Book Description

The wastewater treatment systems described in this book are specifically designed to utilize natural responses to the maximum possible degree when obtaining the intended treatment or management goal. By using the soil and plants to sustain microbial populations, wastewater can be treated in a relatively passive manner. In most cases, this approach will result in a system that costs less to construct and operate and requires less energy than mechanical treatment alternatives.

NATURAL TREATMENT PROCESSES

All wastewater management processes depend on natural responses, such as gravity forces for sedimentation, or on natural components, such as biological organisms. In the conventional case, however, these natural components are supported by an often complex array of energy-intensive mechanical equipment. The term natural system as used in this text is intended to describe those processes that depend primarily on their natural components to achieve the intended purpose. A natural system might typically include pumps and piping for wastewater conveyance and distribution, but would not depend on external energy sources exclusively to maintain the major treatment responses.

 Background

Serious interest in natural methods for waste treatment reemerged in the United States following passage of the Clean Water Act of 1972 (PL 92-500). The primary initial response was to assume that the “zero discharge” mandate of the law could be obtained via a combination of mechanical treatment units capable of advanced wastewater treatment (AWT). In theory, any specified level of water quality could be achieved via a combination of mechanical operations; however, the energy requirements and high costs of this approach soon became apparent, and a search for alternatives commenced.

Land application of wastewater was the first “natural” technology to be rediscovered. In the 1840s in England, it was recognized as avoiding water pollution as well as returning nutrients in wastewater back to the land (Jewell and Seabrook 1979). In the 19th century it was the only acceptable method for waste treatment, but it gradually slipped from use with the invention of modern devices. Studies and research quickly established that land treatment could realize all of the goals of PL 92-500 while at the same time obtaining significant benefit from the reuse of the nutrients, other minerals, and organic matter in the wastes. Land treatment of wastewater became recognized and accepted by the engineering profession as a viable treatment concept during the decade following passage of PL 92-500, and it is now considered routinely in project planning and design.

Other “natural” concepts that have never been dropped from use include lagoon systems and land application of sludges. Wastewater lagoons model the physical and biochemical interactions that occur in natural ponds, while land application of sludges model conventional farming practices with animal manures.

Aquatic and wetland concepts are relatively new developments in the United States with respect to utilization of wastewaters and sludges. Some of these concepts provide other cost-effective wastewater treatment options and are, therefore, included in this text. Several sludge management techniques, including conditioning, dewatering, disposal, and reuse methods, are also covered, as they also depend on natural components and processes. The sludge management (biosolids) procedures discussed in Chapter 9 of this book are compatible with current U.S. Environmental Protection Agency (EPA) regulations and guidelines for the use or disposal of sewage sludge (40 CFR Parts 257, 403, and 503).