Materials and Methods

The composition and selectivity analysis were performed on the streams corresponding to a RO system and NF and RO stages, which are part of the landfill leachate treatment process located at a landfill site in northern Germany. In general, the landfill leachate treatment is composed of different pretreatment steps, which include among others pH adjustment and sand filtration units follow by a RO system and a series of concentrate volume reduction steps.

The pretreated landfill leachate (LL) is fed to a RO system, which consisted of a RO and high pressure RO stages with pressures around 75 and 120 bars respectively where the first generated landfill leachate concentrate (LLC-1) is fed to a NF-stage for further treatment and the high pressure RO permeate (HROP) is directed to a series of adaption ponds before its final release to the environment. The operating pressure in the NF-stage ranged in between 10 to 20 bars.

After the NF-stage the generated landfill leachate permeate (LLP) is fed to a high pressure RO (HPRO) stage and the second generated landfill leachate concentrate (LLC-2) is fed to a RO stage with pressures around 70 bars. The permeate generated in the RO stage (ROP) is mixed with the HROPs and the generated concentrates from the membrane stages are mixed and further treated in an evaporation system.

Additionally, each of the membrane stages are made up of different number of plate and frame modules having thin film composite polyamide as the membrane material and the temperature in the membrane processes can be found in between 30 to 35°C. The overview of the landfill leachate treatment facility and the sampling points are illustrated in figure 19.

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Figure 19. Overview of the landfill leachte treatment faciltiy and sampling points

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The composition analysis in each of the streams were performed by using different analytical methods, which include among others Inductively Coupled Plasma Mass Spectrometry (ICP-MS), Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) and Spectrophotometry. For the elemental analysis the samples were pretreated with aqua regia and parameters such as pH, conductivity and TSS were measured off-site. Furthermore, some characteristics of the analyzed streams such as high salinity, color and complex matrix might have influenced or interfered with the different analytical methods; hence generating uncertainties in the results. Thus, based on previous composition analysis performed on the same streams and the comments given by the University’s central lab for chemical analysis most of the results’ uncertainties were within 5%. However, some substances such as Si yielded high scattered results as well as Pb, Mo, Zn and As whose uncertainties in the results might had been around 10%.

The TSS was analyzed in the landfill leachate and concentrates as described in the Standard Method 2540D for Total Suspended Solids Dried at 103-105°C. The analytical methods used for each of the analyzed substances, the corresponding equipment and the raw data are given in appendixes A, B and C respectively.

3.1.1.1. Analytical Methods

ICP-MS and ICP-OES are techniques used to determine the elemental composition of aqueous samples such as wastewater. The ICP is based on the use of a very hot argon plasma at about 8000 K for the ionization of the analyze elements; the sample to be analyzed is first converted into an aerosol and then introduce into the plasma flame where it is ionized. In the case of ICP-MS, the resulting ions are transferred to the mass spectrometer where they are separated based on the mass-to-charge ratio, then detected and quantified with the help of an external calibration solution (Cöllen &

Frerichs, 2018). For the case of ICP-OES, the emission intensity of the light produced by the excited matter is detected in a wavelength range of 170 to 900 nm and quantified through the use of a calibration solution. The elements are detected based on the wavelength of the spectral line and their quantification is based on the linear relation that exists in between the signal intensity of the emitted light and the concentration of a substance (Fütterer, 2018). Furthermore, spectrophotometry as the OES is a spectroscopy technique in which the interaction of light with matter is analyzed for the determination of properties in a substance such as concentration.

For the case of spectrophotometry, the absorbed light is of importance, which differs from the OES in which the emitted light is the one being analyzed. In general, a spectrophotometer can be divided in two main sections. The first part or spectrometer section is composed of a light source, a collimator (lenses), a monochromator (prism) and a wavelength selector. In this first section, the light emitted by the source is transmitted by the collimator into the monochromator as straight beam where it is separated into its different components and then manipulated by the wavelength selector in order to get the desire wavelength. The second part is the photometer, which is the section that follows the absorption process and where the amounts of photons absorbed by the analyte are estimated by a detector (photocell)

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(Chem.LibreTexts, 2020). The amount of analyte present in the sample is estimated based on the linear relation between absorbance and the analyte concentration, which is described by Beer-Lambert law or just Beer's law. (Holler, et al., 2013).