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

Enhancing sewage sludge anaerobic 're-digestion' with combinations of ultrasonic, ozone and alkaline treatments

This study investigated the feasibility of using ultrasonic (ULS), ozone assisted ultrasonic (ULS-Ozone) and alkaline assisted ultrasonic (ULS+ALK) post-treatment to target the persistent organic fraction in anaerobically digested sludge in order to increase methane recovery. Synergistic COD solubilization in digested sludge was observed when ozone (0.012 g O3 g-1 TS) and alkaline (0.02M for 10 min.) treatment was combined with ULS treatment. The digested sludge Soluble Chemical Oxygen Demand (SCOD) increased from 200 mg/L to 1,500, 2,600 and 2,650 mg/L after the ULS, ULS-Ozone and ULS+ALK treatments, respectively. Different compounds were, however, solubilized after the ULS-Ozone and ULS+ALK treatments as indicated by size exclusion chromatography (SEC). ULS+ALK treatment primarily solubilized macromolecules with molecular weight (MW) over 500 kDa; while, the ULS-Ozone treatment solubilized macromolecules with MW higher than 500 kDa and also organics with MW around 103 kDa. The methane production from “re-digestion” of the treated digested sludge increased by 28.3%, 48.3% and 39.5% after the ULS, ULS-Ozone and ULS+ALK treatments, respectively

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

Fate and behavior of dissolved organic matter in a submerged anoxic-aerobic membrane bioreactor (MBR)

In this study, the production, composition, and characteristics of dissolved organic matter (DOM) in an anoxic-aerobic submerged membrane bioreactor (MBR) were investigated. The average concentrations of proteins and carbohydrates in the MBR aerobic stage were 3.96 ± 0.28 and 8.36 ± 0.89 mg/L, respectively. After membrane filtration, these values decreased to 2.9 ± 0.2 and 2.8 ± 0.2 mg/L, respectively. High performance size exclusion chromatograph (HP-SEC) analysis indicated a bimodal molecular weight (MW) distribution of DOMs, and that the intensities of all the peaks were reduced in the MBR effluent compared to the influent. Three-dimensional fluorescence excitation emission matrix (FEEM) indicated that fulvic and humic acid-like substances were the predominant DOMs in biological treatment processes. Precise identification and characterization of low-MW DOMs was carried out using gas chromatography-mass spectrometry (GC-MS). The GC-MS analysis indicated that the highest peak numbers (170) were found in the anoxic stage, and 54 (32%) compounds were identified with a similarity greater than 80%. Alkanes (28), esters (11), and aromatics (7) were the main compounds detected. DOMs exhibited both biodegradable and recalcitrant characteristics. There were noticeable differences in the low-MW DOMs present down the treatment process train in terms of numbers, concentrations, molecular weight, biodegradability, and recalcitrance

Characterization and biodegradability of sludge from a high rate A-stage contact tank and B-stage membrane bioreactor of pilot-scale AB system treating municipal wastewaters

In light of global warming mitigation efforts, increasing sludge disposal costs, and need for reduction in the carbon footprint of wastewater treatment plants, innovation in treatment technology has been tailored towards energy self-sufficiency. The AB process is a promising technology for achieving maximal energy recovery from wastewaters with minimum energy expenditure and therefore inherently reducing excess sludge production. Characterization of this novel sludge and its comparison with the more conventional B-stage sludge are necessary for a deeper understanding of AB treatment process design. This paper presents a case study of a pilot-scale AB system treating municipal wastewaters as well as a bio- (biochemical methane potential and adenosine tri-phosphate analysis) and physico-chemical properties (chemical oxygen demand, sludge volume index, dewaterability, calorific value, zeta potential and particle size distribution) comparison of the organic-rich A-stage against the B-stage activated sludge. Compared to the B-sludge, the A-sludge yielded 1.4 to 4.9 times more methane throughout the 62-week operation

Performance of A-stage process treating combined municipal-industrial wastewater

A biosorption column and a settling tank were operated for 6 months with combined municipal and industrial wastewaters (1 m3/hr) to study the effect of dissolved oxygen (DO) levels and Fe3þ dosage on removal efficiency of dissolved and suspended organics prior to biological treatment. High DO (>0.4 mg/L) were found to be detrimental for soluble chemical oxygen demand (COD) removals and iron dosing (up to 20 ppm) did not improve the overall performance. The system performed significantly better at high loading rate (>20 kg COD.m3.d1) where suspended solids and COD removals were greater than 80% and 60%, respectively. This is a significant improvement compared to conventional primary sedimentation tank and the process is a promising alternative for the pretreatment of industrial wastewater

Identification of recalcitrant compounds in a pilot-scale AB system: an adsorption (A) stage followed by a biological (B) stage to treat municipal wastewater

This manuscript presents a comparison of the A-stage and B-stage sludges in terms of anaerobic biodegradability and low molecular weight compounds present in the supernatant using Gas Chromatography–Mass Spectrometry (GC–MS). The GC–MS analysis of A-stage and B-stage supernatants identified respectively 43 and 19 organic compounds consisting mainly of aromatics (27.9% and 21%), alcohols (25.6% and 15%) and acids (30.2% and 15%). The methane potential was found to be 349 ± 1 mL CH4/g VS and 238 ± 12 mL CH4/g VS, respectively. After anaerobic digestion of these sludges, a greater proportion of aromatics (42% and 58%) and a lower proportion of acids (10% and 10%) and alcohols (16% and 10%) was observed

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 �greater than or equal to 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

Advanced biological, physical and chemical treatment of waste activated sludge

Recently, research efforts aiming to improve energy efficiency of wastewater treatment processes for large centralized wastewater treatment plants (WWTPs) have been increasing. Global warming impacts, energy sustainability, and biosolids generation are among several key drivers towards the establishment of energy-efficient WWTPs. WWTPs have been recognized as major contributors of greenhouse gas emissions as these are significant energy consumers in the industrialized world. The quantity of biosolids or excess waste activated sludge produced by WWTP will increase in the future due to population growth and this pose environmental concerns and solid waste disposal issues. Due to limited capacity of landfill sites, more stringent environmental legislation, and air pollution from incineration sites, there is a need to rethink the conventional way of dealing with wastewater and the sludge production that comes with it. This book provides an overview of advanced biological, physical and chemical treatment with the aim of reducing the volume of sewage sludge. Provides a comprehensive list of processes aiming at reducing the volume of sewage sludge and increasing biogas production from waste activated sludge. Includes clear process flowsheet showing how the process is modified compared to the conventional waste activated sludge process. Provides current technologies applied on full scale plant as well as methods still under investigation at laboratory scale. Offers data from pilot scale experience of these processe

Anaerobic membrane bioreactor technology for solid waste stabilization

In this study, a simulated Organic Fraction of Municipal Solid Waste (OFMSW) was treated inan anaerobic two-stage membrane process. The OFMSW feedstock was fed to a ten litre hydrolyticreactor (HR) where solid and liquid fractions were separated by a coarse mesh, whilethe leachate was fed to a three litre submerged anaerobic membrane bioreactor (SAMBR) within-situ membrane cleaning by biogas sparging beneath a flat sheet Kubota membrane. Theaim was to develop and optimize this two-stage process where the use of a membrane in bothreactors to uncouple the Solid and Liquid Retention Times (SRT and HRT) would allow us toimprove the current performances obtained with single stage designs. The Denaturing GradientGel Electrophoresis (DGGE) technique was used to monitor the microbial population in the reactorsand have a better understanding of the archaeal and bacterial distribution in a two-stageprocess. It was found that meshes with pore sizes of 10 microns and 150 microns were inappropriateto uncouple the SRT and HRT in the HR. In the former case, the mesh became clogged, whilein the latter case, the large pore size resulted in high levels of suspended solids in the leachatethat built up in the SAMBR. The most important parameter for Volatile Solids (VS) removal in theHR was the SRT. Maximum VS removals of 70-75% could be achieved when the SRT was equalto or greater than 50-60 days. This was achieved at a HRT of 9-12 days and an Organic LoadingRate (OLR) of 4-5 g VS.l-1.day-1.Increasing the SRT to beyond 100 days did not significantlyincrease the VS removal in the HR. However, at an OLR of 10 g VS.l-1.day-1 in the HR the SRThad to be reduced due to a build up of TS in the HR that impeded the stirring. Below 20 daysSRT, 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 and1.8 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 of0.4 day and at a SRT greater than 300 days, while the COD removal was 95%. However, theperformance at such low HRTs was not sustainable due to membrane flux limitations whenthe Mixed Liquor Total Suspended Solids (MLTSS) went beyond 20 g.l-1 due to an increase inviscosity and inorganics concentration. At 35 ?C the SAMBR was found to be stable (SCODremoval 95%) at SRTs down to 45 days and at a minimum HRT of 3.9 days. The SAMBRcould 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 evolutionin the HR and SAMBR with varying SRTs, HRTs, OLRs and temperatures in the biofilm andin suspension. Overall, it was found that stable operation and high COD removal correlatedwith 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 theSAMBR at 35 ?C, but not at ambient temperatures. It was found that some of the dominantspecies in the HR were hydrogenotrophic Archaea such as Methanobacterium formicicum andMethanobrevibacter while the other dominant species were from the genus Methanosarcinaor Methanosaeta. The presence of hydrogenotrophic species in the HR could be fostered byreinoculating the HR with excess sludge from the SAMBR when the SRT of the SAMBR wasgreater than 45 days. Among the bacterial species Ruminococcus flavefaciens, Spirochaeta,Sphingobacteriales, Hydrogenophaga, Ralstonia, Prevotella and Smithella were associated withgood reactor performances.EThOS - Electronic Theses Online ServiceGBUnited Kingdo