E1088
Colombia: Rio Frio Carbon Offset Project
Environmental Assessment
Context
The metropolitan area of Bucaramanga is located 300 km north east of Bogota, along the Eastern branch
of the Andean mountain chain that defines the geography of Colombia. Bucaramanga and is neighboring
municipalities have experienced sustained growth in the past half century. Its population reached 800,000
inhabitants in 1993, and it is estimated now to be home to one million people. This population growth has
come with improvements in basic public services, and with a giant effort to curve soil erosion processes
in its Meseta, terrace. Bucaramanga is also the first city in Colombia to implement wastewater treatment
facilities, and has successfully operated these facilities since 1991.
Wastewater production has increased at a rate of 3.3% per year, demanding that its treatment facilities
expand. In 1991 the flow of wastewater treated at the Plant, was 274 l/s and has grown to 406 l/s by 2003.
The Corporación de Defensa de la Meseta de Bucaramanga, CDMB, the regional environmental
authority, has expanded the treatment facilities as discharges grew. In 2003 a new expansion was
contemplated to treat the growing wastewater generated in its jurisdiction. In this opportunity a fresh
approach was sought to provide a better environmental solution to the environmental and social problems
associated with the existing facility. In particular obnoxious odors affecting an important populated area
in the town of Girón, and the discharge of nutrients (mostly nitrogen) that could developed into a serious
environmental problem downstream.
Existing conditions. Basically the Río Frío WTP consists of:
·
Intake structure: When runoff and sewer exceeds 1,400 l/s a bypass is activated discharging the
diluted wastewaters directly to the stream. The average intake is 480 l/s, with a maximum of 740 l/s.
·
Screening: Retention of coarse materials, including gravel, floating material, and transported
particle with a diameter equal or larger than 0.6 cm. This material is collected daily, dried and disposed in
a small in-house landfill.
·
Sedimentation: Sediments are trapped in three basins, 2 in operation one in maintenance, to
exclude coarse particles, with a retention time of 3.1 minutes. The retained sand is disposed in the sanitary
landfill within the WTP.
·
Primary Treatment: Up-flow anaerobic sludge blanket, UASB, reactors are used to biologically
treat the wastewaters. In this process sludge is produced at a rate of 1m3 per 1,000 m3 of treated water.
The dry sludge is used as soil improver in reforestation programs. In the primary treatment gasses are
produced, mostly methane, which might be capture and use as a source of energy. In the Río Frío WTP
captured biogases are flared.
·
Secondary treatment: Two facultative lagoons promote anaerobic biological digestion of remaining
wastes, through a retention time of 18 hours. The large surface area of the lagoons allow diffuse gasses
and obnoxious odors to escape to the atmosphere.
·
Final discharge: Treated waters are discharged to the stream, Río Frío. In the process organic
matter is removed, as well as sediments, or suspended solids. Organic material and suspended solid
removal are estimated at 84%, in both cases.
The treatment process discharges to the environment: treated wastewaters; sludge and sediments; gasses;
heat; and, noise. Of these discharges the most relevant are wastewaters and gasses. Solids are dried and
disposed in an environmental friendly way; heat is realized to the atmosphere without substantial negative
impact. To minimize the problems associated with noise a wide buffer zone surrounds the facility.
Discharged waters are released to the stream causing a reduction of dissolved oxygen. Most importantly,
nitrogen is injected to the stream possibly contributing to eutriphication of wetlands downstream, and
releasing nitrous oxide along the water bodies.
Emission of gasses are associated with two negative effects: the release of green house gasses, methane
and nitrous oxide; and H2S with its obnoxious odor influencing the area downwind from the plant.
Modernization. The new design for the Río Frío WTP seeks to: improve the removal of suspended
solids and organic matter, reduction of GHG emissions to the atmosphere, and control of obnoxious
gasses releases to the atmosphere. The new treatment process improves the collection of gasses in the
UASB units, optimize their operation by incorporating lessons learned from the past decade of
measurements and research. It also removes H2S by injecting air and degassing the effluent. The lagoons
are replaced by an activated sludge process with strict control of dissolved oxygen levels to facilitate the
organic matter decomposition and reduced nitrous oxide emissions. The biogas produced in the improved
UASB units is collected and used to generate electricity through an efficient combustion process.
In the new plant design, the following discharges to the environment are expected:
·
Treated water: The water to be discharged to Río Frío is less contaminated than today’s discharges,
due to the more advanced nature of the treatment, and the additional control over the biological process
occurring in the digestors of the secondary treatment. It is important to note that nitrous oxide formation
from the receiving stream are expected to be reduced, offsetting the emission of GHG gasses.
·
Sludge and sediments: The higher treatment efficiency associated with the new plant lay out will
increase the production of sludge. Nevertheless, its impact is minor and the existing disposal strategy is
benign to the environment. No additional negative effect is expected fro the added volume of solids to
dispose.
·
Gasses: The proposed design seeks to minimize the production of GHG, in particular of methane
and nitrous oxide. Better control will be exerted in the plant to reduce the leakage of methane from the
digestors. This gas will serve as fuel for a one megawatt cogeneration unit. The reduction of nitrogen in
the effluent waters is associated with a decrease in the emission of nitrous oxide from the stream. This
offset in the emission of GHG is the basis for the estimation of the CERs that financially support the
modernization of the wastewater treatment plant.
·
Heat: In the process flowchart biogas is used to generate electricity, reducing the waste of heat, and
its emission to the atmosphere, even if this environmental impact is minor.
·
Noise: The level of noise will remain at today’s levels, or might increase in the neighborhood of
the cogeneration plant. The contemplated buffer zone is large enough to assert that its impact to activities
in the vicinity of the plant will not be affected.
Environmental impacts during construction
All the proposed construction activities are categorized as minor works. There is ample experience in the
CDMB in designing and supervising this type of activities. In general a detailed EMP has been designed
and will be implemented, under the direct responsibility of the regional environmental authority, and
supervised by the MAVDT. No major negative environmental impact is expected. The mitigation
measures of the EMP are summarized below.
Environmental Management Plan (EMP)
Actions
Construction phase
1. Mobilization and
preparation for
Mitigation measures
Responsibility
Timing

Adequate
Planning
Approval by
CDMB,
Jun 2005 - Dec 2006
operation
2. Soil removal and
excavation work
3. Concrete structure
4. Equipment
5. WTP operation
during construction
6. Monitoring plan
7. Community
information strategy
Operation Phase
1. Monitoring plan

Industrial
Safety plan

Approval by
CDMB of EMP

Separation of
contaminated soils

Adequate
disposal in landfills

Groundwater
level control

Avoid erosion
and sediment transport
downstream

Minimize
wastage

Water use
controls

Adequate
disposal of water used
for cleaning

Adequate
disposal of cleaning
materials

Minimize waste
generation

adequate
disposal

Minimize
untreated discharges

Post
information to
downstream water
users

Soil sampling
for adequate disposal

River
quality/quantity
monitoring

Noise levels

Continuous
information to
community in project
area on project impacts
Responsibility by
contractor who
will present the
plan
By Contractor with
supervision by
CDMB
Implement and
Maintain monitoring
system: GHG and
other gases of
interest, solids and
water quality
Jun 2005 - Dec 2006
By Contractor with
supervision by
CDMB
Jun 2005 - Dec 2006
By Contractor with
supervision by
CDMB
Jun 2005 - Dec 2006
By Contractor with
supervision by
CDMB
Jun 2005 - Dec 2006
By Contractor with
supervision by
CDMB
Jun 2005 - Dec 2006
By Contractor with
supervision by
CDMB
Jun 2005 - Dec 2006
By plant operator
with supervision
by CDMB
As of operation start
2. Discharges
Minimize untreated
discharges
3. Water quality
Continuous
monitoring of water
quality
By plant operator
with supervision
by CDMB
By plant operator
with supervision
by CDMB
As of operation start
As of operation start