Biological treatment of leachate in a submerged anaerobic membrane bioreactor

In this chapter, a simulated Organic Fraction of Municipal Solid Waste (OFMSW) was treated in an anaerobic two-stage membrane process. The OFMSW feedstock was fed to a ten litre hydrolytic reactor (HR) where solid and liquid fractions were separated by a coarse mesh, while the leachate was fed to a three litre submerged anaerobic membrane bioreactor (SAMBR) with in situ membrane cleaning by biogas sparging beneath a flat sheet microfiltration module. The aim was to develop and optimize this two-stage process where the use of a membrane in both reactors to uncouple the Solid and Liquid Retention Times (SRT and HRT) would allow us to improve the current performances obtained with single stage designs. The Denaturing Gradient Gel Electrophoresis (DGGE) technique was used to monitor the microbial population in the reactors and have a better understanding of the archaeal and bacterial distribution in a two-stage process. It was found that Chemical Oxygen Demand (COD) removal was greater than 90% at a Hydraulic Residence Time (HRT) of 1.6-2.3 days at a maximum Organic Loading Rate (OLR) of 20 g COD/L.day. Even though the influent COD of the leachate was constantly changing giving rise to a transitory Food to Microorganisms ratio over time, the permeate COD from the SAMBR was typically between 300 and 500 mg/L, which can therefore be defined as a stabilised leachate. Because of the fluctuating properties of the leachate produced in the HR, the process was deemed more representative because the SAMBR treated a leachate with varying organic strength which is what can happen on a full scale. The COD removal in SAMBR2 was 94.5% on average, and only 1.6% in the subsequent aerobic polishing bioreactor (AMBR-Aerobic Membrane Bioreactor), so that a total COD removal of 96.1% was achieved at 0.4 day HRT. On average, 26% of the recalcitrants from SAMBR2 could be degraded aerobically in the AMBR. However, as in SAMBR1, at HRTs lower than 2 days, particulate solids in the leachate built up at the bottom of the SAMBR, eventually leading to the diffuser blocking. At MLTSS beyond 20 g/L, the transmembrane pressure (TMP) culminated at 850 mbar and the flux dropped to 0.5 L.m-2.hr-1 LMH until the end of the experiment. The permeate of the SAMBR was low in COD and relatively constant which promoted the growth of autotrophic bacteria in the subsequent AMBR, so that 97.7% of the NH4+-N was removed at a maximum nitrogen loading rate of 0.18 kg NH4+-N/m3.day. Calcium in the leachate was found to precipitate in the AMBR because of the higher pH. A sample taken from the membrane consisted most likely of pure hydroxylapatite Ca5(PO4)3(OH) which had a needle shape, whereas the background of the precipitate consisted more of nodules of calcium carbonate with traces of manganese, iron, magnesium, aluminium, sulphur and sodium. The very high molecular weight (MW) aromatic organics in the leachate fed to the SAMBRs were almost fully degraded in the bulk of the SAMBRs. Moreover, their permeate was absolutely free of them which indicates a full rejection of these compounds by the membrane. The medium MW compounds in the range of 395 - 646 kDa were more likely to be rejected by the membrane while the MW ≤ 395 kDa were observed in the permeate. Regarding the evolution of the medium and low MW compounds over the 200 days, it can be stated that overall there was no build-up in the absorbance in any effluent

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)

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

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

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

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

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

Glucoamylase production from food waste by solid state fermentation and its evaluation in the hydrolysis of domestic food waste

In this study, food wastes such as waste bread, savory, waste cakes, cafeteria waste, fruits, vegetables and potatoes were used as sole substrate for glucoamylase production by solid state fermentation. Response surface methodology was employed to optimize the fermentation conditions for improving the production of high activity enzyme. It was found that waste cake was the best substrate for glucoamylase production. Among all the parameters studied, glucoamylase activity was significantly affected by the initial pH and incubation time. The highest glucoamylase activity of 108.47 U/gds was achieved at initial pH of 7.9, moisture content of 69.6% wt., inoculum loading of 5.2×105 cells/gram substrate (gs) and incubation time of 6 d. The enzyme preparation could effectively digest 50% suspension of domestic food waste in 24 h with an almost complete saccharification using an enzyme dose of only 2U/g food waste at 60°C

Optimizing the synergistic effect of sodium hydroxide/ultrasound pre-treatment of sludge

Ultrasound (ULS), sodium hydroxide (NaOH) and combined ultrasound/NaOH pre-treatment were applied to pre-treat waste activated sludge and improve the subsequent anaerobic digestion. Synergistic effect was observed when NaOH treatment was coupled with ultrasound treatment. The highest synergistic Chemical Oxygen Demand (COD) solubilization was observed when 0.02M NaOH was combined with five minutes ultrasonication: an extra 3,000 mg/L was achieved on top of the NaOH (1,975 mg/L) and ultrasonication (2,900 mg/L) treatment alone. Further increase of NaOH dosage increased Soluble Chemical Oxygen Demand (SCOD), but did not increase the synergistic effect. Nine minutes and 18 minutes ultrasonication led to 20% and 24% increase of methane production, respectively; Whereas, 0.05M NaOH pre-treatment did not improve the sludge biodegradability. Combined ultrasound/NaOH (9min+0.05M) showed 31% increase of methane production. A stepwise NaOH addition/ultrasound pre-treatment (0.02M+ULS for 5 min + 0.02M+ULS for 4 min) was tested and resulted in 40% increase of methane production using 20% less chemicals