6 Organic Waste Recycling: Technology and Management
concept of waste recycling rather than simply waste treatment has received wide
attention. A combination of waste treatment and recycling such as through biogas
(methane) production, composting, or aquaculture, besides increasing energy or
food production, will, if carried out properly, reduce pollution and disease transfer
(Rybczynski et al. 1978). Waste recycling also brings about a financial return on
the biogas, compost, and algae or fish which may be an incentive for the local
people to be interested in the collection and handling of wastes in a sanitary
manner.
The technologies to be discussed in this book apply mainly to human waste
(i.e. excreta, sludge, nightsoil, or wastewater), animal wastes and agro-industrial
wastewaters whose characteristics are organic in nature.
1.2 OBJECTIVES AND SCOPE OF ORGANIC WASTE
RECYCLING
The objectives of organic waste recycling are to treat the wastes and to reclaim
valuable substances present in the wastes for possible reuses. These valuable
substances include carbon (C), nitrogen (N), phosphorus (P), and other trace
elements present in the wastes. The characteristics and significance of these
substances are described in Chapter 2.
The possible methods of organic waste recycling are as follows:
1.2.1 Agricultural reuses
Organic wastes can be applied to crops as fertilizers or soil conditioners. However,
direct application of raw wastes containing organic forms of nutrients may not
yield good results because crops normally take up the inorganic forms of nutrients
such as nitrate (NO 3 - ) and phosphate (PO 4 3-). Bacterial activities can be utilized to
break down the complex organic compounds into simple organic and finally
inorganic compounds. The technologies of composting and aerobic or anaerobic
digestion are examples in which organic wastes are stabilized and converted into
products suitable for reuse in agriculture. The use of untreated wastes is undesirable
from a public health point of view because of the occupational hazard to those
working on the land being fertilized, and the risk that contaminated products of the
reuse system may subsequently infect man or other animals contacting or eating the
products.
Wastewater that has been treated (e.g. by sedimentation and/or biological
stabilization) can be applied to crops or grasslands through sprinkling or soil
infiltration. The application of sludge to crops and forest lands has been
practiced in many parts of the world.