Biohazards of Sewage Sludge

Wastewater can come from a variety of sources like homes, businesses, industries, runoff from roads, lawns and fields and is treated by municipal wastewater treatment facilities (Product, cornell). The solid material that remains after the treatment of wastewater is known as sludge (charac, cornell). Sludge can be employed in many different ways, it can be used as a soil additive or growing medium, sent to a composting facility, incinerated or landfilled (Char, cornell).

Biosolids are derived primarily from a combination of primary, secondary, and tertiary sewage sludges. Biosolids do not contain the coarse grit and screenings removed from raw wastewater during preliminary treatment steps or ash generated from incineration of sewage sludge. Another type of biosolids may be derived from domestic septage, the solid or liquid material removed from septic systems, portable toilets, and other systems that receive only domestic sewage. However, since all sludges and biosolids contain potentially harmful cntaminants, beneficial uses must be balanced against acceptable risks for human health and environmental impacts (Beneficial, cornell)

The terms sludge and biosolids are in some cases universally interchangeable, while in some cases there are minor discrepancies between the two definitions. Thus for the sake of this paper we will treat the two definitions as equal and interchangeable.

While in most cases, the composition of the received wastewater is uncontrollable, the makeup of the resultant sludge must be known in order to determine its suitablility for various uses (Prod, cornell). When evaluating the composition of sludge, its physical and chemical properties must be considered. Questions that should be asked are: How much water and solid matter does it contain? How many different metals and nutrients does it have and how much of each? What potentially toxic organic chemicals are contained in the sludge? What pathogen reduction process was used?