Cj. Rivard et al., DEVELOPMENT OF A NOVEL, 2-STEP PROCESS FOR TREATING MUNICIPAL BIOSOLIDS FOR BENEFICIAL REUSE, Applied biochemistry and biotechnology, 70-2, 1998, pp. 569-577
Modern municipal sewage waste treatment plants use conventional mechan
ical and biological processes to reclaim wastewaters. This process has
an overall effect of converting a water pollution problem into a soli
d waste disposal problem (sludges or biosolids). An estimated 10 milli
on tons of biosolids, which require final disposal, are produced annua
lly in the United States. Although numerous disposal options for bioso
lids are available, Including land application, landfilling, and incin
eration, disposal costs have risen, partly because of increased federa
l and local environmental restrictions (1). A novel, thermomechanical
biosolids pretreatment process, which allows for a variety of potentia
l value-added uses, was developed. This two-step process first employs
thermal explosive decompression to inactivate or kill the microbial c
ells and viruses. This primary step also results in the rupture of a s
mall amount of the microbial biomass and increases the intrinsic fluid
ity of the biosolids. The second step uses shear to effect a near-comp
lete rupturing of the microbial biomass, and shears the nondigested or
ganics, which increases the overall surface area. Pretreated biosolids
may be subjected to a secondary anaerobic digestion process to produc
e additional fuel gas, and to provide for a high-quality, easily dewat
ered compost product. This novel biosolids pretreatment process was re
cently allowed a United States patent.