Abstract:
The purpose of this
investigation was to verify the effectiveness
of composting in the sanitization of sludge
from urban sewage (SS). The treatments (T)
used consisted of SS mixed with sugarcane
bagasse (SB), tree pruning residues (TP),
poultry litter (PL) or grass clipping (GC) at a
carbon/nitrogen ratio of approximately 30/1
and ratios of T1 (SS+SB), T2 (SS+SB+TP),
T3 (SS+SB+GC), T4 (SS+SB+PL) or T5
(SS+SB+TP+GC). Temperature was
measured daily for over 280 days of
composting. Every two weeks, the
compounds were analyzed for
thermotolerant coliforms and viable
helminth eggs using the multiple-tube and
Yanko techniques; and once each month to
identify Cryptosporidium spp. and Giardia
spp. (oo)cysts using the sucrose and zinc
sulfate centrifugal flotation technique and
nested PCR followed by sequencing. The
maximum temperatures measured in the
thermophilic phase of the compounds ranged
from 55°C to 64.8°C, and at day 280, weight
reductions of 27% (T1), 48% (T2), 63%
(T3), 66% (T4) and 64% (T5) were
observed. The absence of fecal coliforms
was observed from day 98 (T4), day 126
(T1), day 196 (T3 and T5) and day 210 (T2).
All treatments resulted in helminth egg
inviability and the absence of protozoan
(oo)cysts. Only T4 and T5 were positive for
G. duodenalis according to the sequencing
analysis. In conclusion, high temperatures during the composting thermophilic phase
made the use of pathogens required by
legislation unfeasible; therefore, it is
important to investigate the viability of
protozoa in compounds to ensure a safe final
product for human and animal health.
