19. Why is the discharge of BOD & COD
regulated?
Definition: BOD = Biochemical Oxygen Demand
- The rate at which microorganisms use the oxygen in water or wastewater,
while stabilizing decomposable organic matter under aerobic conditions.
In decomposition, organic matter serves as food for the bacteria and energy
results from its oxidation. The BOD test procedure measures the rate of
oxygen use under controlled conditions, usually incubation in the dark at
20°C for 5 days. |
| EPA regulation 40CFR Part 503 contains rules
for disposal of treated biosolids as fertilizer. The 180 page EPA Publication
832-R-93-003, Plain English Guide to EPA 503 Biosolids Rule, explains
the regulations governing recycling of treated sludge and other biosolids
through anaerobic and aerobic digestion processes, heat treatments etc.
The EPA also issues discharge permits
that specify the limits of chemicals, nutrients, and bacteria that may be
safely discharged to the environment. |
| The above mentioned rules are not arbitrary.
The discharge of pathogenic bacteria and excess nutrients in high BOD must
be controlled to protect the ecology. Depositing large quantities of undigested
nutrients onto the land upsets the balance of the nitrogen cycle. High BOD
waste kills certain plants, leads to the growth of different plants on land
leading to starvation for the indigenous populations of animals, birds,
and insects. Leachate from land applications of this waste can pollute the
water table and nearby rivers and lakes, where these excess nutrients support
different phytoplankton which cannot be digested by the normal populations
of fish, oysters, and shrimp, leading to massive death of aquatic life,
which leads to death of the predators that feed on these species. Other
hazards of depositing high BOD waste into rivers include: the proliferation
of pathogenic species of bacteria, the proliferation of Pfiesteria
(a microorganism which has caused so much fish damage that entire rivers
have been closed during certain seasons), and massive fish kills due to
insufficient oxygen in the water as the high BOD waste uses up the oxygen
that is present. The odors from high BOD waste attract pest and scavenger
birds, insects, fish and animals, thus allowing these populations to increase
at the expense of other species. |
| High COD waste containing chemicals, such as
arsenic, cadmium, chromium, copper, lead, mercury, molybdenum, nickel, selenium,
and zinc can poison the natural population of (unselected, unadapted) waste
degrading bacteria, thereby breaking the food chain and leading to all the
problems associated with a high BOD waste mentioned in the previous paragraph.
High levels of these chemicals can also directly poison higher life forms.
Permits are established limiting the amount of these toxins released to
the environment in a given location. |
| Biosolids produced from a municipal facility
or one that processes restaurant and animal farm waste should be sampled
and tested monthly for the following pathogens to meet the specifications
of this rule: fecal coliform, salmonella sp., enteric virus, viable helminth
ova, inorganic pollutants, specific oxygen uptake (BOD/COD) and
total fixed and volatile solids. |
