Organic Waste Recycling

Characteristics of organic wastes 71

Table 2.27 Tentative microbiological quality guidelines for treated wastewater reuse in
agricultural irrigationa (IRCWD 1985).

Reuse process

Intestinal nematodesb

(arithmetic mean no. of

viable eggs per litre)

Fecal coliforms
(geometric mean no.
per 100 ml)
Restricted irrigationc

Irrigation of trees, industrial
crops, fodder crops, fruit treesd
and pasturee

” 1 Not applicablec

Unrestricted irrigation

Irrigation of edible crops sports
fields, and public parkf

” 1 ” 1000 g

aIn specific cases, local epidemiological, socio-cultural, and hydrogeological factors should be taken
into account, and these guidelines modified accordingly.
bAscaris,Trichuris and hookworms.
c A minimum degree of treatment equivalent to at least a 1-day anaerobic pond followed by a 5-day
facultative pond or its equivalent is required in all cases.
d Irrigation should cease two weeks before fruit is picked, and no fruit should be picked off the
ground.
e Irrigation should cease two weeks before animals are allowed to graze.
f Local epidemiological factors may require a more stringent standard for public lawns, especially
hotel lawns in tourist areas.
g When edible crops are always consumed well-cooked, this recommendation may be less stringent.

Since the organic wastes described in sections 2.1, 2.2 and 2.3 would normally
contain low concentrations of heavy metals, the health risks with respect to heavy
metal contamination resulting from the practice of organic waste recycling should
not be of a great concern.
However, there is a possibility of accumulation of heavy metals (even though at
trace concentrations) in the biological food chain and in soils receiving wastewater
and sludge for a long period of time. This long-term accumulation of heavy metals
can lead to a problem of bio-magnification where organisms in the upper part of the
food chain (e.g. animals or human beings) that feed on the contaminated crops
could have heavy metal concentrations several times greater than those present in
the soil or crops.
Information about standards or guidelines of heavy metal concentrations in
wastewater and sludge to be reused in agriculture or aquaculture are available for
most developed countries in North America and Europe; this information will be
referred to in Chapters 8 and 9 (Land Treatment of Wastewater and Sludge,
respectively).