Encyclopedia of Global Resources part 141 provides a wide variety of perspectives on both traditional and more recent views of Earth's resources. It serves as a bridge connecting the domains of resource exploitation, environmentalism, geology, and biology, and it explains their interrelationships in terms that students and other nonspecialists can understand. The articles in this set are extremely diverse, with articles covering soil, fisheries, forests, aluminum, the Industrial Revolution, the . Department of the Interior, the hydrologic cycle, glass, and placer mineral deposits. . | 1306 Waste management and sewage disposal Global Resources tant reason that separate sewers even though more expensive are favored by public health officials. The biologic processes can also be severely affected by toxic industrial waste that can kill the good bacteria which are crucial to the treatment process. Accordingly many communities require pretreatment for industrial wastes. Tertiar y treatment is the most advanced form of waste treatment. It includes a number of practices such as the use of ozone which is a strong oxidizing agent to remove most of the remaining BOD odor and taste and the addition of alum as a phosphate precipitator. A recent and innovative method of ter-tiar y treatment is to spray chlorinated effluent on either croplands wooded areas or mine tailings after it has been given secondary treatment. This method has several distinct advantages over the traditional direct discharge of the effluent into surface watercourses. First biologic digestion in the soil removes almost all of the remaining BOD. Second soil and plants are capable of absorbing large amounts of nitrogen and phosphorus during the growing season which slows their release into the environment. Other benefits include increased crop and timber yields and groundwater recharge. The land area needed to handle treated wastewater by the spray irrigation method is approximately square kilometers per 100 000 people. Wastewater Disposal in Rural and Suburban Areas In areas where population densities are less than about 1 000 people per square kilometer the cost of a sewer system and treatment plant are difficult to justify. Septic systems are commonly used in residential areas for disposal of domestic wastewaters. Household effluent is piped to a buried septic tank which acts as a small sedimentation basin and anaerobic without oxygen sludge digestion facility. The effluent exits from this tank into a disposal field where aerobic with oxygen biologic breakdown of dissolved and solid
