What Happened?
Washington, D.C., is launching a thermal hydrolysis plant that will convert sewage into 13 megawatts of electricity, enough to light 10,500 homes, as well as fertilizer. The end result of the treatment will be “enriched water” that will provide sources of clean energy to regional customers.
The Goal
The D.C. Water project will be the first of its kind in North America, after several smaller cities in Europe have made the thermal hydrolysis conversion work in their communities. The technology is based on the Cambi model originating from Norway that takes waste products there a series of steps to develop a new source of energy:
- Sewage flows into a thermal hydrolysis plant
- Sewage passes through mesh filters to shed debris
- Sewage heats up to more than 320 degrees under 138 pounds of pressure for 22 minutes
- Sewage moves to a flash tank where temperature and pressure drop and the cells burst
- Product enters the digesters and mixes with methanogen microorganisms to create methane gas
- After purification, the product can be used to fire jet turbine engines and create electricity
The current power plant produces enough Class B waste product to fill 60 dump trucks, or 1,600 tons, each day. The cost is about $16 million annually, The Washington Post reports. The new process will produce a class A product that can be used as a more environmentally-friendly alternative to traditional fertilizer for crops, or a topsoil substitute for green infrastructure projects.
According to D.C. Water, the benefits of launching the conversion plant include:
- $10 million reduction in electrical costs annually
- Reduced cost of hauling away treated waste
- Increase profit by selling the product
- Cutting the plant’s carbon footprint by one-third
- Clean source of energy to keep the local power plant operating and the water safe for drinking
Treatment an International Movement
The Cambi model for thermal hydrolysis has gained popularity in Norway and Spain, where the country’s largest bio-filtration plant will convert sludge into energy and fertilizers for residents in Vigo and surrounding municipalities. The power plant will initially treat 8,000 tons of dry solids annually, with the intent to convert more than 22,000 tons of dry solids each year by 2016. The thermal hydrolysis plant in Stavanger, Norway, is able to convert 11,000 tons of dry matter per year, and will work its way up to 22,000 tons annually.
Based on Cambi studies and results, the biogas generated from the thermal hydrolysis process can be used to provide heat, power a gas engine to produce electricity and heat, or produce compressed bio-methane for vehicle fuel gas once carbon dioxide has been removed.
Municipalities interested in implementing a thermal hydrolysis plant must ensure pre-treatment systems, as well as advanced screening and exit systems exist to sort out unwanted materials before the conversion process begins. The plants must also be equipped with closed air systems to trap odors and heightened oversight to ensure functions meet environmental standards.
Waste Not, Want Not
Gov1 has kept a close eye on how municipalities are reusing their waste to lower energy costs and increase profit potential.