Antoine P. Trzcinski

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 degrees 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 degrees 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 degrees 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 degrees C. In SAMBR300 these alkanes and acids only appeared at 10 degrees C, whereas at 20 degrees 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.

Continuous treatment of the organic fraction of municipal solid waste in an anaerobic two-stage membrane process with liquid recycle

The stability and performance of a two-stage anaerobic membrane process was investigated at different organic loading rates (OLRs) and Hydraulic Retention Times (HRTs) over 200 days. The Hydrolytic Reactor (HR) was fed with the Organic Fraction of Municipal Solid Waste (OFMSW), while the leachate from the HR was fed continuously to two Submerged Anaerobic Membrane Bioreactors (SAMBR1 and 2). The Total COD (TCOD) of the leachate varied over a wide range, typically between 4000 and 26,000 mg/L while the Soluble COD (SCOD) in the permeate was in the range 400-600 mg/L, achieving a COD removal greater than 90% at a HRT of 1.6-2.3 days in SAMBR1. The operation was not sustainable below this HRT due to a membrane flux limitation at 0.5-0.8L/m(2) h (LMH), which was linked to the increasing MLTSS. SCOD in the recycled permeate did not build up indicating a slow degradation of recalcitrants over time. SAMBR2 was run in parallel with SAMBR1 but its permeate was treated aerobically in an Aerobic Membrane Bioreactor (AMBR). The AMBR acted as a COD-polishing and ammonia removal step. About 26% of the recalcitrant SCOD from SAMBR2 could be aerobically degraded in the AMBR. In addition, 97.7 % of the ammonia-nitrogen was converted to nitrate in the AMBR at a maximum nitrogen-loading rate of 0.18 kg NH(4)(+)-N/m(3) day. GC-MS analysis was performed on the reactor effluents to determine their composition and what compounds were recalcitrant.

Microbial oil produced from biodiesel by-products could enhance overall production

Glycerol and rapeseed meal, two major by-products of biodiesel production, have been tested for possible use as low-cost raw materials for the production of microbial bio-oil using the oleaginous yeast Rhodosporidium toruloides. Using fed-batch fermentation with crude glycerol and a novel nitrogen rich nutrient source derived from rapeseed meal as feed, it was shown that 13 g/L lipids could be produced, compared with 9.4 g/L when crude glycerol was used with yeast extract. When 100 g/L pure glycerol was used, the final lipid concentration was 19.7 g/L with the novel biomedium compared to 16.2 g/L for yeast extract. The novel biomedium also resulted in higher lipid yields (0.19 g lipid/g glycerol consumed compared to 0.12 g/L) suggesting it provides a better carbon to nitrogen balance for accumulating lipids. FAMEs produced from the microbial lipids indicated a high degree of unsaturation confirming that the fatty acids produced from the novel biomedium have potential for biodiesel production.

Enhancing the hydrolysis and methane production potential of mixed food waste by an effective enzymatic pretreatment.

In this study, a fungal mash rich in hydrolytic enzymes was produced by solid state fermentation (SSF) of waste cake in a simple and efficient manner and was further applied for high-efficiency hydrolysis of mixed food wastes (FW). The enzymatic pretreatment of FW with this fungal mash resulted in 89.1 g/L glucose, 2.4 g/L free amino nitrogen, 165 g/L soluble chemical oxygen demand (SCOD) and 64% reduction in volatile solids within 24h. The biomethane yield and production rate from FW pretreated with the fungal mash were found to be respectively about 2.3 and 3.5-times higher than without pretreatment. After anaerobic digestion of pretreated FW, a volatile solids removal of 80.4±3.5% was achieved. The pretreatment of mixed FW with the fungal mash produced in this study is a promising option for enhancing anaerobic digestion of FW in terms of energy recovery and volume reduction.

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 4g VSL(-1)day, a solids retention time (SRT) of 66days, a hydraulic retention time (HRT) of 20days, at a temperature of 35 degrees 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 degrees C VS removal dropped to 50% in the HR and some DGGE bands disappeared when compared to 35 degrees 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.

Enhancing the value of nitrogen from rapeseed meal for microbial oil production

Rapeseed meal, a major byproduct of biodiesel production, has been used as a low-cost raw material for the production of a generic microbial feedstock through a consolidated bioconversion process. Various strategies were tested for the production of a novel fermentation medium, rich in free amino nitrogen (FAN): commercial enzymes (CEs) (2.7 mg g⁻¹ dry meal), liquid state fungal pre-treatment (LSF) using Aspergillus oryzae (4.6 mg g⁻¹), liquid state fungal pre-treatment followed by fungal autolysis (LSFA) (9.13 mg g⁻¹), liquid state pre-treatment using fungal enzymatic broth (EB) (2.1 mg g⁻¹), but the best strategy was a solid state fungal pre-treatment followed by fungal autolysis (34.5 mg g⁻¹). The bioavailability of the nitrogen sources in the novel medium was confirmed in fed-batch bioreactor studies, in which 82.3g dry cell L⁻¹ of the oleaginous yeast Rhodosporidium toruloides Y4 was obtained with a lipid content of 48%. The dry cell weight obtained was higher than that obtained using conventional yeast extract, due to a higher total nitrogen content in the novel biomedium. The fatty acids obtained from the microbial oil were similar to those derived from rapeseed oil.

Metabolomic profiling of rhodosporidium toruloides grown on glycerol for carotenoid production during different growth phases

Carotenoid production from three strains of Rhodosporidium toruloides grown on glycerol was studied. A time-dependent metabolomics approach was used to understand its metabolism on glycerol and mechanism for carotenoid production in three strains during different growth phases (1, 4, 7, and 12 days). Strain CBS 5490 was the highest carotenoid producer (28.5 mg/L) and had a unique metabolic profile. In this strain, metabolites belonging to the TCA cycle and amino acids were produced in lower amounts, as compared to the other strains. On the other hand, it produced the highest amounts of carotenoid and fatty acid metabolites. This indicated that the lower production of the TCA cycle and amino acid metabolites promoted energy and metabolic flux toward the carotenoid and fatty acid synthesis metabolic pathways. This study shows that metabolomic profiling is a useful tool to gain insight into the metabolic pathways in the cell and to shed light on the different molecular mechanisms between strains.

Anaerobic digestion of the organic fraction of municipal solid waste in a two-stage membrane process

A batch of the Organic Fraction of Municipal Solid Waste (OFMSW) was treated in a two-step process with effluent recirculation comprising a novel hydrolytic reactor (HR) followed by a Submerged Anaerobic Membrane Bioreactor (SAMBR) operating at a stable permeate flux of 5.6 L/m(2) hr (LMH). A soluble COD removal higher than 95% was obtained from the SAMBR. The soluble COD as well as the Total Suspended Solids (TSS) did not build up due to efficient hydrolysis inside the SAMBR, and no VFA accumulation occurred due to the complete retention of methanogens by the membrane as well as the formation of syntrophic associations. Because of the microfiltration membrane in the second reactor a stabilized leachate was obtained from the very first days of the treatment and the highly stable process enabled shorter treatment periods compared to traditional leach bed processes. This experiment showed that the recycle of the stabilised leachate does not lead to a build up of SCOD. Size exclusion chromatography analysis confirmed that high molecular weight compounds were completely degraded and did not appear in the SAMBR permeate, and that low molecular weight fulvic-like and medium MW material were present in the permeate of the SAMBR but their concentration remained stable with time.

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 °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 CO(2) g VS(-1) day(-1). Sanitization of the digestate at 65 °C for 7 days allowed a mature digestate to be obtained. At 4 g VS L(-1) d(-1) and Solid Retention Times (SRT) greater than 70 days, all the digestates emitted CO(2) at a rate lower than 25 mg CO(2) 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 CO(2) 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.

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).