Encyclopedia of Environmental Science and Engineering, Volume I and II

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NATURAL SYSTEMS FOR WASTEWATER TREATMENT

INTRODUCTION

In the continual search for a simple, reliable, and inexpen-

sive wastewater treatment system, the natural systems are the

latest discovery. They provide not only efficient methods of

wastewater treatment, but also provide some indirect benefi-

cial uses of the facility such as green space, wildlife habitat,

and recreational areas.

In the natural environment, physical, chemical, and bio-

logical processes occur when water, soils, plants, microor-

ganisms, and atmosphere interact. To utilize these processes,

natural systems are designed. The processes involved in the

natural systems include: sedimentation, filtration, gas transfer,

adsorption, ion exchange, chemical precipitation, chemical

oxidation and reduction, and biological conversions plus other

unique processes such as photosynthesis, photooxidation,

and aquatic plant uptake.^1 In natural systems, the processes

occur at “natural” rates and tend to occur simultaneously in

a single “ecosystem reactor” as opposed to mechanical sys-

tems in which processes occur sequentially in separate reac-

tors or tanks in accelerated rates as a result of energy input.

Generally, a natural system might typically include pumps

and piping for wastewater conveyance but would not depend

on external energy sources exclusively to maintain the major

treatment responses.^2

In this paper a general overview of natural systems for

wastewater treatment is presented. The constructed wet-

lands are becoming a viable wastewater treatment alterna-

tive for small communities, individual homes, and rest areas.

Therefore, in this paper, a great deal of information has been

presented on site selection, design of physical facilities, per-

formance expectations, hydraulic and organic loading rates,

and cost of the constructed wetlands.

TYPES OF NATURAL SYSTEMS

Natural systems for effective wastewater treatment are

divided into two major types: terrestrial, and aquatic systems.

Both systems depend on physical and chemical responses as

well as on the unique biological components.^2 Each of these

systems are discussed below.

Terrestrial Treatment Systems

Land application is the sole terrestrial treatment system used

to remove various constituents from the wastewater. It uti-

lizes natural physical, chemical, and biological processes

within the soil-plant-water matrix. The objectives of the land

treatment system includes, irrigation, nutrient reuse, crop

production, recharge of ground water and water reclamation

for reuse. There are three basic methods of land application:

(1) Slow-rate irrigation, (2) Rapid-infiltration–percolation,

and (3) Overland flow. Each method can produce renovated

water of different quality, can be adapted to different site

conditions, and can satisfy different overall objectives. 3,4

Typical design features and performance expectations for

the three basic terrestrial concepts are given in Table 1.

Slow-rate irrigation Irrigation is the most widely used form

of land treatment systems. It requires presence of vegetation

as a major treatment component. The wastewater is applied

either by sprinkling or by surface technologies. In this pro-

cess surface runoff is not allowed. A large portion of water is

lost by evapotranspiration whereas some water may reach the

groundwater table. Groundwater quality criteria may be a lim-

iting factor for the selection of the system. Some factors that

are given consideration in design and selection of irrigation

method are (1) availability of suitable site, (2) type of waste-

water and pretreatment, (3) climatic conditions and storage

needed, (4) soil type, and organic and hydraulic loading rates,

(5) crop production, (6) distribution methods, (7) application

cycle, and (8) ground and surface water pollution. 2,3,5

Rapid-infiltration – percolation In rapid-infiltration-percolation

the wastewater percolates through the soil and treated effluent

reaches the groundwater or underdrain systems. Plants are

not used for evapotranspiration as in irrigation system. The

objectives of rapid infiltration—percolation are (1) ground-

water recharge, (2) natural treatment followed by withdrawal

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