Chapter Six
TECHNOLOGY AND TREATMENT
The NRC's second point discusses the
(2) wastewater treatment technologies and procedures
for agricultural use of these materials;
The wastewater collected from households, business
and commercial establishments and industrial facilities
which contain organic matter, disease causing agents,
nutrients (which can also be toxic), toxic and hazardous
pollutants (both organic and inorganic), and dissolved
minerals, which are concentrated during the treatment
process to produce sludge, are treated by one or more of
the following technologies:
(1) preliminary treatment, includes the screening of
course solids and grit removal of heavy solids that
would interfere with the treatment process.
(2) primary treatment "involves the gravity
sedimentation of screened, degritted wastewater to
remove settled solids; slightly more than one-half
of the suspended solids ordinarily removed."
"At one time during the evolution of domestic
wastewater treatment in the United States,
facilities only practiced primary wastewater
treatment and the primary effluent was commonly
discharged to surface waters offering appreciable
dilution. Now, primary treatment is used as an
economical means for removing some contaminates
prior to secondary treatment. The residue from
primary treatment is concentrated suspension of
particles in water called "Primary Sludge."
(P. 48)
(3) secondary treatment is generally accomplished by
using a biological treatment process in a trickling
filter, or ponds or some other process to remove
biodegradable material.
The NRC Report is rather vague on the results of
the biological process producing "carbon dioxide
and other end products." The "other end products"
include methane and hydrogen sulfide, a very deadly
gas. The Report is also vague on the "constituents"
"incidentally associated" in the secondary sludge
such as pathogens (disease causing organisms),
"trace elements" (toxic and hazardous substances)
and "organic compounds (PCB's as well as other
unknown compounds). (p. 49)
(4) advanced or "tertiary" treatment is used when a
high quality effluent is required. According to the
report, "Disinfection for control of pathogenic
microorganisms and viruses is the most common type
of tertiary treatment." (p. 49).
Sludge may be "conditioned" by "polymers" or
"ferric chloride" of "lime" to help in the
dewatering process or it may go through a
stabilization process which further reduces the
pathogens. (pp. 52-3)
The raw wastewater (domestic sewage) entering a
treatment plant "undergoes preliminary, primary,
secondary, and in some cases additional treatment to
yield treated effluent and a concentrated stream of
solids (generally about 1%) in liquid, called sludge."
The NRC Committee are claiming the wastewater
treatment technologies and procedures are adequate to
control: bacteria, viruses and parasites.
Yet, According to the study, "There are three kinds
of microorganisms in sewage sludge which are of concern
for their effects on human health: bacteria, viruses,
and parasites. All have been found in treated secondary
effluent and sludges"...."Using traditional methods of
virus sampling and assay of water from soil lysimeters
at sites irrigated with undisinfected secondary water
effluent, Moore et al. (1981), have found coliphage
virus particles at a depth of 1.37 meters. Using more
sensitive detection methods, several ground water
samples were taken 27.5 meters below wastewater soil
application sites and were found to be positive for
animal viruses." (p. 79) Couldn't there be a similar
problem when sludge is used for irrigation purposes or
through multiple applications at 98 percent liquid?
The treated wastewater is either discharged into
the surface waters or used to irrigate crops. "Following
treatment, sludges may be disposed of (for example, in a
landfill) or used for food crop production....." (p. 45)
Sludge for use on farmland near a plant is
generally thickened by gravity in a lagoon (5-6%
solids), or dewatered for transport (20-45% solids) or
dried by a number of processes to achieve between 45 to
near 100% solids.
Class B sludge is either thickened or dewatered
sludge processed to "reduce fecal coliform levels to
less than 2,000,000 (two million) colony forming units
per gram of total dry solids." (p. 34)
Class A sludge is processed to further reduce fecal
coliform levels to below detectable levels, not destroy
them.
According to the NRC report, there are also 127
priority pollutants that the Clean Water Act attempts to
regulate under a pretreatment program for industrial
plant wastewater before it gets to the treatment plant:
"Section 307 of the Clean Water Act regulates 127
hazardous compounds, (1) 14 heavy metals and cyanide,
(2) 28 volatile organic compounds, (3) 58 semi-volatile
organic compounds and (4) 25 pesticides and
polchlorinated biphenyls (PCBs) (40 CFR 123.21)." (p.
56) [Treatment] Standards have been set for the first
29 of the 34 categories of industries that the EPA has
identified "based on the best available technology".
(p. 59)
Yet, the EPA does not regulate wastewater used for
irrigation or sold to water lawns; it is only regulating
10 pollutants in sewage sludge for food crop production.
There are two items that should be considered when
evaluating any treatment of sludge. (1) the EPA
acknowledges that anaerobic digestion for stabilization
of sludge is controlled putrefaction. "If sludge is held
for ten to thirty days in a digester, methane
fermentation converts up to half of the organic matter
to gases. A mixture of methane and carbon dioxide is
produced that has about one half the heating value of
natural gas and is contaminated with hydrogen sulfide
and other odorous substances. There is enough energy in
the gas to operate normal mechanical equipment and air
compressors in a sewage treatment plant." The NRC report
notes that approximately 50 percent of sludge applied to
crops is organic matter. When the sludge decays in the
field, it will also produce methane gas, carbon dioxide
and hydrogen sulfide gas. Methane and carbon dioxide
gases have been identified as pollutants which are
effecting the earth's temperature, and creating a
greenhouse effect. Hydrogen sulfide gas is only a
little less deadly than hydrogen cyanide gas. In
effect, large sludge farms are being created which
produce enormous amounts of "greenhouse gases" as well
as other very deadly gases.
(2) The EPA also acknowledges that, "Sludge is
sometimes treated with large doses of chlorine that
produces hydrochloric acid and chlorinated compounds and
destroys ammonia and pathogens." Hydrochloric acid is
the same acid that is used in car batteries.
The EPA acknowledged these two problems in the
Proceedings of the Joint Conference on Recycling
Municipal sludges and effluents on Land, July, 1973.
Furthermore, according to the NRC report, the Clean
Water Act regulates 127 hazardous compounds, (1) 14
heavy metals and cyanide, (2) 28 volatile organic
compounds, (3) 58 semi-volatile organic compounds and
(4) 25 pesticides and polchlorinated biphenyls, yet, the
part 503 sludge regulation doesn't regulation them.
Pretreatment standards have been set for 29 of 34
categories of industries. According to "Sources of Heavy
Metals and Their Impact on Wastewater Treatment and
Receiving Water Bodies' Quality --- Case Study of
Metropolitan Area", "The 1970 to 1972 study of the
sources of heavy metals in New York City wastewater
concluded that even with zero discharge by industry, 94
percent of the zinc, 91 percent of the copper, 84
percent of the cadmium and 80 percent of the chromium
being discharged would continue to be discharged by
sources virtually immune to treatment." (p.133)
Yet, "The National Research Council (1977) reported
that pretreatment has the potential to alleviate
problems of sludge disposal due to heavy metal and toxic
organic compounds. In a study of operating POTWs in
Chicago, Illinois and in a pilot study at a POTW in
Buffalo, New York where significant amounts of
industrial wastewater discharge were received, it was
found that industrial pretreatment programs reduced
toxic heavy metal concentrations by a range of 50 to 90
percent (Zenz, et al., 1975, EPA, 1977)." (p. 59)
While there is little doubt that pretreatment
programs will help eliminate some pollutants from the
wastewater treatment plants, it may not be the answer
the NRC claimed that would make the major difference,
particularly, for New York City. "After pretreatment,
either through local limits or categorical standards,
83% to 84% of New York City sludges would still be
unacceptable for land application." ..."the reason for
this is that non-domestic sources of pollutant loading,
not industrial sources, are primarily responsible for
interfering with this sludge use." (p. 142) (Wat. Sci.
Tech. Vol.19, No. 9, 1987) After Reilly had the
sludge regulation revised, only 6% of New York City
sludge is unacceptable for land application.
NRC says sludge is safe for use on crops, except,
the treatment process does not destroy all of the
bacteria, viruses or parasites. Moreover, no accounting
is made for the deadly gases that form during the decay
process of organic matter in sludge on large farm areas.
In effect, the treatment process produces the
potential for serious health damage from sludge after
it leaves the treatment process, particularly, if the
sludge dump is in a low depression area with little wind
to disperse the deadly gases that will accumulate.
Prev Next
Review of National Academy of Science's (NAS) 1996 literary review report by
its National Research Council (NRC) Committee :
"Use of Reclaimed Water and Sludge in Food Crop Production"
Back