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Biosolids managers should be cautious of hazardous conditions linked to heat drying and dewatering systems, according to experts.
Heat drying can cause fires if treatment plants are not careful, said Webster Hoener, an engineer with Black & Veatch, Overland Park, Kan. Biosolids are combustible material. Heat drying causes auto-oxidation. Grease and dust collects in drying systems.
To prevent fires, managers can eliminate oxygen source in the drying process and storage areas. They also can address smoldering that occurs before a fire erupts and ventilate combustible dust. Managers should design systems to avoid fire dangers by using industry standards, relying on system supplier experience, putting in mitigation systems and installing operable systems to counteract dangers.
"It is critical to make sure there is no dust during high-risk periods and that conditions are in a steady state. Moisture should be at suitable levels," Hoener told CWR.
In Japan, the Institute of Wastewater Engineering conducted a survey to determine how many plants understood dangers associated with biosolids systems. The survey found accidents occur from methane explosions, fires in dryers and during methane gas formations, said Hajime Seki, a scientist with the institute.
The survey discovered Japan has a rising number of accidents after treatment plants are commissioned. Inadequate operating skills, stoppage in storage units and normal operation of dryers are culprits of accidents.
"Managers do not have a general recognition of the dangers associated with biosolids. Systematic prevention measures have not been established," he told CWR.
Treatment plants can precirculate sludge, drain methane gas in areas away from sludge and install carbon monoxide concentration meters. Managers also should purge systems of dust and ensure water content is more than 5 percent. Technical data are useful to enhance safety measures in the future, he said.
In addition, treatment plants should include dryer safety in the safety program for the whole plant, Hoener said.
Contacts: Linda Bond, Black & Veatch, (913) 458-3124, firstname.lastname@example.org; Hajime Seki, Japan Institute of Wastewater Engineering, (011) 81-3-5951-1331, http://www.jiwet.jp.
"Precautionary measures prevent dangers associated with dryers." Clean Water Report 18 Dec. 2006: 244. Academic OneFile. Web. 2 Jan. 2010.
Gale Document Number:A156572436