Keywords (Extracted from title, table of contents and
abstract of thesis)
Management, Ravi, Urbanization,
Combination, Model, River, Wastewater, Treatment, Quality,
Conditions, Water, Outfall |
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Abstract
The Ravi River is one of the five
major rivers in Pakistan and has several beneficial uses,which
include agricultural irrigation,municipal water supplies, fisheries
and recreation. The study reach of the river is a stretch of about
100Km between Ravi Siphon and Balloki
Headworks.Presently the River Ravi is receiving about 3,400,000
m3/day of wastewater form both domestic and industrial sources. Due
to discharge of this large volume of wastewater, most of the Ravi
River reach between Siphon to Balloki Headworks has become anaerobic
and requires urgent implementation of a water quality management
strategy.
A framework for the development of DO model for the Ravi River is
formulated considering both the CBOD and NBOD. The river study reach
is segmented based on locations of wastewater outfalls, surface
drains and freshwater tributaries. Hydrodynamic model is
developed to estimate travel time and reaeration coefficient for DO
modeling of the River
Ravi. Estimation of model parameters and waste inputs is carried out
through a combination of laboratory measurements, field and
monitoring data and sensitivity analysis.Long-term BOD analysis of
the wastewater samples collected at five outfalls and 2 surface
drains are made to determine the ratio between CBOD5 and CBODU,
bottle rate coefficients and ultimate values of BOD, CBOD and NBOD.
The results of these analyses show strong correlations (R2) ranging
between 0.9 and 0.98 both for CBOD and overall BOD rate constants
(i.e., Kc and Kd). R2 for Kn ranges between 0.72 and 0.93. The CBOD
rate coefficient Kc ranges between 0.14 - 0.27 day-1 and the NBOD
rate coefficient “Kn” ranges between 0.09 - 0.26 day-1.These values
are consistent with 0.1- 0.5 day-1reported in literature.
Diurnal variation in both the wastewater concentration and flows at
the Main Outfall was assessed to find out the sampling time for
model calibration and verification and to assess the pollution
loads. Currently about 862,000 Kg/day of BOD pollution load is being
discharged into the River Ravi.This total pollution (BOD) load will
increase to about 1.5 times from different outfalls and surface
drains by the year 2025 due to constant increase in urbanization and
industrialization in the Ravi River catchments.
DO model is formulated by using the wastewater loads estimated in
past studies undertaken for Lahore and findings of present
study.Sensitivity analysis is carried out to find the least
sensitive reaeration rate coefficient relationship for the River
Ravi hydrodynamic characteristics. O’Connor-Dobbins formula to
calculate reaeration rate constant is found to be the least
sensitive under variable flow conditions of the Ravi River. Its
applicability in DO modeling of the Ravi River is reflected by a
close agreement between the model results and the field
measurements.The DO model results considering only CBOD show that
the calculated values do not correlate well with the field
measurements as reflected by SSR value of 13.The DO model results
with nitrificati (NBOD separately with nitrification) have shown the
strongest correlation between the calculated values and field
measurements with
SSR value of only 1.5. These results highlight the importance of
NBOD in the DO modeling of the Ravi River.
For the calibration of the DO model an extensive field survey was
conducted to estimate deoxygenation rate coefficients for BOD, CBOD
and NBOD in the River Ravi. The in-stream CBOD decay rate
coefficient (Kcr) estimated from the River Ravi CBOD profile during
the model calibration is found to be 0.36 day-1. The Kn value from
the nitrification modeling calibrated through the concentrations of
Org-N and NH3-N in the river was 0.34 day-1. Both the values are in
the range reported in literature (0.2 – 0.5 day-1) for the rivers
receiving raw wastewaters.Nitrification is an associated phenomenon
with DO and un-ionized ammonia toxicity beyond the acceptable limits
can kill the fish. Therefore, modeling of ammonia toxicity and
nitrification in Ravi River is also carried out. The DO model is
verified with the IPHER (1978 – 1979) Ravi River monitoring data
under low flow conditions.The results of the model calculations show
reasonable agreement with the river data.
Biokinetic rate coefficients change with level of wastewater
treatment.The CBOD bottle rate (K) is 0.25 day-1 for raw
wastewater.A slight increase to 0.27 day-1 for filtered sample is
observed due to presence of readily biodegradable organic matter. A
direct relationship of K with different levels of biological
treatment has been noted wherein K value reduces from 0.27 day-1 to
0.05 day-1 with increase in biological treatment levels. NBOD rate (Kn)
of 0.21 day-1 was observed for both raw and filtered wastewater
samples. However, in biological treatment, Kn value varies slightly
between 0.08day-1 to 0.06 day-1 for treatment levels corresponding
to 3 and 10 days detention times respectively in a laboratory scale
aerated lagoon. As the Ravi River is currently receiving wastewater
without any treatment, therefore the river rates (Kcr & Kn) are
reduced by a factor ranging between 1.5 to 5 depending on the level
of treatment to achieve desired water quality objectives.
To improve the water quality of the River Ravi wastewater control
alternatives including conventional wastewater treatment, flow
augmentation, wastewater transportation, low cost treatment and
constructed wetlands are evaluated. Model calculations carried out
for water quality management of the River Ravi show that even to
achieve 1mg/L of DO levels in the River Ravi at MA7CD flow (i.e.,
9.2 m3/s) 70% BOD reduction is required.Higher removal efficiencies
of 85 and 90% are required for 3mg/L and 4mg/L DO levels
respectively.To achieve 5mg/L of DO standards, high removal of both
CBOD and NBOD (95%) is required.Ammonia toxicity is also a water
quality problem in the River Ravi.A flow augmentation of about
19m3/s through MR Link canal with 80% of CBOD removal
can achieve 4mg/L DO standards with 30% lower cost than the MA7CD
flow conditions.
Flow required to augment the river flow to achieve 4mg/L DO
standards without any treatment is 416m3/s. The flow that can be
diverted from MR Link canal to the River Ravi will depend on
availability of the water in the River Chenab and may require
remodeling of MR Link canal.The simulation results show that 90%
ammonia removal is required to meet the desired un-ionized ammonia
standards.This removal results in 5mg/L DO level in the River Ravi.
Transportation of wastewater from the city of Lahore trough a
collector channels with primary treatment facility at the confluence
point of QB Link canal is a cost effective option with about 2.5
times lower cost than the alternative with ASP at all the outfalls
and surface drains.Waste stabilization ponds as an alternative for
water quality management of the River Ravi comes out to be the least
cost alternative, but this result in DO level of 3mg/L in the river.
Furthermore, there are issues related to land acquisition that need
to be resolved.However, if the effluent can be reused for
irrigation, pollution load being discharged into the River Ravi can
get reduced.
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