Investigation of methane production by anaerobic co-digestion of food waste, fats, oil and grease, and thickened waste activated sludge using automatic methane potential test system

This project investigated the methane production by anaerobic co-digestion using Automatic Methane Potential Test System (AMPTS). Food waste (FW), waste cooking oil- Canola oil (FOG), and thickened waste activated sludge (TWAS) were used as substrates for anaerobic digestion in two sets of experiments. All the substrates were digested individually in the first set of experiments. In the second set, they were combined in different proportions (four combinations) and were co-digested. All the experiments were carried at mesophilic temperature (37˚C). Results obtained from the first set established that FOG is not a suitable substrate for anaerobic digestion. From the second set of experiments, it was found that FOG did not cause inhibition. However, presence of FOG in co-digestion process caused problems which led to decreased yield of methane in all the four combinations

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

Effects of physico-chemical post-treatments on the semi-continuous anaerobic digestion of sewage sludge

Sludge production in wastewater treatment plants is increasing worldwide due to the increasing population. This work investigated the effects of ultrasonic (ULS), ultrasonic-ozone (ULS-Ozone) and ultrasonic + alkaline (ULS+ALK) post-treatments on the anaerobic digestion of sewage sludge in semi-continuous anaerobic reactors. Three conditions were tested with different hydraulic retention times (HRT, 10 or 20 days) and sludge recycle ratios (R = QR/Qin (%): 50 or 100%). Biogas yield increased by 17.8% when ULS+ALK post-treatment was applied to the effluent of a reactor operating at 20 days HRT and at a 100% recycle ratio. Operation at 10 days HRT also improved the biogas yield (277 mL CH4/g VSadded (VS: volatile solids) versus 249 mL CH4/g VSadded in the control). The tested post-treatment methods showed 4–7% decrease in effluent VS. The post-treatment resulted in a decrease in the cellular ATP (Adenosine tri-phosphate) concentration indicating stress imposed on microorganisms in the reactor. Nevertheless, this did not prevent higher biogas production. Based on the results, the post-treatment of digested sludge or treating the sludge between two digesters is an interesting alternative to pre-treatments

ANAEROBIC MEMBRANE BIOREACTOR TECHNOLOGY FOR SOLID WASTE STABILIZATION

In this study, 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 Kubota membrane. 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 meshes with pore sizes of 10 microns and 150 microns were inappropriate to uncouple the SRT and HRT in the HR. In the former case, the mesh became clogged, while in the latter case, the large pore size resulted in high levels of suspended solids in the leachate that built up in the SAMBR. The most important parameter for Volatile Solids (VS) removal in the HR was the SRT. Maximum VS removals of 70-75% could be achieved when the SRT was equal to or greater than 50-60 days. This was achieved at a HRT of 9-12 days and an Organic Loading Rate (OLR) of 4-5 g VS.l-1.day-1.Increasing the SRT to beyond 100 days did not significantly increase the VS removal in the HR. However, at an OLR of 10 g VS.l-1.day-1 in the HR the SRT had to be reduced due to a build up of TS in the HR that impeded the stirring. Below 20 days SRT, the VS removal reduced to between 30 and 40%. With kitchen waste as its main substrate, however, an OLR of 10 g VS.l-1.day-1 was achieved with 81% VS removal at 23 days SRT and 1.8 days HRT. The SAMBR was found to remain stable at an OLR up to 19.8 g COD.l-1.day-1 at a HRT of 0.4 day and at a SRT greater than 300 days, while the COD removal was 95%. However, the performance at such low HRTs was not sustainable due to membrane flux limitations when the Mixed Liquor Total Suspended Solids (MLTSS) went beyond 20 g.l-1 due to an increase in viscosity and inorganics concentration. At 35 °C the SAMBR was found to be stable (SCOD removal 95%) at SRTs down to 45 days and at a minimum HRT of 3.9 days. The SAMBR could achieve 90% COD removal at 22 °C at an OLR of 13.4 g COD.l-1.day-1 and 1.1 days HRT (SRT = 300 days). The DGGE technique was used to monitor the archaeal and bacterial diversity and evolution in the HR and SAMBR with varying SRTs, HRTs, OLRs and temperatures in the biofilm and in suspension. Overall, it was found that stable operation and high COD removal correlated with a high bacterial diversity, while at the same time very few species (2-4) were dominant. Only a few dominant archaeal species were sufficient to keep low VFA concentrations in the SAMBR at 35 °C, but not at ambient temperatures. It was found that some of the dominant species in the HR were hydrogenotrophic Archaea such as Methanobacterium formicicum and Methanobrevibacter while the other dominant species were from the genus Methanosarcina or Methanosaeta. The presence of hydrogenotrophic species in the HR could be fostered by reinoculating the HR with excess sludge from the SAMBR when the SRT of the SAMBR was greater than 45 days. Among the bacterial species Ruminococcus flavefaciens, Spirochaeta, Sphingobacteriales, Hydrogenophaga, Ralstonia, Prevotella and Smithella were associated with good reactor performances

Effects of physico-chemical post-treatments on the semi-continuous anaerobic digestion of sewage sludge

Sludge production in wastewater treatment plants is increasing worldwide due to the increasing population. This work investigated the effects of ultrasonic (ULS), ultrasonic-ozone (ULS-Ozone) and ultrasonic + alkaline (ULS+ALK) post-treatments on the anaerobic digestion of sewage sludge in semi-continuous anaerobic reactors. Three conditions were tested with different hydraulic retention times (HRT, 10 or 20 days) and sludge recycle ratios (R = QR/Qin (%): 50 or 100%). Biogas yield increased by 17.8% when ULS+ALK post-treatment was applied to the effluent of a reactor operating at 20 days HRT and at a 100% recycle ratio. Operation at 10 days HRT also improved the biogas yield (277 mL CH4/g VSadded (VS: volatile solids) versus 249 mL CH4/g VSadded in the control). The tested post-treatment methods showed 4–7% decrease in effluent VS. The post-treatment resulted in a decrease in the cellular ATP (Adenosine tri-phosphate) concentration indicating stress imposed on microorganisms in the reactor. Nevertheless, this did not prevent higher biogas production. Based on the results, the post-treatment of digested sludge or treating the sludge between two digesters is an interesting alternative to pre-treatments

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

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)

A feasibility study into the bioprocessing of coffee residues

Coffee residues are generated in large quantities from the processing and consumption of coffee, and are generally disposed of as waste through non-sustainable practices. The capacity of coffee residues to support microbial growth was determined, using indigenous bacteria and fungal species- Aspergillus awamori and Aspergillus oryzae as model organisms. Solid and liquid state fermentation by fungal species and indigenous bacteria respectively, were carried out under basic conditions and the results showed that coffee residues contain chemical compounds which can be utilized by micro-organisms in bio-processes to produce value-added products. Increase in free amino nitrogen and total reducing sugars was obtained; and maximum protease activity of 92 U/g dry matter basis was obtained

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

Growth kinetics and lipid accumulation in Rhodosporidium toruloides

The current interest in oleaginous yeasts as a viable source for microbial oil production has led to increasing research in understanding the growth conditions and kinetics of oleaginous yeasts with the aim to optimise productivity. Microbial oils can be used as food supplements and feedstock for biodiesel production, with the current increase in prices of fossil fuel and food, microbial oil is undoubtedly a perfect renewable feedstock alternative for biodiesel production. However the set back in using microbial oil is the high cost of production especial the cost of fermentation. Recently, an oleaginous yeast Rhodosporidium toruloides has attracted great interest in microbial oil production because of its high lipid content and cell density. In this study, growth of Rhodosporidium toruloides on glucose, pure glycerol and crude glycerol were studied with the aim to understand its ability to utilize a by-product from biodiesel processing plant as a cheap carbon source. The result of this study showed that Rhodosporidium toruloides could use glucose, pure glycerol and crude glycerol as carbon source however; while it can grow on high concentration of 100 g/L of glucose and pure glycerol; there was growth inhibition at concentrations of crude glycerol higher than 20g/L as a result of toxic and inhibitory effects of impurities in crude glycerol. R. toruloides accumulated a Lipid content of 47.61% and biomass of 10.55 g/L when grown on glucose. Likewise, a lipid content of 41% and 13.09 g/l biomass in pure glycerol were achieved. R. toruloides can utilize crude glycerol as carbon source and therefore further research in optimizing lipid productivity using crude glycerol as carbon source is recommended