Comparative mesophilic and thermophilic anaerobic digestion of palm oil mill effluent using upflow anaerobic sludge blanket

Investigation of the anaerobic digestion of cosmetic industrial wastes: Feasibility and perspectives

This study assessed the anaerobic digestion (AD) of wastes deriving from cosmetics production: sludge from onsite wastewater treatment plant (sWWTP), residues of shampoo/conditioner (RSC) and sludge from mascara production (MS), considered as single substrates and as mixture according to the produced amounts (54 %-wt sWWTP, 31 %-wt RSC, 13 %-wt MS, plus 2 %-wt food waste from the canteen, FW). Total COD (COD_T) was 624-1436 g O₂/kg _VS, while soluble COD was 5-23 %-wt of COD_T. AD tests at 35 °C achieved the following biogas yields: 0.10 Nm³/kg_vs (70 %-v/v methane) for sWWTP; 0.07 Nm³/kg_vs (62 %-v/v methane) for RSC; 0.04 Nm³/kg_vs (67 %-v/v methane) for MS. The mixed substrates underwent physico-chemical pre-treatments (thermo-alkaline, TA: 120 min at 50 °C; thermo-alkaline-sonication, TAS: 15 min at 40 kHz and 80 °C, both based on the addition of 0.08 g NaOH per each g of total solid in the substrate), reaching 64-66% disintegration rate, and AD tests (5 %-wt dry substance) at 35 and 52 °C. Biogas yields were (for TA and TAS respectively): 0.22 and 0.20 Nm³/kg_VS (62-70% methane); 0.21 and 0.19 Nm³/kg_VS (66-66% methane) at 52 °C. At both temperatures, methane yields considerably improved (+71-100%), compared to mixed untreated substrates, and 5-8 %-wt total solids reductions were observed. A technical-economic scale-up assessment completed the research. The energy analysis highlighted the crucial role of TA pre-treatment in achieving the process energetic sustainability. The economic analysis showed that the AD of the considered cosmetic waste could be sustainable anyway, thanks to the savings related to the disposal of the digestate compared to current waste management costs.

Anaerobic Biodegradation of Biodiesel Industry Wastewater in Mesophilic and Thermophilic Fluidized Bed Reactors: Enhancing Treatment and Methane Recovery

In the past few years, the extraction of value-added compounds from the anaerobic digestion of glycerol has been an option to add value to this waste because biodiesel production is increasing worldwide. The evolution of research on glycerol valorization by anaerobic digestion has reached the use of high-rate reactors. However, no study has evaluated glycerol digestion in an anaerobic fluidized bed reactor (AFBR), a configuration with potential advantages in methane production. Still, the best operating temperature for high-rate glycerol digestion remains unclear. To clarify these gaps, the present study aimed to compare glycerol digestion in mesophilic AFBR (30 °C) and thermophilic AFBR (55 °C). In both reactors, glycerol concentration was increased from 1.0 to 7.0 g L^-1 at a fixed hydraulic retention time of 24 h, resulting in an increase at the organic loading rate from 1.2 to 7.6 kg COD m^-3 day^-1. Thermophilic digestion of glycerol achieved superior removals of organic matter (67.7-94.2%) and methane yield (330.8 mL CH₄ g^-1 COD) than the mesophilic digestion (48.6-93.0% and 266.6 mL CH₄ g^-1 COD). Additionally, the application of the kinetic model of substrate utilization (modified Stover-Kincannon model) indicated a higher substrate utilization coefficient in the thermophilic AFBR (23.09 g L^-1 day^-1) than the mesophilic AFBR (7.14 g L^-1 day^-1). Therefore, the application of glycerol concentrations higher than 7.0 g L^-1 in thermophilic AFBR should be further investigated. Also, given only operational results, the application of the AFBR in the two-stage anaerobic digestion of glycerol is recommended.

Thermophilic versus Mesophilic Anaerobic Digestion of Sewage Sludge: A Comparative Review

During advanced biological wastewater treatment, a huge amount of sludge is produced as a by-product of the treatment process. Hence, reuse and recovery of resources and energy from the sludge is a big technological challenge. The processing of sludge produced by Wastewater Treatment Plants (WWTPs) is massive, which takes up a big part of the overall operational costs. In this regard, anaerobic digestion (AD) of sewage sludge continues to be an attractive option to produce biogas that could contribute to the wastewater management cost reduction and foster the sustainability of those WWTPs. At the same time, AD reduces sludge amounts and that again contributes to the reduction of the sludge disposal costs. However, sludge volume minimization remains, a challenge thus improvement of dewatering efficiency is an inevitable part of WWTP operation. As a result, AD parameters could have significant impact on sludge properties. One of the most important operational parameters influencing the AD process is temperature. Consequently, the thermophilic and the mesophilic modes of sludge AD are compared for their pros and cons by many researchers. However, most comparisons are more focused on biogas yield, process speed and stability. Regarding the biogas yield, thermophilic sludge AD is preferred over the mesophilic one because of its faster biochemical reaction rate. Equally important but not studied sufficiently until now was the influence of temperature on the digestate quality, which is expressed mainly by the sludge dewateringability, and the reject water quality (chemical oxygen demand, ammonia nitrogen, and pH). In the field of comparison of thermophilic and mesophilic digestion process, few and often inconclusive research, unfortunately, has been published so far. Hence, recommendations for optimized technologies have not yet been done. The review presented provides a comparison of existing sludge AD technologies and the gaps that need to be filled so as to optimize the connection between the two systems. In addition, many other relevant AD process parameters, including sludge rheology, which need to be addressed, are also reviewed and presented.

Simultaneous treatment of raw palm oil mill effluent and biodegradation of palm fiber in a high-rate CSTR

A high-rate continuous stirred tank reactor (CSTR) was used to produce biogas from raw palm oil mill effluent (POME) at 55°C at a highest organic loading rate (OLR) of 19 g COD/ld. Physical and chemical pretreatments were not performed on the raw POME. In order to promote retention of suspended solids, the CSTR was installed with a deflector at its upper section. The average methane yield was 0.27 l/g COD, and the biogas production rate per reactor volume was 6.23 l/l d, and the tCOD removal efficiency was 82%. The hydrolysis rate of cellulose, hemicelluloses and lignin was 6.7, 3.0 and 1.9 g/d, respectively. The results of denaturing gradient gel electrophoresis (DGGE) suggested that the dominant hydrolytic bacteria responsible for the biodegradation of the palm fiber and residual oil were Clostridium sp., while the dominant methanogens were Methanothermobacter sp.

Performance comparison between mesophilic and thermophilic anaerobic reactors for treatment of palm oil mill effluent

The anaerobic digestion of palm oil mill effluent (POME) was carried out under mesophilic (37°C) and thermophilic (55°C) conditions without long-time POME storage in order to compare the performance of each condition in the field of Sumatra Island, Indonesia. The anaerobic treatment system was composed of anaerobic hybrid reactor and anaerobic baffled filter. Raw POME was pretreated by screw decanter to reduce suspended solids and residual oil. The total COD removal rate of 90-95% was achieved in both conditions at the OLR of 15kg[COD]/m(3)/d. The COD removal in thermophilic conditions was slightly better, however the biogas production was much higher than that in the mesophilic one at high OLR. The organic contents in pretreated POME were highly biodegradable in mesophilic under the lower OLRs. The biogas production was 13.5-20.0l/d at the 15kg[COD]/m(3)/d OLR, and the average content of carbon dioxide was 5-35% in both conditions.