Determination of the hydrolysis constant in the biochemical methane potential test of municipal solid waste

This article provides the methane yield of municipal solid waste and its main constituents using the biochemical ethane potential (BMP) test. The methane yield of kitchen waste (KW), paper waste (PW), and garden waste (GW) were 357 ( – 24.7), 147 ( – 17.1), and 114 ( – 0.6) mL CH4/g VS, respectively. The hydrolysis constant in the first order kinetic model was 0.25, 0.095, and 0.121 d- 1 for KW, PW, and GW, respectively. The effect of the inoculum to substrate (I/S) ratio in the BMP test was investigated. Methane yields of 297.4 ( – 18.6), 293.5 ( – 33.9), and 378.2 ( – 10.3) mL CH4/g VS were found at I/S ratios of 1.4, 7.2, and 12.9, respectively, whereas the hydrolysis constants were 0.112, 0.151, and 0.221 d- 1. A new method based on the production of soluble chemical oxygen demand (SCOD) while selectively inhibiting methanogenesis has been used to determine the hydrolysis constant (0.25 d- 1) according to its true definition, which is the conversion of particulate COD to SCOD, showing that the method based on methane evolution can underestimate the actual value when hydrolysis is not the rate-limiting step

Contribution of acetic acid to the hydrolysis of lignocellulosic biomass under abiotic conditions

Acetic acid was used in abiotic experiments to adjust the solution pH and investigate its influence on the chemical hydrolysis of the Organic Fraction of Municipal Solid Waste (OFMSW). Soluble chemical oxygen demand (SCOD) was used to measure the hydrolysis under oxidative conditions (positive oxidation–reduction potential values), and pH 4 allowed for 20% (±2%) of the COD added to be solubilized, whereas only 12% (±1%) was solubilized at pH7. Under reducing conditions (negative oxidation–reduction potential values) and pH 4, 32.3% (±3%) of the OFMSW was solubilized which shows that acidogenesis at pH 4 during the anaerobic digestion of solid waste can result in chemical hydrolysis. In comparison, bacterial hydrolysis resulted in 54% (±6%) solubilizatio

Treatment of municipal solid waste leachate using a submerged anaerobic membrane bioreactor at mesophilic and psychrophilic temperatures: analysis of recalcitrants in the permeate using GC-MS

This study investigated the performance of two submerged anaerobic membrane bioreactors (SAMBRs) operating at a mean solids residence time (SRT) of 30 (SAMBR30) and 300 days (SAMBR300) at mesophilic and psychrophilic temperatures. At 35°C results showed that SAMBR30 and 300 could achieve 95% soluble chemical oxygen demand (SCOD) removal at 1.5 and 1.1 days HRT, respectively, whereas at 20°C only SAMBR300 could maintain the same performance. Low temperatures were associated with higher bulk SCOD concentrations, which contributed to reducing the flux, but this was partly reversible once the SCOD was degraded. The utilization rate of compounds was affected differently by the drop in temperature with the concentration of some recalcitrants increasing, while for others such as bisphenol A it decreased when the temperature was decreased. Among the recalcitrants detected in SAMBR30 at 20°C there were not only long chain fatty acids such as undecanoic acid and dodecanoic acid, but also long chain alkanes such as tetracosane and heneicosane that could not be hydrolyzed at 20°C. In SAMBR300 these alkanes and acids only appeared at 10°C, whereas at 20°C complex compounds such as phenol, 2-chloro-4-(1,1-dimethylethyl), 6-tert-butyl-2,4-dimethylphenol, benzophenone, and n-butyl benzenesulfonamide were found

Inorganic fouling of an anaerobic membrane bioreactor treating leachate from the organic fraction of municipal solid waste (OFMSW) and a polishing aerobic membrane bioreactor

The treatment of leachate (Average TCOD = 11.97 g/L, 14.4% soluble) from the organic fraction of municipal solid waste was investigated using a Submerged Anaerobic Membrane BioReactor (SAMBR), followed by an aerobic membrane bioreactor (AMBR) to polish this effluent. This paper investigated the exact nature and composition of the inorganic precipitate in each of the reactors in the process. The flux decreased due to precipitation of calcium as monohydrocalcite (CaCO3�H2O) containing traces of metals onto the SAMBR membrane because of high CO2 partial pressures. Precipitation of calcium in the AMBR was also observed due to a higher pH. In this case, phosphorus also precipitated with calcium in two different phases: the background layer contained calcium, oxygen, carbon and small amounts of phosphorus (2–6.7%), while flakes containing calcium, oxygen and higher amounts of phosphorus (10–17%) were probably hydroxyapatite (Ca5(PO4)3OH)

Parameters affecting the stability of the digestate from a two-stage anaerobic process treating the organic fraction of municipal solid waste

This paper focused on the factors affecting the respiration rate of the digestate taken from a continuous anaerobic two-stage process treating the organic fraction of municipal solid waste (OFMSW). The process involved a hydrolytic reactor (HR) that produced a leachate fed to a submerged anaerobic membrane bioreactor (SAMBR). It was found that a volatile solids (VS) removal in the range 40–75% and an operating temperature in the HR between 21 and 35 degrees C resulted in digestates with similar respiration rates, with all digestates requiring 17 days of aeration before satisfying the British Standard Institution stability threshold of 16 mg CO2 g VS-1 day-1. Sanitization of the digestate at 65 degrees C for 7 days allowed a mature digestate to be obtained. At 4 g VS L-1 d-1 and Solid Retention imes (SRT) greater than 70 days, all the digestates emitted CO2 at a rate lower than 25 mg CO2 g VS-1 d-1 after 3 days of aeration, while at SRT lower than 20 days all the digestates displayed a respiration rate greater than 25 mg CO2 g VS-1 d-1. The compliance criteria for Class I digestate set by the European Commission (EC) and British Standard Institution (BSI) could not be met because of nickel and chromium contamination, which was probably due to attrition of the stainless steel stirrer in the HR

Effect of sparging rate on permeate quality in a submerged anaerobic membrane bioreactor (SAMBR) treating leachate from the organic fraction of municipal solid waste (OFMSW)

This paper focuses on the treatment of leachate from the organic fraction of municipal solid waste (OFMSW) in a submerged anaerobic membrane bioreactor (SAMBR). Operation of the SAMBR for this type of high strength wastewater was shown to be feasible at 5 days hydraulic retention time (HRT), 10 L min-1 (LPM) biogas sparging rate and membrane fluxes in the range of 3e7 L m-2 hr-1 (LMH). Under these conditions, more than 90% COD removal was achieved during 4 months of operation without chemical cleaning the membrane. When the sparging rate was reduced to 2 LPM, the transmembrane pressure increased dramatically and the bulk soluble COD concentration increased due to a thicker fouling layer, while permeate soluble COD remained constant. Permeate soluble COD concentration increased by 20% when the sparging rate increased to 10 LPM

Post-treatment of the permeate of a submerged anaerobic membrane bioreactor (SAMBR) treating landfill leachate

In this study, various methods were compared to reduce the Chemical Oxygen Demand (COD) content of stabilised leachate from a Submerged Anaerobic Membrane Bioreactor (SAMBR). It was found that Powdered Activated Carbon (PAC) resulted in greater COD removals (84%) than Granular Activated Carbon (GAC-80%), an ultrafiltration membrane of 1kDa (75%), coagulation-flocculation with FeCl3 and polyelectrolyte (45%), FeCl3 alone (32%), and polymeric adsorbents such as XAD7HP (46%) and XAD4 (32%). Results obtained on the <1 kDa fraction showed that PAC and GAC had a similar adsorption efficiency of about 60% COD removal, followed by XAD7HP (48%), XAD4 (27%) and then FeCl3 (23 %). The post-treatment sequence UF+GAC would result in a final effluent with less than 100 mg COD/L. Size Exclusion Chromatography (SEC) revealed that the extent of adsorption of low MW compounds onto PAC was limited due to low MW hydrophilic compounds, whereas the kinetics of PAC adsorption depended mainly on the adsorption of high MW aromatics

Denaturing gradient gel electrophoresis analysis of archaeal and bacterial populations in a submerged anaerobic membrane bioreactor treating landfill leachate at low temperatures

This study investigated the evolution of archaeal and bacterial populations of two submerged anaerobic membrane bioreactors (SAMBRs) operating at a mean solids residence time of 30 (SAMBR30) and 300 days (SAMBR300) at mesophilic and psychrophilic temperatures. SAMBRs were fed with leachate produced in a hydrolytic reactor (HR) treating the organic fraction of municipal solid waste. The archaeal fingerprint using denaturing gradient gel electrophoresis showed different populations in the first and second stage of the two-stage anaerobic process. A build up of volatile fatty acids (VFAs) was observed at 20°C in SAMBR30; whereas in SAMBR300, the VFAs only built up at 10°C. The dominant bacterial species in the HR belonged to Prevotella and Thauera, whereas the dominant ones in SAMBR300 belonged to Sphingobacteriales, Anaerovorax, Spirochaetaceae, Hydrogenophaga, Ralstonia, Prevotella, and Smithella. Low bacterial diversity in SAMBR30 compared with SAMBR300 resulted in a persistently high soluble chemical oxygen demand (>2 g/L) in the bulk reactor due to an insufficient residence time for bacteria to carry out the degradation of recalcitrant chemical oxygen demand found in the leachate

Performance of a three-stage membrane bioprocess treating the organic fraction of municipal solid waste and evolution of its archaeal and bacterial ecology

A novel three-stage bioprocess achieved 75% volatile solids (VS) removal at an organic loading rate (OLR) of 4 g VS L−1 day, a solids retention time (SRT) of 66 days, a hydraulic retention time (HRT) of 20 days, at a temperature of 35 °C. The bioprocess consisted of an anaerobic hydrolytic reactor (HR) where the solids and liquid fractions of the Organic Fraction of the Municipal Solid Waste (OFMSW) were separated with a mesh. The leachate was pumped to a Submerged Anaerobic Membrane Bioreactor (SAMBR) and the treated permeate was polished in an Aerobic Membrane Bioreactor (AMBR). Denaturing Gradient Gel Electrophoresis (DGGE) and DNA sequencing analyses indicated that the increase in methane content in the HR caused by the excess sludge recycle from the SAMBR was associated with an increase in the number of hydrogenotrophic species, mainly Methanobrevibacter sp., Methanobacterium formicicum and Methanosarcina sp. At 20°C VS removal dropped to 50% in the HR and some DGGE bands disappeared when compared to 35°C samples, while some bands such as the one corresponding to Ruminococcus flavefaciens were reduced in intensity. The species associated with the COD-polishing properties of the AMBR correspond to the genera Pseudomonas, Hyphomonas and Hyphomicrobiaceae. These results highlight the positive effect of recycling the excess sludge from the SAMBR to re-inoculate the HR with hydrogenotrophic species

Characterization of soluble microbial products (SMPs) in a membrane bioreactor (MBR) treating municipal wastewater containing pharmaceutical compounds

This study investigated the behaviour and characteristics of soluble microbial products (SMP) in two anoxic-aerobic membrane bioreactors (MBRs): MBRcontrol and MBRpharma, for treating municipal wastewater. Both protein and polysaccharides measured exhibited higher concentrations in the MBRpharma than the MBRcontrol. Molecular weight (MW) distribution analysis revealed that the presence of pharmaceuticals enhanced the accumulation of SMPs with macro- (13,091 kDa and 1,587 kDa) and intermediate-MW (189 kDa) compounds in the anoxic MBRpharma, while a substantial decrease was observed in both MBR effluents. Excitation emission matrix (EEM) fluorescence contours indicated that the exposure to pharmaceuticals seemed to stimulate the production of aromatic proteins containing tyrosine (10.1-32.6%) and tryptophan (14.7-43.1%), compared to MBRcontrol (9.9-29.1% for tyrosine; 11.8-42.5% for tryptophan). Gas chromatography - mass spectrometry (GC-MS) analysis revealed aromatics, long-chain alkanes and esters were the predominant SMPs in the MBRs. More peaks were present in the aerobic MBRpharma (196) than anoxic MBRpharma (133). The SMPs identified exhibited both biodegradability and recalcitrance in the MBR treatment processes. Only 8 compounds in the MBRpharma were the same as in the MBRcontrol. Alkanes were the most dominant SMPs (51%) in the MBRcontrol, while aromatics were dominant (40%) in the MBRpharma. A significant decrease in aromatics (from 16 to 7) in the MBRpharma permeate was observed, compared to the aerobic MBRpharma. Approximately 21% of compounds in the aerobic MBRcontrol were rejected by membrane filtration, while this increased to 28% in the MBRpharma