Impact of concentrated leachate recirculation on effectiveness of leachate treatment by reverse osmosis
Introduction
Disposal of leachate is recognized as one of the most difficult task associated with the landfill operation. Different on- and off-site treatments of the leachate are nowadays proposed and adopted to meet different requirements of each landfill (Wiszniowski et al., 2006, Renou et al., 2008a, Renou et al., 2008b, Calabrò et al., 2010). A conventional biological process could be effective for the removal of organic substances, suspended solids and nutrients (Yahmed et al., 2009, Theepharaksapan et al., 2011). To remove recalcitrant compounds advanced treatment processes such physico-chemical and membrane technologies are required (Kurniawan et al., 2006, Theepharaksapan et al., 2011, Ahmed and Lan, 2012, Smol et al., 2014). Reverse osmosis seems to be one of the most promising methods among the new processes for landfill leachate treatment. Several studies were performed, both at lab and on industrial scale, to investigate RO performances on the separation of pollutants from landfill leachate (Bodzek et al., 2006, Chan et al., 2006, Liu et al., 2008, Li et al., 2009, Theepharaksapan et al., 2011, Smol et al., 2015). One of the most debated options, when the RO treatment is adopted, is a recirculation of concentrated leachate (Renou et al., 2008a, Renou et al., 2008b, Liu et al., 2008, Li et al., 2009). Opinions on the consequence of this practice are not unanimous and specific studies present in a scientific literature are rare. According to Bilgili et al. (2007) the advantages of leachate recirculation include distribution of nutrient and enzymes, pH buffering, dilution of inhibitory compounds, liquid storage and evaporation opportunities. Sponza and Ağdağ (2004) reported that the leachate recirculation also shortens the time required for stabilization from several decades to 2–3 years. On the other hand Ledakowicz and Kaczarek (2002) maintain that leachate recirculation can lead to the inhibition of methanogenesis as it may cause a high concentration of organic acids which are toxic for methanogenesis. The concentrated leachate recirculation can change the leachate quality, causing an increase in the concentration of inorganic compounds (due to cyclically leaching/washout) and organic compounds (due to enhanced biodegradation processes in waste body). This can result in a change of the RO effectiveness, as it is limited among other things by fouling and scaling. Organic constituents contribute directly to organic fouling or provide carbon sources for the development of biofilms on the membrane surfaces (Wend et al., 2003). Inorganic compounds can cause gradual build-up on the membrane surface, which may consist of colloidal particles, iron and/or manganese oxides or may be due to inorganic scale formation (Ameen et al., 2011). Scaling is a result of deposition of particles on a membrane, causing it to plug. It occurs due to precipitation of sparingly soluble gas, such as calcium carbonate, calcium sulfate, barium sulfate and strontium sulfate.
Heavily contaminated leachate from a concentrate recirculation landfill can disturb the RO operation and be conducive to the process of fouling and scaling. The membrane fouling and scaling with a consequent reduction in a specific flux can lead to changes in the removal rate and may be a limitation of the membrane filtration process. In spite of many experimental works reported in the literature, at lab and on industrial scale, a systematic investigation of the impact of the RO concentrate recirculation on the RO performance has not yet been performed. The objective of this study is to evaluate the impact of the concentrated leachate recirculation on the effectiveness of the RO process in relation to selected contaminants.
Section snippets
Landfill characteristics
Samples for analysis were taken from municipal landfill in Warminsko-Mazurskie Voivodeship, in north-eastern part of Poland. The landfill began its operation in 1983 opening of a 7.7 ha Area A for waste disposal. The Area A was not equipped with the liner system. This landfill cell is sealed with a natural 31-m clay substrate functioning as a geological barrier. In order to protect from uncontrolled leachate migration a circumferential ditch – around scarp foot of the Area A – was built. After
Concentrate and leachate characteristics
The investigation on leachate and concentrate composition from analyzed landfill were started just after the RO process started and lasted from February 2013 till April 2014. During this time 8 samplings (every 2 months) of concentrate and leachate were taken. Since November 2013 the RO was temporary closed, so since then there was no concentrate recirculation and only leachate samples were collected for analysis. The basic statistics of concentrate and leachate is presented in Table 2.
The
Conclusion
In this paper, a data relating to the first year of RO exploitation and concentrate recirculation at the municipal landfill in north-eastern Poland were analyzed. The data included also the findings from the first six months after recirculation discontinuation.
The concentrate recirculation caused the increase of leachate electroconductivity, chemical oxygen demand and nitrogen ammonia. The consequence of concentrate recirculation is also an increase in leachate concentration of sulphates, which
Acknowledgment
The paper was prepared during scientific project No. S/WBiIS/2/2014 financed by Polish Ministry of Science and Higher Education.
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