Organic Waste Recycling

400 Organic waste reuse and recycling: technology and management

wastewater land treatment system and the need for pre-application (or pre-
treatment) methods must relate the quantity and types of pollutants in the
wastewater to the pollutant removal mechanisms in the soil. These can be
categorized as physical, such as gravitational settling, filtration and dilution;
chemical, such as adsorption and precipitation; and biological, such as microbial
transformations and plant uptake. The need for pre-application can be determined
by evaluating the possibility of overloading the removal mechanisms.

(a) Overland flow followed by rapid filtration

(b) Rapid infiltration followed by slow rate treatment

Figure 8.5 Examples of combined systems (U.S.EPA 1981)

The waste management relationship that occurs with land treatment of
wastewater is shown in Figure 8.6.

8.3.1 Physical removal mechanisms

As wastewater moves through the soil pores, suspended solids are removed by
filtration. The depth at which removal occurs varies with the size of the
particles, soil texture, and rate of water movement. The higher the hydraulic
application rate and the coarser the soil, the greater the distance the particles will
move. However, at the wastewater application rates used with the slow rate

PREAPPLICATION

TREATMENT

STORAGE OVERLAND

FLOW

RAPID

INFILTRATION

OPTIONAL

RECOVERY

WELLS

OVERLAND DISCHARGE

FLOW

PREAPPLICATION

TREATMENT

RAPID

INFILTRATION

RECOVERY

WELLS

SLOW RATE

TREATMENT