolids derived products such as compost to agricultural soils or forests, organic matter is added to the soil (carbon is sequestered)

* Wastewater methane and nitrous oxide emission reduction - when we capture and utilize the methane from digestion, cover sludge lagoons or minimize energy usage, a plant may be eligible for carbon credits

* Renewable energy production and energy efficiency improvements - digester gas and/or biosolids can be used as a renewable source of fuel.

Preconference workshops also provided a wealth of information on ways to minimize our contribution to greenhouse gases.

The session on "Giving Residuals and Biosolids Reuse the Carbon Credit They Deserve" presented "An Overview of Bioenergy Opportunities" by Ned Beecher.  Additional presentations included; "Case Studies of Carbon Footprinting", "Alternatives for Carbon Emissions and Energy Reductions" and "Financial Aspects of Carbon and Energy Credits."

"An Economic Framework for Evaluating Benefits and Costs of Biosolids Management Options"  This workshop pointed out that carbon sequestration resulting from biosolids re-use is a benefit and greenhouse gas emissions are a cost to be considered in evaluating alternatives. A case study compared the greenhouse gas generated by landfill disposal with the avoided energy usage in the manufacture of fertilizer when biosolids are land applied.

"Value Added Products from Municipal, Agricultural and Industrial Waste Residuals" Presentations covered the use of biosolids to create alternative, renewable fuels such as methane gas, ethanol, methanol, and heat from the volatile solids contained in biosolids. 

Papers presented during the conference that addressed the greenhouse gas issues include:

"A Comparison of the Carbon Footprint of Aerobic and Anaerobic Digestion" This paper compares aerobic and anaerobic digestion technologies at two medium sized POTW’s in Georgia. The aerobic digestion case study describes a plant that currently land applies a liquid, Class B biosolids. The anaerobic digestion case study uses digester gas for cogeneration of heat and electricity. The carbon footprint of the anaerobic digestion with cogeneration is approximately 200 metric tons per year of CO2 equivalents (greenhouse gases.) Aerobic digestion produces approximately 325 metric tons per year of CO2 equivalents which is about 60% more than anaerobic digestion. These projected emissions do not take into account the nitrous oxide emissions produced from aerobic digestion because it is not known exactly how much NOx is released from aerobic digestion.

"Biosolids Master Planning from a Greenhouse Gas Perspective-How Different Options Affect the Carbon Footprint" -The most common greenhouse gases produced by wastewater treatment plants are carbon dioxide and nitrous oxide. Biosolids management activities have a large impact on the GHG emissions generated from wastewater. Biosolids represent a potential resource for energy recovery. They also can be used as a fertilizer which then helps plants sequester more carbon from the atmosphere. Biosolids management activities need to be evaluated from the point they enter the wastewater system in homes and offices to their final destination either on fields, landfills or incinerators. If the whole biosolids cycle is not considered then the carbon footprint estimation will be flawed. Increasing the use of digester gas and reducing the use of fossil fuels have major impacts on reducing GHG emissions. The primary recommendation of this paper is to develop a protocol for evaluating the GHG emissions of wastewater and biosolids processing. These protocols should include detailed and accurate carbon footprint baselines.

"Greenhouse Gas Emissions - How Sustainable is your Treatment Process?"

This paper focused on greenhouse gas (GHG) emissions from the processes at a wastewater treatment plant. GHG emissions can greatly be reduced by minimizing the use of fossil fuels and maximizing the use of digester gas. Also solids treatment alternatives that incorporate landfill with gas recovery and/or land application of dewatered cake have the lowest GHG emissions. Using biosolids as a fertilizer (avoiding the use of fossil fuel in the energy intensive fertilizer manufacturing) can reduce GHG emissions. Processes that include extensive use of heat such as incineration have higher GHG emissions because of high electricity use and creation of nitrogen emissions.

"A Greenhouse Gas Accounting Model for Biosolids Management Planning"

The sustainability of biosolids management planning is measured largely by carbon footprint and GHG emissions. A model has been developed to estimate equivalent carbon dioxide emissions rate per dry ton. This model calculates emissions for each unit process so is adaptable for a wide variety of plants. The model is a series of computational worksheets.