**3.7 Hybrid bed filter**

A hybrid bed filter with a filter volume of 2.75 L and HRT of 2.4 d consisted of the combination of an anaerobic filter at the top and an up-flow sludge blanket situated at the bottom resulted in the removal efficiency of 37.5 to 76% COD from landfill leachate [61]. Karabelnik et al. [62] showed that at steady state a hybrid bed filter achieved COD removal efficiencies of 83 to 88% under an OLR of 2.50 kgCOD/m3 /d. Deng et al. [63] found that under the similar operational condition the hybrid bed filter was capable of achieving COD removal of more than 90% from leachate. In another study by Dastyar et al. [64] a hybrid bed filter was able to remove 45% COD from young leachate.

#### **3.8 Anaerobic baffled reactor (ABR)**

This reactor comprises of a progression of UASB reactors in series. The wastewater will stream over and under every baffle, which acts to isolate every chamber or compartment, thus counteracting solids washout and thus helping to retain the solids in the reactor. The successful compartmentalisation of the reactor guarantees phase division inside the compartments of acidogenic and methanogenic stages [38]. According to Rongrong et al. [65], an ABR demonstrated COD and Polyvinyl alcohol (in leachate) removal efficiencies around 42.0% and 18.0%, respectively. In a recent study by Yu et al. [66], leachate treatment by an ABR resulted in 80% of total nitrogen removal. Overview of landfill leachate treatment using different configurations of ABR is shown in **Table 3**.

Performance of an ABR treating landfill leachate was evaluated by Amin et al. [67], The influent COD of landfill leachate was 2700 mg/l and the pH during the treatment varied from 6.1 to 8.2 the maximum COD and nitrate removal obtained were 86 and 96.6%, respectively at an HRT of 48 h. Burbano-Figueroa et al. [68] studied the effect of OLR and sulphate loading rate (SLR) on landfill leachate treatment by a lab-scale ABR. The COD of landfill leachate was 3966–5090 mg/L with no traces of sulphate. Iron-sulphate was fed at a SLR of 0.05 g SO4 2−/L/d during the reactor start-up. The range of organic loading rate was 0.30 up to 6.84 g COD/L/d, while SLR of 0.06–0.13 g SO4 2− /L/d was adopted for SO4 2− in the influent. The maximum value of COD removal obtained at an OLR of 3.58 g COD/L/d and SLR of 0.09 g SO4 2−/L/d with a (COD/SO4 2− = 40) was 66%. Sulphate is added for the consumption of molecular hydrogen and the organic content is degraded during methanogenesis.

ABR system of four compartments (volume = 64 L and HRT = 4 days) was used by Mohtashami et al. [69] to treat the landfill leachate and obtained the COD removal efficiencies of 82.38, 85.19, 82.53, 82.22, and 80.12% for OLR of 1.2, 2, 3, 5, and 7.75 kgCOD/m3 /d, respectively. The performance of an ABR was evaluated by Wang and Shen [70] as a hydrolysis-acidogenesis unit in treating the wastewater (landfill leachate mixed with municipal sewage) in different volumetric ratios. The study revealed that ABR substantially improved the biological treatability of the mixed wastewater by increasing its BOD5/COD ratio to 0.4–0.6 from 0.15–0.3. The effects of the ratios of NH4 + -N/COD and COD/TP in mixed


#### **Table 3.**

*Different configuration of ABR in the treatment of landfill leachate.*

#### *Effectiveness of Anaerobic Technologies in the Treatment of Landfill Leachate DOI: http://dx.doi.org/10.5772/intechopen.94741*

wastewater on the operational performance were also studied, from which it was found that a reasonable NH4 + -N/COD ratio should be lower than 0.02, and the phosphorus supplement was needed when the volumetric ratio was higher than 4: 6 for stable operation of ABR.
