Sludge dewatering represents the general process of removing moisture from sludge in order to reduce its total volume, and this is desirable in most cases for minimizing downstream sludge management and transportation costs. Many different technologies exist to accomplish this goal, such as decanter centrifuge and diverse press-like units. A simple alternative to this mechanical equipment are the geotextile dewatering tubes, which are disposable bags to which sludge is continually fed until a critical volume is reached, and then are allowed to drain naturally. Apart from having a simple operation, these bags allow for sludge accumulation over extended periods of time, until it is transported to the disposal site. The sludge dewatering process is more complex than an ideal sedimentation and it involves the need of additional pressure in order to dewater the material further once a certain threshold concentration is reached, called the gel point.
Composting is an aerobic process of mixing sewage sludge with agricultural byproduct sources of carbon such as sawdust, straw or wood chips. In the presence of oxygen, bacteria digesting both the sewage sludge and the plant material generate heat to kill disease-causing microorganisms and parasites. Maintenance of aerobic conditions with 10 to 15 % oxygen requires bulking agents allowing air to circulate through the fine sludge solids. Compost is rich in nutrients. It is used, for example, in gardens, landscaping, horticulture, urban agriculture and organic farming. The compost itself is beneficial for the land in many ways, including as a soil conditioner, a fertilizer, addition of vital humus or humic acids, and as a natural pesticide for soil. In ecosystems, compost is useful for erosion control, land and stream reclamation, wetland construction, and as landfill cover.