| Summary: | Sanitary landfill leachate (SLL) is produced extensively in sanitary landfills and is loaded with
hazardous substances, causing serious risks to both living organisms and the environment. In recent
years, numerous processes, either single or combined, have been implemented to treat this hazardous
wastewater. However, the treatment of raw leachate is very challenging due to the complexity of its
composition. In almost all processes applied to treat raw landfill leachate, the quality of the final
effluent did not fully comply with the discharge limits imposed by environmental regulations for
release into a water body, while the combined systems developed consisted of mostly expensive
processes.
The objective of the current PhD thesis is to treat real sanitary landfill leachates using single and
combined processes, which are environmentally friendly, easy to operate, cost-effective and highly
effective in removing pollutants from raw landfill leachate.
Initially, a naturally occurring zeolite was examined for the simultaneous removal of ammonium
nitrogen (NH4+-N), dissolved chemical oxygen demand (d-COD) and color from raw SLL in batch
adsorption (AD) experiments, where several operational parameters were applied. Saturation,
desorption and regeneration tests of zeolite were performed. Mechanistic information for NH4+-N was
also obtained by fitting adsorption/desorption data to kinetic and isotherm models using both linear
and non-linear methods. Additional information regarding the assessment of the pathway of pollutants
uptake was obtained by zeolite particles after adsorption, saturation, regeneration and desorption
processes using scanning electron microscopy (SEM), powder X- ray diffraction (XRD) and X-ray
photoelectron spectroscopy (XPS).
In a second stage, the efficiency of a naturally occurring palygorskite as an adsorbent for the
simultaneous removal of color, d‐COD and NH4+-N from raw SLL was investigated. Operational
parameters for adsorption process were also examined in batch adsorption experiments. Saturation and
desorption studies of palygorskite were also performed for all three pollutants simultaneously. Natural
palygorskite was then combined with natural zeolite in both single and sequential adsorption
arrangements to evaluate possible enhancement of the treatment efficiency in terms of the
simultaneous removal of color, d-COD and ΝΗ4+-Ν. After adsorption, saturation and desorption, the
palygorskite solids were characterized using XRD, Fourier-transform infrared spectroscopy (FTIR),
XPS, SEM, energy dispersive spectroscopy (EDS), measurements of BET specific surface area (SSA),
and the zeta potential of the suspended particles.
Next, a parametric evaluation of the electrocoagulation (EC) process on raw SLL was performed to
optimize the process. Then, hybrid systems consisting of EC and AD (with natural zeolite and/or
natural palygorskite) were developed using the optimal conditions of both processes to effectively treat
raw SLL. The efficiency of the systems was examined in terms of simultaneous removal of color, d-
COD, nitrate nitrogen (NO3--N) and NH4+-N. In particular, the optimal arrangement of the combined
EC and AD system using zeolite (ADzeo) was assessed by changing the sequence of the two processes.
Then, AD process using palygorskite (ADpal) was integrated into the first or middle stage of the
optimum hybrid EC and ADzeo system determined, thus resulting in the implementation of two more
hybrid systems: ADpal-ADzeo-EC and ADzeo-ADpal-EC.
Lastly, the effectiveness of a three-stage pilot approach using adsorption (AD), electrocoagulation
(EC) and biological (BIO) processes for the treatment of raw SLL was investigated. Initially, column
adsorption experiments with natural zeolite were performed to examine the removal of toxic NH4+-N
using different initial NH4+-N concentrations and recirculation flow rates. Two sequential treatment
scenarios were then examined, i.e., AD-EC-BIO and AD-BIO-EC, to determine which achieved the
highest removal of pollutants and leachate toxic potential based on Thamnocephalus platyurus
bioassay.
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