The city of Bridgeport, Conn., may be the host of a facility that will recycle sewage sludge into methanol, a viable alternative fuel. The $200 million regional sludge management facility currently a-waits state regulatory approvals.
The facility is the first of its kind. It would use the following processes (see chart), which have been in use for more than 70 years:
* steam drying the sludge;
* gasification of dry solids; and
* methanol synthesis.
After dewatered sludge (20 to 30 percent solids) arrives at the facility, it is dried to increase the solids content through a steam process that has been used in the waste management industry for more than 20 years.
The processed sludge is then placed in a gasifier, which heats the sludge under pressure. This produces a synthesis gas of carbon monoxide, hydrogen and carbon di-oxide. Because the process takes place at temperatures from 2,500 to 3,000 degrees Fahrenheit, the ash produced is a black, sand-like non-leachable aggregate, which permanently binds the heavy metal contaminants contained in the sludge. No combustion products reportedly are released into the at-mosphere. After the synthesis gas is treated, methanol is produced by converting the carbon monoxide and hydrogen in a low pressure catalytic unit.
Gasification technology was de-veloped in the early l900s and used extensively in Europe to manufacture gas before natural gas was discovered. The methanol synthesis process was developed in the 1920s and is currently used in more than 50 plants operating a-round the world.
In addition to methanol and construction aggregate, the process produces elemental sulfur, all of which have established markets.
Methanol can be used to replace diesel fuel, reportedly reducing tail pipe emissions. Methanol also is an essential ingredient in the production of methyl tertiary butyl ether (MTBE), a gasoline additive that re-portedly achieves lower engine e-missions. The United States Clean Air Act requires increased use of oxygenating additives, such as MTBE, in reformulated gasoline.
The proposed facility will be capable of producing 30 million gallons of methanol annually, which will be sold into the meth-anol fuels market.
The New Jersey Department of Environmental Protection and En-ergy has previously qualified the process as a "high technology beneficial-use system." The revenue produced by selling methanol will allow the facility to reduce the cost of sludge disposal by 70 to 75 percent as compared to other beneficial-use options.
Since ocean dumping of sludge was banned by the U.S. government in l988, several disposal technologies have been developed. Cur-rently, the most common options include pelletizing, composting and land spreading of sludge. However, these options are not recommended for sludge containing heavy me-tal contaminants. In urban areas, the costs of these disposal methods range from $500 to $1,000 or more per dry ton of sludge. The sludge-to-methanol technology would re-duce processing fees to approximately $350 to $400 per dry ton, comparable to costs associated with incineration and landfilling.
The proposed facility also will re-portedly create approximately 400 jobs and generate $6 to $8 million in annual revenue for the city of Bridgeport. The community's citizens and organizations have been supportive. The greatest concern - the potential of odors - was ad-dressed in the Host Community Agreement with the city. All areas in which sludge is processed will be fully enclosed and a control system will ensure that odors do not leave the facility.
Regional in nature, the facility was designed to treat 500 tons of sludge per day, sufficient capacity to handle sludge disposal needs of generators throughout Connecti-cut, New York and New Jersey. In-terstate Waste Technology (IWT), St. Charles, Md., which has led the planning and design of the Bridge-port facility, is currently in discussion with several municipalities in the region. Regulatory approval is expected later this year.