MOROCOMP (LIFE TCY05/MA000141) - Unit of Environmental ...

Biochemical Oxygen Demand (BOD 5 ) is a measure of the amount of oxygen that
bacteria will consume while decomposing organic matter under aerobic conditions.
Biochemical oxygen demand is determined by incubating a sealed sample of water for
five days and measuring the loss of oxygen from the beginning to the end of the test
[39]. According to Trujillo et al. leachates originating from wastewater sludge
composting processes are characterized by increased BOD 5 values reaching up to 70
g/L [40]. The initial sample of leachates derived from the 1 st composting trial acquired
an increased initial BOD 5 value of 50.9g/L on the 3 rd day. As the process develops the
organic intermediate products undergo complete bioxidation to CO 2 while the non
biodegradable or less susceptible to degradation compounds accumulate. Therefore
the microbial activity gradually decreases and the used oxygen by the biological
organisms in leachates is reduced as the process continuous. For this reason the BOD 5
evolution during composting presented a downwards inclination and at the end of the
process leachates had been reduced approximately 1/6 of the initial BOD 5 value.
Leachates acquired at the initial stage of composting a light dark colour which was
gradually becoming darker as composting was developing. This is indicative of the
presents of humic/fulvic and other complex compounds which are dark coloured,
hydrophilic organic compounds whose molecular weight varies from few hundreds to
few thousands. Ammonium and nitrates in leachates followed the same pattern as the
ammonium and nitrates of the substrate indicating that the composting process was
well monitored since the conditions were in favor of nitrification. Ammonium ions
concentration presented a steep increase during the first days of composting reaching
to a maximum of 1985.06mg/L on the 7 th day. From that day onwards ammonium
concentration kept reduced and on 23 rd day their concentration in leachates was
450.84mg/L. Nitrates in leachates presented a significant increase throughout the
duration of the 1 st trial. On the 3 rd day their concentration was limited at 34.05mg/L
while on the 23 rd day it had been increased approximately 12 times reaching at
687.51mg/L. Table 6 shows also that heavy metals such as Cd, Cr, Cu, Ni, Pb and Zn
were present in leachates throughout the process. The metal concentrations were
much below the indicative values for wastewater disposal as shown in Table 7.
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