In Tunisia, the anaerobic digestion process is regarded as a new alternative for the treatment of landfill leachate (LFL). Raw LFL contained high amounts of organic matter, high ammonia concentrations and low biodegradability. In order to improve anaerobic conditions and biogas yields, pretreatment using coagulation‐flocculation, Fenton oxidation (FO) and air stripping processes were investigated and compared in terms of biogas production. Air stripping process was optimized using Response Surface Methodology (RSM). Central Composite Design (CCD) was used with three factors. Under optimized conditions, removals of 85% ammonia, 26% chemical oxygen demand (COD) were achieved. Coagulation‐flocculation provided an increase in the effluent biodegradability with 46% of COD reduction. Fenton's oxidation allowed reducing 48% COD, 30% of biological oxygen demand (BOD5). The effect of pretreatments was investigated with the biochemical methane potential (BMP) assay. A comparison of three different pretreatment methods of LFL for biogas production was performed. Air stripping was demonstrated as providing a better biogas yield than other pretreatments which reached 588 mL/g CODint. The best methane yield was obtained using air stripping pretreatment under optimized conditions. It can result in more robust and effective anaerobic digestion. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 1041–1049, 2018

Landfill waste decomposition generates a dark effluent named, leachate which is characterized by high organic matter content. To minimize these polluting effects, it becomes necessary to develop an effective landfill leachate treatment process. The objective of this study was to evaluate the performance of an innovative approach based on air stripping, anaerobic digestion (AD) and aerobic activated sludge treatment. A reduction of 80% of ammonia and an increase of carbon to nitrogen ratio to 25 were obtained, which is a suitable ratio for AD. This latter AD was performed in fixed bed reactor with progressive loading rate that reached 2 and 3.2 g COD/L/d for the raw and diluted leachate (1:2), respectively. The anaerobic treatment led to significant removal of chemical oxygen demand (COD) and biogas production, especially for the diluted leachate. The COD removal was of 78% for the raw leachate and a biogas production of 4 L/d with 70% methane content. The use of the diluted leachate led to 81% of COD removal and 7 L/d biogas with 75% methane content. It allowed a removal of 77% COD and more than 97% of the organic compounds present in the initial leachate sample.

Landfill leachates (LFL) collected from Sfax (Tunisia) discharge area are characterized by high chemical oxygen demand (COD), ammonium and salts contents. They constitute a source of phytotoxicity and pollution for ground water and surface water resources which requires an adequate treatment process. To evaluate the efficiency of the coagulation/flocculation treatment, special attention was paid to the effect of pH, coagulant and flocculant doses. Then, effect of zero valent iron was also studied alone and in combination with coagulation/flocculation pretreatment. Our results indicate high removal efficiencies by coagulation/flocculation (46% COD and 63% turbidity) and Fenton process (48% COD and 76% turbidity). The combined application of coagulation/flocculation and Fenton revealed higher COD removal (62%) and turbidity reduction (90%). These results showed the applicability of this combined treatment method for the degradation of organic compounds and reduction of the treated leachate toxicity.

The present paper aimed to characterize and treat a landfill leachate using a coagulationflocculation process. The leachate was obtained from a landfill in the city of Sousse, Tunisia. Its physicochemical characterization showed high levels of chemical oxygen demand (COD), ammonium, and heavy metal contents. The coagulation-flocculation process was applied as pretreatment effluent to reduce these pollutants. The key operating parameters (pH, coagulant dose, flocculant dose, and mixing speed in the flocculation step) on the coagulation-flocculation process were optimized using response surface methodology to investigate COD removal in landfill leachate. In this regard, a hybrid design was carried out to seek optimal conditions which were as follows: pH: 3.36; concentration of coagulant: 0.87 g/l; concentration of flocculant: 26 mg/l; and mixing speed: 48 rpm. These conditions have been proved experimentally.