Composting

Sludge residuals may also be biochemically digested, stabilized, and perhaps even partially or fully pasteurized using composting operations of the sort shown in Figure 16.49. When exposed to moisture and appropriate environmental conditions, organic, nutrient-rich surfaces will quickly become colonized by bacteria and other microorganisms. Since no organism can be 100 efficient in its metabolism, during the ensuing degradation of the organics, some chemical energy is wasted and given off as an...

Testing for Carcinogenicity and Teratogenicity

Carcinogenic potential can be detected by three types of tests long-term carcinogenicity studies, rapid screening tests, and biomarkers. Long-term tests are the most definitive. These generally use mice or rats and last the lifetime of the animals (18 and 24 months, respectively). Two or three dose levels are usually used, the highest being the maximum tolerated dose'' (MTD). The MTD is estimated from 90-day studies and is chosen so as not to produce severe noncarcinogenic toxicological effects...

Arthropods

Arthropods (jointed legs) include the spiders, centipedes, millipedes, insects, and crustaceans. They represent an evolutionary advance that allowed them to form the greatest diversity and number of species of all the phyla, about 1 million species known. The advance was the development of a jointed exoskeleton made of chitin, a nitrogenous poly-saccharide, bound with protein. In crustaceans the exoskeleton also contains calcium salts for added strength. Other innovations with this phylum are...

Solid Waste Treatment

Biodegradation of dead plant, animal, and other residues has played an important role on our planet's surface since the inception of life eons ago, recycling valuable nutrients back into our biosphere while negating or at least reducing the shear physical burden of this never-ending natural debris stream. At least in theory, therefore, nature provides a highly useful example of a means by which we might manage our own solid waste residuals, taking full advantage of much the same aerobic and...

Ionizing Radiation

An important physical cause of toxic effects is a variety of forms of radiation. Ionizing radiation possesses enough energy to strip an electron from an atom. This can result in the formation of damaging free radicals or directly damage bonds in biochemical substances. The most sensitive system in living things is the DNA, since damage to a single molecule can transform a cell to malignancy. It is not necessary for a radioactive emission to damage a DNA molecule directly. The most abundant...