Hassen Benbelkacem

Effect of leachate injection modes on municipal solid waste degradation in anaerobic bioreactor

Three pilots simulated landfill bioreactors were used to investigate the effect of leachate injection modes on anaerobic digestion and biogas production from municipal solid waste. The technical modes used to increase waste moisture consisted of an initial saturation of the waste by flushing with leachate followed by a quick drainage, or weekly leachate injections with two different rates. The results confirmed that increasing moisture content is a key parameter to boost the biological reactions. Weekly leachate injection with high flow rate led to better results than the initial saturation of the waste in terms of biogas production kinetics. Water percolation was found to be an important factor to accelerate the degradation of solid waste. However, a modelling of the collected data by Gompertz model clearly showed that the intrinsic biogas potential determined on the initial solid waste was not reached with any of the progressive leachate injection modes.

Influence of substrate concentration and moisture content on the specific methanogenic activity of dry mesophilic municipal solid waste digestate spiked with propionate

The objective of this study was to evaluate the influence of substrate concentration and moisture content on the specific methanogenic activity (SMA) of a fresh dry mesophilic digestate from a municipal solid waste digester plant. For this purpose, SMA tests were performed under mesophilic conditions into glass bottles of 500 mL volume used as batch reactors, during a period of 20-25 days. Propionate was used as substrate at concentrations ranging from 1 to 10 gCOD/kg. Four moisture contents were studied: 65%, 75%, 80% and 82%. Experimental results showed that propionate concentration and moisture content strongly influenced the SMA. The highest SMA was observed at a substrate concentration of 10 gCOD/kg (11.3 mgCOD gVS(-1) d(-1) for the second dose of propionate) and at a moisture content of 82% (7.8 mgCOD gVS(-1) d(-1) for the second dose of propionate, at a concentration of 5 gCOD/kg). SMA was found to decrease linearly when decreasing the moisture content.

Liquid mixing and solid segregation in high-solid anaerobic digesters.

An experimental procedure (Residence Time Distribution technique) was used to characterize the macro-mixing of both liquid and solid phases of a laboratory-scale dry anaerobic digester using appropriate tracers. The effects of the waste origin and total solid content were studied. An increase in TS content from 22% to 30% TS (w/w) induced a macro-mixing mode closer to a theoretical Plug Flow Reactor. The segregation of particles having different densities was investigated regarding the RTD of the solid phase. Segregation of dense particles occurred at low TS content. By using different TS content and waste origins, it was also determined that the yield stress was a key parameter in the mechanism of segregation. At high yield stress, dense particles were more stable and thus less subjected to settling. As a consequence, operating at high TS content may permit to prevent the sedimentation of the denser particles.

Experimental and theoretical assessment of the multi-domain flow behaviour in a waste body during leachate infiltration

The optimisation of landfill operation is a key challenge for the upcoming years. A promising solution to improve municipal solid waste (MSW) management is the bioreactor technology. A meso-scale (around 1m(3)) experimental set-up was performed to study the effect of moisture control in low density conditions with different leachate injection operations and bioreactor monitoring including the use of a neutron probe. The moisture content distribution evolution demonstrates a multi-domain flow behaviour. A classic van Genuchten-Mualem description of the connected porosity proved insufficient to correctly describe the observed phenomena. A bimodal description of the connected porosity is proposed as solution and a connected/non-connected porosities numerical model was applied to the results. The model explains the experimental results reasonably well.

Can Biomethane Potential (BMP) Be Predicted from Other Variables Such As Biochemical Composition in Lignocellulosic Biomass and Related Organic Residues

The potential of methane production by anaerobic digestion of lignocellulosic biomass depends not only on the availability of the resources in the considered territory, but also on their physico-chemical characteristics. Relevant methods of characterization are, therefore, needed to select and possibly combine the most appropriate biomass substrates in order to optimize energy recovery through anaerobic digestion processes. The objective of the present study was to determine whether biomethane potential of such substrates could be predicted from a limited number of variables more rapidly or determined more easily. A set of 36 biomass substrates and organic residues from a variety of origins was analyzed for total and easily hydrosoluble organic matter fractions (volatile solid, VS and soluble chemical oxygen demand, SCOD), neutral detergent soluble fraction (SOL), hemicelluloses (HEM), cellulose (CELL), and lignin-like residual fractions (RES). Bioreactivity of all samples was also measured by experimental assays (biochemical oxygen demand, BOD and biochemical methane potential, BMP). The whole set of data thereby obtained was analyzed statistically considering one dependent variable (BMP), and six independent variables (SCOD, SOL, HEM, CELL, RES, and BOD). Partial least square (PLS) analysis revealed very clearly a positive correlation between BMP and BOD, which were both anti-correlated with RES. On the other hand, no correlations were observed between BMP, SCOD, HEM, and CELL contents. PLS analysis showed that BMP was significantly correlated to the six independent variables. The most influential variables were found to be RES and BOD, and a polynomial model was successfully validated for the prediction of BMP from RES and BOD.

Valorization of MSWI bottom ash for biogas desulfurization: Influence of biogas water content

In this study an alternative valorization of Municipal Solid Waste Incineration (MSWI) Bottom Ash (BA) for H2S elimination from landfill biogas was evaluated. Emphasis was given to the influence of water content in biogas on H2S removal efficiency by BA. A small-scale pilot was developed and implemented in a landfill site located in France. A new biogas analyzer was used and allowed real-time continuous measurement of CH4, CO2, O2, H2S and H2O in raw and treated biogas. The H2S removal efficiency of bottom ash was evaluated for different inlet biogas humidities: from 4 to 24gwater/m3. The biogas water content was found to greatly affect bottom ash efficiency regarding H2S removal. With humid inlet biogas the H2S removal was almost 3 times higher than with a dry inlet biogas. Best removal capacity obtained was 56gH2S/kgdryBA. A humid inlet biogas allows to conserve the bottom ash moisture content for a maximum H2S retention.

The effect of the origin of MSWI bottom ash on the H2S elimination from landfill biogas

Municipal Solid Waste Incineration (MSWI) Bottom Ash (BA) is a potential alternative adsorbent for biogas treatment due to its reactivity with hydrogen sulfide (H2S). The quality of BA depends however on the nature of the waste and the process technology of the waste incineration facility. To determine whether the origin of the BA could have an influence on its H2S elimination efficiency, comparative experimental tests were conducted in a landfill site with six bottom ashes from different MSW incinerators. Results showed that one of the BAs (A) had a much higher adsorption capacity than the rest (B-F), with 37g H2S/kg dry BA, compared to 11-16g H2S/kg dry BA for the other bottom ashes. Detailed physico-chemical analyses of the six BA were performed and complemented by principal component analysis to understand the different behaviors. BA iron content and specific surface area provided by the quench product stood out as key factors that promote the elimination of H2S.